Hyperbaric oxygen (HBO) therapy is a medical intervention in which a patient breathes continuous or intermittent 100% oxygen while inside a hyperbaric chamber that is pressurized to an ambient pressure greater than sea level.1 HBO therapy results in the systemic delivery of oxygen that produces supraphysiologic oxygen tension in perfused tissues. The effects of HBO therapy are due to the combined effects of both increased ambient pressure and increased oxygen tension.2
Monoplace chambers accommodate a single occupant. An attendant monitors the patient from the outside and communicates via intercom. Specially designed cardiopulmonary monitoring devices, IV infusion pumps, and ventilators enable critically ill patients to be treated in monoplace chambers. Multiplace chambers (Figure 21-1) can simultaneously treat multiple patients and will accommodate medical personnel inside the chamber to perform hands-on patient assessment and care. Monoplace chambers generally use 100% oxygen for pressurization, whereas multiplace units are pressurized with air and patients breathe oxygen using a tight-fitting facemask, a hood, or an endotracheal tube while inside.
The outer and inner configurations of a multiplace hyperbaric chamber at the University of Pennsylvania Department of Hyperbaric Medicine, Philadelphia, Pennsylvania.
Ambient pressure is an important concept in HBO therapy. At sea level, the pressure exerted by the air column (the atmosphere) above is quantified as 1 atmosphere absolute of pressure (ATA), 760 mm Hg, 760 torr, or 101 kPa. Once a patient is placed inside a chamber, the ambient pressure is increased by the gradual inflow of compressed gas, either oxygen or air. Most HBO therapy uses pressures between 2.0 and 3.0 ATA (202 to 303 kPa). A typical HBO treatment lasts 90 to 120 minutes. HBO therapies are performed using preset protocols that define pressurization level, treatment duration, use of air breaks, and the number of HBO sessions in a course of therapy.
The oxygen content of the blood is the sum of the oxygen carried by hemoglobin and oxygen dissolved in the plasma. Hemoglobin becomes fully saturated around a PO2 of 100 mm Hg (13.3 kPa); fully saturated hemoglobin carries approximately 20 mL of oxygen per 100 mL of blood, which is expressed as 20 vol%. At 1 ATA breathing room air, dissolved oxygen in the plasma is typically only 0.3 vol%. At a pressure of 3 ATA inside an HBO chamber pressurized with 100% oxygen, the arterial oxygen tension (PaO2) will approach 2200 mm Hg (293 kPa), which will bring the dissolved oxygen content up to about 5.4 vol%.2 This amount of dissolved oxygen can sustain basal metabolic functions in the complete absence of hemoglobin.
HBO therapy should be viewed as a drug and the hyperbaric chamber as a delivery device. HBO affects tissues in two ways: there are ...