TY - JOUR
AU - Giesbrecht, Gordon, G
AB - Abstract Introduction Victims of severe hypothermia require external rewarming, as self-rewarming through shivering heat production is either minimal or absent. The US Military commonly uses forced-air warming in field hospitals, but these systems require significant power (600–800 W) and are not portable. This study compared the rewarming effectiveness of an electric resistive heating pad system (requiring 80 W) to forced-air rewarming on cold subjects in whom shivering was pharmacologically inhibited. Materials and Methods Shivering was inhibited by intravenous meperidine (1.5 mg/kg), administered during the last 10 min of cold-water immersion. Subjects then exited from the cold water, were dried and lay on a rescue bag for 120 min in one of the following conditions: spontaneous rewarming only (rescue bag closed); electric resistive heating pads (EHP) wrapped from the anterior to posterior torso (rescue bag closed); or, forced-air warming (FAW) over the anterior surface of the body (rescue bag left open and cotton blanket draped over warming blanket). Supplemental meperidine (to a maximum cumulative dose of 3.3 mg/kg) was administered as required during rewarming to suppress shivering. Results Six healthy subjects (3 m, 3 f) were cooled on three different occasions, each in 8°C water to an average nadir core temperature of 34.4 ± 0.6°C (including afterdrop). There were no significant differences between core rewarming rates (spontaneous; 0.6 ± 0.3, FAW; 0.7 ± 0.2, RHP; 0.6 ± 0.2°C/h) or post-cooling afterdrop (spontaneous; 1.9 ± 0.4, FAW; 1.9 ± 0.3, RHP; 1.6 ± 0.2°C) in any of the 3 conditions. There were also no significant differences between metabolic heat production (S; 74 ± 20, FAW; 66 ± 12, RHP; 63 ± 9 W). Total heat gain was greater with FAW (36 W gain) than EHP (13 W gain) and spontaneous (13 W loss) warming (p < 0.005). Conclusions Total heat gain was greater in FAW than both EHP, and spontaneous rewarming conditions, however, there were no observed differences found in rewarming rates, post-cooling afterdrop or metabolic heat production. The electric heat pad system provided similar rewarming performance to a forced-air warming system commonly used in US military field hospitals for hypothermic patients. A battery-powered version of this system would not only relieve pressure on the field hospital power supply but could also potentially allow extending use to locations closer to the field of operations and during transport. Such a system could be studied in larger groups in prospective trials on colder patients. hypothermia, rewarming, cold stress, afterdrop, portable heat source, military field hospital INTRODUCTION Prolonged exposure to cold and/or wet environments can result in accidental hypothermia. These conditions present an especially significant challenge for military personnel who often reside, train, and/or battle in austere environments where access to advanced medical care is limited. Importantly, military patients often have significant trauma. Trauma itself increases the risk of hypothermia,1–4 and hypothermia increases morbidity and mortality in trauma patients. Mortality rates for trauma patients rise from 10–41% in normothermic patients to 29–100% in hypothermic patients,3–5 with odds ratios for mortality being 2.7–2.9 for hypothermic patients.6,7 A recent study showed that 5% of patients admitted to a major trauma center where hypothermic.8 Compared to normothermic patients, hypothermic patients had longer median hospital stays (7 vs 4 d) and lower survival rates (69 vs 94%). Eidstuen et al. reported that 71% of trauma victims admitted to hospital were already hypothermic at the site of injury, and that 91% of them became colder (by 1.7°C) on scene before evacuation.9 Gentilello et al. demonstrated that rapid warming of trauma patients (with continuous arteriovenous rewarming) decreased mortality rates from 43% (standard rewarming) to 7%.5 These results support the general advice to prevent or reverse core cooling as soon as possible by aggressive rewarming on site before transport to hospital.1,10–13 Rewarming can be either: passive (insulation and relying on endogenous heat production); active external (non-invasive application of exogenous heat source); or active internal (invasive application of exogenous heat source). Several heat sources have been studied. In vigorously shivering subjects, active warming