Jugular bulb temperature: comparison with brain surface and core temperatures in neurosurgical patients during mild hypothermia

Abnormal immune system response in the brain of women with Fibromyalgia after experimental endotoxin challenge

Background

The pathophysiology of fibromyalgia (FM) is thought to include an overactive immune system, leading to central nervous system sensitization, allodynia, and hyperalgesia. We aimed to test this theory using an experimental immune system activation procedure and neuroimaging with magnetic resonance spectroscopic imaging (MRSI).

Methods

Twelve women with FM and 13 healthy women (healthy controls; HC) received 0.3 or 0.4 ng/kg endotoxin and underwent MRSI before and after the infusion. Changes in brain levels of choline (CHO), myo-inositol (MI), N-Acetylaspartate (NAA), and MRSI-derived brain temperature were compared between groups and dosage levels using mixed analyses of variance.

Results

Significant group-by-time interactions in brain temperature were found in the right thalamus. Post-hoc testing revealed that brain temperature increased by 0.55 °C in the right thalamus in FM (t(10) = -3.483, p = 0.006), but not in HCs (p > 0.05). Dose-by-time interactions revealed brain temperature increases in the right insula after 0.4 ng/kg (t(12) = -4.074, p = 0.002), but not after 0.3 ng/kg (p > 0.05). Dose-by-time interactions revealed decreased CHO in the right Rolandic operculum after 0.4 ng/kg endotoxin (t(13) = 3.242, p = 0.006) but not 0.3 ng/kg. In the left paracentral lobule, CHO decreased after 0.3 ng/kg (t(9) = 2.574, p = 0.030) but not 0.4 ng/kg. Dose-by-time interactions affected MI in several brain regions. MI increased after 0.3 ng/kg in the right Rolandic operculum (t(10) = -2.374, p = 0.039), left supplementary motor area (t(9) = -2.303, p = 0.047), and left occipital lobe (t(10) = -3.757, p = 0.004), with no changes after 0.4 ng/kg (p > 0.05). Group-by time interactions revealed decreased NAA in the left Rolandic operculum in FM (t(13) = 2.664, p = 0.019), but not in HCs (p > 0.05). A dose-by-time interaction showed decreased NAA in the left paracentral lobule after 0.3 ng/kg (t(9) = 3.071, p = 0.013) but not after 0.4 ng/kg (p > 0.05). In the combined sample, there was a main effect of time whereby NAA decreased in the left anterior cingulate (F[1,21] = 4.458, p = 0.047) and right parietal lobe (F[1,21] = 5.457, p = 0.029).

Conclusion

We found temperature increases and NAA decreases in FM that were not seen in HCs, suggesting that FM patients may have abnormal immune responses in the brain. The 0.3 and 0.4 ng/kg had differential effects on brain temperature and metabolites, with neither dose effecting a stronger response overall. There is insufficient evidence provided by the study to determine whether FM involves abnormal central responses to low-level immune challenges.

Temperature difference between jugular bulb and pulmonary artery is associated with neurological outcome in patients with severe traumatic brain injury: A post hoc analysis of a brain hypothermia study

BACKGROUND

The purpose of this study was to examine whether the temperature difference between the jugular bulb and pulmonary artery (ΔTjb-pa) is associated with the neurological outcome of patients with severe traumatic brain injury (TBI).

METHODS

We conducted a post hoc analysis of a multicenter randomized controlled trial of mild therapeutic hypothermia (TH, 32.0-34.0°C) or fever control (FC, 35.5-37.0°C) for the patients with severe TBI. ΔTjb-pa averaged every 12 h and the variation in ΔTjb-pa were compared between patients with favorable (n = 39) and unfavorable (n = 37) neurological outcomes. These values were also compared in the TH and FC subgroups.

RESULTS

The average ΔTjb-pa values in patients with favorable and unfavorable outcomes were 0.24 ± 0.23 and 0.06 ± 0.36°C, respectively (P < 0.001). ΔTjb-pa trended significantly higher in the favorable outcome patients than in the unfavorable outcome patients throughout the 120 h after onset of severe TBI (P < 0.001). The variation in ΔTjb-pa from 0 to 72 h was significantly lower in the favorable outcome patients than in the unfavorable outcome patients (0.8 ± 0.8 vs 1.8 ± 2.5°C, respectively, P = 0.013). From 72 to 120 h, there was no significant difference in the variation in ΔTjb-pa. Significant differences between patients with favorable and unfavorable outcomes in ΔTjb-pa and the variation in ΔTjb-pa were similar in the TH subgroup, but not evident in the FC subgroup.

CONCLUSIONS

A reduction in ΔTjb-pa and greater variation in ΔTjb-pa were associated with an unfavorable outcome in patients with severe TBI, especially those treated with TH. When treating severe TBI patients, it is important to understand that there will be differences in temperature reflecting the brain environment and the systemic temperature, depending on the severity and outcome of TBI during TH.

Temperature management on cardiopulmonary bypass: Is it standardised across Great Britain and Ireland?

Temperature management is an essential element of cardiopulmonary bypass (CPB), as indicated in the Guide to Good Practice in Clinical Perfusion, 'The safe conduct of CPB requires the clinical perfusionist to measure and control. . . blood temperature. . . during the period of bypass'. To review current practice, we have conducted a research survey into the management of temperature on CPB. Surveys were distributed to each centre in Great Britain and the Republic of Ireland, investigating numerous temperature management practices, to elucidate current practice and assess if recent research into temperature management marry routine clinical practice. Our results demonstrate that nasopharyngeal temperature is the most common (52%) temperature site used across the many centres, which correlates with previous research as a routine site for cerebral temperature management. The arterial outlet of the oxygenator temperature was used in 33% of centres, however, all centres lacked the knowledge to maintain this temperature below 37°C. There was significant variation between all centres, especially regarding rewarming times (20-40 minutes), demonstrating a lack of uniformity among perfusion centres. Interestingly, most centres have been using the same protocol that has been in place over the previous 10 years.To conclude, the practice of temperature management is changing with the awareness of new research. Lower target temperatures are recommended for rewarming, ensuring a lower temperature gradient and a longer mean rewarming time.

