Medical Files

Introduction

Hyperbaric oxygen therapy (HBOT) is a treatment that involves breathing 100% oxygen while under pressures greater than 1.0 atmosphere absolute (ATA), ie the pressure of air breathed at sea level.

The patient enters an airtight chamber (designed either for single or multiple occupants) and breathes pure oxygen via a hood or mask, while the pressure within the chamber is increased to the desired level, commonly between 2.0 and 2.8 ATA. The pressure is then maintained at this setting for a period of time ranging from 90 minutes to almost 6 hours, before being reduced back to atmospheric pressure, at which time the treatment is complete.

The settings are variable, and so there are different 'prescriptions' of HBOT for different conditions. The pressure setting, the length of time exposed to that pressure, and the number of treatments needed will vary depending on the condition being treated.

HBOT increases the amount of oxygen dissolved in the blood (Henry's Law). This is independent of the patients' red blood cells which are usually the limiting factor in the amount of oxygen transported around the body. HBOT also has the effect of reducing the size of any gas bubbles (Boyle's Law).

These physical laws aid us in understanding the three main ways in which HBOT may act therapeutically:

  1. Bubble size reduction
    For example, in decompression illness where bubbles of nitrogen have formed in the bloodstream and block normal blood flow (commonly known as 'the bends'), HBOT can be used to reduce and eliminate these bubbles.
  2. Achievement of hyperoxia
    For example, in carbon monoxide poisoning carbon monoxide (CO) binds tightly to the haemoglobin molecule, thereby preventing oxygen from binding and resulting in reduced delivery of oxygen to the tissues. HBOT can be used to overwhelm the bloodstream with oxygen and in effect "push" CO off the haemoglobin molecule much more quickly than is otherwise possible. Another example for this mechanism of action is in the number of necrotising infections caused by organisms that thrive in an environment where there is little or no oxygen. Using HBOT to achieve high concentrations of oxygen in the blood and tissues may be directly toxic to these organisms.
  3. Restoration of normoxia in a hypoxic target organ
    For example, wounds that have a poor blood supply (commonly seen with diabetes) often become chronic and non healing as a result. HBOT can be used in these situations to restore good oxygen supply which facilitates wound healing and the formation of new blood vessels.
Research is an active component to the developing field of HBOT, and is ongoing to objectively assess its benefits and the conditions that it will treat.


What hyperbaric oxygen therapy is used for

There are two main lists of indications for hyperbaric oxygen therapy, the Australian and New Zealand Hyperbaric Medicine Group (ANZHMG) list and the Undersea and Hyperbaric Medicine Society (UHMS) list. These outline the conditions for which HBOT has sufficient evidence of treatment benefit.

The ANZHMG indications for HBOT as accepted in November 2006 are:

Patients with conditions other than those above should be regarded as experimental and treatment undertaken in that context.


What hyperbaric oxygen therapy will not treat

In the past HBOT has been used in the attempt to treat a variety of ailments, somewhat indiscriminately. Conditions for which HBOT has not been shown useful include:

  • Cerebral palsy
  • Multiple sclerosis
  • Acquired brain injury
  • Cerebrovascular accident (stroke)
  • Sports injuries
  • Old age...


Further information