Influence of control variables on mannequin temperature in a paediatric operating theatre

BACKGROUND: Core temperature drops in all children having general anaesthesia. Convection heating may be useful, but its effectiveness in the paediatric setting is not established. Additionally, its utility in many paediatric situations is limited by blanket design. METHODS: Using a mannequin model in a sham operation, we assessed the likely safety and effectiveness of a draping technique in association with a 'Bair Hugger' and a heat dissipation unit (HDU). In Part 1 of the study, the influence of ambient temperature was assessed. In Part 2, a simulated laparotomy was set up and a more detailed assessment of air temperatures around the mannequin was made. In addition, the effect of a change in the HDU design was assessed. RESULTS: Part 1: the technique achieved 'near-plateau' temperature within 5-10 min. A difference of 8 degrees C in ambient temperature (between 18 and 26 degrees C) translated only to a 2-3 degrees C difference under the drapes. Part 2: the technique produced sidestream cooler zones at the head and shoulders. Air temperature at these sites was 28-34 degrees C, whereas at other points (irrespective of their distance from the heat source), it was 37-40 degrees C. Warm air reached sufficient skin sites to anticipate adequate heat transfer in the clinical situation. Air temperature at 'skin' surface stayed below 40 degrees C over the 90-min study period. CONCLUSIONS: A customized HDU used in association with a 'Bair Hugger' unit and a careful surgical draping technique provides stable, safe and consistent air temperatures around a mannequin. Net heat gain by a child's body should occur with this arrangement. Further evaluation in a clinical study is underway.     

Effect of forced-air warming on the performance of operating theatre laminar flow ventilation

Forced‐air warming exhaust may disrupt operating theatre airflows via formation of convection currents, which depends upon differences in exhaust and operating room air temperatures. We investigated whether the floor‐to‐ceiling temperatures around a draped manikin in a laminar‐flow theatre differed when using three types of warming devices: a forced‐air warming blanket (Bair Hugger?); an over‐body conductive blanket (Hot Dog?); and an under‐body resistive mattress (Inditherm?). With forced‐air warming, mean (SD) temperatures were significantly elevated over the surgical site vs those measured with the conductive blanket (+2.73 (0.7) °C; p < 0.001) or resistive mattress (+3.63 (0.7) °C; p < 0.001). Air temperature differences were insignificant between devices at floor (p = 0.339), knee (p = 0.799) and head height levels (p = 0.573). We conclude that forced‐air warming generates convection current activity in the vicinity of the surgical site. The clinical concern is that these currents may disrupt ventilation airflows intended to clear airborne contaminants from the surgical site.     

Comparison of forced-air warming systems with lower body blankets using a copper manikin of the human body

Background: Forced‐air warming has gained high acceptance as a measure for the prevention of intraoperative hypothermia. However, data on heat transfer with lower body blankets are not yet available. This study was conducted to determine the heat transfer efficacy of six complete lower body warming systems. Methods: Heat transfer of forced‐air warmers can be described as follows: Q˙=h·ΔT·A ([1]) where Q˙ = heat transfer [W], h = heat exchange coefficient [W m^?2 °C^?1], ΔT = temperature gradient between blanket and surface [°C], A = covered area [m²]. We tested the following forced‐air warmers in a previously validated copper manikin of the human body: ( 1 ) Bair Hugger^® and lower body blanket (Augustine Medical Inc., Eden Prairie, MN); ( 2 ) Thermacare^® and lower body blanket (Gaymar Industries, Orchard Park, NY); ( 3 ) WarmAir^® and lower body blanket (Cincinnati Sub‐Zero Products, Cincinnati, OH); ( 4 ) Warm‐Gard^® and lower body blanket (Luis Gibeck AB, Upplands Väsby, Sweden); ( 5 ) Warm‐Gard^® and reusable lower body blanket (Luis Gibeck AB); and ( 6 ) WarmTouch^® and lower body blanket (Mallinckrodt Medical Inc., St. Luis, MO). Heat flux and surface temperature were measured with 16 calibrated heat flux transducers. Blanket temperature was measured using 16 thermocouples. ΔT was varied between ?10 and +10 °C and h was determined by a linear regression analysis as the slope of ΔT vs. heat flux. Mean ΔT was determined for surface temperatures between 36 and 38 °C, because similar mean skin temperatures have been found in volunteers. The area covered by the blankets was estimated to be 0.54 m². Results: Heat transfer from the blanket to the manikin was different for surface temperatures between 36 °C and 38 °C. At a surface temperature of 36 °C the heat transfer was higher (between 13.4 W to 18.3 W) than at surface temperatures of 38 °C (8–11.5 W). The highest heat transfer was delivered by the Thermacare^® system (8.3–18.3 W), the lowest heat transfer was delivered by the Warm‐Gard^® system with the single use blanket (8–13.4 W). The heat exchange coefficient varied between 12.5 W m^?2°C^?1 and 30.8 W m^?2°C^?1, mean ΔT varied between 1.04 °C and 2.48 °C for surface temperatures of 36 °C and between 0.50 °C and 1.63 °C for surface temperatures of 38 °C. Conclusion: No relevant differences in heat transfer of lower body blankets were found between the different forced‐air warming systems tested. Heat transfer was lower than heat transfer by upper body blankets tested in a previous study. However, forced‐air warming systems with lower body blankets are still more effective than forced‐air warming systems with upper body blankets in the prevention of perioperative hypothermia, because they cover a larger area of the body surface.     

