Intracranial temperature recordings in human subjects. The contribution of the neurosurgeon to thermal physiology

Abstract

Experimental research of the late 1980s and the results of recent clinical trials have shown that small changes in brain temperature have a remarkable effect on the extent of neurological damage following injury and ischaemic insult. The potential benefits and problems associated with mild neuroprotective hypothermia have given the rationale for monitoring the temperature of its target organ, the brain. Though most of these studies were carried out in unconscious patients and those with CNS damage, they have also yielded some information pertinent to major questions on cerebral thermoregulation. 1. Brain temperature was higher than trunk core temperature (usually measured in the rectum) and this difference reached as much as 1–2.3°C in unconscious patients. The difference between the brain and trunk core temperature (measured in the oesophagus) did not change between states of normothermia and fever. 2. Temperature gradients may form within the brain. The gradients increase during brain ischaemia, during functional hyperthermia but not during fever. 3. Tympanic temperature ( T ty) has a causal relationship to brain temperature and in most situations is closest to it from among the externally available core temperatures. Nonetheless, T ty was found to be a worse index of brain temperature in patients with brain damage/ischaemia and the relation T ty– T br shows individual differences due to anatomical factors. 4. Attempts to reduce brain temperature selectively have proved unsuccessful in normothermic subjects and in patients during fever. Nevertheless, it has been shown that local intracranial temperature may be brought to a level below that of the trunk temperature in conscious, neurologically intact patients, during mild functional hyperthermia. This result shows that selective brain cooling is at least not improbable in humans. Recent clinical reports show that brain temperature is an important prognostic factor in brain injury/ischaemia. It is likely that it will be recorded more often in neurosurgical intensive care in the future. Closer cooperation between neurosurgeons and thermal physiologists would help to exploit unique experimental situations where direct recordings of brain temperature in neurosurgical patients is possible.