Who is most susceptible to motor vehicle-related carbon monoxide poisoning?
The US Centers for Disease Control and Prevention (CDC) reports that motor vehicles are the second most common source of CO exposure.4 A study of US news media reports covering a 2.5-year period revealed that 8% of such poisonings were the result of a motor vehicle left running in a garage—the overall mortality rate of which is suggested to be significantly higher than that of other sources of CO exposure.5
Approximately 430 deaths per year are caused by unintentional, nonfire-related CO poisoning,6 and the CDC reports the death rate is highest in persons older than age 65 years.1 The death rate from these exposures is more than three times higher in men than women (Figure 2).6 In addition, older patients are disproportionately affected: In US news media-reported cases of CO poisoning that included patient age, 29% occurred in persons older than age 80 years.5 Moreover, in approximately one-third of motor vehicle-related deaths due to CO poisoning, nearly all of patients older than age 80 years were found dead at the scene of exposure. These reports suggest that the elderly are at greater risk for CO exposure due to age-related cognitive changes, physical inability to escape a toxic environment once becoming symptomatic, and a greater susceptibility to poisoning due to comorbid conditions.5
Case Continued
The husband and wife’s initial carboxyhemoglobin concentrations in this case were 35% and 13%, respectively. Both were treated with hyperbaric oxygen (HBO) without complication. During their inpatient stay, the woman noted that their home did not have a CO detector.
What is the role of hyperbaric oxygen therapy as a treatment option for CO poisoning?
Hyperbaric oxygen therapy greatly accelerates the dissociation of hemoglobin from CO, reduces free radical-related cellular damage, and may have a role in preventing adverse neurological sequelae in the setting of CO poisoning. Although controversy exists, HBO therapy is generally indicated in select patients with elevated CO levels and abnormal neurological findings, cardiovascular findings, or persistent metabolic acidosis. While few ED patients with CO exposure receive HBO therapy, over 20% of patients requiring inpatient hospitalization receive treatment.3
What preventive measures can be taken to reduce motor vehicle-related CO poisoning?
The literature supports the enforcement of motor vehicle emissions standards and the proper use of home CO detectors as primary preventive strategies. Computerized data from the CDC, US Census Bureau, and US Environmental Protection Agency from 1968 to 1998 were used to evaluate the influence of national vehicle emissions policies on CO-related mortality. The Clean Air Act of 1970 set environmental limits on CO emissions from automobiles at 15.0 g/mile in 1975; the EPA further reduced this standard to 3.4 g/mile for automobiles manufactured after 1981. After the enforcement of standards set forth by the Clean Air Act and the introduction of the catalytic converter in 1975, CO emissions from automobiles decreased by an estimated 76.3%, and unintentional motor vehicle-related CO deaths declined by 81.3% (Figure 3).7 (Catalytic converters contain elements [eg, platinum] that catalyze the oxidation of CO to carbon dioxide.)