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Bernoulli's Principle in Anaesthesia

Definition and Basic Physics

P₁ + ½ρv₁² = P₂ + ½ρv₂²

• P = pressure
• ρ = fluid density
• v = velocity

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Applications in Anaesthesia

1. Venturi Mask (Controlled FiO₂ Delivery)

• By varying the diameter of the jet and the size of the entrainment apertures, a precise and fixed oxygen:air ratio is delivered.
• Available FiO₂ range: 24-50% (colour-coded entrainment connectors)
• Total flow delivered: 50-70 L/min - far exceeding patient's peak inspiratory flow, ensuring FiO₂ is independent of tidal volume and respiratory pattern
• Clinical use: First-line oxygen therapy in patients at risk of hypercapnia (COPD), where precise FiO₂ titration is essential - Murray & Nadel's Respiratory Medicine

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2. Rotameter (Constant-Pressure, Variable-Orifice Flowmeter)

• A float (bobbin/ball) is suspended in a vertically tapered glass tube
• Gas flows upward; as flow increases, the float rises to a wider part of the tube (increasing the annular orifice)
• The pressure drop across the float remains constant regardless of flow rate (constant-pressure, variable-orifice)
• The float rises until its weight is just balanced by the pressure difference (constant pressure drop = float weight / cross-sectional area)
• At the annular gap around the float, velocity is high and lateral pressure is low (Bernoulli) - this pressure differential supports the float

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3. Venturi Injector / Jet Ventilation

• A high-pressure jet of oxygen is passed through a narrow nozzle into the airway
• The resulting high velocity creates low lateral pressure (Bernoulli), entraining ambient air/anaesthetic gases into the airway alongside the jet
• This produces ventilation without an endotracheal tube, making it useful for laryngeal and subglottic surgery, rigid bronchoscopy, and laser procedures
• Scott-Brown's (ENT) describes supraglottic or transtracheal jet ventilation using this principle for endolaryngeal surgery

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4. Nebulizers

• A high-velocity gas jet passes across the tip of a liquid feed tube
• Low lateral pressure created at the jet tip draws liquid upward (Venturi/Bernoulli effect)
• The entrained liquid is then shattered into fine aerosol particles by the gas stream
• Used in delivery of bronchodilators, antibiotics, and humidification circuits

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5. Echocardiographic Bernoulli Equation (Relevant to Anaesthesia - TOE/TEE)

ΔP = 4V²

• ΔP = transvalvular pressure gradient (mmHg)
• V = peak jet velocity (m/s) by continuous-wave Doppler

ΔP = 4(V₂² - V₁²)

• Quantify severity of aortic stenosis (peak and mean gradient across aortic valve)
• Assess mitral stenosis gradient
• Estimate pulmonary artery systolic pressure from tricuspid regurgitation jet: PASP = 4(V_TR)² + RA pressure
• Assess severity of valvular regurgitation
• Identify intracardiac shunts and estimate chamber pressures

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6. Pathophysiological Relevance

• Arterial stenosis (atherosclerotic plaque): At a stenosis, velocity increases → lateral pressure falls → vessel wall is at risk of collapse, and the narrowing tends to be self-perpetuating (Bernoulli collapse phenomenon) - Ganong's
• Paediatric airway (subglottic oedema/croup): The narrow subglottis already generates high-velocity, low-pressure flow. Oedema further narrows the lumen → velocity rises further → wall-distending pressure falls even more → the airway tends toward dynamic collapse during inspiration (important consideration in paediatric anaesthesia) - Scott-Brown's
• Airway collapse in obstructive sleep apnoea: Supraglottic collapse during apnoeas is partly mediated by the Bernoulli effect at the narrow pharynx

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Summary Table

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Exam Mnemonics

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Triage in Management of Trauma Patients

Definition

1. Treat the greatest threat to life first
2. The lack of a definitive diagnosis must never impede indicated treatment
3. A detailed history is not essential to begin trauma evaluation

