A CANINE STUDY OF COLD-WATER DROWNING IN FRESH VERSUS SALT-WATER

Objective: To compare the pathophysiologic changes occurring during drowning in cold fresh water and cold salt water with reference to viability. Design: Randomized, prospective, controlled submersion experiments in two contrasting cold liquids. Setting: A laboratory at a large university-affiliated medical institution. Subjects: Thirteen healthy, anesthetized mongrel dogs. Three dogs served as controls and were immersed but not submerged. The remainder were submerged in cold fresh water or cold salt water (4 degrees C). Interventions: Catheters were placed in the femoral artery, right carotid artery and right internal jugular vein. Electrocardiogram, pneumogram, and rectal temperatures were measured continuously during submersion/immersion. Measurements and Main Results: Cold water submersion with drowning produced a large initial decrease in carotid artery temperature (similar to 7.5 degrees C in the first 2 mins) compared with a minor decrease (similar to 0.8 degrees C with immersion). No significant differences were noted in the rate of decrease of temperature between drowning in fresh water and salt water. During cold fresh water drowning, aspiration produced gross hemodilution with an average increase in body weight of 16.5%. Hematocrit values, serum sodium concentrations, and osmolality decreased while serum potassium concentrations, catecholamines, and free hemoglobin increased. All measured biochemical data (except Pao(2)) remained at viable levels. By contrast, during cold salt water drowning, average body weight increased by only 6%, with hemoconcentration and a shrinkage of vascular volume. Hematocrit and hemoglobin values increased by 30%, but initial plasma free hemoglobin values remained unchanged. Serum sodium concentrations, osmolality, and potassium concentrations increased rapidly to critical levels. Conclusions: On submersion in cold water, all of the experimental animals developed tachypnea immediately, followed by aspiration with predictable effects. The biochemical and pathophysiologic changes in cold water drowning approximated those changes reported for warm water drowning for both fresh and salt water with one exception and continued aspiration of cold water produced extremely rapid core cooling as long as the circulation remained intact. This process of acute submersion hypothermia may protect the brain temporarily from lethal damage, as reported in cases of cold fresh water drowning. Concentrations of circulating catecholamines increased exponentially in both groups of test animals. Clinically, their acute effects on the circulation, compounded by significant hypothermia and extreme anoxia, must hamper the detection of residual circulation at rescue and may play a role in sudden death from cold water in the absence of drowning.