Comparison of the effects of propofol and pentobarbital on neurologic outcome and cerebral infarct size after temporary focal ischemia in the rat

Stroke and Translational Research - Review of Experimental Models with a Focus on Awake Ischaemic Induction and Anaesthesia

Animal models are an indispensable tool in the study of ischaemic stroke with hundreds of drugs emerging from the preclinical pipeline. However, all of these drugs have failed to translate into successful treatments in the clinic. This has brought into focus the need to enhance preclinical studies to improve translation. The confounding effects of anaesthesia on preclinical stroke modelling has been raised as an important consideration. Various volatile and injectable anaesthetics are used in preclinical models during stroke induction and for outcome measurements such as imaging or electrophysiology. However, anaesthetics modulate several pathways essential in the pathophysiology of stroke in a dose and drug dependent manner. Most notably, anaesthesia has significant modulatory effects on cerebral blood flow, metabolism, spreading depolarizations, and neurovascular coupling. To minimise anaesthetic complications and improve translational relevance, awake stroke induction has been attempted in limited models. This review outlines anaesthetic strategies employed in preclinical ischaemic rodent models and their reported cerebral effects. Stroke related complications are also addressed with a focus on infarct volume, neurological deficits, and thrombolysis efficacy. We also summarise routinely used focal ischaemic stroke rodent models and discuss the attempts to induce some of these models in awake rodents.

Time-varying caloric vestibular stimulation for the treatment of neurodegenerative disease

Time-varying caloric vestibular stimulation (tvCVS) is a new form of non-invasive neuromodulation similar to, but different from, diagnostic caloric vestibular stimulation (CVS). Using a non-invasive, solid-state delivery device, tvCVS has been successfully used in a human clinical trial with Parkinson’s disease (PD) subjects. Additionally, the effects of tvCVS on brain activation have been studied in healthy human subjects using transcranial Doppler sonography (TCD) and functional magnetic resonance imaging (BOLD fMRI). A novel finding in the TCD and fMRI studies was the induction of cerebral blood flow velocity (CBFv) oscillations. How such oscillations might lead to the observed clinical effects seen in PD subjects will be discussed. Enabling studies of tvCVS with rodents is an attractive goal in support of explorations of the mechanism of action. Male Wistar rats were used in a proof-of-concept study described herein. Rats were anesthetized (isoflurane) and ventilated for the duration of the tvCVS runs. Time-varying thermal stimuli were administered using a digital temperature controller to modulate Peltier-type heater/cooler devices. Blunt ear bars conveyed the thermal stimulus to the external ear canals of the rats. Different thermal waveform combinations were evaluated for evidence of successful induction of the CVS effect. It was found that bilateral triangular thermal waveforms could induce oscillations in CBFv both during and after the application of tvCVS. These oscillations were similar to, but different from those observed in awake human subjects. The establishment of a viable animal model for the study of tvCVS will augment ongoing clinical investigations of this new form of neuromodulation in patients with neurodegenerative disease.

Anesthesia in Experimental Stroke Research

Anesthetics have enabled major advances in development of experimental models of human stroke. Yet, their profound pharmacologic effects on neural function can confound the interpretation of experimental stroke research. Anesthetics have species-, drug-, and dose-specific effects on cerebral blood flow and metabolism, neurovascular coupling, autoregulation, ischemic depolarizations, excitotoxicity, inflammation, neural networks, and numerous molecular pathways relevant for stroke outcome. Both preconditioning and postconditioning properties have been described. Anesthetics also modulate systemic arterial blood pressure, lung ventilation, and thermoregulation, all of which may interact with the ischemic insult as well as the therapeutic interventions. These confounds present a dilemma. Here, we provide an overview of the anesthetic mechanisms of action and molecular and physiologic effects on factors relevant to stroke outcomes that can guide the choice and optimization of the anesthetic regimen in experimental stroke.

Neuroprotective effect of propofol against excitotoxic injury to locomotor networks of the rat spinal cord in vitro

