Vascular access, cerebral air embolism and hyperbaric oxygen therapy

Although very comprehensive, the AAGBI safe vascular access guideline fails to mention the important role of hyperbaric oxygen therapy (HBOT) in the management of air embolism complicating vascular access 1. Depending on the speed and quantity of air/gas entrainment, cardiac arrest may be irreversible. Some patients are resuscitated successfully; others have insidious onset, presenting with air in the coronary or cerebral circulation. The latter present with varied neurological signs, but a ‘peri-procedural stroke’ should trigger suspicion of cerebral air embolism, a life-threatening emergency. Although there are case reports of these being aspirated percutaneously, the most effective treatment is urgent HBOT 2-4. The outcome is dependent on HBOT within 6–8 h, akin to early thrombolysis in thromboembolic stroke. Hyperbaric oxygen therapy beyond this ideal window should still be considered and discussed with experts in the field. Good outcomes from delayed HBOT may be more likely related to retrograde cerebral venous air embolism rather than cerebral arterial air embolism. Peripheral venous lines have been described many times as a source of cerebral gas embolism, and the absence of a central line should not exclude the diagnosis. The pathophysiology of gas bubbles in the cerebral vascular system and the mechanism of HBOT has been clearly described 5. The diagnosis may be difficult, and a high index of suspicion is required in case of a peri-procedural neurological event, including any form of vascular procedure. Sometimes the diagnosis is inevitably associated with delays, but once the diagnosis is made, every minute counts. For that reason, clear guidance is essential. The quoted incidence of 0.8% of all air embolism events translates into several dozen cases per year of significant cerebral gas embolism, which currently may be missed in the UK 1. The incidence may be higher 2-4. Vascular-related air embolism has recently been removed from the ‘Never Event’ list in the UK and it will be interesting to see if the rate of reporting will change. The British Hyperbaric Association has guidance on their website about how to access emergency HBOT in a suitable Category 1 unit (able to deal with critically ill patients) 6.