The effect of spontaneous alterations in brain temperature on outcome: a prospective observational cohort study in patients with severe traumatic brain injury.
ABSTRACT There are few prospective studies reporting the effect of spontaneous temperature changes on outcome after severe traumatic brain injury (TBI). Where studies have been conducted, results are based on systemic rather than brain temperature per se. However, body temperature is not a reliable surrogate for brain temperature. Consequently, the effect of brain temperature changes on outcome in the acute phase after TBI is not clear. Continuous intraparenchymal brain temperature was measured in consecutive admissions of severe TBI patients during the course of the first 5 days of admission to the intensive care unit (ICU). Patients received minimal temperature altering therapy during their ICU stay. Logistic regression was used to explore the relationship between the initial, the 24-h mean, and the 48-h mean brain temperature with outcome for mortality at 30 days and outcome at 3 months. Multifactorial analysis was performed to account for potential confounders. At the 24-h time point, brain temperature within the range of 36.5°C to 38°C was associated with a lower probability of death (10-20%). Brain temperature outside of this range was associated with a higher probability of death and poor 3-month neurological outcome. After adjusting for other predictors of outcome, low brain temperature was independently associated with a worse outcome. Lower brain temperatures (below 37°C) are independently associated with a higher mortality rate after severe TBI. The results suggest that, contrary to current opinion, temperatures within the normal to moderate fever range during the acute post-TBI period do not impose an additional risk for a poor outcome after severe TBI.
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ABSTRACT: Currently, there is very limited ability to measure the temperature of the brain, but a direct technique for its estimation in vivo could improve the detection of patients at risk of temperature-related brain damage, help in the diagnosis of stroke and tumour, and provide useful information on the mechanisms of thermoregulation of the brain. In this article, new calibrations in vitro of MRS thermometry using temperature-stabilised reference phantoms are reported. The phantoms comprise two concentric glass spheres: the inner sphere contains the phantom material to be measured by MRS, and the outer sphere contains a substance with a known temperature stable to within 0.2 °C. The substances were freezing organic fixed-point compounds (diphenyl ether and ethylene carbonate, freezing at 26.3 and 35.8 °C, respectively) or temperature-controlled circulating water. The phantom temperature was continuously monitored with a fluoroptic probe calibrated at the National Physical Laboratory with traceability to the International Temperature Scale 1990 (ITS-90). The MRS temperature calibration was obtained by measuring the chemical shift of water relative to N-acetylaspartate (NAA) in a single voxel as a function of temperature using a 1.5-T Philips Intera scanner. Measurements were made for several phantom materials to assess the effect of tissue composition on the water-NAA chemical shift against temperature calibration. The phantom mixtures contained 25 mm of NAA buffered to pH 6.5 or 7.5 and several ionic salts or bovine serum albumin (BSA). Spectra were acquired from 25 to 45 °C. The correlation between frequency differences and phantom temperature was very linear with small residuals. However, the linear fitting parameters varied with ionic composition and BSA concentration. The 'apparent' temperature (calibrated using the water-NAA frequency differences) decreased by approximately 1 °C for every 100 mm increase in ionic concentration and increased proportionally to the concentration of BSA. Copyright © 2012 John Wiley & Sons, Ltd.NMR in Biomedicine 09/2012; · 3.45 Impact Factor