Prevention of hypothermia during orthotopic liver transplantation: comparison of three different intraoperative warming methods

Hypothermia is a frequent and sometimes clinically importantproblem during orthotopic liver transplantation. Numerous methodshave been suggested to reduce intraoperative heat loss and promoteactive warming. In this study we compared an electric undermattress, a warm air under mattress and a forced warm air convectiveheating blanket. The forced air convective warming system wasshown to produce significantly higher patient temperatures thanthe two other systems.     

Comparison of forced-air warming systems with upper body blankets using a copper manikin of the human body

Background: Forced‐air warming with upper body blankets has gained high acceptance as a measure for the prevention of intraoperative hypothermia. However, data on heat transfer with upper body blankets are not yet available. This study was conducted to determine the heat transfer efficacy of eight complete upper body warming systems and to gain more insight into the principles of forced‐air warming. Methods: Heat transfer of forced‐air warmers can be described as follows: Q˙=h · ΔT · A, where Q˙= heat flux [W], h=heat exchange coefficient [W m^?2 °C^?1], ΔT=temperature gradient between the blanket and surface [°C], and A=covered area [m²]. We tested eight different forced‐air warming systems: (1) Bair Hugger^® and upper body blanket (Augustine Medical Inc. Eden Prairie, MN); (2) Thermacare^® and upper body blanket (Gaymar Industries, Orchard Park, NY); (3) Thermacare^® (Gaymar Industries) with reusable Optisan^® upper body blanket (Willy Rüsch AG, Kernen, Germany); (4) WarmAir^® and upper body blanket (Cincinnati Sub‐Zero Products, Cincinnati, OH); (5) Warm‐Gard^® and single use upper body blanket (Luis Gibeck AB, Upplands Väsby, Sweden); (6) Warm‐Gard^® and reusable upper body blanket (Luis Gibeck AB); (7) WarmTouch^® and CareDrape^® upper body blanket (Mallinckrodt Medical Inc., St. Luis, MO); and (8) WarmTouch^® and reusable MultiCover? upper body blanket (Mallinckrodt Medical Inc.) on a previously validated copper manikin of the human body. Heat flux and surface temperature were measured with 11 calibrated heat flux transducers. Blanket temperature was measured using 11 thermocouples. The temperature gradient between the blanket and surface (ΔT) was varied between ?8 and +8°C, and h was determined by linear regression analysis as the slope of ΔT vs. heat flux. Mean ΔT was determined for surface temperatures between 36 and 38°C, as similar mean skin surface temperatures have been found in volunteers. The covered area was estimated to be 0.35 m². Results: Total heat flow from the blanket to the manikin was different for surface temperatures between 36 and 38°C. At a surface temperature of 36°C the heat flows were higher (4–26.6 W) than at surface temperatures of 38°C (2.6–18.1 W). The highest total heat flow was delivered by the WarmTouch? system with the CareDrape? upper body blanket (18.1–26.6 W). The lowest total heat flow was delivered by the Warm‐Gard^® system with the single use upper body blanket (2.6–4 W). The heat exchange coefficient varied between 15.1 and 36.2 W m^?2 °C^?1, and mean ΔT varied between 0.5 and 3.3°C. Conclusion: We found total heat flows of 2.6–26.6 W by forced‐air warming systems with upper body blankets. However, the changes in heat balance by forced‐air warming systems with upper body blankets are larger, as these systems are not only transferring heat to the body but are also reducing heat losses from the covered area to zero. Converting heat losses of approximately 37.8 W to heat gain, results in a 40.4–64.4 W change in heat balance. The differences between the systems result from different heat exchange coefficients and different mean temperature gradients. However, the combination of a high heat exchange coefficient with a high mean temperature gradient is rare. This fact offers some possibility to improve these systems.     

