Gas expansion occurs within the intestines on ascent and may result in eructation, vomiting, flatus, abdominal discomfort and colicky pains. It is rarely severe, but can occasionally cause syncopal and shock-like states, stomach rupture and even death.
Inexperienced divers are more prone to aerophagia, predisposing to this condition. Swallowing to equalize middle ear pressures is one cause of aerophagia.
Performing the Valsalva manoeuvre while in the head-down position may also cause air to pass into the stomach. Carbonated beverages and heavy meals can contribute and are best avoided before and during exposure to hyperbaric conditions.
Treatment involves slowing the rate of ascent, stopping ascent or even recompression. The simple procedure of releasing tight-fitting restrictions such as belts, girdles and so forth may give considerable symptomatic relief.
Although not common, notable examples of gastrointestinal barotrauma are recorded. Two Norwegian divers were badly affected during 122-metre dives using helium-oxygen, on H.M.S. Reclaim in 1961. An Australian lad, responding very well to hyperbaric oxygen therapy for gas gangrene, drank a ‘flat’ celebratory lemonade at 2.5 ATA and deteriorated into a shock state with abdominal distension and pains before ascent was terminated. A group of officials celebrating the successful construction of a caisson in the United Kingdom experienced a similar embarrassing fate, from imbibing flat champagne.
Rarely, with a large and rapid expansion of gas in the stomach, this organ may rupture with ascent. A review was conducted of 12 cases associated with relatively deep dives, more than 30 metres, with rapid ascents. The abdominal pain and distension were constant, with various other symptoms including vomiting (25 per cent), belching (16 per cent), haematemesis (33 per cent) and dyspnoea (50 per cent). Guarding of the abdomen and shock occasionally developed.
On x-ray examination, pneumoperitoneum was present in all cases, but sometimes this extended to include a pneumomediastinum and even pneumothorax. These radiological abnormalities can, of course, also be produced by pulmonary barotrauma.
Gastroscopy allowed identification and localization of the lesions, and laparoscopy usually showed these to be full thickness, usually on the lesser curvature of the stomach.
Treatment of rupture of the stomach is essentially a surgical procedure; however, breathing 100 per cent oxygen as a first aid measure and even hyperbaric oxygen as an initial treatment may have some value under some circumstances. As a general rule, decompression of the pneumoperitoneum is best achieved using surgical techniques.
If there has been a full-thickness tear, then gastric contents are likely to be present in the peritoneal cavity, and the treatment must then be on general medical and surgical grounds.
In the patients reviewed, an amount of approximately 4 litres or more of gas was necessary before rupture of the stomach would develop, and it usually required a pressure of 96 to 155 mm Hg. The reason given for the localization to the lesser curvature is that there the gastric wall is composed of only one muscular layer, compared with the three layers elsewhere.
It is postulated that rapid distension of the stomach will increase the angle of His and compress the cardia against the right diaphragmatic pillar, thus making the oesophageal-gastric junction act like a one-way valve, obstructing eructation.