Although neuroprotection to contain the initial damage of spinal cord injury (SCI) is difficult, multicentre studies show that early neurosurgery under general anaesthesia confers positive benefits. An interesting hypothesis is that the general anaesthetic itself might largely contribute to neuroprotection, although in vivo clinical settings hamper studying this possibility directly. To further test neuroprotective effects of a widely used general anaesthetic, we studied if propofol could change the outcome of a rat isolated spinal cord SCI model involving excitotoxicity evoked by 1 h application of kainate with delayed consequences on neurons and locomotor network activity. Propofol (5 μm; 4-8 h) enhanced responses to GABA and depressed those to NMDA together with decrease in polysynaptic reflexes that partly recovered after 1 day washout. Fictive locomotion induced by dorsal root stimuli or NMDA and serotonin was weaker the day after propofol application. Kainate elicited a significant loss of spinal neurons, especially motoneurons, whose number was halved. When propofol was applied for 4-8 h after kainate washout, strong neuroprotection was observed in all spinal areas, including attenuation of motoneuron loss. Although propofol had minimal impact on recovery of electrophysiological characteristics 24 h later, it did not further depress network activity. A significant improvement in disinhibited burst periodicity suggested potential to ameliorate neuronal excitability in analogy to histological data. Functional recovery of locomotor networks perhaps required longer time due to the combined action of excitotoxicity and anaesthetic depression at 24 h. These results suggest propofol could confer good neuroprotection to spinal circuits during experimental SCI.

Propofol: Effects on the Central Nervous System

Propofol remains a popular agent for providing intraoperative anesthesia as well as sedation during mechanical ventilation in the intensive care unit (ICU) setting. In addition to its sedative/anxiolytic properties, propofol has been shown to have several beneficial effects on central nervous system (CNS) parameters such as cerebral metabolic rate for oxygen, cerebral blood flow, and intracranial pressure. These properties have been demonstrated in both laboratory animals and in clinical investigations In humans. This article reviews the available literature concerning the effects of propofol on CNS dynamics and discusses its possible application as a therapeutic agent in patients with altered intracranial compliance and/or increased intracranial pressure.

Propofol impairs neurogenesis and neurologic recovery and increases mortality rate in adult rats after traumatic brain injury

OBJECTIVE

Limited data are available on the influence of sedation for critical care therapy with the widely used anesthetic propofol on recovery from acute traumatic brain injury. To establish the influence of propofol on endogenous neurogenesis and functional recovery after traumatic brain injury, rats were sedated with propofol either during or 2 hours after experimental traumatic brain injury.

DESIGN

Randomized controlled animal study.

SETTING

University research laboratory.

SUBJECTS

One hundred sixteen male Sprague Dawley rats.

INTERVENTIONS

Mechanical brain lesion by controlled cortical impact.

MEASUREMENTS AND MAIN RESULTS

This study investigated the dose-dependent influence of propofol (36 or 72 mg/kg/hr) either during controlled cortical impact induction or in a delayed application protocol 2 hours after experimental traumatic brain injury. Infusion of propofol resulted in 1) aggravation of neurologic dysfunction, 2) increased 28-day mortality rate, and 3) impaired posttraumatic neurogenesis (5-bromo-2-deoxyuridine + NeuN-positive cells). Application of propofol during trauma induction afforded a significant stronger effect in the high-dose group compared with low-dose propofol. In the posttrauma protocol, animals were sedated with sevoflurane during the controlled cortical impact injury, and propofol was given after an awake phase. In these animals, propofol increased mortality rate and impaired neurologic function and neurogenesis compared with animals without delayed propofol anesthesia.

CONCLUSIONS

The results show that propofol may prevent or limit reparative processes in the early-phase postinjury. The results therefore indicate that anesthetics may be potentially harmful not only in very young mammalians but also in adult animals following acute cerebral injuries. The results provide first evidence for an altered sensitivity for anesthesia-related negative effects on neurogenesis, functional outcome, and survival in adult rats with brain lesions.

Neuroanesthesia

Neuroanesthesia is a subspecialty area of anesthesia that deals with the complex relationships of anesthetic medications, neurosurgical procedures, and the critical care issues that surround the management of these patients. In this chapter we will focus on a brief overview of the key features associated with the management of patients undergoing neurosurgical procedures, including a review of hemodynamic/neurologic effects of anesthetic agents, neurophysiologic monitoring, and unique medical complications associated with these procedures. For successful patient outcomes, multidisciplinary approaches and effective team communications are essential in these high-intensity environments. This chapter should serve as an introduction to the multitude of issues that face the anesthesiologist and surgeon when dealing with this patient population.

Long-term effects of post-ischaemic oestrogen on brain injury in a rat transient forebrain ischaemia model

BACKGROUND

The current study was conducted to compare the effects of post-treatment with oestrogen on histological and neurological outcomes after short (7-day) and long (28-day) recovery periods in rats subjected to transient forebrain ischaemia.

