Getting to the bottom of scuba diving fatalities

Abstract

The investigation of scuba diving fatalities requires an understanding of diving medicine, the causes of drowning and pulmonary barotrauma/cerebral arterial gas embolism (CAGE) and potential toxic effects of gas under pressure. Drowning is a common terminal event, but the pathologist has to understand the often complex set of events including fatigue, panic, decreased level of consciousness, trauma, entrapment, natural disease, physical disability and equipment failure that lead to drowning. The pathologist must recognise that the diagnosis of drowning at autopsy is based on circumstances of the death together with a variety of non-specific anatomical findings. In order to diagnose drowning it is necessary to have fairly detailed descriptions of the circumstances surrounding the event and a thorough examination of the equipment. The other problem which makes interpreting the autopsy findings of scuba diving fatalities difficult is the high incidence of post-mortem gas formation. This is usually due to post-mortem off-gassing where dissolved nitrogen comes out of the circulation and can be seen on post-mortem CT scan. This raises the issue as to whether a post-mortem CT scan is of any value in the diagnosis of pulmonary barotrauma/cerebral arterial gas embolism (PB/CAGE). Certainly recent evidence suggests that a dive to 18 metres for 45 minutes can produce considerable post-mortem gas formation within 8 hours of death. These authors suggest that post-mortem CT scan is of no value in the diving autopsy. If CT scan is contemplated it must be performed in the first 8 hours after death otherwise it is extremely difficult to interpret. The diagnosis of pulmonary barotrauma and cerebral arterial gas embolism predominantly depends on the history of a rapid ascent followed by a rapid loss of consciousness on the surface. I believe that CT scan imaging may be of help but the CT scanning needs to be performed within the first 8 hours of death. Issues such as nitrogen narcosis, oxygen toxicity, trauma, natural disease particularly long QT syndrome, and fitness to dive particularly in regard to asthma will be discussed as will the data set required to investigate a diving fatality.