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.     

Efficacy of forced-air warming systems with full body blankets

PURPOSE: Postoperative hypothermia after cardiac surgery is still a common problem often treated with forced-air warming. This study was conducted to determine the heat transfer efficacy of 11 forced-air warming systems with full body blankets on a validated copper manikin. METHODS: The following systems were tested: 1) Bair Hugger 505; 2) Bair Hugger 750; 3) Life-Air 1000 S; 4) Snuggle Warm; 5) Thermacare; 6) Thermacare with reusable Optisan blanket; 7) WarmAir; 8) Warm-Gard; 9) Warm-Gard and reusable blanket; 10) WarmTouch; and 11) WarmTouch and reusable blanket. Heat transfer of forced-air warmers can be described as follows: Q = h x DeltaT x A. Where Q = heat flux (W), h = heat exchange coefficient (W x m-2 x degrees C-1), DeltaT = temperature gradient between blanket and manikin surface (degrees C), A = covered area (m2). Heat flux per unit area and surface temperature were measured with 16 heat flux transducers. Blanket temperature was measured using 16 thermocouples. The temperature gradient between blanket and surface (DeltaT) was varied and h was determined by linear regression analysis. Mean DeltaT was determined for surface temperatures between 32 degrees C and 38 degrees C. The covered area was estimated to be 1.21 m2. RESULTS: For the 11 devices, heat transfers of 30.7 W to 77.3 W were observed for surface temperatures of 32 degrees C, and between -8.8 W to 29.6 W for surface temperatures of 38 degrees C. CONCLUSION: There are clinically relevant differences between the tested forced-air warming systems with full body blankets. Several systems were unable to transfer heat to the manikin at a surface temperature of 38 degrees C.     

Comparison of two convective warming systems during major abdominal and orthopedic surgery

PURPOSE: Convective warming is routinely employed to maintain perioperative normothermia. However, due to differences in nozzle temperature and air flow of the power units, there are clinically relevant differences in heat transfer among convective warming systems. The purpose of this study was to evaluate the use of a quieter, convective warming system (WarmAir, sound pressure level 49 dba, air flow 35 cfm). The WarmAir system was compared to the standard, higher air flow system (Bair Hugger Model 750, sound pressure level 55 dba, air flow 48 cfm) with regards to temperature outcome. METHODS: Patients undergoing general anesthesia for major abdominal and orthopedic surgery were randomized into one of two groups: WarmAir or Bair Hugger. Both groups received an upper body, convective blanket using coverage appropriate for the given surgical procedure. Convective warming, at the high setting, was started after prepping and draping, and distal esophageal or nasopharyngeal temperature was measured intraoperatively. Sublingual temperature was measured preoperatively and on admission to the postanesthesia care unit. RESULTS: The WarmAir (n = 89) and Bair Hugger (n = 95) groups were similar with respect to age, gender, body mass index, ASA status, fluid balance, and duration of surgery. There was no difference in temperature outcomes between groups. In the WarmAir group, preoperative, lowest intraoperative, end of surgery, and postanesthesia care unit admission temperatures were (means +/- SD); 36.3 +/- 0.5, 35.4 +/- 1.1, 36.4 +/- 0.7, and 36.4 +/- 0.6 degrees C, respectively. Corresponding temperatures in the Bair Hugger group were; 36.3 +/- 0.6, 35.6 +/- 1.0, 36.5 +/- 0.6, and 36.4 +/- 0.5 degrees C, respectively. CONCLUSION: Despite differences in heating characteristics, both convective warming systems were effective in maintaining perioperative normothermia in patients undergoing major abdominal and orthopedic surgery. Therefore, choice of warming system is dependent on other factors such as ergonomics and cost.     

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)     

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).      

Evaluation of two warming systems after cardiopulmonary bypass

We have compared the Thermomat electric undermattress (JMW Systems, Edinburgh, UK) and the Bair Hugger (Augustine Medical, Courtelary, Switzerland) forced-air warming blanket in 30 adult patients after cardiac surgery. All patients were warmed to an oesophageal temperature of 38 degrees C before termination of cardiopulmonary bypass (CPB); those with oesophageal temperatures < 35.5 degrees C at skin closure were allocated randomly to be rewarmed in the intensive care unit either on the Thermomat (n = 15) or under the Bair Hugger blanket (n = 15), at their highest settings. Oesophageal and lateral thigh skin temperatures were recorded every 15 min for 4 h. There was a significantly faster increase in core temperature (0.5 vs 0.75 degrees C h-1; P < 0.0002) and skin temperature (0.86 vs 1.3 degrees C h-1; P < 0.001) in the Bair Hugger group. However, there was no difference in the number of patients who reached a core temperature of 36 degrees C (15 Bair Hugger, 14 Thermomat) or 37 degrees C (11 Bair Hugger, seven Thermomat), or in the number of patients who reached a skin temperature of 37 degrees C in 4 h (four Bair Hugger, one Thermomat). Twelve patients in the Bair Hugger group reached a skin temperature of 36 degrees C compared with two in the Thermomat group (P < 0.001). The Bair Hugger warmed faster than the Thermomat both centrally and peripherally, and warmed more patients to a core temperature of 37 degrees C in 4 h, but did not reduce the time to tracheal extubation or alter important clinical aspects of postoperative course.      

