Ketamine decreases plasma catecholamines and improves outcome from incomplete cerebral ischemia in rats

Does the choice of induction agent in rapid sequence intubation in the emergency department influence the incidence of post-induction hypotension?

OBJECTIVE

To describe the effects of different induction agents on the incidence of post-induction hypotension (PIH) and its associated interventions during rapid sequence intubation (RSI) in the ED.

METHODS

A single centre retrospective study of patients intubated between 2018 and 2021 was conducted in a regional Australian ED. The impact of induction agent choice, in addition to demographic and clinical factors on the incidence of PIH were determined using descriptive statistics and a multivariate analysis presented as adjusted odds ratios (aORs) and their 95% confidence intervals (CIs).

RESULTS

Ketamine and propofol, used either individually or in conjunction with fentanyl, were significantly associated with PIH (ketamine aOR 4.5, 95% CI 1.35-14.96; propofol aOR 4.88, 95% CI 1.46-16.29). Age >60 years was associated with a greater requirement for vasopressors (aOR 4.46, 95% CI 2.49-7.97) and a higher risk of mortality after RSI (aOR 4.2, 95% CI 1.87-9.40). Patients with a shock index >1.0 were significantly more likely to require vasopressors (aOR 5.13, 95% CI 2.35-11.2) and have a cardiac arrest within 15 min of RSI (aOR 3.56, 95% CI 1.07-11.8).

CONCLUSIONS

Exposure to both propofol and ketamine is significantly associated with PIH after RSI, alongside age and shock index. PIH is likely multifactorial in nature, and this data supports the sympatholytic effect of induction agents as the underlying cause of PIH rather than the choice of agent itself. Further prospective work including a randomised controlled trial between induction agents is justified to further clarify this important clinical question.

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.

Exploration in the Therapeutic and Multi-Target Mechanism of Ketamine on Cerebral Ischemia Based on Network Pharmacology and Molecular Docking

Background

Ketamine is famous for its dissociative anesthetic properties. It is also analgesic, anti-inflammatory and anti-depressant, and even has a cerebral protective effect. We searched the evidence of the correlation between ketamine target and clinical efficacy and utilized network pharmacology to gather information about the multi-target mechanism of ketamine against cerebral ischemia (CI). We found that ketamine’s clinical significance may be more extensive than previously thought.

Methods

The drug target of ketamine and CI-related genes were predicted by SwissTargetPrediction, DrugBank, PubChem, GeneCards and DisGeNET databases. The intersection of ketamine’s drug-targets and CI-related genes was analyzed by using GO and KEGG. We predicted the molecular docking between the potential target and ketamine.

Results

The results indicated that the effect of ketamine on CI was primarily associated with the target of α-synuclein (SNCA), muscarinic acetylcholine receptor M1 (CHRM1) and nitric oxide synthase 1 (NOS1). It principally regulates the signal pathways of circadian transmission, calcium signaling pathway, dopaminergic synapse, cholinergic synapse and glutamatergic synapse. Molecular docking analysis exhibited that hydrogen bond and Pi-Pi interaction were the predominant modes of interaction.

Conclusion

There are protein targets affected by ketamine in the treatment of CI. Three pivotal targets involving 298 proteins, SNCA, CHRM1 and NOS1, have emerged as multi-target mechanisms for ketamine in CI therapy. Similarly, this study also provides a new idea for introducing network pharmacology into the evaluation of multi-targeted drugs for CI and cerebral protection.

The multiple faces of ketamine in anaesthesia and analgesia

Objective

Ketamine is an anaesthetic agent with a unique dissociative profile and pharmacological effects ranging from the induction and maintenance of anaesthesia to analgesia and sedation, depending on the dose. This article provides information for the clinical use of ketamine in anaesthesia, in both conventional and special circumstances.

Methods

This is a non-systematic review of the literature, through a PubMed search up to February 2021.

Results

With a favourable pharmacokinetic profile, ketamine is used in hospital and prehospital settings for emergency situations. It is suitable for patients with many heart conditions and, unlike other anaesthetics, its potential for cardiorespiratory depression is low. Furthermore, it may be used when venous access is difficult as it may be administered through various routes. Ketamine is the anaesthetic of choice for patients with bronchospasm thanks to its bronchodilatory and anti-inflammatory properties.

Conclusion

With a favourable pharmacokinetic profile, ketamine is used in hospital and prehospital settings for emergency situations and is suitable for patients with many cardiac and respiratory conditions.

Volatile and Intravenous Anesthetics for Brain Protection in Cardiac Surgery: Does the Choice of Anesthesia Matter?

Postoperative neurologic complications have a significant effect on morbidity, mortality, and long-term disability in patients undergoing cardiac surgery. The etiology of brain injury in patients undergoing cardiac surgery is multifactorial and remains unclear. There are several perioperative causative factors for neurologic complications, including microembolization, hypoperfusion, and systemic inflammatory response syndrome. Despite technologic advances and the development of new anesthetic drugs, there remains a high rate of postoperative neurologic complications. Moreover, despite the strong evidence that volatile anesthesia exerts cardioprotective effects in patients undergoing cardiac surgery, the neuroprotective effects of volatile agents remain unclear. Several studies have reported an association of using volatile anesthetics with improvement of biochemical markers of brain injury and postoperative neurocognitive function. However, there is a need for additional studies to define the optimal anesthetic drug for protecting the brain in patients undergoing cardiac surgery.

Cortical spreading depolarization and ketamine: a short systematic review

INTRODUCTION

Cortical spreading depolarization (SD) describes pathological waves characterized by an almost complete sustained depolarization of neurons and astrocytes that spreads throughout the cortex. In this study, we carried out a qualitative review of all available evidence, clinical and preclinical, on the use of ketamine in SD.

METHODS

We performed a systematic review of Medline, with no restrictions regarding publishing date or language, in search of articles reporting the use of ketamine in SD. The search string was composed of "ketamine," "spreading," "depolarization," and "depression" in both (AND) and (OR) combinations.

RESULTS

Twenty studies were included in the final synthesis. Many studies showed that ketamine effectively blocks SD in rats, swine, and humans. The first prospective randomized trial was published in 2018. Ten patients with severe traumatic brain injury or subarachnoid hemorrhage were enrolled, and ketamine showed a significant, dose-dependent effect on the reduction of SD.

CONCLUSION

The available evidence from preclinical studies is helping to translate the role of ketamine in blocking spreading depolarizations to clinical practice, in the settings of migraine with aura, traumatic brain injury, subarachnoid hemorrhage, and hemorrhagic and ischemic stroke. More randomized controlled trials are needed to determine whether interrupting the ketamine-blockable SDs effectively leads to an improvement in outcome and to assess the real occurrence of adverse effects.

