Volume 6, No. 1 • Spring 1991

Carbon Monoxide Gas May Be Linked to CO2 absorbent

Richard Moon, M.D.

Twenty-eight instances of unexplained elevation of blood carboxyhemoglobin (COHb) have occurred in three institutions. Al Grady Hospital, Atlanta, GA, 16 cases occurred between May 1985 and March 1990. At Duke University Medical Center, Durham, NC, eight cases occurred from January to October 1990. At Northwestern Memorial Hospital, Chicago, IL, there were three cases observed from July to September 1990. In 8 of 28, cases peak COHb has been 2 8% or greater. In three instances, COHb level has been 30%. Although 12 of the 28 patients were smokers, there was no reason to suspect preoperative CO poisoning in any of the patients, and, in fact, a documented rise in COHb occurred in 12 cases. To date, no severe patient complications have occurred, although COHb levels have been observed that could conceivably contribute to patient morbidity or mortality in some patients. Them were no hemodynamic or other changes suggestive of a problem.

At least 27 of the 28 patients with CO poisoning were the first to be anesthetized after a period of at least 2 4 hours of nonuse of the anesthesia machine (usually a weekend). Carbon monoxide gas has been detected within the C02 absorbent canisters. Preliminary evidence suggests that carbon monoxide accumulation may occur as a result of a slow chemical reaction between one or more fluorinated anesthetics and some C02 absorbents.

These documented abnormalities were detected serendipitously because routine co-oximetry is performed on arterial blood samples in the three institutions. It must be emphasized that neither routine arterial blood gas analysis nor pulse oximetry will provide specific evidence of carbon monoxide poisoning.

The causes of this problem have not been fully defined. Possible procedures for attempting to minimize the risk of CO poisoning have included:

1. Flushing resident gas from the C02 absorbent canisters prior to each anesthetic by using a high flow of oxygen for at least sixty seconds.

2. Use of high fresh gas flows (greater than or equal to five liters per minute) during the course of the anesthetic. Low flows especially should be avoided.

3. Insertion of new C02 absorbent canisters after any period of disuse greater than 24 hours.

We suggest that initial treatment of any patient with elevated CO2 include increasing the inspired 02 concentration to 100%, using high fresh gas flow, and other replacing the C02 absorbers with fresh material or switching to a non-rebreathing circuit.

Any cases observed can be reported to Richard Moon, M.D. (Department of Anesthesiology, Box 3094, Duke University Medical Center, Durham, NC 27710), Charles Ingram, M.D. (Department of Anesthesiology, Thomas K. Glenn Memorial Building, 69 Butler Street, SE, Emory University School of Medicine, Atlanta, GA 30303), or Edward Brunner, M.D., Ph.D,(Professor and Chairman, Department of Anesthesia, Northwestern University Medical Center, 303 E. Superior Street, Chicago, IL 60611).