---

Suggestions for This Session

• Combine questions that are identical or near-identical (e.g., "Malignant hyperthermia" appears 3 times - answered once)
• Combine questions that are subsets of each other (e.g., "TURP Syndrome" + "Signs, symptoms and management of TURP Syndrome" - answered together)
• Keep case-based questions separate from pure topic questions even if the topic overlaps, since examiners expect different framing

• 500-600 words of body content (excluding headings, subheadings, table headers, bullet lead-ins)
• Tables and flowcharts are excluded from the word count
• Drug doses, numerical values, and classifications will be in tables to save word budget

• I will use only the relevant sections from the full format template - not all 24 sections for every question (saves space, improves readability)
• Every answer will have: Definition → Key Physiology/Pathophysiology → Classification (if applicable) → Management → Anaesthetic Relevance → Exam Pearls

1. Monitoring
2. Physics & Equipment
3. Anaesthesia Machine
4. Drugs (Inhalational → LA → IV agents → Muscle relaxants → Opioids → Cardiac drugs)
5. Physiology (Cardiac → Respiratory → Neuro → Obstetric)
6. Subspecialty Anaesthesia (Neuro → Cardiac → Thoracic → Obstetric → Paediatric → Ortho → Uro → Endocrine → Renal → Ophthalmic)
7. Critical Care & ICU
8. Pain
9. Regional Anaesthesia
10. Miscellaneous & Airway

---

• As long as the topic demands - no padding, no cutting corners
• Full 40-50 mark quality - the kind that makes an examiner nod and give full marks
• Structured like a topper's notes - dense, crisp, high-yield, not wordy

• Long topics (e.g., Malignant Hyperthermia, ARDS, Difficult Airway) → full comprehensive answers
• Short topics (e.g., Beer-Lambert Law, Coanda Effect) → concise but complete
• Case-based questions → always include a structured anaesthetic plan
• Every answer ends with Exam Pearls + Recent Advances

---

MONITORING IN ANAESTHESIA

Combined Answer: Invasive Monitoring | Advanced Hemodynamic Monitoring | Mandatory Monitoring During Anaesthesia

---

1. MANDATORY MINIMUM MONITORING DURING ANAESTHESIA

ASA Basic Standards for Intraoperative Monitoring (2020, reaffirmed 2025)

Exam Pearl: ASA mandates continual (repeated regularly) vs. continuous (uninterrupted) for some parameters. SpO2 and ECG are continuous; NIBP may be continual (every 5 min).

---

2. CLASSIFICATION OF MONITORING

MONITORING IN ANAESTHESIA
        |
        |-------- NON-INVASIVE
        |              |-- Clinical (look, listen, feel)
        |              |-- Standard (SpO2, ECG, NIBP, EtCO2, Temp)
        |              |-- Advanced non-invasive (BIS, NMT, TOE, USCOM, NI-CO)
        |
        |-------- INVASIVE
                       |-- Basic invasive (Arterial line, CVP)
                       |-- Advanced invasive (PAC, PICCO, LIDCO, IABP)

---

3. STANDARD (NON-INVASIVE) MONITORING

---

4. INVASIVE MONITORING - TYPES AND FEATURES

A. Arterial Line (Invasive Blood Pressure)

• Sites (preference order): Radial > Femoral > Brachial > Dorsalis pedis > Ulnar
• Indications:
  • Beat-to-beat BP monitoring in haemodynamically unstable patients
  • Frequent ABG sampling
  • Deliberate hypotension / major surgery
  • Patients on vasoactive drugs
• Contraindications: Failed Allen's test, local infection, coagulopathy (relative)
• Normal arterial waveform components:

Systolic peak → Dicrotic notch (aortic valve closure) → Diastolic runoff

Formula: MAP = DBP + 1/3 (SBP - DBP) = DBP + 1/3 PP

• Whip artifact - over-damped vs under-damped waveforms
• Must Remember: Allen's test mandatory before radial arterial cannulation

---

B. Central Venous Pressure (CVP)

• Sites: Right IJV (preferred) > Subclavian > Femoral > Left IJV
• Normal CVP: 2-8 mmHg (or 5-12 cmH2O)
• Waveform components:

• High CVP causes: Cardiac tamponade, RHF, fluid overload, PEEP, pneumothorax
• Low CVP causes: Hypovolaemia, vasodilation, sepsis
• Limitation: CVP is a poor predictor of fluid responsiveness (Marik, Chest 2008) - should NOT be used alone to guide fluid therapy

Exam Pearl: Cannon 'a' waves = complete heart block / nodal rhythm. Giant 'v' waves = tricuspid regurgitation.

---

C. Pulmonary Artery Catheter (PAC) / Swan-Ganz Catheter

• Indications: Complex cardiac surgery, ARDS, refractory shock, cardiac transplant
• Parameters measured:

• Complications: Arrhythmias, PA rupture, infection, knotting, pulmonary infarction
• Current evidence: PAC use has significantly declined - large RCTs (ESCAPE, PAC-Man) showed no mortality benefit in most ICU populations

---

5. ADVANCED HEMODYNAMIC MONITORING

A. Pulse Contour Cardiac Output (PiCCO)

• Combines transpulmonary thermodilution + pulse contour analysis
• Requires: femoral/axillary arterial line + central venous line
• Additional parameters:
  • ITBV (Intrathoracic Blood Volume) - better preload indicator than CVP
  • EVLW (Extravascular Lung Water) - pulmonary oedema quantification
  • SVV (Stroke Volume Variation) - fluid responsiveness
• SVV >13% = likely fluid responder (valid only in sinus rhythm, controlled ventilation)

B. LiDCO (Lithium Dilution Cardiac Output)

• Uses lithium indicator dilution + pulse power analysis
• Less invasive than PAC - requires only peripheral arterial + venous access
• Contraindication: Patients on lithium therapy, first trimester pregnancy

C. Oesophageal Doppler Monitor (ODM/CardioQ)

• Measures descending aortic blood flow velocity
• FTc (Corrected Flow Time): Normal >330 ms - guides fluid therapy
• Non-invasive, real-time CO monitoring
• NICE approved for high-risk surgical patients

D. USCOM (Ultrasound Cardiac Output Monitor)

• Completely non-invasive
• Doppler US of aortic or pulmonary outflow tract
• Portable, bedside use

E. FloTrac/Vigileo

• Arterial waveform analysis without calibration
• Auto-calculates SVV, CO, CI from standard arterial line
• Less accurate in states of high vasopressor requirements

F. NI-CO (Non-Invasive Cardiac Output)

• Based on partial CO2 rebreathing technique (Fick principle)
• Formula: CO = VCO2 / CvCO2 - CaCO2

---

6. DYNAMIC INDICES OF FLUID RESPONSIVENESS

Must Remember: Dynamic indices (PPV, SVV) are valid only in:

• Sinus rhythm
• Fully controlled mechanical ventilation
• Tidal volume ≥ 8 mL/kg
• No right heart failure

---

7. NEUROMONITORING & DEPTH OF ANAESTHESIA

---

8. NEUROMUSCULAR MONITORING

---

9. POINT-OF-CARE MONITORING (POCUS in OT/ICU)

• Cardiac POCUS: LV/RV function, pericardial effusion, volume status
• Lung POCUS: Pneumothorax (loss of lung sliding), B-lines (pulmonary oedema)
• Vascular POCUS: DVT, IVC diameter for preload assessment
• FAST exam: Trauma abdominal free fluid

---

10. IMPORTANT FORMULAE

---

11. RECENT ADVANCES (2024-2026)

• EV1000/HemoSphere platform: integrates multiple haemodynamic parameters on single screen
• Minimally invasive CO monitoring now preferred over PAC in most centres
• AI-based haemodynamic prediction (e.g., Edwards Acumen IQ): predicts hypotension up to 15 min in advance using arterial waveform analysis
• Masimo Root with noninvasive haemoglobin (SpHb) monitoring - reduces unnecessary transfusions
• POCUS integration into standard monitoring - ESAIC 2024 guidelines recommend POCUS competency for all anaesthesiologists

---

12. CURRENT GUIDELINES

• ASA (2020, reaffirmed 2025): Basic monitoring standards - SpO2, EtCO2, ECG, NIBP, Temp mandatory
• ESAIC (2023): Recommends goal-directed haemodynamic therapy using dynamic indices (PPV/SVV) over static (CVP/PCWP) for high-risk surgery
• SCCM/ESICM (2021): Surviving Sepsis Campaign - MAP ≥65 mmHg target; CO-guided resuscitation in refractory shock
• NICE (UK): Oesophageal Doppler monitoring for all major abdominal surgery

---

📌 EXAM PEARLS

1. SpO2 detects desaturation LATE - it lags behind true PaO2 by 30-60 seconds due to the oxyhaemoglobin dissociation curve
2. CVP is NOT a reliable indicator of fluid responsiveness - this is one of the most tested statements in modern anaesthesia exams
3. PPV >13% in fully ventilated patient = fluid responder - cornerstone of goal-directed therapy
4. PAC use has declined due to lack of mortality benefit in RCTs - know the complications
5. Allen's test must be documented before radial arterial line insertion
6. BIS 40-60 for GA; BIS <40 = burst suppression; BIS >60 = awareness risk

---

🔴 HIGH YIELD FACTS

• PCWP >18 mmHg = cardiogenic pulmonary oedema
• SvO2 <65% = increased O2 extraction (shock, anaemia, sepsis)
• ScvO2 (from CVC in SVC) is ~5-8% higher than true SvO2
• IVC diameter >2 cm + <50% collapsibility = fluid non-responder
• Oesophageal Doppler FTc <330 ms = hypovolaemia; >400 ms = vasodilation

---

---

---

PULSE OXIMETRY AND BEER-LAMBERT LAW

Combined Answer: Pulse Oximetry (×5) | Beer-Lambert Law (×2)

---

1. DEFINITION

• Pulse Oximetry: A non-invasive, continuous method of measuring functional oxygen saturation of arterial haemoglobin (SpO2) using differential light absorption at two wavelengths, exploiting the pulsatile nature of arterial blood flow
• SpO2 = peripheral (pulse oximeter) estimate of SaO2 (true arterial O2 saturation from ABG)

---

2. BEER-LAMBERT LAW - THE PHYSICAL BASIS

Statement

"The absorbance of light by a substance is directly proportional to its concentration and the path length through which light travels."

Mathematical Expression

Additional Relationships

• A = 2 - log %T
• A = -log T
• Absorbance and transmittance are inversely related
• Law is valid only for monochromatic radiation and dilute solutions

Deviations from Beer-Lambert Law

• High concentrations (non-linear at A > 2.0)
• Polychromatic light sources
• Changes in pH, ionic strength, temperature
• Scattering substances (lipids, turbid solutions)
• Clinical relevance: SpO2 inaccurate in dyshemoglobinaemias (COHb, MetHb) - these deviate from expected absorbance ratios

---

3. PRINCIPLE OF PULSE OXIMETRY

Key Concept: AC/DC Signal Separation

LIGHT ABSORBED BY TISSUE
         |
         |--- DC component (steady/non-pulsatile)
         |        = venous blood + tissue + bone + pigment
         |
         |--- AC component (pulsatile)
                  = ARTERIAL BLOOD ONLY
                       |
                  This is what pulse oximeter measures

• Two wavelengths used:
  • 660 nm (RED): Deoxy-Hb absorbs more
  • 940 nm (INFRARED): Oxy-Hb absorbs more

The R Ratio (Heart of Pulse Oximetry)

• R is matched against an internal empirical calibration curve built from healthy volunteer data (SpO2 70-100%)
• Accuracy: ±2-3% in SpO2 range 70-100%
• NOT validated below SpO2 of 70% - extrapolated data only

---

4. COMPONENTS OF PULSE OXIMETER

PULSE OXIMETER PROBE
      |
      |-- Light Emitter (2 LEDs: 660nm + 940nm, alternating)
      |-- Photodetector (opposite side = transmission; same side = reflectance)
      |-- Ambient light cancellation (both LEDs off = ambient baseline)

---

5. ISOBESTIC POINT

• Definition: Wavelength at which OxyHb and DeoxyHb have equal absorbance
• Value: 805 nm (also 590 nm)
• At this wavelength, absorbance is independent of O2 saturation
• Used as a reference point in co-oximetry
• Exam Pearl: Pulse oximetry uses 660 nm and 940 nm - NOT the isobestic point (this is important!)

