Intravenous agents and intraoperative neuroprotection. Beyond barbiturates

Pentobarbital inhibits glucose uptake, but not water transport by glucose transporter type 3

To understand the mechanisms underlying the neuroprotective efficacy of barbiturates, the effect of pentobarbital on glucose uptake and water transport was determined in Xenopus oocytes expressing glucose transporter type 3 (GLUT3). Pentobarbital induced a 50% concentration-dependent inhibition in glucose uptake, but exerted no effect on water transport by GLUT3. Eadie-Hofstee analysis showed that pentobarbital decreased Vmax significantly, but not Km of GLUT3 for 2-deoxy-D-glucose. Although the protein kinase C (PKC) activator significantly decreased glucose uptake by GLUT3, no additive or synergistic interactions were observed between the PKC activator and pentobarbital. Our results suggest that pentobarbital may play an important role in neuroprotection by inhibition of glucose uptake by GLUT3 by a mechanism involving PKC.

Guidelines for the management of aneurysmal subarachnoid hemorrhage: a guideline for healthcare professionals from the American Heart Association/american Stroke Association

PURPOSE

The aim of this guideline is to present current and comprehensive recommendations for the diagnosis and treatment of aneurysmal subarachnoid hemorrhage (aSAH).

METHODS

A formal literature search of MEDLINE (November 1, 2006, through May 1, 2010) was performed. Data were synthesized with the use of evidence tables. Writing group members met by teleconference to discuss data-derived recommendations. The American Heart Association Stroke Council's Levels of Evidence grading algorithm was used to grade each recommendation. The guideline draft was reviewed by 7 expert peer reviewers and by the members of the Stroke Council Leadership and Manuscript Oversight Committees. It is intended that this guideline be fully updated every 3 years.

RESULTS

Evidence-based guidelines are presented for the care of patients presenting with aSAH. The focus of the guideline was subdivided into incidence, risk factors, prevention, natural history and outcome, diagnosis, prevention of rebleeding, surgical and endovascular repair of ruptured aneurysms, systems of care, anesthetic management during repair, management of vasospasm and delayed cerebral ischemia, management of hydrocephalus, management of seizures, and management of medical complications.

CONCLUSIONS

aSAH is a serious medical condition in which outcome can be dramatically impacted by early, aggressive, expert care. The guidelines offer a framework for goal-directed treatment of the patient with aSAH.

Aortic atheroma and adverse cerebral outcome: risk, diagnosis, and management options

Aortic atheromatous disease is a common finding in the patient presenting for cardiac surgery. Adverse neurologic outcome has been closely linked to the extent of aortic atherosclerosis. In order to optimize perioperative outcomes, the location and severity of disease needs accurate characterization using multimodal techniques. Although various preoperative radiographic techniques have variably identified patients with significant atheroma, intraoperative echocardiographic imaging has proven most useful in localizing and characterizing the degree of aortic atheroma. Epiaortic assessment of the ascending aorta has been utilized in guiding surgical modifications and interventions aimed at reducing the risk of neurologic injury. Although no particular technique has been definitely studied, avoidance of the identifiable atheromatous aortic region has been a main feature of the various modifications employed to optimize neurologic outcome after cardiac surgery.

Neuroprotective effect of mild hypothermia in the temporary brain ischemia in cats

OBJECTIVE

To evaluate the neuroprotective effect of mild hypothermia during temporary focal ischemia in cats.

METHOD

20 cats underwent middle cerebral artery 60 minutes occlusion and 24 hours reperfusion: 10 under normothermia and 10 under mild hypothermia (32 masculine C). Brain coronal sections 2mm thick were stained with 2,3,5-triphenyltetrazolium hydrochloride, photographed and evaluated with software for volume calculation.

RESULTS

Cortical ischemia was found in 7 and basal ganglia ischemia in 8 animals of group 1 and in both regions in 5 animals of group 2 (no difference: p=0.6499 for cortical; p=0.3498 for basal ganglia). No ischemia was found in 5 animals of group 2 and in none of group 1 (significant difference, p=0.0325). The infarct volume was greater in group 1 than 2 (p=0.0433).

CONCLUSION

Mild hypothermia did not interfere with location of ischemia, but it was effective for reducing the infarct volume.

Brain metabolite levels assessed by lactate-edited MR spectroscopy in premature neonates with and without pentobarbital sedation

BACKGROUND AND PURPOSE

Pentobarbital is known to affect cerebral metabolism; pentobarbital sedation is, however, frequently used for MR imaging and MR spectroscopy, especially in children. Accurate assessment of the brain metabolite levels is important, particularly in neonates with suspected brain injury. We investigated whether pentobarbital sedation has any effect on the ratios of spectral metabolites lactate, N-acetylaspartate, or choline in a group of premature neonates.

