Brain temperature monitoring in newborn infants: Current methodologies and prospects

Brain tissue temperature is a dynamic balance between heat generation from metabolism, passive loss of energy to the environment, and thermoregulatory processes such as perfusion. Perinatal brain injuries, particularly neonatal encephalopathy, and seizures, have a significant impact on the metabolic and haemodynamic state of the developing brain, and thereby likely induce changes in brain temperature. In healthy newborn brains, brain temperature is higher than the core temperature. Magnetic resonance spectroscopy (MRS) has been used as a viable, non-invasive tool to measure temperature in the newborn brain with a reported accuracy of up to 0.2 degrees Celcius and a precision of 0.3 degrees Celcius. This measurement is based on the separation of chemical shifts between the temperature-sensitive water peaks and temperature-insensitive singlet metabolite peaks. MRS thermometry requires transport to an MRI scanner and a lengthy single-point measurement. Optical monitoring, using near infrared spectroscopy (NIRS), offers an alternative which overcomes this limitation in its ability to monitor newborn brain tissue temperature continuously at the cot side in real-time. Near infrared spectroscopy uses linear temperature-dependent changes in water absorption spectra in the near infrared range to estimate the tissue temperature. This review focuses on the currently available methodologies and their viability for accurate measurement, the potential benefits of monitoring newborn brain temperature in the neonatal intensive care unit, and the important challenges that still need to be addressed.

Effects of Hyperthermia on Intracranial Pressure and Cerebral Autoregulation in Patients with an Acute Brain Injury

Hyperthermia is a common detrimental condition in patients with an acute brain injury (ABI), which can worsen their prognosis and outcome. The aim of this study was to evaluate the effects of hyperthermia on intracranial pressure (ICP) and cerebral autoregulation (CA).Eight patients with ABI were studied. CA was assessed on the basis of the pressure reactivity index (PRx) coefficient. The ICP, cerebral perfusion pressure (CPP), and PRx were compared before and during development of hyperthermia. Hyperthermia was defined as an increase in cerebral temperature above 38.3 °C.Thirty-three episodes of hyperthermia were analyzed: 25 of these occurred on a background of initially normal ICP whereas 8 occurred on a background of initially elevated ICP, and 17 of the 33 episodes occurred on a background of initially intact autoregulation whereas 16 occurred on a background of initially impaired autoregulation.During hyperthermia, elevated ICP was found in 52% of instances where it was initially normal, and further progression of intracranial hypertension occurred in 100% of instances where ICP was initially elevated. The median ICP during hyperthermia was 24 [range quartiles 22-28] mmHg in instances where it was initially normal and 31 [quartiles 27-32] mmHg in instances where it was initially elevated (p < 0.01). The correlation coefficient between the brain temperature and ICP was 0.11 (p < 0.01). During hyperthermia, the number of episodes of ICP >20 mmHg increased by 41% in instances with intact autoregulation but ICP was above 20 mmHg and by 38% (p > 0.05) in instances with impaired autoregulation and ICP was 20 mmHg. The cerebral hyperthermia-associated increase in ICP was not associated with impaired autoregulation.

[Influence of cerebral hyperthermia on intracranial pressure and autoregulation of cerebral circulation in patients with acute brain injury]

Background. Hyperthermia is a common symptom in ICU patients with brain injury.

OBJECTIVE

To study the effect of hyperthermia on intracranial pressure (ICP) and cerebral autoregulation (Prx).

MATERIAL AND METHODS

There were 8 patients with acute brain injury, signs of brain edema and intracranial hypertension. Cerebral autoregulation was assessed by using of PRx. ICP, CPP, BP, PRx were measured before and during hyperthermia. We have analyzed 33 episodes of cerebral hyperthermia over 38.30 C. Statistica 10.0 (StatSoft) was used for statistical analysis.

RESULTS

Only ICP was significantly increased by 6 [3; 11] mm Hg (p<0.01). In patients with initially normal ICP, hyperthermia resulted increase of ICP in 48% of cases (median 24 [22; 28] mm Hg). In patients with baseline intracranial hypertension, progression of hypertension was noted in 100% cases (median 31 [27; 32] mm Hg) (p<0.01). Hyperthermia resulted intracranial hypertension regardless brain autoregulation status.

CONCLUSION

Cerebral hyperthermia in patients with initially normal ICP results intracranial hypertension in 48% of cases. In case of elevated ICP, further progression of intracranial hypertension occurs in 100% of cases. Cerebral hyperthermia is followed by ICP elevation in both intact and impaired cerebral autoregulation.

Recent technological advancements in thermometry

Thermometry is the key factor for achieving successful thermal therapy. Although invasive thermometry with a probe has been used for more than four decades, this method can only detect the local temperature within the probing volume. Noninvasive temperature imaging using a tomographic technique is ideal for monitoring hot-spot formation in the human body. Among various techniques, such as X-ray computed tomography, microwave tomography, echo sonography, and magnetic resonance (MR) imaging, the proton resonance frequency shift method of MR thermometry is the only method currently available for clinical practice because its temperature sensitivity is consistent in most aqueous tissues and can be easily observed using common clinical scanners. New techniques are being proposed to improve the robustness of this method against tissue motion. MR techniques for fat thermometry were also developed based on relaxation times. One of the latest non-MR techniques to attract attention is photoacoustic imaging.

Effects of Brain Temperature on the Outcome of Patients with Traumatic Brain Injury: A Prospective Observational Study

A prospective observational study collected temperature data from 51 patients in 11 neurosurgical centers and follow-up outcome information at 6 months in 49 patients. Brain temperature (T_br) was measured directly by an intraventricular temperature sensor. Axillary temperature (T_ax) and rectal temperature (T_re) were measured by electric thermometers. T_br was 0.4 to 1.5°C higher than body temperature. T_re correlated well with the T_br (coefficient: 0.7378; p < 0.05). Among all patients, Glasgow Coma Scale (GCS) scores on admission were significantly lower in the patients with post-operatively extreme peak temperature (T_peak, < 37°C or >39°C in first 24 h) and major temperature variation (T_vari > 1°C in first 12 h; p < 0.05, p < 0.01, respectively). Among the patients with no temperature intervention, the extreme T_peak group showed a lower Glasgow Outcome Scale-Extended (GOS-E) score at 6 months (p < 0.05) with lower GCS scores on admission (p < 0.01), compared with the moderate T_peak group. Remarkably, the major T_vari group showed significantly lower GOS-E scores (p < 0.05) with the same GCS scores as the minor T_vari group. Thus, T_re is the better candidate to estimate T_br. Spontaneously extreme T_peak in TBI represents both more serious injury on admission and worse prognosis, and T_vari might be used as a novel prognostic parameter in TBI. Brain temperature is therefore one of the critical indicators evaluating injury severity, prognostication, and monitoring in the management of TBI. This prospective observational study has been registered in ClinicalTrials.gov ( https://clinicaltrials.gov ), and the registration number is NCT03068143.

