Differences between arterial and expired pump carbon dioxide during robotic cardiac surgery

Objective: To investigate whether expired pump carbon dioxide (PepCO(2)) is an effective arterial carbon dioxide (PaCO(2)) monitor during cardiopulmonary bypass (CPB) in patients undergoing robotic cardiac surgery compared with traditional cardiac surgery.

Design: A prospective control study.

Setting: A university, single-institutional setting.

Participants: Sixty patients undergoing cardiac surgery.

Interventions: PepCO(2) was measured using a standard multigas analyzer with the monitoring catheter connected to the exhaust port of the oxygenator. The authors measured PaCO(2) values of the arterial blood provided to the patient and PepCO(2) from the oxygenator exhaust outlet during the cooling, stable hypothermia, and rewarming phases of CPB.

Measurements and main results: There were significant differences between temperature-uncorrected PaCO(2) (PaCO(2)tu) and PepCO(2) measured during the cooling phase; between temperature-corrected PaCO(2) (PaCO(2)tc) and PepCO(2); and between PaCO(2)tu and PepCO(2) measured during the stable hypothermia phase between the 2 groups (p < 0.001 for all). However, there were no significant differences between PaCO(2)tc and PepCO(2) measured during the cooling phase or between PaCO(2)tc and PepCO(2) or PaCO(2)tu and PepCO(2) measured during the rewarming phase between the 2 groups (p = 0.453, p = 0.122, and p = 0.412, respectively).

Conclusion: These results reveal that PepCO(2) is not suitable for continuous monitoring of PaCO(2) during CPB in patients undergoing robotic cardiac surgery.