Blocking mechanisms of ketamine and its enantiomers in enzymatically demyelinated peripheral nerve as revealed by single-channel experiments

Efficacy and Safety of Adding Ketamine to Lidocaine in Intravenous Regional Anesthesia: A Meta-analysis of Randomized Controlled Trials

PURPOSE

To systematically evaluate the efficacy and safety of adding ketamine (K) to lidocaine (L) for intravenous regional anesthesia (IVRA).

DESIGN

A systematic review and meta-analysis.

METHODS

A comprehensive search of the Cochrane library, Embase, PubMed, Web of Science, and ProQuest databases, and the Google Scholar search engine was conducted from inception to March 2023. All retrieved articles were imported into Endnote X20 software and independently screened by two researchers according to predetermined inclusion and exclusion criteria. The data were analyzed using Revman 5.4 software and the assessed outcomes included the time of sensory and motor block onset, time of sensory and motor block recovery, fentanyl consumption, time of tourniquet pain onset, intraoperative and postoperative visual analog scale scores, and complications.

FINDINGS

A total of 532 patients from 11 randomized controlled trials were included in the meta-analysis. The results showed that the time of sensory (P < .00001) and motor block onset (P < .00001) were shorter in the L + K group than in the L-only group. The time of sensory (P = .01) and motor block recovery (P = .006) and time of tourniquet pain onset (P < .00001) were longer in the L + K group than in the L-only group. There was a significant reduction in fentanyl consumption (P = .0002) in the L + K group compared to the L-only group. Moreover, the visual analog scale scores in the L + K group were significantly lower than the L-only group 10 minutes (P = .04), 20 minutes (P = .0004), 30 minutes (P < .00001), and 40 minutes (P < .0001) after tourniquet inflation, and 5 minutes (P < .00001), 15 minutes (P = .04), 30 minutes (P = .008), 1 hour (P = .002), 2 hours (P < .00001), and 4 hours (P < .00001) after tourniquet deflation. There was no evidence that the use of K as an adjuvant in IVRA increased adverse effects.

CONCLUSIONS

The addition of K to L in IVRA shortened the onset time, prolonged the block time, and reduced intraoperative and postoperative pain without increasing complications.

Is there a risk of esketamine misuse in clinical practice?

In 2019, intranasal esketamine gained approval as a promising therapy for those individuals grappling with treatment-resistant depression. Both clinical trials and real-world studies have underscored its efficacy in alleviating and remitting depressive symptoms, with sustained benefits observed for nearly 4.5 years. As the S-enantiomer of ketamine, esketamine's dosing guidelines and strict medical supervision stem from prior research on ketamine's use in depression and history as a recreational drug. Despite initial concerns, long-term clinical studies have not documented instances of abuse, misuse, addiction or withdrawal, and the same was found in case reports or subsamples of high-risk populations with comorbidities such as substance use disorder or alcohol use disorder. Esketamine has proven to be safe and well tolerated without fostering new-onset substance use in vulnerable groups. Real-world studies reinforced these observations, reporting no adverse events (AEs) related to pharmacological interactions of esketamine with any other substance, and no new-onset drug or alcohol misuse, craving, misuse or diversion of use. Reports of esketamine craving remain rare, with only one case report documented in 2022. Most drug-related AEs reported in pharmacovigilance databases are those identified in the product's technical data sheet and with known reported frequency. More importantly, no register of illicit acquisition of esketamine or its tampering for obtaining ketamine or other altered products was found in our search. Overall, our review confirms esketamine's safety across diverse patient populations, reassuring its responsible use and the scarcity of reports of abuse or misuse since its introduction to the market.

Ketamine Produces a Long-Lasting Enhancement of CA1 Neuron Excitability

Ketamine is a clinical anesthetic and antidepressant. Although ketamine is a known NMDA receptor antagonist, the mechanisms contributing to antidepression are unclear. This present study examined the loci and duration of ketamine’s actions, and the involvement of NMDA receptors. Local field potentials were recorded from the CA1 region of mouse hippocampal slices. Ketamine was tested at antidepressant and anesthetic concentrations. Effects of NMDA receptor antagonists APV and MK-801, GABA receptor antagonist bicuculline, and a potassium channel blocker TEA were also studied. Ketamine decreased population spike amplitudes during application, but a long-lasting increase in amplitudes was seen during washout. Bicuculline reversed the acute effects of ketamine, but the washout increase was not altered. This long-term increase was statistically significant, sustained for >2 h, and involved postsynaptic mechanisms. A similar effect was produced by MK-801, but was only partially evident with APV, demonstrating the importance of the NMDA receptor ion channel block. TEA also produced a lasting excitability increase, indicating a possible involvement of potassium channel block. This is this first report of a long-lasting increase in excitability following ketamine exposure. These results support a growing literature that increased GABA inhibition contributes to ketamine anesthesia, while increased excitatory transmission contributes to its antidepressant effects.

An Update on the Basic and Clinical Science of Ketamine Analgesia

OBJECTIVE

In the context of the current opioid epidemic, there has been a renewed interest in the use of ketamine as an analgesic agent.

METHODS

We reviewed ketamine analgesia.

RESULTS

Ketamine is well-known as an antagonist for N-methyl-D-aspartate receptors. In addition, it can regulate the function of opioid receptors and sodium channels. Ketamine also increases signaling through α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors. These myriad of molecular and cellular mechanisms are responsible for a number of pharmacological functions including pain relief and mood regulation. Clinically, a number of studies have investigated the role of ketamine in the setting of acute and chronic pain, and there is evidence that ketamine can provide analgesia in a variety of pain syndromes.

DISCUSSION

In this review, we examined basic mechanisms of ketamine and its current clinical use and potential novel use in pain management.

