Comparison of the effects of isoflurane and thiopental on neurologic outcome and neuropathology after temporary focal cerebral ischemia in primates

Anesthetics, cerebral protection and preconditioning

BACKGROUND AND OBJECTIVES

Several studies demonstrate that cerebral preconditioning is a protective mechanism against a stressful situation. Preconditioning determinants are described, as well as the neuroprotection provided by anesthetic and non-anesthetics agents.

CONTENT

Review based on the main articles addressing the pathophysiology of ischemia-reperfusion and neuronal injury and pharmacological and non-pharmacological factors (inflammation, glycemia, and temperature) related to the change in response to ischemia-reperfusion, in addition to neuroprotection induced by anesthetic use.

CONCLUSIONS

The brain has the ability to protect itself against ischemia when stimulated. The elucidation of this mechanism enables the application of preconditioning inducing substances (some anesthetics), other drugs, and non-pharmacological measures, such as hypothermia, aimed at inducing tolerance to ischemic lesions.

Anesthetics, cerebral protection and preconditioning

BACKGROUND AND OBJECTIVES

Several studies demonstrate that cerebral preconditioning is a protective mechanism against a stressful situation. Preconditioning determinants are described, as well as the neuroprotection provided by anesthetic and non-anesthetics agents.

CONTENT

Review based on the main articles addressing the pathophysiology of ischemia-reperfusion and neuronal injury and pharmacological and non-pharmacological factors (inflammation, glycemia, and temperature) related to the change in response to ischemia-reperfusion, in addition to neuroprotection induced by anesthetic use.

CONCLUSIONS

The brain has the ability to protect itself against ischemia when stimulated. The elucidation of this mechanism enables the application of preconditioning inducing substances (some anesthetics), other drugs, and non-pharmacological measures, such as hypothermia, aimed at inducing tolerance to ischemic lesions.

Isoflurane induces endothelial apoptosis of the post-hypoxic blood-brain barrier in a transdifferentiated human umbilical vein endothelial cell model

Isoflurane is a popular volatile anesthetic agent used in humans as well as in experimental animal research. In previous animal studies of the blood-brain barrier (BBB), observations towards an increased permeability after exposure to isoflurane are reported. In this study we investigated the effect of a 2-hour isoflurane exposure on apoptosis of the cerebral endothelium following 24 hours of hypoxia in an in vitro BBB model using astrocyte-conditioned human umbilical vein endothelial cells (AC-HUVECs). Apoptosis of AC-HUVECs was investigated using light microscopy of the native culture for morphological changes, Western blot (WB) analysis of Bax and Bcl-2, and a TUNEL assay. Treatment of AC-HUVECs with isoflurane resulted in severe cellular morphological changes and a significant dose-dependent increase in DNA fragmentation, which was observed during the TUNEL assay analysis. WB analysis confirmed increases in pro-apoptotic Bax levels at 4 hours and 24 hours and decreases in anti-apoptotic Bcl-2 in a dose-dependent manner compared with the control group. These negative effects of isoflurane on the BBB after a hypoxic challenge need to be taken into account not only in experimental stroke research, but possibly also in clinical practice.

Are volatile anesthetics neuroprotective or neurotoxic?

Volatile anesthetics are one class of the most commonly used drugs. However, the mechanisms for these drugs to induce anesthesia are not fully understood and have been under intensive investigation. Two other effects of these anesthetics on the central nervous system, volatile anesthetics-induced neuroprotection and neurotoxicity, currently are hot research fields. Although data from animal studies for these two effects are extensive and convincing, clinical data for volatile anesthetics-induced neuroprotection are relatively weak. There is essentially lack of evidence to suggest volatile anesthetics-induced neurotoxicity in humans. In this regard, the contribution of general anesthesia/anesthetics to postoperative cognitive decline, a clinical entity whose existence has been supported by substantial evidence, also has not been established. This paper will be focused on reviewing the evidence, especially the clinical evidence, for volatile anesthetics-induced neuroprotection and neurotoxicity. Efforts will be devoted to facilitating the understanding of the two seemingly contradictory effects of these important drugs on the brain.

