Page 30 - JSOM Fall 2025

FIGURE 2 Fluid temperatures at the inlet and outlet of the risk increases with colder environmental temperatures, precise
intravenous tubing for the environmental temperature range of quantification is challenging, as the impact of colder intra-
–39°C to 20°C.
venous fluid on a patient depends on the administered fluid
volume and individual patient characteristics.

Figure 3b illustrates the relationship between heat loss and the
volumetric flow rate of the glycerol solution. Lower flow rates
result in increased heat loss, corroborating Bissonnette and
Paut’s findings. This creates a compounding effect: lower flow
rates extend the fluid’s exposure to environmental tempera-
ture, further decreasing fluid temperature and subsequently
reducing flow rates.

Mitigation Methods
In addition to temperature measurements, the volumetric flow Insulating IV Tubing
rate of the glycerol solution is monitored. Heat loss through One of the proposed methods of reducing heat loss through
the IV tubing is calculated using the mass flow rate of the the IV tubing is to add insulation to the IV tubing. The effect
glycerol solution, specific heat capacity, and temperature dif- of two parameters, the thickness of the insulation and the in-
ferentials between the inlet and outlet. Figure 3 depicts the sulation material, are investigated in this research study. Fig-
relationship between heat loss and environmental temperature ure 4 illustrates a sketch of IV tubing. In this figure, T and
m,i
across the range of 20°C to –39°C. T m,o represent the inlet and outlet fluid temperatures while
R condtubing , R conv1 , R conv2 refer to the thermal resistances due to
At an environmental temperature of 20°C, a heat loss of 40.9 conduction through the tubing, convection to the tubing, and
(SD 3.4) W is observed. This heat loss increases linearly with convection from the tubing to the environment, correspond-
·
decreasing environmental temperature, as illustrated in Fig- ingly. The mass flow rate is m and the environmental tempera-
ure 3a. The maximum heat loss of 168 (SD 17.4) W occurs ture is denoted with T . In the mathematical model, insulation
∞
at –39°C. Notably, the uncertainty in heat loss calculations materials are differentiated by their thermal conductivities.
increases at lower environmental temperatures, primarily due Both insulation thickness and insulation thermal conductivity
to increased uncertainty in temperature measurements. are variables within the thermal resistance of the insulation.
The significance of this increasing heat loss is evident in Figure The overall heat transfer coefficient takes into account the
2, which depicts the resulting outlet fluid temperatures. None convection and conduction resistances outlined above, and the
of the tested environmental temperatures yielded an outlet insulation as shown in Equation 1 as follows:
fluid temperature of 37°C or higher. The average outlet fluid R total = –1
temperature even reached a minimum of 9.1°C (SD 0.35°C) at mC 1n( T ∞ – T m,o ) = R cond 1 + R cond tubing + R cond insulation + R cond 2
·
p
an environmental temperature of –39°C. Considering healthy T ∞ – T m,i
core body temperature, transfusion administered through The thermal resistance of the insulation is calculated by using
the IV tubing at the tested environmental temperatures may Equation 2 as follows:
present a risk of hypothermia to trauma patients. While the ln(r /r )
2 1
R cond insulation =
2πLk
FIGURE 3 Heat loss through the intravenous tubing as a function
of (A) environment temperatures between –39°C and 20°C and (B) In that equation, the thickness of the insulation and the ther-
volumetric flowrate. mal conductivity of the insulation material are varied by se-
lecting different insulation materials.
(A)
Varying insulation thickness and the thermal conductivity of
the insulation material impact the total thermal resistance
which in turn affects the outlet fluid temperature of the mod-
eled IV tubing as shown in Equation 3 as follows:
– 1
·
T m,o = T ∞ – (T ∞ – T m,i )e mc R total
p
The outlet fluid temperature can be calculated as a function
of the overall heat transfer coefficient, given the known mass
flow rate (m) and mean inlet temperature T from experimen-
·
(B) m,i
tal testing. The thermal conductivity of the insulation mate-
rial is held constant at 0.0432 � , the thermal conductivity
m·K
of polyethylene foam. Polyethylene foam is selected due to its
common use for medical applications.
In Figure 5, the fluid temperature at the inlet of the IV tubing is
38°C (SD 3.3°C). Considering that fluids in blood transfusions
should ideally enter the patient’s body at a normal body tem-
perature of 37°C to prevent hypothermia, several observations

28 | JSOM Volume 25, Edition 3 / Fall 2025