METHODS

Male Sprague-Dawley rats were randomly assigned to one of five groups: vehicle (7-day recovery period), vehicle (28-day recovery period), oestrogen (17β-estradiol 200 μg/kg, 7-day), oestrogen (17β-estradiol 200 μg /kg, 28-day), or sham surgical (n = 8 in each group). After forebrain ischaemia was induced with bilateral carotid artery occlusion and haemorrhagic hypotension (mean arterial pressure = 40 mmHg) for 10 min, the brain was reperfused for 7 or 28 days. Either 17β-estradiol or vehicle was injected intravenously during the initial 2 min of reperfusion. To evaluate histological damage, the number of intact neurons per 1 mm in the hippocampal CA1 subfield was counted at 7 or 28 days after transient forebrain ischaemia.

RESULTS

At 7 days after ischaemia, the number of intact neurons in the hippocampal CA1 subfield was significantly greater in the oestrogen group [57.5 (46.5)/mm: median (interquartile range)] than in the vehicle group [10 (19.5) /mm; P = 0.014]. However, there was no difference between groups at 28 days after ischaemia [vehicle: 11 (20)/mm vs. oestrogen: 6 (11)/mm]. The neurological deficit scores in the oestrogen and vehicle groups were not different from the sham group at any point post-ischaemia.

CONCLUSION

The current study indicates that post-ischaemic administration of oestrogen provided short-term but not long-term neuroprotective effects in transient forebrain ischaemia in rats.

Cognitive function and oxidative stress after carotid endarterectomy: comparison of propofol to sevoflurane anesthesia

OBJECTIVE

To examine the antioxidant role of propofol in ischemia-reperfusion during carotid endarterectomy (CEA) and its influence on cognitive dysfunction after CEA.

DESIGN

A randomized prospective study.

SETTING

Single-center study in a university hospital.

PARTICIPANTS

Forty-four patients.

INTERVENTIONS

Patients underwent elective CEA under general anesthesia with either sevoflurane (group S, n = 21) or propofol (group P, n = 23).

MEASUREMENTS AND MAIN RESULTS

Cognitive function was assessed with the Mini-Mental State Examination (MMSE) before CEA, 1 hour after CEA, and 24 hours after CEA. Blood samples from the radial artery and the internal jugular vein were drawn before carotid clamping and 5 minutes following unclamping, and peripheral blood was obtained 24 hours postoperatively. Samples were analyzed for lactate, S100B, and P-selectin concentrations and for the antioxidative markers malondialdehyde/low-density lipoprotein ratio and nitrate + nitrite concentrations. Compared with group S, patients in group P exhibited a greater increase in their MMSE values 24 hours postoperatively. Patients who had their MMSE performance reduced at 24 hours also were significantly fewer in group P (13% v 43% in group S, p<0.05). Significantly lower levels of lactate and S100B were observed in arterial and jugular vein samples in group P. In addition, the jugular vein-arterial differences of malondialdehyde-to-low-density lipoprotein ratio and nitrates + nitrites concentrations were lower during propofol anesthesia.

CONCLUSIONS

Propofol seemed to improve cognitive performance after CEA. This improvement was associated with decreased indices of ischemic cerebral damage and seemed to be due to antioxidative effect in the ischemic cerebral circulation.

Propofol prevents cerebral ischemia-triggered autophagy activation and cell death in the rat hippocampus through the NF-κB/p53 signaling pathway

Propofol (2,6-diisopropylphenol) has been shown to attenuate neuronal injury under a number of experimental conditions; however, the mechanisms involved in its neuroprotective effects remain unclear. We therefore investigated whether inhibition of p53 induction by propofol contributes to the neuroprotection of cerebral ischemic cell death through both autophagic and apoptotic mechanisms. A transient global cerebral ischemia-reperfusion (I/R) model was produced with a 10-min, 2-vessel occlusion. The change in target genes including damage-regulated autophagy modulator (DRAM), microtubule-associated protein 1 light chain 3 (LC3), Beclin 1, cathepsin D, cathepsin B, p53-upregulated modulator of apoptosis (PUMA), Bax and Bcl-2 upon p53 inhibition was assessed with the co-administration of the intravenous anesthetic propofol and 3-methyladenine (3-MA), Pifithrin-alpha (PFT-α) or SN50. The I/R-induced increases of protein levels of p53 and LC3-II were significantly inhibited by treatment with propofol, 3-MA or PFT-α. The I/R-induced increases of protein levels of DRAM, Beclin 1, active cathepsin D and cathepsin B were significantly inhibited by treatment with propofol, PFT-α or SN50. The negative effects of the I/R-induced up-regulation of PUMA and Bax and the down-regulation of Bcl-2 in the rat hippocampus were all blocked by treatment with propofol, PFT-α or SN50. Our results suggest that cerebral I/R can induce nuclear factor-kappa B-dependent expression of p53. The autophagic and apoptotic mechanisms participate in programed cell death by regulating the p53-mediated pathway. Our results are the first to show that propofol, at clinically relevant concentrations, attenuated cell death through both autophagic and apoptotic mechanisms in the rat hippocampus after a cerebral I/R insult.