Temperature management in studies of barbiturate protection from focal cerebral ischemia: systematic review and speculative synthesis

Our goal was to test the hypothesis that-given the barbiturates' novel ability to reduce brain temperature-the high prevalence of reports describing cerebral protection by barbiturates in animal models are, in part, the result of inadvertent cerebral hypothermia. We reviewed all published reports evaluating barbiturate protection in animal models of focal cerebral ischemia where functional or anatomic endpoints were assessed. Presence or absence of protection, and additionally the year of publication, were tabulated. Temperature monitoring was categorized as: (a) not monitored, (b) inadequately monitored (ie, temperature monitored, but not at appropriate sites or times), or (c) adequately monitored (brain or cranial temperature monitored at appropriate times, with or without core temperature). Twenty eight references published between 1974 and 2008 described 57 separate protocols. Cerebral protection by barbiturates was reported in 35 of 57 (61%) protocols. Temperature was not monitored in 10 protocols (18%), inadequately monitored in 32 (56%), and adequately monitored in 15 (26%). Although the majority (32 of 57; 56%) of the protocols were published before December 1987, none of these properly monitored temperature. In the protocols published in 1988 or later, 15 of 25 (60%) had proper temperature monitoring and 9 of the 15 (60%) reported protection by the barbiturates. Very few (ie, 15 of 57; 26%) protocols were capable of distinguishing between direct cerebral protection by the barbiturates and an artifactual, hypothermia-related, effect. However, among those protocols having proper temperature monitoring, there remained considerable evidence of barbiturate protection.

Inhalational anesthetics as neuroprotectants or chemical preconditioning agents in ischemic brain

This review will focus on inhalational anesthetic neuroprotection during cerebral ischemia and inhalational anesthetic preconditioning before ischemic brain injury. The limitations and challenges of past and current research in this area will be addressed before reviewing experimental and clinical studies evaluating the effects of inhalational anesthetics before and during cerebral ischemia. Mechanisms underlying volatile anesthetic neuroprotection and preconditioning will also be examined. Lastly, future directions for inhalational anesthetics and ischemic brain injury will be briefly discussed.

Anaesthesia induced neuroprotection

Anaesthetic agents display remarkable neuroprotective potential; here, we describe the evidence supporting its use and highlight areas for future development of the field. In particular the application of isoflurane and/or xenon as inhalational neuroprotectants is advocated and evidence for the neuroprotection provided by barbiturates and suppression of cerebral metabolic rate is discussed.

Anesthetic technique influences brain temperature, independently of core temperature, during craniotomy in cats

Because anesthetic technique has the potential to dramatically affect cerebral blood flow and metabolism (two determinants of brain thermoregulation), we tested the hypothesis that, after craniotomy, anesthetic technique would influence brain temperature independent of core temperature. Twenty-one cats (2.7 +/- 0.4 kg; mean +/- SD) undergoing a uniform right parasagittal craniotomy received 1) halothane 1.5% end-expired and normocapnia (HN), 2) halothane 1.5% and hypocapnia (HH), or 3) large-dose pentobarbital and normocapnia (PN) (n = 7 per group). Heating devices initially maintained core and right subdural normothermia (38.0 degrees C). Thereafter, cranial heating was discontinued. Brain-to-core temperature gradients during the 3 h study were greatest in the right subdural area, averaging -2.5 degrees C +/- 0.9 degrees C in HN, -2.5 degrees C +/- 0.8 degrees C in HH, and -4.1 degrees C +/- 1.1 degrees C in PN. Gradients within the unexposed left subdural area and in the right cortex 0.5 and 1.0 cm below the brain surface were -0.8 degrees C +/- 0.5 degrees C to -1.1 degrees C +/- 0.6 degrees C for both HN and HH but were twice this amount in PN (-1.9 degrees C +/- 0.5 degrees C to -2.1 degrees C +/- 0.7 degrees C) (P < 0.05 for PN versus HN and HH). Deep barbiturate anesthesia can reduce brain temperature independently of core temperature, presumably by reducing the metabolic rate and associated brain heat production. The magnitude is sufficient to augment any direct cerebroprotective properties of the barbiturates.