Enhanced beta-1 adrenergic receptor responsiveness in coronary arterioles following intravenous stromal vascular fraction therapy in aged rats

Our past study showed that a single tail vein injection of adipose-derived stromal vascular fraction (SVF) into old rats was associated with improved dobutamine-mediated coronary flow reserve. We hypothesize that i.v. injection of SVF improves coronary microvascular function in aged rats via alterations in beta adrenergic microvascular signaling. Female Fischer-344 rats aged young (3 months, n=32) and old (24 months, n=30) were utilized, along with two cell therapies intravenously injected in old rats four weeks prior to sacrifice: 1x10⁷ green fluorescent protein (GFP+) SVF cells (O+SVF, n=21), and 5x10⁶ GFP+ bone-marrow mesenchymal stromal cells (O+BM, n=6), both harvested from young donors. Cardiac ultrasound and pressure-volume measurements were obtained, and coronary arterioles were isolated from each group for microvessel reactivity studies and immunofluorescence staining. Coronary flow reserve decreased with advancing age, but this effect was rescued by the SVF treatment in the O+SVF group. Echocardiography showed an age-related diastolic dysfunction that was improved with SVF to a greater extent than with BM treatment. Coronary arterioles isolated from SVF-treated rats showed amelioration of the age-related decrease in vasodilation to a non-selective β-AR agonist. I.v. injected SVF cells improved β-adrenergic receptor-dependent coronary flow and microvascular function in a model of advanced age.

The anaesthetic xenon partially restores an amyloid beta-induced impairment in murine hippocampal synaptic plasticity

BACKGROUND

It is controversially discussed whether general anaesthesia increases the risk of Alzheimer's disease (AD) or accelerates its progression. One important factor in AD pathogenesis is the accumulation of soluble amyloid beta (Aβ) oligomers which affect N-methyl-d-aspartate (NMDA) receptor function and abolish hippocampal long-term potentiation (LTP). NMDA receptor antagonists, at concentrations allowing physiological activation, can prevent Aβ-induced deficits in LTP. The anaesthetics xenon and S-ketamine both act as NMDA receptor antagonists and have been reported to be neuroprotective. In this study, we investigated the effects of subanaesthetic concentrations of these drugs on LTP deficits induced by different Aβ oligomers and compared them to the effects of radiprodil, a NMDA subunit 2B (GluN2B)-selective antagonist.

METHODS

We applied different Aβ oligomers to murine brain slices and recorded excitatory postsynaptic field potentials before and after high-frequency stimulation in the CA1 region of hippocampus. Radiprodil, xenon and S-ketamine were added and recordings evoked from a second input were measured.

RESULTS

Xenon and radiprodil, applied at low concentrations, partially restored the LTP deficit induced by pre-incubated Aβ_1-42. S-ketamine showed no effect. None of the drugs tested were able to ameliorate Aβ_1-40-induced LTP-deficits.

CONCLUSIONS

Xenon administered at subanaesthetic concentrations partially restored Aβ_1-42-induced impairment of LTP, presumably via its weak NMDA receptor antagonism. The effects were in a similar range than those obtained with the NMDA-GluN2B antagonist radiprodil. Our results point to protective properties of xenon in the context of pathological distorted synaptic physiology which might be a meaningful alternative for anaesthesia in AD patients.

Nonanesthetic Effects of Ketamine: A Review Article

Ketamine is considered a dissociative anesthetic medication, and it is commonly administered by a parenteral route. It works mainly by blocking the N-methyl-D-aspartate receptor. It inhibits the voltage-gated Na and K channels and serotonin and dopamine reuptake; also, it affects specific receptors, such as α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, kainate, and aminobutyric acid A receptors. Ketamine appears to have particular mechanisms that are potentially involved during analgesic induction, including enhancing of descending inhibition and antiinflammatory effects. More recently, it has been shown that ketamine has potential in clinical practice for the management of chronic pain, cognitive function, depression, acute brain injury, and disorders of the immune system.

In Vogue: Ketamine for Neuroprotection in Acute Neurologic Injury

Neurologic deterioration following acute injury to the central nervous system may be amenable to pharmacologic intervention, although, to date, no such therapy exists. Ketamine is an anesthetic and analgesic emerging as a novel therapy for a number of clinical entities in recent years, including refractory pain, depression, and drug-induced hyperalgesia due to newly discovered mechanisms of action and new application of its known pharmacodynamics. In this focused review, the evidence for ketamine as a neuroprotective agent in stroke, neurotrauma, subarachnoid hemorrhage, and status epilepticus is highlighted, with a focus on its applications for excitotoxicity, neuroinflammation, and neuronal hyperexcitability. Preclinical modeling and clinical applications are discussed.

Blood gases and energy metabolites in mouse blood before and after cerebral ischemia: the effects of anesthetics

The levels of blood gases and energy metabolites strongly influence the outcome of animal experiments, for example in experimental stroke research. While mice have become prominent animal models for cerebral ischemia, little information is available on the effects of anesthetic drugs on blood parameters such as blood gases, glucose and lactate in this species. In this work, we collected arterial and venous blood samples from female CD-1 mice before and after cerebral ischemia induced by middle cerebral artery occlusion (MCAO), and we tested the influence of different anesthetic drugs. We found that all of the injectable anesthetics tested (ketamine/xylazine, chloral hydrate, propofol and pentobarbital) caused a decrease in blood pH and partial pressure of oxygen (pO2) and an increase of partial pressure of carbon dioxide (pCO2), indicating respiratory depression. This was not observed with inhalable anesthetics such as isoflurane, sevoflurane and halothane. Significant and up to two-fold increases of blood glucose concentration were observed under isoflurane, halothane, ketamine/xylazine, chloral hydrate, and propofol anesthesia. Lactate concentration rose significantly by 2-3-fold during inhalation of isoflurane and halothane treatment, but decreased by more than 50% after administration of pentobarbital. Permanent cerebral ischemia induced respiratory acidosis (low pH and pO2, high pCO2) which was most prominent after 24 h. Postsurgical treatment with Ringer-lactate solution (1 mL, intraperitoneal) caused a recovery of blood gases to basal levels after 24 h. Use of isoflurane for surgery caused a minor increase of blood glucose concentrations after one hour, but a strong increase of blood lactate. In contrast, anesthesia with pentobarbital did not affect glucose concentration but strongly reduced blood lactate concentrations one hour after surgery. All values recovered at three hours after MCAO. In conclusion, anesthetic drugs have a strong influence on murine blood parameters, which should be taken into account in experiments in mice.

Neuroprotective effects of racemic ketamine and (S)-ketamine on spinal cord injury in rat

BACKGROUND

The aim of this study was to investigate and to compare the potential neuroprotective effects of racemic ketamine, (S)-ketamine and methylprednisolone after an experimental spinal cord injury model in rats.

