WHAT IS HYPERBARIC AND DIVING MEDICINE?
Hyperbaric medicine is the treatment of health disorders using whole-body exposure to pressures greater than 101.3 kPa (1 atmosphere or 760 mmHg). In practice, this almost always means the administration of hyperbaric oxygen therapy (HBO2T). The Undersea and Hyperbaric Medical Society (UHMS) defines HBO2T as: “a treatment in which a patient breathes 100% oxygen … while inside a treatment chamber at a pressure higher than sea level pressure (i.e., >1 atmosphere absolute or ATA).” The treatment chamber is an airtight vessel variously called a hyperbaric chamber, recompression chamber, or decompression chamber, depending on the clinical and historical context. Such chambers may be capable of compressing a single patient (a monoplace chamber) or multiple patients and attendants as required (a multiplace chamber) (Figs. 477e-1 and 477e-2). Historically, these compression chambers were first used for the treatment of divers and compressed air workers suffering decompression sickness (DCS; “the bends”). Although the prevention and treatment of disorders arising after decompression in diving, aviation, and space flight has developed into a specialized field of its own, it remains closely linked to the broader practice of hyperbaric medicine.
A monoplace chamber. (Prince of Wales Hospital, Sydney.)
A chamber designed to treat multiple patients. (Karolinska University Hospital.)
Despite an increased understanding of mechanisms and an improving evidence basis, hyperbaric medicine has struggled to achieve widespread recognition as a “legitimate” therapeutic measure. There are several contributing factors, but high among them are a poor grounding in general oxygen physiology and oxygen therapy at medical schools and a continuing tradition of charlatans advocating hyperbaric therapy (often using air) as a panacea. Funding for both basic and clinical research has been difficult in an environment where the pharmacologic agent under study is abundant, cheap, and unpatentable. Recently, however, there are signs of an improved appreciation of the potential importance of HBO2T with significant National Institutes of Health (NIH) funding for mechanisms research and from the U.S. military for clinical investigation.
MECHANISMS OF HYPERBARIC OXYGEN
Increased hydrostatic pressure will reduce the volume of any bubbles present within the body (see “Diving Medicine”), and this is partly responsible for the success of prompt recompression in DCS and arterial gas embolism. Supplemental oxygen breathing has a dose-dependent effect on oxygen transport, ranging from improvement in hemoglobin oxygen saturation when a few liters per minute are delivered by simple mask at 101.3 kPa (1 ATA) to raising the dissolved plasma oxygen sufficiently to sustain life without the need for hemoglobin at all when 100% oxygen is breathed at 303.9 kPa (3 ATA). Most HBO2T regimens involve oxygen ...