Carbon monoxide poisoning: how many patients do we miss?

Carbon monoxide (CO) is a colorless, odorless and nonirritating gas. CO poisoning is a preventable cause of morbidity and mortality. After the late diagnosis of some CO-poisoned patients, we undertook a chart review to identify characteristics of patients with CO poisoning to help with management of future patients.

We retrospectively evaluated the charts of 323 adult emergency department patients diagnosed with CO poisoning between January 2002 and December 2003. Demographic, clinical and laboratory findings were extracted. Chi square test was used to evaluate the correlation between carboxyhemoglobin (COHb) levels and syncope; and between syncope and sex.

The mean age of the 323 patients was 29+/-17 years, and most (64%) were females. All of the poisonings were unintentional, and most patients presented during the winter months. The most common sources of CO were coal stoves (29%) and water heaters (24%). Complaints were headache in 55%, nausea in 49%, dizziness in 44%, syncope in 28%, and seizures in 4%. Abnormal physical findings included tachypnea in 79% and tachycardia in 47%. The mean COHb value was 26.3+/-11.5%. Syncope occurred more frequently in patients with high COHb levels (P<0.001) and was more common among females (P=0.003). Seizures occurred significantly more often in patients with a COHb level of > or =20%.

CO exposure in our patients was acute, accidental, and occurred during the winter months. Serious symptoms, such as syncope, occurred more often in patients having increased COHb levels, but normal COHb levels could not be used to rule out CO poisoning.