IMPLICATIONS

Deep barbiturate anesthesia reduced brain temperature independently of body temperature in cats and significantly more than the reduction seen with halothane anesthesia. The magnitude of temperature reduction was sufficient to account for cerebral protection by barbiturates independently of any other properties of the drug.

Checkpoints and pitfalls in the experimental neuropathology of circulatory disturbance

In neural tissue injury many pathological processes are common to different neurological disorders, including cerebral ischemia. Because ischemia has a fundamentally simple impact on neural tissue, good laboratory modeling can help improve the general understanding of the neuropathological processes involved. Summarized here are some basic principles that should be followed to ensure that cerebral ischemia studies are reproducible and informative: (i) selection of an appropriate model of cerebral ischemia in an appropriate species (although rodents are widely used for genomic studies, the use of larger animals, with brain structures macroscopically similar to those of humans, is appropriate for many studies, e.g. of white matter lesions or the pathophysiology of cerebral edema); (ii) correct maintenance of physiological parameters, including body temperature, systemic blood pressure, and blood gas tensions, under appropriate general anesthesia; (iii) selection of an appropriate method of cerebral blood flow (CBF) monitoring (decisions include whether or not the experiment requires real-time monitoring, in vivo measurement, and CBF mapping); (iv) appropriate timing of drug application in therapeutic studies (many drugs that are effective when given immediately after a short period of ischemia are ineffective in clinical trials, probably because of longer periods of ischemia and delayed drug delivery in clinical settings); and (v) multiparametric evaluation of therapeutic effect (with the recent increase in diagnosis of cases of mild stroke, measurement of mortality and infarct size have proven to be insufficient for the evaluation of therapeutic effect). Use of mild ischemia models and batteries of neurological tests for individual neurological functions, such as motor, somatosensory, and visual function, are becoming important in experimental ischemia research. In histological evaluation, assessment of the extent of both selective neuronal loss and the infarct will become mandatory. Regional analysis of each brain structure and coordination of the results with the apparent neurological dysfunction is a promising approach.

Hypothermia and thiopentone sodium: individual and combined neuroprotective effects on cortical cultures exposed to prolonged hypoxic episodes

Because there are many conflicting reports on cerebroprotective effects of hypothermia and barbiturates, we examined the degree of neuroprotection at defined temperatures (normothermia, 37 degrees C; mild hypothermia, 32 degrees C; deep hypothermia, 22 degrees C; and profound hypothermia, 17 degrees C) and various concentrations (low, 4 microM; moderate, 40 microM; and high, 400 & microM) of thiopentone sodium (TPS), alone and in combination in cortical cultures exposed to prolonged hypoxia (24-48 hr). The survival rate of embryonic day (E)16 Wistar rat cortical neurons was evaluated on photomicrographs before and after experiments. During the 24-hr hypoxic period, the survival rate of neurons was maximal with combinations of mild hypothermia with 40 microM (91.6 +/- 0.7%) and 400 microM TPS (90.8 +/- 0.7%) or deep hypothermia combined with all concentrations of TPS (4 microM, 90.6 +/- 1.0%; 40 microM, 91.4 +/- 0.8%; 400 microM, 91.8 +/- 1.2%). During 48 hr hypoxia, the highest survival rate was seen with the combination of deep hypothermia and either 40 microM (90.9 +/- 0.6%) or 400 microM (91.1 +/- 1.4%) TPS. In the presence of profound hypothermia in combination with all concentrations of TPS, the survival rate was significantly reduced (P< 0.01) compared to combined application of either mild or deep hypothermia with TPS. In summary, maximal neuroprotection was attained with hypothermia and TPS in combination rather than applied individually, during prolonged hypoxic episodes (24- 48 hr). During a 24-hr hypoxic period, both mild and deep hypothermia combined with a clinically relevant concentration of TPS (40 microM) offered the highest neuroprotection. Only deep hypothermia provided maximal neuroprotection when combined with 40 microM TPS, during 48-hr hypoxia. Combination of profound hypothermia and TPS did not confer considerable neuroprotection during long lasting hypoxia.

