Objective: Endogenous carbon monoxide (CO) production results from heme metabolism catalyzed by heme oxygenase (HO) enzymes of which HO-1 is inducible by oxidative stress. Cardiopulmonary bypass provokes oxidative stress associated with systemic and pulmonary inflammatory responses. Therefore, the authors hypothesized that cardiopulmonary bypass is associated with an increase in endogenous carbon monoxide production.
Design: A prospective, observational study.
Setting: A cardiothoracic operating room.
Participants: Forty patients undergoing cardiac surgery with cardiopulmonary bypass.
Interventions: None.
Measurements and main results: End-tidal CO levels and arterial carboxyhemoglobin concentrations were measured before and after cardiopulmonary bypass. End-tidal CO concentrations and carboxyhemoglobin levels were increased significantly after cardiopulmonary bypass as compared with prebypass values (median [interquartile range]: end-tidal CO levels: 33 [20-42] ppm v 22 [16-32] ppm, p < 0.01; carboxyhemoglobin 1.3% [1.0%-1.3%] v 0.9% [0.6%-1.0%], p < 0.01). To exclude that the observed increases were caused by CO accumulation during CPB, the authors also assessed carboxyhemoglobin concentrations in the arterial and venous limb of the oxygenator, indicating that CO is eliminated across the membrane oxygenator during CPB.
Conclusions: Cardiac surgery with cardiopulmonary bypass is associated with an increase in endogenous CO production.