MATERIALS AND METHODS

MR spectroscopy was performed in 43 premature neonates, all with normal concurrent MR imaging and normal neurodevelopmental outcome at 12 months of age. Of those neonates, 14 (33%) required pentobarbital (Nembutal 1 mg/kg) sedation during MR spectroscopy; the remaining 29 neonates did not receive any sedation. Ratios of lactate, choline, and N-acetylaspartate were calculated in the basal ganglia, thalami, and corticospinal tracts and compared between those neonates with and without sedation.

RESULTS

Small amounts of brain lactate were detected in all of the premature neonates. The basal ganglia lactate/choline and lactate/N-acetylaspartate ratios were significantly lower, by 17% and 25% respectively, in the neonates with pentobarbital sedation compared with the age-matched neonates without sedation (P < .05). Sedation did not affect the lactate level in the thalami or the corticospinal tracts. The N-acetylaspartate/choline ratios were unaffected by pentobarbital sedation.

CONCLUSION

Pentobarbital sedation is associated with lower lactate/choline and lactate/N-acetylaspartate ratios in the basal ganglia of premature neonates, as determined by proton MR spectroscopy. Investigators should be aware of this phenomenon for accurate interpretation of their MR spectroscopy results.

Etomidate revisited

The major advantage of etomidate is its lack of cardiovascular side effects. In addition, etomidate is supposed to be neuroprotective. The side effects of etomidate include adrenal suppression and myocloni. A review of the recent literature on etomidate, its clinical use, its side effects and its mechanism of action was performed. Among others, major recent advances include a new drug preparation devoid of propylene glycol and its side effects, a new pretreatment technique that may reduce the incidence of myocloni, and the identification of its site of action in the central nervous system.

Neuroprotection (including hypothermia)

There have been over 2000 publications in the last year addressing the topic of neuroprotection. Novel and emerging therapeutic targets that have been explored include cerebral inflammation, hypothermia, neural transplantation and repair and gene therapy. Unfortunately, with few exceptions, the successes of experimental neuroprotection have not been translated into clinical practice. The possible reasons for the discrepancy between experimental success and clinical benefit are explored.

Ketamine and thiopental sodium: individual and combined neuroprotective effects on cortical cultures exposed to NMDA or nitric oxide

BACKGROUND

An N-methyl-D-aspartate (NMDA) blocker, ketamine, has been shown to be neuroprotective both in vivo and in vitro. However, ketamine is not commonly recommended for use in patients suffering from cerebral ischaemia because of its adverse neurological effects. We hypothesized that combined administration of ketamine and thiopental sodium (TPS) would be highly effective in protecting cerebral cortical neurones from ischaemia, with possibly reduced dosages.

METHODS

We examined the degree of neuroprotection provided by various concentrations of ketamine and TPS, alone and in combination, in cortical cultures exposed to NMDA or a nitric oxide-releasing compound (NOC-5) for 24 h. The survival rate (SR) of E16 Wistar rat cortical neurones was evaluated using photomicrographs before and after exposure to these compounds.

RESULTS

The SRs of cortical neurones exposed to 30 microM NMDA or NOC-5 were 15.0 (3.8)%, 12.8 (3.1)%, respectively. Higher doses (5, 10 and 50 microM) but not lower doses (<1 microM) of ketamine improved SRs [57.9 (2.2)%, 61.1 (5.4)%, 76.7 (3.0)%, respectively] against NMDA but not NOC. Enhanced survival was observed with combined administration of 5 or 10 microM ketamine and 50 microM TPS [SR 71.3 (4.8)%, 74.7 (3.7)%, respectively, P<0.05 if ketamine alone, P<0.01 if TPS alone], against NMDA-induced neurotoxicity in vitro. Only the highest dose of TPS (50 microM) improved survival after NOC exposure. This neuroprotection was not influenced by ketamine.

CONCLUSIONS

These data indicate that a low, clinically relevant dose of ketamine offer significant neuroprotection during prolonged exposure to NMDA but not to NOC. Combinations of reduced doses of ketamine and TPS exhibited enhanced neuroprotection against NMDA-induced neurotoxicity. Hence, combinations of these two common i.v. anaesthetics agents could be developed to protect the brain from ischaemia.

