Page 21 - JSOM Spring 2021

units of PRBCs infused simultaneously at the emergent flow The measurements of interest for this study were mean tem-
instead of 1L. These tests were done at ground level and at perature, time to reach mean temperature, change in tempera-
8,000- and 16,000-ft simulated altitude in an altitude cham- ture from inlet to outlet, proportion of time the temperature
ber. The ambient temperature inside the altitude chamber was was ≥32°C and ≥35°C, and battery life.
maintained at 24°C to approximate room temperature in our
laboratory (23.9 ± 0.4°C) in which ground level testing was Statistical Analysis
completed. Two of each device were used in the study and two
tests with each device were completed at each condition. All Temperature differences at specified conditions, NS and
devices were operated on battery power, and the Buddy Liter PRBCs, emergent flow and nonemergent flow rate, and alti-
and Buddy Lite AC were also operated on alternating current tude differences were compared for each device. Mean and SD
(AC) power. The Thermal Angel and M Warmer do not offer were used to summarize data. Comparisons were made using
the option of operating from AC power. the general linear model univariate analysis to create contrasts
that tested specified custom hypotheses. This method was
Battery life was measured under two conditions with each de- preferred to avoid testing all pairwise comparisons, as com-
vice: nonemergent flow of 125mL/h using room temperature parisons were set a priori. Post hoc analysis was completed
NS as described above and using a pressure bag inflated to by comparing the change in temperature prewarmer to post-
300mmHg using iced NS. Each device was operated until the warmer, and time to reach mean temperature was created with
low battery indicator was activated and measured temperature each device at all conditions using the Student t-test. Devices
decreased by >1°C. were compared to each other at all conditions and compared
to themselves using altitude as the independent variable, to
Devices were set up per manufacturer’s instructions. The in- determine if altitude had an effect on device performance. Sta-
fusion pump had preventive maintenance and calibration per- tistical significance was determined at α = .05, two-tailed, and
formed before the study began. Device batteries were charged SPSS Statistics 25 was used for data analysis.
®
for a minimum of 24 hours before use. Standard IV tubing was
used for all nonemergent flows with the infusion pump and Results
pressure bag, and standard blood tubing was used for testing
with PRBCs. A three-way stopcock was placed at the entrance Table 1 shows the physical and operational characteristics of
to and directly after the heater unit of the device being tested, the devices. There was no distinct size or weight advantage of
and a J-type thermocouple (Omega Engineering, https://www one device over the others. The stated maximum flows were
.omega.com/en-us/thermocouple-types) was placed in each of much higher for the Thermal Angel and M Warmer. None of
the stopcocks’ open port and sealed with silicone. The thermo- the devices were able to heat NS or cold PRBCs to a mean
couples were attached to a data acquisition system (National temperature equal to normal human body temperature (37°C)
Instruments, https://www.ni.com/en-us.html), and tempera- at either flow tested. Analysis of the differences in overall tem-
ture data were continuously recorded at 1-second intervals. perature profiles produced by the devices at all conditions was
The Buddy Liter and Buddy Lite use disposable cartridges in- statistically significant (p < .01) except for the Buddy Liter
side the reusable heater unit, and the Thermal Angel and M versus the Buddy Lite at ground level on AC power, at the
Warmer use disposable heater units. All the cartridges/heater nonemergent flow using room temperature NS (p = .42), and
units except the Thermal Angel had tubing before and after the same devices at 16,000-ft altitude on AC power at the
the heater units. These are the points at which the preheater nonemergent flow, using cold PRBCs (p = .24). Figure 2 shows
and postheater temperatures were measured. A 9-inch IV ex- the mean (SD) temperatures for all devices on battery power.
tension tubing supplied with the Thermal Angel was placed The M Warmer produced the highest mean temperatures at
on the output side of the heater so that measurements could the emergent flow using NS and cold PRBCs. Differences in
be taken in the same location with all devices and would sim- mean temperature between devices at the nonemergent flow
ulate the temperature at which the warmed fluid would enter using both NS and PRBCs were within 3°C at each of the
a patient’s circulation. After priming, each warmer was turned altitude conditions, although the temperatures were some-
on, and fluid flow and temperature measurements were started what lower at altitude compared to ground level. Figure 3
simultaneously. shows the mean (SD) temperatures for the Buddy Liter and

TABLE 1 Physical and Operational Characteristics for Each Fluid Warming Device
Buddy Liter Buddy Lite AC ™ Thermal Angel M Warmer
Dimensions (in) (L ´ W ´ H)
Battery housing 4.92 ´ 3.33 ´ 1.36 7.26 ´ 3.33 ´ 1.36 6.4 ´ 3.2 ´ 1.7 7.09 ´ 3.54 ´ 1.38
Heater unit 5.2 ´ 1.5 ´ 0.87 15.2x 1.5 ´ 0.87 9.0 ´ 2.9 ´ 0.95 3.94 ´ 1.97 ´ 0.79
Weight (lb)
Battery and heater unit 1.09 1.46 1.83 1.68
AC power supply 2.64 2.64 N/A 0.55
Power requirement AC, battery AC, battery Battery Battery
Temperature set point (°C) 38 ± 2 38 ± 2 38 ± 3 39 ± 3
High temperature alarm Yes Yes LED only LED only
Low temperature/no heat alarm Yes Yes LED only LED only
30 @ 20°C 80 @ 20°C
Maximum flow rate (mL/min) 150 @ 20°C 150 @ 4°C – 37°C
20 @ 10°C 50 @ 10°C
L ´ W ´ H = length ´ width ´ height, LED = light-emitting diode.

Fluid Warming Technology Performance | 19