Acid-base status of the blood contained in the cardiotomy reservoir during deep hypothermic circulatory arrest at 18 °C

Background: During deep hypothermic circulatory arrest (DHCA) for pulmonary artery endarterectomy (PAE), the blood volume stored in the cardiotomy reservoir circulates through the oxygenator via the arterial shunt line, where it remains oxygenated and decarboxylated. The aim of the study was to investigate the change in the acid-base balance of the blood contained in the cardiotomy reservoir during DHCA. Methods: A four-month retrospective analysis was conducted on patients undergoing PAE. The sweep gas inflow and the inspired fraction of O2 were kept constant throughout the duration of DHCA. Arterial blood gases were sampled at the beginning and at the end of the DHCA and were analyzed according to the alpha-stat and pH-stat strategies. Results: Twenty-four patients were included with a mean age of 59.2 (±15.7) years. The mean duration of DHCA was 15.2 (±4.1) min and the mean sweep gas inflow was 1.4 (±0.8) L/min. Initial pH and PaCO2 were 7.31 (±0.09) and 43.2 (±9.9) mmHg, respectively, and final pH and PaCO2 were 7.51 (± 0.14), p < 0.001 and 23.4 (±11.9) mmHg, p < 0.001. There was a significant correlation between the sweep gas inflow and the post-DHCA pH (r = 0.797). Conclusion: The pH increases significantly during the DHCA according to the sweep gas inflow. Decreasing the sweep gas inflow between 0.5 and 1.0 L/min allows for limiting the pH variation during the DHCA period.