Simultaneous bilateral laser Doppler fluxmetry and electrophysiological recording during middle cerebral artery occlusion in rats

Laser Doppler fluxmetry (LDF) and electrocorticography (ECG) are techniques used to indicate successful occlusion of the middle cerebral artery (MCAO) in the intraluminal filament model of ischemic stroke. However, each method has several advantages and drawbacks. This article describes a simple technique to simultaneously and continuously monitor LDF and ECG over both cerebral hemispheres. We investigated the potential of this method to improve the reliability of the filament model. Thirty male Sprague-Dawley rats were subjected to transient MCAO under three different experimental conditions (n=10 each group): MCAO in [A] normothermic animals, in [B] animals treated with hypothermia and in [C] animals receiving barbiturate for induction of burst suppression. Cortical blood flow was continuously recorded bilaterally by LDF and the electrocorticogram was continuously recorded over both hemispheres. The results show that monitoring of cortical electrophysiological activity by ECG allows detection of subarachnoid hemorrhage (SAH) during normal electrophysiological status and provides continuous control of barbiturate induced burst suppression as well as information about postischemic electrophysiological recovery. ECG did not detect MCAO, premature reperfusion, or SAH during burst suppression induced by barbiturates. In contrast, MCAO, SAH and premature reperfusion were rapidly indicated by LDF. Our findings suggest that simultaneous bilateral LDF and ECG during MCAO are of complementary value, in particular if barbiturates are investigated.

Propofol and thiopental attenuate adenosine triphosphate-sensitive potassium channel relaxation in pulmonary veins

Pulmonary veins (PV) make a significant contribution to total pulmonary vascular resistance. We investigated the cellular mechanisms by which the intravenous anesthetics propofol and thiopental alter adenosine triphosphate-sensitive potassium (KATP+) channel relaxation in canine PV. The effects of KATP+ channel inhibition (glybenclamide), cyclooxygenase inhibition (indomethacin), nitric oxide synthase inhibition (L-NAME), and L-type voltage-gated Ca2+ channel inhibition (nifedipine) on vasorelaxation responses to levcromakalim (KATP+ channel activator) alone and in combination with the anesthetics were assessed. The maximal relaxation response to levcromakalim was attenuated by removing the endothelium and by L-NAME, but not by indomethacin. Propofol (10(-5), 3x10(-5), and 10(-4) M) and thiopental (10(-4) and 3x10(-4) M) each attenuated levcromakalim relaxation in endothelium-intact (E+) rings, whereas propofol (3x10(-5) and 10(-4) M) and thiopental (3x10(-4) M) attenuated levcromakalim relaxation in endothelium-denuded (E-) rings. In E+ rings, the anesthesia-induced attenuation of levcromakalim relaxation was decreased after pretreatment with L-NAME but not with indomethacin. In E-strips, propofol (10(-4) M) and thiopental (3x10(-4) M) inhibited decreases in tension and intracellular Ca2+ concentration ([Ca2+]i) in response to levcromakalim, and these changes were abolished by nifedipine. These findings indicate that propofol and thiopental attenuate the endothelium-dependent component of KATP+ channel-induced PV vasorelaxation via an inhibitory effect on the nitric oxide pathway. Both anesthetics also attenuate the PV smooth muscle component of KATP+ channel-induced relaxation by reducing the levcromakalim-induced decrease in [Ca2+]i via an inhibitory effect on L-type voltage-gated Ca2+ channels.

Comparison of intracarotid anesthetics for EEG silence

The goal of this study was to compare systemic and cerebrovascular effects of three anesthetic drugs (etomidate, thiopental, and propofol) when delivered by intracarotid and intravenous routes in doses that produce electrocerebral silence (electroencephalography [EEG]). EEG activity, mean arterial pressure (MAP), and laser Doppler flow as a proxy of cerebral blood flow (CBF) of 24 anesthetized New Zealand white rabbits were continuously recorded. Data were compared at three timepoints: baseline, during EEG silence, and after recovery of EEG activity. Drugs were randomly injected via the carotid artery to produce 10 minutes of EEG silence. After 30 minutes of rest, intravenous boluses of the same drug were injected to achieve 10 minutes of EEG silence. During EEG silence, transient hypotension was seen with intracarotid propofol, but there was no decrease in CBF. MAP and CBF did not decrease with either intracarotid etomidate or thiopental during EEG silence. Intracarotid/intravenous dose ratio of propofol (26%+/-22%; n=8, P<0.02) was much higher than that of etomidate and thiopental (14%+/-2% and 19%+/-11%, respectively; NS). Collectively, these results suggest intracarotid etomidate and thiopental are more useful than propofol in producing EEG silence because they offer better dose advantage and are less likely to impair cerebral or systemic hemodynamics.