• Tintinalli's Emergency Medicine

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Types of Triage

A. Routine (Everyday) Triage - Single/Few Patients

• Airway assessment and intervention
• Haemodynamic status and resuscitation needs
• Operating room (OR) prioritization

B. Mass Casualty Incident (MCI) Triage

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Triage Systems

1. START Triage (Simple Triage and Rapid Treatment)

2. SALT Triage (Sort, Assess, Lifesaving interventions, Treatment/Transport)

• Immediate (Red): Non-ambulatory; deranged respiration, perfusion, or mental status. Requires: airway opening, tourniquet, chest decompression
• Delayed (Yellow): Significant injuries but care can wait up to 1 hour
• Minimal (Green): Ambulatory, minor injuries, may self-help
• Expectant (Gray): Highly likely to die imminently even with immediate care; still deserving of comfort and compassion
• Dead (Black): No signs of life

3. RAMP (Rapid Assessment of Mentation and Pulse)

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National Field Triage Guidelines (4-Step Algorithm)

• GCS <13
• SBP <90 mmHg
• RR <10 or >29/min → Transport to highest-level trauma centre

• Penetrating injury to head/neck/torso/proximal extremities
• Flail chest, pelvic fracture, skull fracture/paralysis
• Two or more proximal long bone fractures
• Crushed/pulseless/mangled extremity, amputation → Highest-level trauma centre

• Falls >20 feet (adults), >10 feet (children)
• High-risk auto crash: ejection, intrusion >12 inches, death in same compartment
• Pedestrian/cyclist struck at >20 mph → Trauma centre (need not be highest level)

• Age >55 years: SBP <110 mmHg may indicate shock
• Children: triage to paediatric-capable trauma centre
• Anticoagulant use, pregnancy >20 weeks, burns with trauma → Appropriate trauma centre with EMS judgment

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Trauma Scoring Systems Used in Triage

Physiologic Scores

Anatomic Scores

• Abbreviated Injury Scale (AIS): Grades individual injury 1 (minor) to 6 (unsurvivable)
• Injury Severity Score (ISS): Sum of squares of three highest AIS scores from different body regions. Range 1-75. ISS >15 = major trauma (Level I centre)
• Trauma Mortality Prediction Model (TMPM): ICD-based; predicts survival more accurately than ISS

Combined Score

• TRISS (Trauma and Injury Severity Score): Combines RTS + ISS + age + mechanism → probability of survival (Ps). Used for audit and benchmarking.

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ATLS Primary Survey - The Anaesthesiologist's Priority Framework

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Trauma Centre Level Designation

• Tintinalli's Emergency Medicine

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Role of the Anaesthesiologist in Trauma Triage

1. Prehospital liaison: Receives information via D-MIST handoff (Demographics, Mechanism, Injuries, Signs, Treatment given) from EMS; activates appropriate OR and personnel
2. Airway triage: First to identify impending airway catastrophe - intubation, surgical airway
3. Haemodynamic assessment: Guides initial resuscitation; recognizes occult shock (shock index HR/SBP >1 = concern)
4. OR prioritization in multiple casualties: Decides order of patients for surgery based on physiologic stability, injury pattern, and damage control principles
5. Damage Control Resuscitation (DCR):
   • Permissive hypotension (SBP 80-90 mmHg) until surgical haemostasis in penetrating trauma
   • Haemostatic resuscitation: 1:1:1 PRBC:FFP:platelets
   • Avoid crystalloid excess
6. Damage Control Surgery (DCS) over Early Total Care: In severely compromised patients, supports abbreviated surgery (pack and control haemorrhage, temporize) followed by ICU resuscitation and planned re-look. Prolonged procedures in the "lethal triad" (hypothermia, acidosis, coagulopathy) worsen outcomes - Bailey & Love's Surgery

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The Lethal Triad - Triage Urgency Signal