The Role of ADC-Based Thermometry in Measuring Brain Intraventricular Temperature in Children

BACKGROUND AND PURPOSE

To determine the feasibility of apparent diffusion coefficient (ADC)-based thermometry to assess intraventricular temperature in children.

METHODS

ADC maps were generated from diffusion tensor imaging data, which were acquired with diffusion gradients along 20 noncollinear directions using a b-value of 1000 s/mm(2) . The intraventricular temperature was calculated based on intraventricular ADC values and the mode method as previously reported. The calculated intraventricular temperature was validated with an estimated brain temperature based on temporal artery temperature measurements. We included 120 children in this study (49 females, 71 males, mean age 6.63 years), 15 consecutive children for each of the following age groups: 0-1, 1-2, 2-4, 4-6, 6-8, 8-10, 10-14, and 14-18 years. Forty-three children had a normal brain MRI and 77 children had an abnormal brain scan. Polynomial fitting to the temperature distribution and subsequent calculation of mode values was performed. A correlation coefficient and a coefficient of determination were calculated between ADC calculated temperatures and estimated brain temperatures. Linear regression analysis was performed to investigate the two temperature measures.

RESULTS

ADC-based intraventricular temperatures ranged between 31.5 and 39.6 °C, although estimated brain temperatures ranged between 36.3 and 38.1 °C. The difference between the temperatures is larger for children with more than 8,000 voxels within the lateral ventricles compared to children with less than 8,000 voxels. The correlation coefficient between ADC-based temperatures and the estimated brain temperatures is .1, the respective R(2) is .01 indicating that 1% of the changes in estimated brain temperatures are attributable to corresponding changes in ADC-based temperature measurements (P = .275).

CONCLUSIONS

ADC-based thermometry has limited application in the pediatric population mainly due to a small ventricular size.

Brain temperature in neonates with hypoxic-ischemic encephalopathy during therapeutic hypothermia

OBJECTIVE

To noninvasively determine brain temperature of neonates with hypoxic-ischemic encephalopathy (HIE) during and after therapeutic hypothermia.

STUDY DESIGN

Using a phantom, we derived a calibration curve to calculate brain temperature based on chemical shift differences in magnetic resonance spectroscopy. We enrolled infants admitted for therapeutic hypothermia and assigned them to a moderate HIE (M-HIE) or severe HIE (S-HIE) group based on Sarnat staging. Rectal (core) temperature and magnetic resonance spectroscopy data used to derive regional brain temperatures (basal ganglia, thalamus, and cortical gray matter) were acquired concomitantly during and after therapeutic hypothermia. We compared brain and rectal temperature in the M-HIE and S-HIE groups during and after therapeutic hypothermia using 2-tailed t-tests.

RESULTS

Eighteen patients (14 with M-HIE and 4 with S-HIE) were enrolled. As expected, both brain and rectal temperatures were lower during therapeutic hypothermia than after therapeutic hypothermia. Brain temperature in patients with S-HIE was higher than in those with M-HIE both during (35.1 ± 1.3°C vs 33.7 ± 1.2°C; P < .01) and after therapeutic hypothermia (38.1 ± 1.5°C vs 36.8 ± 1.3°C; P < .01). The brain-rectal temperature gradient was also greater in the S-HIE group both during and after therapeutic hypothermia.

CONCLUSION

For this analysis of a small number of patients, brain temperature and brain-rectal temperature gradient were higher in neonates with S-HIE than in those with M-HIE during and after therapeutic hypothermia. Further studies are needed to determine whether further decreasing brain temperature in neonates with S-HIE is safe and effective in improving outcome.

Keep the brain cool--endovascular cooling in patients with severe traumatic brain injury: a case series study

BACKGROUND

As brain temperature is reported to be extensively higher than core body temperature in traumatic brain injury (TBI) patients, posttraumatic hyperthermia is of particular relevance in the injured brain.

OBJECTIVE

To study the influence of prophylactic normothermia on brain temperature and the temperature gradient between brain and core body in patients with severe TBI using an intravascular cooling system and to assess the relationship between brain temperature and intracranial pressure (ICP) under endovascular temperature control.

METHODS

Prospective case series study conducted in the neurologic intensive care unit of a tertiary care university hospital. Seven patients with severe TBI with a Glasgow Coma Scale score of 8 or less were consecutively enrolled. Prophylactic normothermia, defined as a target temperature of 36.5°C, was maintained using an intravascular cooling system. Simultaneous measurements of brain and urinary bladder temperature and ICP were taken over a 72-hour period.

RESULTS

The mean bladder temperature in normothermic patients was 36.3 ± 0.4°C, and the mean brain temperature was determined as 36.4 ± 0.5°C. The mean temperature difference between brain and bladder was 0.1°C. We found a significant direct correlation between brain and bladder temperature (r = 0.95). In 52.4% of all measurements, brain temperature was higher than core body temperature. The mean ICP was 18 ± 8 mm Hg.

CONCLUSION

Intravascular temperature management stabilizes both brain and body core temperature; prophylactic normothermia reduces the otherwise extreme increase of intracerebral temperature in patients with severe TBI. The intravascular cooling management proved to be an efficacious and feasible method to control brain temperature and to avoid hyperthermia in the injured brain. We could not find a statistically significant correlation between brain temperature and ICP.

Age-dependent brain temperature decline assessed by diffusion-weighted imaging thermometry

Brain metabolism declines with age, but cerebral blood flow (CBF) is less age dependent. We therefore hypothesized that the brain temperature would decline with age, and measured the temperatures of the lateral ventricles in healthy volunteers. Diffusion-weighted imaging (DWI) data from 45 healthy volunteers [mean (± standard deviation) age, 30.6 ± 8.66 years; range, 19-56 years] were used for this study. The temperature of water molecules is directly related to the diffusion coefficient, so that the temperature of cerebrospinal fluid can be measured using DWI. Temperature was calculated using the equation, T ( °C) = 2256.74/ln(4.39221/D) - 273.15, where D is the diffusion coefficient. The lateral ventricles were manually extracted by an experienced neuroradiologist on b(0) images. The mean ventricular temperature was determined from the distribution function of the temperature of all selected voxels. The mean lateral ventricular temperature in healthy volunteers showed a linear decrease with age (correlation coefficient R(2)  = 0.8879; p < 0.01), presumably caused by an asynchronous decline in brain metabolism and CBF. DWI-based thermometry demonstrates that ventricular temperature declines with the normal aging process. Further study is warranted to define the relationships between temperature, metabolism and circulation.