---

6. MULTIWAVELENGTH / CO-OXIMETRY

• Standard pulse oximeter uses 2 wavelengths - measures only functional saturation
• Co-oximeter uses up to 12 wavelengths - measures:
  • OxyHb (O2Hb)
  • DeoxyHb (HHb)
  • Carboxyhaemoglobin (COHb)
  • Methaemoglobin (MetHb)
  • Sulphhaemoglobin (SulfHb)
  • Total Hb (SpHb) - Masimo Rainbow technology

Functional vs Fractional Saturation

Must Remember: Standard pulse oximeter gives falsely HIGH SpO2 in COHb poisoning because COHb absorbs at 660 nm similarly to OxyHb!

---

7. CAUSES OF INACCURATE SpO2

Falsely HIGH SpO2

Falsely LOW SpO2

High Yield Fact: In MetHb toxicity, SpO2 plateaus at ~85% regardless of actual saturation - hallmark finding.

---

8. PLETHYSMOGRAPHIC WAVEFORM (PPG)

• Pulse oximeter also functions as a photoplethysmograph
• Waveform variations (PVI - Pleth Variability Index) can predict fluid responsiveness
• PVI >13-14% = likely fluid responder in mechanically ventilated patients
• Perfusion Index (PI) from waveform amplitude = surrogate for peripheral perfusion

---

9. CLINICAL APPLICATIONS IN ANAESTHESIA

---

10. LIMITATIONS OF PULSE OXIMETRY

• Detects hypoxaemia late (lag 30-90 seconds behind true PaO2 fall)
• Cannot detect hyperoxia (no upper alarm once SpO2 = 100%)
• Cannot assess ventilation (CO2 retention undetected - need EtCO2)
• Poor signal in states of low perfusion
• Cannot replace ABG for acid-base, CO2, and precise PaO2 measurement

---

11. IMPORTANT NORMAL VALUES

---

12. PHYSICS SUMMARY TABLE

---

13. RECENT ADVANCES (2024-2026)

• Masimo Rainbow SET technology: SpHb (non-invasive Hb), SpCO, SpMet, SpO2 from single probe
• Equity concern: Multiple studies (2020-2024) showed pulse oximeters overestimate SpO2 in darker skin tones - FDA issued guidance for improved testing across skin tones (2024)
• Wearable continuous SpO2 monitoring (smartwatches, patches) - now entering perioperative pathways
• AI-driven waveform analysis: SpO2 waveform used for non-invasive blood pressure estimation

---

📌 EXAM PEARLS

1. Beer-Lambert Law: A = ε·b·c - must be written with all symbols defined
2. Two wavelengths: 660 nm (RED) and 940 nm (IR) - know which haemoglobin absorbs more at each
3. COHb → falsely HIGH SpO2 | MetHb → SpO2 plateaus at 85% - most common viva traps
4. Isobestic point = 805 nm - where OxyHb and DeoxyHb absorb equally
5. Pulse oximeter calibrated in healthy volunteers at SpO2 70-100% - not valid below 70%
6. Cannot detect CO2 retention - always pair with EtCO2 or ABG

---

🔴 HIGH YIELD FACTS

• SpO2 lags PaO2 by 30-90 seconds - critical during rapid desaturation
• Standard oximeter = 2 wavelengths (functional SpO2); Co-oximeter = up to 12 wavelengths (fractional saturation)
• Methylene blue (used in methHb treatment) transiently drops SpO2 to ~65% - do not panic
• PVI >13% from plethysmograph = fluid responsiveness predictor
• FDA accuracy requirement: SpO2 ≤ ±3% root mean square difference

---

---

---

MIXED VENOUS OXIMETRY (SvO2) AND JUGULAR VENOUS OXYGEN SATURATION (SjvO2)

Combined Answer: Mixed Venous Oximetry | Jugular Venous Oxygen Saturation | SvO2 Conditions Decreased

---

1. DEFINITIONS

• SvO2 (Mixed Venous Oxygen Saturation): O2 saturation of blood in the proximal pulmonary artery - represents the average O2 saturation of blood returning from the entire body to the right heart, weighted by regional blood flows
• ScvO2 (Central Venous O2 Saturation): O2 saturation of blood from the superior vena cava via a central venous catheter - a clinically practical surrogate for SvO2
• SjvO2 (Jugular Venous O2 Saturation): O2 saturation at the jugular bulb - reflects global cerebral O2 supply-demand balance

---

2. PHYSIOLOGICAL BASIS - THE FICK PRINCIPLE

Fick's Equation

Derivation: SvO2 and O2 Extraction Ratio

Key concept: SvO2 is the mirror of O2 extraction ratio. When the body extracts more O2 (ERO2↑), SvO2 falls. When delivery improves, SvO2 rises.

---

3. DETERMINANTS OF SvO2

SvO2 = SaO2 - VO2 / (1.34 × Hb × CO)

SvO2 is DECREASED by:              SvO2 is INCREASED by:
  |                                   |
  |-- ↓ SaO2 (hypoxaemia)             |-- ↑ SaO2 (O2 therapy)
  |-- ↓ Hb (anaemia)                  |-- ↑ Hb (transfusion)
  |-- ↓ CO (cardiogenic shock)        |-- ↑ CO (sepsis, vasodilatory)
  |-- ↑ VO2 (fever, shivering,        |-- ↓ VO2 (hypothermia,
       seizures, pain, sepsis)              sedation, anaesthesia)
                                      |-- Tissue O2 extraction failure
                                           (late sepsis, cyanide toxicity)

---

4. NORMAL VALUES

Must Remember: ScvO2 is normally 2-5% HIGHER than SvO2 (under normal conditions). During shock/haemodynamic instability, this relationship reverses and the gap widens.

---

5. CAUSES OF DECREASED SvO2

A. Decreased O2 Delivery (DO2↓)

B. Increased O2 Consumption (VO2↑)

---

6. CAUSES OF FALSELY HIGH SvO2 (IMPORTANT TRAPS)

Exam Pearl: Normal/high SvO2 does NOT rule out tissue hypoxia - especially in septic shock (microcirculatory failure) and cyanide poisoning. Always correlate with serum lactate.

---

7. MEASUREMENT OF SvO2

Direct Method

• Pulmonary Artery Catheter (PAC):
  • Fibreoptic PAC (e.g., Vigilance, Oximetrix) - continuous SvO2
  • Intermittent blood sampling from distal (PA) port of PAC - spot SvO2
  • Gold standard

Surrogate Method

• ScvO2 from CVC in SVC - widely used in clinical practice
• Rivers et al. (EGDT, NEJM 2001): ScvO2 ≥70% as resuscitation target in septic shock
• Surviving Sepsis Campaign 2021: ScvO2 ≥70% is still used as a guide (though ARISE, ProCESS, ProMISe trials questioned protocolized EGDT)

---

8. CLINICAL APPLICATIONS IN ANAESTHESIA & ICU

---

9. JUGULAR VENOUS OXYGEN SATURATION (SjvO2) - CEREBRAL MONITORING

Principle

• Measures global cerebral O2 supply-demand balance
• Cerebral O2 Extraction = (SaO2 - SjvO2)
• Normal CMRO2 (cerebral metabolic rate for O2) = 3-5 mL/100g/min

Technique

• Retrograde catheterisation of internal jugular vein
• Catheter tip placed in jugular bulb (C1-C2 level) - confirmed by X-ray
• Usually the dominant jugular vein (right in most patients) is cannulated
• Right jugular drains predominantly cortical blood
• Left jugular drains more subcortical regions

Normal Values and Interpretation

Indications for SjvO2 Monitoring

• Traumatic Brain Injury (TBI) - severe head injury
• Neurosurgery with risk of cerebral ischaemia
• Carotid endarterectomy (during cross-clamping)
• Cardiac surgery with circulatory arrest
• SAH and vasospasm monitoring

Causes of Desaturation (SjvO2 < 50%)

• Hypocapnia (hyperventilation → cerebral vasoconstriction)
• Arterial hypotension → ↓ CPP
• Anaemia
• Hypoxaemia
• ↑ CMRO2 (fever, seizures, pain)
• Raised ICP with reduced CPP

Causes of High SjvO2 (>75%)

• Cerebral hyperaemia (e.g., post-hyperventilation rebound)
• Brain death (no O2 consumption → 100%)
• AV malformations (arteriovenous shunting)
• Hypothermia

Limitations

• Global monitor only - focal ischaemia may be missed
• Incomplete intracranial mixing (left ≠ right)
• Extracranial contamination if tip too low (facial vein admixture)
• Requires skilled placement + fluoroscopic confirmation

---

10. CEREBRAL OXIMETRY (rSO2) - NON-INVASIVE ALTERNATIVE

• NIRS (Near-Infrared Spectroscopy) based
• Measures regional cerebral O2 saturation (rSO2) non-invasively
• Sensors placed on forehead (bifrontal)
• Normal rSO2: 60-80% (reflects mixed arterio-venous saturation ~25:75 ratio)
• rSO2 <50% or >20% fall from baseline = intervention threshold
• Used in: cardiac surgery, carotid surgery, beach-chair shoulder surgery

---

11. COMPARISON TABLE: SvO2 vs ScvO2 vs SjvO2

---

12. IMPORTANT FORMULAE

---

13. ANAESTHETIC IMPLICATIONS

Intraoperative

• Falling SvO2 during anaesthesia signals:
  • Inadequate depth (↑ VO2 due to stress)
  • Hypovolaemia (↓ CO)
  • Anaemia (↓ O2 carrying capacity)
  • Hypoxaemia (check SpO2/FiO2)
• Target-directed fluid and inotrope therapy guided by SvO2/ScvO2

ICU

• Low SvO2 + high lactate = serious tissue hypoxia - initiate goal-directed therapy
• Normal SvO2 + high lactate = microcirculatory failure (late sepsis) or cyanide toxicity

---

14. RECENT ADVANCES (2024-2026)

• Continuous non-invasive SvO2 estimation from multiwavelength pulse oximetry (experimental)
• NIRS-guided cerebral protection during cardiac surgery becoming standard at high-volume centres
• Integration of SjvO2 / rSO2 into multimodal neuromonitoring bundles for TBI (BTF 2024 update)
• Growing evidence that ScvO2 > 70% as sole endpoint in sepsis is insufficient - lactate clearance ≥10% is now co-endorsed by SSC 2021

---

📌 EXAM PEARLS

1. SvO2 = 1 - ERO2 - fundamental relationship, always derive this in exams
2. ScvO2 > SvO2 by 2-5% under normal conditions; this reverses in shock
3. SjvO2 < 50% = cerebral ischaemia; >75% = hyperaemia or brain death
4. Normal/high SvO2 in sepsis does NOT mean adequate tissue oxygenation - mitochondrial dysfunction
5. Wedged PAC gives falsely high SvO2 (sampling arterialized blood)
6. Rivers' EGDT (2001) - ScvO2 ≥70% landmark trial - know its limitations (ARISE/ProCESS 2014)

---

🔴 HIGH YIELD FACTS

• PvO2 normal = 40 mmHg | SvO2 normal = 65-75%
• SjvO2 normal = 55-75% | rSO2 (NIRS) normal = 60-80%
• Cyanide toxicity: SvO2 is HIGH (paradoxically), lactate is HIGH - classic exam question
• Brain death: SjvO2 approaches 100% (no cerebral O2 consumption)
• In septic shock: ScvO2 target ≥70% + lactate clearance ≥10% in 2 hours (SSC 2021)

---

---

---

END-TIDAL CO2, CAPNOGRAPHY AND CAPNOMETRY

Combined Answer: EtCO2 | Use of Capnography in Anaesthesia | Capnometry

---

1. DEFINITIONS

Distinction: Capnometry = number only; Capnography = number + waveform. Clinically, capnography is always preferred.

