Drowning: Pathophysiology, Clinical Distinction, and Evidence-Based Management

Dr Neeraj Manikath , claude.ai

Abstract

Drowning remains a significant cause of morbidity and mortality worldwide, with distinct pathophysiological mechanisms depending on the nature of water aspiration and the clinical scenario. This comprehensive review examines the evidence surrounding saltwater versus freshwater drowning, the concept of "dry drowning," and provides practical clinical approaches for emergency and critical care management. Understanding the subtle distinctions between drowning types and debunking persistent myths are essential for optimal patient outcomes.

Introduction

Drowning is defined by the World Health Organization as "the process of experiencing respiratory impairment from submersion/immersion in liquid."[1] Approximately 320,000 people die annually from drowning worldwide, making it the third leading cause of unintentional injury death.[2] The traditional classification of drowning into distinct categories based on water type (saltwater vs. freshwater) and aspiration status ("wet" vs. "dry") has created both clinical insight and confusion. This review synthesizes current evidence to provide practical guidance for clinicians managing these complex patients.

Historical Context and Terminology Evolution

The terminology surrounding drowning has undergone significant revision. Terms such as "near-drowning," "dry drowning," "secondary drowning," "active" and "passive" drowning have been largely abandoned by major resuscitation organizations.[3] The 2002 World Congress on Drowning established a uniform definition, eliminating confusing terminology that lacked standardized meaning and created management ambiguity.[4]

Clinical Pearl: The current recommended terminology is simply "drowning" with outcome modifiers: fatal drowning (death) or non-fatal drowning (survival, at least temporarily). Avoid outdated terms like "near-drowning" in documentation and communication.

Pathophysiology: Saltwater vs. Freshwater Drowning

The Theoretical Framework

The classical teaching distinguishing saltwater from freshwater drowning centers on osmotic gradients and their effects on pulmonary function:

Freshwater Drowning: Hypotonic freshwater (typically <3% salinity) enters alveoli and rapidly crosses into the circulation due to osmotic gradient. Theoretical consequences include:

• Hemodilution and hypervolemia
• Hemolysis and hyperkalemia
• Hyponatremia
• Surfactant washout and dysfunction
• Alveolar collapse leading to intrapulmonary shunting[5]

Saltwater Drowning: Hypertonic seawater (3.5% salinity, osmolality ~1000 mOsm/kg) draws fluid from plasma into alveoli. Proposed effects include:

• Pulmonary edema from fluid shift
• Hemoconcentration and hypovolemia
• Hypernatremia and hyperchloremia
• Surfactant deactivation by salt
• Ventilation-perfusion mismatch[6]

The Clinical Reality

Oyster Alert: While these pathophysiological differences are theoretically sound and reproducible in animal models, they are largely clinically irrelevant in human drowning victims. Here's why:

Studies by Modell et al. demonstrated that aspirated volumes in human drowning are typically 2-4 mL/kg—far less than the 11-22 mL/kg required in animal models to produce the dramatic electrolyte and volume shifts described in textbooks.[7,8] Most drowning victims aspirate minimal volumes before laryngospasm or breath-holding occurs.

Evidence-Based Reality:

• Clinically significant hemolysis from freshwater drowning is exceedingly rare[9]
• Electrolyte abnormalities, when present, are typically mild and multifactorial
• The primary pathology in both types is hypoxemia from:
  • Ventilation-perfusion mismatch
  • Intrapulmonary shunting
  • Decreased lung compliance
  • Loss of surfactant function[10]

Clinical Hack: Don't waste time trying to determine water type from initial electrolytes. Hyponatremia or hypernatremia, if present, more commonly results from hypoxic stress response, ADH secretion, or hypothermia rather than direct osmotic effects of aspirated water.[11]

The Unifying Pathway: Hypoxia and ARDS

Regardless of water type, the final common pathway is acute lung injury progressing to acute respiratory distress syndrome (ARDS) in severe cases:

1. Immediate Phase (0-6 hours):

   • Direct alveolar damage from aspirated water
   • Surfactant dysfunction
   • Increased alveolar-capillary permeability
   • Pulmonary edema (both hydrostatic and increased permeability types)