Skin temperature maps as a measure of carotid artery stenosis

In this study, the effect of carotid artery stenosis on the neck skin temperature maps was investigated. With the presence of stenosis, alterations in the carotid artery hemodynamics bring about changes in the heat transfer to the surrounding tissue. This is expected to be captured in the resulting temperature map over the external neck skin surface; possibly it correlates to the presence of stenosis. A total of twenty carotid artery samples, from ten patients with both sides normal (0% stenosis), stenosis (>50%) on one side, and stenosis (>50%) on both sides, were studied. Duplex Ultrasound and infrared (IR) thermography examinations were performed. A computational study, on an ideal 3-dimensional (3D) carotid artery and jugular vein model encapsulated with a solid neck tissue phantom resembling the human neck, was carried out. Incorporating the patient-specific geometrical (depth of artery and stenosis) and flow (peak systolic and end diastolic inlet velocity) boundary conditions, conjugate bio-heat transfer was studied using a finite volume numerical scheme. Simulation results and in-vivo thermal maps show that the average temperature on the external neck skin surface is significantly higher for normal patients (32.82 ± 0.53 °C versus 32.00 ± 0.37 °C, p < 0.001). Furthermore, the thermal region of interests (TROIs) were extracted from the in-vivo thermal images, which both qualitatively and quantitatively distinguish the normal and diseased cases. This study suggests the potential of thermal feature-based screening of patients with carotid artery stenosis.

Selective brain hypothermia: feasibility and safety study of a novel method in five patients

BACKGROUND/OBJECTIVE

Reduction of brain temperature remains the most common method of neuroprotection against ischemic injury employed during cardiac surgery. However, cooling delivered via the cardiopulmonary bypass circuit is brief and cooling the body core along with the brain has been associated with a variety of unwanted effects. This study investigated the feasibility and safety of a novel selective brain cooling approach to induce rapid, brain-targeted hypothermia independent of the cardiopulmonary bypass circuit.

METHODS

This first-in-human feasibility study enrolled five adults undergoing aortic valve replacement with cardiopulmonary bypass support. During surgery, the NeuroSave system circulated chilled saline within the pharynx and upper esophagus. Brain and body core temperature were continuously monitored. Adverse effects, cardiopulmonary function, and device function were noted.

RESULTS

Patient 1 received cooling fluid for an insignificant period, and Patients 2-5 successfully underwent the cooling procedure using the NeuroSave system for 56-89 minutes. Cooling fluid was 12°C for Patients 1-3, 6°C for Patient 4, and 2°C for Patient 5. There were no NeuroSave-related adverse events and no alterations in cardiopulmonary function during NeuroSave use. Brain temperature decreased by 3°C within 15 minutes and remained at least 3.5°C colder than the body core. During a brief episode of hypotension in one patient, the brain cooled an additional 4°C in 2 minutes, briefly reaching 27.4°C.

CONCLUSION

The NeuroSave system can induce rapid brain-targeted hypothermia and simultaneously maintain a favorable body-brain temperature gradient, even during hypotension. Further studies are required to evaluate the function of the system during longer periods of use.

2016 survey about temperature management during extracorporeal circulation in China

Objective:

In order to assess the current status of temperature management during cardiopulmonary bypass (CPB) in China and, thereby, implement standardized management protocols, the authors carried out a national survey about institutions performing CPB.

Method:

The survey was carried out from September 2015 to February 2016 and was supported by the Chinese Society of ExtraCorporeal Circulation. A total of 114 institutions participated, accounting for 15.64% (114/729) of the total of germane Chinese institutions, whereby, 80.85% (38/47) of the institutions had an annual surgical volume of more than 1000 cases.

Results:

The most common sites of temperature measurement were nasopharyngeal (NP) (99.12%) and rectal (92.98%) while oxygenator blood temperature was less popular (28%). Rectal temperature as the core temperature was chosen by 78.95% of the institutions; 92.11% of the institutions chose nasopharyngeal temperature to represent the cerebral temperature. During deep hypothermia circulatory arrest (DHCA) when there was no cerebral perfusion, 18 to 22℃ was the most common indication of circulatory arrest. However, with cerebral perfusion, more than 40% of the institutions maintained a lowest temperature of 22 to 25℃ for adult and pediatric patients. A NP temperature of 36 to 37℃ was chosen by 70.18% of the institutions while 81.79% chose a rectal temperature of 35 to 36.5℃ as the indication to wean from CPB. The majority of the institutions chose a difference of 10℃ between the water tank and core temperatures as the temperature gradient during rewarming. Auxiliary heat preservation techniques and equipment were used in 91.23% of the institutions, whereas 35.58% of them would lower the indications to wean from CPB.

Conclusions:

This survey accurately reflects the current situation of temperature management during CPB in institutions with an annual surgical volume of >500 cases, but has, hereby, failed to properly represent the institutions with a lower annual surgical volume.

Clinical review: Brain-body temperature differences in adults with severe traumatic brain injury

Surrogate or 'proxy' measures of brain temperature are used in the routine management of patients with brain damage. The prevailing view is that the brain is 'hotter' than the body. The polarity and magnitude of temperature differences between brain and body, however, remains unclear after severe traumatic brain injury (TBI). The focus of this systematic review is on the adult patient admitted to intensive/neurocritical care with a diagnosis of severe TBI (Glasgow Coma Scale score of less than 8). The review considered studies that measured brain temperature and core body temperature. Articles published in English from the years 1980 to 2012 were searched in databases, CINAHL, PubMed, Scopus, Web of Science, Science Direct, Ovid SP, Mednar and ProQuest Dissertations & Theses Database. For the review, publications of randomised controlled trials, non-randomised controlled trials, before and after studies, cohort studies, case-control studies and descriptive studies were considered for inclusion. Of 2,391 records identified via the search strategies, 37 were retrieved for detailed examination (including two via hand searching). Fifteen were reviewed and assessed for methodological quality. Eleven studies were included in the systematic review providing 15 brain-core body temperature comparisons. The direction of mean brain-body temperature differences was positive (brain higher than body temperature) and negative (brain lower than body temperature). Hypothermia is associated with large brain-body temperature differences. Brain temperature cannot be predicted reliably from core body temperature. Concurrent monitoring of brain and body temperature is recommended in patients where risk of temperature-related neuronal damage is a cause for clinical concern and when deliberate induction of below-normal body temperature is instituted.

