Page 29 - JSOM Fall 2025

Two factors that affect the time it takes for fluid to flow temperature, one measures the IV tubing inlet temperature, two
through the IV tubing are flow rate and tubing length. Bisson- measure the outlet temperature, and two gauge the chamber’s
nette and Paut found that low fluid flow rates caused by low environmental temperature. The thermocouples have an SD
environmental temperature can aggravate heat loss through of 2.2°C or 2% accuracy between –50 and 99°C. A Transonic
IV tubing. Tubing length has effects on the time required for ME-5PXL clamp-on flowmeter (Transonic, Ithaca, NY) near
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fluid to flow through the IV tubing. Holt identifies IV tubing the IV tubing outlet measures the volumetric flow rate with SD
as a potential source of heat loss in his study which presents 8.0mL/min accuracy. To quantify the uncertainty associated
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evidence that indicates that shorter IV tubing at the output of with heat loss, the Kline-McClintock method is employed.
inline warming devices produces less heat loss. Greater heat
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loss could cause the fluid temperature to decrease from healthy Experimental measurements were conducted by systematically
temperatures to unhealthy. reducing the environmental chamber temperature in 3°C incre-
ments from 20°C to –39°C, while maintaining the inlet fluid
This research tests the dual hypothesis that (1) heat loss temperature at 38°C (SD 3.3°C). At each temperature setting,
through IV tubing in field blood transfusion kits increases sig- data were collected from all thermocouples and the flow meter.
nificantly with decreasing environmental temperatures, and The collected measurements included fluid temperatures at
(2) modifications to tubing insulation and length can effec- both the inlet and outlet of the IV tubing and the volumetric
tively reduce this heat loss. flow rate of the glycerol solution. Heat loss through the IV
tubing was then calculated by using the measured data.
Methods
According to Frinak et al., the use of 22% glycerol by weight
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A portable in vitro testing apparatus was developed to test in water with a specific gravity of 1.055 at 20°C is confirmed
the FWB transfusion kit in an environmental chamber with as an appropriate blood simulant that provides viscosity char-
an interior volume of 1.81m³. The chamber operates within acteristics similar to whole blood. Hence, a 22% by mass
a temperature range of –80 to 200°C and an altitude range aqueous glycerol solution is used in experiments to mimic the
of 244 to 30,480m. The testing apparatus was built using an fluid properties of FWB. This solution has a density of 1016–
aluminum framing rail and includes two reservoirs: one on 1020kg/m³ and a specific heat capacity of 3913–3914J/(kg∙K),
the ground and one at a desired height. The upper reservoir which means its density is 0.88%–3.78% lower and its spe-
maintains a constant pressure head for fluid flow through IV cific heat capacity is 0.67%–8.39% higher than FWB. Since
tubing using an overflow line that redirects excess fluid back glycerol has a higher density and lower specific heat capacity
to the lower reservoir. To keep the fluid level steady in the up- than water, increasing the glycerol percentage would further
per reservoir, a pump transfers excess fluid from the lower res- align the solution’s properties with those of FWB.
ervoir back to the upper one. An acrylic platform supports the
insulated upper reservoir, which contains an immersion heater Results
to control the fluid temperature at the IV tubing’s inlet to 38°C
(SD 3.3°C), simulating healthy FWB temperature for trauma Heat Loss Analysis
patients. The IV tubing runs from the bottom of the insulated Inlet and outlet fluid temperatures are measured using the
reservoir to a collection reservoir at the bottom of the frame. thermocouples located at the inlet and outlet of the IV tubing
The height differential between the outlet of the IV tubing and component of the FWB transfusion kit. During experiments,
the overflow is 440mm. the temperature within the environmental chamber is system-
atically reduced by 3°C from the first measurement starting at
The field FWB transfusion kits have several components in- 20°C to a final one at –39°C. Based on the cold weather test-
cluding a 450mL blood collection bag, IV tubing, anticoagu- ing standards outlined in the U.S. Army Test and Evaluation
lant citrate phosphate dextrose solution, safety IV catheters, Command (ATEC), MIL-STD-810H, which are used to qual-
needle port, etc. The Fresh Whole Blood Recipient Set (Safe- ify medical equipment for arctic deployment, the lower tem-
guard Medical, Huntersville, NC), purchased from the man- perature limit was chosen as –39°C. The upper limit of 20°C
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ufacturer) was used in our testing protocol. The IV tubing set serves as a control. The temperature of the fluid at the inlet of
“Y-type” with a filter, shown in the middle of Figure 1, is the the IV tubing is 38°C (SD 3.3°C). The measurements from the
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focus of this study and the length of the tubing is 203cm. eight thermocouples and ultrasonic flowmeter are recorded at
each setting of the environmental temperature. Figure 2 pres-
ents the thermocouple measurements of fluid temperatures at
FIGURE 1 Testing apparatus.
the IV tubing inlet and outlet across the environmental tem-
perature range of –39°C to 20°C.
Figure 2 illustrates a significant temperature drop in the glyc-
erol solution from 39.2 to 34.1°C, even at an environmental
temperature of 20°C. The temperature differential between the
inlet and outlet increases linearly as the environmental tem-
perature decreases. At 0°C, a 30% temperature reduction is
observed. When the environmental temperature decreases to
–39°C, the outlet temperature of the glycerol solution drops
to 9.1°C (SD 0.35°C), representing a 75.7% decrease. While
The testing apparatus uses eight K-type thermocouples and an glycerol solution can still be delivered through the IV tubing at
ultrasonic flowmeter to measure temperatures and flow rates. –39°C, this substantial temperature reduction may pose risks
Three thermocouples monitor the insulated reservoir’s fluid to the patient’s core body temperature.

Mitigating FWB Heat Loss During Austere Transfusions | 27