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Anesthetic Management of Burns Patient

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1. PATHOPHYSIOLOGY OVERVIEW

Burn Shock (Biphasic Response)

Fluid Loss Mechanism

• Vascular permeability increases (even with 5% TBSA burn)
• Vasodilatation → ↑ hydrostatic pressure → interstitial fluid shift
• Filtration coefficient increases up to 20-fold
• Colloid osmotic pressure falls (protein leak into interstitium)
• Blister formation is direct evidence of early permeability change

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2. BURN ASSESSMENT

Classification by Depth

Estimation of TBSA

• Rule of Nines (adults): Head 9%, each arm 9%, anterior trunk 18%, posterior trunk 18%, each leg 18%, perineum 1%
• Lund–Browder diagram: More accurate, accounts for age (head larger in children)
• Palmar surface: Palm = ~1% TBSA

Burn Center Referral Criteria (American Burn Association)

• Partial thickness ≥10% TBSA
• Full thickness burns (any size)
• Burns of face, hands, feet, genitalia, perineum, joints
• Inhalation injury
• Electrical/chemical/lightning injuries
• Concomitant trauma or comorbidities
• Poorly controlled pain, pediatric burns (non-accidental trauma)

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3. FLUID RESUSCITATION

Parkland Formula

• Crystalloid: 4 mL/kg/% TBSA in first 24 hours
  • First half in initial 8 hours from time of burn
  • Second half over next 16 hours
• Titrate to urine output: 0.5–1 mL/kg/h in adults; 1 mL/kg/h in children
• Formulae are guides only — titrate to physiologic endpoints

Fluid Creep (Over-Resuscitation)

• Defined as fluid volume exceeding 6 mL/kg/%TBSA/24 h
• Causes: overestimation of burn size, supra-physiologic targets, opioid creep, failure to reduce rates when UO adequate
• Consequences: pulmonary edema, compartment syndromes (abdominal, ocular, extremity), multiorgan failure, nosocomial infection, extension of burn injury
• Abdominal compartment syndrome (ACS): intra-abdominal pressure >25 mmHg + new organ failure → decompression (paracentesis/laparotomy)

Colloid Rescue

• Start colloids at 8–12 hours post-burn (after capillary integrity partially restored)
• Reduces total fluid load and risk of compartment syndromes
• Hypertonic saline: limits volumes but monitor for hypernatremia → acute renal failure

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4. INHALATION INJURY

Diagnosis

• Carbonaceous sputum, singed nasal hairs, facial burns, hoarse voice, stridor
• Flexible bronchoscopy (FOB): gold standard — soot, mucosal edema, hyperemia, erosion, ulceration
• PaO₂/FiO₂ ratio after resuscitation = most reliable indicator of impact
• Other: xenon scanning, CT, pulmonary function tests

Management

• Observation and monitoring for mild cases
• Intubate early if airway patency is threatened — do not wait for maximal edema
• Indications for intubation: anticipated airway swelling, impaired oxygenation/ventilation, CO poisoning with neurologic impairment
• Head elevation (30°): reduces airway edema via venous/lymphatic drainage
• Inhalation injury → requires larger fluid volumes for resuscitation

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5. PREOPERATIVE ASSESSMENT (Box 83.3)

• Age of patient, extent/depth/location of burn, mechanism, elapsed time
• Inhalation injury and lung dysfunction
• Adequacy of resuscitation
• Airway patency — most critical
• Difficult vascular access
• Gastric stasis (risk of aspiration)
• Altered drug responses
• Altered mental states, pain/anxiety
• Presence/susceptibility to infection
• Hematologic issues (anemia, coagulopathy)
• Magnitude of planned surgery

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6. AIRWAY MANAGEMENT

Challenges by Phase

Difficulties

• Mask seal: dressings, nasogastric tubes, facial wounds
• Oral/nasal airways difficult with microstomia/scarred nares
• Jaw thrust/chin lift/neck extension restricted by contractures
• Tracheostomy itself → subglottic stenosis, tracheomalacia, granuloma