---

2. PHYSICAL PRINCIPLE

• Based on Beer-Lambert Law: CO2 absorbs infrared (IR) light at wavelength 4.26 μm
• The amount of IR absorbed is proportional to CO2 concentration in the sample
• Reference cell (CO2-free) compared with sample cell to calculate CO2 %

---

3. TYPES OF CAPNOGRAPHS

Exam Pearl: Sidestream preferred in paediatrics, MAC, non-intubated patients. Mainstream preferred in ventilated adult patients where response time matters.

---

4. THE NORMAL CAPNOGRAM - PHASES

CO2
(mmHg)
  40 ┤         ___________D (Plateau = EtCO2)
     |        /            \
     |       /C             \
     |      /                \
   0 ┤_____/A  B              \___E___
     |
     └──────────────────────────────── Time
         EXPIRATION          INSPIRATION

• Alpha angle (between Phase II and III): Normal ≈ 100-110°; increases in obstructive disease
• Beta angle (between Phase III and downstroke): Normal ≈ 90°; increases with rebreathing

---

5. NORMAL VALUES

Key Formula: PaCO2 = EtCO2 + Dead Space Component Increased dead space → increased (PaCO2 - EtCO2) gradient

---

6. THE PaCO2 - EtCO2 GRADIENT

Causes of INCREASED Gradient (EtCO2 ↓↓ relative to PaCO2)

• Pulmonary embolism (↑ alveolar dead space - classic)
• Air embolism (venous air embolism)
• ↓ Cardiac output (any cause - reduced lung perfusion)
• Hypotension
• Severe COPD / emphysema (V/Q mismatch)
• Low tidal volume / high RR ventilation

Causes of DECREASED Gradient (EtCO2 ≈ PaCO2 or > PaCO2)

• ARDS / Pulmonary oedema (shunt physiology - venous admixture raises EtCO2)
• Possible in pregnancy (↑ CO, ↓ dead space)

---

7. CAUSES OF ABNORMAL CAPNOGRAMS

A. Elevated EtCO2

B. Decreased EtCO2

C. Characteristic Waveform Changes

---

8. CLINICAL USES OF CAPNOGRAPHY IN ANAESTHESIA

A. Confirmation of Tracheal Intubation

• Most reliable bedside test for confirming ETT placement
• Persistent waveform = tracheal intubation
• Absent or rapidly disappearing waveform = oesophageal intubation
• Does NOT detect right mainstem bronchial intubation (both lungs may still have CO2)
• Gold standard remains direct visualisation + fibreoptic confirmation

B. Monitoring Ventilation Adequacy

• Real-time CO2 elimination monitoring
• Guide to ventilator settings (RR, TV)
• Prevents inadvertent hyperventilation (especially in TBI patients where ETCO2 target = 35-40 mmHg)
• In TBI/raised ICP: target EtCO2 35-40 mmHg (avoid hypocapnia unless cerebral herniation)

C. Monitoring During CPR

• EtCO2 > 10 mmHg = adequate chest compressions
• EtCO2 > 40 mmHg = predictor of ROSC (Return of Spontaneous Circulation)
• EtCO2 < 10 mmHg after 20 min of ACLS = poor prognostic sign (AHA 2020)

D. Detection of Air/Gas Embolism

• Rapid fall in EtCO2 = early sign of venous air embolism
• Classic in sitting position neurosurgery, laparoscopy, liver surgery

E. Malignant Hyperthermia

• Earliest monitor to show change - EtCO2 rises rapidly before temperature
• Should trigger immediate action

F. Weaning from Mechanical Ventilation

• EtCO2 trend during spontaneous breathing trial (SBT)
• Rising EtCO2 during SBT = ventilatory failure / weaning failure

G. Assessment of Dead Space

• Normal VD/VT = 0.3 (30%)

H. Volumetric Capnography (CO2 vs Volume)

• EtCO2 plotted against tidal volume (not time)
• Calculates dead space more accurately (Enghoff modification of Bohr equation)
• Allows PEEP optimisation and alveolar recruitment assessment

---

9. CAPNOGRAPHY IN SPECIAL SITUATIONS

---

10. CAPNOGRAPHY IN NON-INTUBATED PATIENTS

• Modified nasal cannula with CO2 sampling port
• Face mask with side port sampling line
• Useful in:
  • MAC / procedural sedation
  • PACU monitoring
  • Endoscopy sedation
  • Emergency department
• Detects apnoea/hypoventilation 45 seconds earlier than pulse oximetry (Barash)
• Respiratory depression 17.6× more likely to be detected with capnography vs standard monitoring alone (meta-analysis, Waugh et al.)

---

11. IMPORTANT COMPARISON TABLE

---

12. RECENT ADVANCES (2024-2026)

• Transcutaneous CO2 (PtcCO2) monitoring: Continuous, non-invasive PaCO2 estimation - useful in neonates and NICU
• Volumetric capnography integration into modern ICU ventilators (Draeger Evita, Hamilton) for dead space calculation and PEEP optimisation
• Capnography for ROSC prediction strengthened in AHA 2020 CPR Guidelines - EtCO2 < 10 mmHg at 20 min = consider stopping resuscitation
• AI-based waveform analysis of capnograms to detect early bronchospasm and circuit issues

---

13. CURRENT GUIDELINES

• ASA Standards (2020): Capnography mandatory for all GA patients and strongly recommended for moderate/deep sedation
• ESAIC: EtCO2 monitoring mandatory during neuraxial anaesthesia with sedation
• AHA (2020 CPR): EtCO2 > 10 mmHg during CPR = adequate compressions; EtCO2 surge = ROSC
• DAS 2015 (reaffirmed 2022): Waveform capnography mandatory for intubation confirmation in difficult airway management

---

📌 EXAM PEARLS

1. Capnometry = number; Capnography = number + waveform - define both clearly
2. Phase III plateau with upward slope (shark fin) = bronchospasm - must describe in answer
3. Earliest sign of MH = rising EtCO2 - before temperature rises
4. EtCO2 sudden fall to zero = disconnect, cardiac arrest, or oesophageal intubation
5. Normal PaCO2 - EtCO2 gradient = 2-5 mmHg - increases with dead space (PE, air embolism, low CO)
6. EtCO2 > 40 mmHg during CPR = likely ROSC - stop and check pulse

---

🔴 HIGH YIELD FACTS

• EtCO2 normal = 35-45 mmHg
• Beer-Lambert Law governs IR absorption at 4.26 μm for CO2
• Sidestream preferred in paediatrics and MAC; Mainstream for intubated adults
• Normal VD/VT = 0.3; Increases with PE, COPD, ARDS ventilation
• Capnography detects apnoea ~45 sec before SpO2 falls
• Rebreathing sign on capnogram: elevated baseline (Phase I not returning to zero)

---

---

---

THROMBOELASTOGRAPHY, VISCOELASTIC COAGULATION TESTS AND ACTIVATED CLOTTING TIME

Combined Answer: TEG (×3) | Viscoelastic Coagulation Tests | ACT | Normal TEG Diagram | Clinical Applications

---

1. INTRODUCTION

Limitations of Conventional Coagulation Tests (PT, aPTT, INR, platelet count)

• Performed on platelet-poor plasma - do not assess whole blood clot dynamics
• Static tests - do not assess clot formation speed, strength, or lysis
• Poor correlation with actual clinical bleeding in complex situations (trauma, cardiac surgery, liver disease, obstetric haemorrhage)
• Results take 45-60 minutes - too slow for acute haemorrhage management

Why Viscoelastic Tests?

• Assess whole blood coagulation
• Measure all three phases of haemostasis simultaneously:
  • Primary (platelet plug)
  • Secondary (coagulation cascade)
  • Tertiary (fibrinolysis)
• Point-of-care (POC) results in 15-30 minutes
• Guide targeted blood component therapy - reduce unnecessary transfusions

---

2. VISCOELASTIC HAEMOSTATIC ASSAYS (VHA) - OVERVIEW

---

3. PRINCIPLE OF TEG/ROTEM

WHOLE BLOOD SAMPLE + ACTIVATOR
           |
           |--- Cup/Pin begins to move
           |--- Initially: no resistance (fluid blood)
           |--- As clot forms: resistance to motion increases
           |--- Signal transmitted → graphical trace generated
           |--- As fibrinolysis occurs: resistance decreases

• The machine detects viscoelastic changes (changes in physical properties of blood) as it transitions from liquid → gel → lysis
• Output = characteristic spindle-shaped waveform (TEG trace)

---

4. THE TEG TRACE - LABELLED DIAGRAM

                              MA
Amplitude                  ___________
(mm)             ___       /           \
                /   \     /             \       LY30
               /     \___/               \___________
              /
     R       K
|←──────→|←→|
|  Clot     Clot  |          Clot          |  Fibrinolysis
| Initiation Form |          Strength      |
|
Time ────────────────────────────────────────────────────→

---

5. TEG PARAMETERS - NORMAL VALUES AND CLINICAL SIGNIFICANCE

Must Remember:

• R time = reflects intrinsic pathway + anticoagulants
• MA = reflects platelet function + fibrinogen (most important parameter clinically)
• LY30 = reflects fibrinolysis (key in trauma, obstetric haemorrhage)

---

6. ROTEM CHANNELS

Exam Pearl: FIBTEM MA normal = 9-25 mm. If FIBTEM MA low → give Fibrinogen/Cryoprecipitate. If EXTEM MA - FIBTEM MA < 15mm → platelet contribution minimal → give platelets.