Success rates and procedure times of oesophageal temperature probe insertion for therapeutic hypothermia treatment of cardiac arrest according to insertion methods in the emergency department

PURPOSE

Therapeutic hypothermia has become the standard treatment for unconscious patients in cardiac arrest. Although various body parts, including the oesophagus, rectum, bladder and tympanum, can be used for measurement of the core temperature, the oesophageal temperature is preferred because of its accuracy and stability. We first investigated the success rate and procedure time of oesophageal temperature probe (ETP) insertion according to the insertion method.

METHODS

The conventional method involved blind insertion through nasal orifices. The alternative method was insertion with Magill's forceps or long forceps under visualisation using a direct laryngoscope. The new method was performed as follows: (1) insertion of another endotracheal tube (ETT) orally into the oesophagus; (2) insertion of a temperature probe into the hole of the ETT; (3) removal of the ETT. To compare the success rates and procedure times according to the insertion method, we collected data retrospectively from the prospective Samsung Medical Centre hypothermia database and medical records.

RESULTS

A total of 91 cases were examined. Insertion was performed using the conventional method in 36 cases, the alternative method in 26, and the new method in 29. Rates of success on the first attempt were 63.9%, 65.4% and 100%, and procedure times were 33.2 ± 13.6, 33.3 ± 17.8 and 27.0 ± 7.9 min, for the conventional, alternative and new methods, respectively. The initial success rates and procedure times were significantly different among the three groups (p<0.01).

CONCLUSIONS

The new ETP insertion method had a better first attempt success rate than the conventional method and the alternative method.

Fever control and application of hypothermia using intravenous cold saline

OBJECTIVES

To describe the use and feasibility of cold saline to decrease body temperature in pediatric neurocritical care.

DESIGN

Retrospective chart review.

SETTING

Pediatric tertiary care university hospital.

PATIENTS

Children between 1 wk and 17 yrs of age admitted to the pediatric intensive care unit with acute brain injury and having received intravenous cold saline between June and August 2009.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Eighteen subjects accounted for 20 infusions with mean infusion volume 18 ± 10 mL/kg. Eight subjects had traumatic brain injury, two had intracranial hemorrhage, six had cardiac arrest, and one each had ischemic stroke and status epilepticus. The mean age was 9.5 ± 4.8 yrs. Temperature decreased from 38.7 ± 1.1°C to 37.7 ± 1.2°C and from 37.0 ± 2.0°C to 35.3 ± 1.6°C 1 hr after infusion for fever (n = 14; p < .05) or hypothermia induction (n = 6; p = .05), respectively. Cold saline was not bloused but rather infused over 10-15 mins. Mean arterial blood pressure and oxygenation parameters (PaO2/FIO2 ratio, mean airway pressure) were unchanged, but heart rate decreased in those with hypothermia (121 ± 4 beats per minute vs. 109 ± 12 beats per minute; p < .05). Serum sodium concentration and international normalized ratio were significantly increased after cold saline infusion. There were no differences between preinfusion and postinfusion serum glucose and hematocrit, or between cerebral perfusion pressure and intracranial pressure in traumatic brain injury patients.

CONCLUSIONS

Cold saline was an effective method of reducing temperature in children with acute brain injury. This approach can be considered to treat fever or to induce hypothermia. A prospective study comparing safety and efficacy vs. other cooling measures should be considered.

Therapeutic hypothermia: benefits, mechanisms and potential clinical applications in neurological, cardiac and kidney injury

Therapeutic hypothermia involves the controlled reduction of core temperature to attenuate the secondary organ damage which occurs following a primary injury. Clinicians have been increasingly using therapeutic hypothermia to prevent or ameliorate various types of neurological injury and more recently for some forms of cardiac injury. In addition, some recent evidence suggests that therapeutic hypothermia may also provide benefit following acute kidney injury. In this review we will examine the potential mechanisms of action and current clinical evidence surrounding the use of therapeutic hypothermia. We will discuss the ideal methodological attributes of future studies using hypothermia to optimise outcomes following organ injury, in particular neurological injury. We will assess the importance of target hypothermic temperature, time to achieve target temperature, duration of cooling, and re-warming rate on outcomes following neurological injury to gain insights into important factors which may also influence the success of hypothermia in other organ injuries, such as the heart and the kidney. Finally, we will examine the potential of therapeutic hypothermia as a future kidney protective therapy.

Recommendations for haemodynamic and neurological monitoring in repair of acute type a aortic dissection

During treatment of acute type A aortic dissection there is potential for both pre- and intra-operative malperfusion. There are a number of monitoring strategies that may allow for earlier detection of potentially catastrophic malperfusion (particularly cerebral malperfusion) phenomena available for the anaesthetist and surgeon. This review article sets out to discuss the benefits of the current standard monitoring techniques available as well as desirable/experimental techniques which may serve as adjuncts in the monitoring of these complex patients.

Safety and feasibility of nasopharyngeal evaporative cooling in the emergency department setting in survivors of cardiac arrest

AIM

Mild therapeutic hypothermia improves survival and neurologic recovery in primary comatose survivors of cardiac arrest. Cooling effectivity, safety and feasibility of nasopharyngeal cooling with the RhinoChill device (BeneChill Inc., San Diego, USA) were determined for induction of therapeutic hypothermia.

METHODS

Eleven emergency departments and intensive care units participated in this multi-centre, single-arm descriptive study. Eighty-four patients after successful resuscitation from cardiac arrest were cooled with nasopharyngeal delivery of an evaporative coolant for 1h. Subsequently, temperature was controlled with systemic cooling at 33 degrees C. Cooling rates, adverse events and neurologic outcome at hospital discharge using cerebral performance categories (CPC; CPC 1=normal to CPC 5=dead) were documented. Temperatures are presented as median and the range from the first to the third quartile.

RESULTS

Nasopharyngeal cooling for 1h reduced tympanic temperature by median 2.3 (1.6; 3.0) degrees C, core temperature by 1.1 (0.7; 1.5) degrees C. Nasal discoloration occurred during the procedure in 10 (12%) patients, resolved in 9, and was persistent in 1 (1%). Epistaxis was observed in 2 (2%) patients. Periorbital gas emphysema occurred in 1 (1%) patient and resolved spontaneously. Thirty-four of 84 patients (40%) patients survived, 26/34 with favorable neurological outcome (CPC of 1-2) at discharge.