General anesthesia improves fetal cerebral oxygenation without evidence of subsequent neuronal injury

Anesthetic exposure during pregnancy is viewed as a relatively routine medical practice. However, recent rodent studies have suggested that common anesthetic agents can damage the developing brain. Here we assessed this claim in a higher order species by exposing previously instrumented near-term pregnant sheep at gestational day 122 (+/-1) to a combination of midazolam, sodium thiopental, and isoflurane at clinically relevant doses and means of anesthetic delivery (i.e., active ventilation). Four hours of maternal general anesthesia produced an initial increase in fetal systemic oxygenation and a sustained increase in fetal cerebral oxygenation, as determined by in utero near-infrared spectroscopy. Postexposure monitoring failed to identify changes in physiologic status that could be injurious to the fetal brain. Finally, through the histologic assessment of noninstrumented sheep at the same gestational time point, we found no evidence for a direct fetal neuro-toxic effect of our triple-drug regimen. Collectively, these results appear to corroborate the presumed safety of inhalational anesthetic use during pregnancy.

Anoxic depolarization of rat hippocampal slices is prevented by thiopental but not by propofol or isoflurane

BACKGROUND

There is strong evidence to suggest that anoxic depolarization (AD) is an important factor in hypoxia/ischaemia-induced neural damage. Treatments that prevent the occurrence of AD may be useful in providing neuronal protection against hypoxia. The current study was designed to determine whether general anaesthetics which have been suggested to 'induce prophylaxis' against hypoxia can attenuate the incidence of AD.

METHODS

The effects of anoxia (3 min) on evoked extracellularly recorded field potentials of CA1 neurons in rat hippocampal slices were assessed in the absence and presence of the i.v. general anaesthetics thiopental and propofol and the volatile anaesthetic isoflurane.

RESULTS

In the absence of anaesthetics, AD occurred in 81% of the preparations tested. Thiopental (2 x 10(-4) M) significantly reduced the incidence of AD (16%, P=0.0006). In comparison, propofol (2 x 10(-4) M) and isoflurane (1.5 vol%) were ineffective (69% and 60%, respectively). Furthermore, in the presence of thiopental, the population spike amplitude recovered with and without AD (90% and 94% of pre-anoxic value, respectively) following 3 min anoxia.

CONCLUSION

The prophylactic effect of thiopental against hypoxia might be induced, in part, by preventing the generation of AD.

Mild intraoperative hypothermia during surgery for intracranial aneurysm

BACKGROUND

Surgery for intracranial aneurysm often results in postoperative neurologic deficits. We conducted a randomized trial at 30 centers to determine whether intraoperative cooling during open craniotomy would improve the outcome among patients with acute aneurysmal subarachnoid hemorrhage.

METHODS

A total of 1001 patients with a preoperative World Federation of Neurological Surgeons score of I, II, or III ("good-grade patients"), who had had a subarachnoid hemorrhage no more than 14 days before planned surgical aneurysm clipping, were randomly assigned to intraoperative hypothermia (target temperature, 33 degrees C, with the use of surface cooling techniques) or normothermia (target temperature, 36.5 degrees C). Patients were followed closely postoperatively and examined approximately 90 days after surgery, at which time a Glasgow Outcome Score was assigned.

RESULTS

There were no significant differences between the group assigned to intraoperative hypothermia and the group assigned to normothermia in the duration of stay in the intensive care unit, the total length of hospitalization, the rates of death at follow-up (6 percent in both groups), or the destination at discharge (home or another hospital, among surviving patients). At the final follow-up, 329 of 499 patients in the hypothermia group had a Glasgow Outcome Score of 1 (good outcome), as compared with 314 of 501 patients in the normothermia group (66 percent vs. 63 percent; odds ratio, 1.14; 95 percent confidence interval, 0.88 to 1.48; P=0.32). Postoperative bacteremia was more common in the hypothermia group than in the normothermia group (5 percent vs. 3 percent, P=0.05).

CONCLUSIONS

Intraoperative hypothermia did not improve the neurologic outcome after craniotomy among good-grade patients with aneurysmal subarachnoid hemorrhage.

