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Global Health Technologies

Undergraduate Lightning Talks

Thermal Optimization of NeoWarm, an Insulated Infant Carrier to Augment Kangaroo Mother Care (KMC) and Combat Neonatal Hypothermia

Saturday, October 26, 2024
12:35 PM – 12:40 PM EST
Location: Room 342

Introduction:  Premature birth, and the complications that come with it, are the leading cause of death among children under five across the globe. One of the leading contributors to neonatal morbidity and mortality is hypothermia, as newborns do not possess the ability to regulate their own temperature. Mortality due to premature birth is especially prevalent in low- and middle-income countries (LMICs) due to a lack of available resources such as incubators and radiant warmers which are proven technological solutions to prevent neonatal hypothermia.

Kangaroo mother care (KMC) is a proven intervention for combating neonatal hypothermia. KMC involves the caregiver swaddling the newborn to their chest, bare-chested, thereby transferring heat to the newborn. While effective, KMC is a physically demanding task for the caregiver and makes it difficult to monitor the baby’s vital signs as the baby is swaddled tightly to the caregiver.

NeoWarm is a novel biomedical device designed to help prevent neonatal hypothermia in LMICs. NeoWarm is an integrated thermal care unit that can provide thermal support in between KMC sessions when the caregiver requires a break to care for themselves and monitor the neonate’s vitals (heart rate, respiration, and blood oxygen). NeoWarm’s heating capabilities have been previously validated on tissue phantoms and in vivo studies in hypothermic piglets. The goal of our current study is to refine NeoWarm’s core thermal management system through various insulation and heating element configurations.

Materials and

Methods:  A 1 L tissue phantom filled with water was placed inside NeoWarm to simulate a 1 kg, 27-week gestational age, premature newborn. Twelve fabric heating pads (grouped in 4 sets of 3) were integrated within NeoWarm’s panels (Fig. 1). The heating pads were powered by 15 V from a benchtop power supply and controlled by an ATmega2560 microcontroller through separate bipolar junction transistors (one for each set of 3 pads). The temperature of the heating pads and internal temperature of the tissue phantom were monitored at least every 10 milliseconds using 10 kΩ negative temperature coefficient bead thermistors connected to the microcontroller. The temperature of the internal fabric (the fabric in contact with the tissue phantom) was regulated to 38 °C (recommended bath water temperature for newborns) to warm the phantom within the target range of 36.5-37.5 °C (normal body temperature).

The tissue phantom was heated from 32 °C (severely hypothermic) until its temperature did not vary by more than 0.1 °C for 1 hour. The final temperature of the tissue phantom, frequency the heaters were on, warming rate, thermal time constant, average temperature of the heaters, and average temperature of the internal fabric were calculated.

To evaluate the effect of insulation on the warming profile, 24.4 g of fleece or synthetic down were evenly distributed across NeoWarm, and the experiment was repeated. To evaluate the effect of the number of heating pads on the warming profile, the number of heating pads were doubled to 8 groups of 3 (“double-layer”).

Results, Conclusions, and Discussions: When modified with synthetic down, NeoWarm achieved warming rates up to 0.92 °C/hr, while fleece only produced a maximum rate of 0.66 °C/hr. Tests with synthetic down required the heating elements to be on around 18% of the time as opposed to 22% with fleece. The tissue phantom also reached its target temperature of 37 °C with all synthetic down trials, while only achieving the target temperature for half the tests with fleece (Fig. 2). It can thus be concluded that synthetic down outperforms fleece as an insulation material for NeoWarm. However, the temperature of internal fabric in contact with the phantom was on average 39.5 °C in both fleece and synthetic down trials which is 1.5 °C higher the set point of 38 °C, and above recommended bath water temperature for newborns. This overtemperature did not occur in our previous studies in hypothermic piglets and would need to be corrected before trials in human can be safely attempted.

A double layer of heating elements required the elements to be on 10% of the time where a single layer of elements was on 20% of the time. A double layer of heating elements required a maximum current of 4.6 A where a single layer required 2.3 A. However, given a double-layer of heating elements were on for half the time of the single layer, the average power consumed in both configurations is roughly equal.

In summary, NeoWarm presents a potential, effective solution to neonatal hypothermia in LMICs when incubators are not available and KMC is infeasible, due to caregivers needing a break to care for themselves. The tests conducted in the present work to optimize heating functionality show synthetic down to be the optimum insulation material to aid in heat retention. However, more research is required to determine the optimal density of synthetic down to maximize thermal performance and comfortability. And more tests are needed to avoid overheating the internal fabric of the device before trials in human can be safely attempted.

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