CONCLUSIONS

Nasopharyngeal evaporative cooling used for 1h in primary cardiac arrest survivors is feasible and safe at flow rates of 40-50L/min in a hospital setting.

Therapeutic hypothermia: implications for acute care practitioners

The use of therapeutic hypothermia (TH) in acute care medicine has evolved over the past 2 centuries, and its use over the past decade has increased in emergency departments, intensive care units, and operating rooms. Therapeutic hypothermia has several potential clinical applications based on its putative mechanisms of action. It appears to improve oxygen supply to ischemic areas of the brain and decreases intracranial pressure. Mild-to-moderate TH (33 degrees C +/- 1 degrees C) after resuscitation from cardiac arrest is neuroprotective, and also acts on the cardiovascular system with evidence of a decrease in heart rate and increase in systemic vascular resistance. Therapeutic hypothermia decreases cardiac output by 7% for each 1 degrees C decrease in core body temperature, but maintains the stroke volume and the mean arterial pressure. Despite a growing amount of data, this life-saving technique is underutilized in hospitals worldwide. The purpose of this comprehensive review is to show the evolution and the clinical use of TH as it pertains to acute care practitioners.

A tertiary care center's experience with therapeutic hypothermia after pediatric cardiac arrest

OBJECTIVE

To describe the use and feasibility of therapeutic hypothermia after pediatric cardiac arrest.

DESIGN

Retrospective cohort study.

SETTING

Pediatric tertiary care university hospital.

PATIENTS

Infants and children (age 1 wk to 21 yrs) without complex congenital heart disease with return of spontaneous circulation after in-hospital or out-of-hospital cardiac arrest from 2000 to 2006.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

We studied 181 patients after cardiac arrest, of which 91% were asphyxial in etiology (vs. cardiac) and 52% occurred in-hospital. Overall survival to hospital discharge was 45%. Forty patients received therapeutic hypothermia; all were admitted during or after 2002. Sixty percent of patients in the therapeutic hypothermia group had an initial temperature <35 degrees C. The median therapeutic hypothermia target temperature was 34.0 degrees C (33.5-34.8 degrees C), was reached by 7 hrs (5-8 hrs) after admission in patients who were not hypothermic on admission, and was maintained for 24 hrs (16-48 hrs). Re-warming lasted 6 hrs (5-8 hrs). In the therapeutic hypothermia group, temperature <32 degrees C occurred in 15% of patients and was associated with higher hospital mortality (29% vs. 11%; p = .02). Patients treated with therapeutic hypothermia differed from those treated with standard therapy, with more un-witnessed cardiac arrest (p = .04), more doses of epinephrine to achieve return of spontaneous circulation (p = .03), and a trend toward more out-of-hospital cardiac arrests (p = .11). After arrest, therapeutic hypothermia patients received more frequent electrolyte supplementation (p < .05). Standard therapy patients were twice as likely as therapeutic hypothermia patients to have a fever (>38 degrees C) after arrest (37% vs. 18%; p = .02) and trended toward a higher rate of re-arrest (26% vs. 13%; p = .09). Rates of red blood cell transfusions, infection, and arrhythmias were similar between groups. There was no difference in hospital mortality (55.0% therapeutic hypothermia vs. 55.3% standard therapy; p = 1.0), and 78% of the therapeutic hypothermia survivors were discharged home (vs. 68% of the standard therapy survivors; p = .46). In multivariate analysis, mortality was independently associated with initial hypoglycemia or hyperglycemia, number of doses of epinephrine during resuscitation, asphyxial etiology, and longer duration of cardiopulmonary resuscitation, but not treatment group (odds ratio for mortality in the therapeutic hypothermia group, 0.47; p = .2).

CONCLUSIONS

This is the largest study reported on the use of therapeutic mild hypothermia in pediatric cardiac arrest to date. We found that therapeutic hypothermia was feasible, with target temperature achieved in <3 hrs overall. Temperature below target range was associated with increased mortality. Prospective study is urgently needed to determine the efficacy of therapeutic hypothermia in pediatric patients after cardiac arrest.

Head and neck cooling after cardiac arrest results in lower jugular bulb than esophageal temperature

PURPOSE

To determine whether during the initial phase of head and neck cooling, jugular bulb temperature (Tjb; which may reflect brain temperature) is lower than esophageal temperature (Tes).

BASIC PROCEDURES

To compare Tes and Tjb, patients received head or head and neck cooling after cardiac arrest.

MAIN FINDINGS

The first series with head cooling (n = 5; mean age 54 with a range of 41-62 years; 1 female and 4 males; mean body weight 80 kg with a range of 70-85 kg) showed a mean difference of 0.22 degrees C (95% CI, -1.14 to 0.70; P = .55; limits of agreement, -3.17 to 2.73) between Tes and Tjb over 12 hours. For the second series, with head and neck cooling (n = 6, mean age 65 with a range of 56-76 years; 3 females and 3 males; mean body weight 75 kg with a range of 65-91 kg), Tjb was lower than Tes with a difference of 0.60 degrees C (95% CI, 0.22 to 0.99; P = .01; limits of agreement, -3.10 to 4.30). During the first 3 hours, Tjb decreased faster than Tes (1.1 degrees C/h [95% CI, 0.4 to 1.8; P < .01]).

PRINCIPAL CONCLUSION

During the initial phase of therapeutic hypothermia, Tjb seems to be lower than Tes.

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.

Therapeutic hypothermia: past, present, and future

Cardiac arrest causes devastating neurologic morbidity and mortality. The preservation of the brain function is the final goal of resuscitation. Therapeutic hypothermia (TH) has been considered as an effective method for reducing ischemic injury of the brain. The therapeutic use of hypothermia has been utilized for millennia, and over the last 50 years has been routinely employed in the operating room. TH gained recognition in the past 6 years as a neuroprotective agent in victims of cardiac arrest after two large, randomized, prospective clinical trials demonstrated its benefits in the postresuscitation setting. Extensive research has been done at the cellular and molecular levels and in animal models. There are a number of proposed applications of TH, including traumatic brain injury, acute encephalitis, stroke, neonatal hypoxemia, and near-drowning, among others. Several devices are being designed with the purpose of decreasing temperature at a fast and steady rate, and trying to avoid potential complications. This article reviews the historical development of TH, and its current indications, methods of induction, and potential future.

