Brain Surface Temperature Research Articles

Intraoperative Cerebral Measurements Using Implantable Cortical Multimodality Probe.

In this study, a multimodality probe that simultaneously measures electroencephalograms, cerebral hemodynamics, and brain surface temperature was developed. This probe has six channels, and each channel has a platinum electrode for cortical electroencephalogram measurements, light emitting diodes, and photodiodes for hemodynamic measurements using near-infrared spectroscopy (NIRS), and a thermistor for measuring the cerebral surface temperature (BrT). A probe with a width of 8.0 mm and maximum total thickness of 0.7 mm was fabricated using flexible printed circuit board technology for chronic intracranial placement. Brain activity using the prototype probe at the resected site was measured and its function performance was evaluated. Characteristic epileptogenic abnormal electroencephalograms accompanied by polarity reversal between channels occurred at 16 min and 38 s. It was concluded that the brain cells consumed oxygen during the occurrence of abnormal electroencephalograms. At this time, no noticeable change in HbT values could be confirmed.

Potential for thermal damage to the blood–brain barrier during craniotomy: implications for intracortical recording microelectrodes

Objective. Our objective was to determine how readily disruption of the blood–brain barrier (BBB) occurred as a result of bone drilling during a craniotomy to implant microelectrodes in rat cortex. While the phenomenon of heat production during bone drilling is well known, practices to evade damage to the underlying brain tissue are inconsistently practiced and reported in the literature. Approach. We conducted a review of the intracortical microelectrode literature to summarize typical approaches to mitigate drill heating during rodent craniotomies. Post mortem skull-surface and transient brain-surface temperatures were experimentally recorded using an infrared camera and thermocouple, respectively. A number of drilling conditions were tested, including varying drill speed and continuous versus intermittent contact. In vivo BBB permeability was assayed 1 h after the craniotomy procedure using Evans blue dye. Main results. Of the reviewed papers that mentioned methods to mitigate thermal damage during craniotomy, saline irrigation was the most frequently cited (in six of seven papers). In post mortem tissues, we observed increases in skull-surface temperature ranging from +3 °C to +21 °C, dependent on drill speed. In vivo, pulsed-drilling (2 s-on/2 s-off) and slow-drilling speeds (1000 r.p.m.) were the most effective methods we studied to mitigate heating effects from drilling, while inconclusive results were obtained with saline irrigation. Significance. Neuroinflammation, initiated by damage to the BBB and perpetuated by the foreign body response, is thought to play a key role in premature failure of intracortical recording microelectrodes. This study demonstrates the extreme sensitivity of the BBB to overheating caused by bone drilling. To avoid damage to the BBB, the authors recommend that craniotomies be drilled with slow speeds and/or with intermittent drilling with complete removal of the drill from the skull during ‘off’ periods. While saline alone was ineffective at preventing overheating, its use is still recommended to remove bone dust from the surgical site and to augment other cooling methods.

Intraoperative assessment of cerebral blood flow changes in normal and pathological brain tissue using an infrared camera

This study attempted to evaluate brain surface temperature using infrared thermography in patients with brain tumours, in particular those located in the vicinity of the eloquent areas. The clinical part of the study was preceded by the experiments on rats undertaken to test time-relation of cerebrocortical microflow (LDF) and brain surface temperature changes using the same infrared camera as in the clinical study. A significant positive correlation (r = 0.88, p < 0.05) between the maximum microflow changes and maximum brain temperature changes was observed. The temperature changes occurred, however, with some delay in comparison with LDF changes. In the clinical study, temperature was recorded before, during and after removal of a tumour in fifteen patients and an abscess in one patient. In patients with tumours located close to eloquent areas, temperature distribution was also measured during the awake part of the surgical procedure. The temperature of the tumour was different from the temperature of the tissues adjacent to the resected pathology. In four patients subjected to the intraoperative awake procedure, the temperature increase in the activated motor cortex region was observed. For the first time, it was possible to identify the cortical arteries supplying the eloquent areas.

