PATHOPHYSIOLOGY OF DROWNING

Drowning occurs when water fills the airways for any reason. It is important to note that progressive aspiration of water can result in hypoxemia. If loss of consciousness occurs, the continued hypoxemia can result in bradycardia and cardiac arrest. In the lungs, aspiration can cause a washout and destruction of alveolar surfactant resulting in severe hypoxia, alveoli derecruitment, reduced pulmonary compliance and noncardiogenic pulmonary edema, all of which can complicate ventilator management. It should also be noted that there is no such thing as “Near Drowning.” Correct terminology includes “Non-Fatal Drowning” and “Fatal Drowning.”

Immersion in water when associated with panic, exhaustion, inadequate water competency, a medical emergency such as lethal cardiac dysrhythmia or seizure, or effects of hypo/hyperthermia can lead to drowning from one of the following mechanisms:10-15

- Airway below the water’s surface → breath hold breakpoint (inability to resist urge to breathe due to hypercapnia and hypoxemia) → progressive aspiration and subsequent hypoxemia (see below) → loss of consciousness (LOC) → apnea and passive airway flooding → bradycardia → cardiac arrest.1
- Aspiration (either sea water or fresh water) causes a degree of surfactant washout/destruction increased alveolar surface tension and diminished integrity of the alveolar-capillary membrane atelectasis/ derecruitment and disruption of the alveolar capillary membrane → unregulated fluid shifts resulting in noncardiogenic pulmonary edema, reduced pulmonary compliance ( ~10-40% with as little as 1-3cc/kg water) → right to left shunting resulting in hypoxemia.1
- Cold water submersion → inadvertent gasp for air (“cold shock response”) → tachypnea, vasoconstriction, tachycardia from sympathetic surge → arrhythmias (especially in patients with long QT syndrome) or parasympathetic mediated bradycardia (“diving response”), altered mental status, diminished strength, and coordination.1 Table 1 shows expected survival times in cold water.