Rapid non-invasive external cooling to induce mild therapeutic hypothermia in adult human-sized swine

AIM OF THE STUDY

Mild therapeutic hypothermia is a promising new therapy for patients resuscitated from cardiac arrest. Early and fast induction of hypothermia seems to be crucial for best results. The aim of the study was to investigate the feasibility and safety of a new surface cooling method using cold metal plates.

SUBJECTS AND METHODS

Twelve adult human-sized swine (79+/-9 kg) were cooled from 38 to 33 degrees C brain temperature. The skin surface was covered with -20 degrees C metal plates (M), as compared to ice packs, alcohol rubs, and fans used in a control group (C). Each method was tested during spontaneous circulation and, after re-warming, during cardiac arrest. Temperatures were recorded continuously. Data are given as mean+/-standard deviation or as median (interquartile range), if not normally distributed. Comparisons between the treatment groups were performed with the independent samples t-test, or the Mann-Whitney rank-sum test.

RESULTS

During spontaneous circulation, cooling rates were 9.3+/-1.4 degrees C/h (M), and 6.1+/-1.4 degrees C/h (C) (p=0.003); no skin lesions were observed. During cardiac arrest, cooling rates were 4.1 degrees C/h (1.8-4.8) (M), and 3.7 degrees C/h (3.1-5.3) (C) (p=0.9); no skin lesions were observed.

CONCLUSION

Cooling with cold metal plates was an effective method for rapid induction of mild therapeutic hypothermia in adult human-sized swine during spontaneous circulation, without any signs of skin damage. This new surface-cooling device, independent of energy supply during use, should be further investigated.

Reliability of temperatures measured at standard monitoring sites as an index of brain temperature during deep hypothermic cardiopulmonary bypass conducted for thoracic aortic reconstruction

OBJECTIVE

It is essential to estimate the brain temperature of patients during deliberate deep hypothermia. Using jugular bulb temperature as a standard for brain temperature, we evaluated the accuracy and precision of 5 standard temperature monitoring sites (ie, pulmonary artery, nasopharynx, forehead deep-tissue, urinary bladder, and fingertip skin-surface tissue) during deep hypothermic cardiopulmonary bypass conducted for thoracic aortic reconstruction.

METHODS

In 20 adult patients with thoracic aortic aneurysms, the 5 temperature monitoring sites were recorded every 1 minute during deep hypothermic (<20 degrees C) cardiopulmonary bypass. The accuracy was evaluated by the difference from jugular bulb temperature, and the precision was evaluated by its standard deviation, as well as by the correlation with jugular bulb temperature.

RESULTS

Pulmonary artery temperature and jugular bulb temperature began to change immediately after the start of cooling or rewarming, closely matching each other, and the other temperatures lagged behind these two temperatures. During either situation, the accuracy of pulmonary artery temperature measurement (0.3 degrees C-0.5 degrees C) was much superior to the other measurements, and its precision (standard deviation of the difference from jugular bulb temperature = 1.5 degrees C-1.8 degrees C; correlation coefficient = 0.94-0.95) was also best among the measurements, with its rank order being pulmonary artery > or = nasopharynx > forehead > bladder > fingertip. However, the accuracy and precision of pulmonary artery temperature measurement was significantly impaired during and for several minutes after infusion of cold cardioplegic solution.

CONCLUSIONS

Pulmonary artery temperature measurement is recommended to estimate brain temperature during deep hypothermic cardiopulmonary bypass, even if it is conducted with the sternum opened; however, caution needs to be exercised in interpreting its measurements during periods of the cardioplegic solution infusion.

Comparing no-touch and tympanic thermometer temperature recordings

Temperature is a vital sign which can be measured using various types of clinical thermometers. Pulmonary artery temperature is considered the 'gold standard', but this measurement is not usually clinically practical. There is currently no consensus for optimal alternative site or equipment. This research compares 178 simultaneous measurements from 5 clinical areas, using two types of thermometers: tympanic and no-touch temporal. No-touch thermometers were all set to oral equivalent. Tympanic thermometers were adjusted to either oral (n=105) or core (n=73) equivalent. Maximum acceptable difference was identified as 1oC. Two data sets (oral/core; oral/oral) were analysed using Bland-Altman method on Excel programmes, comparing all thermometers and separating oral and core-equivalent tympanics. The two thermometers were found not to be equivalent. As a simple comparison between two thermometers, this research cannot identify which thermometer is more accurate.

Cardiopulmonary bypass temperature and brain function

A debate has emerged in recently published studies about the optimum cardiopulmonary bypass temperature for good neurological outcome - warm vs. cold, i.e. normothermic vs. hypothermic. Although many comparative studies have been performed, the results of these studies are inconclusive and are difficult to interpret. Brain function has been studied in terms of neurological and neuropsychological outcome, protein S100beta levels as a marker of brain damage, and cerebral oxygenation using jugular bulb oximetry and near-infrared spectroscopy. The studies produce no conclusive proof of the superiority of warm or cold cardiopulmonary bypass. However, it appears that any degree of bypass hypothermia (< 35 degrees C) may protect the brain. On the other hand, even a slight increase in bypass temperature to > 37 degrees C may cause marked brain injury.

Induced hypothermia in critical care medicine: a review

BACKGROUND

Clinical trials of induced hypothermia have suggested that this treatment may be beneficial in selected patients with neurologic injury.

OBJECTIVES

To review the topic of induced hypothermia as a treatment of patients with neurologic and other disorders.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

Improved outcome was demonstrated in two prospective, randomized, controlled trials in which induced hypothermia (33 degrees C for 12-24 hrs) was used in patients with anoxic brain injury following resuscitation from prehospital cardiac arrest. In addition, prospective, randomized, controlled trials have been conducted in patients with severe head injury, with variable results. There also have been preliminary clinical studies of induced hypothermia in patients with severe stroke, newborn hypoxic-ischemic encephalopathy, neurologic infection, and hepatic encephalopathy, with promising results. Finally, animal models have suggested that hypothermia that is induced rapidly following traumatic cardiac arrest provides significant neurologic protection and improved survival.

