Page 16 - JSOM Winter 2024

Methods FIGURE 1 Temperature trend in trial 3 versus time.
This study was determined to be basic science research and
deemed exempt from institutional review board (IRB)-
approval. All trials were completed on the Okinawa main is-
land. The trials were completed in the same physical locations
outdoors, with approximately 4 hours of direct sunlight daily.
A commercially available 45-liter capacity Yeti cooler (Yeti
Holdings, Austin, TX) was used for each trial. Four 500-mL
saline bags were precooled to 1–6°C and placed in the cooler.
Bags of ice were purchased from the local economy via a con-
venience store (Family Mart) and weighed before being placed
in the cooler. Two thermometers were placed in the cooler
adjacent to each saline bag to measure cooler temperature
throughout each trial. One thermometer allowed for commu-
nication via Bluetooth connection and the other continuously
recorded and stored the data, which we were able to download large-scale combat operations in distributed maritime environ-
after the trial. At t=0, the saline bags, thermometer, and ice ments as well as when healthcare is employed in support of
were placed into the cooler and closed. irregular/unconventional warfare. As war has always been the
mother of invention, it follows that purely civilian humani-
Each trial lasted until t=168 hours. Four separate trials, with tarian applications abound throughout much of the inhabited
14, 16.7, 15.7, and 7kg of ice, were completed. The ice was world.
held at a temperature of –20°C before commercial purchase.
Approximately 20 minutes elapsed between the removal of the Blood banking requires strict environmental control to en-
ice and its placement in the cooler. Temperature was recorded sure safe transfusion in critically ill patients. One aspect of
once per minute for the duration of each trial. The weight of this study’s development was the method to continually mon-
ice varied based on the amount that could be placed within itor the temperature. Two separate off-the-shelf thermometers
the cooler. Different shapes of ice were available commercially, were used, with adequate battery life and one with the ability
which allowed different maximum amounts of ice. Ice in trial to transmit data to smartphones via Bluetooth connectivity. In
4 was approximately half the weight of the ice in the full con- this study, while a thermometer connected to a smartphone via
tainer (7kg). a wired connection was used to collect minute-by-minute tem-
perature data, a wireless temperature probe could likely have
The primary outcome was hours of adequate refrigeration. been used as well and represents a potential area for future
Adequate refrigeration is based on the FDA guidelines on study. Toward the end of each trial, the Bluetooth thermometer
blood storage temperature, between 1 and 6°C. would not always connect, and we suspected that this was due
6
to the influence of liquid water surrounding the thermometer
decreasing the transmission of electromagnetic waves. When
Results
the thermometer would connect to Bluetooth, the authors
All four trials were completed in 168 hours. Trial 3 was con- were very satisfied with the ability to have recorded tempera-
ducted during Typhoon (tropical cyclone) Khanun, and the ex- tures and assess them via smartphones, in a way that could be
posed coolers sustained category 4 winds. Besides the storm, easily used in austere settings.
there were no significant adverse events during the trial. Trials
1–3 achieved the goal temperature in >142 hours, while trial The comparatively low cost of the passive coolers (US$200–
4, with 7 kg of ice, achieved it in 78 hours (Table 1). A repre- 300) compared with active coolers (US$1,000–10,000) allows
sentative graph of the temperature trends from trial 3 is shown for a more economical approach. The simplicity of the passive
in Figure 1. The temperature remained above 1°C for all trials. cooler may also enhance reliability in austere environments.
The active coolers use both batteries that require charging and
refrigeration systems, which can fail. While not assessed in the
Discussion
study, the authors suspect that future evaluations may demon-
This brief evaluation demonstrated the reliability of commer- strate a reliability benefit of passive coolers when compared
cially available passive refrigeration for prolonged blood stor- with active refrigeration.
age in a subtropical environment. Logistic assurance of blood
products is an enabling capability that may offer enhanced The benefit of blood storage in these coolers may extend to
survival in austere, resource-limited, and disaster-affected a variety of settings. The capability to store blood for days
environments. Such capability is particularly poignant when may be impactful in NATO doctrinal Role 2 facilities as well
considering geographically disparate trauma care implied by as disaster settings where prolonged care is not anticipated.
TABLE 1 Experimental Conditions
Trial 1 Trial 2 Trial 3 Trial 4
Start time; date 1800; 24 Jul 2023 1811; 28 Jul 2023 1100; 08 Aug 2023 2023; 16 Aug 2023
Ambient temperature range, °C 28–33 28–33 27–32 28–33
Initial ice weight, kg 14 16.7 15.7 7
Volume of saline 4×500mL 4×500mL 4×500mL 4×500mL
Time at 1–6°C, hr 158 144 142 78

14 | JSOM Volume 24, Edition 4 / Winter 2024