The hypobaric (75-85 kPa) environment of the aircraft cabin, pressurized to resemble altitudes between 1500 and 2500 m, has implications for both patient and equipment. Patients with respiratory failure present particular challenges. Maintaining constant alveolar oxygen tension at reduced barometric pressure requires increased inspired oxygen concentration or may necessitate the use of PEEP. If lung function is marginal, positive pressure ventilation may be necessary at cabin pressure in patients requiring only facemask oxygen at sea level. Gas within the cuff of tracheal tubes expands and may compromise tracheal mucosal perfusion at cabin pressure. Gas can be partially removed during ascent and replaced during descent, or substituted for saline. Ventilation can also be compromised by gaseous expansion within pneumothoraces, intestines, or the abdominal cavity.

Aviation poses particular problems for medical equipment. Ventilators must be able to withstand engine vibration and be compatible with the electromagnetic environment associated with aircraft systems. Pneumatically cycled ventilators are affected by changes in ambient pressure; generally, a reduced ventilatory frequency is offset by increased tidal volume. Microprocessor-controlled ventilators (e.g. LTV-1000, Oxylog 3000) contain transducers that compensate for changes in ambient pressure, although an increase in oxygen concentration will still be required.

The weight of oxygen cylinders is restrictive in long-range transportation and alternatives including liquid oxygen supplies or oxygen concentrators built into aircraft should be considered. Ventilators with minimal gas consumption are preferable in these circumstances. Furthermore, a circle breathing system can be improvised to enhance conservation of oxygen supplies.