Significant head cooling can be achieved while maintaining normothermia in the newborn piglet

Abstract

Background: Hypothermia has been shown to be neuroprotective in animal models of hypoxia-ischaemia. It is currently being evaluated as a potentially therapeutic option in the management of neonatal hypoxic-ischaemic encephalopathy. However, significant hypothermia has adverse systemic effects. It has also recently been found that the stress of being cold can abolish the neuroprotective effects of hypothermia. It is hypothesised that selective head cooling (SHC) while maintaining normal core temperature would enable local hypothermic neuroprotection while limiting the stress and side effects of hypothermia.

Objective: To determine whether it is possible to induce moderate cerebral hypothermia in the deep brain of the piglet while maintaining the body at normothermia (39°C).

Methods: Six piglets (<48 hours old) were anaesthetised, and temperature probes inserted into the brain. Temperature was measured at different depths from the brain surface (21 mm (T_{deep brain}) to 7 mm (T_{superficial brain})). After a 45 minute global hypoxic-ischaemic insult, each piglet was head cooled for seven hours using a cap circulated with cold water (median 8.9°C (interquartile range 7.5–14)) wrapped around the head. Radiant overhead heating was used to warm the body during cooling.

Results: During SHC it was possible to cool the brain while maintaining a normal core temperature. The mean (SD) T_{deep brain} during the seven hour cooling period was 31.1 (4.9)°C while T_rectal remained stable at 38.8 (0.4)°C. The mean T_rectal−T_{deep brain} difference throughout the cooling period was 9.8 (6.1)°C. The mean T_skin required was 40.8 (1.1)°C. There was no evidence of skin damage secondary to these skin temperatures. During cooling only one piglet shivered.

Conclusions: It is possible to maintain systemic normothermia in piglets while significantly cooling the deeper structures of the brain. This method of cooling may further limit the side effects associated with systemic hypothermia and be feasible for premature infants.