methods have similar rewarming rates to shivering alone. However, active warming is more effective than endogenous heat production when shivering is absent (e.g., in severely hypothermic patients). Chemical heat packs,14–18 a charcoal heater,15,19 hot water bottles/bags15 can be used. Body-to-body warming is resource intensive,20 and inhalation warming has limited effectiveness.21,22 Arteriovenous anastomosis (AVA) warming (immersion of distal legs and arms in 42–45°C water, or warm Fluidotherapy silicone) is very effective23,24 but impractical in the field due to the equipment required, and in more advanced cases of hypothermia where a horizontal position is preferred. Warmed IV fluids can be used25–28 but delivering warm fluid in the field can be difficult if not impossible. Finally, forced-air warming (FAW)20 and electric heat pads29–31 may be effective but they require a 120-volt alternating current (VAC) power source. In military operations, initial advanced medical treatment often occurs at a remote field hospital. Electrical power is limited (e.g., one or two 3-kW generators) resulting in competition for power between medical devices, infrastructure, and other equipment. Currently, the US military standard of care for rewarming in a field hospital is a forced-air warming system (average power consumption, 600–800 W). Several limitations exist with FAW: power requirements make up a significant portion of the available power; inability to use this system forward of the field hospital; and, the system is not designed for use during transport.32 It would be a significant advantage to have an alternative, but equally effective, warming system that would not require 120 VAC power. This would relieve pressure on the field hospital power supply, and potentially allow extending use to locations closer to the battlefield or other field of operations, and during transport. The US military commonly uses a Hypothermia Prevention Management Kit (HPMK) in the field. The HPMK consists of a chemical heating blanket within a thin water- and wind-proof shell. This system is small (6.5 L), light (1.6 kg) and easily carried in a backpack. However, the lack of insulation in the HPMK decreases its effectiveness in cold environments (e.g., −20°C).33 Electric resistive heating pads may be effective30,31 but have not been tested in field-relevant conditions. The purpose of this study was to test the hypothesis that warming efficacy of electric resistive heating pads (which are, or could be, adapted for battery power and field use) is at least as effective as, but not worse than, FAW related to core temperature afterdrop and subsequent rewarming rate, in cold but non-shivering subjects. Secondary outcomes include heat delivery and net heat gain. METHODS Subjects The protocol was approved by Health Canada and the Biomedical Research Ethics Board at the University of Manitoba. Prior to participation a signed informed consent was obtained. To achieve 90% power (a = 0.05, 1-tailed test; ß = 0.10; power index of 2.92), the sample size required to detect a statistically significant difference (mean ± SD) for rate of rewarming of 0.5 ± 0.4°C/h, was 6 subjects.15 Measurements For each trial, subjects wore a swim-suit and were instrumented in ambient lab temperature (~22°C). Core temperature (Tco) was monitored with an esophageal thermocouple (Mon-a-therm) inserted to the level of the heart. Heart rate was monitored with a 3-lead electrocardiogram and an intravenous line was introduced into an arm or hand vein for drug and/or saline administration. Cutaneous heat flux (W/m2) and skin temperature (°C) were measured with heat flux disks (Concept Engineering) at eleven sites on the torso, back, legs and arms. Body surface area was calculated,34 and regional percentages for each site were assigned35 according to previous work in our lab. Flux was defined as positive when heat traversed the skin toward the environment (i.e., heat loss). Participants wore a face mask and oxygen consumption was continuously monitored with a metabolic cart (Sensormedics). This allowed real time monitoring of shivering metabolism to inform meperidine injections during rewarming. Rewarming Conditions Following immersion, participants were dried off and they then lay on a hooded thermal rescue bag (APLS Thermal Guard) which had been placed on a 15-mm foam pad on a military litter (Talon II 90 C Collapsible Handle Litter, Green). In