Impaired consciousness when scuba diving associated with vasovagal syncope

Drowning is likely to result from impairment of consciousness when scuba diving. Causes include toxic effects of breathing gas, including nitrogen narcosis and oxygen toxicity, and arterial gas embolism.

Review of the medical records of scuba divers who had impaired consciousness underwater that could not be attributed to toxic effects of breathing gas or arterial gas embolism.

Four scuba divers had episodes of impaired consciousness when at shallow depths (8-18 m) underwater. The descriptions of the episodes were very similar. Three had histories of recurrent episodes of vasovagal syncope on land.

Absence of other causes for their impaired consciousness underwater leads to the conclusion that the probable cause was vasovagal syncope.