Arterial blood gas management in retrograde cerebral perfusion: the importance of carbon dioxide

Objectives: Many interventional physiological assessments for retrograde ce rebral perfusion (RCP) have been explored. However, the appropriate arteria l gas management of carbon dioxide (CO2) remains controversial. The aim of this study is to determine whether al ha-stat or pH-stat could be used for effective brain protection under RCP in terms of cortical cerebral blood fl ow (CBF), cerebral metabolic rate for oxygen (CMRO2), and distribution of r egional cerebral blood flow. Methods: Fifteen anesthetized dogs (25.1 +/- 1 .1 kg) on cardiopulmonary bypass (CPB) were cooled to 18 degreesC under alp ha-stat management and had RCP for 90 min under: (1), alpha-stat; (2), pH-s tat; or (3), deep hypothermic (18 degreesC) antegrade CPB (antegrade). RCP flow was regulated for a sagittal sinus pressure of around 25 mmHg. CBF was monitored by a laser tissue flowmeter. Serial analyses of blood gas were m ade. The regional cerebral blood flow was measured with colored microsphere s before discontinuation of RCP. CBF and CMRO2 were evaluated as the percen tage of the baseline level (%CBF, %CMRO2). Results: The oxygen content of a rterial inflow and oxygen extraction was not significantly different betwee n the RCP groups. The %CBF and %CMRO2 were significantly higher for pH-stat RCP than for alpha-stat RCP. The regional cerebral blood flow, measured wi th colored microspheres, tended to be higher for pH-stat RCP than for alpha -stat RCP, at every site in the brain. Irrespective Of CO2 management, regi onal differences were not significant among any site in the brain. Conclusi ons: CO2 management is crucial for brain protection under deep hypothermic RCP. This study revealed that pH-stat was considered to be better than alph a-stat in terms of CBF and oxygen metabolism in the brain. The regional blo od flow distribution was considered to be unchanged irrespective Of CO2 man agement. (C) 2001 Elsevier Science BN. All rights reserved.