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Active warming , not passive heat retention , maintains normothermia during combined epidural-general anesthesia for hip and knee arthroplasty . STUDY OBJECTIVE to compare passive heat retention by low-flow anesthesia , alone and with additional thermal insulation by reflective blankets , with forced-air warming preventing intraoperative hypothermia during combined epidural-general anesthesia . DESIGN Randomized , controlled study . SETTING Inpatient anesthesia at a university department of orthopedic surgery . PATIENTS 30 ASA physical status I and II patients , who were scheduled for elective hip or knee arthroplasty and were free from systemic disease . INTERVENTIONS Patients received epidural block up to T10 by alkalinized lidocaine 2 % , and then were administered standard general anesthesia by means of low-flow rebreathing system ( fresh gas flow = 1 L/min ) . All procedures started between 8 and 10 AM , and operating room ( OR ) temperature was maintained between 21 degrees and 23 degrees C , with relative humidity ranging between 40 % and 45 % . For heat retention or warming therapy , patients received either low-flow anesthesia only ( control , n = 10 ) , low-flow anesthesia with additional reflective blankets ( blanket , n = 10 ) , or low-flow anesthesia with active forced-air warming ( forced-air , n = 10 ) . Tympanic temperature was measured at OR arrival ( baseline ) ; immediately following general anesthesia induction ; 30 , 60 , 90 , and 120 minutes from general anesthesia induction ; and at the end of surgery . MEASUREMENTS AND MAIN RESULTS Duration of anesthesia , invasiveness of surgery , and baseline core temperature were similar in the three groups . Core temperature decreased in all the three groups 30 minutes after general anesthesia induction compared with baseline ( p < 0.01 ) ; afterwards , it progressively decreased in the control and blankets groups ( p = 0.004 ) , with a reduction from baseline values measured at the end of surgery of 2.0 degrees C and 1.6 degrees C , respectively . In the forced-air group , after the initial significant decrease ( p = 0.01 vs. baseline ) , core temperature progressively increased to 35.8 +/- 0.6 degrees C , which was similar to preoperative values and significantly higher than either the control or blankets groups ( p = 0.004 ) . CONCLUSIONS During combined epidural-general anesthesia for elective hip and knee arthroplasty , passive heat retention by means of low-flow anesthesia alone and in combination with reflective blankets is ineffective in maintaining intraoperative normothermia and definitely inferior to active forced-air warning .
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Intervention_Physical
Active warming
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Intervention_Pharmacological
alkalinized lidocaine 2 %
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Intervention_Physical
low-flow rebreathing system
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Intervention_Physical
low-flow anesthesia only
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Intervention_Physical
low-flow anesthesia with additional reflective blankets
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Intervention_Physical
low-flow anesthesia with active forced-air warming
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Intervention_Physical
low-flow anesthesia alone and in combination with reflective blankets
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Outcome_Physical
normothermia
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Outcome_Physical
Tympanic temperature
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Outcome_Physical
Duration of anesthesia , invasiveness of surgery , and baseline core temperature
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Outcome_Physical
Core temperature
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Outcome_Physical
reduction from baseline values
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Outcome_Physical
core temperature
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Outcome_Physical
maintaining intraoperative normothermia
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Participant_Condition
arthroplasty
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Participant_Sample-size
30
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Participant_Sample-size
I
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Participant_Sample-size
II
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Participant_Condition
systemic disease .