Objective: Cardiopulmonary bypass (CPB) is associated with gut mucosal hypoxia, which may contribute to gastrointestinal complications. We examined gastric mucosal oxygenation together with whole-body oxygen flux in low-risk patients undergoing coronary artery bypass grafting (CABG) with and without CPB.
Methods: Fifty-four patients undergoing primary CABG by the same surgeon were randomized into either on-pump (ONCAB, n=27) or off-pump (OPCAB, n=27) groups. The ONCAB group underwent mild hypothermic (35 degrees C) pulsatile CPB with arterial line filtration. Each patient underwent perioperative monitoring with continuous tonometry and cardiac output devices. Gastric intramucosal pH (pHi), gastric-arterial carbon dioxide partial pressure difference (CO(2) gap), whole-body oxygen delivery (DO(2)) and consumption (VO(2)) and whole-body oxygen extraction fraction were measured at sequential time-points intraoperatively and up to 6 h postoperatively. Anaesthetic management was standardized.
Results: Both groups had similar demographic makeup and extent of revascularization (ONCAB 2.6+/-0.9 grafts versus OPCAB 2.5+/-0.8 grafts; P=0.55). The ONCAB group had a mean (+/-SD) CPB time of 62+/-25 min and aortic cross-clamp time of 32+/-11 min. In both groups there was a similar and progressive drop in pHi intraoperatively. Postoperatively, there was a gradual separation between the groups with ONCAB patients showing no further decline in pHi, while further deterioration was observed in the OPCAB group up to 6 h postoperatively. There was a significant difference between the groups over time (P=0.03). There was a corresponding progressive rise in CO(2) gap perioperatively in both groups, with ONCAB patients demonstrating superior preservation of gastric mucosal oxygenation in the early postoperative period. Global oxygen utilization measurements showed superior DO(2) and VO(2) in the OPCAB group throughout the study.
Conclusions: Despite superior global oxygen flux associated with beating-heart revascularization, gastric mucosal hypoxia occurred to similar extents in both groups with worsening trends for the OPCAB patients postoperatively. The splanchnic pathophysiology during beating-heart revascularization should be further explored.