Brain-systemic temperature gradient is temperature-dependent in children with severe traumatic brain injury

OBJECTIVES

To understand the gradient between rectal and brain temperature in children after severe traumatic brain injury. We hypothesized that the rectal temperature and brain temperature gradient will be influenced by the child's body surface area and that this relationship will persist over physiologic temperature ranges.

DESIGN

Retrospective review of a prospectively collected pediatric neurotrauma registry.

SETTING

Academic, university-based pediatric neurotrauma program.

PATIENTS

Consecutive children (n = 40) with severe traumatic brain injury (Glasgow coma scale of <8) who underwent brain temperature monitoring (July 2003 to December 2008) were studied after informed consent was obtained. A subset of children (n = 24) were concurrently enrolled in a randomized, controlled clinical trial of early-moderate hypothermia for neuroprotection.

INTERVENTIONS

Data extraction of multiple clinical variables, including demographic data, body surface area, and rectal and brain temperature at recorded at hourly intervals.

MEASUREMENTS AND MAIN RESULTS

Paired brain and rectal temperature measurements (in degrees Celsius, n = 4369) were collected hourly and compared by using Pearson correlations. Patients were stratified according to body surface area (<1.0 m, 1.0-1.99 m, 2.0-2.99 m, and >3.0 m) and based on brain temperature (≤34.0, 34.1-36.0; 36.1-38, ≥38.1). Body surface area and brain temperature were compared between groups by using Pearson correlations with correction for repeated measures. Mean brain temperature-rectal temperature difference was calculated for stratified brain temperature ranges. Overall, brain and rectal temperatures were highly correlated (r = .86, p < .001). During brain hyperthermia, brain temperature-rectal temperature was similar to that reported in previous studies with brain temperature higher than rectal temperature (1.75 ± 0.4; r = .54). Surprisingly, this relationship was reversed during brain hypothermia (brain temperature-rectal temperature = -1.87 ± 0.8; r = .37), indicating a reversal of the brain-systemic temperature gradient. When stratified for body surface area, the correlation between rectal temperature and brain temperature remained strong (r = .78, 0.91, 0.79 and 0.95, respectively, p < .001). However, the correlation between brain temperature and rectal temperature was substantially decreased when stratified for brain temperature (r = .37, 0.58, 0.48, 0.54, p < .001). In particular, during moderate brain hypothermia (brain temperature ≤34), the correlation between brain temperature and rectal temperature was weakest, indicating the greatest variability during this condition which is often targeted for therapeutic trials.

CONCLUSIONS

Brain temperature and rectal temperature are generally well-correlated in children with traumatic brain injury. This relationship is different at the extremes of the physiologic temperature range, with the temperature gradient reversed during brain hypothermia and hyperthermia. Given that studies showing neuroprotection from hypothermia in animal models of brain injury generally target brain temperature, our data suggest the possibility that, if brain temperature were the therapeutic target in clinical trials, this would result in somewhat higher systemic temperature and potentially fewer side effects. This relationship may be exploited in future clinical trials to maintain brain hypothermia (for neurologic protection) at slightly higher systemic temperatures (and potentially fewer systemic side effects).

Non-invasive continuous cerebral temperature monitoring in patients treated with mild therapeutic hypothermia: an observational pilot study

AIM OF THE STUDY

To investigate if body temperature as measured with a prototype of a non-invasive continuous cerebral temperature sensor using the zero-heat-flow method to reflect the oesophageal temperature (core temperature) during mild therapeutic hypothermia after cardiac arrest.

METHODS

In patients over 18 years old with restoration of spontaneous circulation after cardiac arrest, a temperature sensor that uses the zero-heat-flow principle was placed on the forehead during the periods of cooling and re-warming. This temperature was compared to oesophageal temperature as the primary temperature-monitoring site. To assess agreement, we used the Bland-Altman approach and Lin's concordance correlation coefficient.

RESULTS

From September 2008 to April 2009, data from 19 patients were analysed. The median time from restoration of spontaneous circulation until temperature sensor application was 53min (interquartile range, 31; 96). All sensors were removed when a core temperature of 36 degrees C was reached. These measurements were in agreement with oesophageal temperature measurements. No allergic reaction, rash or other irritation occurred on the skin around or under the probes. Bland-Altman results showed a bias of -0.12 degrees C and 95% limits of agreement of -0.59 and +0.36 degrees C. Lin's concordance correlation coefficient was 0.98.

CONCLUSIONS

Body temperature measurements using a non-invasive continuous cerebral temperature sensor prototype that uses the zero-heat-flow method accurately reflected oesophageal temperature measurements during mild therapeutic hypothermia in patients with restoration of spontaneous circulation after cardiac arrest.

Mechanisms of action, physiological effects, and complications of hypothermia

BACKGROUND

Mild to moderate hypothermia (32-35 degrees C) is the first treatment with proven efficacy for postischemic neurological injury. In recent years important insights have been gained into the mechanisms underlying hypothermia's protective effects; in addition, physiological and pathophysiological changes associated with cooling have become better understood.

OBJECTIVE

To discuss hypothermia's mechanisms of action, to review (patho)physiological changes associated with cooling, and to discuss potential side effects.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

A myriad of destructive processes unfold in injured tissue following ischemia-reperfusion. These include excitotoxicty, neuroinflammation, apoptosis, free radical production, seizure activity, blood-brain barrier disruption, blood vessel leakage, cerebral thermopooling, and numerous others. The severity of this destructive cascade determines whether injured cells will survive or die. Hypothermia can inhibit or mitigate all of these mechanisms, while stimulating protective systems such as early gene activation. Hypothermia is also effective in mitigating intracranial hypertension and reducing brain edema. Side effects include immunosuppression with increased infection risk, cold diuresis and hypovolemia, electrolyte disorders, insulin resistance, impaired drug clearance, and mild coagulopathy. Targeted interventions are required to effectively manage these side effects. Hypothermia does not decrease myocardial contractility or induce hypotension if hypovolemia is corrected, and preliminary evidence suggests that it can be safely used in patients with cardiac shock. Cardiac output will decrease due to hypothermia-induced bradycardia, but given that metabolic rate also decreases the balance between supply and demand, is usually maintained or improved. In contrast to deep hypothermia (<or=30 degrees C), moderate hypothermia does not induce arrhythmias; indeed, the evidence suggests that arrhythmias can be prevented and/or more easily treated under hypothermic conditions.

