Reduced cerebral perfusion on sudden immersion in ice water: a possible cause of drowning.

Introduction: Near-drowning incidents and drowning deaths after accidental immersion in open waters have been linked to cold shock response. It consists of inspiratory gasps, hyperventilation, tachycardia, and hypertension in the first 2-3 min of cold-water immersion. This study explored the immediate changes in cerebral blood flow velocity (V-mean) during coldwater immersion since cold shock induced hyperventilation may diminish Vmean and lead to syncope and drowning. Methods. There were 13 male volunteers who were lowered into a 0 degrees C immersion tank for 30 S. V-mean in the middle cerebral artery (MCA) was measured together with ventilatory parameters and heart rate before, during, and after immersion. Results. Within seconds after immersion in ice water, heart rate increased from 74 1 16 to 107 +/- 18 bpm (mean +/- SD; p < 0.05). Immersion was associated with a marked elevation in respiratory rate (from 16 +/- 3 to 38 +/- 14 breaths. min-') and tidal volume (883 +/- 360 to 2292 +/- 689 ml). The end-tidal carbon dioxide tension decreased from 38 +/- 4 to 26 5 mmHg and MCA Vmean dropped by 43 +/- 8%. Signs of imminent syncope (drowsiness, blurred vision, loss of responsiveness) were shown by two subjects (MCA Vnican dropped 62% and 68%, respectively). Discussion: Following icewater immersion, hyperventilation induced a marked reduction in MCA Vaican to a level which has been associated with disorientation and loss of consciousness.