METHODS

Fifty-nine Wistar albino rats were divided into three main groups as acute stage (A), subacute stage (SA) and sham groups and then acute and subacute stage groups were divided into four groups regarding the used drug as control (CONT), racemic ketamine (RK), (S)-ketamine (SK) and methylprednisolone (MP) groups. A dorsal laminectomy was performed; and spinal cord injury was induced by using a temporary aneurysm clip. Four hours later from the clip compression, except those of the sham and control groups, the drugs (60 mg/kg racemic ketamine, 60 mg/kg (S)-ketamine or 30 mg/kg methylprednisolone) were administered intraperitoneally. At 72th h and 7th days of the study, the spinal cords of rats were removed from T8 level to the conus medullaris level. The specimens were and evaluated histopathologically, tissue lipid peroxidation (LPO) and myeloperoxidation (MPO) levels were measured and biochemically.

RESULTS

The histopathological results were similar both in the acute and in the subacute stage groups. There was a statistically significant difference among all groups regarding the tissue LPO levels (p<0.001). There was a statistically significant difference between the CONT-A group and the MP-A, RK-A and SK-A groups (p=0.004, p<0.001 and p=0.007, respectively) in acute stage and between the CONT-SA group and SK-SA group (p=0.002) in subacute stage. There was a statistically significant difference among all groups regarding the tissue MPO levels (p=0.001). The median MPO levels were similar among acute stage groups (p=0.057), but there was a statistical difference among subacute stage groups (p=0.046).

CONCLUSION

(S)-ketamine is more effective than methylprednisolone and racemic ketamine to reduce the LPO levels in subacute stage of spinal cord injury in rats. And, it is as effective as methylprednisolone in preventing secondary spinal cord injury histopathologically.

Isoflurane/nitrous oxide anesthesia induces increases in NMDA receptor subunit NR2B protein expression in the aged rat brain

Postoperative cognitive dysfunction, POCD, afflicts a large number of elderly surgical patients following surgery with general anesthesia. Mechanisms of POCD remain unclear. N-methyl-D-aspartate (NMDA) receptors, critical in learning and memory, that display protein expression changes with age are modulated by inhalation anesthetics. The aim of this study was to identify protein expression changes in NMDA receptor subunits and downstream signaling pathways in aged rats that demonstrated anesthesia-induced spatial learning impairments. Three-month-old and 18-month-old male Fischer 344 rats were randomly assigned to receive 1.8% isoflurane/70% nitrous oxide (N(2)O) anesthesia for 4h or no anesthesia. Spatial learning was assessed at 2weeks and 3months post-anesthesia in Morris water maze. Hippocampal and cortical protein lysates of 18-month-old rats were immunoblotted for activated caspase 3, NMDA receptor subunits, and extracellular-signal regulated kinase (ERK) 1/2. In a separate experiment, Ro 25-6981 (0.5mg/kg dose) was administered by I.P. injection before anesthesia to 18-month-old rats. Immunoblotting of NR2B was performed on hippocampal protein lysates. At 3months post-anesthesia, rats treated with anesthesia at 18-months-old demonstrated spatial learning impairment corresponding to acute and long-term increases in NR2B protein expression and a reduction in phospho-ERK1/2 in the hippocampus and cortex. Ro 25-6981 pretreatment attenuated the increase in acute NR2B protein expression. Our findings suggest a role for disruption of NMDA receptor mediated signaling pathways in the hippocampus and cortex of rats treated with isoflurane/ N(2)O anesthesia at 18-months-old, leading to spatial learning deficits in these animals. A potential therapeutic intervention for anesthesia associated cognitive deficits is discussed.

Recurrent hypoglycemia exacerbates cerebral ischemic damage in streptozotocin-induced diabetic rats

BACKGROUND AND PURPOSE

Stroke and heart disease are the most serious complications of diabetes accounting for >65% of mortality among diabetics. Although intensive insulin therapy has significantly improved the prognosis of diabetes and its complications, it is associated with an elevated risk of recurrent hypoglycemia (RH). We tested the hypothesis that RH exacerbates cerebral ischemic damage in a rodent model of diabetes.

METHOD

We determined the extent of neuronal death in CA1 hippocampus after global cerebral ischemia in control and streptozotocin-induced diabetic rats. Diabetic animals included an insulin-treated streptozotocin-diabetic (ITD) group and a group of ITD rats exposed also to 10 episodes of hypoglycemia (ITD+recurrent hypoglycemia: RH). Hypoglycemia (55 to 65 mg/dL blood glucose) was induced twice daily for 5 consecutive days.

RESULTS

As expected, uncontrolled diabetes (streptozotocin-diabetes, untreated animals) resulted in a 70% increase in ischemic damage as compared with the control group. Insulin treatment was able to lower ischemic damage by 64% as compared with the diabetic group. However, ITD+RH rats had 44% more damage when compared with the ITD group. We also observed that free radical release from mitochondria is increased in ITD+RH rats.

CONCLUSIONS

This is the first report on the impact of RH in exacerbating cerebral ischemic damage in diabetic animals. Our results suggest that increased free radical release from mitochondria may be responsible for observed increased ischemic damage in ITD+RH rats. RH thus may be an unexplored but important factor responsible for increased ischemic damage in diabetes.

[Ischaemic and pharmacologic preconditioning: desflurane reduces renal reperfusion injury in rabbits]

BACKGROUND

Anaesthetic preconditioning, i.e. administration of volatile agents before ischemia, is known to have protective effects on several organs, but remains uncertain on the kidney. We developed a rabbit model for acute ischaemia-reperfusion injury, and examined a possible protective effect of desflurane preconditioning on the kidney.

METHODS

Forty New Zealand male rabbits, 3 months old, weighing 2-3 kg, were anaesthetized by titrated intramuscular injections of xylazine-ketamine, mechanically ventilated and monitored. They were randomly assigned into four groups: group ischaemia (I), group ischaemic preconditioning (IPC), group desflurane preconditioning (DPC), and group SHAM (S). Groups I, IPC and DPC were subjected to 45 minutes of bilateral renal ischaemia followed by 3 hours reperfusion. Group IPC was subjected to 3 x 3 minutes ischaemia, 5 minutes before the 45-minute clamping period. Group DPC was administered one MAC desflurane for 30 minutes, before a 30-minute wash-out period. Histological analysis of the cortical zone of both kidneys were blindly performed. Tubular cell damage was graded from 1 (no lesion) to 4 (>50 % cell necrosis). Pycnotic nuclei and intratubular hyaline casts were counted on each section.

RESULTS

DPC (1[1-2]) and S (1[1-1]) groups displayed lower histological grades than group 1(4[3-4]) (p<0.01); IPC had a grade of 3 (2-3), I and IPC groups had higher scores of pycnotic nuclei and hyaline casts than DPC and S.

CONCLUSION

Desflurane preconditioning was associated with a diminution of tubular cell damage. Ischaemic preconditioning did not show a significant renal protective effect.