---

7. INTERPRETATION PATTERNS - VISUAL GUIDE

NORMAL TEG
|     /‾‾‾‾‾‾‾‾‾\
|    /             \
|___/               \___

FACTOR DEFICIENCY (↑R time, normal MA)
|              /‾‾‾‾\
|             /      \
|____________/        \___

THROMBOCYTOPENIA (normal R, ↓MA)
|   /‾‾‾‾\
|  /      \
|_/        \_____

FIBRINOLYSIS (normal initially, then drop in MA)
|   /‾‾‾‾\___________
|  /
|_/

HYPERCOAGULABLE (↓R, ↑α, ↑MA)
| /‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾\
|/                    \__

---

8. CLINICAL APPLICATIONS OF TEG/ROTEM IN ANAESTHESIA

A. Cardiac Surgery and CPB

• Monitor heparin effect (HEPTEM vs INTEM comparison)
• Detect residual heparin after protamine reversal
• Guide protamine dosing
• Detect coagulopathy post-CPB (factor deficiency vs platelet dysfunction vs fibrinolysis)

B. Trauma / Massive Haemorrhage

• Early detection of Trauma-Induced Coagulopathy (TIC)
• Detect hyperfibrinolysis - LY30 > 3% = fibrinolysis → give Tranexamic Acid immediately
• Guide 1:1:1 MTP (Massive Transfusion Protocol) vs targeted therapy
• CRASH-2 trial basis: TXA within 3 hours saves lives in trauma with coagulopathy

C. Liver Transplantation

• Best monitor for complex coagulopathy
• Guides each phase: anhepatic phase (heparinoid effect, fibrinolysis), reperfusion (massive fibrinolysis)
• Reduces blood product usage by 50%

D. Obstetric Haemorrhage (PPH)

• Rapid detection of consumptive coagulopathy and fibrinogen depletion
• FIBTEM MA < 12 mm → Fibrinogen replacement (target > 2 g/L)
• WOMAN trial: TXA reduces PPH mortality

E. Neurosurgery

• Detect hypercoagulable states (DVT risk)
• Monitor anticoagulation reversal

F. Sickle Cell / Haematological Disorders

• Monitor hypercoagulable tendency

---

9. TEG-GUIDED TRANSFUSION ALGORITHM

PATIENT BLEEDING → TEG/ROTEM
           |
    ┌──────┴──────────────────┐
    |                         |
   ↑R time                  ↓MA
   (Factor deficiency)      |
    |                   ┌───┴────────┐
    ↓                   |            |
   FFP/PCC         FIBTEM ↓MA    FIBTEM normal MA
                         |            |
                   Fibrinogen/    Platelets
                   Cryoprecipitate
           |
          ↑LY30 (>3%)
           |
         Tranexamic Acid / Epsilon-ACA

---

10. ACTIVATED CLOTTING TIME (ACT)

Definition

• A whole blood point-of-care clotting test that measures time from sample contact with an activator to clot formation, reflecting the intrinsic + common coagulation pathways
• Described by Hattersley (1966) as a modification of Lee-White whole blood clotting time

Principle

• Blood added to a tube containing a contact activator (celite/kaolin/glass beads)
• Tube rotated or agitated; clot formation detected mechanically (magnet displacement) or optically
• Two common systems: Hemochron (magnet-based), Hepcon HMS Plus (plumb bob)

Normal Values

Clinical Uses of ACT

Factors Affecting ACT (Causes of Falsely Prolonged ACT)

Limitations of ACT

• Insensitive at low heparin concentrations
• Poor reproducibility in some systems
• Cannot assess platelet function or fibrinolysis
• Not a substitute for full haemostasis assessment
• Aprotinin causes falsely prolonged Celite-ACT but not Kaolin-ACT

---

11. COMPARISON: CONVENTIONAL TESTS vs VISCOELASTIC TESTS vs ACT

---

12. RECENT ADVANCES (2024-2026)

• TEG 6s (Haemonetics): Cartridge-based, no pipetting, 4 simultaneous channels, minimal operator skill - now entering many Indian cardiac centres
• ROTEM Sigma: Fully automated ROTEM - reduces operator variability
• Viscoelastic-guided MTP: Multiple RCTs (ITACTIC 2020, CRYOSTAT-2 2023) show TEG/ROTEM-guided transfusion reduces blood product use and is non-inferior to empirical 1:1:1 MTP
• SSC 2021 / ESICM 2023: Recommend viscoelastic monitoring for coagulopathy in sepsis and major haemorrhage
• FIBTEM-guided fibrinogen supplementation now standard of care in obstetric haemorrhage management (OAA/RCOG 2023)

---

13. CURRENT GUIDELINES

• European Trauma Guidelines (2023): VHA recommended for guiding haemostatic resuscitation in major trauma
• ESAIC/ESA (2023): TEG/ROTEM recommended for all major surgeries with expected significant blood loss
• COBS/OAA (2023): FIBTEM-guided fibrinogen replacement in PPH
• STS/AHA Cardiac Surgery (2021): TEG/ROTEM for coagulation management during and after CPB

---

📌 EXAM PEARLS

1. R time (TEG) = CT (ROTEM) = clot initiation = factor deficiency → give FFP/PCC
2. MA (TEG) = MCF (ROTEM) = clot strength = platelet + fibrin → if low, check FIBTEM
3. LY30 > 3% = pathological fibrinolysis → give Tranexamic Acid immediately
4. FIBTEM MA = fibrinogen contribution only (platelets blocked) → if low, give cryoprecipitate/fibrinogen concentrate
5. Normal ACT = 107 ± 13 sec; CPB target = >480 sec
6. Hypothermia and haemodilution both prolong ACT - correct temperature before interpreting

---

🔴 HIGH YIELD FACTS

• TEG rotating cup vs ROTEM fixed cup - remember this distinction (favourite viva question)
• ACT measures intrinsic + common pathway - used for heparin monitoring in cardiac surgery
• Aprotinin + Celite ACT = falsely prolonged; use Kaolin ACT with aprotinin
• TEG/ROTEM identifies the type of coagulopathy → targeted therapy saves blood products
• FIBTEM channel = fibrinogen quantification in whole blood without platelet interference
• Normal LY30 < 8% in TEG; pathological fibrinolysis = >3% (Trauma threshold)

---

---

---

TRANSOESOPHAGEAL ECHOCARDIOGRAPHY (TOE/TEE) IN ANAESTHESIA PRACTICE

Combined Answer: Use of TOE in Anaesthesia (×2)

---

1. DEFINITION

• TOE (Transoesophageal Echocardiography) / TEE (Transesophageal Echocardiography): A semi-invasive cardiac imaging modality in which an ultrasound transducer mounted on a modified endoscope is introduced into the oesophagus and stomach to obtain high-resolution real-time images of cardiac structures, function, and haemodynamics
• Provides superior image quality compared to transthoracic echocardiography (TTE) due to proximity of the oesophagus to the heart (posterior cardiac structures especially) and absence of lung/rib interference

---

2. RELEVANT ANATOMY

Anatomical Basis for TOE Windows

OESOPHAGUS POSITION RELATIVE TO HEART:
Oesophagus → lies directly POSTERIOR to left atrium
                     ↓
         Excellent views of:
         • Left atrium (LA)
         • Mitral valve
         • Left atrial appendage (LAA)
         • Pulmonary veins
         • Descending aorta
         • Aortic arch (from gastric window)

• Distance from incisors:
  • Upper oesophageal (UE): 20-25 cm - aortic arch views
  • Mid-oesophageal (ME): 30-35 cm - most common views (4-chamber, AV, bicaval)
  • Trans-gastric (TG): 40-45 cm - LV short axis, RV inflow-outflow

---

3. PROBE AND EQUIPMENT

---

4. THE 20 STANDARD TOE VIEWS (ASE/SCA Guidelines)

Key Views for Anaesthesia Practice

Exam Pearl: TG Mid SAX (Transgastric Midpapillary Short Axis) at 0° is the most important single view - shows all 3 coronary territories simultaneously for wall motion analysis.

---

5. INDICATIONS FOR INTRAOPERATIVE TOE

Class I Indications (Strong Evidence - Recommended)

• All open heart surgeries (valve repair/replacement, CABG, aortic surgery)
• Cardiac transplantation
• Congenital heart disease repair
• Thoracic aortic disease (aortic dissection, aneurysm)
• Haemodynamic instability intraoperatively when cause is unclear
• Lung transplantation

Class II Indications (Good Evidence - May Be Used)

• High-risk non-cardiac surgery (major vascular, orthotopic liver transplant)
• Suspected cardiac embolism source
• Pericardial effusion / cardiac tamponade
• Intracardiac thrombus detection (esp. LAA)
• Assessment of volume status in high-risk surgical patients
• Air embolism detection (sitting craniotomy, hepatic surgery)
• Thoracic surgery - lung resection (tumour invasion, RV function)
• Repair of structural heart disease (TAVI, MitraClip, ASD closure - on CPB or percutaneous)

Class III Indications (Limited Evidence)

• Routine monitoring in non-cardiac low-risk surgery
• Haemodynamically stable patients on CPB for minor procedures

---

6. WHAT TOE MEASURES/ASSESSES

A. Ventricular Function

B. Valvular Assessment

• Mitral valve: Area, regurgitation, repair assessment (post-repair SAM)
• Aortic valve: Stenosis (PHT, continuity equation), regurgitation (vena contracta)
• Tricuspid valve: Regurgitation, PA pressure estimation (TR jet velocity)
• Pulmonary valve: Regurgitation, RVOT obstruction

C. Aortic Pathology

• Aortic dissection: Intimal flap, true/false lumen, involvement of coronary ostia
• Ascending aortic aneurysm: Size, morphology
• Atheroma: Grading (Grades I-V) - important for cannulation site in CABG

D. Structural Defects

• Patent Foramen Ovale (PFO): Bubble contrast study
• ASD/VSD: Size, flow direction, Qp:Qs ratio
• Intracardiac thrombus (esp. LAA)
• Pericardial effusion: Size, tamponade physiology (RA/RV collapse)

E. Haemodynamic Parameters from TOE

---

7. CLINICAL APPLICATIONS IN ANAESTHESIA (SYSTEM-WISE)

A. Cardiac Surgery (CPB)

• Pre-CPB: Confirm diagnosis, assess valvular anatomy, LV/RV function baseline, check for PFO, grade aortic atheroma
• During CPB: Detect air in cardiac chambers before weaning
• Post-CPB: Assess adequacy of repair/replacement, detect residual lesions, assess RV/LV function, detect paravalvular leaks
• De-airing: Confirm all chambers free of air before removing aortic cross-clamp

B. Non-Cardiac Surgery

• Haemodynamic instability: Rapid diagnosis - hypovolaemia vs cardiogenic vs obstructive shock
• Suspected PE: RV dilatation + McConnell sign + D-sign on LV
• Pericardial tamponade: RA/RV diastolic collapse, IVC plethora, swinging heart
• Aortic dissection: Intimal flap in descending aorta

C. Thoracic Surgery

• RV function monitoring during pneumonectomy
• Tumour invasion of heart/great vessels
• Detection of PFO (right-to-left shunt during OLV/PEEP)
• Air embolism detection

D. Liver Transplantation

• Monitor volume status in all 3 phases
• Detect portopulmonary hypertension
• Post-reperfusion myocardial dysfunction

E. Obstetric Anaesthesia

• Cardiac arrest in pregnancy - diagnose cause
• Peripartum cardiomyopathy assessment

---

8. CONTRAINDICATIONS

Absolute Contraindications

• Oesophageal obstruction / stricture
• Oesophageal tumour / perforation
• Active oesophageal varices (relative - Grade III/IV)
• Recent oesophageal surgery

Relative Contraindications

• Oesophageal varices (Grade I/II - use with caution)
• Cervical spine instability
• Coagulopathy (INR > 2.5 or platelets < 50,000)
• Recent upper GI surgery
• Uncooperative awake patient (unless sedated)
• Oropharyngeal pathology

---

9. COMPLICATIONS

Must Remember: TOE is semi-invasive - complications are rare but the oesophageal perforation is potentially fatal.

