Oxygen forms about 21% of the air we breathe. Oxygen masks are commonly used to give more than this percentage in medical treatments. In some situations, it is necessary to give even more oxygen than can be delivered by ordinary masks - to do this, it is breathed at a pressure greater than one atmosphere. This is HYPERBARIC OXYGEN (HBO). Hyper" means increased and "baric" relates to pressure.

HBO physically dissolves extra oxygen into the plasma and tissues. Breathing pure (100%) oxygen at above ambient pressures while inside a Hyperbaric therapy chamber increases the tissue oxygen pressure in compromised tissues to normal or greater-than-normal values.

HBO induces the formation of new capillaries in ischaemic or poorly perfused wounds due to the extreme oxygen gradient between the well-oxygenated and hypoxic areas. Oxygen also diffuses two to three times as far from capillaries into surrounding tissues when breathed under pressure.

Hyperbaric oxygen causes vasoconstriction in normal tissues while maintaining oxygenation. This narrowing does not occur in injured, ischaemic tissues. HBO is therefore extremely useful in crush injuries and other traumatic ischaemias.

HBO inhibits the growth of a number of anaerobic organisms and enhances white cell killing of aerobic organisms. HBO can double or triple the bacteria-killing ability of white cells. It is particularly useful in patients where resistance factors are compromised.

HBO can be given using a monoplace (one person) chamber or a multiplace (more than one person) chamber. London Hyperbaric and Wound Healing Centre has both kinds of chamber.

LHM 14m Therapy Table

A typical treatment session involves slowly pressurising the therapy chamber on air to 2.4 atmospheres (the equivalent of 14 metres sea water) then holding the pressure constant for 95 minutes. During this time the patients breath 100% oxygen for 2 x 45 minute sessions with a 5 minute break in the middle, either through a mask or wearing a hood tent. An attendant accompanies the patients at all times during treatment. At the end of the therapy session the pressure in the chamber is gradually released over a ten-minute period.