Dose-dependent effect of S(+) ketamine on post-ischemic endogenous neurogenesis in rats

BACKGROUND

Ketamine is a non-competitive antagonist at N-methyl-D-aspartate (NMDA) receptors and reduces neuronal injury after cerebral ischemia by blocking the excitotoxic effects of glutamate. However, cerebral regeneration by means of endogenous neurogenesis may be impaired with blockade of NMDA receptors. The effects of S(+) ketamine on post-ischemic neurogenesis are unknown and investigated in this study.

METHODS

Thirty-two male Sprague-Dawley rats were randomly assigned to the following treatment groups with intravenous S(+) ketamine anesthesia: S(+) ketamine 0.75 mg/kg/min with or without cerebral ischemia and S(+) ketamine 1.0 mg/kg/min with or without cerebral ischemia. Eight non-anesthetized, non-ischemic animals were investigated as naïve controls. Forebrain ischemia was induced by bilateral common carotid artery occlusion in combination with hemorrhagic hypotension. 5-bromo-2-deoxyuridine (BrdU) was injected intraperitoneally for seven consecutive post-operative days. BrdU-positive neurons in the dentate gyrus and histopathological damage of the hippocampus were analyzed after 28 days.

RESULTS

The number of new neurons was not affected by S(+) ketamine in the absence of cerebral ischemia. The ischemia-induced increase in neurogenesis was reduced by high-dose S(+) ketamine. Cell death of ischemic animals did not vary between low- and high-dose S(+) ketamine.

CONCLUSION

While low concentrations of S(+) ketamine allow an ischemia-induced increase in the number of new neurons, high S(+) ketamine concentrations block the post-ischemic increase in newly generated neurons. This effect is irrespective of the extent of other histopathological damage and in line with studies showing that NMDA receptor antagonists like MK-801 inhibit neurogenesis after cerebral ischemia.

Impact of anesthetic agents on cerebrovascular physiology in children

The role of the pediatric neuroanesthetist is to provide comprehensive care to children with neurologic pathologies. The cerebral physiology is influenced by the developmental stage of the child. The understanding of the effects of anesthetic agents on the physiology of cerebral vasculature in the pediatric population has significantly increased in the past decade allowing a more rationale decision making in anesthesia management. Although no single anesthetic technique can be recommended, sound knowledge of the principles of cerebral physiology and anesthetic neuropharmacology will facilitate the care of pediatric neurosurgical patients.

Estimation of the regional cerebral metabolic rate of oxygen consumption with proton detected 17O MRI during precision 17O2 inhalation in swine

Despite the importance of metabolic disturbances in many diseases, there are currently no clinically used methods for the detection of oxidative metabolism in vivo. To address this deficiency, (17)O MRI techniques are scaled from small animals to swine as a large animal model of human inhalation and circulation. The hemispheric cerebral metabolic rate of oxygen consumption (CMRO(2)) is estimated in swine by detection of metabolically produced H(2)(17)O by rapid T(1rho)-weighted proton magnetic resonance imaging on a 1.5T clinical scanner. The (17)O is delivered as oxygen gas by a custom, minimal-loss, precision delivery breathing circuit and converted to H(2)(17)O by oxidative metabolism. A model for gas arterial input is presented for the deeply breathing large animal. The arterial input function for recirculation of metabolic water is measured by arterial blood sampling and high field (17)O spectroscopy. It is found that minimal metabolic water "wash-in" occurs before 60s. A high temporal resolution pulse sequence is employed to measure CMRO(2) during those 60s after delivery begins. Only about one tidal volume of (17)O enriched oxygen gas is used per measurement. Proton measurements of signal change due to metabolically produced water are correlated with (17)O in vivo spectroscopy. Using these techniques, the hemispheric CMRO(2) in swine is estimated to be 1.23+/-.26 micromol/g/min, consistent with existing literature values. All of the technology used to perform these CMRO(2) estimates can easily be adapted to clinical MR scanners, and it is hoped that this work will lead to future studies of human disease.

Racemic, S(+)- and R(-)-ketamine do not increase elevated intracranial pressure

BACKGROUND

There is controversy regarding the influence of ketamine and its enantiomers on cerebral haemodynamics at increased intracranial pressure (ICP). This study was designed to compare cerebrovascular responses, with particular respect to ICP, to bolus injections of racemic, S(+)- and R(-)-ketamine in an experimental model of intracranial hypertension.

METHODS

Nine pigs were anaesthetised with fentanyl and vecuronium during mechanical normoventilation. The ICP was raised with extradural balloon catheters to 23 mmHg. The intra-arterial xenon clearance technique was used to determine cerebral blood flow (CBF). Three 60-s bolus injections of racemic ketamine (10 mg/kg), S-ketamine (5 mg/kg) and R-ketamine (20 mg/kg) were given in a randomised sequence. Cerebral and systemic haemodynamic responses were evaluated before and at 1, 5, 10, 15, 30 and 45 min after each injection.

RESULTS

Racemic ketamine decreased ICP (P=0.026) by maximally 10.8%, whereas there was no effect on ICP of S- (P=0.178) or R-ketamine (P=0.15). All study drugs had similar biphasic effects on CBF, with maximal initial decreases by 25-29%, followed by transient increases by 7-15%, and a reduction of mean arterial pressure by maximally 22-37%.

CONCLUSIONS

A decrease or a lack of an increase in ICP in response to intravenous bolus injections of racemic, S- or R-ketamine suggests that the administration of racemic or S-ketamine might be safe in patients with intracranial hypertension due to a space-occupying lesion. The ICP-lowering effect indicates that racemic ketamine might offer a therapeutic advantage over S-ketamine.

Evolving therapeutic approaches to treating acute ischemic stroke

Stroke contributes significantly to death, disability, and healthcare costs; however, recombinant tissue plasminogen activator (rt-PA) is the only approved thrombolytic therapy for acute ischemic stroke. One area of development for new ischemic stroke treatment options is focused on neuroprotection of viable tissue in the ischemic vascular bed. The ischemic penumbra is recognizable on MRI by decreased perfusion, in contrast to the core area of ischemia, which includes diffusion and perfusion abnormalities. Understanding the mechanisms of neuronal death, including the role of excitotoxic neurotransmitters, free radical production, and apoptotic pathways, is important in developing new therapies for stroke. This article reviews these causes and results of stroke, as well as current and future neuroprotective treatment options. Several compounds have shown neuroprotective effects in animal studies, but have failed to be effective in human clinical trials. Several promising therapeutic areas include targeting of free radicals, modulation of glutamatergic transmission, and membrane stabilization via ion channels.

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.

Ketamine for rapid sequence induction in patients with head injury in the emergency department

OBJECTIVE

To examine the evidence regarding the use of ketamine for induction of anaesthesia in patients with head injury in the ED.

METHOD

A literature review using the key words ketamine, head injury and intracranial pressure.