---

10. TOE vs TTE - COMPARISON TABLE

---

11. FOCUSED CARDIAC ULTRASOUND (FOCUS) vs COMPREHENSIVE TOE

---

12. TRAINING AND COMPETENCY

• Level I (Basic): Understanding of TOE, limited views, interpretation with supervision
• Level II (Advanced): Comprehensive perioperative TOE - 300 supervised examinations
• Level III (Expert): Teaching and research

• NBE (National Board of Echocardiography) - USA: PTEeXAM (Basic) and DBNPE (Advanced)
• ASE/SCA Guidelines (2020): Training standards for perioperative echocardiography

---

13. RECENT ADVANCES (2024-2026)

• 3D/4D TOE: Real-time 3D imaging for structural interventions (TAVI, MitraClip, Watchman LAA occlusion) - now standard
• AI-assisted TOE interpretation: Automated EF calculation, wall motion analysis, valve quantification - FDA-approved tools (EchoGo, Caption Health)
• Point-of-care TOE (handheld TOE probes - CX50, Vscan Ultra) now available
• TOE for ECMO cannulation guidance - indispensable for VA-ECMO and VV-ECMO
• ESAIC 2023: Recommends TOE competency as core skill for cardiac anaesthesiologists
• TAVI guidance: TOE has become indispensable for transcatheter valve interventions - guides device sizing, deployment, leak assessment

---

14. CURRENT GUIDELINES

• ASE/SCA (2010, reaffirmed 2022): Indications, training standards, 20 standard views
• ESA/ESAIC (2021): Perioperative TOE recommended for all cardiac surgery and high-risk non-cardiac surgery
• ACC/AHA (2021 Valve Guidelines): TOE mandatory for intraoperative valve assessment
• SCCM (2023): POCUS/TOE recommended for haemodynamic assessment in ICU shock states

---

📌 EXAM PEARLS

1. ME 4-Chamber view at 0° = first and most informative view in any emergency
2. TG Mid SAX at 0° = gold standard for wall motion analysis (all 3 coronary territories: LAD, LCx, RCA)
3. Hypovolaemic LV on TOE = small, hyperkinetic ventricle with "kissing papillaries" (walls touch in systole)
4. Cardiac tamponade on TOE = RA collapse in systole + RV collapse in diastole + IVC plethora (non-collapsing)
5. Post-MVR on TOE = always look for SAM (systolic anterior motion of MV) after repair
6. TOE is contraindicated in oesophageal stricture, perforation, active varices - always ask history before inserting probe

---

🔴 HIGH YIELD FACTS

• TOE probe frequency: 3.5-7 MHz - lower frequency = better penetration (vice versa for resolution)
• Normal LV EF = >55% | Mildly reduced = 45-54% | Moderately reduced = 30-44% | Severely reduced = <30%
• PA systolic pressure estimation: 4 × (TR jet velocity)² + CVP (simplified Bernoulli)
• E/e' > 14 = elevated LV filling pressures (diastolic dysfunction)
• LAA thrombus is best seen on TOE (ME bicaval or ME 4-chamber with probe at 0-90°)
• 3D TOE revolutionised structural heart disease interventions - TAVI, MitraClip now TOE-guided routinely

---

---

---

NEUROMUSCULAR MONITORING

Combined Answer: Neuromuscular Monitoring (×3) | Train of Four + Post-Tetanic Count | Double Burst Stimulation (×2) | Various Modes of Nerve Stimulation + Interpretation | Utility of Peripheral Nerve Stimulator

---

1. DEFINITION AND IMPORTANCE

• Neuromuscular monitoring: Objective assessment of the degree of neuromuscular blockade (NMB) using a peripheral nerve stimulator (PNS) applied over a motor nerve, and measuring the evoked muscle response
• Why essential:
  • NMBDs (neuromuscular blocking drugs) have narrow therapeutic window
  • Residual NMB (TOF ratio < 0.9) occurs in 30-60% of patients arriving in PACU without objective monitoring
  • Residual NMB causes: pharyngeal dysfunction, aspiration, hypoxaemia, upper airway obstruction, impaired hypoxic ventilatory response
  • ASA 2023 / ESAIC 2023: Objective quantitative NMB monitoring is recommended as standard of care

---

2. RELEVANT PHYSIOLOGY

Neuromuscular Junction (NMJ) - Brief

Motor nerve axon
       |
  Presynaptic terminal
       |--- ACh synthesised & stored in vesicles
       |--- α3β2 presynaptic nicotinic receptors (autoreceptors)
              → Mobilises ACh release for sustained stimulation
  Synaptic cleft
       |--- AChE degrades ACh
  Postsynaptic membrane
       |--- α1β1δε nicotinic receptors (muscle type)
       |--- 2 α-subunits must be occupied by ACh for channel opening

• Non-depolarising NMBDs block postsynaptic α1 receptors (competitive antagonism) AND presynaptic α3β2 receptors (explaining fade on TOF/tetanus)
• Depolarising NMBDs (Succinylcholine): Bind α1 → persistent depolarisation → fasciculations → flaccid paralysis

---

3. MONITORING SITES AND ELECTRODE PLACEMENT

Exam Pearl: The adductor pollicis (thumb) is most sensitive to NMBDs. Recovery here lags behind the diaphragm and larynx. So TOF ratio ≥0.9 at thumb does NOT mean larynx/diaphragm is fully recovered - they recover EARLIER. This is why extubation should wait for TOF ≥ 0.9 at thumb.

---

4. STIMULATION PARAMETERS (PNS Settings)

---

5. MODES OF NERVE STIMULATION

A. Single Twitch Stimulation

• Frequency: 0.1 Hz (1 stimulus every 10 sec) or 1 Hz (1/sec)
• What it measures: Height of single muscle twitch compared to control (pre-NMB baseline)
• Requires baseline recording before NMB administration
• Interpretation:

• Limitation: Cannot assess residual block (cannot compare T1 to baseline at end of surgery without initial recording)
• Use: Monitoring onset and depth of block; not for recovery assessment

---

B. Train-of-Four (TOF) Stimulation ⭐ (Most Important)

• Introduced by Ali et al. (1970)
• Frequency: 2 Hz - four stimuli given over 2 seconds
• Repeat interval: Every 15 seconds minimum (to avoid potentiation)
• No baseline recording needed - uses ratio of T4/T1

TOF Response Pattern

SEQUENCE: T1 → T2 → T3 → T4 (at 2 Hz over 2 sec)

ONSET OF BLOCK (Deepening):
T4 disappears first → T3 → T2 → T1 (last to disappear)

RECOVERY (Regression):
T1 returns first → T2 → T3 → T4 (last to return)

TOF Count vs Depth of Block

TOF Ratio

Must Remember: TOF ratio ≥ 0.9 = current definition of adequate reversal (Kopman 1995, reaffirmed ESAIC 2023). NOT 0.7 - this is an outdated threshold.

---

C. Tetanic Stimulation

• Frequency: 50 Hz (standard) or 100 Hz (high sensitivity)
• Duration: 5 seconds
• Principle: High-frequency stimulation depletes presynaptic ACh at a rate faster than mobilisation → if partial NMB exists → fade of tetanic response
• Post-tetanic facilitation (PTF): After tetanus, subsequent single twitches are enhanced for 1-2 min due to increased ACh mobilisation

• 50 Hz fade correlates with TOF ratio ≈ 0.4
• 100 Hz fade correlates with TOF ratio ≈ 0.85 (more sensitive)
• Limitation: Painful in awake patients; must wait 2-3 min before repeating

---

D. Post-Tetanic Count (PTC) ⭐

• Used when TOF count = 0 (intense/deep NMB)
• Technique:
  1. Apply 50 Hz tetanus for 5 seconds
  2. Wait 3 seconds
  3. Apply 1 Hz single twitches × 15
  4. Count the number of twitches that appear (PTC)
• Interpretation:

Exam Pearl: PTC is the only mode useful in profound/intense block where TOF = 0. Essential during RSI for difficult airway, or when intense block is required for surgical access (e.g., laparoscopy, spinal surgery).

---

E. Double Burst Stimulation (DBS) ⭐

• Introduced by Viby-Mogensen (1989)
• Designed to overcome the limitation of subjective TOF fade detection
• Technique: Two short bursts of 50 Hz tetanic stimulation
  • DBS 3,3: Two bursts of 3 stimuli each at 50 Hz, separated by 750 msec
  • Each burst: 3 impulses at 50 Hz (60 msec duration)

DBS 3,3 Pattern:
Burst 1: |||  (750 msec gap)  Burst 2: |||
         3 stimuli at 50 Hz           3 stimuli at 50 Hz
         →  Response 1                →  Response 2

• What it detects: If Response 2 < Response 1 = fade present = residual NMB
• Advantage over TOF fade: Human tactile and visual detection of fade is more sensitive with DBS than with TOF
  • DBS detects fade corresponding to TOF ratio down to 0.6
  • TOF subjective fade detection: only down to 0.3-0.4

DBS Interpretation

High Yield: DBS is better than TOF for subjective/manual residual block detection. But neither replaces objective quantitative monitoring (acceleromyography, electromyography).

---

6. SUMMARY TABLE: ALL STIMULATION MODES

---

7. OBJECTIVE vs SUBJECTIVE MONITORING

Subjective Methods (using PNS alone)

• Tactile or visual assessment of thumb movement
• Cannot reliably detect TOF ratio between 0.4 and 0.9 (the "blind zone")
• 10-20% of clinicians cannot subjectively detect fade when TOF ratio is 0.7-0.9

Objective Methods (Quantitative NMB Monitoring)

AMG TOF ratio must be normalised to baseline - uncorrected AMG may read 1.0-1.2 at full recovery, so TOF ratio ≥0.9 must be confirmed against a pre-NMB baseline recording.

---

8. DEPTH OF NMB CLASSIFICATION

---

9. CLINICAL APPLICATIONS IN ANAESTHESIA

Intraoperative

• Monitor NMB depth throughout surgery
• Guide redosing of NMBD
• Reversal timing:
  • Neostigmine: TOF count ≥ 4 twitches (TOF ratio ≥ 0.4)
  • Sugammadex: Can reverse at any depth
    • Shallow: 2 mg/kg (TOF ratio ≥ 0.2)
    • Deep (TOF 1-2): 4 mg/kg
    • Profound/Intense (TOF 0): 16 mg/kg

Post-Extubation

• Before extubation: Objective TOF ratio ≥ 0.9 mandatory
• Clinical signs unreliable for residual NMB detection:
  • 5-second head lift (TOF ratio ≈ 0.6 - not sufficient!)
  • Sustained 5-sec hand grip
  • Tongue protrusion
  • These correspond to TOF ≈ 0.6 - NOT 0.9

Must Remember: Classic clinical tests (head lift for 5 sec, hand grip, leg lift) only require TOF ratio of approximately 0.6 - they CANNOT confirm adequate reversal to TOF ≥ 0.9.

