24.2 Environmental Injury: Drowning, Diving, Altitude, Heat, Cold, Electrical & Radiation

Drowning

• Pathophysiology: the fundamental insult is hypoxemia. Aspirated water washes out surfactant, causing alveolar collapse, shunt, and noncardiogenic pulmonary edema. Fresh and salt water differ little clinically; electrolyte shifts are rarely significant.
• Resuscitation: begin with ventilation and oxygenation, because the arrest is hypoxic (this is the one adult arrest where rescue breathing matters most). Cervical spine precautions apply only with a plausible mechanism, such as a dive.
• Hospital care:
  • Oxygen with PEEP (noninvasive ventilation or intubation with lung-protective settings), since the problem is shunt and atelectasis.
  • No prophylactic antibiotics and no corticosteroids; treat pneumonia if it develops (watch for Aeromonas and Pseudomonas in fresh water, and fungi in contaminated water).
  • Rewarming for hypothermia, which frequently coexists.
  • Observation for 4 to 8 hours in asymptomatic patients with normal oxygenation; symptoms of significance develop within that window, and "delayed drowning" days later is a myth.
• Prognosis: depends on submersion duration and the initial neurologic examination. Cold-water submersion with rapid cooling occasionally permits survival after prolonged arrest, so rewarm before prognosticating.

Diving Injuries

Air travel after diving, and transport in an unpressurized aircraft, worsens bubble disease. For transport, fly low (below about 1,000 feet of cabin altitude change) or in a pressurized aircraft at sea-level cabin pressure.

High-Altitude Illness

Acetazolamide (125 mg twice daily) prevents acute mountain sickness by inducing a metabolic acidosis that drives ventilation; it is a sulfonamide derivative.

Heat Illness

• Heat exhaustion: volume and salt depletion with a core temperature usually below 40 °C and preserved mental status. Treat with rest, cooling, and oral or intravenous salt-containing fluids.
• Heat stroke: core temperature above 40 °C with central nervous system dysfunction.
  • Classic (non-exertional): older adults in heat waves, often anhidrotic, with chronic illness and drugs (anticholinergics, diuretics, antipsychotics).
  • Exertional: athletes, military recruits, and laborers; often still sweating, with rhabdomyolysis, acute kidney injury, disseminated intravascular coagulation, and hepatic injury.
  • Treatment: cool fast. The target is a core temperature below about 39 °C within 30 minutes. Cold-water immersion is the fastest method for exertional heat stroke; evaporative cooling with mist and fans suits older classic cases. Use ice packs to the groin, axillae, and neck and cold intravenous fluids as adjuncts; stop active cooling at about 38.5 °C to avoid overshoot.
  • Antipyretics do not work (the hypothalamic set point is normal), and dantrolene is ineffective in heat stroke. Treat shivering with benzodiazepines.
  • Manage complications: rhabdomyolysis with fluids, hepatic failure (which can be fulminant), coagulopathy, seizures, and ARDS.

Accidental Hypothermia

• Rewarming:
  • Passive external (dry blankets, warm environment) for mild cases.
  • Active external (forced-air warming, heating pads) and minimally invasive (warm intravenous fluids, warm humidified oxygen).
  • Active internal: bladder, gastric, or thoracic lavage; and extracorporeal rewarming (ECMO or cardiopulmonary bypass) for hypothermic cardiac arrest or severe instability, which is the treatment of choice when available.
• Handling: move the patient gently, because rough handling can precipitate ventricular fibrillation.
• Arrest management: continue CPR during rewarming. Defibrillation and drugs often fail below about 30 °C, so warm the patient while resuscitating. A patient is not dead until warm and dead; neurologically intact survival has been reported after hours of arrest. A serum potassium above about 12 mEq/L suggests death preceded cooling (for example, avalanche asphyxia), and other markers of non-survivability include a frozen chest and severe hyperkalemia with asystole.
• Frostbite: rapid rewarming in 37 to 39 °C water, analgesia, no rubbing, delayed debridement, and iloprost or thrombolysis in severe, early presentations at experienced centers.

Electrical Injury and Lightning Strike

• Alternating current causes tetanic muscle contraction (the victim cannot let go), with a risk of ventricular fibrillation; direct current causes a single large contraction and throws the victim.
• Deep tissue injury far exceeds skin findings. Watch for compartment syndrome, rhabdomyolysis with pigmented urine, and long bone and spine fractures from falls.
• Cardiac: arrhythmias, including asystole and ventricular fibrillation; monitor patients with loss of consciousness, abnormal ECG, or high-voltage exposure.
• Lightning is a massive direct-current-like exposure causing immediate asystole (which often resolves spontaneously while respiratory arrest persists, so prolonged ventilation can be life-saving), keraunoparalysis (transient limb paralysis with cool mottled extremities), Lichtenberg figures, and tympanic membrane rupture. Reverse triage applies in a mass lightning event: resuscitate the apparently dead first, because they may only be in respiratory arrest.
• Fluid resuscitation is guided by myoglobinuria and measured injury; burn formulas underestimate requirements in deep electrical injury.

Radiation Injury and Chemical Agents

• Acute radiation syndrome: a prodrome of nausea and vomiting whose latency predicts dose (vomiting within an hour suggests a high dose), then hematopoietic (cytopenias at 2 to 4 weeks), gastrointestinal (mucosal failure at higher doses), and neurovascular syndromes.
  • The rate of absolute lymphocyte count decline over the first 48 hours is the best early dose estimate (the Andrews nomogram).
  • Management: decontaminate (remove clothing, wash), treat trauma first, give G-CSF or GM-CSF early, transfuse irradiated products, use antimicrobial prophylaxis for neutropenia, and consider specific internal contamination therapy: potassium iodide for radioiodine, Prussian blue for cesium and thallium, and DTPA for transuranics.
• Chemical agents:
  • Nerve agents and organophosphates: cholinergic crisis treated with large, escalating doses of atropine titrated to secretions, pralidoxime, and benzodiazepines for seizures.
  • Vesicants (mustard, lewisite): decontaminate, supportive airway and skin care; dimercaprol for lewisite.
  • Cyanide: hydroxocobalamin, or sodium nitrite plus thiosulfate.
  • Phosgene and chlorine: delayed pulmonary edema with observation and supportive care.
  • Protect staff: decontamination before entry into the department, with appropriate personal protective equipment.