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  • AutorenbildMichael Mutter

How little is needed for a lung barotrauma?

Pulmonary barotrauma with cerebral arterial gas embolism (CAGE) is a dramatic clinical picture in which air enters the systemic circulation, reaches the brain and causes stroke-like symptoms. Pulmonary barotrauma with CAGE can occur during scuba diving if divers ascend while holding their breath. This case report illustrates how little it takes.


Foto: Patrick Oswald

Case report

A 26-year-old female soldier was taking part in a rescue exercise from a submerged vehicle using a short-term air-supply system (STASS) in a pool. The STASS supplies a maximum of 70 liters of air from a small compressed air cylinder (200 bar) via a regulator with a short supply hose.


Because the soldier had problems breathing through the STASS, she had to repeat the exercises several times. After the sixth time, she experienced severe headaches. Nevertheless, the training was continued. After the seventh and final escape exercise, she stood up, briefly lost consciousness and developed slurred speech, sensory deficits and right-sided hemiparesis.


A CT scan of the head and chest was performed in the emergency room approximately 90 minutes after the accident. It showed no cerebral hemorrhage. No free air could be detected either in the brain or in the chest. There was also no pneumothorax (“ruptured lung”). A classical stroke was initially diagnosed. However, after consultation with the Navy's diving physician, the patient was transferred by air transport to the nearest hyperbaric chamber 1400 km away on the assumption of a CAGE.


11 hours after the incident, hyperbaric oxygen therapy (pressure chamber treatment) was initiated in accordance with Navy Table 6. This led to an almost complete recovery of symptoms within one hour. The hyperbaric chamber treatments over the following two days further improved the condition. Two MRI (magnetic resonance imaging) examinations of the brain revealed no pathological findings. The soldier was discharged four days after the incident with only minor sensory disturbances.


Additional examinations, including spirometry (lung function test), coagulation markers, transthoracic echocardiogram (heart ultrasound) and a CT angiogram (CT examination of the blood vessels), revealed no abnormalities. A technical examination ruled out a malfunction of the STASS. A re-analysis of the accident revealed that the maximum water depth at which the soldier had breathed through the STASS was only 75 cm.


Discussion

CAGE following pulmonary barotrauma is a well-described complication of scuba diving. According to the Boyle-Marriotte law, a gas expands in proportion to the decreasing ambient pressure. This occurs in the lungs when scuba divers inhale at depth and hold their breath during ascent. The expanding air can cause the alveoli and adjacent vessels to rupture, allowing air bubbles to pass directly into the pulmonary vessels and on into the systemic circulation. If they reach the brain, they can block the small cerebral vessels and thus trigger symptoms of a stroke such as impaired consciousness, speech disorders and paralysis (etc.).


Even a transpulmonary pressure (difference between the pressure in the alveoli and the ambient pressure) between 73-90 mm Hg can trigger a pulmonary barotrauma. The equivalent pressure of 1 meter of fresh water is 75 mmHg. This means that pulmonary barotrauma is possible at very shallow depths if divers hold their breath during ascent after a maximal inhalation. In this case, the depth of the injuring breath was only approx. 75 cm. The symptoms are most likely due to the fact that the soldier held her breath during the ascent after a (maximum) breath through the STASS. It remains a matter of speculation whether the repeated holding of breath during the exercises in quick succession led to increasing overinflation of the lung and ultimately provoked the barotrauma of the otherwise healthy lung. It is remarkable that thorough examinations did not reveal any pre-existing pulmonary problems.


Conclusion

This case highlights the potential for CAGE in shallow water diving as a result of pulmonary barotrauma. If symptoms such as loss of consciousness and neurological deficits occur immediately after surfacing, especially after an emergency ascent, CAGE must always be considered. This applies in particular after the use of emergency systems for a short-term air supply, such as those used in white-water kayaking or after a tragic drowning death in the America's Cup, as the risk of breath holding due to panic or overexertion is even higher in such situations. The treatment of choice is hyperbaric oxygen therapy (pressure chamber treatment).


Repeated escape exercises in a short period of time, as in the case described, must be discouraged due to the risk of increasing lung hyperinflation.



Not for everyone! Commercially available fun devices, which function in the same way as a STASS, should only be used with great caution and only by certified scuba divers due to the risk of lung barotrauma.



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