Nerve excitability differences in slow and fast motor axons of the rat: more than just Ih

The objective was to determine biophysical differences between fast and slow motor axons using threshold tracking and demonstrate confounds related to anesthetic. Nerve excitability of motor axons innervating the slow-twitch soleus (SOL) and fast-twitch tibialis anterior (TA) muscles was tested. The experiments were conducted with pentobarbital sodium (SP) anesthetic and compared with previous results that used ketamine-xylazine (KX). Nerve excitability indices measured with SP show definitive differences between TA and SOL motor axons that extend beyond previous reports. Nerve excitability indices sensitive to changes in I_h indicated an increase in SOL axons compared with TA axons [e.g., S3 t = 7.949 (df = 10), P < 0.001; hyperpolarizing threshold electrotonus (90-100 ms), t = 2.659 (df = 20); P = 0.01; hyperpolarizing I/V slope, t = 4.308 (df = 19); P < 0.001]. SOL axons also had a longer strength-duration time constant [t = 3.35 (df = 20); P = 0.003] and a longer and larger magnitude relative refractory period [RRP (ms) t = 3.53 (df = 12); P = 0.004; Refractoriness at 2 ms, t = 0.0055 (df = 9); P = 0.006]. Anesthetic choice affected many measures of peripheral nerve excitability with differences most apparent in tests of threshold electrotonus and recovery cycle. For example, recovery cycle with KX lacked a clear superexcitable and late subexcitable period. We conclude that KX had a confounding effect on nerve excitability results consistent with ischemic depolarization. Results using SP revealed the full extent of differences in nerve excitability measures between putative slow and fast motor axons of the rat. These results provide empirical evidence, beyond conduction velocity, that the biophysical properties of motor axons vary with the type of muscle fiber innervated. These differences suggest that fast axons may be predisposed to dysfunction during hyperpolarizing stresses, e.g., electrogenic sodium pumping following sustained impulse conduction.NEW & NOTEWORTHY Nerve excitability testing is a tool used to provide insight into the properties of ion channels in peripheral nerves. It is used clinically to assess pathophysiology of axons. Researchers customarily think of motor axons as homogeneous; however, we demonstrate there are clear differences between fast and slow axons in the rat. This is important for interpreting results with selective motor neuronopathy, like aging where fast axons are at high risk of degeneration.

Ketamine for the treatment of major depressive disorder and bipolar depression: A review of the literature

Introduction

Over the past decade, ketamine has been studied for major depressive disorder and bipolar depression. Ketamine is believed to exert its antidepressant properties through N-methyl-D-aspartate receptor antagonism.

Methods

Study authors completed a literature review of seven randomized controlled trials of ketamine usage in major depressive disorder and bipolar depression.

Results

Ketamine demonstrated a statistically significant improvement over placebo or midazolam in major depressive disorder. Ketamine also exhibited a statistically significant improvement over placebo in bipolar depression.

Discussion

Ketamine has shown promise in quickly reducing symptoms in patients with treatment resistant depression and bipolar depression. Using ketamine may be helpful for patients that have exhausted other therapeutic options.

Ketamine-induced neuronal damage and altered N-methyl-D-aspartate receptor function in rat primary forebrain culture

Ketamine, a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, is frequently used in pediatric general anesthesia. Accumulating evidence from animal experiments has demonstrated that ketamine causes neuronal cell death during the brain growth spurt. To elucidate the underlying mechanisms associated with ketamine-induced neuronal toxicity and search for approaches or agents to prevent ketamine's adverse effects on the developing brain, a primary nerve cell culture system was utilized. Neurons harvested from the forebrain of newborn rats were maintained under normal control conditions or exposed to either ketamine (10 µM) or ketamine plus L-carnitine (an antioxidant; 1-100 µM) for 24h, followed by a 24-h withdrawal period. Ketamine exposure resulted in elevated NMDA receptor (NR1) expression, increased generation of reactive oxygen species (ROS) as indicated by higher levels of 8-oxoguanine production, and enhanced neuronal damage. Coadministration of L-carnitine significantly diminished ROS generation and provided near complete protection of neurons from ketamine-induced cell death. NMDA receptors regulate channels that are highly permeable to calcium, and calcium imaging data demonstrated that neurons exposed to ketamine had a significantly elevated amplitude of calcium influx and higher intracellular free calcium concentrations ([Ca(2+)]i) evoked by NMDA (50 µM), compared with control neurons. These findings suggest that prolonged ketamine exposure produces an increase in NMDA receptor expression (compensatory upregulation), which allows for a higher/toxic influx of calcium into neurons once ketamine is removed from the system, leading to elevated ROS generation and neuronal cell death. L-Carnitine appears to be a promising agent in preventing or reversing ketamine's toxic effects on neurons at an early developmental stage.

To use or not to use: an update on licit and illicit ketamine use

Ketamine, a derivative of phencyclidine that was developed in the 1960s, is an anesthetic and analgesic with hallucinogenic effects. In this paper, the pharmacological and toxicological effects of ketamine are briefly reviewed. Ketamine possesses a wide safety margin but such a therapeutic benefit is somewhat offset by its emergence phenomenon (mind-body dissociation and delirium) and hallucinogenic effects. The increasing abuse of ketamine, initially predominantly in recreational scenes to experience a “k-hole” and other hallucinatory effects but more recently also as a drug abused during the workday or at home, has further pushed governments to confine its usage in many countries. Recently, urinary tract dysfunction has been associated with long-term ketamine use. In some long-term ketamine users, such damage can be irreversible and could result in renal failure and dialysis. Although ketamine has not yet been scheduled in the United Nations Conventions, previous studies using different assessment parameters to score the overall harms of drugs indicated that ketamine may cause more harm than some of the United Nations scheduled drugs. Some countries in Southeast and East Asia have reported an escalating situation of ketamine abuse. Dependence, lower urinary tract dysfunction, and sexual impulse or violence were the most notable among the ketamine-associated symptoms in these countries. These results implied that the danger of ketamine may have been underestimated previously. Therefore, the severity levels of the ketamine-associated problems should be scrutinized more carefully and objectively. To prevent ketamine from being improperly used and evolving into an epidemic, a thorough survey on the prevalence and characteristics of illicit ketamine use is imperative so that suitable policy and measures can be taken. On the other hand, recent findings that ketamine could be useful for treating major depressive disorder has given this old drug a new impetus. If ketamine is indeed a remedy for treating depression, more research on the risks and benefits of its clinical use will be indispensable.

