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Difficult separation from cardiopulmonary bypass and PCO₂

From the Department of Anesthesiology, Research Center, Montreal Heart Institute, 5000 Belanger Street East, Montreal, Quebec, H1T 1C8, Canada.

Address correspondence to: Dr. A. Denault, Phone: 514-376-3330; Fax: 514-376-1355; E-mail: denault{at}videotron.ca

Purpose: Veno-arterial and regional differences of the partial pressure in CO₂ (PCO₂), may be used as index to evaluate the adequacy of the cardiac output to the oxygen consumption. To determine the incidence of elevated PCO₂ and its relationship with difficult separation from bypass (DSB) in patients undergoing cardiac surgery, we conducted a prospective observational cohort study.

Methods: Data were collected from 58 consecutive patients undergoing various cardiac operations requiring cardiopulmonary bypass (CPB). During the procedure, arterial and venous blood gases and lactate were sampled. Blood was drawn after induction of anesthesia, during bypass and at the closure of the chest wall. Difficult separation from bypass was defined as a systolic arterial pressure < 80 mmHg, and diastolic pulmonary artery pressure > 15 mmHg during progressive separation from CPB with inotropic or mechanical support of cardiac function, or hemodynamic instability resulting in reintroduction of extra-corporeal circulation or insertion of an intra-aortic balloon pump.

Results: In our study, 65% of the samples were associated with elevated PCO₂ (>6mmHg). Variables associated with difficult weaning were LVEF, duration of bypass and aortic cross-clamping, pre-bypass PCO₂ and in-bypass lactate values (P < 0.05). Multivariable analysis identified the pre-bypass PCO₂ and the duration of bypass as predictors of DSB.

Conclusion: Elevated PCO₂ is frequently observed during cardiac surgery and values obtained before bypass were associated with DSB. The PCO₂ gradients could be used as marker of the adequacy of tissue perfusion during cardiac surgery.

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