Thoracic epidural anesthesia as an adjunct to general anesthesia for cardiac surgery: Effects on ventilation-perfusion relationships

Objective: To determine the effects of thoracic epidural anesthesia (IEA) o n ventilation-perfusion (V-A/Q) relationships, atelectasis, and oxygenation before and after coronary artery bypass graft surgery (CABG). Design: Prospective, controlled, unblinded,randomized trial. Setting: Cardiothoracic clinic at a major university referral center. Participants:Twenty-eight patients undergoing elective CABG. Interventions: Perioperative and postoperative TEA was added to general ane sthesia (GA) in 14 patients, and 14 patients receiving GA alone served as c ontrols. Measurements and Main Results: V-A/Q relationships were measured by the mul tiple inert gas elimination technique, and, 20 hours postoperatively, atele ctasis was assessed by computerized tomographic scans. Arterial and mixed v enous blood gases and hemodynamic variables were measured by standard techn iques. TEA per se caused no change in shunt, V-A/Q matching, or oxygenation . Induction of GA in the control group and-induction of TEA caused similar reductions in mean arterial pressure. The TEA patients needed less morphine analgesia postoperatively and were extubated earlier. Extubation caused si gnificant improvement in V-A/Q matching. On the first postoperative day, a slight reduction in PaCO2 was Seen in the TEA group, but no differences in shunt, V-A/Q matching, or oxygenation compared with the GA group.. Both gro ups showed extensive bilateral atelectasis. Conclusion: TEA can reduce respirator time and the need for morphine analge sics after CABG without negative effects on V-A/Q matching, oxygenation, or atelectasis formation. Copyright (C) 1999 by W.B. Saunders Company.