This is a topic we discuss every year because CO exposure has potential for devastating sequela.
At one time CO was thought to simply occupy a place on the hemoglobin molecule (carboxyhemoglobin) and create a functional anemia. Unfortunately, CO has additional mechanisms of toxicity. CO shifts the oxyhemoglobin dissociation curve to the left, so that hemoglobin holds onto oxygen much tighter, reducing the amount of oxygen released to the tissues. CO also causes a malfunction of cytochrome oxidase (oxidizing enzyme in mitochondria which transfers electrons from cytochromes to oxygen molecule) which may last for up to three days after a single exposure. The organ systems most impacted by CO exposure are the heart and nervous system.
The symptoms of CO poisoning are nonspecific. Headache, myalgia, and dizziness may be initial symptoms. Cerebral impairment, confusion, coma and death may subsequently occur. One of the consequences of exposure to CO may be delayed (or persistent) neuropsychological sequela which includes memory and concentration impairment, loss of executive function, decrease in IQ, personality changes, neurologic deficits (such as incontinence) and symptoms of Parkinsons syndrome. The problem is neither the carboxyhemoglobin (COhgb) concentration nor the clinical presentation at the time of evaluation predicts who will develop this sequelae.
Studies are conflicting regarding the efficacy of hyperbaric oxygen (HBO) and/or normobaric oxygen in preventing or improving this syndrome. There is the possibility that HBO may increase CNS free radicals-although the clinical implications of this are unknown. There are no conclusive studies. There is agreement that HBO is a reasonable treatment for pregnant women as fetal hemoglobin has a higher affinity for CO than adult hemoglobin. Tennessee Poison Center recommends HBO for pregnant women. For other significant exposures, TPC usually recommends NBO for at least 12 hours, sometimes longer.
Recommendation: In cases of CO exposure, call the Poison Center, document that you called the PC and their recommendations. These recommendations will vary between poison centers. Know what your PC recommends. AND tell all your patients to have a CO detector in their house. Prevention of the exposure is easier than treatment of the sequelae.
This question prepared by: Donna Seger, MD Medical Toxicologist
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Donna Seger, M.D.
Tennessee Poison Center
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