Skin-surface warming: heat flux and central temperature

The authors determined the efficacy of four postoperative warming devices by measuring cutaneous and tympanic membrane temperatures, and heat loss/gain using 11 thermocouples and ten thermal flux transducers in five healthy, unanesthetized volunteers. Overall thermal comfort was evaluated at 5-10 min intervals using a 10-cm visual analog scale. The warming devices were: 1) a pair of 250-W infrared heating lamps mounted 71 cm above the abdomen; 2) the Thermal Ceiling MTC XI UL (500 W) set on "high" and mounted 56 cm above the volunteer; 3) a 54-by-145-cm circulating-water blanket set to 40 degrees C placed over the volunteer; and 4) the Bair Hugger forced air warmer with an adult-sized cover set on "low" (approximately 33 degrees C), "medium" (approximately 38 degrees C), and "high" (approximately 43 degrees C). Following a 10-min control period, each device was placed over the volunteer and activated for a 30-min period. All devices were started "cold" and warmed up during the study period. The Bair Hugger set on "medium" decreased heat loss more than each radiant warming device and as much as the circulating-water blanket. All methods reached maximum efficacy within 20 min. Set on "high," the Bair Hugger increased skin-surface temperature more than the circulating-water blanket. The Bair Hugger (all settings) and the water blanket raised skin temperature more than the radiant heaters. The circulating-water blanket was the most effective device for heating an optimally placed transducer on the chest (directly under and parallel to the radiant heat sources, and touching the water and Bair Hugger blankets).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of a radiant patient warming device with forced air warming during laparoscopic cholecystectomy

The importance of maintaining a patient's core body temperature during anaesthesia to reduce the incidence of postoperative complications has been well documented. The standard practice of this institution is the use of a forced air device for intraoperative warming. The purpose of this study was to compare this standard with an alternative warming device using a radiant heat source which only heated the face. This prospective, randomized controlled trial compared the efficacy of two methods of intraoperative warming: the BairHugger (Augustine Medical, U.S.A.) forced air device and the SunTouch (Fisher & Paykel Healthcare, N.Z.) radiant warmer during laparoscopic cholecystectomy in 42 female patients. Oesophageal core temperatures were recorded automatically on to computer during operations using standardised anaesthesia, intravenous infusions and draping. The study failed to show any statistical or clinical difference between the two patient groups in terms of mean core temperature both intraoperatively (P = 0.42) and in the recovery period (P = 0.54). Mean start to end core temperature differences were marginally lower in the radiant group (0.08 degree C) but not statistically or clinically significantly different. Given some of the drawbacks with forced air systems, such as the expense of the single use blanket, this new radiant warming device offers an alternative method of active warming with advantages in terms of cost and possible application to a wide variety of surgical procedures.     