Ketamine, but not phencyclidine, selectively modulates cerebellar GABA(A) receptors containing alpha6 and delta subunits

Phencyclidine (PCP) and ketamine are dissociative anesthetics capable of inducing analgesia, psychomimetic behavior, and a catatonic state of unconsciousness. Despite broad similarities, there are notable differences between the clinical actions of ketamine and PCP. Ketamine has a lower incidence of adverse effects and generally produces greater CNS depression than PCP. Both noncompetitively inhibit NMDA receptors, yet there is little evidence that these drugs affect GABA(A) receptors, the primary target of most anesthetics. alpha6beta2/3delta receptors are subtypes of the GABA(A) receptor family and are abundantly expressed in granular neurons within the adult cerebellum. Here, using an oocyte expression system, we show that at anesthetically relevant concentrations, ketamine, but not PCP, modulates alpha6beta2delta and alpha6beta3delta receptors. Additionally, at higher concentrations, ketamine directly activates these GABA(A) receptors. Comparatively, dizocilpine (MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate]), a potent noncompetitive antagonist of NMDA receptors that is structurally unrelated to PCP, did not produce any effect on alpha6beta2delta receptors. Of the recombinant GABA(A) receptor subtypes examined (alpha1beta2, alpha1beta2gamma2, alpha1beta2delta, alpha4beta2gamma2, alpha4beta2delta, alpha6beta2gamma2, alpha6beta2delta, and alpha6beta3delta), the actions of ketamine were unique to alpha6beta2delta and alpha6beta3delta receptors. In dissociated granule neurons and cerebellar slice recordings, ketamine potentiated the GABAergic conductance arising from alpha6-containing GABA(A) receptors, whereas PCP showed no effect. Furthermore, ketamine potentiation was absent in cerebellar granule neurons from transgenic functionally null alpha6(-/-) and delta(-/-)mice. These findings suggest that the higher CNS depressant level achieved by ketamine may be the result of its selective actions on alpha6beta2/3delta receptors.

Interactions of anesthetics with their targets: non-specific, specific or both?

What makes a general anesthetic a general anesthetic? We shall review first what general anesthesia is all about and which drugs are being used as anesthetics. There is neither a unique definition of general anesthesia nor any consensus on how to measure it. Diverse drugs and combinations of drugs generate general anesthetic states of sometimes very different clinical quality. Yet the principal drugs are still considered to belong to the same class of 'general anesthetics'. Effective concentrations of inhalation anesthetics are in the high micromolar range and above, and even for intravenous anesthetics they do not go below the micromolar range. At these concentrations, many molecular and higher level targets are affected by inhalation anesthetics, fewer probably by intravenous anesthetics. The only physicochemical characteristic shared by anesthetics is the correlation of their anesthetic potencies with hydrophobicity. These correlations depend on the group of general anesthetics considered. In this review, anesthetic potencies for many different targets are plotted against octanol/water partition coefficients as measure of hydrophobicity. Qualitatively, similar correlations result, suggesting several but weak interactions with proteins as being characteristic of anesthetic actions. The polar interactions involved are weak, being roughly equal in magnitude to hydrophobic interactions. Generally, intravenous anesthetics are noticeably more potent than inhalation anesthetics. They differ considerably more between each other in their interactions with various targets than inhalation anesthetics do, making it difficult to come to a decision which of these should be used in future studies as representative 'prototypical general anesthetics'.

Ketamine impairs excitability in superficial dorsal horn neurones by blocking sodium and voltage-gated potassium currents

Ketamine shows, besides its general anaesthetic effect, a potent analgesic effect after spinal administration. We investigated the local anaesthetic-like action of ketamine and its enantiomers in Na+ and K+ channels and their functional consequences in dorsal horn neurones of laminae I-III, which are important neuronal structures for pain transmission receiving most of their primary sensory input from Adelta and C fibres. Combining the patch-clamp recordings in slice preparation with the 'entire soma isolation' method, we studied action of ketamine on Na+ and voltage-activated K+ currents. The changes in repetitive firing behaviour of tonically firing neurones were investigated in current-clamp mode after application of ketamine. Concentration-effect curves for the Na+ peak current revealed for tonic block half-maximal inhibiting concentrations (IC50) of 128 microM and 269 microM for S(+) and R(-)-ketamine, respectively, showing a weak stereoselectivity. The block of Na+ current was use-dependent. The voltage-dependent K+ current (K(DR)) was also sensitive to ketamine with IC50 values of 266 microM and 196 microM for S(+) and R(-)-ketamine, respectively. Rapidly inactivating K+ currents (K(A)) were less sensitive to ketamine. The block of K(DR) channels led to an increase in action potential duration and, as a consequence, to lowering of the discharge frequency in the neurones. We conclude that ketamine blocks Na+ and K(DR) channels in superficial dorsal horn neurones of the lumbar spinal cord at clinically relevant concentrations for local, intrathecal application. Ketamine reduces the excitability of the neurones, which may play an important role in the complex mechanism of its action during spinal anaesthesia.