Brain Surface Heating After Exposure to Ultrasound: An Analysis Using Thermography

Ultrasound is the imaging modality of choice to monitor brain pathologies in neonates after complicated deliveries. Animal studies have indicated that ultrasound may cause heating of brain tissues. To date, no study has explored brain surface heating by ultrasound during clinically relevant exposure. Hence, we investigated heating effects of B-mode and pulsed Doppler (PD) mode on ex vivo lamb brains using thermography. Five brains were scanned for 5 min in B-mode or for 3 min, 1 min, 30 s or 15 s in PD mode. Brain surface temperature was measured pre- and post-exposure using thermography. The highest mean temperature increase was recorded by B-mode (3.82 ± 0.43°C). All five PD exposure protocols were associated with surface temperature increases of 2.1–2.7°C. These outcomes highlight for the first time that B-mode ultrasound can contribute to brain surface heating during a routine cranial scan. Scan duration should be minimised whenever possible.

Physiological and thermographic response to heat stress in zebu cattle

The objective of this study was to evaluate the heat tolerance of five zebu breeds using physical, physiological and hematological traits as well as thermographic responses. Forty cows of the Gir, Girolando, Nelore, Sindhi and Indubrasil breeds (eight cows each), approximately three years of age, were evaluated. Body weight, withers and hump heights as well as thoracic circumference were recorded. The density and length of the hair was obtained by collecting one square centimeter in the rump region and skin color using the CIELAB system. Rectal temperature, heart and respiratory rates were evaluated during the morning at 4:30h, and in the afternoon, at 14:30h, with six repetitions. Blood samples were collected for hematological evaluation. The surface temperature was obtained using an infrared camera FLIR® T400. Two images were taken from each animal, one laterally of the whole body and the other of the head region. Air temperature, wind speed, relative humidity were obtained from a mobile weather station. The statistics analysis included an analyzes of variance, principal factors, as well as cluster, discriminant and canonical analyzes, logistic regression and calculation of odds ratio. There were significant differences in the rectal temperature, heart and respiratory rates between breeds. Gir and Indubrasil breeds had the highest rectal temperatures. Breed was significant for surface temperatures and showed that physical and physiological factors affected breeds in different ways. Eye and brain surface temperatures were the most affected by environmental parameters. Also, environmental parameters affected packed cell volume and red cell number. Odds ratio test showed that the Gir breed was three times more likely to have higher rectal temperature compared with Sindhi as confirmed by the logistic regression. When the black globe temperature approached 35°C, the probability of the Gir animals having rectal temperatures above normal was approximately 70%. Gir was the breed least adapted to climate conditions of the experiment while the Sindhi and Girolando breeds showed the best physiological response to thermal stress.

Brain surface temperature under a craniotomy

Many neuroscientists access surface brain structures via a small cranial window, opened in the bone above the brain region of interest. Unfortunately this methodology has the potential to perturb the structure and function of the underlying brain tissue. One potential perturbation is heat loss from the brain surface, which may result in local dysregulation of brain temperature. Here, we demonstrate that heat loss is a significant problem in a cranial window preparation in common use for electrical recording and imaging studies in mice. In the absence of corrective measures, the exposed surface of the neocortex was at ∼28°C, ∼10°C below core body temperature, and a standing temperature gradient existed, with tissue below the core temperature even several millimeters into the brain. Cooling affected cellular and network function in neocortex and resulted principally from increased heat loss due to convection and radiation through the skull and cranial window. We demonstrate that constant perfusion of solution, warmed to 37°C, over the brain surface readily corrects the brain temperature, resulting in a stable temperature of 36-38°C at all depths. Our results indicate that temperature dysregulation may be common in cranial window preparations that are in widespread use in neuroscience, underlining the need to take measures to maintain the brain temperature in many physiology experiments.

Clinical implications of intraoperative infrared brain surface monitoring during superficial temporal artery–middle cerebral artery anastomosis in patients with moyamoya disease

Surgical revascularization for moyamoya disease prevents cerebral ischemic attacks by improving cerebral blood flow (CBF). Symptomatic cerebral hyperperfusion is a potential complication of this procedure, but its treatment is contradictory to that for ischemia. Because intraoperative techniques to detect hyperperfusion are still lacking, the authors performed intraoperative infrared monitoring in moyamoya disease using a novel infrared imaging system. During superficial temporal artery-middle cerebral artery anastomosis in 25 patients (26 hemispheres) with moyamoya disease, the authors monitored the brain surface temperature intraoperatively with the IRIS-V infrared imaging system. The average gradation value change (indicating temperature change) was calculated using commercial software. Magnetic resonance imaging, MR angiography, and N-isopropyl-p-[(123)I]iodoamphetamine SPECT studies were performed routinely before and within 10 days after surgery. Patency of bypass, detailed local hemodynamics, and changes in cortical surface temperature around the anastomosis site were well recognized by the IRIS-V infrared imaging system in all cases. In the present study, 10 patients suffered transient neurological symptoms accompanied by an increase in CBF around the anastomosis site, recognized as symptomatic hyperperfusion. The increase in temperature was significantly higher in these patients. Intensive blood pressure control was undertaken, and free-radical scavengers were administered. No patient in the present study suffered a permanent neurological deficit. Although the present method does not directly monitor surface CBF, temperature rise around the anastomosis site during surgery might be an indicator of postoperative hyperperfusion. Prospective evaluation with a larger number of patients is necessary to validate this technique.

