Hyperbaric Oxygen in Acute Ischemic Stroke
To the Editor:
Dr Rusyniak et al1 have recently presented the results of a clinical trial of hyperbaric oxygen (HBO) in acute ischemic stroke. The authors are aware of previous human studies in stroke patients indicating that 100% oxygen at pressure of 1.5 atm absolute (ATA) is better tolerated than higher pressures by the brain injured by acute ischemia. Safety of HBO is not an issue here, as pressure of 2.5 ATA is used safely for other indications. The authors mention that 400 stroke patients have been treated with HBO in previously reported studies. This number exceeds 2000 and references to these studies are easily available in a standard text on this subject.2 The majority of these patients were treated by HBO pressures under 2 ATA. I do not understand why the authors chose to ignore this experience and decided to follow the results of animal studies, some of which have been conducted at higher pressures but no correlation has been established between pressure and efficacy of HBO treatment in these studies. I am not surprised that the patients who received oxygen at 1.14 ATA did better than those who received it at 2.5 ATA because the former is closer to the ideal pressure of 1.5 ATA.
My other criticism of the study is that it was not restricted to patients in the first 3 hours following stroke or even the first 6 hours. There are logistic problems in applying HBO treatments in a time window that overlaps with thrombolytic therapy. Potential solutions to these problems were discussed in a conference more than 5 years ago and the proceedings were published.3 Since HBO is used as a neuroprotective, it can be combined with thrombolytic therapy, which is directed at the cause. Clinical trials of combination of HBO and thrombolytic therapy are being conducted.
I believe that the study did not serve any useful purpose or contribute to knowledge of stroke or HBO beyond what is already known. With negative results, the authors have closed the door to further trials on this topic. It would have been better if they had had another group of patients treated at 1.5 ATA so that the results could be compared with those treated at 2.5 ATA.
Rusyniak DE, Kirk MA, May JD, Kao LW, Brizendine EJ, Welch JL, Cordell WH, Alonso RJ. Hyperbaric oxygen therapy in acute ischemic stroke: results of the Hyperbaric Oxygen in Acute Ischemic Stroke Trial Pilot Study. Stroke. 2003; 34: 571–574.
Jain KK. Role of hyperbaric oxygenation in the management of stroke. In: Jain KK, ed. Textbook of Hyperbaric Medicine. 3rd ed. Göttingen, Germany: Hogrefe & Huber; 1999:282–317. 4th ed; 2003. In press.
Jain KK, Toole JF, eds. Hyperacute hyperbaric oxygen therapy for stroke: proceedings of a conference. Undersea & Hyperbaric Medical Society of the USA. Bethesda, Maryland; 1998.