        Hypothermia
           /\
          /  \
         /    \
Acidosis ------  Coagulopathy

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Special Triage Considerations

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Psychological/Ethical Dimension of MCI Triage

• Expectant category: The decision to withhold intervention from salvageable-looking but non-survivable patients is ethically the hardest aspect of MCI triage. It requires specific training.
• Critical Incident Stress Management (CISM): Must be planned in advance; tools like Psy-START help psychological triage post-event
• Austere environments: Tactical EMS (TEMS) teams operate in hostile environments; scene safety always before patient access - Rosen's Emergency Medicine

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Summary Flow for Exam

SCENE → Field Triage (START/SALT) → Transport Decision (Trauma Level)
         ↓
HOSPITAL → Primary Survey (ABCDE) + Simultaneous Resuscitation
         ↓
         Life-threatening injury identified? → IMMEDIATE intervention
         ↓
         Secondary Survey + Adjuncts (FAST, X-ray, CT)
         ↓
         Scoring (GCS, RTS, ISS, TRISS) → Audit/Outcome
         ↓
         OR Prioritization → Damage Control Surgery vs Early Total Care
         ↓
         ICU → Tertiary Survey (24-48 h)

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Oxygen - Vacuum Insulated Evaporator (VIE)

Definition

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Properties of Oxygen Relevant to VIE

• Nitrous oxide (critical temperature +36.5°C) can be stored as a liquid at room temperature under pressure in cylinders
• Oxygen cannot - it must be stored below -118°C to exist as a liquid
• This is why the VIE is necessary and why oxygen cylinders contain compressed gas, not liquid

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Construction of the VIE

         ┌─────────────────────────────┐
         │   OUTER SHELL (Carbon Steel) │
         │  ┌─────────────────────────┐ │
         │  │    VACUUM SPACE          │ │  ← ~0.3 kPa vacuum
         │  │  ┌───────────────────┐  │ │     (excellent insulator)
         │  │  │  INNER SHELL      │  │ │
         │  │  │  (Stainless Steel) │  │ │
         │  │  │                   │  │ │
         │  │  │  VAPOUR PHASE ↑   │  │ │  ← Gaseous O₂ at top
         │  │  │  ─────────────    │  │ │
         │  │  │  LIQUID PHASE     │  │ │  ← Liquid O₂ at bottom
         │  │  │  at -150 to -180°C│  │ │
         │  │  └───────────────────┘  │ │
         │  └─────────────────────────┘ │
         └─────────────────────────────┘

Structural Components:

1. Inner vessel - stainless steel; contains liquid oxygen
2. Outer jacket - carbon steel; structural support
3. Vacuum space between the two shells - the key insulating layer (~0.3 kPa vacuum). The vacuum virtually eliminates conductive and convective heat transfer (same principle as Dewar flask/thermos). Minimal heat enters by radiation only.
4. Superheater/evaporator coil - a U-shaped or serpentine pipe on the way out of the tank that acts as a heat exchanger, warming the liquid oxygen to gas before it enters the hospital pipeline
5. Safety blow-off (pressure relief) valve - set at 17 bar (1700 kPa); opens if internal pressure becomes dangerously high
6. Pressure raising valve and vaporizer - used during high-demand periods (see working below)
7. Weighing mechanism - the entire tank sits on a platform scale; weight is the only reliable way to determine remaining oxygen content (you cannot assess content by pressure alone since liquid-vapour equilibrium is maintained)
8. Refill inlet - accepts liquid oxygen delivery from a tanker truck

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Working Principle

Normal Operation (Low/Moderate Demand)

1. Liquid oxygen is stored at approximately -150 to -180°C and 10 bar (1000 kPa)
2. In normal conditions, gaseous oxygen from the vapour phase at the top of the tank is piped out
3. This gas passes through a superheater coil (ambient-temperature heat exchanger) where it warms to safe temperature for pipeline delivery
4. It then passes through a series of pressure reducing valves that step down the pressure:
   • Tank pressure: ~10 bar
   • Intermediate: reduced stepwise
   • Pipeline pressure delivered to hospital: 4.1 bar (410 kPa / ~60 psi)
5. Pressure reducing valves at the theatre wall reduce this further to 50 psi (3.4 bar) for the anaesthesia machine