Nitric oxide-induced cytotoxicity attenuation by thiopentone sodium but not pentobarbitone sodium in primary brain cultures

1. We describe the effects of barbiturates on the neurotoxicity induced by nitric oxide (NO) on foetal rat cultured cortical and hippocampal neurones. Cessation of cerebral blood flow leads to an initiation of a neurotoxic cascade including NO and peroxynitrite. Barbiturates are often used to protect neurones against cerebrovascular disorders clinically. However, its neuroprotective mechanism remains unclear. 2. In the present experiment, we established a new in vitro model of brain injury mediated by NO with an NO-donor, 1-hydroxy-2-oxo-3-(3-aminopropyl)-3-isopropyl-1-triazene (NOC-5) on grid tissue culture wells. We also investigated the mechanisms of protection of CNS neurones from NO-induced neurotoxicity by thiopentone sodium, which contains a sulphydryl group (SH-) in the medium, and pentobarbitone sodium, which does not contain SH-. 3. Primary cultures of cortical and hippocampal neurones (prepared from 16-day gestational rat foetuses) were used after 13-14 days in culture. The cells were exposed to NOC-5 at the various concentrations for 24 h in the culture to evaluate a dose-dependent effect of NOC-5. 4. To evaluate the role of the barbiturates, neurones were exposed to 4, 40 and 400 microM of thiopentone sodium or pentobarbitone sodium with or without 30 microM NOC-5. In addition, superoxide dismutase (SOD) at 1000 u ml(-1) and 30 microM NOC-5 were co-administered for 24 h to evaluate the role of SOD. 5. Exposure to NOC-5 induced neural cell death in a dose-dependent manner in both cortical and hippocampal cultured neurones. Approximately 90% of the cultured neurones were killed by 100 microM NOC-5. 6. This NOC-5-induced neurotoxicity was significantly attenuated by high concentrations of thiopentone sodium (40 and 400 microM) as well as SOD, but not by pentobarbitone sodium. The survival rates of the cortical neurones and hippocampal neurones that were exposed to 30 microM NOC-5 were 11.2+/-4.2% and 37.2+/-3.0%, respectively, and in the presence of 400 microM thiopentone sodium, the survival rate increased to 65.3+/-3.5% in the cortical neurones and 74.6+/-2.2% in the hippocampal neurones. 7. These findings demonstrate that thiopentone sodium, which acts as a free radical scavenger, protects the CNS neurones against NO-mediated cytotoxicity in vitro. In conclusion, thiopentone sodium is one of the best of the currently available pharmacological agents for protection of neurones against intraoperative cerebral ischaemia.

Anesthetic technique influences brain temperature during cardiopulmonary bypass in dogs

BACKGROUND

Because different anesthetics have different effects on cerebral blood flow and cerebral metabolism, we hypothesized that they also may have different effects on brain temperature during hypothermic cardiopulmonary bypass (CPB) and subsequent rewarming.

METHODS

Sixteen dogs were anesthetized either with inhaled halothane, 1.0 minimum alveolar concentration (ie, an anesthetic that should increase cerebral blood flow and minimally affect cerebral metabolism; n = 8), or with intravenous high-dose pentobarbital (ie, an anesthetic that should reduce cerebral blood flow and cerebral metabolism by approximately one half; n = 8). Normocapnia (alpha-stat technique) and a blood pressure near 90 mm Hg were maintained. Thermistors were placed in the esophagus (ie, the body core), in the parietal epidural space, and in the parietal brain parenchyma at depths of 1 and 2 cm. Initially, all temperatures were controlled at 38.0 degrees +/- 0.2 degrees C (mean +/- standard deviation). Thereafter, atrial-femoral artery CPB was initiated, and after 15 minutes at 38 degrees C, the core temperature was decreased to 28 degrees C over approximately 21 minutes. After 30 minutes at 28 degrees C, the core temperature was returned to 38 degrees C over approximately 21 minutes and was maintained at 38 degrees C for the next 30 minutes.