---

10. RESIDUAL NMB - KEY FACTS

---

11. RECENT ADVANCES (2024-2026)

• ESAIC 2023 Consensus Statement: Quantitative NMB monitoring is now a standard of care recommendation - not optional
• TOFscan (Idmed): Compact, acceleromyographic device with automatic normalization - increasingly adopted
• Stimpod NMS450X: EMG-based NMB monitor - superior accuracy over AMG
• TetraGraph: Surface EMG device - validated against MMG gold standard
• Closed-loop NMB delivery: Automated NMB dosing system using real-time TOF feedback - Phase III trials ongoing (2024-2025)
• AI integration: Algorithms predicting residual NMB and optimal reversal timing

---

12. CURRENT GUIDELINES

• ESAIC Consensus (2023): Quantitative NMB monitoring recommended; TOF ratio ≥0.9 for extubation; sugammadex preferred reversal agent
• ASA (2023 Practice Advisory Update): Objective NMB monitoring recommended for all patients receiving NMBDs
• POQI (Perioperative Quality Initiative 2019/2023): Sugammadex + quantitative monitoring bundle reduces residual NMB and respiratory complications
• DAS 2015 guidelines: NMB monitoring integral to difficult airway management - know block depth before reversal in failed intubation drill

---

📌 EXAM PEARLS

1. TOF = 4 twitches at 2 Hz over 2 sec - repeat every 15 sec minimum
2. TOF ratio ≥ 0.9 = adequate recovery - NOT 0.7 (old threshold)
3. PTC = only useful when TOF count = 0 (intense block) - do not confuse with TOF
4. DBS 3,3 = better subjective residual block detection than TOF (detects down to ratio 0.6)
5. 5-second head lift = TOF ratio ≈ 0.6, NOT 0.9 - unreliable for adequate reversal
6. Adductor pollicis (thumb) recovers LAST - most sensitive and conservative monitoring site

---

🔴 HIGH YIELD FACTS

• Fade on TOF/tetanus = non-depolarising block (prejunctional α3β2 receptor blockade)
• No fade (sustained block) = depolarising block (Phase I SCh block)
• TOF T4 disappears first, T1 last with deepening non-depolarising block
• PTC 1-2 = expect TOF response in ~10-15 min (time to allow for surgical closure)
• Sugammadex 16 mg/kg reverses even intense block (TOF count 0, PTC 0) in < 3 min
• Neostigmine is unreliable when TOF count < 4 (blocks already deep - ceiling effect)

---

---

---

BISPECTRAL INDEX (BIS) MONITORING

Combined Answer: BIS Guidelines (×2) | Depth of Anaesthesia Monitoring | Awareness Prevention

---

1. DEFINITION

• BIS (Bispectral Index): A processed EEG (electroencephalography) parameter derived from a proprietary algorithm that analyses the EEG signal from the frontal cortex and converts it into a single dimensionless number (0-100) representing the depth of anaesthesia / sedation
• 0 = electrically silent brain (isoelectric EEG)
• 100 = fully awake, alert
• Originally developed by Aspect Medical Systems (now Medtronic)

---

2. PHYSIOLOGICAL BASIS - EEG AND ANAESTHESIA

EEG Frequency Bands

Effect of Anaesthetics on EEG

AWAKE → Low amplitude, high frequency (Beta)
         ↓ (light sedation)
       Increasing amplitude, decreasing frequency (Alpha → Theta)
         ↓ (surgical anaesthesia)
       High amplitude, slow waves (Delta)
         ↓ (deep anaesthesia)
       Burst suppression pattern
         ↓ (overdose)
       Isoelectric (flat line)

---

3. HOW BIS IS DERIVED

Exam Pearl: BIS is not a single EEG parameter - it is a composite derived index from multiple EEG analyses. This is why it can differ from raw EEG interpretation.

---

4. BIS VALUE SCALE AND CLINICAL INTERPRETATION

Must Remember: BIS 40-60 = target for general anaesthesia. BIS <40 = burst suppression = risk of postoperative cognitive dysfunction (POCD) and delirium in elderly.

---

5. BIS COMPONENTS DISPLAYED ON MONITOR

---

6. BIS SENSOR PLACEMENT

• Site: Forehead - left or right side (frontal lobe)
• Sensor: 4-electrode adhesive strip (BIS Quatro sensor)
• Electrode positions:
  • Electrode 1: Above eyebrow (Fp1/Fp2)
  • Electrode 2: Temple region (F3/F4)
  • Electrode 3: Next to outer canthus of eye
  • Electrode 4: On forehead between eyes (reference)
• Impedance: Must be < 5 kΩ for reliable reading
• Must clean skin with alcohol and allow to dry before applying

---

7. CLINICAL USES OF BIS IN ANAESTHESIA

A. Prevention of Intraoperative Awareness

Key Conclusion: BIS is not superior to end-tidal anaesthetic agent concentration (ETAC) monitoring for awareness prevention in non-high-risk patients. However, in TIVA (no volatile agent), BIS is the only objective depth monitor.

B. TIVA (Total Intravenous Anaesthesia)

• Most important indication for BIS - no ETAC available
• Propofol-remifentanil TIVA: BIS target 40-60
• Guides propofol infusion rate

C. High-Risk Patients for Awareness

• Cardiac surgery (haemodynamically compromised, low MAC required)
• Obstetric GA (low anaesthetic concentration used pre-delivery)
• Major trauma surgery
• Patients with prior awareness episodes
• Patients with chronic alcohol/drug use (higher MAC requirement)

D. Titration of Anaesthetic Dose

• Avoids both over-dosing (BIS <40) and under-dosing (BIS >60)
• Reduces anaesthetic consumption by 10-30% with BIS guidance
• Reduces recovery time and PACU stay

E. Sedation Monitoring in ICU

• BIS-guided sedation protocol
• Target BIS 60-70 for light sedation (RASS -1 to -2)
• Target BIS 40-60 for deep sedation (RASS -3 to -4)
• Reduces excessive sedation, delirium, ventilator days

F. Detection of Burst Suppression

• BSR > 0% in surgical anaesthesia = excessive depth
• Associated with postoperative delirium and POCD in elderly (CODA trial, 2019)
• Avoid BIS < 40 in patients > 65 years

---

8. OTHER PROCESSED EEG MONITORS (DEPTH OF ANAESTHESIA)

Exam Pearl: Response Entropy (RE) > State Entropy (SE) = patient is mounting a response to noxious stimulus (frontal EMG activity) - suggests inadequate analgesia, not just light anaesthesia.

---

9. FACTORS AFFECTING BIS (CAUSES OF INACCURATE READINGS)

Falsely LOW BIS (reads deeper than actual)

Falsely HIGH BIS (reads lighter than actual)

Must Remember: Ketamine is a major confounding agent for BIS - it can cause dissociative anaesthesia while BIS remains > 70. BIS should NOT be relied upon to guide ketamine anaesthesia depth.

---

10. BIS AND AWARENESS - INCIDENCE DATA

• TIVA without EEG monitoring
• Haemodynamic instability requiring low anaesthetic dose
• Difficult airway (paralysed but under-anaesthetised)
• Chronic drug/alcohol use (↑ MAC)
• Prior awareness episode

---

11. NEUROMONITORING IN ICU (BIS FOR SEDATION)

Richmond Agitation-Sedation Scale (RASS) vs BIS Correlation

Sedation Scales in ICU

---

12. BIS IN SPECIAL SITUATIONS

---

13. BIS vs ETAC MONITORING - COMPARISON

---

14. RECENT ADVANCES (2024-2026)

• CODA Trial (2019): Avoiding burst suppression (BIS < 40) reduces postoperative delirium in elderly - reinforced in ESAIC 2023 guidelines
• SedLine (Masimo PSi): 4-channel EEG (bilateral frontal) - better spatial coverage than single-channel BIS; detects hemispheric asymmetry
• NeuroSENSE (WAM): Bilateral frontal EEG with WAVCNS index - parallel channels detect asymmetry
• AI-enhanced EEG interpretation: Real-time spectrogram displays (hot maps) now integrated into anaesthesia workstations (Draeger, GE)
• Closed-loop propofol delivery guided by BIS/EEG - multiple Phase III trials showing faster recovery and fewer awareness events (2023-2025)

---

15. CURRENT GUIDELINES

• ASA Practice Advisory on Intraoperative Awareness (2006, updated 2023): BIS or ETAC monitoring recommended for high-risk awareness cases (TIVA, cardiac, obstetric GA, trauma)
• ESAIC (2023): Quantitative EEG monitoring recommended during TIVA; avoid burst suppression (BIS <40) in elderly
• SCCM PAD-ICU Guidelines (2018, update 2023): Objective sedation monitoring (RASS + BIS-guided) reduces ventilator days, ICU-LOS, and delirium

---

📌 EXAM PEARLS

1. BIS 40-60 = target for GA - the single most asked numerical value about BIS
2. BIS < 40 = burst suppression - associated with POCD and delirium in elderly - avoid
3. BIS not reliable with ketamine - ketamine causes unconsciousness with high BIS values
4. EMG interference raises BIS falsely - muscle relaxation removes EMG contamination and may cause BIS to DROP even though anaesthesia depth hasn't changed
5. B-Aware (2004): BIS reduces awareness; B-Unaware/BAG-RECALL (2008/2011): ETAC equally effective - know all three trials
6. TIVA without BIS = highest risk of awareness - BIS is essential in TIVA

---

🔴 HIGH YIELD FACTS

• BIS is a dimensionless number 0-100 derived from frontal EEG processing
• SQI > 80% needed for reliable BIS reading
• BIS based on: BetaRatio + SynchFastSlow + BSR + QUAZI (4 sub-parameters)
• Awareness incidence in general surgery = 0.1-0.2% (1-2 per 1000 anaesthetics)
• Nitrous oxide and dexmedetomidine can give high BIS despite adequate sedation (different EEG mechanism)
• Spectral Edge Frequency (SEF 95): Normal awake = ~20-25 Hz; GA = 8-12 Hz

---

---

---

RECEPTORS IN ANAESTHESIA: ALPHA-2 AGONISTS AND OPIOID RECEPTORS

Combined Answer: Role of Alpha-2 Receptor Agonists in Anaesthesia (×2) | Opioid Receptors

---

PART A: OPIOID RECEPTORS

---

1. CLASSIFICATION OF OPIOID RECEPTORS

Must Remember: Clinically relevant opioid receptors = μ, κ, δ. All are Gi/Go protein-coupled receptors (inhibitory G-proteins).

---

2. SIGNAL TRANSDUCTION MECHANISM

Opioid agonist + receptor
          ↓
    Gi/Go protein activation
          |
          |──► ↓ Adenylyl cyclase → ↓ cAMP → ↓ PKA activity
          |
          |──► ↑ K+ channel opening → HYPERPOLARISATION → ↓ neuronal firing
          |
          |──► ↓ Voltage-gated Ca²+ channels → ↓ Ca²+ influx
                    → ↓ Neurotransmitter release (presynaptic)

---

3. EFFECTS MEDIATED BY EACH RECEPTOR TYPE

Exam Pearl: μ receptor = primary target of all clinically used opioid analgesics (morphine, fentanyl, remifentanil). Respiratory depression is μ-mediated - medullary respiratory centres.

---

4. MU RECEPTOR SUBTYPES

Clinical significance: Partial μ1 selectivity is a target of drug design (μ1 agonist / μ2 sparing) to achieve analgesia without respiratory depression - e.g., Oliceridine (TRV130), a biased μ agonist.

