The Impact of Brain Temperature and Core Temperature on Intracranial Pressure and Cerebral Perfusion Pressure:

Brain Temperature Influences Intracranial Pressure and Cerebral Perfusion Pressure After Traumatic Brain Injury: A CENTER-TBI Study

Background

After traumatic brain injury (TBI), fever is frequent. Brain temperature (BT), which is directly linked to body temperature, may influence brain physiology. Increased body and/or BT may cause secondary brain damage, with deleterious effects on intracranial pressure (ICP), cerebral perfusion pressure (CPP), and outcome.

Methods

Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI), a prospective multicenter longitudinal study on TBI in Europe and Israel, includes a high resolution cohort of patients with data sampled at a high frequency (from 100 to 500 Hz). In this study, simultaneous BT, ICP, and CPP recordings were investigated. A mixed-effects linear model was used to examine the association between different BT levels and ICP. We additionally focused on changes in ICP and CPP during the episodes of BT changes (Δ BT ≥ 0.5 °C lasting from 15 min to 3 h) up or downward. The significance of ICP and CPP variations was estimated with the paired samples Wilcoxon test (also known as Wilcoxon signed-rank test).

Results

Twenty-one patients with 2,435 h of simultaneous BT and ICP monitoring were studied. All patients reached a BT of 38 °C and experienced at least one episode of ICP above 20 mm Hg. The linear mixed-effects model revealed an association between BT above 37.5 °C and higher ICP levels that was not confirmed for lower BT. We identified 149 episodes of BT changes. During BT elevations (n = 79) ICP increased, whereas CPP was reduced; opposite ICP and CPP variations occurred during episodes of BT reduction (n = 70). All these changes were of moderate clinical relevance (increase of ICP of 4.5 and CPP decrease of 7.5 mm Hg for BT rise, and ICP reduction of 1.7 and CPP elevation of 3.7 mm Hg during BT defervescence), even if statistically significant (p < 0.0001). It has to be noted, however, that a number of therapeutic interventions against intracranial hypertension was documented during those episodes.

Conclusions

Patients after TBI usually develop BT > 38 °C soon after the injury. BT may influence brain physiology, as reflected by ICP and CPP. An association between BT exceeding 37.5 °C and a higher ICP was identified but not confirmed for lower BT ranges. The relationship between BT, ICP, and CPP become clearer during rapid temperature changes. During episodes of temperature elevation, BT seems to have a significant impact on ICP and CPP.

The influence of hyperthermia on intracranial pressure, cerebral oximetry and cerebral metabolism in traumatic brain injury

BACKGROUND

Hyperthermia is a common secondary insult in traumatic brain injury (TBI). The aim was to evaluate the relationship between hyperthermia and intracranial pressure (ICP), and if intracranial compliance and cerebral blood flow (CBF) pressure autoregulation affected that relationship. The relationships between hyperthermia and cerebral oximetry (BtipO2) and cerebral metabolism were also studied.

METHODS

A computerized multimodality monitoring system was used for data collection at the neurointensive care unit. Demographic and monitoring data (temperature, ICP, blood pressure, microdialysis, BtipO2) were analyzed from 87 consecutive TBI patients. ICP amplitude was used as measure of compliance, and CBF pressure autoregulation status was calculated using collected blood pressure and ICP values. Mixed models and comparison between groups were used.

RESULTS

The influence of hyperthermia on intracranial dynamics (ICP, brain energy metabolism, and BtipO2) was small, but individual differences were seen. Linear mixed models showed that hyperthermia raises ICP slightly more when temperature increases in the groups with low compliance and impaired CBF pressure autoregulation. There was also a tendency (not statistically significant) for increased BtipO2, and for increased pyruvate and lactate, with higher temperature, while the lactate/pyruvate ratio and glucose were stable.

CONCLUSIONS

The major finding was that the effects of hyperthermia on intracranial dynamics (ICP, brain energy metabolism, and BtipO2) were not extensive in general, but there were exceptional cases. Hyperthermia treatment has many side effects, so it is desirable to identify cases in which hyperthermia is dangerous. Information from multimodality monitoring may be used to guide treatment in individual patients.

Fever management practices of neuroscience nurses: what has changed?

Current evidence shows that fever and hyperthermia are especially detrimental to patients with neurologic injury, leading to higher rates of mortality, greater disability, and longer lengths of stay. Although clinical practice guidelines exist for ischemic stroke, subarachnoid hemorrhage, and traumatic brain injury, they lack specificity in their recommendations for fever management, making it difficult to formulate appropriate protocols for care. Using survey methods, the aims of this study were to (a) describe how nursing practices for fever management in this population have changed over the last several years, (b) assess if institutional protocols and nursing judgment follow published national guidelines for fever management in neuroscience patients, and (c) explore whether nurse or institutional characteristics influence decision making. Compared with the previous survey administered in 2007, there was a small increase (8%) in respondents reporting having an institutional fever protocol specific to neurologic patients. Temperatures to initiate treatment either based on protocols or nurse determination did not change from the previous survey. However, nurses with specialty certification and/or working in settings with institutional awards (e.g., Magnet status or Stroke Center Designation) initiated therapy at a lower temperature. Oral acetaminophen continues to be the primary choice for fever management, followed by ice packs and fans. This study encourages the development of a stepwise approach to neuro-specific protocols for fever management. Furthermore, it shows the continuing need to promote further education and specialty training among nurses and encourage collaboration with physicians to establish best practices.

