Hyperbaric Oxygen in acute stroke – a critical hyperbaric view

Human studies of hyperbaric oxygen (HBO) in thromboembolic acute stroke have yielded conflicting results. A reason might be the difference in in-clusion criteria. One positive study used HBO within 24 hours, a subsequent negative one within same time period, a preceding within 14 days of symptom onset. Additionally, interventions were different (HBO alone, combined with vitamin E, and combined with low-dose heparin). Besides, surplus pressure, its application time, and intervals of repeated HBO treatment units varied substantially indicating different dosage and dosage intensity.

Available human studies used HBO regimens with surplus pressures ranging from 0.5 to 1.5bar. Treatment time varied between 40 to 60min, intervals between single treatments varied from 8 to 24 hrs. The comparison of such different HBO regimens is questionable. Animal studies and human reports in cerebral decompression sickness (DCS) and cerebral arterial gas embolism (CAGE) use higher surplus pressures (>1.5bar) and longer treatment time (>60min).

None of the studies informs about usage of HBO in addition to thrombolytic therapy. In some trials thrombolytic therapy constituted an exclusion criterion. One might reasonably argue how to efficiently deliver increased oxygen amount without prior establishment of some level of perfusion. Es-tablishment of perfusion might be mandatory for any if positive effect of HBO in acute stroke. HBO affects perfusion enhancement or establishment by increased surplus pressure and concentration difference between oxygen content of blood and vasoocclusive gaseous bubble itself in CAGE or DCS. In thromboembolic stroke this effect is highly unlikely due to occluding material.

Pressure increase during HBO requires repeated pressure equalization of middle ear by any means. Using Vasalva technique implies risk of cerebral hemorrhage due to rapid increase of cerebral pressure. This is even a more prominent danger when using thrombolytics concomitantly. Available human studies have not addressed this issue as they have not addressed effect of reduced cerebral blood flow. Additionally, cerebral perfusion pressure might be lowered due to fall of arterial blood pressure when using rapid compression.

Using experience from other HBO indications with cerebral affection as CAGE or DCS or carbon monoxide poisoning, more intensive HBO regimens show feasibility and safety. Ultimately, they require proof of efficacy in randomized controlled trials.