MULTIVARIATE DETERMINANTS OF EARLY POSTOPERATIVE OXYGEN-CONSUMPTION IN ELDERLY PATIENTS

Background: Previous investigators have proposed that postoperative sh ivering may be poorly tolerated by patients with cardiopulmonary disea se because of the associated significant increase in total-body oxygen consumption, However, the often-quoted 300-400% Increase in oxygen co nsumption with shivering was derived from relatively few studies perfo rmed in a small number of younger persons specifically selected on the basis of clinically recognizable shivering. We hypothesized that the average elderly postoperative patient has a shivering response that is associated with a relatively small increase in total-body oxygen cons umption. Methods: One hundred eleven elderly patients (age >60 yr) und ergoing surgery were studied to assess the determinants of shivering a nd total-body oxygen consumption in the early postoperative period, An esthetic technique, postoperative analgesia, and thermal management we re controlled by protocol. The clinical variables associated with shiv ering and increased total-body oxygen consumption were determined by u nivariate and multivariate analyses. Results:mean total-body oxygen co nsumption in shivering patients was 38% greater than in nonshivering p atients. Regardless of whether data from shivering patients were inclu ded in the analysis, oxygen consumption was directly proportional to m ean body temperature, Despite similar core temperatures, men had a gre ater incidence of clinically recognizable shivering and greater total- body oxygen consumption than did women, Conclusions: The metabolic dem ands associated with post; operative shivering in elderly patients are less than those reported previously in younger persons, These finding s suggest that if hypothermia predisposes to cardiovascular complicati ons in the postoperative period, these complications are not likely to be mediated by shivering and increased metabolism.