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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

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• 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

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MONITORING IN ANAESTHESIA

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

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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).

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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)

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3. STANDARD (NON-INVASIVE) MONITORING

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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

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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.

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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

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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

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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

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7. NEUROMONITORING & DEPTH OF ANAESTHESIA

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8. NEUROMUSCULAR MONITORING

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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

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10. IMPORTANT FORMULAE

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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

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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

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📌 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

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🔴 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

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PULSE OXIMETRY AND BEER-LAMBERT LAW

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

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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)

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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

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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

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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)

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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!)

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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!

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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.

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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

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9. CLINICAL APPLICATIONS IN ANAESTHESIA

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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

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11. IMPORTANT NORMAL VALUES

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12. PHYSICS SUMMARY TABLE

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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

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📌 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

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🔴 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

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

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

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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

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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.

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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)

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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.

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5. CAUSES OF DECREASED SvO2

A. Decreased O2 Delivery (DO2↓)

B. Increased O2 Consumption (VO2↑)

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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.

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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)

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8. CLINICAL APPLICATIONS IN ANAESTHESIA & ICU

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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

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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

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11. COMPARISON TABLE: SvO2 vs ScvO2 vs SjvO2

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12. IMPORTANT FORMULAE

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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

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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

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📌 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)

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🔴 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)

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END-TIDAL CO2, CAPNOGRAPHY AND CAPNOMETRY

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

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1. DEFINITIONS

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

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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 %

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3. TYPES OF CAPNOGRAPHS

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

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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

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5. NORMAL VALUES

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

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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)

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7. CAUSES OF ABNORMAL CAPNOGRAMS

A. Elevated EtCO2

B. Decreased EtCO2

C. Characteristic Waveform Changes

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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

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9. CAPNOGRAPHY IN SPECIAL SITUATIONS

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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.)

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11. IMPORTANT COMPARISON TABLE

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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

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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

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📌 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

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🔴 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)

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THROMBOELASTOGRAPHY, VISCOELASTIC COAGULATION TESTS AND ACTIVATED CLOTTING TIME

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

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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

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2. VISCOELASTIC HAEMOSTATIC ASSAYS (VHA) - OVERVIEW

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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)

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4. THE TEG TRACE - LABELLED DIAGRAM

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

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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)

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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.

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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)
| /‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾\
|/                    \__

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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

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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

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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

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11. COMPARISON: CONVENTIONAL TESTS vs VISCOELASTIC TESTS vs ACT

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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)

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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

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📌 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

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🔴 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)

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TRANSOESOPHAGEAL ECHOCARDIOGRAPHY (TOE/TEE) IN ANAESTHESIA PRACTICE

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

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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

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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

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3. PROBE AND EQUIPMENT

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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.

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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

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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

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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

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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

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9. COMPLICATIONS

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

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10. TOE vs TTE - COMPARISON TABLE

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11. FOCUSED CARDIAC ULTRASOUND (FOCUS) vs COMPREHENSIVE TOE

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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

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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

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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

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📌 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

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🔴 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

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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

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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

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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

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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.

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4. STIMULATION PARAMETERS (PNS Settings)

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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

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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.

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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

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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).

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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).

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6. SUMMARY TABLE: ALL STIMULATION MODES

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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.

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8. DEPTH OF NMB CLASSIFICATION

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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.

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10. RESIDUAL NMB - KEY FACTS

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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

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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

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📌 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

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🔴 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)

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BISPECTRAL INDEX (BIS) MONITORING

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

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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)

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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)

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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.

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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.

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5. BIS COMPONENTS DISPLAYED ON MONITOR

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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

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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

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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.

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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.

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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

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11. NEUROMONITORING IN ICU (BIS FOR SEDATION)

Richmond Agitation-Sedation Scale (RASS) vs BIS Correlation

Sedation Scales in ICU

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12. BIS IN SPECIAL SITUATIONS

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13. BIS vs ETAC MONITORING - COMPARISON

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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)

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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

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📌 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

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🔴 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

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