Factors predictive of oxygen consumption during the immediate postoperative period in open heart surgery

Postoperative oxygen consumption (VO2) is critical during the recovery period that follows open heart surgery and depends on patient characteristics and surgical factors.

To explore the surgical and patient-related factors that may influence VO2 during the early postoperative period.

Prospective study.

Postoperative intensive care unit.

Study participants were 50 consecutive patients undergoing elective open heart surgery. There were 39 men and 11 women, with a mean age of 58+/-10 years.

VO2, oxygen extraction and arterial lactate were measured 1, 4, 12 and 24 h postoperatively. VO2 increased significantly during the first 12 h and stabilized thereafter. Oxygen extraction remained stable through the first 24 h. Covariance analysis on repeated measures showed that the extracorporeal circulatory period (P<0.01), age (P<0.01), body temperature (P<0.05) and use of noradrenalin (P<0.05) were predictive factors influencing postoperative VO2. Although arterial lactate increased significantly during the first 12 h period, no correlation with VO2 was found. However, covariance analysis showed that female sex, patient age (older than 65 years) and bypass period were positive correlating factors for the increase in arterial lactate.

Patient VO2 need is decreased early after open heart surgery and returns to normal after 12 h. Surgical and patient-specific factors are responsible for these changes. Arterial lactate measurements were not found to be reliable indexes of VO2 need during this period.