Drowning and Near-Drowning

• Primary Hypoxic Injury: Upon submersion, the drowning victim experiences the diving response (mediated by trigeminal and vagal stimulation), manifesting as bradycardia, vasoconstriction, and blood flow redistribution toward the heart and brain. However, initial panic and struggle trigger hyperpnea followed by involuntary gasping, leading to water aspiration into the lungs. Freshwater aspiration causes osmotic fluid shift from the bloodstream into alveolar spaces (leading to pulmonary edema and surfactant washout), while saltwater aspiration creates a hypertonic gradient that draws fluid from the pulmonary interstitium into alveolar spaces. Both mechanisms result in severe ventilation-perfusion (V/Q) mismatch, intrapulmonary shunting (blood perfusing non-ventilated alveoli), and profound hypoxemia refractory to supplemental oxygen in severe cases. The degree of aspiration does not reliably correlate with clinical severity ("dry drowning" or laryngospasm-mediated asphyxia occurs in approximately 10% of cases with minimal water aspiration).

• Cellular Hypoxia and Ischemic Cascade: Progressive hypoxemia (arterial PO₂ <40 mmHg) combined with hypercarbia triggers anaerobic metabolism, shifting ATP production from oxidative phosphorylation to glycolysis and lactate production. This leads to profound metabolic acidosis (pH often <7.0) that impairs myocardial contractility, increases dysrhythmia susceptibility, and activates cell death pathways. The hypoxia-inducible factor (HIF-1α) pathway is activated, upregulating erythropoietin and vascular endothelial growth factor (VEGF), contributing to secondary inflammation. Ischemic cascade activation includes excitotoxicity from glutamate release, calcium influx through NMDA receptors, mitochondrial dysfunction with increased reactive oxygen species (ROS), lipid peroxidation, and activation of calpains and caspases driving necrotic and apoptotic neuronal death, particularly affecting the cerebral cortex, basal ganglia, and hippocampus.

• Pulmonary Injury and Post-Aspiration Pneumonitis: Water aspiration disrupts pulmonary surfactant, increases alveolar surface tension, promotes alveolar collapse (atelectasis), and triggers innate immune activation. Aspirated water (particularly contaminated freshwater) introduces pathogenic organisms and inflammatory mediators that induce pneumonitis within 24-48 hours. Both freshwater and saltwater aspiration damage the alveolar-capillary membrane, increasing permeability and promoting non-cardiogenic acute respiratory distress syndrome (ARDS) with protein-rich pulmonary edema. Surfactant depletion is a hallmark finding, with decreased amounts of surfactant proteins A and D, compromising the lung's defense mechanisms.

• Electrolyte Disturbances and Cardiac Effects: Massive freshwater aspiration can induce acute hypervolemia and hyponatremia (dilutional), while saltwater aspiration causes hypervolemia and hypernatremia (osmotic). Hyponatremia (<120 mEq/L) may precipitate cerebral edema and seizures. Aspiration of contaminated water introduces hypoxemia and electrolyte shifts that combine with cold-induced metabolic depression (in cold-water drowning) to create profound hypothermia, which paradoxically can be neuroprotective via reduced cerebral metabolic rate (CMRO₂ approximately decreases 50% per 5°C). However, hypothermia also increases myocardial irritability and dysrhythmia susceptibility (including "Osborn wave" or J wave on ECG). Acidemia, hypoxemia, and catecholamine surge predispose to ventricular fibrillation, particularly in the "rescue collapse" phenomenon where rewarming of severely hypothermic patients triggers VF.

• Secondary Cerebral Injury and Neuroinflammation: Beyond acute hypoxic-ischemic encephalopathy (HIE), the submersion injury triggers post-resuscitation disease characterized by systemic inflammation, cerebral edema, blood-brain barrier disruption, and microglial activation. Circulating damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs) activate toll-like receptor (TLR) signaling, driving nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation and pro-inflammatory cytokine release (TNF-α, IL-1β, IL-6, IL-8). This secondary neuroinflammation compounds primary ischemic injury and determines neurological recovery potential. Cold water immersion may offer neuroprotection through reduced metabolic rate and decreased inflammatory cascade activation.

• Unintentional Submersion (Primary Cause): The vast majority of drowning cases are unintentional, occurring in various aquatic environments including swimming pools (most common for young children <5 years), natural bodies of water (lakes, rivers, beaches), and bathtubs. Lack of supervision is the single greatest modifiable risk factor in pediatric populations; the American Academy of Pediatrics emphasizes that drowning occurs silently and rapidly (within 2 minutes) without characteristic splashing or calls for help.