Negative pressure rewarming vs. forced air warming in hypothermic postanesthetic volunteers

We compared changes in core temperature and systemic heat balance with a new negative pressure/warming device (Vital Heat(R) ) that uses negative pressure combined with heat to facilitate warming in vasoconstricted postoperative patients to those resulting from passive insulation or forced air. Seven healthy volunteers were anesthetized and cooled to a tympanic membrane temperature near 34 degrees C. Anesthesia was discontinued and shivering was prevented by using meperidine. The vasoconstricted volunteers were rewarmed for 2 h using three randomly assigned methods: 1) Vital Heat plus cotton blanket; 2) one layer of cotton blanket; 3) forced-air warming. Thermal flux was recorded from 15 skin-surface sites; metabolic heat production was estimated from total body oxygen consumption. Metabolic heat production remained constant throughout the study. Systemic heat loss remained constant during warming with cotton blankets but decreased significantly during the other treatments. Systemic heat balance increased significantly more with forced air (140 +/- 21 kcal) than with Vital Heat (66 +/- 19 kcal) or cotton blankets (47 +/- 18 kcal). Core temperature increased no faster with Vital Heat warming (1.3 +/- 0.4 degrees C) than with a cotton blanket (1.2 +/- 0.4 degrees C). In contrast, core temperature increased more rapidly with forced air warming (2.6 +/- 0.6 degrees C). In this study we show that calories from a negative pressure rewarming device are largely constrained to the forearm and that heat does not flow to the core thermal compartment.     

Influence of a Forced Air Warming System on Morbidly Obese Patients Undergoing Roux-en-Y Gastric Bypass

Background: Hypothermia during and after major abdominal surgery decreases host defenses, increases the incidence of coagulopathy and may alter blood pressure, cardiac contractility and myocardial stability. Methods: We designed a prospective randomized study to compare the benefits of a forced air warming system with warm blanket treatments in minimizing the effects of hypothermia on 64 morbidly obese patients undergoing Roux-en-Y gastric bypass. Results: Patients in the forced air warming group (n = 32) had significantly higher perioperative body core temperature, lower central venous pressure and blood pressure readings, lower incidence of shivering, less blood loss intraoperatively and achieved a higher post anesthesia Aldrete Score than those patients in the warmed blanket group (n = 32). Conclusion: The forced air warming system is safe, cost effective and beneficial in minimizing the undesirable consequences of hypothermia in morbidly obese patients undergoing Roux-en-Y gastric bypass.     

Randomized prospective comparison of forced air warming using hospital blankets versus commercial blankets in surgical patients

BACKGROUND: The purpose of this study was to evaluate the efficacy of an experimental approach to forced air warming using hospital blankets or a Bair Hugger warming unit (Augustine Medical Inc., Eden Prairie, MN) to create a tent of warm air. METHODS: Adult patients undergoing major surgery were studied. Patients were randomized to receive forced air warming using either a commercial Bair Hugger blanket (control group, n = 44; set point, 43 degrees C) or standard hospital blankets (experimental group, n = 39; set point, 38 degrees C). Distal esophageal temperatures were monitored. Patients were contacted the following day regarding any problems with the assigned warming technique. RESULTS: Surface area covered was 36 +/- 12% (mean +/- SD) in the experimental group and 40 +/- 10% in the control group. Final temperatures at the end of surgery were similar between groups: experimental, 36.2 +/- 0.6 degrees C; control, 36.4 +/- 0.7 degrees C. A similar number of patients had esophageal temperature less than 36 degrees C at the end of surgery in both groups (experimental, 12 of 39 [31%]; control, 12 of 44 [27%]). The majority of patients were satisfied with their anesthetic and warming technique: experimental, 38 of 39 patients; control, 44 of 44 patients. There were no thermal injuries. CONCLUSIONS: Standard hospital blankets heated to 38 degrees C forced air were equally as effective as commercial blankets heated with forced air at 43 degrees C. However, based on concerns expressed by the manufacturer, this experimental technique should not be used until further safety evaluation has been undertaken.     

Convective warming combined with vasodilator therapy accelerates core rewarming after coronary artery bypass surgery

In a prospective, randomized, controlled study, we have investigated the effect of forced air warming on the rate of change of nasopharyngeal and rectal temperatures in 20 patients after coronary artery bypass grafting. All patients had nasopharyngeal temperatures less than 36 degrees C on arrival in the intensive care unit and received an infusion of glyceryl trinitrate 15 mg h-1, but none received inotropes. Ten patients were warmed under an aluminized plastic "space" blanket (control group) and 10 were warmed under a "Bair Hugger" blanket connected to its power unit on "high" setting (Bair Hugger group). The rates of increase in nasopharyngeal temperature were 0.4 and 0.95 degrees C h-1, respectively, in the control and Bair Hugger groups (P < 0.01) during the first 2 h after operation. Over the same period of time, rectal temperatures increased at a rate of 0.25 and 0.75 degrees C h-1 in the control and Bair Hugger groups, respectively (P < 0.01).      