RESULTS

Advice from early literature guiding against the use of ketamine in head injury has been met with widespread acceptance, as reflected by current practice. That evidence is conflicting and inconclusive in regards to the safety of using ketamine in head injury. A review of the literature to date suggests that ketamine could be a safe and useful addition to our available treatment modalities. The key to this argument rests on specific pharmacological properties of ketamine, and their effects on the cerebral haemodynamics and cellular physiology of brain tissue that has been exposed to traumatic injury.

CONCLUSION

In the modern acute management of head-injured patients, ketamine might be a suitable agent for induction of anaesthesia, particularly in those patients with potential cardiovascular instability.

The interaction between ketamine and some crown ethers in common organic solvents studied by NMR: the effect of donating atoms and ligand structure

1H NMR spectroscopy was used to investigate the stoichiometry and stability of the drug ketamine cation complexes with some crown ethers, such as 15-crown-5 (15C5), aza-15-crown-5 (A15C5), 18-crown-6 (18C6), aza-18-crown-6 (A18C6), diaza-18-crown-6 (DA18C6), dibenzyl-diaza-18-crown-6 (DBzDA18C6) and cryptant [2,2,2] (C222) in acetonitrile (AN), dimethylsulfoxide (DMSO) and methanol (MeOH) at 27 degrees C. In order to evaluate the formation constants of the ketamine cation complexes, the CH3 protons chemical shift (on the nitrogen atom of ketamine) was measured as function of ligand/ketamine mole ratio. The formation constant of resulting complexes were calculated by the computer fitting of chemical shift versus mole ratio data to appropriate equations. A significant chemical shift variation was not observed for 15C5 and 18C6. The stoichiometry of the mono aza and diaza ligands are 1:1 and 1:2 (ligand/ketamine), respectively. In all of the solvents studied, DA18C6 formed more stable complexes than other ligands. The solvent effect on the stability of these complexes is discussed.

The effect of ketamine on acute muscular ischaemia reperfusion in rats

BACKGROUND AND OBJECTIVE

The aim of this study was to investigate any possible protective effect of ketamine in acute muscular ischaemia and reperfusion injury by measuring malondialdehyde using thiobarbituric acid assay in rats.

METHODS

Twelve female Wistar albino rats were anaesthetized with chloral hydrate and randomly assigned into two groups to receive ketamine 1 mg kg(-1) min(-1) or saline infusion. Blood and gastrocnemius muscle samples were obtained 10 min after onset of infusion, before ischaemia. Then, femoral arteries were clamped for 30 min. Blood and muscle samples were obtained at the 30th minute of ischaemia and 10 min after reperfusion.

RESULTS

Muscle malondialdehyde concentrations were 27.88 +/- 2.45, 27.62 +/- 3.98 before ischaemia, 32.10 +/- 4.19, 30.77 +/- 2.73 in the 30th minute of ischaemia and 44.34 +/- 2.45, 34.83 +/- 2.78 after reperfusion in saline and ketamine-treated rats, respectively (nmol g(-1), mean +/- SD). The muscle malondialdehyde level after reperfusion was lower in ketamine-treated rats compared to saline group (P < 0.002). Plasma malondialdehyde levels were 3.77 +/- 0.16, 3.78 +/- 0.18 before ischaemia, 3.81 +/- 0.25, 4.00 +/- 0.86 at the 30th minute of ischaemia and 4.00 +/- 0.53, 3.94 +/- 0.95 after reperfusion, respectively, in saline and ketamine-treated rats (micromol L(-1), mean +/- SD). The effect of ketamine on muscular malondialdehyde was not observed in concurrent plasma malondialdehyde levels.

CONCLUSION

Ketamine was found to attenuate acute ischaemia-reperfusion injury in muscle tissue in rats (muscular protective). Ketamine may attenuate lipid peroxidation in muscle tissue in tourniquet-requiring manoeuvres.

A systematic review of currently available pharmacological neuroprotective agents as a sole intervention before anticipated or induced cardiac arrest

We conducted a Medline search for controlled studies evaluating currently available drugs for pharmacological neuroprotection. They had to be administered prior to transient global cerebral ischaemia without further non-pharmacological measures. We deliberately excluded focal ischaemia since its pathophysiology is substantially different from global ischaemia. A total of 45 articles conducted exclusively in laboratory animals met these criteria. The following classes of agents were evaluated: anaesthetics, GABAergic drugs, calcium-antagonists, anticonvulsives, sodium-channel blockers, potassium-channel activators, NMDA-receptor antagonists, hormones, vasodilators, dopamine- and alpha2-agonists, magnesium, xanthine oxidase- and cyclooxygenase inhibitors, a nootropic, a protease inhibitor, and immunosuppressants. Some of them were applied chronically and others administered via clinically impracticable routes. The available literature favours isoflurane, phenytoin, lamotrigine, magnesium, and potentially, nimodipine, and flunarizine. If factors like costs, toxicity, side effects, route and mode of application are considered, isoflurane and MgSO4 that have also been safely applied to patients with compromised left ventricular pump function are advantageous but their true role in human neuroprotection remains unclear.

Effect of ketamine on apoptosis by energy deprivation in astroglioma cells using flow cytometry system

Apoptosis is a programmed, physiologic mode of cell death that plays an important role in tissue homeostasis. As for the central nervous system, ischemic insults can induce pathophysiologic cascade of apoptosis in neurophils. Impairment of astrocyte functions during brain ischemia can critically influence neuron survival by neuronglia interactions. We aimed to elucidate the protective effect of ketamine on apoptosis by energy deprivation in astrocytes. Ischemic insults was induced with iodoacetate/ carbonylcyanide m-chlorophenylhydrazone (IAA/CCCP) 1.5 mM/20 microm or 150 microm/2 microm for 1 hr in the HTB-15 and CRL-1690 astrocytoma cells. Then these cells were reperfused with normal media or ketamine (0.1 mM) containing media for 1 hr or 24 hr. FITC-annexin-V staining and propidium iodide binding were determined by using flow cytometry. Cell size and granularity were measured by forward and side light scattering properties of flow cytometry system, respectively. An addition of ketamine during reperfusion increased the proportion of viable cells. Ketamine alleviated cell shrinkage and increased granularity during the early period, and ameliorated cell swelling during the late reperfusion period. Ketamine may have a valuable effect on amelioration of early and late apoptosis in the astrocytoma cells, even though the exact mechanism remains to be verified.

Comparative tolerability of sedative agents in head-injured adults

Sedative agents are widely used in the management of patients with head injury. These drugs can facilitate assisted ventilation and may provide useful reductions in cerebral oxygen demand. However, they may compromise cerebral oxygen delivery via their cardiovascular effects. In addition, individual sedative agents have specific and sometimes serious adverse effects. This review focuses on the different classes of sedative agents used in head injury, with a discussion of their role in the context of clinical pathophysiology. While there is no sedative that has all the desirable characteristics for an agent in this clinical setting, careful titration of dose, combination of agents, and a clear understanding of the pathophysiology and pharmacology of these agents will allow safe sedative administration in head injury.

