THE INFLUENCE OF CONVECTIVE WARMING VERSUS RADIANT HEAT ON TOTAL BODY HEAT CONTENT AFTER CORONARY BYPASS SURGERY

Abstract

Introduction. A fall in body core temperature following rewarming from hypothermic cardiopulmonary bypass, termed the afterdrop, can result in postoperative shivering, increased oxygen consumption and hemodynamic instability. Convective warming is highly effective in treating postoperative hypothermia in a general surgical population [1]. However, data on its efficacy in postcardiac surgery patients have been conflicting, perhaps because previous works focused primarily on core temperature changes [2-3]. This study compared the efficacy of convective warming to conventional radiant heat after coronary bypass surgery (CABG) in terms of core temperature (CT), mean skin temperature (MST), and total body heat content (THBC). In addition, data on shivering, oxygen consumption and hemodynamic changes were collected. Methods. With ethical approval and informed consent, 20 patients undergoing elective CABG were divided to 2 groups. Utilizing a standardized technique, patients were cooled to 28[degree sign]C during bypass. Bypass was terminated after core rewarming to a nasopharyngeal temperature of >37.5[degree sign]C. Postoperatively, patients received either an overhead radiant heater (Air-Shields Vickers, USA) or a convective air blanket (Bair Hugger[registered sign], Augustine Medical, USA), both set at maximum. CT was taken as the pulmonary artery blood temperature. MST was averaged from 11 cutaneous sites with insulated skin thermocouples (Mon-a-therm[registered sign], Mallinkrodt, Ireland). Total body heat content (TBHC) was calculated: THBC = [(CT x 0.66) + (MST x 0.34)] x body weight(kg) x 3.48 (specific heat of body tissue). Oxygen consumption was measured from a metabolic cart (Deltatrac, Datex, Finland) and cardiac indices from a pulmonary artery catheter (CCO/SVO2, Baxter, USA). All data were collected half-hourly till core temperature was >37.5[degree sign]C. Data was analyzed with t-test or chi-squared test as appropriate. A P value of <0.05 was considered significant. Results. There was no difference in demography, operative data, hemodynamic parameters, cardiac output studies, oxygen consumption, or vasodilator use between both groups. The afterdrop was 0.8[degree sign]C for both groups. 3 patients in each group shivered. Figure 1Figure 1Discussion. Convective warming does not confer any advantage over conventional radiant heat in terms of shivering, oxygen consumption or hemodynamic parameters. However, it improves skin rewarming and promotes a more rapid but non-significant increase in total body heat content.