Randomized Prospective Comparison of Forced Air Warming Using Hospital Blankets versus Commercial Blankets in Surgical Patients

Background: The purpose of this study was to evaluate the efficacy of an experimental approach to forced air warming using hospital blankets or a Bair Hugger warming unit (Augustine Medical Inc., Eden Prairie, MN) to create a tent of warm air.

Methods: Adult patients undergoing major surgery were studied. Patients were randomized to receive forced air warming using either a commercial Bair Hugger blanket (control group, n = 44; set point, 43[degrees]C) or standard hospital blankets (experimental group, n = 39; set point, 38[degrees]C). Distal esophageal temperatures were monitored. Patients were contacted the following day regarding any problems with the assigned warming technique.

Results: Surface area covered was 36 +/- 12% (mean +/- SD) in the experimental group and 40 +/- 10% in the control group. Final temperatures at the end of surgery were similar between groups: experimental, 36.2 +/- 0.6[degrees]C; control, 36.4 +/- 0.7[degrees]C. A similar number of patients had esophageal temperature less than 36[degrees]C at the end of surgery in both groups (experimental, 12 of 39 [31%]; control, 12 of 44 [27%]). The majority of patients were satisfied with their anesthetic and warming technique: experimental, 38 of 39 patients; control, 44 of 44 patients. There were no thermal injuries.     

A reusable, custom-made warming blanket prevents core hypothermia during major neonatal surgery

PURPOSE: To introduce a reusable model of neonatal forced air warming blanket for intraoperative use during major noncardiac neonatal surgery and to determine clinical efficacy of this reusable blanket compared with the commonly used disposable blankets. METHODS: Delivered air temperature and calorie uptake of standard thermal bodies within the reusable blankets, Bair Hugger(R) blanket model 530 and model 555 were studied. Also, an efficacy study was conducted in 90 neonatal patients scheduled for major noncardiac surgery comparing the reusable blanket, the Bair Hugger(R) blanket model 530 and passive heat conservation as a control. The covered reusable blanket was used as a rescue procedure if the core temperature was < 35.5 degrees C. RESULTS: Delivered air temperature and heat transfer from the covered reusable blanket did not differ significantly from those of the Bair Hugger(R) blanket model 530 and model 555 (despite 0.75 degrees C-1.2 degrees C of heat trapped under the sheet and 1.3 Kcal less energy transfer). Temperatures measured underneath patients (correlated to poorly perfused areas) were highest using the Bair Hugger(R) blanket model 555. The reusable blanket was efficacious in preventing intraoperative core hypothermia and not different from the Bair Hugger(R) blanket model 530. About 1/3 of the patients in the control group had presented a core temperature < 35.5 degrees C but were successfully rescued using the reusable blanket. No adverse events were associated with any of these warming methods. CONCLUSION: This study shows the clinical efficacy of our reusable blanket for the prevention of core hypothermia during major neonatal surgery, which is not different from commonly used disposable blankets.     

Effects of a circulating-water garment and forced-air warming on body heat content and core temperature