Transient ischemia of the retina results in massive degeneration of the retinotectal projection: long-term neuroprotection with brimonidine

In adult rats, we have induced retinal ischemia and investigated anterogradely labeled surviving retinal ganglion cell (RGC) afferents to the contralateral superior colliculus (SC). The animals received topically in their left eyes two 5-microl drops of saline or saline-containing 0.5% brimonidine (BMD), 1 h before 90 min of retinal ischemia induced by ligature of the left ophthalmic vessels. Two months after ischemia, the anterogradely transported neuronal tracer cholera toxin B subunit (CTB) was injected in the ischemic eyes and animals were processed 4 days later. As controls and for comparison, the retinotectal innervation of unlesioned age-matched control rats was also examined with CTB. In control and experimental animals, serial coronal sections of the mesencephalon and brainstem were immunoreacted for CTB and the area and thickness of the two most superficial layers of the SC containing densely CTB-labeled profiles were estimated with an image analysis system. Ninety minutes of ischemia resulted 2 months later in reduced density of CTB-labeled profiles in the contralateral SC of the vehicle-treated rats, representing less than one half the area occupied by CTB-labeled profiles in control rats. This resulted in shrinkage of these layers and in the presence of areas virtually devoid of CTB immunoreactivity, suggesting orthograde degeneration of retinal terminals and/or decrease of anterograde axonal transport. Topical pretreatment with BMD resulted 2 months later in CTB immunoreactivity that occupied the superficial layers of the contralateral SC in an area of approximately 86% of that observed in the unlesioned control group of animals, indicating that BMD protects against ischemia-induced degeneration of the retinotectal projection, and preserves anterograde axonal transport.

Effects of local and intravenous anesthetics on the activity of glutamate transporter type 2

Glutamate transporters may be important targets for anesthetic action in the central nervous system. The authors investigated the effects of the intravenous anesthetics, thiopental and ketamine, and the local anesthetics, lidocaine and bupivacaine, on the activity of glutamate transporter type 2, EAAT2. EAAT2 was expressed in Xenopus oocytes by injection of its mRNA. By using two-electrode voltage clamping, membrane currents were recorded after the application of L-glutamate (30 microM) in the presence or absence of various concentrations of anesthetics. Lidocaine and bupivacaine did not change glutamate-induced inward currents at the tested concentrations (1-1000 microM). Thiopental and ketamine also did not affect the activity of EAAT2 at the tested concentrations (0.3-300 microM). Our results suggest that the two commonly used local anesthetics (lidocaine and bupivacaine) and intravenous anesthetics (thiopental and ketamine) do not affect the activity of EAAT2 expressed in oocytes. EAAT2 may not be a target for these anesthetics.

Ketamine blocks Ca2+-activated K+ channels in rabbit cerebral arterial smooth muscle cells

Although ketamine and Ca2+-activated K+ (KCa) channels have been implicated in the contractile activity regulation of cerebral arteries, no studies have addressed the specific interactions between ketamine and the KCa channels in cerebral arteries. The purpose of this study was to examine the direct effects of ketamine on KCa channel activities using the patch-clamp technique in single-cell preparations of rabbit middle cerebral arterial smooth muscle. We tested the hypothesis that ketamine modulates the KCa channel activity of the cerebral arterial smooth muscle cells of the rabbit. Vascular myocytes were isolated from rabbit middle cerebral arteries using enzymatic dissociation. Single KCa channel activities of smooth muscle cells from rabbit cerebral arteries were recorded using the patch-clamp technique. In the inside-out patches, ketamine in the micromolar range inhibited channel activity with a half-maximal inhibition of the ketamine concentration value of 83.8 +/- 12.9 microM. The Hill coefficient was 1.2 +/- 0.3. The slope conductance of the current-voltage relationship was 320.1 +/- 2.0 pS between 0 and +60 mV in the presence of ketamine and symmetrical 145 mM K+. Ketamine had little effect on either the voltage-dependency or open- and closed-time histograms of KCa channel. The present study clearly demonstrates that ketamine inhibits KCa channel activities in rabbit middle cerebral arterial smooth muscle cells. This inhibition of KCa channels may represent a mechanism for ketamine-induced cerebral vasoconstriction.

Safety of sedation with ketamine in severe head injury patients: comparison with sufentanil

OBJECTIVE

The aim of the study was to compare the safety concerning cerebral hemodynamics of ketamine and sufentanil used for sedation of severe head injury patients, both drugs being used in combination with midazolam.

DESIGN

Prospective, randomized, double-blind study.

SETTING

Intensive care unit in a trauma center.

PATIENTS

Twenty-five patients with severe head injury.

INTERVENTIONS

Twelve patients received sedation with a continuous infusion of ketamine-midazolam and 13 with a continuous infusion of sufentanil-midazolam. All patients were mechanically ventilated with moderate hyperventilation.

MEASUREMENTS AND MAIN RESULTS

Prognostic indicators (age, Glasgow Coma Scale scores, computed tomography diagnosis, and Injury Severity Scale score) were similar in the two groups at study entry. Measurements were carried out during the first 4 days of sedation. The average infusion rates during this time were 82 +/- 25 micro x kg x min ketamine and 1.64 +/- 0.5 microg x kg x min midazolam in the ketamine group and 0.008 +/- 0.002 microg x kg x min sufentanil and 1.63 +/- 0.37 microg x kg x min midazolam in the sufentanil group. No significant differences were observed between the two groups in the mean daily values of intracranial pressure and cerebral perfusion pressure. The numbers of intracranial pressure elevations were similar in both groups. The requirements of neuromuscular blocking agents, propofol, and thiopental were similar. Heart rate values were significantly higher in the ketamine group on therapy days 3 and 4 ( <.05). With regard to arterial pressure control, more fluids were given on the first therapy day and there was a trend toward greater use of vasopressors in the sufentanil group. Sedative costs were similar in the two groups.

CONCLUSION

The results of this study suggest that ketamine in combination with midazolam is comparable with a combination of midazolam-sufentanil in maintaining intracranial pressure and cerebral perfusion pressure of severe head injury patients placed under controlled mechanical ventilation.

Central sympathetic blockade ameliorates brain death-induced cardiotoxicity and associated changes in myocardial gene expression

OBJECTIVE

Brain death results in cardiac injury and hemodynamic instability. After brain death, catecholamine levels surge in concert with increased expression of select myocardial gene products. Sympathetic blockade was used to investigate the effects of the adrenergic nervous system on myocardial gene expression in a rabbit model of brain death.

METHODS

A balloon expansion model of brain death in rabbits (n = 42) was used with and without sympathetic blockade (xylazine, acetylpromazine, and ketamine). Sham-operated and naive rabbits served as control animals. Over 4 hours, mean arterial pressure, heart rate, electrocardiographic results, catecholamine levels, myocardial histology, and messenger RNA levels were assessed.