CONCLUSIONS

Therapeutic hypothermia is a highly promising treatment, but the potential side effects need to be properly managed particularly if prolonged treatment periods are required. Understanding the underlying mechanisms, awareness of physiological changes associated with cooling, and prevention of potential side effects are all key factors for its effective clinical usage.

Use of therapeutic hypothermia for term infants with hypoxic-ischemic encephalopathy

Newborn encephalopathy represents a clinical syndrome with diverse causes, many of which may result in brain injury. Hypoxic-ischemic encephalopathy represents a subset of newborns with encephalopathy and, in contrast to other causes, may have a modifiable outcome. Laboratory research has demonstrated robust neuroprotection associated with reductions of brain temperature following hypoxia-ischemia in animals. The neuroprotective effects of hypothermia reflect antagonism of multiple cascades of events that contribute to brain injury. Clinical trials have translated laboratory observations into successful interventions. Hypoxicischemic encephalopathy is often unanticipated, unavoidable, and may occur in any obstetric setting. Pediatricians and other providers based in community hospitals play a critical role in the initial assessment, recognition, and stabilization of infants who may be candidates for therapeutic hypothermia.

Induced hypothermia in acute ischemic stroke

BACKGROUND

Induced hypothermia is a promising neuroprotective treatment for acute ischemic stroke. Data from both global and focal ischemia animal models have been encouraging. However, only a few small clinical studies have investigated its use in humans.

OBJECTIVE

To review the background, possible mechanisms of action, and the preclinical and clinical data supporting the neuroprotective role of induced hypothermia following acute ischemic stroke.

METHODS

A literature search was performed using the PubMed database. Only papers in English were reviewed.

RESULTS/CONCLUSIONS

Induced hypothermia is effective as a neuroprotectant in animal models of acute ischemic stroke. Its multimodal mechanism of action makes it a very attractive method of neuroprotection. Although human studies suggest it is safe and feasible, larger randomized controlled trials are necessary to address clinical efficacy and to refine the methods and parameters of induced hypothermia protocols.

Elevated temperature after hypoxic-ischemic encephalopathy: risk factor for adverse outcomes

OBJECTIVE

The goal was to determine whether the risk of death or moderate/severe disability in term infants with hypoxic-ischemic encephalopathy increases with relatively high esophageal or skin temperature occurring between 6 and 78 hours after birth.

METHODS

This was an observational secondary study within the National Institute of Child Health and Human Development Neonatal Research Network randomized trial comparing whole-body cooling and usual care (control) for term infants with hypoxic-ischemic encephalopathy. Esophageal and skin temperatures were recorded serially for 72 hours. Each infant's temperatures for each site were rank ordered. The high temperature was defined for each infant as the mean of all temperature measurements in the upper quartile. The low temperature was similarly defined as the mean of the lower quartile. Outcomes were related to temperatures in 3 logistic regression analyses for the high, median, and low temperatures at each temperature site for each group, with adjustment for the level of encephalopathy, gender, gestational age, and race.

RESULTS

In control infants, the mean esophageal temperature was 37.2 +/- 0.7 degrees C over the 72-hour period, and 63%, 22%, and 8% of all temperatures were >37 degrees C, >37.5 degrees C, and >38 degrees C, respectively. The mean skin temperature was 36.5 +/- 0.8 degrees C, and 12%, 5%, and 2% of all temperatures were >37 degrees C, >37.5 degrees C, and >38 degrees C, respectively. The odds of death or disability were increased 3.6-4 fold for each 1 degrees C increase in the highest quartile of skin or esophageal temperatures. There were no associations between temperatures and outcomes in the cooling-treated group.

CONCLUSIONS

Relatively high temperatures during usual care after hypoxia-ischemia were associated with increased risk of adverse outcomes. The results may reflect underlying brain injury and/or adverse effects of temperature on outcomes.

Temperature management in acute neurologic disorders

Temperature management in acute neurologic disorders has received considerable attention in the last 2 decades. Numerous trials of hypothermia have been performed in patients with head injury, stroke, and cardiac arrest. This article reviews the physiology of thermoregulation and mechanisms responsible for hyperpyrexia. Detrimental effects of fever and benefits of normalizing elevated temperature in experimental models are discussed. This article presents a detailed analysis of trials of induced hypothermia in patients with acute neurologic insults and describes methods of fever control.

Induced hypothermia and fever control for prevention and treatment of neurological injuries

Increasing evidence suggests that induction of mild hypothermia (32-35 degrees C) in the first hours after an ischaemic event can prevent or mitigate permanent injuries. This effect has been shown most clearly for postanoxic brain injury, but could also apply to other organs such as the heart and kidneys. Hypothermia has also been used as a treatment for traumatic brain injury, stroke, hepatic encephalopathy, myocardial infarction, and other indications. Hypothermia is a highly promising treatment in neurocritical care; thus, physicians caring for patients with neurological injuries, both in and outside the intensive care unit, are likely to be confronted with questions about temperature management more frequently. This Review discusses the available evidence for use of controlled hypothermia, and also deals with fever control. Besides discussing the evidence, the aim is to provide information to help guide treatments more effectively with regard to timing, depth, duration, and effective management of side-effects. In particular, the rate of rewarming seems to be an important factor in establishing successful use of hypothermia in the treatment of neurological injuries.

Does brain temperature correlate with intracranial pressure?

OBJECTIVE

A positive correlation between brain temperature and intracranial pressure (ICP) has been proposed for patients under intensive care conditions.

DESIGN AND METHODS

Data were recorded at 5-minute intervals in patients under ICP monitoring conditions. Brain temperature: combined ICP/temperature probe (Raumedic), core temperature: indwelling urinary catheter with temperature probe (Rüsch). The correlation between brain temperature and ICP was assessed by computing an estimated mean correlation coefficient (re) and by a time series analysis.

PATIENTS

Forty consecutive neurosurgical patients receiving intensive care therapy for trauma, cerebrovascular malformation, and spontaneous hemorrhage were studied. A total of 48,892 measurements (9778 h) were analyzed. No additional interventions were performed.

RESULTS

The median ICP was 14 mm Hg (range: -13 to 167). The brain temperature (median 38 degrees C; range 23.2 to 42.1) was 0.3 degrees C (range: -3.6 to 2.6) higher than the core temperature (median 37.7 degrees C; range 16.6 to 42.0), P<0.001. The mean Pearson correlation between ICP and brain temperature in all patients was re=0.13 (P<0.05); the time series analysis (assuming a possible lagged correlation between ICP and brain temperature) revealed a mean correlation of 0.05+/-0.25 (P<0.05). Both correlation coefficients indicate that any relationship between brain temperature and ICP accounts for less than 2% of the variability [coefficient of determination (r)<0.02].

