Effect of lateral position on arterial and venous blood gases in postoperative cardiac surgery patients

Abstract

Investigators have suggested that lateral position may have clinically significant effects on oxygenation in cardiac surgery patients. Presence of lung disease and type of cardiac surgery may be important considerations. To determine the effect of position (left, right, supine) on blood gases in patients who have had coronary artery bypass or cardiac valvular surgery and to compare the effect of position on blood gases in cardiac surgery patients having preoperatively diagnosed lung disease with those having no lung disease. A repeated measures design was used to study 120 mechanically ventilated, postoperative cardiac surgery patients. Subjects were randomly assigned a sequence of three positions (supine, and 45; right and left lateral) after cardiac surgery. Heart rate, respiratory rate, and arterial blood gas values were collected in each position. Venous blood gas values were collected from a subset of 40 subjects. A statistically significant effect of position on PaO2 was found in the group as a whole. The mean PaO2 in the left lateral position was lower than the value in the right or supine positions. No significant effects for position and pH, PaCO2, or bicarbonate were detected. No significant effects were found for type of surgery or the presence of absence of preoperative lung disease. A significant effect of position on venous pH was detected. No significant position effects were found for PvO2, PvCO2, bicarbonate, or venous saturation. No significant position effects were found for the calculated arterial-venous oxygen difference. The results of this study support those of previous research, which reported lower PaO2 in postoperative coronary artery bypass graft patients in the left lateral position. Mean differences in PaO2 were small, suggesting that the known benefits of lateral positioning in the early postoperative period outweigh the potential risks.