Anesthesia-associated carbon monoxide exposures among surgical patients

OBJECTIVE: To estimate the extent of, and evaluate risk factors for, elevat ed carboxyhemoglobin levels among patients undergoing general anesthesia an d to identify the source of carbon monoxide. DESIGN: Matched case-control study to measure carboxyhemoglobin levels. SETTING: Large academic medical center. PARTICIPANTS: 45 surgical patients who underwent general anesthesia. RESULTS: Case-patients were more likely than controls to undergo surgery on Monday or Tuesday (10/15 vs 7/30; matched odds ratio [mOR], 7.7; 95% confi dence interval [CI95], 1.8-34; P=.01), in one particular room (7/15 vs 4/30 ; mOR, 8.5; CI95,1.5-48; P=.03) or in a room that was idle for greater than or equal to 24 hours (11/15 vs 1/30; mOR, 95.5; CI95, 8.0-1,138; P less th an or equal to .001). In a multivariate model, only rooms, and hence the an esthesia equipment, that were idle for greater than or equal to 24 hours we re independently associated with elevated intraoperative carboxyhemoglobin levels (OR, 22.4; CI95, 1.5-338; P=.025). Moreover, peak carboxyhernoglobin levels were correlated with the length of time that the room was idle (r=0 .7; CI95, 0.3-0.9). Carbon monoxide was detected in the anesthesia machine outflow during one case-procedure. No contamination of anesthesia gas suppl ies or CO2 absorbents was found. CONCLUSIONS: Carbon monoxide may accumulate in anesthesia circuits left idl e for greater than or equal to 24 hours as a result of a chemical interacti on between CO2-absorbent granules and anesthetic gases. Patients administer ed anesthesia through such circuits may be at increased risk for elevated c arboxyhemoglobin levels during surgery or the early postoperative period.