CONCLUSIONS

These data do not support the notion of a clinically useful correlation between brain temperature and ICP.

Effects of propofol and halothane on long-term potentiation in the rat hippocampus after transient cerebral ischaemia

BACKGROUND

Propofol is reported to have protective effects on cerebral ischaemia-induced neuronal death. The aim of this study was to explore whether propofol and halothane can protect hippocampal neuronal function from ischaemic injury during general anaesthesia in rats.

METHODS

Rats were divided into 2-vessel occlusion (incomplete cerebral ischaemia) and 4-vessel occlusion (complete cerebral ischaemia) groups consisting of three subgroups each (sham-operated, propofol and halothane groups). One hour after starting propofol 1 mg kg(-1) min(-1) with 30% O2 and N2 or halothane 0.8% in 30% O2 and N2 rats with or without bilateral vertebral artery occlusion had bilateral common carotid arteries occluded by vessel clips for 10 min. Anaesthesia was maintained for another 1 h. Seven days after ischaemia-reperfusion, hippocampal long-term potentiation in the perforant path-dentate gyrus synapse was determined as an index of cerebral outcome.

RESULTS

In the propofol groups, the formation of long-term potentiation was significantly impaired in the 2-vessel and 4-vessel occlusion groups compared to the respective sham-operated groups (P < 0.01 and P < 0.05, respectively). Impaired formation of long-term potentiation in propofol groups was comparable to that in halothane groups. The formation of long-team potentiation in the propofol and halothane 2-vessel group was not significantly different from that in the awake 2-vessel group.

CONCLUSIONS

Propofol and halothane administered during ischaemia do not possess protective effects against hippocampal neuronal dysfunction induced by cerebral ischaemia-reperfusion as evaluated by our transient ischaemic rat models.

[Intracerebral monitoring of a patient with vasopasm]

Delayed neurological deficit occurs among 30% of patients after aneurysmal subarachnoid haemorrhage, mainly related to cerebral vasospasm. The early detection of cerebral ischemia remains problematic. Conventional cerebral monitoring (as intracranial pressure and cerebral perfusion pressure) appears to be insufficient, because cerebral ischemia may occur without elevated intracranial pressure. Global cerebral monitoring as venous jugular oxygen saturation are useful for regional monitoring. Local monitoring as oxygen tissue partial pressure (PtiO2) and microdialysis are sensible for brain ischemia detection, but may also ignore episodes occurring in non-monitored brain area. For the detection of most episodes of brain ischemia, several monitoring system should be use performing a multimodal intracerebral monitoring. Brain microdialysis and oxygen tissue partial pressure are promising monitoring system.

Klinische Möglichkeiten zur Steuerung der Körpertemperatur

The constancy of body temperature (CBT) is a cornerstone of homeostatic, homothermic organisms and is essential for a regulated course of biochemical and biophysical reactions. Severe deviations from normothermia (36.8+/-0.4 degrees C) are life threatening and even a moderate perioperative reduction of the CBT is coupled with an increased morbidity and mortality especially in high-risk patients. The relevant factors are coagulation disturbances, increased infection rate and increased cardiac risk. Normothermia should be achieved by the consistent use of warmth-conserving measures. On the other hand, a deliberate reduction in temperature or induced hypothermia is a neuroprotective procedure, which offers a therapeutic option to minimize neuronal secondary damage after primary hypoxic-ischemic events as well as extending the neuronal tolerance to ischemia. Management includes the practice of cooling down to a defined temperature, rewarming as well as a differentiated control of various parameters. Furthermore, side-effects which increase in severity with decreasing temperature must be taken into consideration.

Unexpected fatal neurological deterioration after successful cardio-pulmonary resuscitation and therapeutic hypothermia

A 77-year-old woman was admitted to the intensive care unit after successful cardiopulmonary resuscitation for out-of-hospital cardiac arrest due to pulseless electrical activity. She was treated with mild therapeutic hypothermia to minimise secondary anoxic brain damage. After a 24 h period of therapeutic hypothermia with a temperature of 32.5 degrees C, the patient was rewarmed and sedation discontinued. Neurological evaluation after 24 h revealed a maximum Glasgow Coma Score of E4M4Vt with spontaneous breathing. However the patient developed a fever reaching 39 degrees C for several hours that was unresponsive to conventional cooling methods. In the subsequent 24 h patient developed apnoea, hypotension and bradycardia with deterioration of the coma score. Diabetes insipidus was confirmed. Cerebral CT was performed which showed diffuse brain oedema with herniation and brainstem compression. The patient died within hours. Autopsy showed massive brain swelling and tentorial herniation. Hyperthermia possibly played a pivotal role in the development of this fatal insult to this vulnerable brain after cardiac arrest and therapeutic hypothermia treatment. The acute histopathological alterations in the brain, possibly caused by the deleterious effects of fever after cardiac arrest in human brain, may be considered a new observation.

Therapeutische Hypothermie und Säure-Basen-Management

Moderate hypothermia is being increasingly advocated for acute neurological clinical situations. In case of proved clinical success, however, it is relatively time consuming and requires personal and structural resources. In addition, profound knowledge and a sound understanding of the physiology of hypothermia are necessary prerequisites. In particular, the variety of untoward effects, which increase with decreasing temperature, underline the need for specific diagnostic and therapeutic skills. A further challenge is associated with the adaptation of the parameters of homoeostasis to a basically altered temperature. Among these, management of acid-base balance is a managerial cornerstone. In principle, two different regimens may be used, i.e. the pH-stat and the alpha-stat regimes. Applying pH-stat during hypothermia means keeping the pH constant, whereas the H(+)/OH(-) quotient is held constant when relying on the alpha-stat regime. Because of the lack of prospective clinical data any comparative evaluation of the two alternatives actually remains a matter of speculation. However, experimental data as well as physiological considerations may support an illness-oriented differentiated approach (e.g. increased cerebral pressure vs. cardiac arrest vs. stroke). Prospective studies are required to allow an evidence-based and substantiated clinical decision regarding the management of pCO(2) and pH during therapeutic hypothermia.