RESULTS

In halothane-anesthetized dogs, the mean brain-to-core temperature gradient always was 1.0 degrees C or less for all brain sites during all phases of CPB. In contrast, in pentobarbital-anesthetized dogs, the mean brain temperature during active cooling typically exceeded the core temperature by 1.7 degrees to 2.2 degrees C. This brain-to-core temperature gradient persisted into the period of stable hypothermia. During the rewarming phase of CPB, the mean brain temperature was 2.9 degrees to 3.4 degrees C cooler than the core temperature. This trend of relative cerebral hypothermia persisted well into the period in which the core temperature was 38 degrees C.

CONCLUSIONS

Deep barbiturate anesthesia resulted in a brain-to-core temperature gradient during CPB that was of a magnitude greater than the 1 degrees C previously reported to modulate ischemic neurologic injury. We speculate that the timely administration of barbiturates (eg, during the latter stages of CPB) may be useful as part of a cerebroprotective regimen in humans undergoing CPB, in part because the barbiturates influence brain temperature.

Cerebral hypoxia after etomidate administration and temporary cerebral artery occlusion

Neurovascular surgical procedures often require temporary cerebral arterial occlusion. Although clinical validation is lacking, etomidate has often been used to attenuate the effects of cerebral ischemia in this setting. The purpose of this study was to evaluate the effects of etomidate and temporary cerebral arterial occlusion on human brain tissue oxygen pressure (PO2), carbon dioxide pressure (PCO2), and pH during intracranial aneurysm surgery. We studied nine patients presenting for cerebral aneurysm surgery. A Paratrend probe was used to determine brain tissue pH and gas tensions. Etomidate was administered to produce electroencephalographic burst suppression before temporary cerebral arterial occlusion. After etomidate administration in nine patients, brain tissue PO2 decreased 30% compared with baseline (P < 0.05). During temporary brain artery occlusion in 8 patients, tissue PO2 decreased 32% below preclip values (P < 0.05) in conjunction with a tissue PCO2 increase of 23% (P < 0.05) and a 0.1-unit decrease in pH (P < 0.05). In patients in whom PO2 decreased below 10 mm Hg during temporary clipping, tissue pH decreased, compared with patients in whom PO2 remained above 10 mm Hg (P < 0.05). These results demonstrate that etomidate administration during cerebral aneurysm surgery decreases tissue PO2 and that in these patients, tissue PO2 does not increase with increases in inspired oxygen concentration. Low tissue PO2 during temporary clipping significantly increases the risk of tissue acidosis.

IMPLICATIONS

Etomidate administration alone resulted in cerebral deoxygenation. Subsequent temporary cerebral artery occlusion resulted in additional tissue deoxygenation and acidosis. These results suggest that etomidate enhances hypoxic risk in the setting of cerebral ischemia.

Early reperfusion in the anesthetized baboon reduces brain damage following middle cerebral artery occlusion: a quantitative analysis of infarction volume

BACKGROUND AND PURPOSE

Because in humans the clinical benefits of reperfusion remain controversial, it is important to determine whether reperfusion per se reduces infarct volume. In the nonhuman primate, mostly semiquantitative assessments of infarction have been performed. When ischemic volumes have been calculated, it has been for the acute or subacute stages of experimental stroke and may thus not adequately reflect the total volume of consolidated infarction.

METHODS

Anesthetized baboons were subjected to 6 hours of either reversible or permanent middle cerebral artery occlusion (MCAO). Approximately 4 weeks later, the brains were processed for neuropathological examination to allow assessment of the final infarct volume determined by the difference of healthy tissue between occluded and nonoccluded hemispheres.

RESULTS

Reversible MCAO resulted in a small essentially subcortical infarction (mean+/-SD, 0.58+/-0.31 cm3) in 6 of 10 baboons: the infarct (pannecrosis) was restricted to the head of the caudate nucleus, internal capsule, and putamen; 4 of 10 baboons showed no evidence of macroscopic infarction. Permanent MCAO produced a larger subcortical infarct in all 7 baboons studied (2.37+/-1.32 cm3; P=.0006 by Wilcoxon-Mann-Whitney test); the lesion was more extensive and encompassed the external capsule and, in 2 baboons, the adjacent insular cortex.

