By Alexander E. Merkler, MD, MS
Assistant Professor of Neurology and Neuroscience, Weill Cornell Medical College, and Assistant Attending Neurologist, New York-Presbyterian Hospital
SYNOPSIS: Variations in brain temperature appear to be a normal physiological variable. An absence of brain temperature variation may be a novel predictor of mortality among patients with brain injury.
SOURCE: Rzechorzek NM, Thrippleton MJ, Chappell FM, et al. A daily temperature rhythm in the human brain predicts survival after brain injury. Brain 2022;145:2031-2048.
Identifying strategies to improve outcomes among patients with brain injury is critically important. Targeted temperature management (TTM) remains the mainstay of therapy for patients with cardiac arrest and hypoxic-ischemic brain injury, although recent trial data raise doubt of its neuroprotectant effect.1 Moreover, as this article by Rzechorzek et al points out, there is a lack of information regarding the relationship between brain and body temperature. We have been cooling patients in the hope of cooling the brain and preserving brain function, yet we know little about brain temperature.
In this current study, Rzechorzek et al sought to determine the clinical relevance of brain temperature in healthy and brain-injured patients. The study identified 114 patients recruited to the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) High Resolution Intensive Care Unit Sub-Study who had direct brain temperature measurements using an intracranial monitor. The study also enrolled 40 healthy adults (20 males and 20 females, aged 20-40 years) in whom they evaluated brain temperature using noninvasive magnetic resonance spectroscopy (MRS). These 40 patients underwent MRS imaging at various points during the day, throughout the year, and, for women, at different times of the menstrual cycle.
First, the study found that among healthy volunteers, brain temperature was on average 1°C to 3°C above core body temperature. This is of critical importance, since despite the use of invasive brain temperature recordings among brain-injured patients, clinicians currently do not know how to interpret these findings. Put simply, although clinicians record brain temperatures from severely brain-injured patients, these data are not clinically applicable given the lack of normative data. If these current findings are replicated, further studies could successfully interpret and incorporate brain temperatures in brain-injured patients.
Second, the study found that healthy volunteers have diurnal variations in brain temperature and that the lack of brain temperature variation was strongly associated with mortality among those patients with brain injury included in CENTER-TBI. The brain appears to need variation, and this finding is perhaps not surprising. Lack of variation or reactivity on electroencephalogram, lack of autoregulation using invasive neuromonitoring, and lack of differentiation on brain magnetic resonance imaging all are predictors of poor outcome among patients with brain injury. Now it seems the lack of brain temperature variation is another potential predictor of poor outcome.
COMMENTARY
Overall, this study adds to our growing understanding of the role of temperature in brain-injured patients. The article highlights the fact that our understanding of brain temperature is nominal at best. It justifiably casts doubt on the use of TTM, given the fact that variation of brain temperature appears to be normal and TTM works by eliminating such variation. Furthermore, brain temperature varies by sex, time of day, and hormonal status, and thus it may be imprudent to fail to use a personalized approach to cooling for neuroprotection.
REFERENCE
- Dankiewicz J, Cronberg T, Lilja G, et al. Hypothermia versus normothermia after out-of-hospital cardiac arrest. N Engl J Med 2021;384:2283-2294.
