Acute neurological symptoms during hypobaric exposure: consider cerebral air embolism

Cerebral arterial gas embolism (CAGE) is well known as a complication of invasive medical procedures and as a risk in diving and submarine escape. In the underwater environment, CAGE is caused by trapped air, which expands and leads to lung vessel rupture when ambient pressure decreases during ascent. Pressure decrease also occurs during hypobaric activities such as flying and, therefore, CAGE may theoretically be a risk in hypobaric exposure. We reviewed the available literature on this subject. Identified were 12 cases of CAGE due to hypobaric exposure. Based on these cases, we discuss pathophysiology, diagnosis, and treatment of CAGE due to hypobaric exposure. The low and slow pressure decrease during most hypobaric activities (as opposed to diving) account for the low incidence of CAGE during these exposures and suggest that severe air trapping must be present to cause barotrauma. This is also suggested by the large prevalence of air filled cysts in the case reports reviewed. We recommend considering CAGE in all patients presenting with acute central neurological injury during or shortly after pressure decrease such as flying. A CT scan of head and chest should be performed in these patients. Treatment with hyperbaric oxygen therapy should be initiated as soon as possible in cases of proven or probable CAGE.