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.     

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.     

Convection heating in pediatric general surgery - a comparison of warming alternatives in a mannequin study

BACKGROUND: Numerous methods of patient warming are used to prevent intraoperative hypothermia in children. Commercially available forced air warming blankets are effective, but are single-use items. We tested a custom-designed heat dissipation unit (HDU) against one such commercially available blanket. METHODS: Air temperatures at various points around a mannequin under simulated operating conditions were recorded using thermistors and thermal imaging. The only variable changed was the heating method: a forced air blanket or a customized HDU with two draping techniques - cotton drapes with and without a plastic 'undersheet'. RESULTS: The three methods produced similar temperature increases and plateaux across the 11 thermistor points measured. There were no significant differences between temperatures at 1 h. A plastic sheet did not appear to enhance the effectiveness of the HDU in this study. Thermal imaging photography suggested more uniform heating of the mannequin with the HDU arrangements. CONCLUSIONS: The custom-built HDU compares favorably in our mannequin study with a Bair Hugger forced air warming blanket. As it is reusable, it offers considerable potential savings.     

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.     

Delayed forced air warming prevents hypothermia during abdominal aortic surgery

We have evaluated the efficacy of the delayed forced air warming during abdominal aortic surgery in 18 patients. Patients were allocated randomly to one of two groups: the control group (n = 9) received no intraoperative warming device; the Bair-Hugger group (n = 9) had active skin surface warming with an upper body cover. The device was activated when core temperature decreased to less than 36 degrees C. The reduction in core temperature was 0.6 degrees C during the first hour after induction and 0.4 degrees C during the second hour in both groups. In the control group, core temperature continued to decrease until the end of surgery, whereas in the Bair-Hugger group, the reduction in core temperature stopped after 1 h of warming, and then rewarming began. At the end of surgery, core temperature in the Bair- Hugger group was similar to core temperature before induction, and was higher than core temperature in the control group (P < 0.003).      

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.     

Prevention of hypothermia by cutaneous warming with new electric blankets during abdominal surgery

We have evaluated the efficacy of new electric warming blankets, which meet the requirements of the international standard for perioperative electrical and thermal safety, in preventing intraoperative hypothermia. We studied 18 patients undergoing abdominal surgery, allocated to one of two groups: in the control group, there was no prevention of intraoperative hypothermia (n = 8) and in the electric blanket group, two electric blankets covered the legs and upper body (n = 10). Anaesthesia duration was similar in the two groups (mean 201 (SEM 11) min), as was ambient temperature (20.5 (0.1) degrees C). Core temperature decreased during operation by 1.5 (0.1) degrees C in the control group, but only by 0.3 (0.2) degree C in the electric blanket group (P < 0.01). Five patients shivered in the control group compared with one in the electric blanket group (P < 0.05). We conclude that cutaneous warming with electric blankets was an effective means of preventing intraoperative hypothermia during prolonged abdominal surgery.      

Efficacy of postoperative rewarming after cardiac surgery.

OBJECTIVE: To compare the efficacy of forced-air warmers and radiant heaters on rewarming after cardiac surgery in a prospective randomized study. METHODS: Fifty male patients who had undergone coronary artery bypass graft surgery were studied. The control group (Gr. C, n=10) was nursed under a standard hospital blanket. Two groups were treated with forced-air warmers: WarmTouch 5700 (Gr. WT, n=10) and Bair Hugger 500 (Gr. BH, n=10). Two other groups were treated by radiant heaters: the Aragona Thermal Ceilings CTC X radiant heater (Gr. TC, n=10) and a self assembled radiant heater of 4 Hydrosun 500 infrared lamps (Gr. HY, n=10). Changes of oesophageal temperature, mean skin temperature, mean body temperature and relative heat balance were calculated from oesophageal temperature, 4 skin temperatures and oxygen consumption (VO(2)). RESULTS: All actively treated groups with exception of the TC group showed significantly faster oesophageal warming than the control group. The mean body temperature increased 1.1 (0.7-1.7) degrees Ch(-1) in Gr. WT, 1.3 (0.7-1.5) degrees Ch(-1) in Gr. BH, 0.8 (0.5-1.4) degrees Ch(-1) in Gr. TC and 0.7 (0.4-1.0) degrees Ch(-1) in Gr. HY compared to Gr. C with 0.4 (0.2-0.7) degrees Ch(-1). The mean VO(2) and the maxima of the VO(2) during the study period did not differ significantly between the groups. CONCLUSION: In the current setting active warming, forced-air warming more than radiant warming, increased speed of rewarming two- to threefold in comparison to insulation with a blanket.     