RESULTS

Sympathetic blockade decreased basal catecholamine levels and blocked the catecholamine surge accompanying brain death. The typical hemodynamic instability, adverse electrocardiographic changes, and myocellular injury associated with brain death were all significantly decreased. Sympathetic blockade not only suppressed the previously reported increases in myocardial gene expression (cardiac and skeletal alpha-actin, egr-1, and heat shock protein 70) but also suppressed the expression of multiple other genes (alpha and beta myosin heavy chain, calcium ATPase [sarcoplasmic reticulum Ca(2+)-adenosine triphosphatase pump, SERCA-2a], phospholamban [ryanodine receptor], and c-jun).

CONCLUSION

Central sympathetic blockade minimizes the hemodynamic instability associated with brain death and neutralizes the increased expression of multiple myocardial gene products associated with brain death.

Similar half-octave TTS protection of the cochlea by xylazine/ketamine or sympathectomy

Cochlear efferents, sympathetic control and stress conditions have been shown to influence sound-induced hearing loss. These factors are also known to be modified by sedation/anesthesia. We tested here the effect of sedation/anesthesia on temporary threshold shift (TTS) compared to that in the same awake animals. The effect of sympathectomy was also tested. We employed awake guinea pigs with a chronically implanted electrode on the round window of each of the cochleae. Each ear was tested for its sensitivity to TTS induced by a 1 min or a 10 min exposure to an 8 kHz pure tone at 96 dB sound pressure level. After an intramuscular injection of xylazine or ketamine together with xylazine, TTS at half-octave frequencies was reduced compared to that in awake animals. The second half-octave frequencies were less affected. This specific pattern of protection was also observed here after surgical ablation of a superior cervical ganglion. The data lead to the speculation that protection from TTS under sedation/anesthesia might be due to diminished sympathetic influence. Xylazine is a pre-synaptic alpha2-adrenoreceptor agonist which blocks noradrenaline release from the sympathetic system. Ketamine is a N-methyl-D-aspartic acid receptor antagonist which could reduce glutamate excitotoxicity as well as reduce sympathetic activity.

Transient ischemia of the retina results in altered retrograde axoplasmic transport: neuroprotection with brimonidine

In adult rats we have induced retinal ischemia and investigated retrograde axonal transport in ganglion cells. The animals received in their left eyes, 1 h prior to ischemia, two 5-microl drops of saline or 0.5% brimonidine (BMD). Retinal ischemia was induced by transient ligature of the left ophthalmic vessels for 90 min. One hour or 1 week after ischemia, Fluorogold (FG) was applied to both superior colliculi, the animals were processed 1 week after FG application, and FG-labeled retinal ganglion cell (RGC) densities were estimated in the right control and left experimental retinas. In the left retinas of the saline-pretreated animals, RGC densities diminished to 39 or 30% of the densities found in their right control retinas, 7 or 14 days after ischemia, respectively. Because in a previous similar study in which FG was applied 7 days before ischemia, the percentages of FG-labeled RGCs were 54 and 48%, 7 and 14 days after ischemia, respectively, this suggests that retrograde axonal transport was impaired in some surviving RGCs. This was confirmed in an additional group of rats in which 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate was applied to both SCi 3 weeks before ischemia, and FG was applied to the intraorbitally cut optic nerve 9 days after ischemia and 5 days before euthanization. In the left retinas of the BMD-pretreated animals, RGC densities amounted to 90% of the RGC population 7 or 14 days after ischemia and were comparable to those obtained in their contralateral nonischemic retinas. Retinal ischemia causes RGC loss and induces alterations of retrograde axonal transport in a proportion of surviving RGCs. BMD rescues RGCs from ischemia-induced cell death and preserves retrograde axonal transport in surviving RGCs.

Brain protection during neurosurgery

The initial concept of brain protection during neurosurgery is based on research done in the 1970s-1980 which established the concept that by decreasing cerebral metabolic rate the brain could survive longer periods of ischemia. The first section of this chapter reviews some of this initial research that promoted the use of barbiturates for cerebral protection. The second section reviews current anesthetic drugs and their potential for cerebral protection in addition to the benefits of blood pressure, temperature and glucose control. The final section discusses the "new mechanisms of cerebral protection" and the role old and new drugs may play in the future for brain protection during neurosurgery.

Neuroprotective effects of brimonidine against transient ischemia-induced retinal ganglion cell death: a dose response in vivo study

The purpose of this study was to investigate the dose-response effects of topically administered brimonidine (BMD) on retinal ganglion cell (RGC) survival, short and long periods of time after transient retinal ischemia. In adult Sprague-Dawley rats, RGCs were retrogradely labeled with the fluorescent tracer fluorogold (FG) applied to both superior colliculi. Seven days later, the left ophthalmic vessels were ligated for 90 min. One hr prior to retinal ischemia, two 5 microl drops of saline alone or saline containing 0.0001, 0.001, 0.01 or 0.1% BMD were instilled on the left eye. Rats were processed 7, 14 or 21 days later and densities of surviving RGCs were estimated by counting FG-labeled RGCs in 12 standard regions of each retina. The following have been found. (1) Seven days after 90 min of transient ischemia there is loss of approximately 46% of the RGC population. (2) topical pre-treatment with BMD prevents ischemia-induced RGC death in a dose-dependent manner. Administration of 0.0001% BMD resulted in the loss of approximately 37% of the RGC population and had no significant neuroprotective effects. Administration of higher concentrations of BMD (0.001 or 0.01%) resulted in the survival of 76 or 90%, respectively, of the RGC population, and 0.1% BMD fully prevented RGC death in the first 7 days after ischemia. (3) Between 7 and 21 days after ischemia there was an additional slow cell loss of approximately 25% of the RGC population. Pre-treatment with 0.1% BMD also reduced significantly this slow cell death. These results indicate that the neuroprotective effects of BMD, when administered topically, are dose-dependent and that the 0.1% concentration achieves optimal neuroprotective effects against the early loss of RGCs. Furthermore, this concentration is also effective to diminish the protracted loss of RGCs that occurs with time after transient ischemia.

S(+)-ketamine/propofol maintain dynamic cerebrovascular autoregulation in humans

PURPOSE

This study investigates the effects of S(+)-ketamine and propofol in comparison to sevoflurane on dynamic cerebrovascular autoregulation in humans.

METHODS

Twenty-four patients were randomly assigned to one of the following anesthetic protocols: group I (n=12): 2.5 mg.kg(-1)*hr(-1) S(+)-ketamine, 1.5-2.5 microg*mL(-1) propofol-target plasma concentration; group II (n=12): 2.0 MAC (4.0 %) sevoflurane. Patients were intubated and ventilated with O(2)/air (PaO(2)=0.33). Following 40 min of equilibration dynamic cerebrovascular autoregulation was measured and expressed as the autoregulatory index (ARI), describing the duration of cerebral hemodynamic recovery in relation to changes in mean arterial blood pressure.