CONCLUSIONS

Induced hypothermia has a role in selected patients in the intensive care unit. Critical care physicians should be familiar with the physiologic effects, current indications, techniques, and complications of induced hyperthermia.

The importance of brain temperature in patients after severe head injury: relationship to intracranial pressure, cerebral perfusion pressure, cerebral blood flow, and outcome

Brain temperature was continuously measured in 58 patients after severe head injury and compared to rectal temperature, intracranial pressure, cerebral blood flow, and outcome after 3 months. The temperature difference between brain and rectal temperature was also calculated. Mild hypothermia (34-36 degrees C) was also used to treat uncontrollable intracranial pressure (ICP) above 20 mm Hg when other methods failed. Brain and rectal temperature were strongly correlated (r = 0.866; p < 0.001). Four groups were identified. The mean brain temperature ranged from 36.9 +/- 0.4 degrees C in the normothermic group to 38.2 +/- 0.5 degrees C in the hyperthermic group, 35.3 +/- 0.5 degrees C in the mild therapeutic hypothermia group, and 34.3 +/- 1.5 degrees C in the hypothermia group without active cooling. The mean DeltaT(br-rect) was positive for patients with a T(br) above 36.0 degrees C (0.0 +/- 0.5 degrees C) and negative for patients during mild therapeutic hypothermia (-0.2 +/- 0.6 degrees C) and also in those with a brain temperature below 36 degrees C without active cooling (0.8 +/- -1.4 degrees C) - the spontaneous hypothermic group. The cerebral perfusion pressure (CPP) was increased significantly by active cooling compared to the normothermic and hyperthermic groups. The mean cerebral blood flow (CBF) in patients with a brain temperature between 36.0 degrees C and 37.5 degrees C was 37.8 +/- 14.0 mL/100 g/min. The lowest CBF was measured in patients with a brain temperature <36.0 degrees C and a negative brain-rectal temperature difference (17.1 +/- 14.0 mL/100 g/min). A positive trend for improved outcome was seen in patients with mild hypothermia. Simultaneous monitoring of brain and rectal temperature provides important diagnostic and prognostic information to guide the treatment of patients after severe head injury (SHI) and the wide differentials that can develop between the brain and core temperature, especially during rapid cooling, strongly supports the use of brain temperature measurement if therapeutic hypothermia is considered for head injury care.

Effect of etiology and topography of lesion on body temperature at stroke onset

BACKGROUND AND PURPOSE

Hyperthermia is a well-known factor for neurologic deterioration, morbidity, and mortality in the early phase of stroke. However, the timing, localization of lesion, origin of stroke, which may influence body temperature, have not been clearly established.

METHODS

The purpose of this study was to determine the relationship between body temperature and origin, lesion topography, and prognosis at 3 months after onset of stroke. Axillary temperature was taken every hour for 72 hours in 473 patients with supra- or infratentorial cerebral vascular lesion. The time at which hyperthermia (>38 degrees C) appeared was evaluated by logistic regression analyses regarding to stroke origin and lesion localization. The correlation between body temperature and stroke outcome was quantified by Barthel index and American Heart Association Stroke Outcome Classification by recording in each 12- hour interval from stroke onset during 72 hours and after 3 months.

RESULTS

The body temperature was higher in patients with large-artery atherosclerosis (odds ratio [OR], 3.98; 95% confidence interval [CI] = 2.16-8.97; P = .001) and hemorrhagic stroke (OR = 2.05, 95% CI = 1.07-8.68, P = .001) than those with small-artery disease. In patients with posterior circulation infarct, the body temperature was higher than those with anterior circulation infarct (OR = 3.71, 95% CI = 2.07-6.67, P = .001), whereas there was no difference between patients with infratentorial hemorrhage and those with supratentorial hemorrhage (OR = 1.04, 95% CI = 0.75-1.43, P = .80). High body temperature at 24 hours of stroke onset (OR = 2.17, 95% CI = 2.09-7.57, P = .001) and 48 hours (OR = 1.27, 95% CI = 1.06-4.84, P = .02) was correlated with poor outcome and mortality.

CONCLUSION

An association between hyperthermia within 72 hours of ictus and stroke subtypes was observed among patients with ischemic and hemorrhagic stroke. Hyperthermic patients with total anterior circulation infarct, posterior circulation infarct, and supratentorial hemorrhage were associated with a marked increase of 3-months' mortality. Large-artery atherosclerosis, cardioembolism, and supra-infratentorial hemorrhage associated with hyperthermia may increase the severity of neurologic deficits.

Jugular bulb oximetry during cardiac surgery

Imbalance between cerebral oxygen supply and demand is thought to play an important role in the development of cerebral injury during cardiac surgery. This article presents an overview of cerebral oxygenation monitored by jugular bulb oximetry during cardiac surgery with cardiopulmonary bypass. The general principles of jugular bulb oximetry including physiology, intermittent and continuous monitoring, technical considerations, limitations and potential complications are discussed. Different applications of jugular bulb oximetry during bypass surgery and the possible therapeutic approaches to impaired cerebral oxygenation are described.

Jugular vein temperature reflects brain temperature during hypothermia

PURPOSE

The neuroprotective properties of mild to moderate hypothermia are well recognized but may not be employed correctly because brain temperature cannot usually be measured directly. This study investigated the jugular vein as a more accessible site that accurately reflects the actual brain temperature during mild, induced hypothermia.

METHODS

We selected ten mongrel dogs (mean weight 12 +/- 2 kg) and measured temperatures of the brain, jugular vein, cisterna magna, pulmonary artery and rectum during hypothermia, including cooling and rewarming. The brain temperature needle probe was inserted 2.0 cm into the parenchyma. A temperature probe was placed in the cisterna magna with an epidural needle. Swan-Ganz thermistor probes measured the jugular venous and pulmonary artery blood temperatures.

RESULT

The brain temperature decreased from 37.5 +/- 0.3 to 33.0 +/- 0.3 degrees C over an average 150 +/- 45 min cooling period. Stable cool was maintained for 245 +/- 32 min, followed by 165 +/- 50 min for rewarming from 33.5 +/- 0.3 to 37.5 +/- 0.3 degrees C. Jugular, cisterna magna and pulmonary arterial blood (PAB), but not rectal temperature, were close to brain temperature during stable cool. The mean jugular and cisterna magna temperatures were near the brain temperature at 0.1 degrees C higher and 0.1 degrees C lower, respectively. No significant effects of hypothermia were noted on hemodynamics in any phase.

