July 2005 - The Hong Kong College of Anaesthesiologists

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Bull HK Coll Anaesthesiol Volume 14, Number 2 July, 2005Table 1. Patient characteristics. Data are presented as mean ± SD, or number of patients. ASA = AmericanSociety of Anesthesiologists; OT = operating theatre; HMW = heat and moisture exchanger; CWM =circulating water mattress.Upper Body Lower Body P valueNumber of patients 45 42Age (years) 62.1 ± 14.9 61.0 ± 16.5 0.74Sex (Male/Female) 21/24 20/22 0.93Weight (kg) 53.8 ± 10.7 54.7 ± 9.6 0.67ASA Class I/II/III 14/24/7 15/19/8 0.75Type of surgical procedure 0.68Upper gastrointestinal 11 10Lower gastrointestinal 12 16Hepatobiliary 13 10Gynecological 9 6Elective/Emergency procedure 37/8 33/9 0.67Ambient OT temperature ( o C)Start of surgery 20.3 ± 0.9 20.2 ± 0.7 0.67End of surgery 20.6 ± 0.9 20.7 ± 0.8 0.53Preoperative patient temperature ( o C) 37.5 ± 0.6 37.3 ± 0.6 0.21Intraoperative blood loss (ml) 477.1 ± 531.7 475.2 ± 556.1 0.99Time Interval (min)Induction ‐ Warmer application 14.0 ± 6.9 13.2 ± 7.2 0.59Induction ‐ Skin incision 19.5 ± 6.6 19.0 ± 6.6 0.69Induction ‐ Wound closed 185.9 ± 78.4 209.0 ± 96.8 0.22Additional warming equipment used 0.93Warming coil, HME, CWM 6 7Warming coil, CWM 9 9HME, CWM 6 4CWM 24 22intraoperative blood loss. The time intervalsfrom induction of anesthesia to application ofwarmer, from induction to incision, and frominduction to the end of surgery were similarbetween groups. There was also no difference inthe use of additional warming equipmentbetween groups.Changes of nasopharyngeal temperature inboth groups are shown in Figure 1. Thirty‐fourpatients in the upper body group and 37patients in the lower body group had surgerythat lasted over 2 hours. For the remaining 16patients, their procedure ended up taking lesstime than initially anticipated. However, basedon the intention to treat, data from all patientsthat were initially enlisted in the study wereanalysed, up till the end of their procedure orthe 180‐minute interval, whichever is earlier.The upper body group showed a significantlyhigher mean nasopharyngeal temperaturecompared with the lower body group,beginning from 60 minutes post induction ofanaesthesia, and persisting till 180 minutes postinduction.Changes of rectal temperature duringsurgery are shown in Figure 2. In common withthe nasopharyngeal temperature, rectaltemperature in the upper body group wassignificantly higher compared to the lower bodygroup, from 60 minutes post induction till 180minutes after induction of anesthesia. However,there was a difference in the number of patients73
Bull HK Coll Anaesthesiol Volume 14, Number 2 July, 2005Figure 1. Changes of nasopharyngeal temperatureafter the start of surgery. *P = 0.001; **P < 0.001.Figure 2. Changes of rectal temperature after thestart of surgery. *P = 0.02; **P = 0.001; ***P < 0.001because the rectal thermistor probe wasdislodged in 3 patients in the upper body group.DiscussionWith the increased awareness of possibleadverse effects with inadvertent hypothermia,there has been widespread adoption to the useof forced air warming. Although there havebeen many studies that proved the effectivenessof forced air warming over other methods ofpatient warming, few have compared he relativeeffectiveness of the sites of applications.This study showed that, in patientsundergoing prolonged open abdominal surgery,forced air warming is more effective whenapplied to the upper part of the body than thelower part. After an initial decrease intemperature after anesthesia, it stabilized andreturned to normothermia by 30 to 60 min in theupper body group. In contrast, the temperaturein the lower body group increased onlygradually 60 min after induction. At 1 hourafter induction, the mean nasopharyngealtemperature was 0.39 o C higher in the upperbody group. This difference increased to 0.73 o C3 hours after induction.The body surface area covered by the upperor lower body forced air warming blankets wassimilar in this study. It is postulated that theincreased effectiveness of upper body forced airwarming might be related to the betterperfusion of the upper limbs and trunkcompared with the lower limbs, especially sincepatients undergoing open abdominal surgerytended to be older.Patients undergoing prolonged openabdominal surgery were selected for this studybecause with exposure of the intestines, thelikelihood of developing hypothermia increased.Therefore, there is a better chance to detect adifference in effectiveness between the upperand lower body forced air warming.Although all patients in this study receivedgeneral anesthesia, the actual conduct ofanesthesia was not standardized. This wasdeliberately so, because we intended to test theeffectiveness of forced air warming in twodifferent sites during daily and highly variableclinical practice. It is also consideredinappropriate to standardize the use ofadditional patient warming methods, but theywere recorded and analysed as confoundingvariables. Notwithstanding this, most patients inthis study received general anesthesia withintravenous induction, followed by maintenancewith low flow inhalational anesthesia usingsevoflurane or isoflurane with nitrous oxide andoxygen mixture, supplemented withintravenous opioids and muscle relaxants.74
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Page 12 and 13: Clinical InvestigationsBull HK Coll
Page 36 and 37: Case ReportsBull HK Coll Anaesthesi

July 2005 - The Hong Kong College of Anaesthesiologists

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