Caudal Additives in Pediatrics: A Comparison Among Midazolam, Ketamine, and Neostigmine Coadministered with Bupivacaine

Single-shot "kiddie caudal" with bupivacaine alone is losing popularity because of its duration of 4-8 h. In a prospective randomized double-blind clinical study, we assessed and compared the efficacy of ketamine, midazolam, and neostigmine coadministered with bupivacaine in a caudal epidural to provide intraoperative and postoperative pain relief. Eighty children (ASA status I) aged 5-10 yr undergoing unilateral inguinal herniotomy were allocated randomly in equal numbers (n = 20) into 4 groups to receive a caudal injection of 0.25% bupivacaine (1 mL/kg) with or without ketamine (0.5 mg/kg), midazolam (50 microg/kg), and neostig-mine (2 microg/kg), after the induction of standardized general anesthesia without premedication. Monitoring for pain, sedation, postoperative nausea/vomiting, dizziness, and pruritus was performed by anesthesiologists blinded to the study allocation. The time to first analgesic administration (paracetamol syrup) was longer (P < 0.05) in the bupivacaine-neostigmine group and the bupivacaine-midazolam group than in the other groups. Undesirable effects, such as emesis, pruritus, and dizziness, were comparable in all groups. However, the incidence of hallucination was more frequent in the bupivacaine-ketamine group compared with the other groups. This study shows that single-shot caudal coadministration of bupivacaine-neostigmine and bupivacaine-midazolam was associated with an extended duration of postoperative pain relief.

Ketamine Stereoselectively Inhibits Spontaneous Ca2+-Oscillations in Cultured Hippocampal Neurons

Spontaneous Ca2+-oscillations are a result of periodic increases and decreases of cytosolic Ca2+. In neurons, they are thought to possess integrative properties because amplitude and frequency influence axon outgrowth, neuronal growth cone migration, and long distant wiring within the developing cortex. Ketamine stereoisomers differ in their affinities for the N-methyl-D-aspartic acid receptor and analgesic and anesthetic effects. Using a dual-excitation Ca2+ ratiometric fluorescence technique with the Ca2+-sensitive dye fura-2 AM, we detected spontaneous Ca2+-oscillations in neurons of hippocampal cell cultures. Spontaneous Ca2+-oscillations development is dependent on external Ca2+, and their amplitude and frequency increased in Mg2+-free solution. Ca2+-oscillations are glutamate dependent because blocking of the N-methyl-D-aspartic acid, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic, or kainate receptor resulted in a complete disruption of the oscillations. The ketamine stereoisomers dose-dependently and reversibly suppressed the amplitude and frequency of the spontaneous Ca2+-oscillations. This effect was highly stereoselective with the S+ isomer being nearly four times more potent than the R(-) enantiomer. These results correlate well with the clinical anesthetic and analgesic potency of the stereoisomers and therefore our experimental approach might represent a model system to study mechanisms of anesthetic action on Ca2+-dependent integration of neuronal information.

The combination of epidural clonidine and S(+)-ketamine did not enhance analgesic efficacy beyond that for each individual drug in adult orthopedic surgery

STUDY OBJECTIVES

To evaluate the benefit of epidural clonidine and S(+)-ketamine combination through the epidural route in adult orthopedic surgery.

DESIGN

Randomized double-blinded study.

SETTING

Teaching hospital.

PATIENTS

Scheduled to undergo knee surgery, 56 American Society of Anesthesiologists physical status 1 and 2 adult patients.

INTERVENTIONS

Patients were randomized to 1 of 4 groups to receive the combined epidural-intrathecal technique. A 10-mL epidural injection of either study drug or normal saline was first administered to all patients. Intrathecal anesthesia was performed with 15 mg of bupivacaine. The control group (CG) received epidural saline. The 0.1-mg/kg S(+)-ketamine epidural group received 0.1 mg/kg epidural S(+)-ketamine. The 0.5-microg/kg clonidine epidural group received 0.5 microg/kg epidural clonidine. The S(+)-ketamine/clonidine group received 0.1 mg/kg epidural S(+)-ketamine plus 0.5 microg/kg epidural clonidine.

MEASUREMENTS AND MAIN RESULTS

Pain and adverse effects were evaluated by visual analog scale. Rescue analgesics were available to patients. The groups were demographically similar. Sensory level to pinprick, surgical and anesthetic time, and visual analog scale scores for pain at first rescue medication were similar among the groups. The time to first rescue analgesic (minute) was lowest in CG (P < .005). The CG required more rescue analgesics in 24 hours than any of the other groups (P < .0005). Patients who received either epidural clonidine, S(+)-ketamine, or both displayed similar analgesia. The frequency of adverse effects was similar among groups (P > .05).

CONCLUSIONS

The association of epidural clonidine or S(+)-ketamine did not result in a greater analgesic effect in the model of acute postoperative pain studied, although the interaction of epidural clonidine and S(+)-ketamine is not attributable to sharing of a common second messenger system.

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.

Is the Effect of Inguinal Field Block With 0.5% Bupivacaine on Postoperative Pain After Hernia Repair Enhanced by Addition of Ketorolac or S(+) Ketamine?

OBJECTIVE

The aim of the study was to assess whether coadministration of S(+) ketamine or ketorolac would enhance or prolong local analgesic effect of bupivacaine after inguinal hernia repair.

DESIGN

Prospective double-blind randomized study evaluating pain intensity after surgery under general anesthesia.

SETTING

Outpatient facilities of the University Hospital of Lausanne.

PATIENT

Thirty-six ASA I-II outpatients scheduled for elective day-case inguinal herniorraphy.

INTERVENTION

Analgesia strategy consisted of a wound infiltration and an inguinal field block either with 30 mL bupivacaine (0.5%) or with the same volume of a mixture of 27 mL bupivacaine (0.5%) + 3 mL S(+) ketamine (75 mg) or a 28 mL bupivacaine (0.5%) + 2 mL ketorolac (60 mg). Postoperative analgesic regimen was standardized.

OUTCOME MEASURES

Pain intensity was assessed with a Visual Analog Scale, a verbal rating score, and by pressure algometry 2, 4, 6, 24, and 48 hours after surgery.