BACKGROUND: Forced-air warming is sometimes unable to maintain perioperative normothermia. Therefore, the authors compared heat transfer, regional heat distribution, and core rewarming of forced-air warming with a novel circulating-water garment. METHODS: Nine volunteers were each evaluated on two randomly ordered study days. They were anesthetized and cooled to a core temperature near 34 degrees C. The volunteers were subsequently warmed for 2.5 h with either a circulating-water garment or a forced-air cover. Overall, heat balance was determined from the difference between cutaneous heat loss (thermal flux transducers) and metabolic heat production (oxygen consumption). Average arm and leg (peripheral) tissue temperatures were determined from 18 intramuscular needle thermocouples, 15 skin thermal flux transducers, and "deep" hand and foot thermometers. RESULTS: Heat production (approximately 60 kcal/h) and loss (approximately 45 kcal/h) were similar with each treatment before warming. The increases in heat transfer across anterior portions of the skin surface were similar with each warming system (approximately 65 kcal/h). Forced-air warming had no effect on posterior heat transfer, whereas circulating-water transferred 21+/-9 kcal/h through the posterior skin surface after a half hour of warming. Over 2.5 h, circulating water thus increased body heat content 56% more than forced air. Core temperatures thus increased faster than with circulating water than forced air, especially during the first hour, with the result that core temperature was 1.1 degrees +/- 0.7 degrees C greater after 2.5 h (P < 0.001). Peripheral tissue heat content increased twice as much as core heat content with each device, but the core-to-peripheral tissue temperature gradient remained positive throughout the study. CONCLUSIONS: The circulating-water system transferred more heat than forced air, with the difference resulting largely from posterior heating. Circulating water rewarmed patients 0.4 degrees C/h faster than forced air. A substantial peripheral-to-core tissue temperature gradient with each device indicated that peripheral tissues insulated the core, thus slowing heat transfer.     

The effect of a forced‐air warming blanket on patients' end‐tidal and transcutaneous carbon dioxide partial pressures during eye surgery under local anaesthesia: a single‐blind,randomised controlled trial

Surgical drapes used during eye surgery are impermeable to air and hence risk trapping air underneath them. We investigated the effect of a forced‐air warming blanket on carbon dioxide accumulation under the drapes in patients undergoing eye surgery under local anaesthesia without sedation. Forty patients of ASA physical status 1 and 2 were randomly assigned to either the forced‐air warmer (n = 20) or a control heated overblanket (n = 20). All patients were given 1 l.min^?1 oxygen. We measured transcutaneous and end‐tidal carbon dioxide partial pressures, heart rate, arterial pressure, respiratory rate, temperature and oxygen saturation before and after draping, then every 5 min thereafter for 30 min. The mean (SD) transcutaneous carbon dioxide partial pressure in the forced‐air warming group stayed constant after draping at 5.7 (0.2) kPa but rose to a maximum of 6.4 (0.4) kPa in the heated overblanket group (p = 0.0001 for the difference at time points 15 min and later). We conclude that forced‐air warming reduces carbon dioxide accumulation under the drapes in patients undergoing eye surgery under local anaesthesia.     

Self-warming blanket versus forced-air warming blanket during total knee arthroplasty under spinal anaesthesia: A randomised non-inferiority trial

Background

Arthroplasty patients are at high risk of hypothermia. Pre-warming with forced air has been shown to reduce the incidence of intraoperative hypothermia. There is, however, a lack of evidence that pre-warming with a self-warming (SW) blanket can reduce the incidence of perioperative hypothermia. This study aims to evaluate the effectiveness of an SW blanket and a forced-air warming (FAW) blanket peri-operatively. We hypothesised that the SW blanket is inferior to the FAW blanket.

Methods

In total, 150 patients scheduled for primary unilateral total knee arthroplasty under spinal anaesthesia were randomised to this prospective study. Patients were pre-warmed with SW blanket (SW group) or upper-body FAW blanket (FAW group) set to 38°C for 30 min before spinal anaesthesia induction. Active warming was continued with the allocated blanket in the operating room. If core temperature fell below 36°C, all patients were warmed using the FAW blanket set to 43°C. Core and skin temperatures were measured continuously. The primary outcome was core temperature on admission to the recovery room.

Results

Both methods increased mean body temperature during pre-warming. However, intraoperative hypothermia occurred in 61% of patients in the SW group and in 49% in the FAW group. The FAW method set to 43°C could rewarm hypothermic patients. Core temperature did not differ between groups on admission to the recovery room, p = .366 (CI: −0.18–0.06).

Conclusions

Statistically, the SW blanket was non-inferior to the FAW method. Yet, hypothermia was more frequent in the SW group, requiring rescue warming as we strictly held to the NICE guideline.