Load-distributing band improves ventilation and hemodynamics during resuscitation in a porcine model of prolonged cardiac arrest

Background

The use of mechanical cardiopulmonary resuscitation (CPR) has great potential for the clinical setting. The purpose of present study is to compare the hemodynamics and ventilation during and after the load-distributing band CPR, versus the manual CPR in a porcine model of prolonged cardiac arrest, and to investigate the influence of rescue breathing in different CPR protocols.

Methods

Sixty-four male pigs (n = 16/group), weighing 30 ± 2 kg, were induced ventricular fibrillation and randomized into four resuscitation groups: continuous load-distributing band CPR without rescue ventilation (C-CPR), load-distributing band 30:2 CPR (A-CPR), load-distributing band CPR with continuous rescue breathing (10/min) (V-CPR) or manual 30:2 CPR (M-CPR). Respiratory variables and hemodynamics were recorded continuously; blood gas was analyzed.

Results

Tidal volume produced by compressions in the A-, C- and V-CPR groups were significantly higher compared with the M-CPR group (all p < 0.05). Coronary perfusion pressure of the V-CPR group was significantly lower than the C-CPR group (p < 0.01), but higher than the M-CPR group. The increasing of lung dead space after restoration of spontaneous circulation was significantly greater in the M-CPR group compared with the A-, C- and V-CPR groups (p < 0.01). Blood pH gradually decreased and was lower in the M-CPR group than that in the A-, C- and V-CPR groups (p < 0.01). PaO₂ of the A-, C- and V-CPR groups were significantly higher and PaCO₂ were significantly lower compared with the M-CPR (both p < 0.05). Cerebral performance categories were better in the A-, C- and V-CPR groups compared with the M-CPR group (p < 0.0001).

Conclusions

The load-distributing band CPR significantly improved respiratory parameters during resuscitation by augmenting passive ventilation, and significantly improved coronary perfusion pressure. The volume of ventilation produced by the load-distributing band CPR was adequate to maintain sufficient gas exchange independent of rescue breathing.

Optically measured NADH concentrations are unaffected by propofol induced EEG silence during transient cerebral hypoperfusion in anesthetized rabbits

The neuroprotective benefit of intra-operative anesthetics is widely described and routinely aimed to invoke electroencephalographic (EEG) silence in anticipation of transient cerebral ischemia. Previous rat survival studies have questioned an additional benefit from achieving EEG silence during transient global cerebral hypoperfusion. Surgical preparation on twelve New Zealand white rabbits under ketamine-propofol anesthesia, included placement of skull screws for bilateral EEG monitoring, skull shaving for laser Doppler probes, and a 5 mm diameter right temporal craniotomy for the NADH probe. Transient global cerebral hypoperfusion was achieved with bilateral internal carotid artery occlusion and pharmacologically induced systemic hypotension. All animals acted as controls, and had cerebral hypoperfusion under baseline propofol anesthesia with an active EEG. Thereafter, animals were randomized to receive bolus injection of intracarotid (3-5 mg) or intravenous (10-20 mg) 1% propofol to create EEG silence for 1-2 min. The data collected at baseline, peak hypoperfusion, and 5 and 10 min post hypoperfusion was analyzed by repeated measures ANOVA with post hoc Bonferroni-Dunn test. Eleven of the twelve rabbits completed the protocol. Hemodynamics and cerebral blood flow changes were comparable in all the animals. Compared to controls, the increase in NADH during ischemia was unaffected by EEG silence with either intravenous or intraarterial propofol. We failed to observe any significant additional attenuation of the elevation in NADH levels with propofol induced EEG silence during transient global cerebral hypoperfusion. This is consistent with previous rat survival studies showing that EEG silence was not required for full neuroprotective effects of pentothal anesthesia.

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.

Propofol: neuroprotection in an in vitro model of traumatic brain injury

Introduction

The anaesthetic agent propofol (2,6-diisopropylphenol) has been shown to be an effective neuroprotective agent in different in vitro models of brain injury induced by oxygen and glucose deprivation. We examined its neuroprotective properties in an in vitro model of traumatic brain injury.

