Paul G. Harch and Richard A. Neubauer

INTRODUCTION

For a discussion of the effectiveness of hyperbaric oxygen (HBO) therapy in global cerebral ischemia/anoxia and coma, we define HBO as a medical treatment that uses high pressure oxygen as a drug by fully enclosing a person or animal in a pressure vessel and then adjusting the dose of the drug to treat pathophysiologic processes of the diseases. Like all drugs, the dose of HBO is crucial and should be customized to each patient's response. It is dictated by the pathological target and is determined by the pressure of oxygen, duration of exposure; frequency, total number of treatments, and timing of the dose in the course of the disease. As diseases and their pathologies evolve, different doses of HBO are required at different times. In addition, patients have individual susceptibility to drags, manifest side-effects and toxicity. Unfortunately, the ideal dose of HBO in acute or chronic global ischemia/anoxia and coma is unknown. The studies reviewed below suggest higher pressures (2 ATA or higher) and lesser numbers of treatments very early in the disease process whereas lower pressures (2 ATA or lower) and a greater number of treatments have been used as the brain injury matures. While this general trend seems justified, the absolute or effective pressures delivered to the patients in these reports may be slightly less than what is stated since many studies do not specify the HBO delivery system that was employed. For example, an oxygen pressurized chamber has an effective HBO pressure equal to the plateau pressure administered during the treatment, whereas an air pressurized chamber in which oxygen is administered by aviators mask can achieve a far lower effective HBO pressure, depending on the fit of the mask and the amount of its air/oxygen leak. In the later cases, the dose of oxygen is less. This concept is particularly important when analyzing the studies in this chapter performed prior to the late 1980s when the aviator mask dominated delivery systems in multiplace chambers.

In reviewing the data in this chapter, it is surprising that HBO has not enjoyed widespread use for neurological diseases in the United States. This has been parfly due to institutional reservations and overt therapeutic nihilism for neurological injuries, both of