Determination of regional brain temperature using proton magnetic resonance spectroscopy to assess brain-body temperature differences in healthy human subjects

Proton magnetic resonance spectroscopy ((1)H MRS) was used to determine brain temperature in healthy volunteers. Partially water-suppressed (1)H MRS data sets were acquired at 3T from four different gray matter (GM)/white matter (WM) volumes. Brain temperatures were determined from the chemical-shift difference between the CH(3) of N-acetyl aspartate (NAA) at 2.01 ppm and water. Brain temperatures in (1)H MRS voxels of 2 x 2 x 2 cm(3) showed no substantial heterogeneity. The volume-averaged temperature from single-voxel spectroscopy was compared with body temperatures obtained from the oral cavity, tympanum, and temporal artery regions. The mean brain parenchyma temperature was 0.5 degrees C cooler than readings obtained from three extra-brain sites (P < 0.01). (1)H MRS imaging (MRSI) data were acquired from a slice encompassing the single-voxel volumes to assess the ability of spectroscopic imaging to determine regional brain temperature within the imaging slice. Brain temperature away from the center of the brain determined by MRSI differed from that obtained by single-voxel MRS in the same brain region, possibly due to a poor line width (LW) in MRSI. The data are discussed in the light of proposed brain-body temperature gradients and the use of (1)H MRSI to monitor brain temperature in pathologies, such as brain trauma.

Hyperthermia and central nervous system injury

Fever is a common occurrence in patients following brain and spinal cord injury (SCI). In intensive care units, large numbers of patients demonstrate febrile periods during the first several days after injury. Over the last several years, experimental studies have reported the detrimental effects of fever in various models of central nervous system (CNS) injury. Small elevations in temperature during or following an insult have been shown to worsen histopathological and behavioral outcome. Thus, the control of fever after brain or SCI may improve outcome if more effective strategies for monitoring and treating hyperthermia were developed. Because of the clinical importance of fever as a potential secondary injury mechanism, mechanisms underlying the detrimental effects of mild hyperthermia after injury have been evaluated. To this end, studies have shown that mild hyperthermia (>37 degrees C) can aggravate multiple pathomechanisms, including excitotoxicity, free radical generation, inflammation, apoptosis, and genetic responses to injury. Recent data indicate that gender differences also play a role in the consequences of secondary hyperthermia in animal models of brain injury. The observation that dissociations between brain and body temperature often occur in head-injured patients has again emphasized the importance of controlling temperature fluctuations after injury. Thus, increased emphasis on the ability to monitor CNS temperature and prevent periods of fever has gained increased attention in the clinical literature. Cooling blankets, body vests, and endovascular catheters have been shown to prevent elevations in body temperature in some patient populations. This chapter will summarize evidence regarding hyperthermia and CNS injury.

Temperature Management in Acute Neurologic Disorders

Temperature management in acute neurologic disorders has received considerable attention in the last 2 decades. Numerous trials of hypothermia have been performed in patients with head injury, stroke, and cardiac arrest. This article reviews the physiology of thermoregulation and mechanisms responsible for hyperpyrexia. Detrimental effects of fever and benefits of normalizing elevated temperature in experimental models are discussed. This article presents a detailed analysis of trails of induced hypothermia in patients with acute neurologic insults and describes methods of fever control.

[Controlled mild-to-moderate hypothermia in the intensive care unit]

Controlled hypothermia is used as a therapeutic intervention to provide neuroprotection and (more recently) cardioprotection. The growing insight into the underlying pathophysiology of apoptosis and destructive processes at the cellular level, and the mechanisms underlying the protective effects of hypothermia, have led to improved application and to a widening of the range of potential indications. In many centres hypothermia has now become part of the standard therapy for post-anoxic coma in certain patients, but for other indications its use still remains controversial. The negative findings of some studies may be partly explained by inadequate protocols for the application of hypothermia and insufficient attention to the prevention of potential side effects. This review deals with some of the concepts underlying hypothermia-associated neuroprotection and cardioprotection, and discusses some potential clinical indications as well as reasons why some clinical trials may have produced conflicting results. Practical aspects such as methods to induce hypothermia, as well as the side effects of cooling are also discussed.

Randomized controlled trial of effects of the airflow through the upper respiratory tract of intubated brain-injured patients on brain temperature and selective brain cooling

BACKGROUND

Pyrexia is common after brain injury; it is generally believed to affect outcome adversely and the usual clinical methods of reducing temperature are not effective. The normal physiological mechanisms of brain cooling are heat loss from the upper airways and through the skull, and these can produce selective brain cooling.

METHODS

Air at room temperature and humidity was continuously administered to 15 brain-injured, intubated and mechanically ventilated patients via a sponge-tipped oxygen catheter in each nostril at a combined rate of 115 ml kg(-1) min(-1). Brain temperature was measured using a pressure-temperature Camino catheter which is designed to site the thermistor 1 cm into the parenchyma in the frontal lobe. Oesophageal temperature was measured using an oesophageal stethoscope with a thermistor. After establishing baseline for 30 min, patients were randomized to receive airflow or no airflow for 6 h and then crossed over for a further 6 h.

RESULTS

Airflow replicating normal resting minute volume did not produce clinically relevant or statistically significant reductions in brain temperature [0.13 (SD 0.55) degrees C; 95% CI, 0.43-0.17 degrees C]. However, we serendipitously found some evidence of selective brain cooling via the skull, but this needs further substantiation.

CONCLUSIONS

A flow of humidified air at room temperature through the upper respiratory tracts of intubated brain-injured patients did not produce clinically relevant or statistically significant reductions in brain temperature measured in the frontal lobe.

Rapid Brain Cooling by Hypothermic Retrograde Jugular Vein Flush

BACKGROUND

Although whole-body hypothermia recently has been reported effective in improving the neurologic outcome after cardiac arrest, it is contraindicated in the management of trauma patients with hemorrhagic shock. To provide selective brain cooling in this situation, the authors speculated about the feasibility of hypothermic retrograde jugular vein flush (HRJVF). This preliminary study was conducted to test the effectiveness of brain cooling after HRJVF in rats without hemorrhagic shock.

METHODS

After jugular vein cannulation with cranial direction, Sprague-Dawley rats were randomized into a normal control group, a group that underwent flush with cold saline at 4 degrees C, or a group that underwent flush with saline at a room temperature of 24 degrees C. A Servo-controlled heat lamp was applied for all the rats to keep their rectal temperature at 37 +/- 0.5 degrees C. Their brain temperature and cerebral blood flow were checked.

RESULTS

Within the 10-minute period of cold saline flush (1.7 mL/100 g), brain temperature was immediately decreased, and this cooling effect could be maintained for at least 20 minutes. Cerebral blood flow was significantly increased after HRJVF, then returned gradually to the baseline as brain temperature elevated.

CONCLUSIONS

This study successfully demonstrated a significant cooling effect in rat brain by HRJVF. For preservation of brain function, HRJVF may be useful in resuscitation for trauma patients with hemorrhagic shock after further studies on animals with shock.

Resuscitative mild hypothermia as a protective tool in brain damage: is there evidence?