RESULTS

The 3 groups of patients experienced the highest Visual Analog Scale pain score at 24 hours, which was different from those at 6 and 48 hours (P < 0.05). Apart from a significantly lower pain sensation (verbal rating score) in the ketorolac group at 24 and 48 hours and only at 48 hours with ketamine, there were no other differences in pain scores, pain pressure thresholds, or rescue analgesic consumption between groups throughout the 48-hour study period.

CONCLUSION

The addition of S(+)-ketamine or ketorolac only minimally improves the analgesic effect of bupivacaine. This may be related to the tension-free hernia repair technique associated with low postoperative pain.

Analgesic effects of epidurally administered levogyral ketamine alone or in combination with morphine on intraoperative and postoperative pain in dogs undergoing ovariohysterectomy

OBJECTIVE

To evaluate the analgesic and adverse effects of epidurally administered levogyral (S[+]) ketamine alone or in combination with morphine on intraoperative and postoperative pain in dogs undergoing ovariohysterectomy.

ANIMALS

30 dogs scheduled for ovariohysterectomy.

PROCEDURE

Dogs were randomly allocated to 1 of 3 groups. Dogs in group 1 received S(+) ketamine (1 mg/kg), dogs in group 2 received S(+) ketamine (0.5 mg/kg) and morphine (0.05 mg/kg), and dogs in group 3 received S(+) ketamine (1 mg/kg) and morphine (0.025 mg/kg). The skin was incised 15 minutes after epidural administration of analgesics. Heart rate (HR), respiratory rate (RR), systolic blood pressure (SBP), oxygen saturation as measured by pulse oximetry, and arterial blood gases were obtained before anesthesia, 15 minutes after epidural administration of analgesics, 15 and 30 minutes after initiation of surgery, and at the end of surgery. During the intraoperative period, an increase of > or =20% in baseline values for HR, RR, and SBP was considered a sign of intraoperative pain. Signs of pain and adverse effects were assessed at 2, 4, and 8 hours postoperatively.

RESULTS

There were no significant differences in intraoperative or postoperative measurements among the 3 groups. No dogs had intraoperative signs of pain. Mean postoperative pain assessment scores were <3.5 in all 3 groups. Salivation was the most frequent adverse effect in dogs in groups 1 and 3, and sedation occurred more frequently in dogs in groups 2 and 3.

CONCLUSIONS AND CLINICAL RELEVANCE

All 3 analgesic regimens provided good respiratory and cardiovascular stability intraoperatively and adequate postoperative analgesia with minimal adverse effects.

Caudal analgesia in children: S(+)-ketamine vs S(+)-ketamine plus clonidine

BACKGROUND

The aim of this study was to evaluate postoperative analgesia provided by caudal S(+)-ketamine and S(+)-ketamine plus clonidine without local anesthetic.

METHODS

Forty-four children aged 1-5 years consecutively scheduled for inguinal hernia repair, hydrocele repair or orchidopexy were randomly assigned to receive a caudal injection of either S(+)-ketamine 1 mg x kg(-1) (group K) or S(+)-ketamine 0.5 mg x kg(-1) plus clonidine 1 microg x kg(-1) (group KC). Postoperative analgesia and sedation were evaluated by CHEOPS and Ramsay scale from emergence from general anesthesia for 24 h.

RESULTS

No statistical difference was observed between study groups with respect to pain and sedation assessment. A slight trend toward a reduced requirement for rescue analgesia in group KC was observed, although not statistically significant.

CONCLUSIONS

Caudal S(+)-ketamine 1 mg x kg(-1) and S(+)-ketamine 0.5 mg x kg(-1) plus clonidine 1 microg x kg(-1) are safe and provide effective postoperative analgesia in children without adverse effects.

Pre-Emptive Epidural Ketamine or S(+)-Ketamine in Post-incisional Pain in Dogs: A Comparative Study

OBJECTIVE

To compare the pre-emptive analgesic effects of epidural ketamine or S(+)-ketamine on post-incisional hyperalgesia.

STUDY DESIGN

Prospective randomized study.

ANIMALS

Twenty-four mongrel dogs (1-5 years, weighing 11.9+/-1.8 kg).

METHODS

Dogs were anesthetized with propofol (5 mg/kg intravenously) and a lumbosacral epidural catheter was placed. Dogs were randomly allocated to 3 groups, each with 8 dogs. The control group (CG) was administered saline solution (0.3 mL/kg); the ketamine group (KG) ketamine (0.6 mg/kg); and the S(+)-ketamine group (SG) S(+)-ketamine (0.6 mg/kg). The final volume was adjusted to 0.3 mL/kg in all groups. Five minutes after the epidural injection a surgical incision was made in the common pad of the right hind limb and was immediately closed with simple interrupted nylon suture. Respiratory (RR) and heart (HR) rates, rectal temperature (T), sedation (S), lameness score, and mechanical nociceptive threshold by von Frey filaments were evaluated before the propofol anesthesia and at 15, 30, 45, 60, 75, and 90 minutes and then at 2, 4, 6, 8, 12, and 24 hours after epidural injection.

RESULTS

There were no differences in RR, HR, T, or S between groups. Motor blockade of the hind limbs was observed during 20+/-3.6 minutes in KG and during 30.6+/-7.5 minutes in SG (mean+/-SD). Mechanical force applied to obtain an aversive response was higher from 45 minutes to 12 hours in KG and from 60 to 90 minutes in SG, when compared with CG.

CONCLUSIONS

Pre-emptive epidural ketamine induced no alterations in RR and HR, and reduced post-incisional hyperalgesia for a longer time than did S(+) ketamine.

CLINICAL RELEVANCE

Although anesthetic and analgesic potency of S(+) ketamine is twice that of ketamine, the racemic form is seemingly better for post-incisional hyperalgesia.

