HBO Nuggets of the Week
A forum to discuss interesting aspects of hyperbaric medicine.

Wednesday, December 4, 2013

HBO Nugget 9

Hyperbaric oxygen therapy is very well tolerated. The patient lies comfortably while breathing 100% oxygen typically at 2.0 ATA (atmospheres absolute). The most common complication that we discussed previously is barotrauma, particularly to the tympanic membranes. However, another area of risk, although extremely low, is CNS oxygen toxicity.

Oxygen is a toxic gas if breathed at high concentrations for prolonged periods of times. Paul Bert, a 19th century French zoologist and physiologist is credited with the description. The risk for CNS oxygen toxicity rises if breathing 100% oxygen at pressures greater than 3.0 ATA or the equivalent of 99 feet of seawater. There may be little warning before convulsions occur.  The risk associated with HBOT is approximately 0.01% if patients are screened for risk. Typically for our wound patients, risks would include fever or hyperthyroidism although both are not absolute contraindications for HBOT.

Another option to consider is that if a wound patient is thought to be at high risk for CNS oxygen toxicity they can be provided with periods of normoxia, or, air breaks. In a monoplace chamber, the patient would be provided with a mask connected to a tank of medical air located outside the chamber.  The patient would breathe air for 5 minutes every half hour or a total of 10 minutes. Using the typical parameters for treating wound patients, a 90 minute ‘dive’ at, 2.0 ATA, CNS oxygen toxicity is very rare.