Resuscitative mild hypothermia is and will increasingly be used in the emergency department as protection for the brain after an ischaemic insult. The clinical application of resuscitative mild hypothermia and its limitations will be summarized in this paper. The evidence for each application and its underlying mechanism will also be reviewed.

Neurophysiological monitoring, magnetic resonance imaging, and histological assays confirm the beneficial effects of moderate hypothermia after epidural focal mass lesion development in rodents

OBJECTIVE

To assess the effects of moderate intraischemic hypothermia on neurophysiological parameters in an epidural balloon compression model in rats and to correlate the results with magnetic resonance imaging and histological findings.

METHODS

Neurophysiological monitoring included laser Doppler flow, tissue partial oxygen pressure, and intracranial pressure measurements and electroencephalographic assessments during balloon expansion, sustained inflation, and reperfusion. Moderate intraischemic cooling of animals was extended throughout the reperfusion period, and results were compared with those for normothermic animals. Moreover, histological morphometric and magnetic resonance imaging volumetric analyses of the lesions were performed.

RESULTS

Laser Doppler flow decreased slightly during ischemia (P < 0.05) in animals treated with hypothermia, and flow values demonstrated complete reperfusion, compared with incomplete flow restoration in untreated animals (P < 0.05). During ischemia, the tissue partial oxygen pressure was less than 4.3 mm Hg in both groups. After reperfusion, values returned to the normal range in both groups, but the tissue partial oxygen pressure in hypothermic animals was significantly higher (P = 0.042) and demonstrated 19% higher values, compared with normothermic animals, before rewarming. Moderate hypothermia attenuated a secondary increase in intracranial pressure (P < 0.05), and electroencephalographic findings indicated a trend toward faster recovery (P > 0.05) after reperfusion. Lesion size was reduced by 35% in magnetic resonance imaging volumetric evaluations and by 24.5% in histological morphometric analyses.

CONCLUSION

Intraischemic hypothermia improves cerebral microcirculation, attenuates a secondary increase in intracranial pressure, facilitates electroencephalographic recovery, and reduces the lesion size.

Hypothermic retrograde jugular vein flush in heatstroke rats provides brain protection by maintaining cerebral blood flow but not by hemodilution

OBJECTIVE

To determine the fundamental mechanism of brain protection by hypothermic retrograde jugular vein flush (HRJVF) in heatstroke rats.

DESIGN

Randomized, controlled, and prospective study.

SETTING

University physiology research laboratory.

SUBJECTS

Sprague-Dawley rats (270-320 g, males).

INTERVENTIONS

Rats were randomized into four groups as follows: a) normothermic control (NC, n = 8); b) heatstroke rats without cold saline delivery (HS, n = 8); c) heatstroke rats treated with cold saline via femoral vein (HS+F, n = 8); and d) heatstroke rats treated with HRJVF (HS+J, n = 8). Right external jugular vein and right femoral vein were cannulated in each rat. The cannulation in the jugular vein was with cranial direction. To produce heatstroke, rats were placed in a chamber with an ambient temperature of 43 degrees C. The cold saline (4 degrees C, 1.7 mL/100 g) was delivered via the cannula in either the femoral vein or jugular vein immediately after the onset of heatstroke. Glutamate release in the brain, cerebral blood flow (CBF), and hematocrit of arterial blood were determined.

MEASUREMENTS AND MAIN RESULTS

After onset of heatstroke, HRJVF significantly decreased the glutamate release. In contrast, cold saline delivery via femoral vein could only delay the elevation of glutamate release in the brain. The CBF of HS and HS+F rats decreased rapidly after the onset of heatstroke, but the CBF of HS+J rats was initially elevated by HRJVF and was maintained at baseline 30 mins after onset of heatstroke. Hematocrit in all the rats did not change after testing.

CONCLUSIONS

HRJVF protects the brain by maintaining cerebral blood flow in rats after heatstroke. To preserve brain function and prolong survival after severe heatstroke, maintenance of cerebral blood flow is important in the management of heatstroke.

Rapid and selective cerebral hypothermia achieved using a cooling helmet

OBJECT

Hypothermia is by far the most potent neuroprotectant. Nevertheless, timely and safe delivery of hypothermia remains a clinical challenge. To maximize neuroprotection yet minimize systemic complications, ultra-early delivery of selective cerebral hypothermia by Emergency Medical Service (EMS) personnel in the field would be advantageous. The authors (W.E. and H.W.) have developed a cooling helmet by using National Aeronautics and Space Administration spinoff technology. In this study its effectiveness in lowering brain temperature in patients with severe stroke or head injury is examined.

METHODS

Patients were randomly assigned to groups receiving either the cooling helmet or no cooling, and brain temperatures (0.8 cm below the cortical surface) were continuously monitored for a mean of 48 to 72 hours with a Neurotrend sensor and then compared with the patients' core temperatures. There were eight patients in the study group and six in the control group. The mean change in temperature (brain-body temperature) calculated from 277 data hours in the study group was -1.6 degrees C compared with a mean change in temperature of +0.22 degrees C calculated from 309 data hours in the control group. This was statistically significant (p < 0.0001). On average, 1.84 degrees C of brain temperature reduction (range 0.9-2.4 degrees C) was observed within 1 hour of helmet application. It took a mean of 3.4 hours (range 2-6 hours) to achieve a brain temperature lower than 34 degrees C and 6.67 hours (range 1-12 hours) before systemic hypothermia (< 36 degrees C) occurred. Use of the helmet resulted in no significant complications. There was, however, one episode of asymptomatic bradycardia (heart rate < 40) that responded to a 0.5 degrees C body temperature increase.

CONCLUSIONS

This helmet delivers initial rapid and selective brain cooling and maintains a significant temperature gradient between the core and brain temperatures throughout the hypothermic period to provide sufficient regional hypothermia yet minimize systemic complications. It results in delayed systemic hypothermia, creating a safe window for possible ultra-early delivery of regional hypothermia by EMS personnel in the field.

Hypothermic retrograde jugular perfusion reduces brain damage in rats with heatstroke

OBJECTIVE

To determine whether direct retrograde ice saline infusion in the jugular vein without cardiopulmonary bypass protects rat brains after heatstroke.

DESIGN

Randomized, controlled, prospective study.

SETTING

University physiology research laboratory.

SUBJECTS

Sprague-Dawley rats (270-320 g, males).

INTERVENTIONS

Rats were randomized into three groups and given a) no resuscitation after onset of heat stroke (HS, n = 8); b) ice saline infusion in the femoral vein after onset of heat stroke (HS + F, n = 8); or c) retrograde ice saline infusion in the external jugular vein after onset of heat stroke (HS + J, n = 8). Rats were exposed to an ambient temperature of 43 degrees C after vessel cannulation. Their mean arterial pressure, heart rate, colonic temperature, and brain temperature were continuously recorded. Survival time and brain pathology were checked.

