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: email@example.com
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
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