EFFECT OF FORCED-AIR WARMING DURING ABDOM INAL-SURGERY ON THE EARLY POSTOPERATIVE HEAT-BALANCE OF VENTILATED PATIENTS

Hypothermia (core temperature <36 degrees C) is common after longer-la sting surgical procedures. Heat loss mainly occurs during anaesthesia and surgery and leads to increased risk, especially in the early recov ery period of elderly patients. In the present study we investigated t he effects of intraoperative forced-air warming, administered via an u pper-body blanked (''Warm Touch'', Mallinckrodt, USA), with the specif ic aims of: (1) drawing up heat balances; and (2) analysing postoperat ive thermoregulation, oxygen consumption (VO2) and cardiovascular reac tions of mechanically ventilated patients. The general aim of our stud y was to compare intraoperative forced-air-warming and conventional pa tient-insulation with cotton blankets. Methods. Twenty four ASA II and III patients sheduled for elective colon surgery were randomly assign ed to a control group (n=12, no warming therapy, upper body covered wi th a cotton hospital blanket) or a convective warming group (n=12). An aesthesia was administered with etomidate (0.2 mg/kg), fentanyl (appro ximately 10 mu g/kg) and vecuronium bromide (0.1 mg/kg). During surger y the lungs were mechanically ventilated with 70% nitrous oxide in oxy gen and enflurane (end-tidal-concentration max. 0.7%) using a semiclos ed circuit with a fresh gas flow of 3 l/min. A hygrophobe heat and moi sture exchanger (''Sterivent,'' Darex Corp., Italy) was used. At the e nd of surgery patients were transferred to the ICU, covered with a hos pital cotton-quilt and normo-ventilated using a Bennett 7200 a. Patien ts were sedated/kept free of pain by administering titrated doses of m idazolam and/or piritramide. Postoperative oxygen consumption (VO,) wa s recorded continuously with a Deltatrac Metabolic Monitor (Datex Corp ., Finland). Pre-, intra- and postoperative measurements included hear trate, invasive blood pressure, core-temperature (before and after ope ration: urinary bladder-temperature, during surgery: oesophageal tempe rature) and mean-skin-temperature (according to Ramanathan) up to 180 min from the end of surgery. Shivering, pharmacological interventions (e.g. pethidine) and time of extubation were noted. Data are presented as median, minima and maxima. The results were analysed using the Man n-Whitney U test or Chi-Square test (shivering). Statistical significa nce was assumed when P < 0.05. Results. Both groups were comparable fo r gender, body weight, height, age, duration of their operations and a mount of intraoperative fluids, narcotics and muscle relaxants. Room t emperatures in the control group were significantly higher than in the forced air group (24 vs 22 degrees C). Initial setting of the forced- air blower was ''high'' (42-46 degrees high air flow). When thp oesoph ageal-temperature reached 36,5 degrees C, the blower temperature was r educed to 36-40 degrees C. Reduction was necessary approximately 60 mi n from start in the operation. At the end of surgery/administration to the ICU core-temperatures of both groups differed significantly (35.2 /35.4 degrees C vs 36.3/36.2 degrees C). Mean-skin temperatures were h igher, too, but no statistical analysis was carried out for the intrao perative period, because warm air influenced skin thermometers located on the upper body. At admission to the ICU patients: in the control g roup had a heat loss of 4.4 kJ/kg; those in the convective warming gro up had a heat-gain of 0.8 kJ/kg. Further measurements of postoperative core temperatures did not differ significantly, but the skin-temperat ures of patients who received forced-air warming in the theatre remain ed higher (P < 0.05) until 120 min from the end of surgery. Shivering was more frequent and lasted longer in the control group (8 patients, 20 min vs 4 patients, 9 min; P < 0.05). Patients in the control group needed more drugs to stop increased cardiovascular reactions (hyperten sion, tachycardia) or shivering. Therefore oxygen consumption (VO2) an d cardiovascular reactions (heart rate, systolic, diastolic and mean a rterial pressure) showed no significant differences between intraopera tively warmed and cold patients. Extubation of warmed patients was pos sible 3.45 h after the end of surgery, cold patients were extubated 8 h from the end of their operations (P < 0.05). Requirements for extuba tion of our patients were consciousness, sufficient spontaneous breath ing patterns with the ventilator (decreased SIMV frequency, moderate P SV level), haemodynamic stability and core temperature >36 degrees C. Conclusions. 1. Farced-air warming maintains normothermia during elect ive abdominal surgery. 2. Preserved normothermia reduces postoperative shivering.