Iwata, S; (2014) Brain temperature, perfusion and metabolism under thermo-neutral condition and with induced hypothermia. Doctoral thesis , UCL (University College London).

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Abstract

Background: Therapeutic hypothermia following perinatal hypoxia-ischaemia improves survival and neurological functioning at 18 months of age. Precise brain temperature control commenced shortly after birth may improve the benefit. Aims: The aim of this thesis was (i) to clarify associations between regional brain temperatures, body weight, ambient temperature, cerebral perfusion and oxygen metabolism under normothermia/hypothermia; and (ii) to develop safe/reliable cooling device for pre-hospital cooling. Methods: 1. Brain temperatures were monitored in 14 anaesthetised newborn piglets with normothermia, whole-body cooling and selective-head cooling. 2. The rectal temperature (Trectal), non-invasive (zero-heat-flux) brain temperatures, relative superior vena-cava (rSVC) flow (echocardiography) to the brain weight, and the cerebral metabolic rate of oxygen (near-infrared spectroscopy) relative to rSVC flow (CMRO2 index), were obtained in 32 newborn infants. 3. Eleven anaesthetised newborn piglets were cooled to 33-34ºC 2-26h after hypoxia-ischaemia using either water bottles or phase-changing material (PCM; a heat buffer at 32ºC). Results: 1. In piglet models, brain temperatures were positively correlated with the body weight under normothermia, whole-body cooling and selective-head cooling, the influence of which was prominent under selective-head cooling. 2. In normothermic infants, rSVC flow was positively correlated with CMRO2 index. The rSVC flow, but not CMRO2 index, was positively associated with superficial brain temperatures. Ambient temperatures were negatively associated with temperature gradients between the scalp surface and body core. 3. In piglet models, therapeutic hypothermia was induced and maintained with both water bottles and PCM; the latter provided more stable cooling within the target range. Conclusions: Brain cooling was more efficient with lower body weight due to greater surface-to-volume ratios; body-size adjustment may be required to accomplish consistent regional temperatures. In healthy newborn infants, cerebral perfusion and ambient temperature, but not cerebral metabolism, were associated with brain temperatures. PCM provided stable hypothermia, which may substitute for electronic cooling devices during transportation.

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