• Seizure Disorders and Cardiac Arrhythmias: Individuals with epilepsy have a 15-40 times increased risk of drowning compared to the general population, particularly with generalized tonic-clonic seizures occurring in water (the "sudden unexpected nocturnal death in epilepsy" [SUDEP] equivalent in aquatic environments). Long QT syndrome, Brugada syndrome, and other inherited arrhythmias predispose to cardiac arrhythmias triggered by cold water immersion or hypoxemia. Sudden cardiac death during swimming has been reported in apparently healthy young people with undiagnosed channelopathies.

• Substance Use and Intoxication: Alcohol intoxication is implicated in 40-50% of adolescent and adult drowning deaths, impairing judgment, swimming ability, and thermoregulation. Drugs affecting consciousness (sedatives, benzodiazepines, opioids) and those causing cardiac effects (stimulants, antipsychotics) increase drowning risk. The combination of alcohol + cold water immersion dramatically increases risk through vasodilation and heat loss.

• Age-Related Vulnerability: Children ages 1-4 years have the highest drowning mortality rates for unintentional submersion, with peak incidence in boys. Adolescents and young adults (15-24 years) show peak rates due to risk-taking behaviors, substance use, and poor swimming ability. Elderly individuals are at increased risk due to comorbidities, medication effects (beta-blockers impairing cardiac response to cold), and balance disorders.

• Inability to Swim and Low Supervision: Lack of swimming ability, absence of life jackets, and inadequate supervision are major preventable risk factors. Drowning can occur in shallow water (< 2 feet) and is often silent, making supervision critical.

• Secondary Submersion: Severe underlying conditions predisposing to loss of consciousness in water include myocardial infarction, arrhythmias, stroke, severe hypoglycemia, or head trauma. These cases represent secondary drowning where the primary event (cardiac arrest, stroke) occurs first, followed by submersion and aspiration.

• Cold Water Immersion: While hypothermia offers some neuroprotection through metabolic suppression, it also increases arrhythmia risk and complicates resuscitation decisions. Cold water drowning cases have occasionally survived prolonged submersion (>1 hour in children) due to profound hypothermia-induced metabolic depression.

• Acute Respiratory Distress: Survivors rescued from water typically present with coughing, gasping for breath, and visible respiratory effort. Tachypnea is nearly universal, with respiratory rates often >30 breaths/min. Frothy or pink sputum may be present, reflecting pulmonary edema from alveolar-capillary membrane disruption. Some patients present with apnea or gasping respirations (agonal breathing) requiring immediate ventilatory support.

• Altered Mental Status and Loss of Consciousness: This ranges from mild confusion and lethargy in mild cases to profound coma in severe drowning. The degree of altered consciousness correlates with submersion duration and resuscitation quality. Severe cases present unresponsive with fixed, dilated pupils (indicating severe cerebral edema or brainstem involvement), though pupil reactivity can be preserved even in severe drowning and should not preclude aggressive resuscitation attempts (see Prognosis section).

• Cardiovascular Instability: Hypotension, tachycardia (or paradoxical bradycardia in cold-water drowning), and dysrhythmias are common. In cold-water immersion, the diving response may produce severe bradycardia despite profound hypoxemia. Asystole or ventricular fibrillation may be the presenting rhythm, particularly if water aspiration was massive and hypoxemia prolonged. The "rescue collapse" phenomenon describes sudden cardiac arrest occurring upon removal from water or during rewarming in severely hypothermic patients.

• Pulmonary Edema and Respiratory Compromise: Physical examination reveals crackles (rales) throughout lung fields, often with wheezing, indicating pulmonary edema and bronchospasm. Decreased air movement bilaterally suggests severe pulmonary edema or aspiration pneumonitis. Stridor may indicate laryngeal edema from aspirated water.

• Cold Skin and Core Hypothermia: In cold-water drowning, the skin is markedly cold to palpation (particularly extremities), and core body temperature may be severely depressed (<30°C). The presence of profound hypothermia does not preclude survival ("no one is dead until they are warm and dead") and mandates continued resuscitation.

• Abdominal Distension: Gastric distension from aspiration of water and air is common, particularly in patients who panic and swallow large volumes of water. Severe distension may impair diaphragmatic excursion and complicate bag-valve-mask ventilation.

• Seizures: Generalized tonic-clonic seizures may occur acutely from severe hypoxemia and cerebral edema or represent a recurrent seizure disorder that precipitated the submersion event.

• Clinical Assessment and Scene History: The diagnosis of drowning/near-drowning is largely clinical, based on the history of submersion and current clinical presentation. Critical information includes estimated submersion duration (major prognostic factor), water temperature (cold water offers some neuroprotection), water type (salt vs. fresh, contaminated), state of consciousness at rescue, resuscitation initiated (timing and quality of bystander CPR), and Glasgow Coma Scale (GCS) score at presentation and after resuscitation.