During High Demand (e.g., Mass Casualty/High Surgical Throughput)

• High gas extraction causes rapid vaporization → latent heat of vaporization is absorbed from remaining liquid → liquid temperature and saturated vapour pressure (SVP) drop
• This reduces the pressure in the vapour phase
• The drop in vapour pressure activates the pressure raising valve, which:
  • Pipes liquid oxygen from the bottom of the tank through a separate pressure raising vaporizer
  • The warmed gas re-joins the main gas stream, boosting pressure back to normal supply pressure
• The pressure raising vaporizer pipe is typically encrusted with ice from the extreme cold of vaporizing liquid oxygen - this is a normal and expected finding

During Low Demand / Hot Weather

• Ambient heat gradually enters despite insulation → temperature and SVP rise
• If pressure rises above 17 bar → blow-off valve opens, releasing oxygen to atmosphere
• This evaporative loss cools the remaining liquid (gas law: pressure loss = temperature loss), restoring normal working pressure
• This continuous loss of oxygen when demand is low is an inherent inefficiency of VIE systems

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Operating Parameters - Summary Table (Key Exam Numbers)

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How to Measure Remaining Content

• As long as both liquid and vapour phases coexist, the vapour pressure remains constant (determined only by temperature, not amount of liquid)
• Pressure only falls once all liquid has evaporated (all oxygen is then in gas phase)

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Comparison: VIE vs Oxygen Cylinders

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Safety Features of the VIE System

1. Pressure blow-off (relief) valve at 17 bar - prevents catastrophic rupture
2. Vacuum insulation - prevents heat ingress; minimizes uncontrolled evaporation
3. Superheater coil - ensures only warm gas enters pipeline (prevents ice formation in pipes)
4. Pressure reducing valves (staged) - stepped pressure reduction to safe pipeline level
5. Pressure raising valve + vaporizer - maintains supply during high demand
6. Weight-based content measurement - accurate regardless of temperature
7. Sited outdoors - spilled/vented liquid oxygen cannot accumulate in enclosed spaces (oxygen-enriched atmospheres are fire hazards)
8. Backup cylinder manifold - automatic switchover if VIE fails
9. Pipeline alarms - low-pressure alarms in theatre and anaesthesia machine

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Hospital Pipeline Distribution - From VIE to Theatre

VIE (Outdoor, -150°C, 10 bar)
   ↓ Superheater/Evaporator coil
   ↓ Pressure reducing valves → 4.1 bar
   ↓ Hospital pipeline (copper tubing, colour-coded GREEN)
   ↓ Wall outlet (DISS/Quick-connect connector - gas specific)
   ↓ Anaesthesia machine DISS inlet → 50 psi (≈3.4 bar)
   ↓ Pipeline check valve (prevents retrograde flow)
   ↓ Pressure gauge (pipeline)
   ↓ Flow control → Rotameter → Vaporizer → Common Gas Outlet

• Pipeline connectors are Diameter Index Safety System (DISS) - non-interchangeable between gases
• Colour coding: Oxygen = Green (UK/Europe: White)
• Pipeline gas always takes priority over cylinder supply (50 psi vs 45 psi cylinder output)
• If pipeline crossover is suspected: (1) Turn on cylinder backup → (2) Disconnect pipeline supply (mandatory - machine preferentially uses higher-pressure pipeline even if wrong gas)
• Miller's Anesthesia, 10e; Morgan & Mikhail's Clinical Anesthesiology, 7e; Barash Clinical Anesthesia, 9e

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Production of Medical Oxygen