Intraoperative infrared brain surface blood flow monitoring during superficial temporal artery–middle cerebral artery anastomosis in patients with childhood moyamoya disease

To monitor patency of the bypass and to accomplish comprehensive visualized evaluation of brain surface hemodynamics in childhood moyamoya patients, we performed intraoperative monitoring using novel infrared imaging system. Intraoperative monitoring of brain surface blood flow by IRIS V infrared imaging system has been conducted during superficial temporal artery-middle cerebral artery anastomosis on seven sides of five pediatric patients with moyamoya disease (man/woman = 2:3, 7-8 years old). The range of recipient artery was 0.7-0.8 mm (average 0.75 mm). Magnetic resonance imaging and magnetic resonance angiography were performed routinely before and after surgery. In all cases, patency of bypass, as well as detailed local hemodynamics and changes of brain surface temperature distribution could be evaluated. Intraoperative infrared system will be a feasible monitoring not only for noninvasive intraoperative evaluation of bypass patency but also for local hemodynamics even in patients with childhood moyamoya disease.

The use of near-infrared spectroscopy (NIRS) in surgical clipping of giant cerebral aneurysm

EDITOR: A 49-yr-old male patient was scheduled for clipping of a giant right middle cerebral artery (MCA) aneurysm. He presented with Grade IV subarachnoid haemorrhage (SAH) and large intracerebral haemorrhage. Upon admission, the patient's Glasgow Coma Scale score was 8 (E2V2M4) with left-sided hemiplegia. The patient was transferred to the operating room, sedated and intubated. Two 18-G peripheral intravenous lines and a left radial arterial line were placed. In addition to the routine standard monitors, electroencephalograph (EEG) electrodes were placed over the midline and left cerebral hemisphere. Two near-infrared spectroscopy (NIRS) sensors (model INVOS-4100; Somanetics Corporation, Troy, MI, USA) were applied, one on either side of the forehead. The sensors were covered with adhesive cover to shield them from ambient light. Baseline rSO2 recordings from both sides were 71-73%. Baseline systemic temperature was 37.0°C. General anaesthesia was maintained with sevoflurane (0.5% MAC (minimum alveolar concentration)), oxygen/air (40-60%) and remifentanil (0.15 μg kg−1 min−1). Mechanical ventilation was adjusted to maintain a PCO2 in the 30-35 mmHg range. Following right fronto-temporal craniotomy, right femoral artery to right carotid artery (FA-CA) extracorporeal hypothermic bypass was instituted. After 40 min of cooling and right brain surface temperature of 23°C, a temporary clip was placed on the right MCA. Systemic temperature was 37.3°C. Shortly after temporary clip application, the right rSO2 recordings were in the range of 55-60%. After 26 min of temporary clip application, right rSO2 readings dropped below 50% on two separate occasions 5 min apart each episode lasted for 3 min. Left-sided rSO2 recordings remained unchanged and EEG recording from midline and left hemisphere did not show any changes suggestive of ischaemia. In response to the episodes of cerebral desaturation, the neurosurgeon was informed and the temporary clip position was adjusted. Propofol infusion (3-5 mg kg−1 h−1) was started to reduce cerebral metabolic rate and titrated until EEG burst suppression was achieved. Right cerebral oxygen saturation readings returned to baseline values after 5 min of temporary clip adjustment (Fig. 1). Total temporary clipping time was 67 min and 54 s and the total duration of surgery was 12 h and 15 min.Figure 1: Time course of changes in cerebral oxygen saturation. Point A: correspond to temporary clip application, areas B&C: represent periods of desaturation, Point D: correspond to temporary clip adjustment.Postoperatively, the patient was transferred to the ICU on mechanical ventilation. The patient was extubated 3 days following surgery and discharged from ICU on day 4. He was awake, obeying commands. His preoperative left-sided hemiplegia did not change. There was no new neurological deficit and postoperative cerebral angiography did not reveal any evidence of new infarction or haemorrhage. Discussion Intraoperative cerebral ischaemic complications may be due to improper temporary or permanent clip application, prolonged temporary clipping time, retraction injury and cerebral vasospasm. With respect to intraoperative neuromonitoring, in addition to EEG, NIRS was used to monitor cerebral oxygen saturation during periods of potentially compromised cerebral blood flow (in this case, prolonged temporary parent artery occlusion of 67 min). Several investigators have reported the use of NIRS during carotid endarterectomy and found rSO2 recordings less than 50% is indicative of cerebral ischaemia [1,2]. However, the efficacy and clinical outcome associated with the use of NIRS during cerebral aneurysm surgery has not yet been established. In this case report, the patient developed two episodes of right rSO2 desaturation (<50%) which were not detected clinically or by EEG. This could have resulted in significant cerebral ischaemia. NIRS can provide a useful feedback to the anaesthesiologist and neurosurgeon that could allow early detection of cerebral ischaemia and thus early intervention. In this case report, in response to the episodes of cerebral desaturation and after discussion with the surgeon, the potential cerebral protection of propofol was considered [3,4]. The findings of this report are consistent with earlier studies showing the clinical utility of multimodal neuromonitoring in the prevention of uncommon but possibly catastrophic cerebral ischaemia [5]. This modality is relatively new in neurosurgery and appears to be a promising technology that could support clinical decisions regarding detection of cerebral ischaemia. Since limited data are available, more research is needed to establish its clinical efficacy and justify its routine use in neurosurgery.

