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02-16-09 Who suffers delayed Neuropsychiatric Sequelae following Carbon Monoxide Exposure?

Tough Question. In the 1980s it was assumed that CO bound to the hemoglobin molecule and created a functional anemia. Once the CO was gone, everything was fine as long as anoxia hadnt occurred during the time the CO was attached to hgb. However, in Korea, where homes were frequently heated with charcoal briquettes under the slats of the floor, there were over 2000 admissions/year for CO poisoning. A simple telephone survey calling the patients that had been discharged with the diagnosis of CO poisoning demonstrated that up to 30% of these patients had persistent or delayed neuropsychological (NP) findings such as memory impairment, personality change, incontinence, neurological deficits. The presence of NP findings could not be determined by any parameters including level of COhgb, signs and symptoms at presentation, or length of exposure to CO. Subsequent case reports validated the occurrence of persistent and/or delayed NP deficits following CO exposure. The young and the old are the most vulnerable.

The memory and concentration deficits, as well as impairment of executive function are diagnosed by formal NP testing done by a neuropsychologist. Bedside tests are not sensitive enough to delineate these cognitive losses.

The problem is, we dont know who will develop delayed NP sequelae. And, we dont know if any treatment will prevent or ameliorate it.

There has been a great deal of controversy regarding the use of hyperbaric oxygen (HBO) vs. normobaric oxygen in CO exposed patients. Studies are conflicting- one study implies HBO improves NP outcome compared to NBO and another study implies that NBO improved NP outcome compared to HBO, theoretically due to the HBO-induced generation of free radicals. What a mess.

Our approach at the TN Poison Center is to put all acute CO exposed patients on face mask (100% O2) for 12 hours. For the asymptomatic or minimally symptomatic patients whose symptoms resolve in 12 hours, no further treatment is recommended. Patients with more severe symptomatology or symptoms that dont resolve, are admitted for 24 hours and 100% O2 normobaric oxygen therapy is continued. HBO is recommended for pregnant women due to the prolonged binding of fetal hgb to CO. A physician is called regarding any significant CO exposures. A Poison Specialist or Medical Toxicologist would be happy to discuss any patients you see with CO exposure.

Question prepared by: Donna L. Seger, M.D. Medical Toxicologist