order to increase external validity of the results, each condition was applied according to manufacturer recommendations and as they would be used in practice (e.g., the electric pads as used in pre-hospital settings with a rescue bag, and FAW as used in the hospital setting with a cotton blanket over top) (see Fig. 1). FIGURE 1 Open in new tabDownload slide Forced-air warming blanket (top left) with single cotton hospital blanket placed on top (top right). Two electric heating pads applied to the chest and upper back (bottom left; the shirt was removed during the test) with rescue blanket strapped to the stretcher (bottom right). FIGURE 1 Open in new tabDownload slide Forced-air warming blanket (top left) with single cotton hospital blanket placed on top (top right). Two electric heating pads applied to the chest and upper back (bottom left; the shirt was removed during the test) with rescue blanket strapped to the stretcher (bottom right). Spontaneous Rewarming The recue bag was closed and no exogenous heat was applied. Subjects where then secured to the litter with chest and leg straps. Forced-Air Warming (FAW) A forced-air warming heater (Bair Hugger 750, Augustine Med) was placed on the “high” setting and attached to a warming blanket (Model 300, full body blanket) which was placed over the subjects (Fig. 1 top). A light cotton blanket was draped over the warming blanket. The rescue bag was not closed but the hood was worn. This configuration was used because: this is the standard procedure in hospital settings; and enclosing the forced-air blanket within the rescue bag would collapse the blanket, preventing air flow and thus eliminating convective heating. Electric Resistive Heating Pads (EHP) Two electric resistive heating pads (Gentherm Inc., Northville MI, USA) were placed on each side of the torso covering the lateral chest, arm pit and part of the upper back (Fig. 1 bottom). The pads were powered by 120 VAC and independently controlled to provide a maximum surface temperature of 43°C in order to prevent burning the skin. The rescue bag was closed and subjects where secured to the litter with chest and leg straps. This is the configuration that would be used in field conditions until a patient could be delivered to a hospital setting. Protocol Each trial was separated by at least 5 days to allow for washout of meperidine. The subjects were cooled at the same time of the day to control for circadian effects. The order of trials followed a modified balanced design, with spontaneous warming being first and FAW and EHP subsequently being balanced.15,20 This design was used because external heat donation increases the skin temperature and reduces the thermal stimulus for shivering, thus the shivering stimulus is expected to be maximum during spontaneous warming. Therefore, a higher dose of meperidine would be required to inhibit shivering during spontaneous warming compared with the active warming conditions. Since we wanted to use the same dosing amount for all conditions, the dosing schedule from spontaneous warming was used for the subsequent active warming conditions. The participants sat quietly for 10 min of baseline measurements. They were then immersed to the level of the sternal notch in 21°C water which was cooled to 8°C within 10 min with ~60 kg of ice. Participants were cooled for a maximum of 60 min, or Tco decreased to 35°C or a researcher advised exit. During the last 10 min of immersion, 1.5 mg/kg of IV meperidine was infused slowly in five 2-mL aliquots at 2-min intervals. Participants then exited the water, were dried off and lay on the rescue bag. During warming, additional meperidine was administered in doses of 0.3 mg/kg, as necessary (to a maximum cumulative dose of 3.3 mg/kg) to continuously inhibit shivering. Treatment continued for 120 min. Participants then rewarmed in 40–42°C water. Data Analysis Tco afterdrop (°C) was calculated as the difference between Tco on exit from cold water and its nadir. Core rewarming rate (°C/h) was calculated by linear regression for Tco data from the point of steady increase. Total heat flux (HFTotal) was calculated by adding values from all sites.35 Since the warming devices covered different regions of the body, regional heat fluxes were calculated for all three conditions for the areas that were, or would be, covered by the heat pads (pad area) and the forced-air blanket (blanket area). Metabolic heat production (M) was determined from the oxygen consumption and respiratory heat loss (RHL).36 Net heat gain (W) was then calculated as follows: $$\textrm{Net heat gain}(\textrm{W}) = \textrm{M} (\textrm{W})-\textrm{RHL} (\textrm{W})-\textrm{HF}_\textrm{Total}(\textrm{W}).