---

5. CLINICALLY USED OPIOIDS AND RECEPTOR PROFILE

---

6. ENDOGENOUS OPIOID PEPTIDES

---

7. OPIOID RECEPTOR DISTRIBUTION (CNS)

---

PART B: ALPHA-2 ADRENERGIC RECEPTOR AGONISTS IN ANAESTHESIA

---

8. ALPHA-2 RECEPTOR - BASIC PHARMACOLOGY

Receptor Classification

• All α2 receptors are Gi protein-coupled → ↓ adenylyl cyclase → ↓ cAMP
• Also activate inwardly rectifying K+ channels → hyperpolarisation
• Selectivity ratio (α2:α1):
  • Clonidine: 200:1
  • Dexmedetomidine: 1620:1 (highly selective)

---

9. MECHANISM OF ACTION - α2 AGONISTS

α2 agonist → Presynaptic α2A receptor (locus coeruleus)
                    ↓
           ↓ Noradrenaline release
                    ↓
        ↓ Sympathetic tone → Sedation + Analgesia + Anxiolysis
        ↓ BP + ↓ HR (central sympatholysis)

α2 agonist → Spinal cord (dorsal horn α2A)
                    ↓
           Inhibits substance P + glutamate release
                    ↓
               Spinal analgesia

α2 agonist → Presynaptic at sympathetic nerve terminals (peripheral)
                    ↓
           ↓ Noradrenaline release → ↓ BP

---

10. CLINICAL PHARMACOLOGY OF KEY α2 AGONISTS

A. DEXMEDETOMIDINE ⭐

Systemic Effects of Dexmedetomidine

Advantages (Unique Profile)

• Sedation without respiratory depression - key differentiator from opioids/benzodiazepines
• Arousable: patient can respond to commands while sedated ("cooperative sedation")
• Analgesia-sparing: reduces opioid consumption by 30-50%
• Reduces MAC of volatile agents (by 40-90%)
• Reduces sympathetic stress response
• Anti-shivering
• Neuroprotective properties (preclinical evidence)
• Reduces emergence agitation in children

Disadvantages / Adverse Effects

• Bradycardia (most common - may need atropine)
• Hypotension (especially with loading dose infusion)
• Initial transient hypertension (peripheral α2B vasoconstriction)
• Dry mouth
• Not approved for procedural sedation (FDA: only ICU sedation; though widely used off-label)

Clinical Uses in Anaesthesia

---

B. CLONIDINE

Uses of Clonidine in Anaesthesia

• Premedication (anxiolysis, ↓ MAC, stable haemodynamics)
• Neuraxial adjuvant - spinal and epidural (prolongs block, enhances analgesia)
• Attenuation of laryngoscopy response
• Chronic pain management (complex regional pain syndrome)
• Anti-shivering
• Management of opioid and alcohol withdrawal

---

11. COMPARISON: DEXMEDETOMIDINE vs CLONIDINE

---

12. COMPARISON: α2 AGONISTS vs OPIOIDS IN ANAESTHESIA

---

13. RECENT ADVANCES (2024-2026)

• Biased opioid agonism: Oliceridine (TRV130) - G-protein biased μ agonist (analgesia without β-arrestin recruitment → less respiratory depression, less constipation) - FDA approved 2020
• NKTR-181: PEGylated opioid with slower CNS entry - reduces abuse potential
• PAM (Positive allosteric modulators) of opioid receptors - Phase II trials

• Perioperative dexmedetomidine for opioid-sparing analgesia strategy - WHO Essential Medicines List 2023 addition
• Dexmedetomidine for prevention of postoperative delirium (MENDS-2 trial 2021 - dexmed vs propofol in ICU: no difference in delirium; but better in ventilator weaning)
• Intranasal dexmedetomidine for paediatric procedural sedation - now standard in many centres
• ESAIC 2023: Recommends dexmedetomidine as part of multimodal opioid-sparing strategy

---

14. CURRENT GUIDELINES

• SCCM PAD-ICU 2018 (update 2023): Dexmedetomidine or propofol preferred for ICU sedation over benzodiazepines; reduces delirium
• ESAIC ERAS 2023: Dexmedetomidine as opioid-sparing adjunct in multimodal analgesia
• WHO Essential Medicines (2023): Dexmedetomidine added for ICU sedation in resource-limited settings
• ASA (2022): α2 agonists recommended as component of multimodal analgesia reducing opioid consumption

---

📌 EXAM PEARLS

1. μ receptor = responsible for analgesia AND respiratory depression - both via μ2; analgesia also via μ1
2. All opioid receptors are Gi-coupled - inhibit adenylyl cyclase, open K+ channels, close Ca2+ channels
3. Dexmedetomidine selectivity = 1620:1 (α2:α1) - Clonidine = 200:1 - dexmed 8× more potent
4. Dexmedetomidine = sedation WITHOUT respiratory depression - unique and examiner-favourite property
5. Miosis = μ receptor at Edinger-Westphal nucleus - does NOT show tolerance (useful in opioid OD diagnosis)
6. κ receptor → dysphoria (opposite to μ euphoria) - explains pentazocine/nalbuphine hallucinations

---

🔴 HIGH YIELD FACTS

• Naloxone reverses all opioid receptors (μ, κ, δ) - dose 0.4 mg IV for opioid reversal
• Buprenorphine = partial μ agonist + κ antagonist - ceiling effect on respiratory depression
• β-Endorphin is the most potent endogenous opioid (μ-selective)
• Dexmedetomidine reduces MAC by 40-90% and opioid consumption by 30-50%
• Locus coeruleus (brainstem) = primary site of dexmedetomidine sedative action
• Transient initial hypertension with dexmedetomidine bolus = peripheral α2B vasoconstriction (disappears as central effects dominate)

---

---

---

PHYSICS IN ANAESTHESIA

Combined Answer: Venturi Effect/Principle (×4) | Coanda Effect | Gas Laws | Laminar Flow & Poiseuille's Law | Alveolar Gas Equation

---

PART A: BERNOULLI'S PRINCIPLE AND VENTURI EFFECT

---

1. BERNOULLI'S PRINCIPLE

Statement

"In a flowing fluid, an increase in velocity is accompanied by a decrease in pressure, and vice versa — provided the flow is steady, laminar, and the fluid is incompressible."

Mathematical Expression

• Simplified (horizontal flow): P₁ + ½ρv₁² = P₂ + ½ρv₂²
• When v↑ → P↓ (and vice versa) - energy conservation in flowing fluid

---

2. VENTURI EFFECT (VENTURI PRINCIPLE)

Definition

"When a fluid flows through a constriction (narrowing) in a tube, its velocity increases and its lateral pressure decreases at the point of constriction - this is the Venturi effect."

Venturi Tube Structure

Wide lumen         Constriction        Wide lumen
(Inlet)           (Throat/Jet)         (Outlet)

|=============|___________|=============|
   Low velocity   HIGH velocity   Low velocity
   HIGH pressure  LOW pressure    HIGH pressure
                       ↑
              Entrainment port here
              (gas/fluid sucked in)

---

3. CLINICAL APPLICATIONS OF THE VENTURI PRINCIPLE

Venturi Mask - Fixed Performance Device

Exam Pearl: Venturi masks are fixed performance (deliver predictable FiO2 regardless of patient's breathing pattern) because the total flow always exceeds peak inspiratory flow. Ideal for COPD patients where precise FiO2 control is essential.

---

4. COANDA EFFECT

Definition

"The tendency of a jet of fluid to stay attached to a nearby curved or flat surface rather than following a straight path."

• Named after Romanian engineer Henri-Marie Coandă (1910)
• Occurs because the jet entrains surrounding fluid → creates a low-pressure zone on the near-surface side → pressure difference "pulls" the jet toward the surface

Mechanism

Jet of fluid →→→→
                  ↘ (curves toward surface due to low pressure zone)
  ─────────────────────── SURFACE ───────────────────────

Clinical Applications in Anaesthesia

High Yield Fact: Coanda effect explains why, in a T-piece or bifurcated airway circuit, gas flow preferentially follows one limb. Also relevant in neonatal ventilation where fluidic logic ventilators exploit this principle.

---

PART B: GAS LAWS AND APPLICATIONS IN ANAESTHESIA

---

5. GAS LAWS - SUMMARY TABLE

Important Gas Constants

BTPS vs STPD Correction (Spirometry)

---

PART C: LAMINAR AND TURBULENT FLOW

---

6. LAMINAR vs TURBULENT FLOW

Laminar Flow

• Definition: Fluid moves in parallel layers (streamlines) with no disruption between layers; outermost layer stationary, central layer fastest
• Flow profile: Parabolic velocity profile

     → →  → (fastest - centre)
    → → → →
   → → → → →
  → → → → → →  (slowest - walls)
  |__TUBE WALL__|

Turbulent Flow

• Definition: Fluid moves in irregular eddies and swirls - no organised streamlines
• Flow is chaotic, energy-wasting
• Higher driving pressure needed for same flow rate

Reynolds Number (Re) - Predicts Flow Type

Factors Promoting Turbulent Flow

• High velocity (fast flow rates)
• Large tube diameter (trachea > bronchi)
• Low viscosity (helium - promotes laminar; O2 normal)
• Irregular surfaces (secretions, foreign body, tumour)
• Branching points (carina, larynx)
• Constrictions (subglottic stenosis, laryngospasm)

Clinical Pearl: During upper airway obstruction, turbulent flow predominates → greatly increased work of breathing. Heliox (He:O2 = 70:30 or 80:20) reduces density → lower Reynolds number → converts turbulent to laminar flow → reduces work of breathing.

---

7. POISEUILLE'S LAW (HAGEN-POISEUILLE)

Statement

"For laminar flow of a viscous fluid through a cylindrical tube, the flow rate is directly proportional to the fourth power of the radius and the pressure gradient, and inversely proportional to the length and viscosity."

Formula

Clinical Implications - The CRITICAL r⁴ Relationship

Must Remember - r⁴ Rule: The most important clinical implication is that small changes in airway or cannula radius have ENORMOUS effects on flow. This is why:

• Largest ETT possible should be chosen (r⁴ effect on resistance)
• Glottic oedema (small ↓ in radius) causes catastrophic airway resistance increase
• Croup/epiglottitis: 1 mm oedema in a neonatal airway reduces cross-sectional area by 75% and flow by 75-80%
• Wide-bore IV cannulas: 14G ≫ 18G for rapid fluid infusion

Resistance Formula

• Airway resistance normal = 0.5-2 cm H2O/L/sec
• Increases markedly with small airway diameter changes

Poiseuille's Law - Only Valid For:

1. Laminar flow (not turbulent)
2. Newtonian fluids (constant viscosity)
3. Straight cylindrical tubes
4. Steady, non-pulsatile flow
5. Rigid (non-distensible) tubes

---

PART D: ALVEOLAR GAS EQUATION

---

8. ALVEOLAR GAS EQUATION

Formula

Worked Example (Room Air, Sea Level)

---

9. ALVEOLAR-ARTERIAL OXYGEN GRADIENT (A-a Gradient)

Causes of Elevated A-a Gradient

Exam Pearl: Normal A-a gradient + low PaO2 = hypoventilation (no lung pathology). Elevated A-a gradient = intrinsic lung/vascular disease.