CONCLUSION

Jugular vein temperature, along with cisterna magna and pulmonary artery blood and rectal temperature, reflected brain temperature during hypothermia. The jugular vein and cisterna magna sites more sensitively reflected brain temperature than other sites.

Cerebrovenous blood temperature-influence of cerebral perfusion pressure changes and hyperventilation: evaluation in a porcine study and in man

The objective of the first part of this study was to use an animal model to investigate the relationship between temperature in the cerebrovenous compartment and cerebral perfusion pressure. In the second part of the study, the objective was to examine the influence of hyperventilation and hypothermia on jugular bulb temperature and body temperature in patients undergoing elective neurosurgery. Intracranial pressure was increased artificially by inflating an infratentorial supracerebellar placed balloon catheter in nine pigs under general anesthesia. Temperature was monitored by thermocouples inserted in the sagittal sinus, white matter of the left lobe and abdominal aorta during the ensuing decrease in cerebral profusion pressure (CPP). Cerebrovenous blood temperature (jugular bulb) and body temperature (urinary bladder) were simultaneously monitored in 24 patients undergoing craniotomy. Moderate hyperventilation was performed in all patients. Cerebrovenous blood and core body temperature were recorded and differences between these two temperatures calculated at the beginning and the end of hyperventilation. At the beginning of the intracranial pressure (ICP), increase mean temperatures of cerebrovenous blood and cerebral tissue (left lobe) were lower than core body temperature. During CPP reduction the difference between core body temperature and cerebrovenous blood temperature increased significantly from 0.86+/-0.44 degrees C prior to ICP rise to 1.19+/-0.58 degrees C at maximum ICP. Before hyperventilation, cerebrovenous blood temperature was higher in 19 patients (+/- difference: 0.34 degrees C +/- 0.27) and equal or lower in five patients (difference: -0.08 degrees C +/- 0.11), than core body temperature. At the end of hyperventilation, the difference between cerebrovenous blood temperature and core body temperature increased (+0.42 degrees C +/- 0.24) in those 19 patients who had started with a higher cerebrovenous blood temperature and decreased (-0.10 degrees C +/- 0. 18) in the other five patients. Both studies demonstrated that the temperature of cerebrovenous blood is influenced by maneuvers which are supposed to decrease cerebral blood flow.

[Protective effect of hypothermia in cerebral ischemia]

The use of hypothermia to protect the brain from ischaemic insults is an old concept. During the last decades, studies have mainly shown a modulating effect of hypothermia on biochemical cerebral responses to ischaemia, in addition to the basic effect of energy savings. Thus, the beneficial effects of decreased brain temperature, even when limited during transient ischaemic insults, whether global or focal, complete or incomplete, have been established. The deeper the hypothermia, the longer the ischaemia can be prolonged with acceptable neurological outcome. Conversely, the effects of postischaemic hypothermia remain unclear, while extracerebral deleterious effects cannot be overlooked, and many parameters remain to be evaluated before undertaking a beneficial clinical trial. The only indication for therapeutic postischaemic hypothermia in the near future could be in the control of impending intracranial hypertension occurring after cerebral ischaemia.

Systemic hypothermia after spinal cord compression injury in the rat: does recorded temperature in accessible organs reflect the intramedullary temperature in the spinal cord?

This article addresses one basic issue regarding the use of systemic hypothermia in the acute management of spinal cord injury, namely, how to interpret temperature recordings in accessible organs such as the rectum or esophagus with reference to the spinal cord temperature. Thirty-six rats, divided into six groups, were randomized to laminectomy or to severe spinal cord compression trauma, and were further randomized to either a cooling/rewarming procedure or continuous normothermia (esophageal temperature 38 degrees C) for 90 min. The first procedure comprised normothermia during the surgical procedure, followed by lowering of the esophageal temperature from 38 degrees C to 30 degrees C (the hypothermic level), a 20-min steady-state period at 30 degrees C, rewarming to 38 degrees C, and finally a 20-min steady-state period at 38 degrees C. The esophageal, rectal, and epidural temperatures were recorded in all animals. The intramedullary temperature was also recorded invasively in four of the six groups. We conclude that the esophageal temperature is safe and easy to record and, in our setting, reflects the epidural temperature. The differences registrated may reflect a true deviation of the intramedullary temperature due to initial environmental exposure and secondary injury processes. Our results indicate that the esophageal temperature exceeds the intramedullary temperature during the initial recording and final steady state following rewarming, but not during the most crucial part of the experiment, the hypothermic period. The core temperature measured in the esophagus can therefore be used to evaluate the intramedullary temperature during alterations of the systemic temperature and during hypothermic periods.

Occurrence of potentially detrimental temperature alterations in hospitalized patients at risk for brain injury

OBJECTIVE

To ascertain the incidence and timing of fever in patients at risk for temperature modulation of brain injury resulting from ischemia or trauma.

DESIGN

We retrospectively reviewed the medical records of patients admitted between January 1991 and December 1994.

MATERIAL AND METHODS

We investigated three groups of hospitalized patients considered at risk for ongoing brain injury resulting from a prior cerebral insult: successful resuscitation from out-of-hospital cardiac arrest (CA), subarachnoid hemorrhage (SAH), or traumatic closed-head injury (CHI). Forty patients per condition were randomly selected from those who survived for more than 24 hours after hospital admission.

RESULTS

During the initial 72 hours of hospitalization, temperature increases to 38 degrees C or more (that is, temperatures previously reported to worsen neurologic outcome after brain injury) were noted in 83% of patients with CA, 70% of those with SAH, and 68% of those with CHI. Within the cohort of febrile patients, 18 to 44% of all temperature measurements were 38 degrees C or higher, and the febrile episodes occurred randomly throughout the study interval. Fewer than one-eighth of the febrile patients received drugs possessing antipyretic properties (such as aspirin or acetaminophen) in a dose appropriate to treat fever. No other method of temperature control (for example, physical means) was used in any patient. The fractions of patients who were dismissed from the hospital with permanent neurologic injury were as follows: CA, 20%; SAH, 45%; and CHI, 43%.

