Carbon monoxide poisoning is a rare cause of problems when diving, it does occur when there is contaminated air in recreational diving tanks. CO poisoningis the leading cause of poisoning deaths in the U.S.(about 8600 deathsper year) and is easily missed unless health care providers are especiallyvigilant.

The most commonly observed result related to CO poisoningis neurological dysfunction; abnormalities in the cardiac, pulmonary andrenal organ systems do occur. About 14% of patients sustain permanent braindamage, and delayed neurological sequelae do occur 3-21 days later in about12% of people.

CO risk factors include:

• Pre-existing cardiovascular disease
• Age greater than 60 years
• An interval of unconsciousness (longer the higher the risk)
• Little association with COHgb (carboxy hemoglobin)

• Tachycardia (rapid pulse)
• Tachypnea (rapid breathing)
• Retinal venous engorgement (as seen through an ophthalmoscope)
• Ekg conduction defects
• COHgb greater than 20%

Carbon monoxide in diving is the product of incompletecombustion of hydrocarbons and is usually from compressors. In additionto the effect on the hemoglobin molecule, it has a toxic effect on thecytochrome A3 system. Prevention requires periodic air sampling. The maximalallowable level is 20 ppm (0.002%)