$$ All statistical analyses were accomplished with SigmaPlot 14. Repeated measures two-way analysis of variance (ANOVA) (factor A, warming condition; factor B, time) compared all continuous variables. As well, a repeated measures one-way ANOVA compared the derived variables of afterdrop and rewarming rate. Post hoc analyses for significant differences were accomplished using the Holm-Sidak post hoc test. Results are reported as means ± SD. Statistical significance was set at p < 0.05. RESULTS Six healthy subjects (3 female) (29 ± 3 yr; height, 179 ± 13 cm; mass, 76.5 ± 13 kg; body surface area, 1.9 ± 0.2 m2; and body fat, 18 ± 6%) participated. Core Temperature Average cooling time was 44.5 ± 17 min (range 23.5–60 min). There were no significant differences in Tco between the three conditions during baseline or at end-immersion. During immersion, Tco decreased from 37.4 ± 0.4°C to 36.2 ± 0.6°C and, early during rewarming, fell to a nadir of 34.4 ± 0.6°C. Likewise, there were no significant differences for either afterdrop or core rewarming rates (Fig. 2). Afterdrop values for spontaneous, electric pad and forced-air warming were 1.9 ± 0.4, 1.6 ± 0.2 and 1.9 ± 0.3°C respectively. Rewarming rates were 0.6 ± 0.3, 0.6 ± 0.2 and 0.7 ± 0.2°C.h−1 respectively. Tco increased significantly from 60 to 120 min of rewarming in all conditions (p < 0.005) but was not different between conditions at any time during rewarming. FIGURE 2 Open in new tabDownload slide Mean change in core temperature (°C) during rewarming for spontaneous warming, electric heating pads and forced-air warming. Time 0 and temperature 0°C indicates exit from the cold water. For clarity, SD bars are only included for top and bottom lines. Horizontal brackets separate periods of significant difference within a condition; bracket color corresponds to figure legend for condition (p < 0.05). FIGURE 2 Open in new tabDownload slide Mean change in core temperature (°C) during rewarming for spontaneous warming, electric heating pads and forced-air warming. Time 0 and temperature 0°C indicates exit from the cold water. For clarity, SD bars are only included for top and bottom lines. Horizontal brackets separate periods of significant difference within a condition; bracket color corresponds to figure legend for condition (p < 0.05). Metabolic Heat Production No significant differences were found for metabolic heat production among the three conditions throughout the protocol. When data were pooled, metabolic heat production significantly increased from 84 ± 10 W during baseline to a maximal metabolic heat production of 363 ± 119 W during cooling until the meperidine infusion. From 0 – 15 min post-immersion, heat production (115 ± 21 W) was slightly, but not significantly, higher than baseline. For the remaining 105 mins of rewarming, supplemental meperidine suppressed shivering, and heat production decreased to 70 ± 17 W. Total Heat Flux Total heat gain (e.g., negative flux) throughout rewarming was greater with FAW than both EHP and spontaneous warming (p < 0.005) and also greater with EHP than spontaneous warming (p < 0.01) (Fig. 3 top). FIGURE 3 Open in new tabDownload slide Total (top) and regional (bottom) heat flux during rewarming for spontaneous warming, electric heating pads, and forced-air warming. Negative values indicate heat gain; time 0 indicates exit from the cold water. Values are means for six subjects. For clarity, SD bars are only included for top and bottom lines. For total heat flux (top), * separates values that are significantly different (p < 0.05). Horizontal brackets separate periods of significant difference within a condition; bracket color corresponds to figure legend for condition (p < 0.05). For regional heat flux (bottom), * and vertical brackets indicate conditions that are significantly different from each throughout the experiment (p < 0.05); ŧ, forced-air warming (blanket area) significantly different than electric heating pads (pad area) (p < 0.05). FIGURE 3 Open in new tabDownload slide Total (top) and regional (bottom) heat flux during rewarming for spontaneous warming, electric heating pads, and forced-air warming. Negative values indicate