Activation of peripheral NMDA receptors contributes to human pain and rat afferent discharges evoked by injection of glutamate into the masseter muscle

Peripheral N-methyl-d-aspartate (NMDA) receptors are found in deep tissues and may play a role in deep tissue pain. Injection of the endogenous NMDA receptor agonist glutamate into the masseter muscle excites deep craniofacial afferent fibers in rats and evokes pain in human subjects. It is not clear whether peripheral NMDA receptors play a role in these effects of glutamate. Accordingly, the effect of NMDA on afferent activity as well as the effect of locally administered NMDA receptor antagonists on glutamate-evoked afferent discharges in acutely anesthetized rats and muscle pain in human subjects was examined. Injection of NMDA into the masseter muscle evoked afferent discharges in a concentration-related manner. It was found that the NMDA receptor antagonists 2-amino-5-phosphonvalerate (APV, 10 mM), ketamine (10 mM), and dextromethorphan (40 mM) significantly decreased glutamate-evoked afferent discharges. The effects of APV and ketamine, but not dextromethorphan, were selective for glutamate-evoked afferent discharges and did not affect hypertonic saline-evoked afferent discharges. In human experiments, it was found that 10 mM ketamine decreased glutamate-evoked muscle pain but had no effect on hypertonic saline-evoked muscle pain. These results indicate that injection of glutamate into the masseter muscle evokes afferent discharges in rats and muscle pain in humans in part through activation of peripheral NMDA receptors. It is conceivable that activation of peripheral NMDA receptors may contribute to masticatory muscle pain and that peripherally acting NMDA receptor antagonists could prove to be effective analgesics for this type of pain.

Nonopioid additives to local anaesthetics for caudal blockade in children: a systematic review

BACKGROUND

Caudal epidural injection with local anaesthetics is a popular regional technique used in infants and children. A disadvantage of caudal blockade is the relatively short duration of postoperative analgesia. Opioids have traditionally been added to increase the duration of analgesia but have been associated with unacceptable side-effects. A number of nonopioid additives have been suggested to increase the duration of analgesia.

METHODS

A systematic review was conducted to identify randomized control trials comparing the use of local anaesthetic to local anaesthetic with nonopioid additives for caudal blockade in children. The increase in duration of analgesia and side-effects were compared.

RESULTS

The addition of clonidine to the local anaesthetic solution produces an increase in the duration of analgesia following caudal blockade in children (pooled weighted mean difference of 145 min with 95% confidence interval of 132-157 min). Side-effects include sedation and the potential for neonatal respiratory depression. Ketamine and midazolam further increase the duration of analgesia, however, the potential for neurotoxicity remains a concern.

CONCLUSION

The evidence examined shows an increased duration of analgesia with clonidine, ketamine and midazolam. However, we are not convinced that the routine use of these adjuvants in the setting of elective outpatient surgery shows improved patient outcome. It is unclear if the potential for neurotoxicity is outweighed by clinical benefits. Further testing, including large clinical trials, is required before recommending routine use of nonopioid additives for caudal blockade in children.

Peripheral antihyperalgesic and analgesic actions of ketamine and amitriptyline in a model of mild thermal injury in the rat

In this study, we examined antihyperalgesic and analgesic actions after local peripheral administration of ketamine and amitriptyline in a rat model of mild thermal injury. Exposure of the hindpaw to 52 degrees C for 45 s under anesthesia produced a subsequent thermal hyperalgesia lasting at least 2 h. The local peripheral administration of ketamine (100-1000 nmol) 15 min before the thermal injury produced an antihyperalgesic effect when injected into the ipsilateral paw, whereas amitriptyline produced both antihyperalgesic (300 nmol) and analgesic (1000 nmol) effects. Administered after the thermal injury, ketamine had no effect, whereas amitriptyline retained its analgesic but not its antihyperalgesic effect. Amitriptyline (300 and 1000 nmol) produced an analgesic action when administered into the normal nonsensitized hindpaw. Both drugs increase paw volume, particularly at larger doses; biogenic amines are not involved in the action of amitriptyline, as was shown previously for ketamine. These results indicate that (a) ketamine produces antihyperalgesia, but not analgesia, when administered locally with a mild thermal injury model; (b) amitriptyline produces both antihyperalgesia and analgesia when administered locally; and (c) the increase in paw volume produced by these drugs occurs by different mechanisms.

IMPLICATIONS

This study examines the pain-relieving properties of the local peripheral administration of ketamine and amitriptyline, two drugs in current clinical use, in a thermal injury model of hyperalgesia and demonstrates both antihyperalgesic and analgesic properties. These observations provide support for their potential use as local (e.g., topical) analgesics.

Evaluation of the local analgesic effect of ketamine in the palmar digital nerve block at the base of the proximal sesamoid (abaxial sesamoid block) in horses

OBJECTIVE

To evaluate the local analgesic effect of ketamine in a palmar digital nerve block at the base of the proximal sesamoid (abaxial sesamoid block) in horses.

ANIMALS

36 mature healthy Andalusian horses.

PROCEDURE

Horses were randomly assigned to 4 groups of 9 horses each and received an abaxial sesamoid block in a randomly chosen forelimb with 1 of the following: saline (0.9% NaCl) solution, 1% ketamine solution, 2% ketamine solution, or 3% ketamine solution. To determine analgesia, the radiant heat lamp-hoof withdrawal model was used as a noxious thermal stimulus. Before each nerve block, baseline hoof withdrawal reflex latency (HWRL, time between lamp illumination and withdrawal of the hoof) was determined; after the nerve block, local analgesic effects were determined by measuring HWRL at 2 and 5 minutes after injection and then every 5 minutes for a total period of 1 hour.

RESULTS

Significant differences in HWRL were found between baseline values and values at 2 to 15 minutes following a nerve block with ketamine. Significant differences were found between HWRL values at every time point from 2 to 10 minutes following a nerve block with saline solution, compared with 1 or 2% ketamine solution. Similarly, significant differences were found between HWRL values at every time point from 2 to 15 minutes following a nerve block with saline solution, compared with 3% ketamine solution.