• Blood Gas Analysis: Arterial blood gas (ABG) analysis typically reveals hypoxemia (PaO₂ <60 mmHg despite supplemental oxygen in moderate-severe cases), hypercarbia (PaCO₂ often >50 mmHg), and metabolic acidosis (pH <7.2, base deficit >-10 mEq/L) reflecting tissue hypoxia and anaerobic metabolism. Severe cases show profound acidemia (pH <7.0) with elevated lactate (>4 mEq/L). These values guide severity assessment and prognosis but do not preclude aggressive resuscitation.

• Serum Electrolytes and Osmolality: Severe freshwater aspiration may cause hyponatremia (Na⁺ <120 mEq/L) and hypo-osmolality, while saltwater aspiration causes hypernatremia (Na⁺ >150 mEq/L) and hyperosmolality. However, clinically significant electrolyte abnormalities from aspiration alone are uncommon in modern case series, with most patients maintaining relatively normal electrolytes. Extreme hyponatremia (Na⁺ <110 mEq/L) can cause seizures and cerebral edema and requires careful correction.

• Complete Blood Count and Coagulation Studies: Hemolysis from freshwater aspiration can cause mild anemia and hyperkalemia (from RBC lysis). Severe cases may develop disseminated intravascular coagulation (DIC) from hypoxemia, shock, and hypothermia; coagulation studies (PT, PTT, fibrinogen, D-dimer) should be obtained in severe cases.

• Renal Function and Muscle Injury Markers: Acute kidney injury (AKI) may develop from shock, rhabdomyolysis (from the submersion struggle), and myoglobinuria. Obtain serum creatinine, BUN, and urinalysis. Creatine kinase (CK) levels may be markedly elevated (>1,000 U/L) from musculature injury during resuscitation and struggle.

• Lactate and Other Metabolic Markers: Serum lactate >4 mEq/L indicates significant tissue hypoxia and has prognostic value; lactate clearance during resuscitation correlates with survival and neurological outcome.

• Chest Radiography: The initial chest X-ray may be falsely reassuring or show subtle findings, as pulmonary edema develops over hours post-submersion. Classic findings include bilateral interstitial and alveolar opacities (pulmonary edema), often with a "white-out" appearance in severe ARDS. Aspiration pneumonitis may appear as segmental or lobar infiltrates. Pneumothorax or pneumomediastinum may occur from barotrauma (rare in freshwater drowning but more common in deep-water diving incidents).

• Computed Tomography of Brain: Head CT is indicated for patients with unexplained altered consciousness, focal neurological deficits, or signs of trauma. Findings may include cerebral edema (loss of gray-white matter differentiation, compressed ventricles), infarction in watershed zones, or evidence of preceding stroke/cardiac event (in secondary drowning cases). However, negative early CT does not exclude severe hypoxic-ischemic encephalopathy.

• Electrocardiogram: ECG may show the Osborn wave (J wave), a distinctive deflection at the junction of QRS complex and ST segment, characteristic of severe hypothermia. Bradycardia, prolonged PR interval, widened QRS, and prolonged QT interval are seen in cold-water immersion. Dysrhythmias including atrial fibrillation ("atrial fibrillation of hypothermia") or ventricular fibrillation may be present.

• Classification Systems: The Szpilman score (incorporating age, estimated submersion duration, period of unconsciousness before CPR, artificial ventilation before CPR, and pH) has been validated to predict neurological outcomes, with scores >6 predicting poor prognosis (though this should not preclude resuscitation attempts). The Orlowski classification predicts outcome based on submersion duration: <5 minutes generally good prognosis, 5-10 minutes variable, >10 minutes poor prognosis (exceptions exist with cold-water drowning).

• Differential Diagnosis Considerations: Rule out secondary drowning (cardiac event, stroke, seizure preceding submersion), trauma (head injury, cervical spine injury from diving), drug intoxication (contributing to loss of consciousness), hypothermia as primary vs. secondary process, and other causes of acute respiratory failure and altered mental status (sepsis, metabolic derangement).