CONCLUSIONS

We conclude that under optimal experimental conditions, an ischemic episode of 6 hours in duration is well tolerated in the anesthetized adolescent baboon, with 4 animals showing no signs of macroscopic brain damage. Thus, early reestablishment of cerebral blood flow after a focal ischemic insult is not detrimental but indeed is beneficial in terms of the final infarct volume (both at the subcortical and cortical levels) produced by occlusion of a major cerebral artery. The data further suggest a feasible time window in which to initiate and continue therapeutic interventions.

The protective effects of thiopental on brain stem ischemia

Thiopental, a barbiturate anesthetic, which at high doses suppresses cortical electroencephalogram activity, was evaluated as a neuroprotective agent in a dog model of reversible, hindbrain ischemia. Fourteen dogs were exposed to 20 minutes of isolated brain stem ischemia after pretreatment with 35 mg per kg of thiopental or placebo. Brain stem auditory evoked potentials (BAEPs) and regional cerebral blood flow were measured before and during the ischemia and for 5 hours after reperfusion. During the ischemic period, both control and thiopental-treated animals experienced dramatic declines in the BAEPs to less than 10% of baseline. On reperfusion for 30 minutes, the BAEPs increased in both groups to near 40% of baseline. In the thiopental-treated animals, the BAEPs continued to recover variably to a mean of 70% of baseline by 5 hours of reperfusion. In contrast, untreated animals showed a decline in BAEPs after 30 minutes of reperfusion. The improved recovery of BAEPs in the thiopental-treated animals suggests that thiopental may be of some value as a cerebroprotective agent, although the mechanism remains unclear. The variability in recovery in this group implies that other factors play a significant role in mediating functional recovery from ischemic brain stem damage.

Intraoperative anesthetic management of patients undergoing glomus tumor resection using a low-dose isoflurane-fentanyl technique

Glomus jugulare and vagale tumors present unique problems to both anesthesiologists and surgeons. The anesthetic plant must be tailored to each patient and provide hemodynamic stability, a consistent intraoperative environment, and rapid awakening after prolonged administration. In this report, we describe our anesthetic method used for paraganglioma resection, which utilizes a combination technique of low-dose isoflurane with a narcotic infusion initiated after bolus administration. Results from the last three patients anesthetized by this "balanced" technique were compared to a similar patient who received isoflurane anesthesia exclusively for a major portion of the surgical procedure. The patients receiving the balanced anesthesia required no hemodynamic support during the procedure and were awakened within 15 to 25 minutes of surgical completion. The patient receiving high-dose isoflurane, however, had a prolonged anesthetic wake-up time and did not follow verbal commands for approximately 12 hours after surgical completion. This patient also required hemodynamic support with a phenylephrine infusion during tumor resection. The balanced technique seems to be superior to a straight inhalational technique. Neurological assessment and intubation times after prolonged surgery were reduced with superb hemodynamic stability throughout. This anesthetic method produces a stable intraoperative environment and provides deep surgical anesthesia during periods when muscle relaxants cannot be utilized.

Paraplegia following thoracic aortic cross-clamping in dogs. No difference in neurological outcome with a barbiturate versus isoflurane

BACKGROUND AND PURPOSE

We compared the incidence and severity of paraplegia following thoracic aortic cross-clamping in dogs for two anesthetic regimens. Animals were randomly assigned to receive methohexital (group M; n = 9) or isoflurane (group I; n = 9). We expected a better neurological outcome in animals administered methohexital because of superior neuronal protection and greater spinal cord perfusion pressure (mean arterial pressure below the cross-clamp site minus mean cerebrospinal fluid pressure).

METHODS

After surgical preparation and a 30-minute stabilization period, dogs in group M received 14 +/- 6 mg.kg-1 i.v. methohexital to induce an isoelectric electroencephalogram followed by a continuous infusion of methohexital at 20 mg.kg-1 x h-1. Dogs in group I received 1.4 +/- 0.2% end-tidal isoflurane (1 minimum alveolar concentration). The thoracic aorta was then occluded 2.5 cm distal to the left subclavian artery for 30 minutes and then released. Hemodynamics and cerebrospinal fluid pressure were measured at (1) baseline, (2) 2 minutes after aortic cross-clamping, (3) 20 minutes after aortic cross-clamping, (4) 5 minutes after aortic unclamping, and (5) 30 minutes after resuscitation. At 24 hours a neurological assessment was performed. After the clinical assessment the dogs were killed and the spinal cord removed immediately for histopathologic study.