Simulated clinical evaluation of four fluid warming devices*

The fluid warming capabilities of the Bair Hugger, Hotline, Standard Ranger and Fluido devices were evaluated in the laboratory with gravity flow via a 14G cannula (1 m head of fluid) and with the fluid bag pressurised to 300 mmHg. The resulting flows (70-450 ml.min(-1)) were recorded. At a room temperature of 22 degrees C, no device warmed the fluid to 37 degrees C. However, the Standard Ranger with gravity flow and the Fluido with both gravity and pressurised flow achieved 35 degrees C, whereas the Bair Hugger and Hotline with both gravity and pressurised flow, and the Standard Ranger with pressurised flow, achieved only 24-31 degrees C. However, from the way delivered temperatures changed with flow, we calculated that all four devices would achieve close to 37 degrees C at the flows specified by the manufacturers: 17, 83, 150 and 800 ml.min(-1) for the Bair Hugger, Hotline, Standard Ranger and Fluido, respectively.     

Perioperative thermal insulation

To determine the efficacy of passive insulators advocated for prevention of cutaneous heat loss, we determined heat loss in unanesthetized volunteers covered by one of the following: a cloth "split sheet" surgical drape; a Convertors disposable-paper split sheet; a Thermadrape disposable laparotomy sheet; an unheated Bair Hugger patient-warming blanket; 1.5-mil-thick plastic hamper bags; and a prewarmed, cotton hospital blanket. Cutaneous heat loss was measured using 10 area-weighted thermal flux transducers while volunteers were exposed to a 20.6 degrees C environment for 1 h. Heat loss decreased significantly from 100 +/- 3 W during the control periods to 69 +/- 6 W (average of all covers) after 1 h of treatment. Heat losses from volunteers insulated by the Thermadrape (61 +/- 6 W) and Bair Hugger covers (64 +/- 5 W) were significantly less than losses from those insulated by plastic bags (77 +/- 11 W). The paper drape (67 +/- 7 W) provided slightly, but not significantly, better insulation than the cloth drape (70 +/- 4 W). Coverage by prewarmed cotton blankets initially resulted in the least heat loss (58 +/- 8 W), but after 40 min, resulted in heat loss significantly greater than that for the Thermadrape (71 +/- 7 W). Regional heat loss was roughly proportional to surface area, and the distribution of regional heat loss remained similar with all covers. These data suggest that cost and convenience should be major factors when choosing among passive perioperative insulating covers. It is likely that the amount of skin surface covered is more important than the choice of skin region covered or the choice of insulating material.     

Wet forced-air warming blankets are ineffective at maintaining normothermia

Background:  Forced-air warming systems have proven effective in preventing perioperative hypothermia. To date, reported adverse events relate primarily to overheating and thermal injuries. This study uses a simple model to show that forced-air warming blankets become ineffective if they get wet.
Methods:  Temperature sensor probes were inserted into three 1-liter fluid bags. Group C bags served as the control. Groups D (dry) and W (wet) bags were placed on Bair Hugger® Model 555 (Arizant Healthcare, Inc., Eden Prairie, MN, USA) pediatric underbody blankets. The warming blanket for Group W bags was subsequently wet with irrigation fluid. Temperature was documented every 5 min. This model was repeated two times for a total of three cycles. Statistical analysis was performed using anova for repeated measures.
Results:  Starting temperatures for each model were within a 0.3°C range. Group C demonstrated a steady decline in temperature. Group D maintained and slightly increased in temperature during the observation period, while Group W exhibited a decrease in temperature at a rate similar to Group C. These results were significant at P  < 0.005.
Conclusions:  A wet forced-air warming blanket is ineffective at maintaining normothermia. Once wet, the warming blanket resulted in cooling similar to the control group.     

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.     

The efficacy of carbon-fiber resistive-heating in prevention of core hypothermia during major abdominal surgery

BACKGROUND: Perioperative hypothermia causes numerous severe complications, such as coagulopathy, surgical wound infections, and morbid myocardial outcomes. For prevention of intraoperative hypothermia, an inexpensive, non-disposable carbon fiber resistive warming system has been developed. METHODS: We evaluated the efficacy of resistive-heating, comparing to circulating-water mattress and forced-air warming system. Twenty four patients undergoing elective abdominal surgery were randomly assigned to warming with: 1) a circulating water mattress, 2) a lower-body forced-air system, or 3) a carbon-fiber, resistive-heating blanket. RESULTS: Tympanic membrane temperature in the first two hours of surgery decreased by 1.9 +/- 0.5 degrees C in the water mattress group, 1.0 +/- 0.6 degree C in the forced-air group, 0.8 +/- 0.2 degree C in the resistive-heating group. The decreases in core temperature by the end of surgery were 2.0 +/- 0.8 degrees C in the water mattress group, 0.6 +/- 1.1 degrees C in the forced-air group, and 0.5 +/- 0.4 degree C in the resistive blanket group, respectively. There was no significant difference in the changes of core temperature between the forced-air group and the resistive-heating group. No side effects related to resistive-heating blanket were observed. CONCLUSIONS: Even during major abdominal surgery, carbon-fiber resistive-heating maintains core temperature as effectively as forced air.