1. Atmospheric air is filtered and cooled far below the boiling points of its constituents until it liquefies
2. The liquid air is slowly warmed
3. Constituents evaporate sequentially as they reach their boiling points:
   • Nitrogen boils off at -195.8°C
   • Liquid oxygen remains behind at -183°C
4. Further purification yields medical-grade oxygen (≥99.5% purity)

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Anaesthesia Machine Interface (Exam-Relevant Details)

• Pipeline oxygen enters the machine at 50 psig (3.4 bar); this drives flow through flowmeters and powers pneumatic ventilators
• E-cylinders on the machine deliver at 45 psig - intentionally lower so pipeline gas is preferred
• Oxygen flush valve bypasses vaporizers and delivers high-flow 100% O₂ (35-75 L/min) directly to the breathing circuit from the intermediate-pressure circuit
• Second-stage regulator inside the machine reduces 50 psig pipeline supply to a stable intermediate pressure (~16-26 psig) for the flowmeter circuits
• Fail-safe device (oxygen pressure failure device/Bosun whistle): cuts off or reduces N₂O flow proportionally if oxygen pipeline pressure falls

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VIE Failure - Anaesthetic Implications

• Tank rupture (as occurred in 2002 - 8,000 gallons of liquid oxygen released)
• Pipeline crossover (most catastrophic - misconnection of O₂ and N₂O pipelines; caused 23 deaths in Sudbury, Ontario)
• Valve malfunction, pressure regulator failure

1. Switch to cylinder supply (turn on E-cylinders)
2. Disconnect pipeline hose from the wall (otherwise machine preferentially uses wrong gas at higher pipeline pressure)
3. Use oxygen analyser in breathing circuit - last line of defence
4. Conserve oxygen: reduce fresh gas flow, use closed circuit
5. Cancel or expedite surgery; notify hospital engineering

• Barash Clinical Anesthesia, 9e; Miller's Anesthesia, 10e

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Key Exam Summary Points

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Burns in MD Anaesthesia

Classification of Burns

By Depth

By Extent - Rule of Nines (Wallace's Rule of Nines)

Major Burn (Criteria for Burn Unit Admission)

• 25% TBSA in adults (>20% in elderly or children)

• Full thickness burns >10% TBSA
• Burns involving face, hands, feet, genitalia, perineum, major joints
• Inhalation injury
• Electrical or chemical burns
• Burns with associated trauma or significant pre-existing disease

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Pathophysiology of Burn Injury

Local Response - Jackson's Zones (3 Concentric Zones)

         ┌──────────────────────────────────┐
         │  Zone of HYPERAEMIA (outermost)  │  ← Vasodilation; recovers fully
         │   ┌────────────────────────────┐ │
         │   │  Zone of STASIS (middle)   │ │  ← Ischaemia; can be saved with
         │   │  ┌──────────────────────┐  │ │    optimal resuscitation
         │   │  │  Zone of COAGULATION │  │ │  ← Central core; irreversible
         │   │  │  (innermost)         │  │ │    necrosis
         │   │  └──────────────────────┘  │ │
         │   └────────────────────────────┘ │
         └──────────────────────────────────┘

Systemic Response

• Massive capillary leak → fluid, protein, electrolytes lost into interstitium
• Most severe in first 8 hours; continues up to 24-48 hours
• Hypovolaemia → reduced cardiac output → organ hypoperfusion
• Catecholamine surge → peripheral vasoconstriction

• Cardiac output rises to supernormal levels (2-3 x normal)
• Hypermetabolism: elevated BMR up to 200% of normal in severe burns
• Persistent catabolism, weight loss, muscle wasting
• Elevated body temperature set-point (~38.5°C)
• This phase can persist for up to 2 years post-injury

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Fluid Resuscitation

Parkland (Baxter) Formula - Most Widely Used

4 mL × body weight (kg) × % TBSA burned Using Lactated Ringer's (Hartmann's) solution

• First half given in the first 8 hours (from time of burn, NOT from time of arrival)
• Second half given over the next 16 hours
• Only superficial partial thickness, deep partial thickness, and full thickness burns are included in TBSA calculation. Superficial (1st degree/erythema) are excluded.