RESULTS

There were no differences in nasopharyngeal temperature, PaCO2, pH, or hemoglobin at any time between groups. With cross-clamping, the spinal cord perfusion pressure decreased precipitously. However, there was no difference in spinal cord perfusion pressure between groups at any time (P = .5555). The neurological outcome, assessed at 24 hours after thoracic aortic cross-clamping by a veterinarian unaware of the anesthetic protocol, was not different between groups (P > .5, two-tailed Mann-Whitney rank-sums test). When anesthetized with methohexital 5 of 9 dogs were paraplegic; with isoflurane 7 of 9 dogs were paraplegic. By Spearman's rank test, a strong inverse correlation between the Tarlov score and the ratio of dead to total lumbar anterior spinal cord neurons was seen (Spearman's correlation coefficient = -.8358; P = .0001).

CONCLUSIONS

We conclude that no advantage was offered by the choice of anesthesia to neurological outcome after 30 minutes of thoracic aortic cross-clamping in this canine model.

Three balanced anesthetic techniques for neuroanesthesia: infusion of thiopental sodium with sufentanil or fentanyl compared with inhalation of isoflurane

STUDY OBJECTIVE

To compare emergence from anesthesia and the hemodynamic and respiratory depressant effects of thiopental sodium infusion plus sufentanil or fentanyl with those of isoflurane as the primary component of a balanced technique for neuroanesthesia.

DESIGN

Randomized, double-blind, prospective study.

SETTING

University hospital and its affiliated Veterans Affairs Medical Center.

PATIENTS

Thirty patients undergoing elective craniotomy for aneurysm or tumor.

INTERVENTIONS

Thiopental with infusion of sufentanil 0.1 microgram/kg/hr, thiopental with infusion of fentanyl 1 microgram/kg/hr, or inhalation of 0.25% to 2% isoflurane as the major component of a balanced anesthesia technique that included nitrous oxide (N2O) and vecuronium (potency ratio of sufentanil to fentanyl, 10:1).

MEASUREMENTS AND MAIN RESULTS

Intraoperative stress response (as indicated by intraoperative hypertension) was said to be the percentage of time the patient required administration of an antihypertensive drug, measuring from the first dose of thiopental to discontinuation of N2O at the end of the procedure, excluding any period of induced hypotension. Rapidity of emergence was measured by the number of minutes from discontinuation of N2O to first opening of the eyes on command. Adequacy of spontaneous ventilation was evaluated by determining partial pressure of arterial carbon dioxide 1, 2, and 3 hours after discontinuation of N2O. Extent of vasoactive drug administration for control of intraoperative hypertension (as determined by the clinicians caring for the patients) was described by minutes of vasodilator infusion and milligrams of propranolol or labetalol administered. The frequency of postoperative hypertension was defined as the number of patients in each group who required medication for postoperative hypertension. No significant differences in variables were found for thiopental/sufentanil, thiopental/fentanyl, or isoflurane when these drugs were used with N2O and vecuronium.

CONCLUSIONS

Any one of these balanced anesthetic techniques appears appropriate for craniotomy.

An assessment of the cerebral protective effects of etomidate in a model of incomplete forebrain ischemia in the rat

