Effects of propofol and sevoflurane on the excitability of rat spinal motoneurones and nociceptive reflexes in vitro

Nicardipine constant rate infusion alleviates the cardiovascular effects of dexmedetomidine infusions without affecting the minimal alveolar concentration in sevoflurane-anesthetized dogs

Two randomized crossover trials evaluated the effects of nicardipine constant rate infusion (CRI) on 1) the anesthetic potency of sevoflurane and 2) the ability to attenuate dexmedetomidine-induced cardiovascular depression in anesthetized dogs. First, six healthy Beagle dogs weighing 11.7 ± 0.9 kg were allocated to one of three treatments that administered a CRI of carrier (saline) or dexmedetomidine 0.5 or 3.0 μg/kg/h following a loading dose. The minimum alveolar concentration (MAC) of sevoflurane was determined utilizing electric stimuli before and after the loading dose of nicardipine (20 μg/kg intravenously for 10 min), followed by CRI at 40 μg/kg/h with 60 min of equilibration. Subsequently, cardiovascular and blood gas variables were evaluated in another trial under sevoflurane anesthesia at the individual 1.5 MAC. After baseline measurements, the dogs were assigned to two treatments (dexmedetomidine CRI at 0.5 or 3.0 μg/kg/h following a loading dose) with sevoflurane doses adjusted to 1.5 times of MAC equivalent, and the measurements were repeated every 15 min for 120 min. After 60 min, nicardipine CRI at 40 μg/kg/h with a loading dose was added to the dexmedetomidine CRI. Dexmedetomidine infusions significantly decreased the sevoflurane MAC but nicardipine did not significantly alter the MAC either with or without dexmedetomidine CRI in dogs. Dexmedetomidine dose-dependently decreased the cardiac index and increased the systemic vascular resistance index; these effects were fully counteracted by concomitant nicardipine CRI. Nicardipine CRI can be useful for controlling the cardiovascular depression elicited by dexmedetomidine in anesthetized dogs without affecting the anesthetic potency of sevoflurane.

Chronic outpatient treatment with topical sevoflurane in patients with vascular ulcers

OBJECTIVE

To show the effectiveness and safety of topical sevoflurane after ambulatory and prolonged administration in patients with refractory vascular ulcers.

METHODS

Retrospective observational study analyzing clinical improvement and vascular ulcers surface area variation after topical application of sevoflurane. Inclusion criteria were patients with painful vascular ulcers refractory to usual therapies and who were treated with topical sevoflurane for at least 36 months. The following variables were collected: age, sex, medical history, associated comorbidity, ulcer etiology and medical treatment. The visual analog scale was used to measure baseline and break through pain intensity before and after treatment.

RESULTS

Nine patients met the inclusion criteria of the total number of patients treated whose median age was 74.8 ± 7.5 years. Cases 2 and 9 died during follow-up. In all cases, the analgesic action of topical sevoflurane was rapid (3.1 ± 2.1 minutes), intense (visual analog scale: 7 ± 1.1 to 1.4 ± 1.1 points) and long-lasting (6 to 24 h). With the exception of case 4, all patients experienced a large reduction in vascular ulcers surface area (15.1 ± 5.0 a 2.7 ± 4.2) and tolerance was not observed over time.

CONCLUSION

Topical application of sevoflurane is an analgesic and re-epithelializing strategy for vascular ulcers with a successful safety profile.

Impact of inhalational anesthetic agents on the baseline monitorability of motor evoked potentials during spine surgery: a review of 22,755 cervical and lumbar procedures

BACKGROUND CONTEXT

During spine surgery, motor evoked potentials (MEPs) are often utilized to monitor both spinal cord function and spinal nerve root or plexus function. While there are reports evaluating the impact of anesthesia on the ability of MEPs to monitor spinal cord function, less is known about the impact of anesthesia on the ability of MEPs to monitor spinal nerve root and plexus function.

PURPOSE

To compare the baseline monitorability and amplitude of MEPs during cervical and lumbar procedures between two cohorts based on the maintenance anesthetic regimen: a total intravenous anesthesia (TIVA) versus a regimen balanced with volatile inhalational and intravenous agents.