MEASUREMENTS AND MAIN RESULTS

Although colonic temperature decreased 0.8-1.0 degrees C 15 mins after heatstroke in all groups, no treatment-related changes in colonic temperature were noted in any group. However, significant changes were observed in brain temperature. Fifteen minutes after heatstroke, brain temperature was 37.6 +/- 0.4 degrees C, 36.1 +/- 0.4 degrees C, and 33.6 +/- 0.8 degrees C in HS, HS + F, and HS + J, respectively. Survival time was 16.1 +/- 2.1, 33.0 +/- 3.8, and >120 mins in these groups, respectively. Neuron damage score was significantly lower in HS + J and without lateralization.

CONCLUSIONS

We successfully demonstrated that direct retrograde hypothermic perfusion via the jugular vein without cardiopulmonary bypass protected the brain after heat stroke. This technique cooled the brain but did not significantly interfere with body temperature.

Effect of mild hypothermia on focal cerebral ischemia. Review of experimental studies

The purposes of this review are to clarify the effect of hypothermia therapy on focal cerebral ischemia in rats, and to consider the relevancy of its application to human focal cerebral ischemia. Since 1990, 26 reports confirming the brain-protecting effect of hypothermia in rat focal cerebral ischemia models have been published. Seventy-four experimental groups in these 26 reports were classified as having transient middle cerebral arterial occlusion (MCAO) with mild hypothermia (group A; 43 groups), permanent MCAO with mild hypothermia (group B; 14 groups), permanent MCAO with deep hypothermia (group C; 8 groups) and transient or permanent MCAO with mild hyperthermia (group D; 9 groups). The results were evaluated as the % infarct volume change caused by hypothermia or hyperthermia compared with the infarct volume in normothermic animals. The effectiveness was confirmed in 36 (83%) of the 43 groups in group A, 10 (71%) of the 14 in group B, and six (75%) of the eight in group C. The infarct volume of eight of the nine groups in group D was markedly aggravated. The percent infarct volume change was 55.3% +/- 27.1% in group A, 57.6% +/- 24.7% in group B, 60.8% +/- 45.5% in group C, and 189.7% +/- 89.4% in group D. For effective reduction of the infarct volume, hypothermia should be started during ischemia or within 1 h, at latest, after the beginning of reperfusion in the rat transient MCAO model. However, it is not clear whether this neuroprotective effect of hypothermia can also be observed in the chronic stage, such as several months later. Keeping the body temperature normothermic in order to avoid mild hyperthermia seems to be rather important for not aggravating cerebral infarction. Clinical randomized studies on the efficacy of mild hypothermia for focal cerebral ischemia and sophisticated mild hypothermia therapy techniques are mandatory.

Reduced brain infarct volume and improved neurological outcome by inhibition of the NR2B subunit of NMDA receptors by using CP101,606-27 alone and in combination with rt-PA in a thromboembolic stroke model in rats

OBJECT

A novel postsynaptic antagonist of N-methyl-D-aspartate (NMDA) receptors, CP-101,606-27 may attenuate the effects of focal ischemia. In current experiments, the authors investigated its neuroprotective effect alone and in combination with recombinant tissue plasminogen activator (rt-PA) in thromboembolic focal cerebral ischemia in rats.

METHODS

Forty-eight male Wistar rats underwent embolization of the right middle cerebral artery to produce focal cerebral ischemia. After random division into six groups (eight rats in each group), animals received: vehicle; low-dose (LD) CP-101, 606-27, 14.4 mg/kg; high-dose (HD) CP- 101,606-27, 28.8 mg/kg; rt-PA, 10 mg/kg; low-dose combination (LDC) CP- 101,606-27, 14.4 mg/kg plus rt-PA, 10 mg/kg; or high-dose combination (HDC) CP- 101,606-27, 28.8 mg/kg plus rt-PA, 10 mg/kg) 2 hours after induction of embolic stroke. Animals were killed 48 hours after the onset of focal ischemia. Brain infarction volume, neurobehavioral outcome, poststroke seizure activity, poststroke mortality, and intracranial hemorrhage incidence were observed and evaluated. Compared with vehicle-treated animals (39.4 +/- 8.6%) 2 hours posttreatment with CP-101,606-27 or rt-PA or in combination a significant reduction in the percentage of brain infarct volume was seen (LD CP-101,606-27: 20.8 +/- 14.3%, p < 0.05; HD CP-101,606-27: 10.9 +/- 3.2%, p < 0.001; rt-PA: 21.1 +/- 7.3%, p < 0.05; LDC, 18.6 +/- 11.5%, p < 0.05; and HDC: 15.2 +/- 10.1%, p < 0.05; compared with control: 39.4 +/- 8.6%). Combination of CP-101,606-27 with rt-PA did not show a significantly enhanced neuroprotective effect. Except for the control and LDC treatment groups, neurobehavioral outcome was significantly improved 24 hours after embolic stroke in animals in all other active therapeutic groups receiving CP-101,606-27 or rt-PA or in combination. The authors also observed that treatment with HD CP-101,606-27 decreased poststroke seizure activity.

CONCLUSIONS

The data in this study suggested that postischemia treatment with CP-101,606-27 is neuroprotective in the current stroke model; however, the authors also note that although rt-PA may offer modest protection when used alone, combination with CP-101,606-27 did not appear to enhance its effects.

Significance of temperature difference between cerebral cortex and axilla in patients under hypothermia management

It is believed that the brain temperature is about 1 degree C higher than the other peripheral temperature. But the result has been mostly obtained in normothermia patients. The objective of this study was to evaluate whether the brain temperature is still higher than the axillary one in the hypothermia patients. Sixty-three patients who underwent craniotomy with implantation of the thermal diffusion thermometer were included in this study. Fifty-four patients were in normothermia and nine patients were managed with mild to moderate hypothermia (about 32 degrees C). The temperature of the cerebral cortex and axilla was measured simultaneously every 2 hours. 1900 paired sample data were collected and analyzed. The temperature difference between the cerebral cortex and the axilla was 1.04 +/- 0.67 degrees C in normothermia patients and 0.91 +/- 0.84 degree C in hypothermic patients. The temperature difference has no statistical significance between the two groups (unpaired t-test, P > 0.05). Our results demonstrate that the brain temperature in the patients under hypothermia management appears to be still about 1 degree C higher than the axilla throughout the study period almost in the same fashion as in normothermia patients.