heat gain; time 0 indicates exit from the cold water. Values are means for six subjects. For clarity, SD bars are only included for top and bottom lines. For total heat flux (top), * separates values that are significantly different (p < 0.05). Horizontal brackets separate periods of significant difference within a condition; bracket color corresponds to figure legend for condition (p < 0.05). For regional heat flux (bottom), * and vertical brackets indicate conditions that are significantly different from each throughout the experiment (p < 0.05); ŧ, forced-air warming (blanket area) significantly different than electric heating pads (pad area) (p < 0.05). Regional Heat Flux For the blanket area (Fig. 3 bottom), regional heat gain throughout rewarming was greater with FAW than both EHP and spontaneous warming (p < 0.001) and also greater with EHP than spontaneous warming from 30–90 min (p < 0.05). For the pad area, regional heat gain throughout rewarming was greater with EHP than both FAW and spontaneous warming (p < 0.05). When comparing the actively-heated areas, heat gain was greater in the blanket area Net Heat Gain Net heat gain did not change over time with FAW or spontaneous warming (Fig. 4). With EHP however, net heat gain decreased from 30 to 90 min (p < 0.01). Values were greater for FAW than spontaneous warming throughout. EHP was greater than spontaneous warming at 30 min (p < 0.05). From 60 to 120 min, EHP values were between but not significantly different from FAW and spontaneous warming, except compared to FAW at 90 min (p < 0.05). FIGURE 4 Open in new tabDownload slide Net heat gain (W) during rewarming for spontaneous warming, electric heating pads, and forced-air warming. Values are means for six subjects. For clarity, SD bars are only included for top and bottom lines. *, separates values that are significantly different (p < 0.05), ŧ, forced-air warming different than spontaneous warming (p < 0.05). Horizontal brackets separate periods of significant difference within a condition; bracket color corresponds to figure legend for condition (p < 0.05). FIGURE 4 Open in new tabDownload slide Net heat gain (W) during rewarming for spontaneous warming, electric heating pads, and forced-air warming. Values are means for six subjects. For clarity, SD bars are only included for top and bottom lines. *, separates values that are significantly different (p < 0.05), ŧ, forced-air warming different than spontaneous warming (p < 0.05). Horizontal brackets separate periods of significant difference within a condition; bracket color corresponds to figure legend for condition (p < 0.05). DISCUSSION This study is the first to compare the rewarming effectiveness of a forced-air warming system (which is commonly used in US military field hospitals) with a novel electric resistive heating pad system which could be adapted to be powered by a portable 12 V battery/control unit. When shivering was pharmacologically inhibited in cold subjects, there were no differences between either of these active warming methods or spontaneous warming for post cooling afterdrop or core rewarming rate. Our results are consistent with the only other study in a non-surgical setting to compare both FAW and electric heating (using a whole body mattress and blanket) in non-shivering (pharmacological inhibition) hypothermic individuals.29 Although there were similarly no differences in rewarming rates between FAW and electric heating, the rewarming rates in that study were slightly higher (pooled average, 0.95°C/h) than our present study (0.65°C/h). Our lower rewarming rates may be because our subjects were ~10 kg heavier, thus presenting a greater mass to rewarm. The electric heat source studied in this previous study is not applicable for field use for several reasons: it is designed for perioperative use; the power source is not portable (e.g., not battery powered); it uses a full body mattress and blanket; and the system is larger and heavier than could be practically carried. We are unaware of any other rewarming studies of electric heating pads when shivering is pharmacologically inhibited. However, our results for both afterdrop (1.9°C) and rewarming rate (0.6°C/h) are non-inferior to multiple non-120 VAC rewarming methods in non-shivering subjects, including: a charcoal heater applying heat to either the head (afterdrop 1.3°C, rewarming rate 0.8°C/h)42 or torso (afterdrop 1.2–1.8°C, rewarming rate 