高感度赤外線画像システムＩＲＩＳ‐Ｖを用いたもやもや病術中血行動態モニタリングによる術後過灌流の予測―２症例の検討―

Surgical revascularization for moyamoya disease prevents cerebral ischemic attacks by improving cerebral blood flow (CBF). But little is known about the change in intraoperative cerebral hemodynamics and its effect on postoperative neurological status, including symptomatic cerebral hyperperfusion. To address this issue, we applied a novel infrared imaging system (IRIS-V infrared imaging system) for intraoperative monitoring of surface hemodynamics in 2 patients with moyamoya disease. We investigated the correlation between clinical, radiological findings, and changes of the gradation value in infrared imaging using imaging software. The camera showed apparent revascularization during surgery in both cases. In case 1, a 36-year-old male who presented with transient ischemic attack (TIA) underwent superficial temporal artery-middle cerebral artery (STA-MCA) anastomosis with pial synangiosis. His cerebrovascular reactivity was significantly compromised as shown by preoperative IMP-SPECT. Intraoperative infrared imaging disclosed an increase in brain surface temperature due to increase in blood flow around the anastomosis. The gradation value gradually increased after recanalization of bypass during several minutes. Postoperative IMP-SPECT showed a focal increase in CBF around the site of anastomosis 1 day after surgery. Beginning on the next day, he suffered fluctuated aphasia, numbness and fine movement disturbance on his right hand for 7 days. Intensive blood pressure control relieved his symptoms, and he was discharged without neurological deficit. The anatomical location and the temporal profile of hyperperfusion accorded with the neurological deficits. In case 2, a 29-year-old female who presented with TIA had already undergone surgical revascularization on the symptomatic right side. Then she underwent left STA-MCA anastomosis on the asymptomatic side with decreased cerebrovascular reserve capacity. Intraoperative infrared imaging disclosed no significant increase in brain surface color around the site of anastomosis except for the apparent revascularization through STA-MCA bypass. The gradation value did change significantly before or after recanalization of bypass. Postoperative IMP-SPECT showed a mild increase in CBF on the entire MCA territory without focal intense accumulation. Her postoperative course was uneventful, and she was discharged without neurological deterioration. Characteristic patterns of the intraoperative cerebral hemodynamics as delineated by IRIS-V may be the optimal predictor for postoperative transient symptomatic hyperperfusion after direct bypass in patients with moyamoya disease.