Immediate Resuscitation (In-Water and Scene Management)

• In-water resuscitation: If trained, bystanders should initiate rescue breathing in the water if the victim is in cardiac arrest, as hypothermia and the diving response may allow prolonged apnea tolerance. However, priority is rapid removal from water. Chest compressions should not be initiated until the victim is on a firm surface to allow adequate

Pulmonary — the dominant early problem

• Acute respiratory distress syndrome: surfactant washout plus alveolar-capillary membrane injury produces protein-rich, non-cardiogenic edema; signaled by worsening hypoxemia with rising FiO₂ requirement and diffuse bilateral opacities on chest radiograph developing over hours. Emergency — manage with lung-protective low tidal volume ventilation and PEEP per the ATS/ESICM/SCCM ARDS guideline; consider ECMO at an experienced center for refractory hypoxemia.
• Delayed pulmonary deterioration: initially well-appearing patients may develop hypoxemia hours later, which is why observation rather than immediate discharge is standard for symptomatic patients. Current WHO/Utstein-style consensus drowning nomenclature discourages the terms "dry drowning," "secondary drowning," and "near-drowning"; where earlier sections of this article use them, treat them as historical labels only (laryngospasm-predominant drowning, delayed post-immersion respiratory deterioration, and non-fatal drowning, respectively).
• Aspiration pneumonia: distinguished from early chemical pneumonitis by fever, leukocytosis, and new focal infiltrate after 48 hours. Contaminated or stagnant water raises the risk of atypical organisms (Aeromonas, Pseudomonas, filamentous fungi such as Scedosporium). Prophylactic antibiotics are not recommended; they select resistant flora without improving outcome.
• Barotrauma from treatment: pneumothorax or pneumomediastinum from positive-pressure ventilation — sudden hypotension with rising peak pressures and unilateral absent breath sounds signals tension pneumothorax, an emergency requiring needle decompression.

Cardiac, neurologic, and systemic

• **Ventricular fibrillation / pulseless VT and *rescue collapse*: cold myocardium is electrically irritable, and afterdrop during rewarming can precipitate arrest. Emergency**. In hypothermic arrest, the AHA advises performing defibrillation and giving ACLS medications per the standard algorithm concurrently with active rewarming; response to both may be diminished below roughly 30°C, and ECMO/cardiopulmonary bypass is the preferred rewarming modality. Some non-AHA bodies (e.g., the European Resuscitation Council) limit repeated shocks and withhold drugs until the core is warmer — a genuine area of guideline variation.
• Hypoxic-ischemic encephalopathy with cerebral edema: heralded by persistent coma, seizures, or loss of gray-white differentiation on CT. Seizures raise cerebral metabolic demand and are an emergency; treat with benzodiazepines.
• Acute kidney injury: from shock, rhabdomyolysis, and hemoglobinuria — rising creatinine with markedly elevated CK and heme-positive urine without RBCs.
• Coagulopathy/DIC and hypothermia-induced platelet dysfunction: oozing from puncture sites with prolonged PT/PTT and falling fibrinogen.

• Hypoxia is the entire pathophysiology: drowning arrest is asphyxial, not primarily arrhythmic. Per the AHA, drowning is the classic exception to compression-only CPR — give rescue breaths first and use an airway-breathing-first approach. The single best next step in an apneic drowning victim is ventilation/oxygenation, not defibrillation.
• **Never perform abdominal thrusts or the Heimlich maneuver to "drain water"**: aspirated volume is small and rapidly absorbed; the maneuver delays ventilation and provokes gastric regurgitation. This is the most common distractor in drowning stems.
• Fresh versus salt water is a board trap: despite the textbook osmotic mechanisms, clinically significant electrolyte derangements are uncommon, and management is identical for both. Do not pick "give hypertonic saline for freshwater drowning."
• "No one is dead until they are warm and dead": in hypothermic arrest, continue resuscitation during active rewarming; extracorporeal rewarming (ECMO/bypass) is the preferred modality for a hypothermic patient in arrest. Fixed dilated pupils and a flat exam in a cold patient do not establish death.
• **The *Osborn (J) wave* — a positive deflection at the QRS–ST junction — is the ECG buzzword for significant hypothermia, along with bradycardia. Note that shivering artifact** belongs to mild-to-moderate hypothermia: shivering ceases as the core falls to roughly 30–32°C, so a cold, non-shivering patient with Osborn waves and bradycardia suggests severe hypothermia.
• The association examiners love: unexplained drowning in an adolescent or young adult should prompt evaluation for long QT syndrome, catecholaminergic polymorphic VT, or a seizure disorder — swimming is a classic LQTS type 1 trigger. In toddlers, ask about supervision and pool fencing; in adults, ask about alcohol.
• Do not give prophylactic antibiotics or corticosteroids: neither improves outcome; antibiotics are reserved for grossly contaminated water exposure or documented pneumonia developing after the first day.
• Spinal immobilization is selective, indicated only when the mechanism suggests trauma (diving into shallow water, surfing, high-speed watercraft) — routine collars impede airway management.