STUDY DESIGN

Baseline MEP data from a total of 16,559 cervical and 6,196 lumbar extradural spine procedures utilizing multimodality intraoperative neuromonitoring (IONM) including MEPs between January 2017 and March 2020 were obtained from a multi-institutional database. Two cohorts for each region of spine surgery were delineated based on the anesthetic regimen: a TIVA cohort and a Balanced anesthesia cohort.

PATIENT SAMPLE

Age 18 and older. Fellowship support for 65,000 for year 2021.

OUTCOME MEASURES

Percent monitorability and amplitudes of baseline MEPs.

METHODS

The baseline monitorability of each muscle MEP was evaluated by the IONM team in real-time and recorded in the patient's electronic medical record. The relation between anesthetic regimen and baseline monitorability was estimated using mixed effects logistic regression, with distinct models for cervical and lumbar procedures. Subsets of cervical and lumbar procedures from each anesthesia cohort in which all MEPs were deemed monitorable were randomly selected and the average peak-to-trough amplitude of each muscle MEP was retrospectively measured. Mixed-effects linear regression models were estimated (one each for cervical and lumbar procedures) to assess possible differences in average amplitude associated with anesthesia regimen.

RESULTS

At the time of surgery, baseline MEPs were reported monitorable from all targeted muscles in 86.8% and 83.0% of cervical and lumbar procedures, respectively, for the TIVA cohort, but were reported monitorable in just 59.3% and 61.0% of cervical and lumbar procedures, respectively, in the Balanced cohort, yielding disparities of 27.5% and 22.0%, respectively. The model-adjusted monitorability disparity between cohorts for a given muscle MEP ranged from 0.2% to 16.6% but was smallest for distal intrinsic hand and foot muscle MEPs (0.2%-1.1%) and was largest for proximal muscle MEPs (deltoid: 10.8%, biceps brachii: 8.8%, triceps: 13.0%, quadriceps: 16.6%, gastrocnemius: 7.8%, and tibialis anterior: 3.7%) where the monitorability was significantly decreased in the Balanced cohort relative to the TIVA cohort (p<.0001). Relative to the TIVA cohort, the model-adjusted amplitude of an MEP in the Balanced cohort was smaller for all muscles measured, ranging from 27.5% to 78.0% smaller. Relative to the TIVA cohort, the model-adjusted amplitude of an MEP was significantly decreased (p<.01) in the Balanced cohort for the most proximal muscles (Percent smaller: deltoid: 74.3%, biceps: 78.0%, triceps: 54.9%, quadriceps: 54.8%).

CONCLUSIONS

TIVA is the preferred anesthetic regimen for optimizing MEP monitoring during spine surgery. Inhalational agents significantly decrease MEP monitorability and amplitudes for most muscles, and this effect is especially pronounced for proximal limb muscles such as the deltoid, biceps, triceps, and quadriceps.

Topical Sevoflurane: A Novel Treatment for Chronic Pain Caused by Venous Stasis Ulcers

In the US, an estimated 1 - 2% of chronic venous insufficiency (CVI) patients (of 6 - 7 million nationwide) develop at least one venous stasis ulcer (VSU) during their illness. Of these, approximately 40% develop subsequent ulcers, making VSU prognostically poor. Current management of VSU is costly, with poor prognosis, high recurrence rate, inadequate pain management, and significantly reduced quality of life (QoL). Topical volatile anesthetic agents, such as sevoflurane, offer improved pain relief and symptom control in patients suffering from chronic VSU. The immediate impact of topical sevoflurane in reducing pain associated with ulcer bed debridement has several implications in improving the quality of life in patients with CVI induced ulcers and in the prognosis and healing of the ulcers. This review summarizes a topical formulation of a volatile anesthetic and its implications for the management of VSUs.

Do Small Incisions Need Only Minimal Anesthesia?-Anesthetic Management in Laparoscopic and Robotic Surgery

Laparoscopic techniques have established themselves as a major part of modern surgery. Their implementation in every surgical discipline has played a vital part in the reduction of perioperative morbidity and mortality. Precise robotic surgery, as an evolution of this, is shaping the present and future operating theatre that an anesthetist is facing. While incisions get smaller and the impact on the organism seems to dwindle, challenges for anesthetists do not lessen and could even become more demanding than in open procedures. This review focuses on the pathophysiological effects of contemporary laparoscopic and robotic procedures and summarizes anesthetic challenges and strategies for perioperative management.