Pre-clinical testing of a phased array ultrasound system for MRI-guided noninvasive surgery of the brain—A primate study

MRI-guided and monitored focused ultrasound thermal surgery of brain through intact skull was tested in three rhesus monkeys. The aim of this study was to determine the amount of skull heating in an animal model with a head shape similar to that of a human. The ultrasound beam was generated by a 512 channel phased array system (Exablate ® 3000, InSightec, Haifa, Israel) that was integrated within a 1.5-T MR-scanner. The skin was pre-cooled by degassed temperature controlled water circulating between the array surface and the skin. Skull surface temperature was measured with invasive thermocouple probes. The results showed that by applying surface cooling the skin and skull surface can be protected, and that the brain surface temperature becomes the limiting factor. The MRI thermometry was shown to be useful in detecting the tissue temperature distribution next to the bone, and it should be used to monitor the brain surface temperature. The acoustic intensity values during the 20 s sonications were adequate for thermal ablation in the human brain provided that surface cooling is used.

Epidural cooling for selective brain hypothermia in porcine model

Hypothermia has been shown to be neuroprotective in many animal models and several human trials of brain ischemic and trauma. However systemic hypothermia may result in fatal complications. This study was undertaken to test epidural cooling as a new method of inducing selective brain hypothermia. Six adult swine (mean mass, 33.8+/-3.6 kg) were studied. Anesthesia was maintained with pentobarbital sodium (25 mg kg-1, i.v.) and pancuronium bromide (0.5 mg kg-1 h-1, i.v.). Five probes were placed in the rectum, deep brain, brain surface, epidural space, and room air for temperature monitoring respectively. Epidural cooling was performed using cold-saline (4 degrees C) perfusion into the epidural space through a flexible double-lumen catheter. The dripping speed of cold saline was controlled to maintain the target temperature. The changes of the epidural space pressure, complete blood counts, basic metabolic panels, tests for fibrinolysis and coagulation status were monitored to assess hypothermia-induced changes. Following the epidural cooling perfused with cold-saline (4 degrees C) at mean dripping speed of 720 ml per hour, the local brain surface temperature could decrease rapidly to 17.3-21.6 degrees C within one minute, and deep brain temperature decreased to 27.2-29.7 degrees C within 5 minutes. The target temperatures were easily controlled by the dripping speed of cold saline (from mild to deep hypothermia). The rectal temperature was maintained at normal range within 6 perfusion hours. No arrhythmia was observed, and all hematological variables were within the normal range for swine. No increased intracranial pressure was induced by the cooling method. The data demonstrate that epidural space cooling was technically feasible and useful for selective brain hypothermia, and the target temperatures are easily controlled. The induction of hypothermia was rapid and maintained for a long period of time, whereas the body temperature was maintained within the normal range and without hemodynamic instability.

Evidence that peripheral rather than intracranial thermal signals induce thermoregulation

Numerous effector mechanisms have been discovered, which change body temperature and thus serve to maintain the thermal integrity of homeothermic animals. These mechanisms are driven by thermal signals that are processed by neurons in the hypothalamic preoptic area. To keep a tight control over body temperature, these neurons have to receive accurate thermal information. Although in vitro studies have shown the direct thermosensitive ability of neurons in the preoptic area, other observations suggest the existence of peripheral thermosensation and an ascending thermal pathway to the thermoregulatory center. Direct evidences for either one, or both are still missing. In the present study, brain, rectal, subcutaneous and skin surface temperatures were measured during 15, 30, 60 and 120 min of cold exposure (4°C) in rats and compared with neuronal activation due to cold stress shown by c-fos in situ hybridization histochemistry. Subcutaneous and skin surface temperatures dropped continuously throughout the 120 min of cold exposure by 1.4°C and 6.5°C, respectively. However, during the first 30 min, brain and rectal temperatures increased by 0.3°C and 0.25°C, respectively, and even after 60 min of cold stress, brain temperature did not decrease under the level measured at 0 min. Since the brain temperature did not decrease, it is unlikely that intracranial thermoreceptors are involved in the transmission of “cold” thermal signal to induce thermoregulation. At 30 min of cold exposure, neurons in all known thermoregulatory areas (like the ventrolateral part of the medial preoptic nucleus, the lateral retrochiasmatic area, the lateral parabrachial nucleus and the peritrigeminal nucleus) were already maximally activated. These observations clearly indicate that the activation of neurons in the preoptic and several other thermoregulatory nuclei is induced in vivo by thermal signals originating in the periphery, and not in the CNS.

A new method of inducing selective brain hypothermia with saline perfusion into the subdural space: effects on transient cerebral ischemia in cats.