Comparing the Bispectral Index and Suppression Ratio with Burst Suppression of the Electroencephalogram During Pentobarbital Infusions in Adult Intensive Care Patients

OBJECTIVE

The bispectral index (BIS), a processed variable derived from the raw electroencephalogram (EEG) used to guide sedation in the intensive care unit (ICU), has not been tested during barbiturate therapy for elevated intracranial pressure. We determined the BIS and suppression ratio (SR) values during traditional burst monitoring of the raw EEG during pentobarbital infusions.

DESIGN

Prospective, observational cohort study.

SETTING

A 42-bed multidisciplinary ICU in a tertiary care medical center.

PATIENTS

Twelve consecutive patients with elevated intracranial pressure treated with pentobarbital infusions.

INTERVENTION

All patients were monitored continuously with the Aspect Medical Systems A-1050 bedside EEG monitor using a bilateral referential montage. Pentobarbital doses were titrated based on the raw EEG to attain a burst-suppression pattern with a goal of 3-5 bursts/minute. Drug dosage, intracranial pressure, cerebral perfusion pressure values, EEG bursts/minute, BIS version 3.2, and SR were recorded daily.

MEASUREMENTS AND MAIN RESULTS

The 12 patients were monitored for 62 patient-days. Mean +/- SD age was 32 +/- 15 years, seven (58%) patients were male, mean Acute Physiology and Chronic Heath Evaluation II score was 17.0 +/- 5.0, and hospital mortality was 42%. The mean pentobarbital infusion rate was 124 +/- 49 mg/hour or 2.3 +/- 1.3 mg/kg/hour, and mean pentobarbital serum concentration was 29.7 +/- 13 microg/ml. The mean BIS value was 18 +/- 14, mean SR 56% +/- 36%; BIS correlated well with SR (r=-0.99, p<0.001). For patient-days with a burst-suppression pattern, BIS 3.2 (r=0.90, p<0.001) and SR (r=-0.89, p<0.001) strongly correlated with the number of bursts/minute. The mean BIS value corresponding to 3-5 bursts/minute was 15 (95% confidence interval [CI] 10-20); SR value was 71 (95% CI 61-80).

CONCLUSION

The Aspect A-1050 applied to patients and monitored by nurses and physicians works well as a bedside EEG monitor, providing a raw EEG signal to titrate barbiturate therapy. The continuous data trend and real-time digital output for the BIS and SR quantify the degree of EEG suppression well and may prove helpful in facilitating titration of barbiturate infusions.

Barbiturates induce mitochondrial depolarization and potentiate excitotoxic neuronal death

Barbiturates are widely used as anesthetics, anticonvulsants, and neuroprotective agents. However, barbiturates may also inhibit mitochondrial respiration, and mitochondrial inhibitors are known to potentiate NMDA receptor-mediated neurotoxicity. Here we used rat cortical cultures to examine the effect of barbiturates on neuronal mitochondria and responses to NMDA receptor stimulation. The barbiturates tested, secobarbital, amobarbital, and thiamylal, each potentiated NMDA-induced neuron death at barbiturate concentrations relevant to clinical and experimental use (100-300 microm). By using rhodamine-123 under quenching conditions, barbiturates in this concentration range were shown to depolarize neuronal mitochondria and greatly amplify NMDA-induced mitochondrial depolarization. Barbiturate-induced mitochondrial depolarization was increased by the ATP synthase inhibitor oligomycin, indicating that barbiturates act by inhibiting electron transport sufficiently to cause ATP synthase reversal. Barbiturates similarly amplified the effects of NMDA on cytoplasmic free calcium concentrations. The cell-impermeant barbiturate N-glucoside amobarbital did not influence mitochondrial potential or potentiate NMDA neurotoxicity or calcium responses. However, all of the barbiturates attenuated NMDA-induced calcium elevations and cell death when present at millimolar concentrations. Whole-cell patch-clamp studies showed that these effects may be attributable to actions at the cell membrane, resulting in a block of NMDA-induced current flux at millimolar barbiturate concentrations. Together, these findings reconcile previous reports of opposing effects on barbiturates on NMDA neurotoxicity and show that barbiturate effects on neuronal mitochondria can be functionally significant. Effects of barbiturates on neuronal mitochondria should be considered in experimental and clinical application of these drugs.