Intracranial temperature and pressure measurement: in vitro temperature sensing characteristics of the dual sensing element

A pressure sensor has been used to measure temperature concurrently. We have designed, and characterized the measurement of temperature from the same sensor to allow simultaneous monitoring of intracranial temperature and pressure. The temperature measurement has a sensitivity of 85.08 mV/°C across the measurement range 20-45 °C. The time constant of the temperature sensor is 150 ms. We have evaluated the accuracy of the temperature measurement and the long term drift of 13 sensors over 28 days. The mean difference of the temperature measurements from the reference measurements was less than 0.2 °C.

Better Glasgow outcome score, cerebral perfusion pressure and focal brain oxygenation in severely traumatized brain following direct regional brain hypothermia therapy: A prospective randomized study

BACKGROUND

Induced hypothermia for treatment of traumatic brain injury is controversial. Since many pathways involved in the pathophysiology of secondary brain injury are temperature dependent, regional brain hypothermia is thought capable to mitigate those processes. The objectives of this study are to assess the therapeutic effects and complications of regional brain cooling in severe head injury with Glasgow coma scale (GCS) 6-7.

MATERIALS AND METHODS

A prospective randomized controlled pilot study involving patients with severe traumatic brain injury with GCS 6 and 7 who required decompressive craniectomy. Patients were randomized into two groups: Cooling and no cooling. For the cooling group, analysis was made by dividing the group into mild and deep cooling. Brain was cooled by irrigating the brain continuously with cold Hartmann solution for 24-48 h. Main outcome assessments were a dichotomized Glasgow outcome score (GOS) at 6 months posttrauma.

RESULTS

A total of 32 patients were recruited. The cooling-treated patients did better than no cooling. There were 63.2% of patients in cooling group attained good GOS at 6 months compared to only 15.4% in noncooling group (P = 0.007). Interestingly, the analysis at 6 months post-trauma disclosed mild-cooling-treated patients did better than no cooling (70% vs. 15.4% attained good GOS, P = 0.013) and apparently, the deep-cooling-treated patients failed to be better than either no cooling (P = 0.074) or mild cooling group (P = 0.650).

CONCLUSION

Data from this pilot study imply direct regional brain hypothermia appears safe, feasible and maybe beneficial in treating severely head-injured patients.

Measuring brain temperature while maintaining brain normothermia in patients with severe traumatic brain injury

The aim of this study was to evaluate the relationship between superficial temporal artery temperature (Tt), rectal temperature (Tr) and intracranial temperature (ICT) when attempting to keep the brain in a normothermic condition in patients with severe traumatic brain injury (TBI). We also compared the incidence of temperature gradient reversal in patients who survived (survivors) and patients who did not (non-survivors) and the difference in temperature gradient reversal between survivors and non-survivors. Tr is normally lower than and ICT and temperature gradient reversal, when Tr exceeds ICT, has been demonstrated to be an early sign of brain death. A total of 28 patients with severe TBI were enrolled retrospectively in our study between November 2008 and February 2010. Each patient's Tt, Tr and ICT was recorded every hour for 4 days. Our results show that the frequency of brain hyperthermia in our participants (ICT>38°C) was 17.7%. Using a paired t-test and Bland-Altman plots, it was shown that a significant temperature difference existed between Tt, Tr and ICT (p<0.001). The use of Spearman's correlation method revealed that Tt, Tr and ICT were positively correlated (p<0.001). Brain death occurred in five patients at a mean of 9.6 hours (range: 8-12 hours) after a temperature gradient reversal between Tt, Tr and ICT. Fisher's exact test showed that there was a significant difference in the incidence of temperature gradient reversal between Tt, Tr and ICT in survivors and non-survivors (p<0.001). We conclude that a significant temperature difference exists between Tt, Tr and ICT when maintaining brain normothermia. The daily practice of non-invasive Tt measurement may cause doctors to underestimate ICT; reversal of the ICT and Tt and/or Tr temperatures could be an early marker of a poor prognosis for patients with severe TBI.

Clinical management of fever by nurses: doing what works

AIMS

The specific aims were to (1) define fever from the nurse's perspective; (2) describe fever management decision-making by nurses and (3) describe barriers to evidence-based practice across various settings.

BACKGROUND

Publication of practice guidelines, which address fever management, has not yielded improvements in nursing care. This may be related to differences in ways nurses define and approach fever.

METHOD

The collective case study approach was used to guide the process of data collection and analysis. Data were collected during 2006-7. Transcripts were coded using the constant comparative method until themes were identified. Cross-case comparison was conducted. The nursing process was used as an analytical filter for refinement and presentation of the findings.

FINDINGS

Nurses across settings defined fever as a (single) elevated temperature that exceeded some established protocol. Regardless of practice setting, interventions chosen by nurses were frequently based on trial and error or individual conventions -'what works'- rather than evidence-based practice. Some nurses' accounts indicated use of interventions that were clearly contraindicated by the literature. Participants working on dedicated neuroscience units articulated specific differences in patient care more than those working on mixed units.

CONCLUSIONS

By defining a set temperature for intervention, protocols may serve as a barrier to critical clinical judgment. We recommend that protocols be developed in an interdisciplinary manner to foster local adaptation of best practices. This could further best practice by encouraging individual nurses to think of protocols not as a recipe, but rather as a guide when individualizing patient care. There is value of specialty knowledge in narrowing the translational gap, offering institutions evidence for planning and structuring the organization of care.