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

The most commonly observed result related to CO poisoning is neurological dysfunction; abnormalities in the cardiac, pulmonary and renal organ systems do occur. About 14% of patients sustain permanent brain damage, and delayed neurological sequelae do occur 3-21 days later in about 12% 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)

Carbon Monoxide signs:

• 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 incomplete combustion of hydrocarbons and is usually from compressors and cigarette smoking. In addition to the effect on the hemoglobin molecule, it has a toxic effect on the cytochrome A3 system. Prevention requires periodic air sampling. The maximal allowable level is 10 ppm (0.001%).