Propofol reduces infarct size and striatal dopamine accumulation following transient middle cerebral artery occlusion: a microdialysis study

Acute cerebral ischemia is associated with an increased extracellular dopamine accumulation. Attenuation or prevention of excessive dopamine accumulation alleviates the cerebral ischemic damage. Propofol, an intravenous anesthetic, has been suggested to have neuroprotective properties. The effect of propofol on dopaminergic neurotransmitters is unclear. The in vivo microdialysis technique was used in this study to examine the effect of propofol on infarct size and striatal dopamine accumulation in rat model of temporary middle cerebral artery occlusion. Sixteen rats were fitted with a right striatal microdialysis probe. Ischemia was induced by inserting a 4-0 monofilament nylon suture into the middle cerebral artery. Propofol was intravenously infused in eight rats during ischemia (60 min) and reperfusion (60 min) at an average dose of 36 mg/kg/h. Control rats (n=8) received vehicle infusion. The infarct size was determined at the end of the experiment. Propofol significantly reduced infarct size, the median (interquatile range) value was 6.84% (7.68%), significantly lower than that in the control group, which was 28.04% (32.28%) (p<0.01). The middle cerebral artery occlusion significantly increased dopamine accumulation in the striatum. Propofol infusion significantly attenuated this middle cerebral artery occlusion-induced dopamine accumulation. The data demonstrate that propofol, when administered during ischemia and reperfusion, provides neuroprotection in our middle cerebral artery occlusion in rat model. The data also suggest that attenuated dopamine accumulation may be one of the factors contributing to the neuroprotective property of propofol.

Free radicals, antioxidants, and neurologic injury: possible relationship to cerebral protection by anesthetics

Oxygen-centered free radicals cause brain injury associated with trauma and stroke. These reactive oxygen species may be detoxified by endogenous antioxidants, but cell death occurs after antioxidants become depleted. General anesthetics penetrate into brain parenchyma, where they may abrogate oxidative injury to neurons by several mechanisms that prevent the initiation of free radical chain reactions or terminate the propagation of highly reactive radicals. First, general anesthetics may inhibit free radical generation because these drugs slow cerebral utilization of oxygen and glucose, inhibit oxidative metabolism in neutrophils, and prevent redox changes in hemoglobin. Second, antioxidant anesthetics, such as thiopental and propofol, directly scavenge reactive oxygen species and inhibit lipid peroxidation. Finally, anesthetics may prevent the elevation of extracellular glutamate concentration and inhibit the activation of excitatory glutamatergic receptors that augment oxidative stress after ischemia.

Intravenous anesthetics differentially reduce neurotransmission damage caused by oxygen-glucose deprivation in rat hippocampal slices in correlation with N-methyl-d-aspartate receptor inhibition

OBJECTIVE

To examine the relation between the effect of intravenous anesthetics on ischemic neurotransmission damage and their actions on N-methyl-d-aspartate (NMDA) receptors in an in vitro cerebral ischemic model.

DESIGN

Prospective, randomized study in freshly prepared rat hippocampal slices.

SETTING

University research laboratory.

SUBJECTS

Hippocampal slices were prepared from male Wistar rats (4-5 wks old).

INTERVENTIONS AND MEASUREMENTS

In vitro ischemia was induced by exposing slices to glucose-free Krebs solution gassed with 95% N2 /5% CO2 at 37.1-37.3 degrees C. Ischemic neurotransmission damage was indicated by the amplitudes of population spikes (PS) recorded from the CA1 pyramidal layer after stimulation of the Schaffer collaterals. The effect of anesthetics on NMDA receptors was determined by measuring the NMDA-mediated changes in intracellular calcium in the CA1 pyramidal layer with a calcium indicator, fura-2.

RESULTS

Following 4, 6, and 7.5 mins ischemia in vitro, the recoveries of PS (% control) were 100%, 17.5 +/- 21.8%, and 5.4 +/- 2.1%, respectively. 3-(R)-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP, 5 microM), an NMDA receptor antagonist, increased the recovery of PS to 88.3 +/- 24.5% after 6 mins ischemia, and to 42.1 +/- 18.7% after 7.5 mins ischemia. Thiopental (400 microM), thiamylal (400 microM), and ketamine (100 microM), but not propofol (100 microM) and etomidate (10 microM), improved the recovery of PS after 6 and 7.5 mins ischemia; the degrees of their protection were comparable to that of 5 microM CPP. The NMDA-mediated increases in intracellular calcium were almost completely inhibited by thiamylal, reduced to half by ketamine and thiopental, augmented by propofol, and not affected by etomidate.

CONCLUSIONS

The results indicate that the efficacy of intravenous anesthetics in attenuating ischemic neuronal damage varies among agents, relating to their effects on NMDA receptors.

