Air transport of patients with intracranial air: computer model of pressure effects

Abstract

Introduction: Air is commonly trapped within the skull in patients who have been treated for trauma or intracranial hemorrhage. In Sweden, when such a patient is transported by air ambulance it is standard procedure to maintain sea-level pressure in the cabin to prevent increased intracranial pressure (ICP). However, this type of flight operation is more difficult and expensive. Maintenance of sea-level cabin pressure is not common practice all over the world, and the criteria supporting the choice of pressurization during transport are inadequate and in need of evaluation. The purpose of this study was to develop and evaluate a model to simulate the influence of intracranial air on ICP during air transport.

Methods: We identified an existing nonlinear model of the cerebral spinal fluid and intracranial pressure dynamics, then added intracranial air as a new component and evaluated the model through simulations.

Results: The model behaved as expected, and the simulations indicated that under normal flying conditions with decreased cabin pressure the initial intracranial air volume will increase by approximately 30% at normal maximum cabin altitude, 8000 ft. The increase in ICP depends upon both the initial air volume and the rate of change in cabin altitude. For an intracranial air volume of 30 ml the estimated worst-case increments of ICP from sea level to maximum altitude would be from 10 mm Hg to 21.0 mm Hg, or from 20 mm Hg to 31.8 mm Hg.

Discussion: Our results support the need for maintenance of sea-level pressure during air transport of patients with suspected intracranial air, since an ICP increment could potentially impair the patient's clinical condition.