Trial Registration

Clinicaltrials.gov identifier: NCT03408197.     

Warming by resistive heating maintains perioperative normothermia as well as forced air heating

Background. Even mild perioperative hypothermia is associatedwith several severe adverse effects. Resistive heating has possibleadvantages compared with other active warming systems becauseit can heat several fields independently. To assess this newwarming system, we measured core temperature in patients duringsurgery who were warmed with circulating water mattresses, forcedair covers or resistive heating covers. Methods. Twenty-four patients undergoing laparoscopic cholecystectomywere randomly assigned to (i) circulating water mattress (38°C),(ii) forced air warming (set to ‘medium’) or (iii)carbon-fibre resistive warming (38°C). Warming was appliedthroughout anaesthesia and surgery. The groups were comparedusing one-way ANOVA and Student–Newman–Keuls tests. Results. Confounding factors were similar among the groups.Core temperatures in each group decreased for 20 min, but subsequentlyincreased in the forced air and resistive heating groups. Therewas no significant difference between the forced air and resistiveheating groups at any time. In contrast, core temperature inthe circulating water group continued to decrease. Consequently,core temperature in the circulating water group was significantlylower than in the other groups 30 min after anaestheticinduction and at later times. Conclusions. Resistive heating maintains core body temperatureas well as forced air heating and both are better than circulatingwater. Resistive heating offers the advantage of adjustableheating pods. Br J Anaesth 2003; 90: 689–91     

Full body forced air warming: commercial blanket vs air delivery beneath bed sheets

Purpose

Single-use commercial forced air warming blankets serve only to distribute heated air from a blower. Standard bed sheets may be equally effective in delivering hot air within a lower body field and at lower cost.

Methods

Heated forced air at 38° and 43° was delivered within a simulated full-body field beneath standard hospital bed sheets or via a BAIR Model 315 commercial blanket. The air temperatures maintained within, as well as the caloric uptake of standard bodies containing 1000 ml water, were studied under standard simulated operating room conditions. Thermal input was provided by one Bair Hugger Model 500 Warming Unit and hospital acquisition cost for materials were calculated.

Results

Air temperatures measured within the full body field at the three test sites were as great or greater using bed sheets (33.4–35.8°) as with the commercial blanket (31.1–33.9°), in spite of the 5° cooler outlet temperature air settings @ 38° vs 43°, respectively (P = 0.003). Forced air delivered beneath bed sheets heated standardized thermal bodies twice as effectively as commercial blankets using identically warmed (38°) forced air and heated as well as, or better, at the 38° setting than did the commercial blanket at the 43° setting. Calculated acquisition costs for sheets vs commercial blankets were $0.76 vs $18.00 US, respectively.

Conclusion

The simplicity, efficacy and economy of containing 38° warm air beneath bed-sheets offer several advantages over commercial blankets and warrant further study.     

Reflective Blankets Are as Effective as Forced Air Warmers in Maintaining Patient Normothermia During Hip and Knee Arthroplasty Surgery

Background

The use of forced air warming devices in the operating room has been shown to cause disruption of laminar airflow and a potential for increase in surgical site contamination. In contrast, conductive warming devices such as reflective blankets do not disrupt airflow and therefore have no potential for this increase in surgical site infection. However, some studies have shown them to be inferior to forced air warming devices in maintaining normothermia. We tested the hypothesis that the use of reflective blankets is as effective as forced air warming devices in maintaining intraoperative normothermia after adequate prewarming.

Heat conservation during abdominal surgery]

Intraoperative hypothermia is a major problem in anesthetic management. We compared the heat conserving effect of a forced air warming system (Bair Hugger, Augustine Medical Inc.) with that of a warming blanket. Sixteen patients undergoing abdominal surgery were studied. Patients were anesthetized with nitrous oxide and oxygen combined with epidural anesthesia. Patients received tympanic, rectal, bladder and core temperature monitorings. Patients were divided randomly to Bair Hugger group (BH, n = 8) or warming blanket group (WB, n = 8). Temperature were measured every one hour over three hours. The BH group showed significantly higher temperatures than WB group. Bair Hugger system is an efficient way to maintain intraoperative body temperature.