Methods

In this controlled laboratory study organotypic hippocampal brain-slice cultures were gained from six- to eight-day-old mice pups. After 14 days in culture, hippocampal brain slices were subjected to a focal mechanical trauma and subsequently treated with different molar concentrations of propofol under both normo- and hypothermic conditions. After 72 hours of incubation, tissue injury assessment was performed using propidium iodide (PI), a staining agent that becomes fluorescent only when it enters damaged cells via perforated cell membranes. Inside the cell, PI forms a fluorescent complex with nuclear DNA.

Results

A dose-dependent reduction of both total and secondary tissue injury could be observed in the presence of propofol under both normo- and hypothermic conditions. This effect was further amplified when the slices were incubated at 32°C after trauma.

Conclusions

When used in combination, the dose-dependent neuroprotective effect of propofol is additive to the neuroprotective effect of hypothermia in an in vitro model of traumatic brain injury.

Anesthetics and brain protection

PURPOSE OF REVIEW

There is a considerable risk of cerebral ischemia during anesthesia and surgery. Anesthetic agents have been shown to have a profound effect on the pathophysiology of cerebral ischemia. The present review provides a brief historical review and details new information about the anesthetic effects on the ischemic brain.

RECENT FINDINGS

Although anesthetics have been shown to reduce ischemic cerebral injury, the durability of this neuroprotection has been questioned. Recent data indicate that, under the right circumstances, anesthetic neuroprotection can be sustained for at least 2-4 weeks; the durability of this protection is dependent upon the experimental model, control of physiologic parameters and the assurance of the adequacy of reperfusion. In addition, volatile anesthetics have been shown to accelerate postischemic neurogenesis; this suggests that anesthetics may enhance the endogenous reparative processes in the injured brain.

SUMMARY

The available data indicate that anesthetics can provide long-term durable protection against ischemic injury that is mild to moderate in severity. Experimental data do not provide support for the premise that anesthetics reduce injury when the ischemic injury is severe.

Neuroprotective effects of propofol in acute cerebral injury

Propofol (2,6-diisopropylphenol) is one of the most popular agents used for induction of anesthesia and long-term sedation, owing to its favorable pharmacokinetic profile, which ensures a rapid recovery even after prolonged administration. A neuroprotective effect, beyond that related to the decrease in cerebral metabolic rate for oxygen, has been shown to be present in many in vitro and in vivo established experimental models of mild/moderate acute cerebral ischemia. Experimental studies on traumatic brain injury are limited and less encouraging. Despite the experimental results and the positive effects on cerebral physiology (propofol reduces cerebral blood flow but maintains coupling with cerebral metabolic rate for oxygen and decreases intracranial pressure, allowing optimal intraoperative conditions during neurosurgical operations), no clinical study has yet indicated that propofol may be superior to other anesthetics in improving the neurological outcome following acute cerebral injury. Therefore, propofol cannot be indicated as an established clinical neuroprotectant per se, but it might play an important role in the so-called multimodal neuroprotection, a global strategy for the treatment of acute injury of the brain that includes preservation of cerebral perfusion, temperature control, prevention of infections, and tight glycemic control.

Propofol exerts greater neuroprotection with disodium edetate than without it

The main objective of this study, on mice, was to compare the neuroprotective effects of propofol with those of propofol plus disodium edetate (propofol EDTA). We also administered propofol EDTA (0.005% (w/v) EDTA) to mice intravenously, and measured the changes in zinc concentrations occurring after permanent middle cerebral artery occlusion. In the in vivo study, propofol EDTA displayed stronger neuroprotective effects than propofol alone. Furthermore, we examined the neuroprotective effects of EDTA administered alone, and found that EDTA Na significantly reduced the infarct volume. The number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling-positive cells in the ischemic penumbra was reduced more by propofol EDTA than by propofol alone. We performed in the in vitro study in five groups (aerobic, vehicle (control), propofol, EDTA, and propofol plus EDTA). Propofol and EDTA each protected PC12 cells against oxygen-glucose deprivation-induced cell damage, and the effect of propofol was increased by adding EDTA. Because the chelating action of EDTA was a potential causal mechanism, we examined the effect of propofol EDTA on intracerebral zinc homeostasis. When propofol EDTA was given intravenously 10 mins before cerebral ischemia, the zinc concentration decreased significantly in the cortical area, but not in the subcortex. In conclusion, (a) propofol provides neuroprotection against both in vivo and in vitro ischemic damage, and its effects are enhanced when EDTA is added; and (b) EDTA itself protects against ischemic neuronal damage, possibly, owing to its zinc-chelating action.

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.

