Pneumocephalus and air travel: an experimental investigation on the effects of aircraft cabin pressure on intracranial pressure

Abstract

This study investigates the effects of aircraft cabin pressure on intracranial pressure (ICP) elevation of a pneumocephalus patient. We propose an experimental setup that simulates the intracranial hydrodynamics of a pneumocephalus patient during flight. It consists of an acrylic box (skull), air-filled balloon [intracranial air (ICA)], water-filled balloon (cerebrospinal fluid and blood) and agarose gel (brain). The cabin was replicated using a custom-made pressure chamber. The setup can measure the rise in ICP during depressurization to levels similar to that inside the cabin at cruising altitude. ΔICP, i.e. the difference between mean cruising ICP and initial ICP, was found to increase with ICA volume and ROC. However, ΔICP was independent of the initial ICP. The largest ΔICP was 5 mmHg; obtained when ICA volume and ROC were 20 ml and 1,600 ft/min, respectively. The postulated ICA expansion and the subsequent increase in ICP in pneumocephalus patients during flight were successfully quantified in a laboratory setting. Based on the quantitative and qualitative analyses of the results, an ICA volume of 20 ml and initial ICP of 15 mmHg were recommended as conservative thresholds that are required for safe air travel among pneumocephalus patients. This study provides laboratory data that may be used by doctors to advise post-neurosurgical patients if they can safely fly. Craniotomy refers to the surgical removal of a portion of the skull to gain access to the contents of the intracranial cavity. The procedure usually involves exposing the brain after opening its membranous coverings 1 , which inevitably expose the human brain to surrounding air. Varying amounts of air within the intracranial cavity (ICA) (known as pneumocephalus) remain after craniotomy 2. In most cases, pneumocephalus is not life-threatening as the ICA is normally absorbed into the systemic circulation over a period of several weeks 3-5. Safety concerns arise when patients with pneumocephalus engage in air travel before the ICA is fully absorbed. Air safety regulations require cabins of commercial aircraft to be pressurized to a standardized minimum of 75 kPa, which is approximately 75% that of atmospheric pressure at sea level (101.3 kPa), at cruising altitude 6,7. Consequently, during air travel, the ambient pressure may be as much as 25 kPa lower than the initial pressure of the ICA, which is at 101.3 kPa. According to Boyle's law, the difference in pressure between the aircraft cabin and the ICA would result in an increase in the ICA volume, as the ICA expands to equilibrate with the cabin pressure. The expansion, which takes place inside the rigid cranium, may cause cerebral compression that can lead to elevations in the intracranial pressure (ICP). A mild increase in ICP is tolerable. However, if the increase in ICP is too large, cerebral herniation may occur, which severely endangers the life of the pneumocephalus patient. In spite of the potential life-threatening event, pneumocephalus and air travel safety remains a controversial topic 8...

Air travel with pneumocephalus: a systematic review

“…The hydrodynamics of a pneumocephalus patient during flight was investigated in an experimental setup using an acrylic box (skull), air-filled balloon (intracranial air), water-filled balloon (cerebrospinal fluid and blood) and agarose gel (brain) all placed in a custom-made pressure chamber [ 14 ]. An intracranial air volume of 20 ml and an initial intracranial pressure of 15 mm Hg were recommended as conservative thresholds that are required for safe air travel among pneumocephalus patients.…”

“…The model in both simulation studies [ 2 , 5 ] assumes that the pressure inside the intracranial air equilibrates with the surrounding cabin pressure [ 14 ]. In other words, the model assumes the intracranial gas to expand until its pressure is equivalent to that of the cabin [ 14 ]. The underlying assumption of the model has been criticised, as the rigidity of the surrounding brain is not factored in [ 14 ].…”

“…In other words, the model assumes the intracranial gas to expand until its pressure is equivalent to that of the cabin [ 14 ]. The underlying assumption of the model has been criticised, as the rigidity of the surrounding brain is not factored in [ 14 ]. In contrast, we argue that an intact physical barrier, consisting inter alia of dura and cranium, creates, under normal circumstances, a positive pressure environment relative to the atmosphere (i.e.…”

“…In the only laboratory experiment conducted so far to investigate pneumocephalus during flight, four grooves were cut into the lid of the acrylic box (skull model) in order to allow the intracranial air to react with the changes in air pressure inside the pressure chamber [ 14 ].…”

Pneumocephalus Secondary to Cerebral Air Embolism After Acute Bleeding in an Emphysema Bulla

“…Also, air may enter the pulmonary venous system when a direct connection with the atmosphere is created through a bronchial venous fistula or the pulmonary artery, then pass to the pulmonary capillary bed and then to the pulmonary venous system [ 4 , 5 ]. Cerebral air embolism causes edema secondary to capillary leak syndrome and local ischemia due to embolism, with multifocal lesions resulting in various neurological deficits [ 6 ].…”