0.6–0.8°C/h);15,20,42 hot water packs (afterdrop 1.6°C, rewarming rate 0.7°C/h);15 or body-to-body rewarming (afterdrop 1.5°C, rewarming rate 0.5°C/h).20 Likewise, afterdrop values were similar with chemical heat pads (1.5°C)15 and warm-air inhalation (1.2°C),21 but the rewarming rates were lower (0.2°C/h for both methods) than in the present study. Lower rewarming rates with these chemical heat pads may be because: heat production of the heat pads dropped significantly within 20 min; and the pads were applied to the back and chest but not the axillae. Slow rewarming with inhalation warming is not surprising because heat donated by air is minimal.21 Our core rewarming rate for FAW was comparable to other similar-powered heating/blower units (e.g., 600 – 700 W),20 however higher powered-units (850 – 4,800 W) reduced afterdrop (0.9°C) and increased rewarming rates (1.5°C/h with an 850 W unit; 2.4°C/h with a prototype unit using four 1,200 W heaters).20,21 It should be noted that when shivering is present the application of external heat attenuates shivering heat production by an amount approximately equal to the heat donated.19,38–42 Accordingly, body-to-body warming38,39, forced-air warming21 application of electrical and hot water perfused heating pads39,40 and charcoal heaters19,41 have similar rewarming rates to spontaneous shivering alone. However, active external rewarming is still indicated,42 as it provides several possible advantages such as increasing comfort, decreasing cardiac work (due to decreased shivering), and preserving substrate availability. Our most relevant result was that core rewarming rates were the same for both FAW and EHP conditions. Net heat gain for FAW was similar to EHP for the first hour of warming and slightly, though not significantly, higher during the second hour (except at 90 min). Indeed, average total heat flux was greater for FAW (36 W) than EHP (13 W). However, regional values at least partially explain our rewarming results. Although heat flux to the area that would be covered by the FAW blanket was higher during FAW (36 W) than EHP (5 W), heat delivered to the area that would be covered by the EHP pad was greater during EHP (23 W) than FAW (5 W). Therefore, electric pads seem to apply heat more efficiently. All of the heat from the electric pad is directed towards the torso, an area of high surface heat transfer and close to vital organs such as the heart and lungs,17,20,37–40,44 while not wasting energy by applying heat below the waist to poorly perfused tissue.15,20 Thus, electric heating pads could provide a beneficial alternative to forced-air warming because of portability to the point of injury, and decreased power requirements when plugged into the power supply of a mobile hospital. The afterdrop in our spontaneous warming condition (1.9°C) was consistent with the range observed in previous studies (1.5–2.2°C).15,20,41 The spontaneous rewarming rate of 0.6°C/h was not significantly different than the active warming conditions. This rate is consistent with the most recent study from our lab (0.7°C/h),41 but was slightly higher than in our previous work (0.4°C/h).20,21 This may be due in part to differences in our cooling/meperidine-dosing protocol. In our initial shivering-inhibition study, Tco was lowered by 1.1°C and the low meperidine dose (1.5 mg/kg) did not completely inhibit shivering, therefore the spontaneous rewarming rate was high (1.2°C/h).43 In subsequent studies, smaller Tco reductions (0.1–0.8°C) and larger doses of meperidine (2.5–3.2 mg/kg) completely eliminated shivering, and rewarming rates were reduced to 0.4°C/h.20,21 In the present study, the 1.1°C decrease in Tco may have temporarily provided too great a shivering stimulus. Although shivering heat production was completely eliminated during the last 105 min of rewarming, heat production in the first 15 min (115 W) may at least partially explain the slightly higher rewarming rate. Future studies aimed at shivering suppression should involve smaller decreases in Tco. Practical Implications The EHP system could be valuable in military operations. First, this system extends the reach of the treatment/warming team from the field hospital closer to the point of injury and/or cold exposure. Unit portability also allows for warming cold patients during transport as core temperature can continue to drop in initially stable patients, making them unstable.17,42 Future