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Virginia Mason Medical Center, Seattle, WA
Correspondence to: Neil B. Hampson, MD, FCCP, Section of Pulmonary and Critical Care Medicine, Virginia Mason Medical Center, 1100 Ninth Avenue, Seattle, WA 98111; e-mail: cidnbh@vmmc.org
To the Editor:
In the case report by Vossberg and Skolnick (February 1999),1 it is stated that catalytic converters in automobiles have changed the clinical presentation of intentional carbon monoxide (CO) poisoning. As evidence, the authors describe a confused patient with a blood carboxyhemoglobin (COHb) level of 4.8% following 8 to 10 h of continuous exposure to exhaust from a running automobile in a closed garage. They point out that his maximum COHb level could not have been > 10% because the sample was obtained 1 h after the patient was removed from the exposure and treated with 100% oxygen. It is suggested that even prolonged exposures of this type can result in only minimal increases in COHb levels.
The case raises several questions. It would be extremely unusual for an automobile to continue running for this length of time in a tightly enclosed space. At our regional referral facility for severe CO poisoning, we have treated > 400 cases of intentional CO poisoning in the past 2 decades, 90% of which were due to automobile exhaust. The engine has typically stopped running when the victim is found, either because the vehicle runs out of fuel or because it stalls when the ambient oxygen is consumed to a sufficient degree. It should be noted that CO emission actually increases as oxygen availability decreases and combustion becomes less efficient. I would raise the possibilities that the patient's exposure was not as long as was reported to the authors and/or that the garage was relatively well ventilated.
Although the authors are correct about the half-time of COHb clearance with oxygen (60 to 80 min), the subsequent level drawn 3.5 h later (three half-times) should have been significantly < 3.0%. If the initial value was erroneous and the latter value correct, back extrapolating four half-lives would yield a predicted initial COHb > 20%, which is more consistent with the history.
Catalytic converters were introduced in the United States in the 1970s. Although the number of accidental CO deaths due to automobile exhaust have declined since that time,2 there are few data that demonstrate a decrease in intentional CO deaths. In fact, a study by the Centers for Disease Control and Prevention found that intentional CO deaths increased in the United States in the decade of the 1980s, thereby largely offsetting the decline in accidental CO deaths.2
References
This article has been cited by other articles:
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  E. Weir Identifying and managing adverse environmental health effects: a new series Can. Med. Assoc. J., April 1, 2002; 166(8): 1041 - 1043. [Full Text] [PDF]
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