CONCLUSION

In these hospitalized patients at risk for ongoing brain injury, the incidence of temperature increases within the range reported to worsen neurologic outcome (elevations of 1.0 degree C or more) was very high. The characterization of these potentially injurious, randomly occurring, and traditionally undertreated temperature increases may have implications for the design of future protocols aimed at providing cerebral protection.

Comparison of brain temperature with bladder and rectal temperatures in adults with severe head injury

OBJECTIVE

The purpose of this study was to compare brain temperature (Tbr) with conventional indicators of core body temperature (i.e., rectal temperature [Tre] and bladder temperature [Tbl]), in adults with severe head injury.

METHODS

The relationships between Tbr and Tbl and between Tbr and Tre are described in terms of differences in temperature in eight patients with severe head injury.

INSTRUMENTATION

Brain tissue temperature was measured every minute, with a thermocouple embedded 2 cm from the tip of a ventriculostomy catheter used to measure intracranial pressure. Tbl was measured with a thermistor embedded in a bladder catheter, and Tre was measured with a thermistor in a rectal probe.

RESULTS

Tbr was usually greater than Tbl and Tre. The average difference between Tbr and Tbl for each patient ranged from 0.32 to 1.9 degrees C, with standard deviations of the difference ranging from 0.30 to 0.80 degrees C. The average difference between Tbr and Tre for each patient ranged from 0.1 to 2.0 degrees C, with standard deviations of the difference ranging from 0.32 to 1.08 degrees C. In the majority of patients, the differences (Tbr - Tbl and Tbr - Tre) were greater at temperatures outside of the normal temperature range (Tbr < or =36 degrees C and >38 degrees C).

CONCLUSION

Tbl and Tre often underrepresent Tbr after traumatic brain injury, particularly when the patient is hypo- or hyperthermic.

Comparison between continuous brain tissue pO2, pCO2, pH, and temperature and simultaneous cerebrovenous measurement using a multisensor probe in a porcine intracranial pressure model

Local brain tissue oxygenation (p(ti)O2) and global cerebrovenous hemoglobin saturation (SjO2) are increasingly used to continuously monitor patients after severe head injury (SHI). In patients, simultaneous local and global oxygen measurements of these types have shown different results regarding the comparability of the findings during changes in CPP and ICP. This is in contrast to theoretical expectations. The aim of this study was to compare p(ti)O2 measurement with cerebrovenous oxygen partial pressure measurement (p(cv)O2) in an animal intracranial pressure model. To this end, a multisensor probe was placed in the left frontoparietal white matter to measure p(ti)O2, pCO2 (p(ti)CO2), pH (pH[ti]), and temperature (t[ti]) while simultaneously measuring these same parameters (p(cv)O2, p(cv)CO2 pH(cv), t[cv]) in the sagittal sinus of 9 pigs under general anesthesia. By stepwise inflating a balloon catheter, placed in supracerebellar infratentorial compartment, ICP was increased and CPP was decreased. The baseline levels of p(ti)O2, p(ti)CO2, and pH(ti) in the noninjured brain tissue showed more heterogeneity compared to the findings in cerebrovenous blood. Both, p(ti)O2 and p(cv)O2 were significantly correlated to the induced CPP decrease. PCO2 was inversely correlated to the course of CPP in both measurement compartments. Temperature measurement showed a positive correlation with CPP in both compartments. These findings demonstrate that brain tissue oximetry and cerebrovenous PO2 measurement are sensitive to CPP changes. The newly available continuous parameters in multisensor probes could be helpful in interpreting findings of cerebral oxygen measurement in man by analyzing the interrelationship of these parameters.

Brain temperature exceeds systemic temperature in head-injured patients

OBJECTIVE

To identify the temperature differences in readings taken from the brain, jugular bulb, and core body in head-injured patients.

DESIGN

Prospective, observational study.

SETTING

Neurosurgical intensive care unit of a university-affiliated county hospital.

PATIENTS

Thirty patients with severe head injuries had measurements of brain and core body temperatures. Fourteen patients also had measurements of jugular venous blood at the level of the jugular bulb.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Brain temperature was increased an average of 2.0 degrees F (1.1 degrees C) over the core body temperature. In individual patients, the average brain temperature increase over the core body temperature ranged from -0.5 degrees to 3.8 degrees F (-0.30 degrees to 2.1 degrees C). Jugular vein and core body temperatures were similar. The difference in the brain and body temperatures increased when cerebral perfusion pressure decreased to between 20 and 50 mm Hg. The difference in the brain and body temperatures decreased in those patients treated with barbiturate coma.

CONCLUSIONS

Direct measurement of temperature in head-injured patients is a safe procedure. Temperatures in the brain are typically increased over the core body temperature and the jugular bulb temperatures. Jugular vein temperature measurement is not a good measurement of brain temperature since it reflects body, not brain temperature. These findings support the potential importance of monitoring brain temperature and the importance of controlling fever in severely head-injured patients since brain temperature may be higher than expected.

Direct intraoperative measurement of human brain temperature

OBJECTIVE

Because hypothermia enhances human tolerance for cerebral ischemia, profound hypothermia is induced in many centers so that the circulation can be arrested while clips are applied to high-risk giant cerebral aneurysms. Brain temperature is measured directly with an intracerebral probe that avoids the uncertainty of surrogate monitoring. However, when there is a large thermal gradient between brain temperature and that of the operating room, even direct measurements can sometimes be misleading. This study was undertaken to determine how deeply a thermal sensor must be embedded in the cerebral parenchyma to ensure that the ambient environment does not distort the measurement of brain temperature.

METHODS

Each of 39 normothermic patients had a thermocouple sensor inserted into a temporal lobe seizure focus just before its resection. Brain temperature was measured as the sensor was withdrawn in stages.

RESULTS

At both 3 and 2 cm beneath the cortical surface, the temperature of the brain was essentially the same. However, when the sensor was withdrawn to 1 cm, recorded temperature decreased from 35.7 +/- 0.9 to 34.3 +/- 1.4 degrees C (P < 0.001) and irrigation in the vicinity caused major thermal change. At shallower depths, even lower brain temperatures were recorded. No morbidity was attributable to the temperature measurements.

CONCLUSION

Direct intraoperative measurement of human brain temperature is feasible and safe, but accuracy requires that the temperature sensor be inserted at least 2 cm into the cerebral cortex.