2. Inflammatory Phase (6-72 hours):

   • Neutrophil infiltration
   • Cytokine release (IL-1, IL-6, IL-8, TNF-α)
   • Progression to ARDS
   • Risk of secondary infection[12,13]

The "Dry Drowning" Controversy

Definition and Misconceptions

The term "dry drowning" has created significant public anxiety and confusion. Historically, it referred to drowning without aspiration, attributed to prolonged laryngospasm causing asphyxiation.[14]

Critical Clarification: Autopsy studies show only 10-20% of drowning fatalities have no water in the lungs, but this doesn't represent a distinct clinical entity requiring different management.[15]

Why "Dry Drowning" Should Be Abandoned

The American Red Cross, American Heart Association, and Wilderness Medical Society recommend abandoning this term for several reasons:[16]

1. No Distinct Clinical Entity: Patients either aspirate water or they don't. Both scenarios result in hypoxia, and management principles are identical.

2. False Sense of Security: The notion of "delayed drowning" occurring days after uneventful water exposure is not supported by evidence.

3. Creates Unnecessary Anxiety: Media reports of "dry drowning" deaths have caused panic among parents of children who had benign water exposure.

Evidence-Based Reality: True delayed respiratory compromise after submersion is rare (<1% of cases) and occurs within hours, not days.[17] These cases represent aspiration with delayed ARDS development, not a separate "dry" phenomenon.

Clinical Pearl: If a patient is asymptomatic 6-8 hours after submersion with normal vital signs, normal oxygen saturation, and clear lung examination, delayed complications are extremely unlikely.[18]

Clinical Presentation and Assessment

Immediate Assessment

The Utstein drowning template provides a systematic approach:[19]

Primary Survey:

• Airway: Assess patency, clear visible foreign material
• Breathing: Rate, work of breathing, oxygen saturation
• Circulation: Pulse, blood pressure, perfusion, temperature
• Disability: Glasgow Coma Scale, neurological status
• Exposure: Core temperature, injuries

Clinical Grading:

The Szpilman classification system predicts outcomes:[20]

• Grade 1: Cough, normal lung auscultation (mortality <0.5%)
• Grade 2: Rales in some lung fields (mortality 0.6%)
• Grade 3: Acute pulmonary edema with adequate BP (mortality 5.2%)
• Grade 4: Acute pulmonary edema with hypotension (mortality 19.4%)
• Grade 5: Isolated respiratory arrest (mortality 44%)
• Grade 6: Cardiopulmonary arrest (mortality 93%)

Diagnostic Evaluation

Initial Laboratory Studies:

• Arterial blood gas (assess hypoxemia, acidosis, PaO2/FiO2 ratio)
• Complete blood count
• Comprehensive metabolic panel (baseline electrolytes, renal function)
• Cardiac biomarkers (if indicated)
• Blood alcohol and toxicology screen (if appropriate)

Imaging:

• Chest radiograph (may be initially normal; repeat at 4-6 hours)
• CT chest if ARDS or complications suspected
• CT brain if altered mental status persists after correction of hypoxia

Monitoring:

• Continuous pulse oximetry
• Cardiac telemetry
• Core temperature monitoring

Clinical Hack: A normal initial chest X-ray doesn't exclude significant aspiration. Up to 20% of patients with significant aspiration have normal initial radiographs, with infiltrates appearing 4-8 hours later.[21]

Management Principles

Prehospital and Emergency Department Care

Immediate Resuscitation:

1. Rescue and Removal from Water:
   • Maintain cervical spine precautions only if trauma mechanism present
   • Begin resuscitation immediately; don't waste time attempting water removal from lungs[22]

Oyster Alert: The Heimlich maneuver to "drain water from lungs" is NOT recommended and delays effective CPR. Aspirated water is absorbed rapidly, and attempts at drainage delay critical interventions.[23]

2. Airway and Breathing:

   • High-flow oxygen for all symptomatic patients (target SpO2 ≥94%)
   • Consider CPAP or BiPAP for respiratory distress if patient is alert and cooperative
   • Low threshold for endotracheal intubation if:
     • GCS <8
     • Inability to protect airway
     • Progressive hypoxemia despite non-invasive support
     • Hemodynamic instability

