Effects on Lung Function in Patients Undergoing Coronary Artery Surgery on versus off Cardiopulmonary Bypass: A Randomized Trial

Abstract

Background

Coronary revascularization is associated with respiratory dysfunction and poor gas exchange postoperatively. Cardiopulmonary bypass (CPB) has been implicated as a possible explanation for this phenomenon. This study investigated respiratory function in patients undergoing coronary artery bypass grafting (CABG) on-CPB versus off-CPB to determine whether the off-CPB condition results in improved postoperative pulmonary function.

Methods

Forty patients were randomized into 1 of 2 groups: CABG on-CPB (group A) or off-CPB (group B). Pulmonary function tests, including spirometry and diffusion studies, were performed preoperatively and on postoperative day 5. Arterial blood gases on 100% oxygen were taken preoperatively (TP1), 15 minutes after sternal closure (TP2), and 3 hours postoperatively (TP3).

Results

The arterial partial pressure of oxygen (PaO₂) on FiO₂ 1.0 decreased from 59.5 ± 11.5 kPa and 55.7 ± 12.2 kPaat TP1 to 39.5 ± 16 kPa and 39.7 ± 13 kPa at TP2 in groups A and B, respectively (P < 0.001), with no significant difference between groups. At TP3, the PaO₂ partially recovered toward preoperative levels (P < 0.05). Spirometry revealed a significant reduction in FEV1 and FVC on the fifth postoperative day (P < 0.001), with no significant difference between groups. The corrected transfer factor for carbon monoxide reduced significantly in group A from 7.9 ± 2.5 mmolmin^–1 · kPa^–1 preoperatively to 5.1 ± 1.6 mmolmin^–1 · kPa^–1 postoperatively (P < 0.05). This reduction was not seen in group B.

Conclusions

Coronary artery surgery is associated with a marked reduction in lung function as measured by pulmonary function tests and PaO₂. Diffusion studies revealed that on-CPB patients had significantly reduced diffusion capacities postoperatively compared with patients in the off-CPB group.