Original Article

Automatic Control of Gas Exchange During Cardiopulmonary Bypass

¹ MC3 Inc., Ann Arbor, Michigan
² The University of Michigan, Ann Arbor, Michigan

^* Address correspondence to: Scott Merz, PhD MC3 Inc. 245 Jackson Industrial Drive, Ste. J Ann Arbor, Ml 48103

Abstract

An automatic control system was devised that regulates gas exchange during cardiopulmonary bypass (CPB). The Automated Extracorporeal Gas Exchange System (AEGES) controls the blood flow rate and/or the flow of gas to the oxygenator in order to meet user-defined setpoints for PO₂ and PCO₂ of blood drained from the patient while maintaining safe pressures in the CPB circuit and/or the patient’s circulation. Venous blood gases were used as the basis for control because they reflect the amount of oxygen/CO₂ consumed/produced by the patient given the present rate of delivery via CPB. In the event of an alarm or upon the perfusionist’ s command, AEGES reverts to manual control of blood flow and/or sweep flow.

AEGES was tested in a hypothermia model of CPB in sheep, where it successfully regulated PO₂ and PCO₂ within 5% of setpoint during cooling from 38 to 25°C. In order to control the blood gases to setpoints of PO₂=45 mmHg and PCO₂=40 mmHg in the venous drainage, AEGES reduced blood flow from 2.4 to 1.6 L/min and sweep flow from 2.2 to 0.7 L/min.

AEGES is intended to act as a tool for the perfusionist to assist in maintaining consistent blood gas conditions. AEGES can be integrated with other control systems (e.g., reservoir level control and blood temperature control), further automating the CPB procedure; however, in no way could this system replace the perfusionist.