Other Formulae

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Inhalation Injury

Three Components

1. Heat Injury to Upper Airway

• Supraglottic structures primarily affected (larynx, pharynx, oral cavity)
• Steam/hot air → mucosal oedema, erythema, ulceration
• Rapid, progressive swelling → airway obstruction can occur within hours
• Infraglottic thermal injury is rare (heat dissipated in upper airway)

• Hoarseness, stridor, voice change
• Singed nasal hairs, eyebrows
• Carbonaceous sputum
• Intra-oral soot
• Oropharyngeal burns, erythema, blistering
• Burns to face, neck, anterior chest

2. Toxic Gas Inhalation

• CO binds haemoglobin with 250 times the affinity of oxygen → shifts oxygen dissociation curve left (Haldane effect) → tissue hypoxia
• SpO₂ by pulse oximetry is falsely normal (cannot distinguish COHb from OxyHb)
• Treatment: 100% O₂ - reduces CO half-life from 4-5 hours (room air) to 60-90 minutes (100% O₂) to 20-25 minutes (hyperbaric O₂ at 3 atm)
• Hyperbaric O₂ indicated for: COHb >25%, unconsciousness, neurological symptoms, pregnancy, cardiac involvement - Morgan & Mikhail's Clinical Anesthesiology, 7e

• Formed from combustion of nitrogen-containing polymers (wool, silk, polyurethane, vinyl)
• Binds cytochrome oxidase → uncouples mitochondrial oxidative phosphorylation → profound cellular hypoxia despite adequate O₂ delivery
• Suspect if: unexplained metabolic acidosis with elevated lactate despite adequate oxygenation
• Treatment: Hydroxocobalamin (Cyanokit) - binds cyanide to form cyanocobalamin; 100% O₂; sodium thiosulphate

3. Chemical Burn - Lower Airway

• Carbonaceous particles carry toxic aldehydes, acids deep into bronchi
• Mucosal injury → oedema, ciliary dysfunction, mucus plugging
• Manifestations of acute lung injury (ALI) and ARDS typically appear 2-3 days after injury
• Loss of ciliary activity impairs clearance → bacterial colonization → pneumonia - Morgan & Mikhail's Clinical Anesthesiology, 7e

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Anaesthetic Management

Preoperative Assessment - Key Focus Points (Box 83.3, Miller's)

1. Time and extent of burn - when did the injury occur? Which phase (ebb or flow)?
2. Airway evaluation - contractures, limited mouth opening, oedema, previous difficult intubation, tracheostomy
3. Inhalation injury - CO poisoning, airway oedema, bronchospasm, ARDS
4. Fluid received - cumulative fluid balance, adequacy of resuscitation, signs of over-resuscitation
5. Vascular access - where are viable IV access sites (may need to insert through burned tissue)?
6. NPO status and enteral feeding - when last fed? post-pyloric feeding tubes?
7. Current medications - opioid tolerance (chronic), antibiotics, vasopressors
8. Laboratory results - haemoglobin, electrolytes (K⁺), coagulation, albumin, ABG

Airway Management in Burns

• Progressive oedema (worst at 8-24 hours) → plan early intubation
• Facial burns → mask seal difficult; exudate contaminates mask
• Neck burns/contractures → limited neck mobility, restricted mouth opening
• Airway distortion from direct burn or oedema

• Scar contractures of face, neck, mouth (microstomia)
• Restricted neck extension
• Receding chin from scar tissue

• Awake fibreoptic intubation (FOI) - gold standard when difficult airway anticipated
• Pre-oxygenate thoroughly
• Nebulised or spray-as-you-go topical lidocaine for awake FOI
• If uncooperative/paediatric: ketamine sedation (maintains airway tone) + FOI
• Video laryngoscopy as alternative - also permits assessment of hypopharyngeal anatomy
• Tracheostomy under local anaesthesia if airway access is extreme
• Surgeon capable of surgical tracheostomy must be present and scrubbed when airway difficulty is anticipated - Miller's Anesthesia, 10e

