Page 14 - JSOM Winter 2022

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(~110mL/min). When combined with a Blizzard Blanket, recommend the enFlow as the ideal fluid warmer with cer-
the Thermal Angel demonstrated effectiveness when infus- tainty. However, the authors extrapolate that saline and blood
ing 10°C Hextend and 4°C blood-shed at 150mL/min in a trials may yield similar warming outputs. A variety of blood
hemorrhagic swine model under simulated combat condi- products (LTOWB, PRBCs, and liquid plasma) are cooled to
tions. Despite a nadir core temperature dropping to 35.2°C 1–6°C in combat theaters, the enFlow is able to warm ice-
6
during the experiment, the Thermal Angel and Blizzard cold saline (5°C) to 37.1°C at 100mL/min. The Thermal An-
Blanket actively rewarmed swine to >37°C. 14 gel’s standard battery pack component is able to warm cold
blood to >35°C at 110mL/min, but its battery life has not been
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Time to Peak Heating, Maximum Flow Rates, and Battery tested. The Thermal Angel’s UB1 quick battery depletion lim-
Characteristics. No studies have directly measured time to its its use in a massive blood resuscitation.
peak heating. Maximum flow rates through a 14-gauge PIV
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pressurized system yields 296mL/min and 345mL/min. De- The enFlow demonstrates aluminum elution into IV fluids at
pending on the model, two different batteries exist with the varying concentrations dependent upon flow rates, type of
Thermal Angel. The UB1 (30 wh) offers a weight roughly one- crystalloid, and type of blood product. The FDA recommends
sixth of the standard battery and has a significantly smaller the maximum level of aluminum in IV nutrition to not exceed
3,4
profile. Reported discrepancies in average fluid output tem- 25 µg/L. Independent of flow rate, blood products demon-
peratures with cold isotonic solutions revealed the UB1 and a strated a lesser amount of aluminum elution when compared
standard battery pack perform differently. to crystalloids. Independent of flow rate, 0.9% saline demon-
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strated a considerably less aluminum elution compared to
4
Plasma-Lyte. A limitation to the research is that the primary
Discussion
flow rates analyzed (i.e., 2mL/min) may not be of practical
In battlefield operations, many factors predispose IV flu- clinical application during a resuscitation. Regardless of its
ids to cold temperatures, such as night operations, seasonal clinical applicability, the enFlow manufacturer is in the pro-
changes, aeromedical transport, and extremes in altitude. Un- cess of redesigning their cartridges to eliminate the aluminum
der these conditions, IV fluid warmers must perform reliably elution problem.
with ice-cold isotonic solutions at a range of flow rates. The
enFlow demonstrates effective warming capabilities across all Figure 5 is a concept map to assist medical personnel in their
studies. The Thermal Angel is capable of warming ice-cold decision-making process regarding battery-operated IV fluid
solutions, but not as well as the enFlow. In contrast, the Buddy warmers. Mission requirements are the central themes to the
Lite produced conflicting results, though most studies demon- decision-making process; medical personnel must clearly iden-
strate effective heating outcomes when limited to flow rates tify mission variables in order to mitigate potential negative
≤50mL/min. 7,13 impacts on patient care. Common mission variables include
the following: A/C power supply availability, evacuation times
Ideally, IV fluid warmer battery life should support aeromed- to the next echelon of care, likelihood for prolonged field care,
ical and ground casualty evacuation transport times, which and weight/space limitations. Consider employing risk miti-
vary greatly depending on such things as weather status, en- gation measures with the enFlow to reduce aluminum elution
emy presence, and location. The Thermal Angel’s UB1 (30 wh) exposure to the patient (shown in Figure 5).
depletes quickly with cold solutions and high flow rates; com-
paratively, the enFlow’s battery (66 wh) outlasts the Thermal FIGURE 5 Concept Map for IV Fluid Warmer Selection

Angel under similar conditions. The authors cannot conclude
whether the Thermal Angel’s standard battery outlasts the
newer UB1, because no experiments have compared the two.
The Buddy Lite’s battery (89 wh) life is sustainable, but its
heating element is not reliable with cold fluids at high flow
rates.

In terms of size and weight, the enFlow (3.04 lb) is larger and
weighs more than the Thermal Angel (2.16 lb) and the Buddy
Lite (1.69 lb). Despite these differences, the enFlow and its
accessories fit into a standardized combat medic M9 bag. For
medics that carry medical equipment, their decision to choose
a specific IV fluid warmer should depend on space limitations,
likelihood for prolonged field care, and access to durable items
unique to each fluid warmer (cartridges, tubing, etc.). Con-
versely, due to their ability to offload and stage equipment,
the enFlow may be most useful for aeromedical platforms and
FSEs. Nevertheless, aeromedical and FSE personnel should NS = normal saline; IVF = intravenous fluids; PRBC = packed red
consider space/weight limitations, transport times to the next blood cell; FFP = fresh frozen plasma.
echelon of care, and their ability to recharge batteries.
Conclusion
The enFlow may be the ideal fluid warmer for massive resus- FSEs are highly mobile teams that carry small, light, durable,
citation due to its ability to reach peak temperature faster, and battery-operated medical equipment in order to provide
maximal flow rates, and sustained battery life. The enFlow has DCS and DCR in remote locations that often lack standard
yet to trial blood, which makes it difficult for the authors to hospital utilities (electricity, heat, water, etc.). Battery-operated

12 | JSOM Volume 22, Edition 4 / Winter 2022