Propofol reverses oxidative stress-attenuated glutamate transporter EAAT3 activity: Evidence of protein kinase C involvement

The authors investigated the effects of propofol on EAAT3 (excitatory amino acid transporter 3) activity under oxidative stress induced by tert-butyl hydroperoxide (t-BHP), and the mediation of these effects by protein kinase C (PKC). Rat EAAT3 was expressed in Xenopus oocytes and L-glutamate (30 microM)-induced membrane currents were measured using the two-electrode voltage clamp technique. Exposure of these oocytes to t-BHP (1-20 mM) for 10 min dose-dependently decreased EAAT3 activity, and t-BHP (5 mM) significantly decreased the Vmax, but not the Km of EAAT3 for glutamate, and propofol (1-100 microM) dose-dependently reversed this t-BHP-attenuated EAAT3 activity. Phorbol-12-myristate-13-acetate (a PKC activator), also abolished this t-BHP-induced reduction in EAAT3 activity, whereas staurosporine (a PKC inhibitor), significantly decreased EAAT3 activity. However, as compared with staurosporine or t-BHP alone, t-BHP and staurosporine in combination did not further reduce EAAT3 activity. A similar pattern was observed for chelerythrine (also a PKC inhibitor). In oocytes pretreated with combinations of t-BHP and PMA (or staurosporine), propofol failed to change EAAT3 activity. Our results suggest that propofol restores oxidative stress-reduced EAAT3 activity and that these effects of propofol may be PKC-mediated.

Xenon: elemental anaesthesia in clinical practice

The 'noble' gases have been known to have anaesthetic properties for 50 years yet only recently has their application become a clinical reality. In this review we describe the preclinical and clinical studies that have led to a resurgence of interest in the use of the element xenon as an anaesthetic. Furthermore, we highlight specific areas where xenon demonstrates advantages over other anaesthetics, including safety, beneficial pharmacokinetics, cardiovascular stability, analgesia and neuroprotection.

The Effect of Sevoflurane and Propofol on Cerebral Neurotransmitter Concentrations During Cerebral Ischemia in Rats

Sevoflurane and propofol are neuroprotective possibly by attenuating central or peripheral catecholamines. We evaluated the effect of these anesthetics on circulating catecholamines and brain neurotransmitters during ischemia in rats. Forty male Sprague-Dawley rats were randomly assigned to one of the following treatment groups: fentanyl and N(2)O/O(2) (control), 2.0% sevoflurane, 0.8-1.2 mg x kg(-1) x min(-1) of propofol, and sham-operated rats with fentanyl and N(2)O/O(2). Ischemia (30 min) was produced by unilateral common carotid artery occlusion plus hemorrhagic hypotension to a mean arterial blood pressure of 32 +/- 2 mm Hg. Pericranial temperature, arterial blood gases, and pH value were maintained constant. Cerebral catecholamine and glutamate concentrations, sampled by microdialysis, and plasma catecholamine concentrations were analyzed using high-pressure liquid chromatography. During ischemia, circulating catecholamines were almost completely suppressed by propofol but only modestly decreased with sevoflurane. Sevoflurane and propofol suppressed brain norepinephrine concentration increases by 75% and 58%, respectively, compared with controls. Intra-ischemia cerebral glutamate concentration was decreased by 60% with both sevoflurane and propofol. These results question a role of circulating catecholamines as a common mechanism for cerebral protection during sevoflurane and propofol. A role of brain tissue catecholamines in mediating ischemic injury is consistent with our results.

IMPLICATIONS

During incomplete cerebral ischemia, the neuroprotective anesthetics sevoflurane and propofol suppressed cerebral increases in norepinephrine and glutamate concentrations. In contrast, propofol, but not sevoflurane, suppressed the ischemia-induced increase in circulating catecholamines to baseline levels. The results question a role for plasma catecholamines in cerebral ischemic injury.

Neuroprotection in cardiac surgery

This article reviews past and present neuroprotective efforts and outlines a framework for the future development of techniques for neuroprotection during cardiac surgery.

Effects of propofol on the activity of rat glutamate transporter type 3 expressed in Xenopus oocytes: the role of protein kinase C

We investigated the effects of propofol on one type of glutamate transporter, excitatory amino acid transporter 3 (EAAT3) and the role of protein kinase C (PKC) in mediating these effects. Rat EAAT3 was expressed in Xenopus oocytes. L-glutamate (30 microM)-induced membrane currents were measured. Propofol increased glutamate-induced inward currents significantly at two tested concentrations (30 and 100 microM) but not at other concentrations. Propofol (30 microM) significantly increased V(max), but not K(m) of EAAT3 for glutamate. The combination of phorbol-12-myrisate-13-acetate (PMA, a PKC activator) and propofol did not increase the responses further compared with PMA or propofol alone. Three PKC inhibitors (staurosporine, calphostin C, and chelerythrine) did not affect basal EAAT3 activity but significantly inhibited the propofol-enhanced EAAT3 activity. Our results suggest that propofol enhances EAAT3 activity at clinically relevant concentrations and PKC may mediate these effects.