CONCLUSIONS AND CLINICAL RELEVANCE

Abaxial sesamoid block with ketamine ensures adequate analgesia in horses with an onset of action of 2 minutes and a maximal duration of action of 15 minutes.

Blockade of voltage-operated neuronal and skeletal muscle sodium channels by S(+)- and R(-)-ketamine

Besides its general anesthetic effect, ketamine has local anesthetic-like actions. We studied the voltage- and use-dependent interaction of S(+)- and R(-)-ketamine with two different isoforms of voltage-operated sodium channels, with a special emphasis on the difference in affinity between resting and inactivated channel states. Rat brain IIa and human skeletal muscle sodium channels were heterologously expressed in human embryonic kidney 293 cells. S(+)- and R(-)-ketamine reversibly suppressed whole-cell sodium inward currents; the 50% inhibitory concentration values at -70 mV holding potential were 240 +/- 60 microM and 333 +/- 93 microM for the neuronal isoform and 59 +/- 10 microM and 181 +/- 49 microM for the skeletal muscle isoform. S(+)-ketamine was significantly more potent than R(-)-ketamine in the skeletal muscle isoform only. Ketamine had a higher affinity to inactivated than to resting channels. However, the estimated difference in affinity between inactivated and resting channels was only 8- to 10-fold, and the time course of drug equilibration between inactivated and resting channels was too fast to cause use-dependent block at 10 Hz up to a concentration of 300 microM. These results suggest that ketamine is less effective than lidocaine-like local anesthetics in stabilizing the inactivated channel state.

IMPLICATIONS

Blockade of sodium channels by ketamine shows voltage dependency, an important feature of local anesthetic action. However, ketamine is less effective than lidocaine-like local anesthetics in stabilizing the inactivated state. Because it does not elicit phasic blockade at small concentrations, its ability to reduce the firing frequency of action potentials may be small.

Effects of ketamine on exocytotic and non-exocytotic noradrenaline release

To characterise ketamine-induced sympathomimetic action, we examined the effects of ketamine on in vivo cardiac sympathetic nerve endings function. Using adult cats given anaesthesia with pentobarbital, dialysis probes were implanted in the left ventricular myocardium and dialysate noradrenaline (NA) concentrations were measured as an indicator of NA output at the cardiac sympathetic nerve endings. Ketamine was locally administered through the dialysis probe, and dialysate NA responses were obtained in the following conditions. (1) In the resting state, ketamine (10 mM) increased dialysate NA concentration. This increase in dialysate NA was not altered by addition of omega-conotoxin GVIA (N-type Ca(2+) channel blocker) or desipramine (membrane NA uptake blocker). (2) Sympathetic activation by electrical stimulation of the stellate ganglia (ES-SG; exocytotic NA release): ES-SG caused an increase in dialysate NA, which was further augmented by addition of desipramine. During co-administration of desipramine and ketamine, dialysate NA response to ES-SG was smaller than with desipramine alone. Further, there was no significant difference in the dialysate NA response to ES-SG between ketamine and ketamine + desipramine. These data suggested that both exocytosis and NA uptake function were impaired by ketamine. (3) Non-exocytotic NA release by ouabain: ouabain caused increases in dialysate NA. These increases in dialysate NA were suppressed by ketamine, which impaired the membrane outward NA transport evoked by ouabain. We conclude that ketamine impaired exocytotic and non-exocytotic NA release. However, ketamine spontaneously evoked NA efflux that was independent of exocytosis and insensitive to NA transporter.

S(+)-ketamine attenuates myogenic motor-evoked potentials at or distal to the spinal alpha-motoneuron

We investigated the effect of S(+)-ketamine on spinal cord evoked potentials (ESCPs) and myogenic motor-evoked potentials after electrical stimulation of the motor cortex in a rabbit model. This study was designed to characterize the relationship between ESCP characteristics and corresponding changes in compound muscle action potentials (CMAPs) derived from fore and hind limbs. Direct (D) and indirect (I) corticospinal volleys (ESCP) from the upper and lower thoracic spinal cord, recorded by two bipolar epidural electrodes, were assessed during IV administration of 0.02, 0.05, 0.1, and 0.2 mg. kg(-1) x min(-1) of S(+)-ketamine, each before and after neuromuscular blockade (0.4 mg/kg of cisatracurium), in 16 New Zealand White rabbits after single-pulse bipolar electrical stimulation of the motor cortex at 50 (threshold), 60, and 70 V. CMAP amplitudes at fore and hind limbs were significantly suppressed (P < 0.01) during infusion at 0.1 and 0.2 mL x kg(-1) x min(-1), whereas neither corresponding D- nor I-waves were altered. Similar findings were obtained during variation of stimulus amplitude (50-70 V). Multivariate regression analysis of CMAP amplitudes and various ESCP characteristics demonstrated no apparent interparametric association. These findings indicate that S(+)-ketamine modulates CMAP independent from corticospinal D- and I-wave-mediated facilitation at or distal to the spinal alpha-motoneuron.

IMPLICATIONS

S(+)-Ketamine combines several anesthetic properties suitable for total IV neuroanesthesia, including minimal effects on neurophysiological monitoring. Recording of neural and myogenic responses after electrical stimulation of the motor cortex indicates that S(+)-ketamine modulates myogenic motor-evoked potentials by a peripheral mechanism at or distal to the spinal alpha-motoneuron.

