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

BACKGROUND: Postoperative oxygen consumption (VO2) is critical during the r ecovery period that follows open heart surgery and depends on patient chara cteristics and surgical factors. OBJECTIVE: To explore the surgical and patient-related factors that may inf luence VO2 during the early postoperative period. DESIGN: Prospective study. SETTING: Postoperative intensive care unit. PATIENTS: Study participants were 50 consecutive patients undergoing electi ve open heart surgery. There were 39 men and 11 women, with a mean age of 5 8+/-10 years. MEASUREMENTS AND MAIN RESULTS: VO2, oxygen extraction and arterial lactate were measured 1, 4, 12 and 24 h postoperatively. VO2 increased significantl y during the first 12 h and stabilized thereafter. Oxygen extraction remain ed stable through the first 24 h. Covariance analysis on repeated measures showed that the extracorporeal circulatory period (P<0.01), age (P<0.01), b ody temperature (P<0.05) and use of noradrenalin (P<0.05) were predictive f actors influencing postoperative VO2. Although arterial lactate increased s ignificantly during the first 12 h period, no correlation with VO2 was foun d. However, covariance analysis showed chat female sex, patient age (older than 65 years) and bypass period were positive correlating factors for the increase in arterial lactate. CONCLUSIONS: Patient VO2 need is decreased early after open heart surgery a nd returns to normal after 12 h. Surgical and patient-specific factors are responsible for these changes. Arterial lactate measurements were nor found to be reliable indexes of VO2 need during this period.