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Cortical brain temperatures changes during whole body cooling of piglets

Presented at the Neonatal Society 2009 Autumn Meeting (programme).

Liu X, Hoque N, Chakkarapani E, Thoresen M

Child Health, University of Bristol, Bristol, UK

Introduction: Moderate whole body hypothermia (33.50C, HT) commenced within 6h of delivery and continued for 72h for term-born neonates is neuroprotective. Routine clinical care during HT treatment may increase the cortical brain temperature inadvertently with unchanged core temperature, thus reducing the therapeutic effect of HT. In humans with an exposed head there is a degree of “natural head cooling” resulting in the cortex being ~2°C colder than the deep brain.

Methods: Whole body cooling (Trectal =33.5°C) was induced using a servocontrolled “body wrap” circulated with water (“Criticool” MTRE) in 5 anaesthetised newborn piglets (1.7-2.2kg). A brain temperature probe recording at every 5mm depth was inserted parasagitally through a burrhole entering the cortex and basal ganglia at 0.4 and 2.5 cm depth respectively. The piglets were nursed in an open incubator (Giraffe Omnibed). The air temperatures were changed and also additional covers were added onto the pigs’ head (i.e the hood of the wrap or a cotton hat).

Results: Piglets’ brain cortex temperatures follow temperature changes in the wrap while the hood of the wrap covers the head. When the hood of the wrap was removed, the cortical brain temperature did not follow the water temperature changes in the wrap. Piglets wearing cotton hats had higher brain cortex temperatures than those not wearing a hat during HT (difference 2°C±0.2) and normothermia (NT) (difference 1°C±0.1). During NT increasing ambient temperature from 24-28°C by closing the incubator increased cortex temperature by 0.6-0.8°C without affecting Trectal.

Conclusion: Our observations in piglets suggest that babies undergoing total body HT should not have anything covering the head and the environmental temperature should not be high The practice of placing anything around the head (I,.e a hat) increases brain temperature and may reduce the benefit of HT.

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