Postoperative oxygenation following coronary artery bypass grafting. A multivariate analysis of perioperative factors

Pulmonary oxygenation is generally temporarily impaired following cardiac surgery. We studied the factors influencing postoperative oxygenation using multivariate analysis.

This study was retrospectively performed in University hospital. Fifty patients undergoing solitary coronary artery bypass grafting were included in this study. Patients were divided into two groups by mean age; older group (n=25) and younger group (n=25). Alveolar-arterial oxygen difference (A-aDO2) and respiratory index (RI) were measured at 3 hours after surgery and on postoperative day 1. Statistical analysis was performed using forward selection stepwise regression of 12 perioperative variables.

In all patients, A-aDO2 and RI significantly (p<0.01) increased after surgery and remained high on POD1. In stepwise regression analysis, preoperative A-aDO2 and RI were significant factors in the equations for postoperative A-aDO2 and RI in general, which was the most important factor in the older group. In the older group, preoperative A-aDO2 or RI and water balance were significant (p<0.05) factors which were responsible for half the oxygenation impairment just after surgery, and PCWP showed a significant (p<0.01) negative correlation with both A-aDO2 and RI on POD1. In the younger group, PCWP was a significant (p<0.01) factor for A-aDO2 and CVP and CI were significant for RI on POD1.

Postoperative oxygenation was mainly influenced by the preoperative respiratory condition, especially in old patients, indicating that preoperative management by a physiotherapist may be necessary. Pleurotomy also had a negative influence. Careful intraoperative and postoperative volume control is important in old patients.