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Description
Abstract: Hyperthermia has been demonstrated to increase neuronal injury when present during or after an acute brain injury. The assumption that core temperature equals brain temperature exists. If the temperature of an injured brain is higher than core temperature, episodes of neural hyperthermia may go undetected. The objectives of this study were to (1) determine if differences exist between brain temperature and core temperature in subjects with acute neurological injuries in both normothermic and febrile states and (2) investigate the impact of brain and core temperatures on intracranial pressure (ICP) and cerebral perfusion pressure (CPP). The study was conducted through a retrospective chart audit of patients age 18 years or older admitted to a level I trauma center with a diagnosis of brain injury whose condition warranted placement of a pulmonary artery catheter (which measured core temperature) and an intraventricular catheter (which measured brain temperature). Thirty-one charts contained complete data; nine charts provided partial data. Mean brain temperature (100.8[degrees]F, SD = 0.69) was found to be significantly higher than mean core temperature (100.2[degrees]F, SD = 0.74; p = .00). Brain temperature means were hyperthermic ([greater than or equal to]100.9[degrees]F), while matching core temperatures were normothermic in almost one-third of the subjects. There was no significant difference found between hyperthermic ICP or CPP and normothermic ICP or CPP determined by brain or core temperature. No significant correlation was found between temperature and intracranial dynamics. Future research is needed with prospectively collected data of adequate sample size to continue to investigate the impact of core and brain temperature on the intracranial dynamics of ICP and CPP.
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Both animal models and human studies have demonstrated that hyperthermia, when present during or after a period of brain injury or ischemia, exacerbates the degree of resulting neuronal injury. Before the inception of technology to measure direct brain temperature, it had been assumed that core temperature was an accurate reflection of brain temperature. However, a systematic review of published studies examining brain and core temperatures found brain temperatures to be higher (Mcilvoy, 2004). The review examined studies of brain temperature and core temperature measured by direct contact with the brain or in any of the spaces surrounding the brain (excluding intraoperative measurements) and core temperatures (blood, rectal, bladder, and esophageal). All 12 studies that compared rectal temperature with brain temperature found brain temperature to be higher with mean differences of 0.3[degrees]C to 2.0[degrees]C (Henker, Brown, & Marion, 1998; Hirashima et al., 1998; Mariak, Jadeszko, Lewko, Lewkowski, & Lyson, 1998; Mellergard, 1994, 1995; Mellergard & Nordstrom, 1990, 1991; Schwab, Schwarz, Aschoff, Keller, & Hacke, 1998; Schwab, Spranger, Aschoff, Steiner, & Hacke, 1997; Soukup et al., 2002; Verlooy, Heytens, Veeckmans, & Selosse, 1995; Zauner et al., 1998). The five studies that used bladder temperature as a measure of core temperature found brain temperature higher by gradients of 0.5[degrees]C to 2.5[degrees]C (Henker et al., 1998; Schwab et al., 1998; Schwab et al., 1997; Sternau et al., 1991; Verlooy et al., 1995). Studies that compared bladder, rectal, and brain temperatures found bladder temperature to be the core temperature that was closest to brain temperature (Henker et al., 1998; Verlooy et al., 1995). Only one study used pulmonary artery temperature (considered the gold standard) as the core temperature measurement. This study also found mean brain temperatures higher than mean pulmonary artery temperatures by 0.3[degrees]C [+ or -] 0.3[degrees]C (Rossi, Zanier, Mauri, Columbo, & Stocchetti, 2001). Only three studies employed a t test to examine the differences between brain and core temperatures; all found statistical significance. The remaining 12 studies reported mean temperature only and made conclusions based on the degree to which they differed. If the temperature of an injured brain is higher than core temperature, episodes of neural hyperthermia may go undetected. However, in the human population, the degree of neural hyperthermia that might lead to further neurological injury has not been established. In determining the impact of brain temperature, the physiological effect of hyperthermia and the prevalence of hyperthermia in brain-injured patients must be considered. The purpose of this study was to examine the differences between core temperature and brain temperature using gold standard measurements by means of a retrospective chart audit of acutely brain injured patients. The physiological effect hyperthermia has on the brain is discussed, as well as the influence temperature has on the intracranial dynamics of intracranial pressure (ICP) and cerebral perfusion pressure (CPP).
Hyperthermia and Brain Injury
With an acute brain injury, secondary cellular brain damage occurs within minutes to days after the initial injury. A series of destructive cellular events transpire that either activates cascades that increase interneuronal calcium or becomes activated by excess calcium (Mcilvoy, 2005). The processes involved in secondary brain injury are thought to extend the neural damage and therefore increase the severe physical, cognitive, and emotional disabilities found in these patients. The effect temperature has on these processes is the focus of current research.
Animal studies have demonstrated that elevated core temperatures before, during, and after ischemic insults exacerbate the degree of brain injury (Busto, Globus, & Dietrich, 1989; Chen, Chopp, & Welch, 1991; Dietrich, 1992; Dietrich, Busto, Valdes, & Loor, 1990; Dietrich, Halley, Valdes, & Busto, 1991; Kil, Zhang, & Piantadosi, 1996). In the human population, mortality and hyperthermia have been strongly correlated in stroke patients (Jorgensen, Reith, Pedersen, Nakayama, & Olsen, 1996; Kammersgaard et al., 2002; Wang, Lim, Levi, Heller, & Fisher, 2000). Hyperthermia occurring within the first 24 hours of an... |
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