Drowning Submersion Injuries

Introduction for MCCQE1 Candidates

Drowning is a leading cause of accidental death in Canada, particularly among toddlers and young men. For the MCCQE1, you must understand the pathophysiology of submersion injuries, the critical importance of hypoxic-ischemic injury, and the specific management protocols regarding resuscitation and hypothermia, which are highly relevant in the Canadian climate.

According to the World Health Organization (WHO) and accepted Canadian standards, drowning is defined as:

“The process of experiencing respiratory impairment from submersion/immersion in liquid.”

Epidemiology and Canadian Context

Understanding the demographics helps in risk stratification and prevention counseling (CanMEDS Health Advocate).

• Bimodal distribution:
  • Toddlers (1–4 years): Often bathtubs or private pools.
  • Young Males (15–24 years): High-risk behavior, alcohol use, natural bodies of water.
• Canadian Specifics:
  • Seasonality: High incidence in summer (swimming/boating) and winter (snowmobiling/ice fishing).
  • Indigenous Populations: Disproportionately higher rates of drowning in northern and rural Canadian communities.

Pathophysiology

The primary insult in drowning is hypoxia, leading to multi-organ dysfunction.

1. Breath-holding: Initial panic leads to voluntary breath-holding.
2. Aspiration: Break point is reached; water enters the airway.
3. Surfactant Washout:
   • Water washes out or inactivates surfactant.
   • Leads to alveolar collapse (atelectasis) and non-cardiogenic pulmonary edema (ARDS).
   • Result: V/Q mismatch and shunting.
4. Systemic Effects:
   • CNS: Hypoxic-ischemic brain injury (primary determinant of outcome).
   • Cardiovascular: Hypoxia leads to tachycardia $\rightarrow$ bradycardia $\rightarrow$ PEA/Asystole.
   • Acid-Base: Mixed respiratory and metabolic acidosis.

Clinical Presentation

Diagnostic Evaluation

Laboratory Investigations

• Arterial Blood Gas (ABG): Assess for hypoxemia and acidosis (metabolic/respiratory).
• Electrolytes: Usually normal, but check for imbalances if massive aspiration occurred.
• Creatinine/BUN: Risk of Acute Tubular Necrosis (ATN) from hypoxia or rhabdomyolysis.
• CBC: Leukocytosis is common due to stress (demargination), not necessarily infection.
• Coagulation Profile: DIC is a potential complication.
• Toxicology Screen: Ethanol and drug levels.

Imaging

• Chest X-Ray (CXR):
  • May vary from normal to patchy infiltrates to frank pulmonary edema.
  • Note: Initial CXR may be normal; infiltrates can appear 6–12 hours later.
• CT Head/C-Spine:
  • Indicated if history of diving, unwitnessed fall, signs of trauma, or altered LOC not improving with oxygenation.

Management

The management of drowning follows the ABCDE approach, with specific modifications for the drowning victim.

Disposition Criteria

Canadian Guidelines & Prevention

• Lifejackets (PFDs): The Canadian Red Cross emphasizes that wearing lifejackets could eliminate up to 90% of boating-related drownings.
• Fencing: Four-sided fencing with self-latching gates for private pools is the single most effective prevention for toddlers.
• Supervision: “Touch supervision” (within arm’s reach) for non-swimmers.

Key Points to Remember for MCCQE1

1. Prioritize Oxygenation: The cardiac arrest is hypoxic. Rescue breaths are critical.
2. C-Spine: Do not immobilize routinely; only if trauma is suspected (diving).
3. Surfactant: Pathophysiology involves surfactant washout leading to ARDS.
4. No Prophylaxis: Do not give prophylactic antibiotics or steroids.
5. Hypothermia: Aggressive rewarming is required. Defibrillation and drugs may be ineffective at core temps <30°C.
6. Observation: Asymptomatic patients need 6-8 hours of observation due to delayed pulmonary edema.

Sample Question

Clinical Scenario

A 23-year-old male is brought to the Emergency Department after being submerged in a freshwater lake for approximately 4 minutes. He was pulled out by bystanders and received rescue breaths immediately. On arrival, he is alert but anxious. He complains of shortness of breath and a cough.

Vitals:

• Temp: 36.1°C
• HR: 110 bpm
• BP: 128/76 mmHg
• RR: 28/min
• SpO2: 88% on room air

Physical Exam:

• Chest auscultation reveals diffuse crackles bilaterally.
• Neurological exam is normal (GCS 15).
• No signs of head or neck trauma.

Chest X-ray: Shows bilateral patchy infiltrates.

Question

Which one of the following is the most appropriate initial management step for this patient?

• A. Administer prophylactic broad-spectrum antibiotics
• B. Perform endotracheal intubation immediately
• C. Administer supplemental oxygen and consider non-invasive positive pressure ventilation (NIPPV)
• D. Administer IV furosemide
• E. Immobilize the cervical spine and obtain a CT scan

Explanation

The correct answer is:

• C. Administer supplemental oxygen and consider non-invasive positive pressure ventilation (NIPPV)

Detailed Analysis:

• C is correct: This patient has signs of pulmonary edema (crackles, hypoxia, infiltrates) due to surfactant washout from submersion. He is conscious (GCS 15) and hemodynamically stable. The first line of treatment is supplemental oxygen. If hypoxia persists or work of breathing is high, CPAP or BiPAP (NIPPV) is excellent for recruiting alveoli and improving oxygenation without the need for immediate intubation.
• A is incorrect: Prophylactic antibiotics are not indicated in drowning. Pneumonia is a late complication; early infiltrates represent pulmonary edema, not infection.
• B is incorrect: While the patient is hypoxic, he is alert and protecting his airway. Intubation is reserved for those with GCS <8, severe hypoxemia refractory to NIPPV, or respiratory fatigue. Less invasive measures should be tried first.
• D is incorrect: The pulmonary edema in drowning is non-cardiogenic (due to capillary leak and surfactant loss), not volume overload. Diuretics are generally not effective and may worsen hypovolemia/hypotension.
• E is incorrect: Routine cervical spine immobilization is not indicated unless there is a mechanism of injury suggesting trauma (e.g., diving, signs of injury). This patient was swimming, has no signs of trauma, and is alert.

References

1. Medical Council of Canada. MCCQE Part I Objectives: Population Health and Ethics, Emergency Medicine.
2. Schmidt, A.C., et al. (2016). Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Drowning. Wilderness & Environmental Medicine.
3. Szpilman, D., et al. (2012). Drowning. New England Journal of Medicine.
4. Heart & Stroke Foundation of Canada. 2020 Guidelines for CPR and ECC. Link 
5. Canadian Red Cross. Drowning Research and Prevention. Link 
6. Weisbrod, L., et al. (2023). Drowning. StatPearls [Internet].