Approach

1. If difficult airway anticipated: confirm ability to mask-ventilate BEFORE giving apnea-producing drugs, OR maintain spontaneous ventilation throughout
2. Fiberoptic intubation (awake if cooperative) — preferred for suspected difficult airway
   • If uncooperative: inhalational induction or ketamine to preserve spontaneous ventilation + FOB
   • Topicalize airway: nebulized lidocaine pre-induction, lidocaine spray on cords via fiberscope
3. Video laryngoscopy: alternative with hypopharyngeal/glottic assessment
4. LMA: useful as airway device and as conduit for fiberoptic intubation; limited by microstomia/fixed neck flexion
5. Tracheostomy under local anesthesia: viable option; surgeon must be available
6. In children: awake intubation not practical → ketamine-sedation + FOB

ETT Securing

• Adhesive tape contraindicated on facial burns
• Use: circumferential head tie, wire to tooth, arch bars

RSI

• Required if ileus/delayed gastric emptying (sepsis, opioids, intestinal edema)
• Succinylcholine: contraindicated after 24–48 hours (upregulated extrajunctional nAChRs → massive K⁺ release → cardiac arrest)

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7. ALTERED DRUG PHARMACOLOGY IN BURNS

Succinylcholine

• Safe in first 24 hours only
• After 24–48 h: proliferation of extrajunctional acetylcholine receptors → exaggerated K⁺ efflux → life-threatening hyperkalemia/cardiac arrest
• Contraindicated from 24–48 h post-burn until wound healed

Non-depolarizing Muscle Relaxants (NDMRs)

• Resistance (increased dose requirement) — due to:
  • Upregulation of acetylcholine receptors
  • Increased α₁-acid glycoprotein (protein binding)
  • Increased volume of distribution
  • Hypermetabolic state with increased hepatic/renal clearance
• Onset may be delayed; neuromuscular monitoring mandatory

Opioids

• Often increased requirements due to tolerance (from repeated procedures)
• Tolerance develops faster in children
• IV ketamine often used instead/adjunct

Ketamine (Drug of Choice in Burns)

• Hemodynamic stability (catecholamine release)
• Preserves hypoxic and hypercapnic ventilatory responses
• Preserves airway reflexes and muscle tone → avoid airway manipulation
• Decreases airway resistance
• Anti-inflammatory effects
• Peripheral vasoconstriction → reduces heat loss
• NMDA antagonism → prevents central sensitization, reduces opioid tolerance/hyperalgesia
• Antidepressant effect (via norketamine metabolite)

• Bolus dose can cause hypotension in burns patients (desensitized/downregulated β-adrenoceptors from chronic catecholamine excess → direct myocardial depression unmasked)
• Side effects: nausea/vomiting, hallucinations, emergence delirium (reduced by co-administration of benzodiazepine)

Volatile Anesthetics

• Generally can be used; no specific contraindication
• Anesthetic-induced vasodilation aggravates heat loss

Propofol / Barbiturates

• Hypotension risk in hypovolemic/shocked patients
• Use with caution; reduced doses

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8. INTRAOPERATIVE MANAGEMENT

Vascular Access

• Often very difficult — burned/scarred skin over peripheral veins
• Central venous access: jugular, subclavian, femoral (rotate sites)
• CVCs can remain >7–14 days with strict aseptic technique
• Secure adequate access before excision/grafting begins (rapid, substantial blood loss)

Monitoring Challenges

• ECG electrodes may not adhere → use needle electrodes or surgical staples; place on back/dependent sites
• Pulse oximetry: alternative sites — ear, nose, tongue
• BP cuff over burned/grafted tissue: use sterile cuff, protect underlying area
• Arterial line: recommended for extensive procedures (continuous BP, blood sampling, hemodynamic assessment)
• Temperature monitoring: mandatory (detect hypothermia and transfusion reactions)
• Neuromuscular monitoring: mandatory (dose requirements significantly altered)

Ventilator Management

• Lung-protective ventilation intraoperatively (same as ICU)
• During hypermetabolic phase: O₂ consumption and CO₂ production markedly increased → minute ventilation may exceed 20 L/min
• Faster O₂ desaturation during apnea/hypopnea (high metabolic demand)
• Extubation: only when hemodynamically stable, normothermic, no sepsis/coagulopathy/worsening pulmonary function
• Assess air leak around deflated ETT cuff before extubation; direct laryngoscopy/FOB to assess glottis

Blood Loss and Transfusion

• Excision and grafting: rapid, substantial blood loss possible
• Transfusion trigger: typically Hb 7–8 g/dL; higher threshold if cardiorespiratory compromise
• Topical vasoconstrictors (epinephrine-soaked dressings) reduce donor site bleeding
• Tumescent local anesthesia at donor sites reduces blood loss and provides analgesia

