The pathophysiology of drowning

The effects of drowning, both fatal and non-fatal, on the different major organ systems within the body, and the process of hypoxia are reviewed. Pulmonary fluid aspiration results in an increase in low ventilation-perfusion ratio areas and decreased compliance. However, in most victims variable quantities of the liquid medium are aspirated. It is believed that in at least 10% of drowned people laryngospasm occurs, but practical evidence conflicts with the theory that the closed larynx keeps water from entering the trachea. Widespread atelectasis occurs after surfactant is denatured, leading to large shunts and perfusion mismatch. Five to twenty five per cent of patients progress to life-threatening acute respiratory failure. The effects of immersion on the cardiovascular system are an increased venous return and a central shift of blood volume, but the cardiovascular system has been stated to show remarkable stability, and the changes in blood volume are not significant enough to be life threatening. There are differences in biochemical changes in the blood with inhalation of fresh water and sea water. However, these are minimal and not clinically significant. A severe lactic acidosis develops secondary to the hypoxia. The most common renal complication is oliguria due to acute tubular necrosis. The roles of the diving reflex and hypothermia in cerebral protection are still not well understood. The overall pathophysiological processes in drowning and near drowning are complex but ultimately are determined by the degree and duration of hypoxia.