Effects of propofol on lactate accumulation and oedema formation in focal cerebral ischaemia in hyperglycaemic rats

BACKGROUND

In cerebral ischaemia, hyperglycaemia brings about severe lactate accumulation and neuronal damage when compared with normoglycaemia. Propofol has been known to suppress glucose metabolism in the brain and possess neuroprotective properties in cerebral ischaemia. Therefore, in this study we examined if propofol could attenuate lactate accumulation and neuronal damage in cerebral ischaemia under hyperglycaemic conditions.

METHODS

Ten male wistar rats were divided into two experimental groups: low-dose (approximately 12 mg kg(-1) h(-1)) and high-dose (approximately 60 mg kg(-1) h(-1)) propofol groups (n=5 for each). Following injection of 2 g kg(-1) glucose intraperitoneally, the middle cerebral artery was occluded for 1 h, and then reperfused for the following 2 h. Lactate accumulation and oedema formation were estimated consecutively using nuclear magnetic resonance (NMR) techniques.

RESULTS

Lactate accumulation and oedema formation increased continuously during ischaemia and reperfusion in the low-dose propofol group, which was attenuated in the high-dose propofol group. Lactate/NAA (N-acetylaspartate) ratio (as an index of lactate accumulation) 60 and 120 min after reperfusion were 2.67 and 3.26 in low-dose group and 0.30 and 0.10 in high-dose group. For NMR images the number of pixels with a low average diffusion coefficient (an index of the oedema formation), 60 and 120 min after reperfusion were 250.0 and 317.8 in low-dose group, and 16.0 and 12.4 in high-dose group.

CONCLUSION

High-dose propofol attenuated lactate accumulation and oedema formation in cerebral ischaemia in hyperglycaemic rats.

Use of sedative and analgesic agents in neurotrauma patients: effects on cerebral physiology

Sedation and analgesia is used primarily in the intensive care unit (ICU) to limit the stress response to critical illness, provide anxiolysis, improve ventilatory support, and facilitate adequate ICU care. However, in the neurotrauma ICU there are many other reasons for the use of these agents. The primary aim is to prevent secondary cerebral damage by maintaining adequate cerebral perfusion pressures. This is accomplished in several different ways. Controlling intracranial pressure (ICP) and maintaining an adequate mean arterial pressure (MAP) is at the cornerstone of this management. Lowering the metabolic demands of the brain is also an important consideration as a treatment strategy. Analgesic and sedative agents are utilized to prevent undesirable increases in ICP and to lower cerebral metabolic demands. Concerns surrounding the use of these agents include time to awakening after discontinuation, effect on the cerebrovasculature, and the effect on patient outcome. There are many different pharmacological agents available, each with their distinct advantages and disadvantages. The purpose of this review is to evaluate the pharmacokinetic and pharmacological effects of each of these agents when used in neurotrauma patients.

Hyperbaric oxygen therapy for treatment of postischemic stroke in adult rats

The efficacy of hyperbaric oxygen (HBO) therapy for treatment of stroke remains to be validated in the laboratory. We report here that adult rats subjected to occlusion of the middle cerebral artery and subsequently exposed to HBO (3 atm, 2 x 90 min at a 24-h intervals; animals terminated shortly after the second treatment) or hyperbaric pressure (HBP; 3 atm, 2 x 90 min at a 24-h interval; animals terminated shortly after the second treatment) immediately after the ischemia or after a 60-min delay generally displayed recovery from motor deficits at 2.5 and 24 h of reperfusion, as well as a reduction in cerebral infarction at 24 h of reperfusion compared to ischemic animals subjected to normal atmospheric pressure. While both HBO and HBP treatments promoted beneficial effects, HBO produced more consistent protection than HBP. Treatment with HBO immediately or 60 min after reperfusion equally produced significant attenuations of cerebral infarction and motor deficits. In contrast, protective effects of HBP treatment against ischemia were noted only when administered immediately after ischemia, which resulted in a significantly reduced infarction volume, but only produced a trend toward decreased behavioral deficits. The present results demonstrate that HBO and, to some extent, HBP reduced ischemic brain damage and behavioral dysfunctions.

Intraoperative variables and early outcome after aneurysm surgery

BACKGROUND

The purpose of this study was to investigate the effects of blood pressure, temperature, and anesthetic agents on outcome in patients undergoing craniotomy for cerebral aneurysms.