The cerebral protective effects of etomidate were evaluated in a model of incomplete forebrain ischemia. Fourteen Wistar-Kyoto rats were anesthetized with halothane. After preparation, the rats were alloted to either the control group (halothane anesthesia, n = 7) or the etomidate group (n = 7). In the etomidate group, immediately before and during the period of ischemia, the animals received etomidate in sufficient concentration to achieve electroencephalogram burst suppression (loading dose, 7.5 mg/kg; infusion, 0.3-0.5 mg/kg/min). Both groups were subjected to a 10-minute ischemic insult accomplished by bilateral carotid artery occlusion and simultaneous hypotension (mean arterial pressure, 35 mm Hg). Histological evaluation of the brain was performed after a 4-day recovery period. Injury was evaluated in coronal brain sections in five structures: neocortex, striatum, reticular nucleus of the thalamus, and the CA1 and CA3 areas of the hippocampus. The location of the sections in the rostral-caudal axis was chosen to encompass anterior areas within the core of the ischemic territory as well as more posterior regions within the anticipated "watershed" zone between the occluded anterior and the intact posterior circulations. In the animals that received etomidate, statistically significant (P less than 0.05) reduction in the severity of the ischemic injury was observed in the CA3 area and in the ventral portion of the CA1 area of the hippocampus in the more posterior sections. There was an apparent trend toward protection in other structures in both rostral and caudal sections, but these changes were not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral protection during aneurysm surgery with isoflurane anesthesia. Technical note

A strategy for intraoperative cerebral protection is described in which intraoperative electroencephalography is used to titrate the level of inspired isoflurane given for anesthesia to obtain isoelectricity prior to temporary vessel occlusion during repair of difficult aneurysms. During temporary vessel occlusion, arterial blood pressure is maintained or increased with an inotropic or vasopressor agent. After clipping of the aneurysm, the concentration of isoflurane is reduced to allow the patient to awaken in the operating room for early postoperative neurological examination. The combination of a high concentration of isoflurane, temporary vessel occlusion, and maintenance of arterial blood pressure may be a useful protective regimen during neurovascular procedures.

Reversible focal ischemia in the rat: effects of halothane, isoflurane, and methohexital anesthesia

Barbiturates and the volatile anesthetic isoflurane reduce CMR to similar values. If the mechanism of barbiturate protection against focal ischemic injury is due to a reduction in cellular energy requirements, then isoflurane should similarly reduce ischemic injury. To evaluate this, spontaneously hypertensive rats underwent 2 h of reversible middle cerebral artery occlusion (MCAO) while receiving deep methohexital, isoflurane, or halothane anesthesia. Ninety-six hours postischemia, neurologic deficits were present but without a difference between groups. Mean +/- SD infarct volume, as assessed by triphenyl tetrazolium chloride staining and computerized planimetry, was significantly less in the methohexital group (n = 8; 166 +/- 74 mm3) than in either the halothane (n = 9; 249 +/- 71 mm3; p less than 0.04) or the isoflurane (n = 9; 243 +/- 62 mm3; p less than 0.03) groups. One possible explanation for the lack of protective effect for isoflurane might be related to its vasodilative properties, which could result in a cerebral vascular steal. To examine this possibility, rats anesthetized with methohexital or isoflurane underwent autoradiographic determination of CBF with or without MCAO. In isoflurane-anesthetized sham rats (n = 5; no ischemia), CBF was approximately three times greater than in methohexital-treated (n = 5) sham rats. During ischemia, although a regional reduction in flow was noted in both anesthetic groups, mean flow remained greater in the isoflurane group.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of the area of histochemical dysfunction after focal cerebral ischaemia during anaesthesia with isoflurane and halothane in the rat

The investigations that have thus far evaluated the cerebral protective properties of isoflurane have provided conflicting results. Protection would be most likely to occur in the circumstances of incomplete cerebral ischaemia in which there is a penumbral zone of marginal perfusion. The present investigation sought to evaluate further the protective properties of isoflurane in that circumstance. Middle cerebral artery occlusion (MCAO) was performed in Sprague-Dawley rats anaesthetized with 1.2 MAC concentrations of either halothane or isoflurane. At the end of four hours of MCAO, the brains were removed, sectioned and incubated in the histochemical stain 2-3-triphenyltetrazolium (TTC). An image analysis system was used to measure the area of reduced or absent TTC staining in four coronal planes spanning the distribution of the middle cerebral artery. There was no difference between halothane and isoflurane anaesthetized animals with respect to the area of brain with evidence of histochemical dysfunction. It is concluded that isoflurane is not protective (relative to the status of halothane anaesthetized control animals) when administered at 1.2 MAC concentration during four hours of focal (incomplete) cerebral ischaemia in the rat.