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a patient’s circulation. Using the emergent flow with iced NS of the thermocouples and the data acquisition system was
produced statistically significant differences in battery life and 0.9°C and 1°C, respectively, which may explain some of the
mean temperatures (p < .001). This testing scheme evaluated differences in temperature. However, the same thermocouples
the warming ability of the different devices under the most and data acquisition system were used for the entire study, so
extreme conditions possible—very high flows combined with any variation in measurement was consistent throughout the
very cold fluids. These are conditions that may be encountered evaluation.
in prehospital and austere environments due to use in cold
weather conditions and/or blood administration. As shown in Conclusions
Table 3, the Buddy Liter had the longest battery life but also
produced the lowest temperatures. Conversely, the M Warmer Although none of the devices warmed fluids to normal body
had the shortest battery life but was much more effective at temperature (37°C), likely due to the high flows used, the M
warming the cold fluid. There was an inverse relationship be- Warmer was the only warmer tested that heated NS and PR-
tween battery life and warming ability under this condition. BCs to ≥32°C and PRBCs to ≥35°C more than 80% of the time
Similar results were shown in a study by Lehavi et al. with the at the emergent flow. The M Warmer and, in some cases, the

Buddy Lite fluid warmer. 14 Thermal Angel performed better at the higher flows, whereas
the Buddy Liter and Buddy Lite did not. Altitude appeared to
We chose the thresholds for the percentage of time that each have a small effect on the output temperatures in some testing
device heated fluid to ≥32°C and ≥35°C based on work by scenarios, but the differences were not clinically important.
Jurkovich et al. and Dubick et al. 12,16 The authors reported Future evaluation of the devices at altitude, within the doc-

a 40% mortality in trauma patients if core temperature was umented operational flow range for each device, may show
<34°C, 69% if core temperature was <33°C, and 100% if core more accurate warming differences. Future studies should
temperature was <32°C. Based on these data, the ideal goal for evaluate presence of hemolysis created by infusing PRBCs un-
fluid warmers should be to deliver fluid temperatures >34°C; der pressure through the warming devices.
therefore, we chose the threshold of ≥35°C. The M Warmer
was the only device we tested that was able to reach this Disclosure
threshold ≥80% of the time at the emergent flow using both The authors have no financial relationships related to this ar-
NS and PRBCs, which were the most challenging conditions. ticle to disclose.
This is an important finding in that core body temperature
decreases approximately 0.25°C for every unit of cold PRBCs Conflicts of Interest
and 1L of ambient temperature fluids administered, and main- The fluid warming devices evaluated in the study were pur-
taining/increasing core body temperature is an important con- chased with funding provided by the United States Air Force
sideration with fluid administration. We chose the threshold Research Laboratory. The authors have not relationships to
17
of ≥32°C as the absolute acceptable minimum for two reasons: disclose with the manufacturers or sellers of the devices.
core temperature <32°C is when shivering, the human body’s
mechanism for raising core temperature, ceases. 18,19 Addition- Funding
ally the reported mortality rate below this threshold is 100%. This work was funded by the United States Air Force Re-
The Buddy Liter and Buddy Lite failed to reach this threshold search Laboratory Basic Cooperative agreement, Task order
using NS at the emergent flow and reached it <15% of the time #FA8650-16-2-6G10.
using PRBCs at the emergent flow (Figure 4).
Author Contributions
Temperatures produced by the warmers using the nonemergent DR, RB, and MP developed the study concept. DR and RB
flows of 125mL/h were lower than expected, especially when created the proposal and study protocol. TB and JF completed
warming cold PRBCs. This can be attributed to the slow flow the study procedures and collected data. DR, RB, and TB ana-
(~2mL/min) allowing the fluid to cool toward room tempera- lyzed the data. TB wrote the first draft of the manuscript, and
ture after exiting the warmer while flowing through the exten- all authors read and approved the final manuscript.
sion tube to the postwarmer temperature measurement. The
extension tubing provided with the warmers was a minimum of References
15cm in length. The minimum reported tubing length to main- 1. Mitra B, Tullio F, Cameron PA, et al. Trauma patients with the
“triad of death.” Emerg Med J. 2012;29(8):622–625.
tain postwarmer fluid temperature >32°C is <10cm. Using the 2. Garcia GD, Modesto VL, Lee KT. Avoiding hypothermia in
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shortest IV tubing possible between the warmer and the patient trauma: use of the flawless heater pack, meal ready to eat, as a
may help to increase the delivered fluid temperature. field-expedient means of warming crystalloid fluid. Mil Med. 2000;
165(12):903–904.
3. Nolan JP, Dow AAC. The Level 1 fluid warmer. Anaesthesia. 1991;
Limitations 46(4):318–319.
4. Handrigan MT, Wright RO, Becker BM, et al. Factors and meth-
Per operator’s manuals, maximum output temperature for the odology in achieving ideal delivery temperatures for intravenous
devices vary: Buddy Liter and Buddy Lite were 38 ± 2°C; Ther- and lavage fluid in hypothermia. Am J Emerg Med. 1997;15(4):
mal Angel was 38 ± 3°C; and M Warmer was 39 ± 3°C. The 350–353.
devices lack a temperature readout so there was no way of 5. Bielman GJ, Blondet JJ, Nelson TR, et al. Nathens AB, Moore FA,
knowing the actual operating temperature for each test con- Rhee P, et al. Early hypothermia in severely injured trauma patients
dition. The emergent flow using a pressure bag was greater is a significant risk factor for multiple organ dysfunction syndrome
than the maximum flow published for each device, but this but not mortality. Ann Surg. 2009;249(5):845–850.
method of rapidly infusing fluids or PRBCs is common prac- 6. Durrer B, Brugger H, Syme D; International Commission for
Mountain Emergency Medicine. The medical on-site treatment of
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