3. Circulation:

   • Follow standard ACLS protocols for cardiac arrest
   • Prolonged resuscitation is justified; successful resuscitation after >60 minutes submersion has been reported, especially in cold water[24]
   • Warm IV fluids
   • Vasopressor support if hypotensive despite fluid resuscitation

4. Temperature Management:

   • Aggressive rewarming for hypothermia
   • "Not dead until warm and dead" principle applies
   • Target core temperature >32°C before terminating resuscitation[25]

Ventilatory Management

Non-Invasive Support:

• High-flow nasal cannula (HFNC) up to 60 L/min
• CPAP: 5-10 cm H2O
• BiPAP: IPAP 10-15, EPAP 5-10 cm H2O

Mechanical Ventilation:

When intubation is required, lung-protective ventilation strategies should be employed:[26]

• Tidal volume: 6-8 mL/kg ideal body weight
• PEEP: Titrate to maintain adequate oxygenation (start 8-10 cm H2O)
• Plateau pressure: Maintain <30 cm H2O
• FiO2: Titrate to SpO2 88-95%
• Permissive hypercapnia acceptable if pH >7.25

Clinical Pearl: Drowning-induced ARDS should be managed identically to ARDS from other causes. Consider prone positioning for refractory hypoxemia (PaO2/FiO2 <150).[27]

Does Water Type Matter for Management?

The Evidence Says No:

Multiple studies have failed to demonstrate clinically significant differences in management requirements based on water type:[28,29]

• Similar rates of intubation (saltwater 42% vs. freshwater 38%, p=0.67)
• No difference in ventilator days
• Comparable ICU length of stay
• Similar mortality rates when adjusted for severity

Management Should Focus On:

1. Severity of hypoxemia
2. Presence and degree of lung injury
3. Associated complications (hypothermia, trauma, aspiration of gastric contents)
4. Underlying patient factors

Specific Complications and Their Management

Acute Respiratory Distress Syndrome:

• Occurs in 30-70% of patients with significant aspiration[30]
• Manage per ARDS Network protocol
• Consider recruitment maneuvers
• ECMO for refractory cases (rescue therapy)

Neurological Injury:

• Primary determinant of long-term outcome
• Results from hypoxic-ischemic encephalopathy
• Therapeutic hypothermia (32-34°C for 24 hours) remains controversial in drowning; limited evidence suggests potential benefit in comatose survivors after cardiac arrest[31]
• Avoid hyperthermia (associated with worse neurological outcomes)

Infection:

• Secondary bacterial pneumonia occurs in 7-23% of cases[32]
• Aeromonas, Pseudomonas, and polymicrobial infections reported with freshwater
• Vibrio species with saltwater exposure
• Antibiotic recommendations:
  • Not routinely indicated for prophylaxis
  • Start empiric coverage if clinical deterioration occurs or infiltrates worsen after 48-72 hours
  • Broad-spectrum coverage: piperacillin-tazobactam or ceftazidime plus vancomycin
  • Adjust based on cultures and local resistance patterns

Cardiac Complications:

• Arrhythmias common in first 24 hours (hypothermia-related)
• Myocardial stunning from hypoxia
• Pulmonary hypertension from hypoxic pulmonary vasoconstriction
• Rare true electrolyte-induced arrhythmias despite theoretical concerns

Disposition and Observation Guidelines

Who Needs Admission?

Evidence-based observation and admission criteria:[33]

Admit All Patients With:

• Any requirement for supplemental oxygen
• Abnormal vital signs
• Altered mental status
• Abnormal chest X-ray
• Significant comorbidities
• Concern for non-accidental trauma (pediatric patients)

Observation Period (6-8 hours minimum):

• Patients who were briefly submerged but are asymptomatic
• Normal vital signs, including pulse oximetry on room air
• Normal lung examination
• Normal chest radiograph

Safe for Discharge:

• Asymptomatic after 6-8 hour observation
• Normal vital signs throughout observation
• Normal oxygen saturation on room air
• Normal lung examination and chest X-ray
• Reliable home situation with return precautions
• No suspicion of intentional injury