In this study, we tested brain surface cooling as a new method of inducing selective brain hypothermia, and evaluated its effects on focal cerebral ischemia using a cat model of transient middle cerebral artery (MCA) occlusion. Cats underwent 1 h of MCA occlusion followed by 5 h of reperfusion. Brain surface cooling was induced for 4 h during and after MCA occlusion in the hypothermia group, but not in the normothermia group. Brain surface cooling was performed using saline perfusion into the subdural space. Rectal temperature, brain surface temperature, and deep brain temperature were monitored, and regional cerebral blood flow (rCBF) and somatosensory evoked potential (SEP) were serially measured. After 5 h of reperfusion, water content was also measured. Although the rectal temperature was maintained at about 37 degrees C, the brain surface temperature decreased rapidly to 33 degrees C and was maintained at that temperature. For 3 h following reperfusion, the rCBF was lower in the hypothermia group than in the normothermia group. At 4 and 5 h after reperfusion, the recovery of SEP amplitude was significantly more enhanced in the hypothermia group than in the normothermia group. In the gray matter, the water content was significantly more diminished in the hypothermia group than in the normothermia group. These results demonstrate that our method is useful for protecting the ischemic brain from a transient MCA occlusion. This method may be adapted for neurological surgery.

Decrease in intraoperative brain surface temperature in patients with subarachnoid haemorrhage.

Recent experimental and clinical evidence of hypothermic protection against neuronal injury creates new interests regarding human brain temperature. However, very little information is available for the brain temperature under certain pathological conditions. In this study, intra-operative brain temperature in patients with subarachnoid haemorrhage (SAH) is particularly addressed. Brain surface temperature and oxygen saturation of jugular bulb (SjO2) were monitored during early surgery undergone within 48 hours after the onset in patients with SAH (n = 16). Those were also measured in patients with unruptured aneurysms during elective surgery as control (n = 15). The brain surface temperature was significantly lower in SAH than control (35.3 +/- 0.8 vs. 36.1 +/- 0.5 degrees C, P < 0.01). The reduction in brain surface temperature was correlated with the severity of the Hunt and Kosnik's aneurysmal grade (r = 0.837, P < 0.01). SjO2 was significantly lower in SAH than control (51.5 +/- 7.3 vs. 68.5 +/- 7.6%, P < 0.01), and was positively correlated with brain surface temperature (r = 0.642, P < 0.01). These results suggest that the brain temperature and/or the temperature gradient within the brain may be altered in an early period after SAH. Since brain temperature is determined by cerebral blood flow (CBF), metabolism, temperature of both circulating blood and surrounding environment, the brain surface temperature reduction may be explained by depressed CBF and metabolism in SAH.

Treatments with Lead Expedite Hyperthermia-Induced Thromboembolism in Mouse Pial Microvessels

Three trials were carried out to study the influence of acute and chronic treatments with lead on hyperthermia-induced thromboembolic activity in pial microvessels of adult male mice. Each trial consisted of four groups, 10 mice (∼33 g) per group. Three groups were injected with lead acetate dissolved in a 5% glucose solution (vehicle) at doses of 0.1, 0.5 and 1.0mg/kg and the control group received only the vehicle. Acute treatments were by a single injection made 1 h (i.p.) in one trial and 24 h (i.p.) in another, prior to the a hyperthermic exposure at 45°C. In the third trial, a single injection was given daily (s.c.) for 7 days. Mice were anesthetized by urethane (1–2 mg/kg, i.p.), the trachea was intubated, a craniotomy was performed and the mouse was placed on the microscope stage of an intravital microscopy set-up. Core body and brain surface temperatures were raised first to 37°C, the animal was stabilized for 30 min then only the brain surface temperature was raised to 45°C by heating the irrigating artificial cerebrospinal fluid. The hyperthermic exposure lasted for 45 min. In all trials, lead at the three doses given (low, medium and high) significantly reduced (p > 0.001) the time of initial thromboembolic activity seen. Lead exerted its influence as quickly as in 1 h, even with the low dose administered. Neither the acute nor chronic treatments affected the degree of arteriolar constriction observed or caused venular diameter change. Arteriolar patency rate at the end of experiment was higher for control than for all lead-treated groups. Data evidenced the rapidity of the adverse influence of lead on the susceptibility to thrombosis, in vivo. The enhanced initiation of thrombotic activity may be attributed to facilitated damage to the microvascular endothelium caused by lead, when challenged by hyperthermia.