STATISTICS

Mann-Whitney U test (statistical significance was assumed when P <0.05).

RESULTS

Dynamic cerebrovascular autoregulation was intact in all patients with S(+)-ketamine/propofol anesthesia as indicated by an ARI of 5.4 +/- 1.1. In contrast, dynamic cerebrovascular autoregulation was significantly delayed with 2.0 MAC sevoflurane (ARI=2.6 +/- 0.7) CONCLUSION: Dynamic cerebrovascular autoregulation is maintained with S(+)-ketamine/propofol-based total iv anesthesia. In contrast, 2.0 MAC sevoflurane delayed dynamic cerebrovascular autoregulation. This supports the use of S(+)-ketamine in combination with propofol in neurosurgical patients based on its neuroprotective potential along with maintained cerebrovascular physiology.

Effects of ketamine on in vivo cardiac sympathetic nerve endings

Using the dialysis technique, we examined the effect of ketamine on dialysate norepinephrine (NE) levels in the myocardial interstitial space in anesthetized cats. Dialysis probes were implanted in the left ventricular myocardium, and we measured the dialysate NE levels serving as an indicator of NE output at the cardiac sympathetic nerve endings. During local administration of ketamine (10 mM), we examined the time-course of the change in dialysate NE levels and the dialysate NE response to coronary occlusion. Dialysate NE levels significantly increased from 39+/-7 pg/ml at control to 133+/-22 pg/ml 30 min after beginning the ketamine administration. Addition of either omega-conotoxin GVIA (N-type calcium channel blocker) at 10 microg/kg intravenously or desipramine (neuronal NE transport blocker) at 100 microM did not inhibit the increment in dialysate NE evoked by ketamine. These findings suggest that the increase in dialysate NE evoked by ketamine is dependent neither on the activity of NE exocytosis nor on the neuronal NE transport. Left descending coronary artery occlusion evoked increments in dialysate NE. The addition of ketamine augmented the dialysate NE response to coronary occlusion. A ketamine-induced increment in dialysate NE might occur as a consequence of NE exocytosis independent or membrane NE transport insensitive efflux of NE.

The effects of topical and intravenous ketamine on cerebral arterioles in dogs receiving pentobarbital or isoflurane anesthesia

To evaluate the effects of ketamine on cerebral arterioles, we used a closed cranial window technique in mechanically ventilated, anesthetized dogs. Fourteen dogs were assigned to one of the following two basal-anesthesia groups: pentobarbital 2 mg. kg(-1). h(-1) or isoflurane 0.5 MAC (n = 7 each). We administered three different concentrations of ketamine (10(-7), 10(-5), and 10(-3) M) under the window and measured arteriolar diameters. For comparison, in another 14 dogs we examined the effect of systemic (IV) ketamine (1 mg/kg and 5 mg/kg) using the same two basal anesthetics. We measured diameters before and after ketamine administration, and we evaluated the effect of ketamine on CO(2) reactivity of the cerebral arterioles. Neither topical nor systemic ketamine dilated pial arterioles in either basal-anesthesia group. CO(2) reactivity of pial arterioles was reduced under systemic ketamine in both basal-anesthesia groups. The results indicate that although ketamine does not dilate pial arteriolar diameters when topically or IV administered, IV ketamine does attenuate hypercapnic vasodilation in dogs under basal pentobarbital or isoflurane anesthesia. These results provide some insight that ketamine is suitable for supplementary neurosurgical anesthesia.

Neuroprotection of S(+) ketamine isomer in global forebrain ischemia

The non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist ketamine can block the action of excitotoxic amino acids in the central nervous system. S(+) ketamine has a 2-3 times higher anesthetic potency compared with the ketamine-racemate and also shows a higher neuroprotective efficacy in vitro. To determine the neuroprotective activity of S(+) ketamine compared with its R(-) stereoisomer in vivo, we examined the functional and neurohistological outcome in rats treated 15 min after global forebrain ischemia with S(+) ketamine in different dosages compared with R(-) ketamine. Influence of the treatment on regional cerebral blood flow (rCBF) and cortical oxygen saturation (HbO2) was monitored over 1 h after the ischemia using laser doppler flowmetry and microphotospectrometry respectively. Sixty and ninety mg/kg of S(+) ketamine but not R(-) ketamine significantly reduced neuronal cell loss in the cortex compared with the saline treated group. No significant neuroprotection was observed in the hippocampus. Although no significant change in rCBF was found, S(+) ketamine restored the cortical HbO2 to preischemic values. These results indicate that S(+) ketamine in higher dosages can reduce neuronal damage in the cortex after cerebral ischemia, possibly by improving the ratio of oxygen supply to consumption in the postischemic tissue.

Central representation of the sympathetic nervous system in the cerebral cortex

The sympathetic-related regions of the cerebral cortex were identified in rats after pseudorabies virus injections were made in functionally different targets: adrenal gland, stellate ganglion which regulates the heart, or celiac ganglion which innervates the gastrointestinal tract. Extensive transneuronal labeling was found in limbic system areas: (1) extended amygdaloid complex, (2) lateral septum, and (3) infralimbic, insular, and ventromedial temporal cortical regions (viz., ectorhinal cortex=Brodmann's area 36, perirhinal cortex=area 35, lateral entorhinal=area 28, and ventral temporal association cortex=Te3 region). Deep temporal lobe structures were prominently labeled, including the amygdalopiriform and amygdalohippocampal transition areas, ventral hippocampus and ventral subiculum. The cortical circuits mediating emotional-autonomic changes (i.e., mind-body control) are discussed.

Ketamina, da anestesia ao uso abusivo

Objetivo. Realizar uma revisão bibliográfica sobre a ketamina, enfocando aspectos químicos e farmacocinéticos, seus mecanismos de ação, efeitos farmacológicos, usos terapêuticos, bem como aborda o uso da ketamina como droga de abuso. Ketamina. Método. Estudo de revisão bibliográfica através das bases de dados Pubmed, SciELO, Lilacs e Medline, na qual foram selecionados estudos clássicos e recentes relevantes para a discussão do tema abordado. Resultados. Após análise dos artigos selecionados, conclui-se que a ketamina apresenta perspectivas promissoras. Alguns estudos demonstraram propriedades analgésicas em relação à dor pós-operatória e outros revelaram uma ação antidepressiva rápida. Além disto, a ketamina também apresentou efeitos neuroprotetores em vários estudos animais. Embora a ketamina seja um campo promissor, essas ações precisam ser melhor investigadas. Atualmente, observou-se que o seu uso não se restringe apenas à prática clínica ou pesquisa, sendo frequentemente utilizada como droga de abuso pelos jovens em festas como um potente alucinógeno. Conclusão. Pesquisas sobre o uso recreacional da ketamina também são necessárias, especialmente no Brasil, assim como dados que mostrem a morbidade e mortalidade pelo uso desta substância como droga de abuso.