An exceptional case of complete neurologic recovery after more than 5-h cardiac arrest

We describe a case of more than 5 h cardiac arrest in a 60-year-old patient who underwent general anesthesia for a urologic operation. Before extubation, the patient suddenly developed ventricular fibrillation, pulseless ventricular tachycardia and asystole which was immediately treated by advanced life support (ALS) measures. Thirty minutes later seizures developed and were controlled by 200 mg of thiopentone and 10 mg of diazepam. A pattern of ventricular tachycardia, coarse ventricular fibrillation and asystole lasted for nearly 120 min. Termination of resuscitation maneuvers was considered, but long-term life support was continued for 5 h. After this time, peripheral pulses, with a supraventricular tachycardia-like rhythm and regular spontaneous breathing reappeared. Seven hours later, the patient had a Glasgow Coma Scale (GCS) of 5, dilated unresponsive, absence of pupils, and a systolic arterial pressure of 100 mmHg. He was then transferred to intensive care unit (ICU). The morning after, the patient was awake, responded to simple orders, breathing spontaneously, and free from sensomotor deficit. He was, therefore, extubated. Subsequently, other episodes of transitory ST-line upper wave followed by ventricular fibrillation appeared, suggesting Prinzmetal angina. This was successfully treated by percutaneous coronary angioplasty. The first electroencephalogram recorded the day after cardiac arrest showed a mild widespread background slowing. An electroencephalogram 6 days later showed a return to alpha rhythm with only mild theta-wave abnormalities. Four weeks after the first cardiac arrest the patient was discharged. This is an exceptional experience compared with the others reported. We believe that all the efforts must not be given up when such an event occurs during anesthesia and there are optimal conditions for resuscitation maneuvers.

No additional neuroprotection provided by barbiturate-induced burst suppression under mild hypothermic conditions in rats subjected to reversible focal ischemia

OBJECT

Mild-to-moderate hypothermia is increasingly used for neuroprotection in humans. However, it is unknown whether administration of barbiturate medications in burst-suppressive doses-the gold standard of neuroprotection during neurovascular procedures-provides an additional protective effect under hypothermic conditions. The authors conducted the present study to answer this question.

METHODS

Thirty-two Sprague-Dawley rats were subjected to 90 minutes of middle cerebral artery occlusion and randomly assigned to one of four treatment groups: 1) normothermic controls; 2) methohexital treatment (burst suppression); 3) induction of mild hypothermia (33 degrees C); and 4) induction of mild hypothermia plus methohexital treatment (burst suppression). Local cerebral blood flow was continuously monitored using bilateral laser Doppler flowmetry and electroencephalography. Functional deficits were quantified and recorded during daily neurological examinations. Infarct volumes were assessed histologically after 7 days. Methohexital treatment, mild hypothermia, and mild hypothermia plus methohexital treatment reduced infarct volumes by 32%, 71%, and 66%, respectively, compared with normothermic controls. Furthermore, mild hypothermia therapy provided the best functional outcome, which was not improved by additional barbiturate therapy.

CONCLUSIONS

The results of this study indicate that barbiturate-induced burst suppression is not required to achieve maximum neuroprotection under mild hypothermic conditions. The magnitude of protection afforded by barbiturates alone appears to be modest compared with that provided by mild hypothermia.

Inhibition of glucose transport and direct interactions with type 1 facilitative glucose transporter (GLUT-1) by etomidate, ketamine, and propofol: a comparison with barbiturates

Ketamine, etomidate, propofol, and pentobarbital were compared for effects on and interactions with the type 1 facilitative glucose transporter (GLUT-1). Fluxes of radiolabeled hexoses were used to determine the effects of anesthetics on GLUT-1 function. Hypotonic hemolysis of human erythrocytes was used to assess perturbations of membrane integrity. Quenching of intrinsic protein fluorescence was used to assess the direct interactions of anesthetics with purified GLUT-1. Pentobarbital, ketamine, etomidate, and propofol inhibited glucose transport in murine fibroblasts with IC(50) values of 0.8, 1. 6, 0.1, and 0.4 mM, respectively. Pentobarbital, ketamine, etomidate, and propofol also inhibited sugar transport in human erythrocytes. The IC(50) values for pentobarbital and ketamine exhibited substrate dependence for equilibrium exchange but not unidirectional effluxes. This was not observed for etomidate. Propofol did not inhibit equilibrium exchange but did inhibit unidirectional efflux with little substrate dependence. Pentobarbital protected against hemolysis, whereas etomidate and ketamine promoted hemolysis of erythrocytes. Propofol had no effect on membrane integrity. Pentobarbital, ketamine, and etomidate all interacted directly with GLUT-1, with apparent K(d) values of 2.2, 0.8, and 0.5 mM, respectively. Like barbiturates, ketamine, etomidate, and propofol inhibited GLUT-1 at concentrations near to those used pharmacologically. Inhibition of GLUT-1 by these intravenous general anesthetics was complex, exhibiting differential kinetic effects on equilibrium exchange versus unidirectional fluxes and contrasting substrate dependencies. Like barbiturates, ketamine and etomidate bound to GLUT-1 with affinities that paralleled inhibition of glucose transport. As a class, intravenous general anesthetics, in contrast to inhalation anesthetics, inhibit GLUT-1-mediated glucose transport.