• Adhesive tape useless on burned or moist skin
• Options: circumferential tie around head, wire fixation to teeth, arch bars, umbilical tape harness

• Consider early if prolonged mechanical ventilation anticipated
• Indications: large burn, inhalation injury, advanced age, chronic pulmonary disease, facial burns needing repeated OR access

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Pharmacology - Altered Drug Responses in Burns (Critical Exam Topic)

Succinylcholine - CONTRAINDICATED after 48 hours

• Safe within first 24-48 hours of injury
• Contraindicated from 48 hours until full wound healing (may persist for months/years)
• Even small doses (0.1 mg/kg) may cause hyperkalemia - inadequately studied - Miller's Anesthesia, 10e

Non-Depolarising Muscle Relaxants (NDMRs) - Increased Requirements

• The same upregulation of ACh receptors that makes succinylcholine dangerous also makes NDMRs less effective (more receptors to block)
• Patients require higher doses (often 2-5x normal) and may have shorter duration of action
• Monitor with neuromuscular monitor (train-of-four) - never rely on standard dosing
• Response unpredictable; titrate carefully

Opioids - Increased Requirements

• Hypermetabolism → accelerated drug metabolism
• Opioid tolerance develops rapidly (especially with repeated procedures)
• Increased Vd from fluid resuscitation/protein changes → lower peak concentrations
• May require very high opioid doses; patient-controlled analgesia (PCA) useful
• Methadone useful for opioid rotation in chronic cases

Propofol and Barbiturates

• Increased Vd early (fluid resuscitation, oedema) → larger induction doses needed
• Late phase: normal or decreased requirements due to protein binding changes (decreased albumin)

Volatile Agents

• Generally safe; no specific contraindication
• Maintain normothermia - patients are highly vulnerable to hypothermia (loss of skin, large exposed wound surface)

Local Anaesthetics

• Altered pharmacokinetics: changes in hepatic function, protein binding, Vd
• Caution with neuro/cardiotoxic risk in critically ill patients
• Liposomal bupivacaine offers longer duration with potentially better safety profile - Miller's Anesthesia, 10e

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Intraoperative Management

Monitoring

• Standard ASA monitors + arterial line (A-line) for beat-to-beat BP and frequent ABG
• Central venous access (may need to place through burned tissue - tunnelled if possible)
• Temperature monitoring - essential (hypothermia is a major risk)
• Urine output (catheter) - target 0.5-1 mL/kg/h

Temperature Management

• Burns destroy the skin barrier → massive heat and insensible fluid losses
• Operating theatre temperature raised to >28-30°C (feels uncomfortable for staff)
• Warm IV fluids, warm irrigation, forced-air warming, radiation lamps
• Hypothermia worsens coagulopathy (the "lethal triad" also applies in burns surgery)

Blood Loss

• Excision of burned tissue is highly vascular → massive blood loss expected
• Full-thickness burn excision: approximately 0.75-1 mL blood loss per cm² excised
• For large excisions: have cross-matched blood immediately available; cell salvage may be used
• Epinephrine-soaked (1:200,000) dressings applied to donor sites reduce blood loss
• Tumescent technique (subcutaneous injection of dilute epinephrine/LA) reduces donor site bleeding
• Tourniquets used for limb excisions

Positioning

• Large wounds may require frequent repositioning → pressure area care, padding, secure monitoring
• Prone positioning may be required (back burns)

Ventilation

• In patients with inhalation injury: lung-protective ventilation (TV 6 mL/kg IBW, PEEP 5-10, plateau pressure <30 cmH₂O)
• High-frequency oscillatory ventilation (HFOV) for severe ARDS
• Nebulised N-acetylcysteine and heparin alternating 4-hourly: mucolytic + anticoagulant; reduces cast formation and plugging in lower airway