studies could determine effectiveness of a comparable battery/control unit in cold field conditions. Second, the EHP system uses about one-tenth the power (80 W) of FAW (800 W). This considerable saving is because with EHP, virtually all power is applied to the pads, whereas with FAW, power is required not only for the heating element, but also the blower fan; power is also wasted as air cools along the tubing which connects the heater to the blanket. The EHP battery/control unit (not used in this study) has a low power consumption when plugged into 120 VAC in any of three configurations: power the pads directly (80 W); recharge the battery (70 W); or simultaneously power the pads and recharge the battery (150 W). Future studies could compare effectiveness of the EHP system when powered by 120 VAC compared to a portable rechargeable 12 V battery/control unit. The battery/control unit could also be studied in colder ambient temperatures and on colder subjects/patients. Potential Limitations The order of conditions followed a modified balanced design with spontaneous rewarming being conducted first; this is consistent with our previous studies.15,20,21,41 The shivering stimulus is maximal in this condition (no skin warming occurs) and thus would require the maximum dose of meperidine. Since, we wanted to standardize meperidine dosing for all conditions, the dosing schedule from spontaneous warming was used for both active warming conditions. This design is unlikely to affect our conclusions. Six subjects participated in this study in accordance with our power calculations and standard procedures in our laboratory. The lack of significant difference between FAW and EHP warming is likely not due to a lack of power, rather it is because there are likely no clinical/practical differences. It was not ethically possible to make subjects severely hypothermic (i.e., Tco < 28°C). However, our shivering-inhibition protocol has been used in the past to represent cold patients who are not shivering.15,20,21,29,41,43 Thus, we feel these results are qualitatively valid for any cold, but non-shivering patients. CONCLUSIONS The novel electric heat pad system rewarmed cold subjects at a similar rate to a FAW system which is commonly used in US military field hospitals for hypothermic patients. Although the FAW heater provides more heat, much of this heat is either lost from the delivery hose and the top of the blanket, or delivered to areas that are less efficient for heat transfer to the body core (e.g., below the waist). If the EHP system could be adapted to provide similar warming power with a portable battery system, this system could be a viable alternative, or adjunct, to the current forced-air rewarming system now used in US military field hospitals. Further studies, with larger subject groups and/or in prospective studies of colder patients, would improve our ability to fully gauge the efficacy of this portable warming system. FUNDING Gentherm Inc.; Natural Sciences and Engineering Research Council (NSERC) of Canada. CONFLICT OF INTEREST This study was conducted under a contract with Gentherm Inc. None of the authors have any ongoing financial support from the contractor. The views expressed are solely those of the authors and do not reflect the official policy or position of the US Army, US Navy, US Air Force, the Department of Defense, or the US Government. References 1. Arthurs Z , Cuadrado D , Beekley A , et al. : The impact of hypothermia on trauma care at the 31st combat support hospital . Am J Surg 2006 ; 191 ( 5 ): 610 – 614 . Google Scholar Crossref Search ADS PubMed WorldCat 2. Bennett BL , Holcomb JB : Battlefield trauma-induced hypothermia: transitioning the preferred method of casualty rewarming . Wilderness Environ Med 2017 ; 28 ( 2s ): S82 – s89 . Google Scholar Crossref Search ADS PubMed WorldCat 3. Jurkovich GJ , Greiser WB , Luterman A , et al. : Hypothermia in trauma victims: an ominous predictor of survival . J Trauma 1987 ; 27 : 1019 – 1024 . 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TI - Comparison of Electric Resistive Heating Pads and Forced-Air Warming for Pre-hospital Warming of Non-shivering Hypothermic Subjects
JF - Military Medicine
DO - 10.1093/milmed/usz164
DA - 2020-02-13
UR - https://www.deepdyve.com/lp/oxford-university-press/comparison-of-electric-resistive-heating-pads-and-forced-air-warming-2FKeZx0Os5
SP - e154
VL - 185
IS - 1-2
DP - DeepDyve
ER -