---

10. CLINICAL APPLICATIONS OF THE ALVEOLAR GAS EQUATION

---

11. ALL IMPORTANT PHYSICS FORMULAE - SUMMARY TABLE

---

12. VENTURI vs COANDA - COMPARISON

---

📌 EXAM PEARLS

1. Poiseuille's Law: Flow ∝ r⁴ - halving the radius reduces flow to 1/16. This is the most testable formula in physics
2. Venturi principle = Bernoulli applied at constriction - know all clinical applications (mask colours and FiO2 values are high yield)
3. Re > 4000 = turbulent; < 2000 = laminar - Reynolds Number formula
4. Alveolar Gas Equation: PAO2 = FiO2 (760-47) - PaCO2/0.8 - derive step by step in exam
5. A-a gradient normal < 10 mmHg on room air; if normal → pure hypoventilation; if elevated → lung pathology
6. Coanda effect = fluidic flip-flop - basis of fluidic ventilators with no moving parts

---

🔴 HIGH YIELD FACTS

• Venturi mask is fixed performance - FiO2 independent of breathing pattern
• Heliox reduces Re (less dense than O2) → converts turbulent → laminar flow in airway obstruction
• 1 mm subglottic oedema in a 4 mm neonatal airway = 75% reduction in cross-sectional area and 94% ↑ resistance (r⁴)
• Normal PAO2 on room air ≈ 100 mmHg; on 100% O2 ≈ 660 mmHg (PB - 47 - PaCO2)
• Water vapour pressure = 47 mmHg at 37°C - must subtract from barometric pressure in all gas calculations
• R (respiratory quotient) = 0.8 on mixed diet; = 1.0 on pure carbohydrate diet

---

---

---

ANAESTHESIA FOR RENAL TRANSPLANTATION

Combined Answer: End Stage Renal Disease & Anaesthesia Issues | Anaesthetic Management for Renal Transplant

---

1. DEFINITION AND OVERVIEW

• End Stage Renal Disease (ESRD): Irreversible decline in renal function with GFR < 15 mL/min/1.73m² requiring renal replacement therapy (dialysis or transplantation)
• Renal transplantation is the treatment of choice for ESRD - superior to dialysis in terms of life expectancy, quality of life, and cost-effectiveness
• Renal transplant anaesthesia is complex because:
  • Patient has multiple systemic comorbidities of ESRD
  • Altered pharmacokinetics and pharmacodynamics
  • Immunosuppression management
  • Intraoperative haemodynamic goals critical for graft function

---

2. CAUSES OF ESRD (RECIPIENT PROFILE)

---

3. SYSTEMIC EFFECTS OF ESRD - PREOPERATIVE ASSESSMENT

A. Cardiovascular System (Most Important)

• 50% of mortality on dialysis = cardiac causes
• Cardiovascular disease = leading cause of death after renal transplant
• Manifestations:
  • Hypertension (volume + renin-angiotensin mediated)
  • LVH (pressure + volume overload)
  • Dilated cardiomyopathy (uraemic, anaemia-related)
  • Pericardial effusion / uraemic pericarditis
  • Accelerated atherosclerosis → CAD, PVD
  • Cardiac arrhythmias (hyperkalaemia, uraemia)
  • Pulmonary hypertension (chronic AV fistula, volume overload)

B. Respiratory System

• Pulmonary oedema (volume overload)
• Pleural effusion
• Kussmaul's breathing (metabolic acidosis compensation)
• Restricted lung volumes (ascites, pleural fluid)

C. Haematological

• Normochromic normocytic anaemia (↓ EPO, ↓ RBC survival, blood loss from dialysis)
  • Target Hb pre-transplant: 10-12 g/dL (with EPO therapy)
• Uraemic platelet dysfunction (impaired platelet aggregation, adhesion)
  • Bleeding time prolonged despite normal platelet count
  • Treated with DDAVP 0.3 μg/kg pre-op if needed

D. Metabolic/Biochemical

Must Remember: Dialyse the patient within 24 hours before surgery to:

• Correct hyperkalaemia (K⁺ < 5.5)
• Remove excess fluid (euvolaemic state)
• Correct acidosis
• Remove uraemic toxins (reduce platelet dysfunction)

E. Neurological

• Uraemic encephalopathy (altered sensorium, seizures)
• Peripheral neuropathy (autonomic + sensorimotor)
• Autonomic neuropathy (orthostatic hypotension, delayed gastric emptying)
• Dialysis disequilibrium syndrome risk

F. Gastrointestinal

• Delayed gastric emptying (diabetic gastroparesis, uraemia)
• Nausea, vomiting, anorexia
• Full stomach risk → RSI indicated

G. Immunological

• Already immunosuppressed (uraemia depresses immunity)
• Post-transplant further immunosuppression → infection risk

H. Vascular Access

• AV fistula / Tenckhoff catheter / HD catheter present
• Protect AV fistula arm (no BP cuff, no IV, no arterial line on fistula side)
• Check fistula thrill pre and post-op

---

4. PREOPERATIVE ASSESSMENT AND OPTIMISATION

Preoperative Checklist

Contraindications to Renal Transplant

• Active malignancy
• Active untreated infection
• Severe cardiac/hepatic/pulmonary disease
• Active substance abuse
• Uncontrolled psychiatric disease

---

5. RELEVANT PHARMACOLOGY IN ESRD

Drug Pharmacokinetics Altered in ESRD

Drug Choices in ESRD/Renal Transplant

Exam Pearl: Cisatracurium is the NMBD of choice in renal transplant - eliminated by Hofmann degradation (pH + temperature dependent, independent of renal/hepatic function). Atracurium also acceptable but produces laudanosine (neurological effects). Succinylcholine raises K+ by 0.5 mEq/L - relatively safe if K+ < 5.5 mEq/L.

---

6. INTRAOPERATIVE MANAGEMENT

Surgical Procedure Overview

Incision: Right iliac fossa (most common)
          ↓
Iliac vessels exposed (internal iliac artery + external iliac vein)
          ↓
Renal artery anastomosis (end-to-end or end-to-side to internal iliac artery)
          ↓
Renal vein anastomosis (end-to-side to external iliac vein)
          ↓
Vascular clamps released (REPERFUSION) - critical haemodynamic moment
          ↓
Ureter anastomosed to bladder (ureteroneocystostomy)
Duration: 2-4 hours

Monitoring

• Standard ASA monitoring (ECG, SpO2, NIBP, EtCO2, Temperature)
• Arterial line (on non-fistula arm): beat-to-beat BP, serial ABG, K+ monitoring
• Central venous catheter (CVP): Guide fluid therapy; target CVP 10-15 mmHg at reperfusion
• Urinary catheter (to monitor urine output of transplanted kidney)
• Temperature monitoring (prevent hypothermia)
• Do NOT place IV/art line/BP cuff on fistula arm

Induction

Maintenance

Fluid Management (CRITICAL for Graft Function)

Exam Pearl: Why 0.9% NaCl preferred over Hartmann's (Ringer's Lactate)?

• Hartmann's contains potassium 5 mEq/L - contraindicated in hyperkalaemic ESRD patients
• PlasmaLyte (no K+, pH 7.4) is an alternative
• Recent evidence (SPLIT trial, SMART trial) suggests balanced crystalloids may be preferable to reduce hyperchloraemic acidosis - use PlasmaLyte if available

Vasoactive Drugs

Must Remember: At the moment of vascular unclamping (reperfusion):

1. Give Mannitol 0.5 g/kg IV
2. Give Furosemide 80-120 mg IV
3. Ensure CVP 12-15 mmHg
4. MAP ≥ 70-80 mmHg
5. Watch for:
   • Hypotension (reperfusion of cold ischaemic organ → vasodilation)
   • Hyperkalaemia (K+ from cold preservation solution released into circulation)
   • Bradycardia (hyperkalaemia)
   • Metabolic acidosis (acid load from preservation fluid)

Haemodynamic Goals (MAP Targets)

---

7. IMMUNOSUPPRESSION - PERIOPERATIVE MANAGEMENT

Induction Immunosuppression (Given Perioperatively)

Maintenance Immunosuppression (Started Perioperatively)

Important Drug Interactions with Immunosuppressants

---

8. POSTOPERATIVE MANAGEMENT

Immediate Post-op Goals

Complications - Post-operative

---

9. DELAYED GRAFT FUNCTION (DGF)

• Definition: Need for dialysis in first week post-transplant
• Incidence: 20-30% (deceased donor kidneys)
• Risk factors: Long cold ischaemia time, high KDPI score, DCD donors, recipient hypovolaemia intraoperatively
• Prevention: Adequate intraoperative hydration (CVP 12-15), MAP ≥ 70-80 mmHg, mannitol + furosemide at reperfusion, short cold ischaemia time
• Management: Continue dialysis support while awaiting graft function recovery

---

10. REGIONAL ANAESTHESIA FOR RENAL TRANSPLANT

• Technically possible (spinal/epidural)
• Advantages: Avoids airway manipulation, opioid sparing, reduces PONV
• Concerns:
  • Uraemic platelet dysfunction → coagulopathy risk
  • Residual heparin from pre-op haemodialysis
  • Autonomic neuropathy → exaggerated hypotension
  • Long surgery (3-4 hours) → patient discomfort
• Current practice: Most centres prefer GA for renal transplant; combined GA + epidural used in selected centres

---

11. DONOR CONSIDERATIONS

Living Donor Nephrectomy (Laparoscopic)

• Young, healthy donor
• Laparoscopic approach (pneumoperitoneum considerations)
• Goal: minimise surgical time, prevent hypothermia, maintain urine output, ensure adequate hydration
• Pre-harvest: IV fluids to ensure good graft perfusion
• Post-harvest: Monitor for complications (haemorrhage, pneumothorax, ureteral injury)

Deceased Donor (Brain Death Management)

• Goals: Maintain MAP > 70 mmHg, CVP 8-12 mmHg, SpO2 > 95%, normothermia, avoid hormonal changes
• Vasopressin infusion to treat diabetes insipidus
• Thyroid hormone (T3/T4) + methylprednisolone + insulin + vasopressin = "hormonal resuscitation" protocol for organ preservation

---

12. IMPORTANT SCORING SYSTEMS

CKD Staging (KDIGO 2012)

---

13. RECENT ADVANCES (2024-2026)

• Normothermic Machine Perfusion (NMP): Perfusing donor kidney at 37°C with oxygenated blood - reduces DGF by 50% vs cold storage (COPE RCT 2023)
• Hypothermic Machine Perfusion (HMP): Now standard for marginal kidneys (DCD donors)
• Desensitisation protocols: Plasmapheresis + rituximab + IVIG for highly sensitised recipients - allows transplant across HLA barriers
• Belatacept-based immunosuppression: CD28-costimulation blocker - reduces nephrotoxicity vs calcineurin inhibitors
• SGLT2 inhibitors post-transplant: Empagliflozin/dapagliflozin showing graft protection in CKD progression (2024 RCTs)
• PlasmaLyte vs 0.9% NaCl in renal transplant (SPLIT/SMART evidence): Balanced crystalloids reduce hyperchloraemic acidosis and AKI risk

---

14. CURRENT GUIDELINES

• KDIGO (2023): CKD management, transplant criteria, immunosuppression protocols
• ASA/ACC/AHA (2023): Perioperative cardiovascular evaluation for transplant recipients undergoing non-cardiac surgery - standard cardiac workup
• ERAS for Kidney Transplant (ERAET Protocol 2022): Multimodal analgesia, early mobilisation, avoid opioids, goal-directed fluid therapy
• ESICM (2023): Machine perfusion preferred for DCD kidney preservation

---

📌 EXAM PEARLS

1. Cisatracurium = NMBD of choice in ESRD - Hofmann elimination, independent of renal function
2. Dialyse within 24 hrs pre-op - ensure K⁺ < 5.5, euvolaemia, correct acidosis
3. CVP 12-15 mmHg + MAP ≥ 70-80 mmHg at reperfusion = critical haemodynamic targets for graft function
4. Mannitol 0.5 g/kg + Furosemide given at vascular unclamping - reduces DGF
5. Hartmann's contains K+ - use 0.9% NS or PlasmaLyte for fluid therapy in ESRD
6. RSI mandatory in diabetics/uraemic patients (gastroparesis risk)
7. Succinylcholine raises K⁺ by 0.5 mEq/L - safe only if pre-op K+ < 5.5 mEq/L

---

🔴 HIGH YIELD FACTS

• Renal transplant is the treatment of choice for ESRD - better survival than dialysis
• Cardiovascular disease = #1 cause of death after renal transplant
• Urine output from transplanted kidney within 30-60 min of reperfusion = good graft function
• AV fistula arm: no BP cuff, no IV line, no arterial line - protect at all times
• Acute rejection treatment: Pulse methylprednisolone 500 mg IV × 3 days
• DGF definition: Need for dialysis in first 7 days post-transplant; risk factor = long cold ischaemia time
• Morphine active metabolite M6G accumulates in ESRD - causes prolonged sedation and respiratory depression; use fentanyl instead

---

---