METHODS

All ruptured and unruptured intracranial aneurysms operated on from 1992 to 1998 were reviewed retrospectively. The data included 297 aneurysms (190 ruptured and 107 unruptured). Data were collected on variables known to influence outcome after aneurysmal subarachnoid hemorrhage as well as on intraoperative factors that might influence outcome (intraoperative blood pressure, temperature, temporary clipping, anesthetic agents). Outcome was assessed at discharge using the Glasgow Outcome Scale.

RESULTS

In univariate analysis of patients with ruptured aneurysms, younger age, better clinical grade, lower Fisher grade, lower intraoperative blood pressure (maximum systolic and mean blood pressure), smaller decrease in intraoperative compared to preoperative systolic blood pressure, shorter duration of surgery, and use of propofol, pancuronium, or N(2)O were associated with significantly better outcome. In patients with unruptured aneurysms, increased intraoperative minimum diastolic and mean blood pressure, a decrease in the difference between multiple measures of preoperative and intraoperative blood pressure, and a shorter duration of surgery were associated with significantly better outcome. Intraoperative temperature did not affect outcome in either group. In multivariate analysis of patients with ruptured aneurysms, younger age, better clinical grade, lower maximum systolic intraoperative blood pressure, shorter duration of surgery, and use of propofol were independently associated with better outcome.

CONCLUSIONS

Multivariate analysis of intraoperative factors affecting outcome in patients undergoing craniotomy for ruptured aneurysms shows that decreased intraoperative blood pressure and use of propofol are associated with improved outcome. Univariate analysis suggests that decreasing the magnitude of drop in blood pressure intraoperatively from preoperative values in patients with ruptured or unruptured aneurysms is associated with better outcome. Intraoperative hypothermia did not affect outcome.

[Neuroprotective effects of anesthetics]

During cerebral ischaemia, energetic failure of injured cells together with excessive release of glutamate the most common excitatory amino acid in the brain, lead to excitotoxicity and immediate or delayed neuronal death. There is strong experimental evidence to support the neuroprotective role played by anaesthetic agents. Hence, barbiturates, volatile anesthetics or ketamine exhibit significant protective effects against ischaemic injury in numerous experimental models of ischaemia in vitro or in vivo. The neurobiological substrate of this action is probably a reduction of the activity of glutamate receptors (N-methyl-D-aspartate and kainate), and/or downstream biochemical events. Reduction of cerebral metabolism by these agents seems not to be their primary neuroprotective mechanism. However, no data are available at the present time to support any clinical benefit of these actions in neurosurgical patients, head trauma in contrast to mild hypothermia or cerebrovascular disease. Future research should develop models as close as possible to the clinical situation to examine further pathophysiological hypotheses and clinical implications.

Phenylephrine-induced hypertension does not improve outcome after closed head trauma in rats

Phenylephrine-induced hypertension (increase of 30-35 mm Hg for 15 min) is reported to increase cerebral perfusion pressure and collateral flow to ischemic areas of the brain in a rat model of focal cerebral ischemia. In the present study, we examined whether phenylephrine-induced hypertension of similar magnitude and duration was beneficial in a rat model of closed head trauma (CHT). Forty-eight rats were randomized into four experimental conditions: CHT at time 0 min (yes/no), plus phenylephrine-induced hypertension (increase of 30-35 mm Hg for 15 min) at 65 min (yes/no). CHT was delivered using a weight-drop device (0.5 J). Outcome measures were neurological severity score (NSS) at 1, 4, and 24 h, and brain tissue specific gravity (microgravimetry) and injury volume (2,3,5-triphenyltetrazoium chloride) at 24 h. After CHT, NSS at 24 h (median +/- range) and brain tissue specific gravity (mean +/- SD, injured hemisphere) were 7+/-2 and 1.033+/-0.007 without phenylephrine and 8+/-2 and 1.035+/-0.005 with phenylephrine (P = 0.43), respectively. Tissue injury volume (mean +/- SD) was 335+/-92 mm3 without phenylephrine and 357+/-154 mm3 with phenylephrine (P > 0.62). The results of our study indicate that postinjury treatment with 15 min of phenylephrine-induced hypertension does not attenuate brain edema, reduce tissue injury volume, or improve neurological outcome after CHT in rats.

IMPLICATIONS

Phenylephrine-induced hypertension is reported to increase cerebral perfusion pressure and blood flow in a rat model of focal cerebral ischemia. In our study, phenylephrine-induced hypertension did not decrease brain edema or tissue injury volume or improve neurological outcome in a rat model of closed head trauma.