Pathophysiology of Drowning and Near-Drowning
Advanced, Clinical Subspecialties
With accidental or planned submersion, breath holding is the first conscious response. After the initiation of breath holding several events occur in parallel.
Continued apnea, either from breath holding, laryngospasm or some combination of both will lead to desaturation and loss of consciousness. Desaturation can lead to laryngeal loss of muscular tone and frank aspiration of fluid. At this point, the aspirated fluids will directly fill alveoli, dilute pulmonary surfactant leading to atelectasis and increase the transcapillary hydrostatic gradients to disrupt capillary barriers. This leads to an acute lung injury much like ARDS and increased transpulmonary shunting, up to 75% in some studies of seawater drowning.
Finally, if continued, apnea and aspiration of fluids in drowning can lead to respiratory acidosis, ventricular fibrillation and cardiac arrest.