Reduced palmitate turnover in brain phospholipids of pentobarbital-anesthetized rats

Our laboratory has reported that pentobarbital-induced anesthesia reduced the incorporation of intravenously injected radiolabeled palmitic acid into brain phospholipids. To determine if this decrease reflected a pentobarbital-induced decrease in palmitate turnover in phospholipids, we applied our method and model to study net flux and turnover of palmitate in brain phospholipids (1). Awake, light and deep pentobarbital (25-70 mg/kg, iv) anesthetized rats were infused with [9,10-3H]palmitate over a 5 min period. Brain electrical activity was monitored by electroencephalography. An isoelectric electroencephalogram characterized deep pentobarbital anesthesia. Net incorporation rates (J(FA,i)) and turnover rates (Fi) of palmitate were calculated. J(FA,i) for palmitate incorporated into phospholipids was dramatically reduced by pentobarbital treatment in a dose-dependent manner, by 70% and 90% respectively for lightly and deeply anesthetized animals, compared with awake controls. Turnover rates for palmitate in total phospholipid and individual phospholipid classes were decreased by nearly 70% and 90% for lightly and deeply anesthetized animals, respectively. Thus, pentobarbital decreases, in a dose-dependent manner, the turnover of palmitate in brain phospholipids. This suggests that palmitate turnover is closely coupled to brain functional activity.

EEG burst suppression is not necessary for maximum barbiturate protection in transient focal cerebral ischemia in the rat

Barbiturates have been demonstrated to reduce the cerebral metabolic rate (CMR) in a dose-dependent manner but investigations of a dose-response relationship for their neuroprotective efficacy are scant. It has been suggested that barbiturates possess other mechanism of action that may be critical to their protective effect. If so, it is conceivable that the peak effect of such mechanisms does not parallel the reduction in CMR. Thus, maximal neuroprotection may be achieved with a substantially lower dose of the drug. Thirty Sprague-Dawley rats were subjected to 2 h of middle cerebral artery occlusion while either anesthetized with (1) halothane (control) or (2) intravenous thiopental titrated to cause mild EEG suppression or (3) thiopental titrated to maintain EEG burst suppression. Cortical blood flow was recorded by continuous bilateral laser Doppler flowmetry (LDF). Infarct volume was assessed after 3 h of reperfusion. Low-dose thiopental decreased blood flow to 80% of baseline and high-dose thiopental to 70% of baseline. LDF did not indicate improvement of blood flow by thiopental in the ischemic area. Compared to controls, low-dose thiopental significantly decreased infarct volume by 28% and high-dose thiopental by 29%. The results of this study and a review of literature indicate that barbiturates provide cerebral protection but that the magnitude of this effect has been overestimated. Other mechanisms than CMR reduction seem to contribute to their beneficial effects, and high doses administered to the point of burst suppression may not be required to obtain maximal protection.

Barbiturates impair astrocyte glutamate uptake

Barbiturates are widely used as neuroprotective agents during status epilepticus and during surgical procedures that cause cerebral ischemia. The efficacy of this practice is unproved, however, and while barbiturates may counter neuronal excitotoxicity, they can also inhibit mitochondrial ATP production. Since glutamate uptake is energetically costly, mitochondrial inhibition could impair glutamate uptake. To examine this possibility, glutamate uptake was measured in primary rat astrocyte cultures in the presence of several barbiturates. Different barbiturates had differing effects on glutamate uptake at normal glucose concentrations, but all potentiated inhibition of glutamate uptake during glucose deprivation. Thiamylal and thiopental were the most potent barbiturates examined, with 0.3 mM causing approximately 40% reduction in glutamate uptake rates. Barbiturates also potentiated ATP depletion during glucose deprivation, supporting mitochondrial inhibition as the mechanism of these effects. These findings suggest that barbiturates can, under some conditions, impair glutamate uptake at concentrations relevant to their clinical use.