Enhancement of delayed-rectifier potassium conductance by low concentrations of local anaesthetics in spinal sensory neurones

Combining the patch-clamp recordings in slice preparation with the 'entire soma isolation' method we studied action of several local anaesthetics on delayed-rectifier K(+) currents in spinal dorsal horn neurones. Bupivacaine, lidocaine and mepivacaine at low concentrations (1 - 100 microM) enhanced delayed-rectifier K(+) current in intact neurones within the spinal cord slice, while exhibiting a partial blocking effect at higher concentrations (>100 microM). In isolated somata 0.1 - 10 microM bupivacaine enhanced delayed-rectifier K(+) current by shifting its steady-state activation characteristic and the voltage-dependence of the activation time constant to more negative potentials by 10 - 20 mV. Detailed analysis has revealed that bupivacaine also increased the maximum delayed-rectifier K(+) conductance by changing the open probability, rather than the unitary conductance, of the channel. It is concluded that local anaesthetics show a dual effect on delayed-rectifier K(+) currents by potentiating them at low concentrations and partially suppressing at high concentrations. The phenomenon observed demonstrated the complex action of local anaesthetics during spinal and epidural anaesthesia, which is not restricted to a suppression of Na(+) conductance only.

Caudal clonidine prolongs analgesia from caudal S(+)-ketamine in children

We performed a prospective randomized double-blinded study to test preservative-free S(+)-ketamine alone or in combination with clonidine for intra- and postoperative caudal blockade in pediatric surgery over a 24-h period. Fifty-three children (1-72 mo) scheduled for inguinal hernia repair were caudally injected with either S(+)-ketamine 1 mg/kg alone (Group K) or with additional clonidine (Group C1 = 1 microg/kg; Group C2 = 2 microg/kg) during sevoflurane anesthesia via a laryngeal mask. Intraoperative monitoring included heart rate, blood pressure, and pulse oximetry; postoperative monitoring included a pain discomfort scale and a sedation score. No additional analgesic drugs were required during surgery. The mean duration of postoperative analgesia was 13.3 +/- 9.2 h in Group K, 22.7 +/- 3.5 h in Group C1, and 21.8 +/- 5.2 h in Group C2 (P < 0.0001, Group K versus other groups). Groups C1 and C2 received significantly fewer analgesics in the postoperative period than Group K (15% and 18% vs 63%; P < 0.01). The three groups had similar postoperative sedation scores. We conclude that the combination of S(+)-ketamine 1 mg/kg with clonidine 1 or 2 microg/kg for caudal blockade in children provides excellent analgesia without side effects over a 24-h period.

IMPLICATIONS

Caudally administered preservative-free S(+)-ketamine combined with 1 or 2 microg/kg clonidine provides excellent perioperative analgesia in children and has minimal side effects.

Comparison of nerve conduction blocks by an opioid and a local anesthetic

The experiments were done on frog sciatic nerves, using a sucrose-gap recording technique. The aim of our study was to investigate and to compare the tonic and phasic conduction blocking potency of tramadol and lidocaine on whole nerve and their interactions with Ca(2+). The concentration of a tramadol solution producing the same amount of tonic and phasic conduction blocks was three and six times higher than that needed for lidocaine, respectively. Increasing the Ca(2+) concentration in the test solution enhanced the conduction blocking potency of tramadol, but decreased that of lidocaine. It is concluded that tramadol blocks nerve conduction like a local anesthetic but with a weaker effect than that of lidocaine. Interactions of Ca(2+) and these drugs suggested that these drugs might have either different binding sites or different action mechanisms.

Ketamine blockage of both tetrodotoxin (TTX)-sensitive and TTX-resistant sodium channels of rat dorsal root ganglion neurons

Ketamine, a general anesthetic, has been reported to block sodium channels. Two types of Na(+) channels, tetrodotoxin (TTX)-sensitive (TTX-s) and TTX-resistant (TTX-r), are expressed in dorsal root ganglion (DRG) neurons. The present study was to investigate the effects of ketamine on both types, particularly on TTX-r channels, using whole-cell patch-clamp recordings in dissociated rat DRG neurons. In addition to confirming ketamine-induced blockage of TTX-s Na(+) current, we showed for the first time that ketamine blocked TTX-r Na(+) channels on small DRG neurons in dose-dependent and use-dependent manner. Half-maximal inhibitory concentration (IC(50)) was 866.2 microM for TTX-r Na(+) channels. TTX-r Na(+) channels were more sensitive to ketamine in inactivated state (IC(50) = 314.8 microM) than in resting state (IC(50) = 866.2 microM). IC(50) was 146.7 microM for TTX-s Na(+) current. Activation and inactivation properties of both TTX-s and TTX-r Na(+) channels were affected by ketamine. Since TTX-r Na(+) channels were preferentially expressed in small DRG neurons known as nociceptors, blockage of TTX-r Na(+) channels by ketamine may result in reducing nociceptive signals conducting to the spinal cord. Moreover, both TTX-r and TTX-s Na(+) channels would be non-selectively blocked by ketamine at high concentration, suggesting that the high dose of ketamine might produce an action of local anesthesia.

Patch-clamp analysis of anesthetic interactions with recombinant SK2 subtype neuronal calcium-activated potassium channels

Small conductance calcium-activated potassium channels (SK) mediate spike frequency adaptation and underlie the slow afterhyperpolarization in central neurons. We tested the actions of several anesthetics on the SK2 subtype of recombinant SK channels, cloned from rat brain and functionally expressed in a mammalian cell line. Butanol, ethanol, ketamine, lidocaine, and methohexital blocked recombinant SK2 channel currents, measured in the whole-cell patch clamp recording mode. The block was reversible, dose-dependent, and of variable efficacy. The inhaled anesthetics chloroform, desflurane, enflurane, halothane, isoflurane, and sevoflurane produced little or no block when applied at 1 minimum alveolar anesthetic concentration; varying degrees of modulation were observed at very large concentrations (10 minimum alveolar concentration). The extent of block by inhaled anesthetics did not appear to depend on concentration or membrane voltage.

IMPLICATIONS

We describe differential effects of anesthetics on cloned small conductance calcium-activated potassium channels from brain that may play a role in generating the effects or side effects of anesthetics.