Effect of a μ-Selective Opioid Antagonist on CCK-8–Induced Changes in Thermoregulation in the Rat

We examined the effects of ICV injection of CCK-8 alone and in combination with CTAP, a μ-selective antagonist, on brain surface temperature (Tb), oxygen consumption (VO 2), and heat exchange (Q) in unrestrained male S-D rats at an ambient temperature of 20 ± 0.5°C. CCK-8 (300 ng, ICV) produced hyperthermia (Δ Tb: 0.86 ± 0.22°C) lasting for 30–60 min, which was associated with an increase in VO 2 (1.42 ± 0.28 ml/g/h). There was an increase in Q (1.87 ± 1.2 cal/g/h) beginning 15 min after injection and lasting for 60 min. The CCK-8–induced hyperthermia was attenuated by a postinjection increase in Q. During the 60–120 min postinjection period, VO 2 and Q returned to baseline followed by the return of Tb to preinjection levels. CCK-8–induced increases in Tb, Q, and VO 2 were blocked by pretreatment with CTAP (0.75 nmol, ICV) 15 min earlier. CTAP alone did not significantly affect ΔTb, ΔVO 2, and ΔQ. These results suggest that, within the thermoneutral zone, the thermoregulatory effects of CCK-8 in the rat involve participation of μ-opioid receptors.

Topical ice slurry prevents brain rewarming during deep hypothermic circulatory arrest in newborn sheep

Objectives: To measure the effect of ice slurry topical cooling on brain surface temperature during deep hypothermic circulatory arrest. Design: This was a prospective, controlled experiment. Setting: Animal laboratory at a university hospital. Participants: Five control lambs, five treatment (ice slurry) lambs. Interventions: Animals were studied in two groups: the study group had topical cooling of the head with ice slurry started immediately before circulatory arrest and continued throughout the period of circulatory arrest; control group lambs received no supplemental topical cooling. Measurements and Main Results: Brain surface temperature, scalp, nasopharyngeal, and rectal temperatures were measured at 5-minute intervals during 45 minutes of circulatory arrest. Lambs receiving topical cooling of the head with ice slurry had a statistically significant decrease in brain surface temperature of 2.2 ± 1.2°C during circulatory arrest, whereas brain surface temperature increased 1.2 ± 0.3°C, in control lambs. Equilibration of temperature between the scalp and brain in control lambs produced rewarming of the brain surface. Conclusions: Topical cooling of the head with ice slurry in newborn lambs lowers brain surface temperature during deep hypothermic circulatory arrest. Surrogate temperature monitoring locations such as nasopharyngeal and rectal temperatures varied significantly and do not accurately reflect changes in brain surface temperature.

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

Blood temperature at the jugular bulb was monitored in 10 patients undergoing neurovascular procedures that used induced mild hypothermia, and its correlation with surface brain, core, and peripheral temperatures was determined. The study was motivated by the difficulty encountered in directly measuring global brain temperature and the poor correlations between various core and peripheral sites temperatures and brain temperature, particularly during deep hypothermia. Although not statistically significant, previous studies have suggested a trend toward higher brain temperatures. Temperatures from the jugular bulb (collected using a No. 5 French Swan-Ganz catheter) as well as from subdural, pulmonary artery, esophagus, tympanic membrane, and bladder sites were analyzed during three surgical conditions: prior to incision, with the dura open, and after closure of the dura. No complications related to placement of the jugular bulb catheter, induced hypothermia, or temperature monitoring were seen. The authors found that jugular bulb temperature was similar to pulmonary artery and esophageal temperatures; although prior to incision it tended to be higher than that found at the pulmonary artery, most commonly by 0.2 degrees C. Surface brain temperature was cooler than all other temperatures (p < 0.05), except that of the tympanic membrane, and was particularly sensitive to environmental variations. Finally, as has been shown by others, bladder temperature lagged substantially behind core temperatures particularly during rapid cooling and rewarming of the patient. In summary, monitoring of jugular bulb temperature is a feasible technique, and temperatures measured in the jugular bulb are similar to core temperatures.

Annual meeting of the Society of Neurosurgical Anesthesia and Critical Care. Atlanta, Georgia, October 20, 1995.

Annual meeting of the Society of Neurosurgical Anesthesia and Critical Care. Atlanta, Georgia, October 20, 1995.