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Pain Management in Burns - Multimodal Analgesia

• Background pain - continuous; treated with regular opioids ± adjuncts
• Procedural pain - dressing changes, physiotherapy, surgery - treated with additional analgesia

• NMDA antagonist → dissociative anaesthesia + analgesia + amnesia
• Maintains airway tone and spontaneous ventilation
• Ideal for dressing changes, debridements, minor procedures
• Prevents central sensitisation and opioid-induced hyperalgesia
• IV ketamine: rapid onset; can be run as infusion on ward
• Anti-depressant effect via norketamine metabolite (useful in burns)
• Side effects: emergence delirium (give midazolam concurrently), hallucinations, nausea - Miller's Anesthesia, 10e

• Peripheral nerve blocks (lateral femoral cutaneous nerve, fascia iliaca block) - ideal for thigh donor sites
• TAP blocks and paravertebral blocks for trunk donor sites; catheters for prolonged analgesia
• Central neuraxial (spinal/epidural) - possible but concerns about infection risk in heavily colonised patients
• Tumescent local anaesthesia for donor sites pre-harvest - Miller's Anesthesia, 10e

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Electrical Burns

• AC (household) at 50 Hz → tetanic muscle contraction → cannot release hold → prolonged contact
• DC (lightning) → single strong contraction → usually thrown away from contact → shorter exposure

• Low voltage (<1000V): damage at contact site
• High voltage (>1000V): deep tissue damage, especially muscle around bone (bone has highest resistance → most heat)

• Rhabdomyolysis → myoglobinuria → acute kidney injury (AKI)
  • If myoglobinuria present: urine output 1-2 mL/kg/h until urine clears
  • NaHCO₃ to alkalinise urine, mannitol ± furosemide to facilitate excretion
• Cardiac arrhythmias - sinus tachycardia most common; VF and cardiac standstill in severe cases
• Compartment syndrome - limbs may need fasciotomy within 24 hours
• Spinal cord injury from tetanic contraction (vertebral fractures)
• Cutaneous burn often underestimates the true extent of deep injury - formula-based fluid resuscitation is inadequate; must titrate to urine output and clinical response
• Entry and exit wounds always present - look for them - Miller's Anesthesia, 10e

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Chemical Burns

• Acid burns: Coagulation necrosis - self-limiting protein layer prevents deeper penetration
• Alkali burns: Liquefaction necrosis - no limit to penetration, continue to deepen → often deeper than acid burns of same contact time
• Immediate treatment: Copious water irrigation for at least 20-30 minutes (do not neutralise - neutralisation reactions generate heat)
• Hydrofluoric acid (HF): unique - fluoride ions penetrate deeply; chelates Ca²⁺ and Mg²⁺; causes hypocalcaemia, hypomagnesaemia, life-threatening arrhythmias; treat with IV/topical calcium gluconate

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Perioperative Complications and the "Burn Triad"

           Hypothermia
           /\
          /  \
         /    \
Coagulopathy --- Metabolic Acidosis

• Aggressive warming throughout
• Damage control approach for massive haemorrhage (1:1:1 blood products)
• Correct acidosis (adequate resuscitation, not sodium bicarbonate)

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Infection and Sepsis

• Leading cause of late morbidity and mortality
• Loss of skin barrier + immunosuppression + invasive devices = major infection risk
• Most common sources: pneumonia, central line infection, burn wound infection
• Do NOT give prophylactic systemic antibiotics - promotes resistance
• Topical antimicrobials for wound: silver sulfadiazine, silver nitrate, mafenide acetate
• SIRS criteria unreliable in burns (>90% meet criteria regardless of infection status)
• Antibiotics should be culture-directed; dose-adjust for altered pharmacokinetics
• Miller's Anesthesia, 10e

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Summary: Key Exam Points

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