Scuba diving death: Always due to drowning? Two forensic cases and a review of the literature

Introduction

Scuba diving is a popular recreational activity.^1,2 We report two cases of diving deaths due to pulmonary barotrauma (PBT) and consequent arterial gas embolism (AGE). Boyle’s law explains why barotrauma occurs since it is a consequence of the effect of pressure changes on the body. During descent, tissue injuries result if the pressure in these body cavities does not equalize with the ambient pressure, and result from the forces generated by this pressure difference. During ascent, the decrease in ambient pressure raises the risk of pulmonary over-distension. The latter causes an alteration of the trans-pulmonary gradient and can rupture the alveoli. In this case, the gas can pass into different sites and cause pneumomediastinum, subcutaneous emphysema, pneumothorax and AGE. ³

In AGE, the gas reaches the left side of the heart. Therefore, these gas bubbles can reach the organs via the systemic circulation and cause ischemic injuries. The most sensitive organ to hypoxia is the central nervous system and cerebral air embolism can be fatal.^1,4,5

Case reports

The first case concerns a 49-year-old man, whose body was found in the sea near the Tyrrhenian coasts, in Italy. Diver’s scuba tank and dive computer were also recovered.

The second case concerns a 62-year-old man, whose body was found underwater, about two miles off the Ionian coast, in Italy, lying on the seabed at a depth of 50 m, without an air regulator in his mouth. The diver’s tanks were also recovered.

Both bodies, found 4–5 h after death, were transported to the morgue and stored in refrigerated cells, reducing artefacts due to putrefaction gas formation. Inspection and autopsy were carried out in both cases. We found subcutaneous crepitus on palpation of the chest. Internally, bubbles were found in the basilar artery. The samples of the organs were stained using haematoxylin-eosin. A microscopic analysis of the slides was then performed. In the first case, the exam showed fatty infiltration of the right ventricular myocardium. In the second case, the exam showed widespread bullous pulmonary emphysema, hyperinsufflation of air in the lungs and micro-foci of chronic bronchiolitis.

Toxicological investigation was also performed and was negative in both cases.

Before autopsy, the CT of the head, shoulders, chest and abdomen was carried out in the first case. In the second case, a total body CT was performed. This exam pointed out air bubbles in the brain and neck, an emptied appearance of the cardiac chambers and aorta, empty upper suprahepatic veins and bubbles in subcutaneous soft tissues because of the emptying of vessels.

Analyses of the dive computers and on the gas cylinder manometers were also carried out.

Discussion

In most cases, the cause of death during diving is drowning, followed by cardiovascular disease and AGE.^5,6 It is important to know the physiology of diving to find probable signs of death due to PBT at autopsy.^7,8 One of the aims of our work is to underline the importance of involving a multidisciplinary team to determine the causes of death in fatal diving accidents as in these two cases. Indeed, AGE was the cause of death, resulting from PBT subsequent to pulmonary over-distension. The AGE probably resulted in neuronal injury with loss of consciousness and cardio-circulatory arrest. In the first case, the over-distension was provoked by a rapid ascent without fulfilling decompression stops and without breathing any gas. In addition, histological examination showed that the deceased was suffering from arrhythmogenic right ventricular dysplasia. We assume that he decided to ascend in this way because his tank was empty or because he had developed an arrhythmia. The rapid ascent and omitted decompression stops were responsible for the formation of the gas collections identified by the investigations. In the second case, the over-lung distension was a consequence of both changes in pressure occurring during the dive and pre-existing bullous emphysema noted in the histological examination. In the last few years, procedural modifications for autopsy in divers have been recommended. There are interesting methods of investigation such as the use of diving computer data, the reenactment of diving accidents and postmortem CT scans. Furthermore, it is necessary to have information about water temperature, the direction of sea currents and medical history. During autopsy, it is possible to demonstrate the presence of gas in atypical sites, such as in the cardiac ventricles, vessels, pleura and peritoneum. This can be achieved by opening these anatomical structures underwater or by perfusing vessels with inserted gas traps. This captured gas can be analysed to detect its composition and therefore its origin. CT is a more sensitive and less invasive technique to detect the site and the volume of abnormal gas spaces in the body and has an important role in explaining the cause of deaths during diving, especially if the scan is performed as early as possible. Generally, gas embolism subsequent to PBT is characterised by large volumes of intravascular gas, appearing from an arterial origin.^9,10,11 The complete pneumatisation of the supra-aortic trunks is the best Post Mortal Computer Tomography (PMCT) parameter in detecting a death due to fatal decompression sickness, when CT is performed within 24 h after death.

Some pathological conditions represent risk factors for diving accidents. In the first of our cases, the histological examination of the heart showed arrhythmogenic right ventricular dysplasia. It can induce fatal sudden arrhythmias. ¹² In the second case, the deceased suffered from bullous emphysema. This condition leads to pulmonary over-distension because of the phenomena of air trapping, destruction of the alveolar walls and the formation of larger air spaces and thin walls (bullae). This exposed the diver to an increased risk of developing pulmonary barotrauma and arterial gas embolism (AGE). For this reason, people with similar conditions should be advised not to dive.^4,5