Temperature Management

• Burns patients are poikilothermic — highly susceptible to hypothermia
• Hypothermia causes: ↑ oxygen consumption, exaggerated catabolism, ↓ CO, arrhythmias, abolition of HPV, coagulopathy, ↓ hepatic/renal drug clearance, graft loss from shivering
• Shivering can increase O₂ consumption up to 500% and dislodge grafts
• OR temperature maintained at 27°C–38°C (80°F–100°F)
• Methods: forced-air warming blankets, water mattresses (convection, most effective), fluid/blood warmers, wrapping head and extremities, pre-warming transport area

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9. PAIN MANAGEMENT

Multimodal Approach

Regional Anesthesia in Burns

• Tumescent LA at donor sites: pre-harvest injection → reduces blood loss and provides analgesia
• Subcutaneous catheter infusions, peripheral nerve blocks
• Central neuraxial blockade
• Placement must account for: burned/infected skin over intended injection sites, coagulopathy, altered anatomy
• Frequently used as analgesic adjunct rather than primary technique

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10. SPECIAL SITUATIONS

Electrical Burns

• Morbidity far exceeds what burn size suggests
• High-voltage: loss of consciousness, arrhythmias, myoglobinuria, compartment syndromes, extensive deep tissue damage
• Evaluate: associated trauma, rhabdomyolysis, compartment syndromes
• ECG monitoring for arrhythmias
• Treat myoglobinuria: aggressive fluids, urine alkalinization
• May need surgery within 24 hours (fasciotomy, escharotomy)

Pediatric Burns

• Greater surface-area-to-body-weight ratio → more rapid heat loss
• Resuscitation: UO target 1 mL/kg/h
• Risk of cerebral edema from resuscitation (blood-brain barrier more vulnerable)
• Opioid tolerance develops faster
• Awake intubation not practical → ketamine-sedation for FOB
• Cuffed ETTs recommended regardless of age
• Up to 20% may be non-accidental trauma — always consider

Elderly Burns

• Higher mortality for same TBSA (age is major independent outcome predictor)
• Thinner skin → deeper burns; poor wound healing
• Reduced metabolic reserve; often cannot mount hypermetabolic response
• Comorbidities (cardiac, pulmonary, renal) complicate resuscitation
• Lower threshold for ventilatory support
• Aspiration risk with enteral feeding (delirium)
• Pain often under-treated

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11. SURGICAL CONSIDERATIONS FOR ANESTHESIOLOGIST

• Early excision (<72 h): reduces infection, improves cardiac function, decreases blood transfusion, reduces hypermetabolic response, decreases mortality
• Staged excision: multiple shorter procedures for unstable patients
• Excision down to viable tissue only
• Maximum safe excision in one setting: up to 50% TBSA in stable patients
• Close communication between surgeon and anesthesiologist — be prepared to abort if patient becomes unstable
• Postoperative ventilation may be needed after extensive procedures (tumescent fluid reabsorption, cytokine/bacterial release → worsening lung function)

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KEY EXAM POINTS — QUICK SUMMARY

1. Succinylcholine is absolutely contraindicated from 24–48 h post-burn to wound healing (extrajunctional AChR upregulation → fatal hyperkalemia)
2. Ketamine is the agent of choice — preserves airway reflexes, hemodynamically stable, analgesic, anti-inflammatory
3. Fluid resuscitation: Parkland formula (4 mL/kg/%TBSA/24 h), titrate to UO 0.5–1 mL/kg/h; colloid rescue at 8–12 h
4. Airway: intubate early when indicated — edema worsens over hours; consider fiberoptic intubation for anticipated difficult airway
5. Temperature: OR at 27–38°C; hypothermia is life-threatening in burns
6. Monitoring: modified sites for ECG/SpO₂/BP; arterial line for extensive surgery; NMJ monitoring mandatory
7. NDMRs: resistance due to receptor upregulation and pharmacokinetic changes
8. Inhalation injury: FOB is gold standard; early intubation for at-risk patients
9. Blood loss: plan access before excision; arterial line; rapid transfusion capability
10. Pain: multimodal — ketamine + opioids + gabapentin + regional anesthesia

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