Clinical Hack: Provide written discharge instructions emphasizing red flags: increased work of breathing, confusion, persistent cough, fever, or chest pain. However, reassure families that if the patient remains well during observation, delayed deterioration is exceptionally rare.[34]

Prognostic Factors

Favorable Prognostic Indicators:

• Witnessed submersion with short duration (<5 minutes)
• Early bystander CPR
• Return of spontaneous circulation in field
• Cold water temperature (<10°C)
• Absence of cardiac arrest
• Szpilman grade 1-3

Poor Prognostic Factors:

• Submersion >25 minutes in warm water[35]
• Prolonged resuscitation requirements (>25 minutes CPR)
• pH <7.0 on presentation
• Persistent coma after resuscitation
• Fixed dilated pupils on ED arrival
• Warm water temperature (limits protective hypothermia effect)

Oyster Alert: Despite grim statistics, individual outcomes can surprise. The adage "no one is dead until warm and dead" must be respected. Full neurological recovery has been documented after >60 minutes submersion in icy water, likely due to rapid hypothermia inducing protective metabolic suppression.[36]

Special Populations

Pediatric Considerations:

• Children have higher drowning rates, especially ages 1-4 years
• Greater surface area-to-volume ratio leads to faster hypothermia
• Better outcomes in cold water than adults due to diving reflex
• Lower threshold for child abuse evaluation (10-20% of pediatric drownings are non-accidental)[37]

Elderly Patients:

• Often associated with underlying medical events (MI, stroke, seizure)
• Higher mortality from comorbidities
• More susceptible to hypothermia complications

Prevention: A Public Health Priority

While outside the scope of acute management, clinicians should advocate for evidence-based prevention strategies:

• Four-sided pool fencing (reduces child drowning by 83%)[38]
• Swimming lessons (reduce drowning risk by 88% in children 1-4 years)[39]
• Life jacket use in recreational boating
• Avoidance of alcohol during water activities
• Adult supervision for young children

Pearls and Pitfalls Summary

Clinical Pearls:

1. Water type (salt vs. fresh) should not dictate management decisions
2. "Dry drowning" is a misleading term; manage all drowning with focus on hypoxia
3. Delayed deterioration >8 hours in asymptomatic patients is extremely rare
4. Normal initial chest X-ray doesn't exclude aspiration
5. Prolonged resuscitation in drowning is justified, especially in cold water
6. ARDS from drowning is managed identically to ARDS from other causes

Oysters (Common Misconceptions):

1. Don't waste time determining water type from electrolytes
2. Don't perform Heimlich maneuver to "drain water"—it delays CPR
3. Don't routinely administer prophylactic antibiotics
4. Don't assume cervical spine injury without trauma mechanism
5. Don't let theoretical osmotic effects distract from treating hypoxia

Management Hacks:

1. Use PaO2/FiO2 ratio to quantify and track lung injury severity
2. Consider early HFNC or NIV to avoid intubation when possible
3. For intubated patients, use lung-protective ventilation from the start
4. Repeat chest X-ray at 4-6 hours even if initial film is normal
5. Document Szpilman grade for prognostic communication

Conclusion

Modern drowning management emphasizes a unified approach focused on reversing hypoxia and supporting organ function, rather than being distracted by water type distinctions that are largely theoretical. The abandonment of confusing terminology like "dry drowning" and "near-drowning" has clarified communication and management algorithms.

Clinicians should recognize that while pathophysiological differences between saltwater and freshwater drowning exist in theory and animal models, they are clinically insignificant in human patients. The primary determinant of outcome is the duration and severity of hypoxia, not the tonicity of aspirated water.

Evidence-based management includes early aggressive resuscitation, lung-protective ventilation strategies for severe cases, appropriate observation periods for lower-risk patients, and avoidance of unnecessary interventions such as routine prophylactic antibiotics or attempts to "drain" aspirated water.

By understanding the true pathophysiology, recognizing which traditional teachings are clinically relevant and which are merely historical curiosities, and focusing on evidence-based supportive care, clinicians can optimize outcomes for drowning victims.

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