Effect of caudal ketamine on minimum local anesthetic concentration of ropivacaine in children: a prospective randomized trial

Background

Caudal ketamine has been shown to provide an effective and prolonged post-operative analgesia with few adverse effects. However, the effect of caudal ketamine on the minimum local anesthetic concentration (MLAC) of ropivacaine for intra-operative analgesia is unclear.

Methods

One hundred and sixty-nine children were randomized to five groups: Group C (caudal ropivacaine only), Group K_0.25 (caudal ropivacaine plus 0.25 mg/kg ketamine), Group K_0.5 (caudal ropivacaine plus 0.5 mg/kg ketamine), Group K_0.75 (caudal ropivacaine plus 0.75 mg/kg ketamine), and Group K_1.0 (caudal ropivacaine plus 1.0 mg/kg ketamine). The primary outcome was the MLAC values of ropivacaine with/without ketamine for caudal block.

Results

The MLAC values of ropivacaine were 0.128% (0.028%) in the control group, 0.112% (0.021%) in Group K_0.25, 0.112% (0.018%) in Group K_0.5, 0.110% (0.019%) in Group K_0.75, and 0.110% (0.020%) in Group K_1.0. There were no significant differences among the five groups for the MLAC values (p = 0.11). During the post-operative period the mean durations of analgesia were 270, 381, 430, 494, and 591 min in the control, K_0.25, K_{0. 5}, K_0.75, and K_1.0 groups respectively, which shown that control group is significantly different from all ketamine groups. Also there were significant differences between K_0.25 and K_0.75 groups, and between K_1.0 groups and the other ketamine groups.

Conclusions

Adding caudal ketamine to ropivacaine prolong the duration of post-operative analgesia; however, it does not decrease the MLAC of caudal ropivacaine for intra-operative analgesia in children.

Clinical trial registration

ChiCTR-TRC-13003492. Registered on 13 August 2013.

Effects of constant rate infusions of dexmedetomidine, remifentanil and their combination on minimum alveolar concentration of sevoflurane in dogs

OBJECTIVE

To evaluate the effects of constant rate infusions (CRIs) of dexmedetomidine and remifentanil alone and their combination on minimum alveolar concentration (MAC) of sevoflurane in dogs.

STUDY DESIGN

Randomized crossover experimental study.

ANIMALS

A total of six (three males, three females) healthy, adult neutered Beagle dogs weighing 12.6 ± 1.4 kg.

METHODS

Anesthesia was induced with sevoflurane in oxygen until endotracheal intubation was possible and anesthesia maintained with sevoflurane using positive-pressure ventilation. Each dog was anesthetized five times and was administered each of the following treatments: saline (1 mL kg^-1 hour^-1) or dexmedetomidine at 0.1, 0.5, 1.0 or 5.0 μg kg^-1 loading dose intravenously over 10 minutes followed by CRI at 0.1, 0.5, 1.0 or 5.0 μg kg^-1 hour^-1, respectively. Following 60 minutes of CRI, sevoflurane MAC was determined in duplicate using an electrical stimulus (50 V, 50 Hz, 10 ms). Then, CRI of successively increasing doses of remifentanil (0.15, 0.60 and 2.40 μg kg^-1 minute^-1) was added to each treatment. MAC was also determined after 30 minutes equilibration at each remifentanil dose. Isobolographic analysis determined interaction from the predicted doses required for a 50% MAC reduction (ED₅₀) with remifentanil, dexmedetomidine and remifentanil combined with dexmedetomidine, with the exception of dexmedetomidine 5.0 μg kg^-1 hour^-1, obtained using log-linear regression analysis.

RESULTS

The sevoflurane MAC decreased dose-dependently with increasing infusion rates of dexmedetomidine and remifentanil. Remifentanil ED₅₀ values were lower when combined with dexmedetomidine than those obtained during saline-remifentanil. Synergistic interactions between dexmedetomidine and remifentanil for MAC reduction occurred with dexmedetomidine at 0.5 and 1.0 μg kg^-1 hour^-1.

CONCLUSIONS AND CLINICAL RELEVANCE

Combined CRIs of dexmedetomidine and remifentanil synergistically resulted in sevoflurane MAC reduction. The combination of dexmedetomidine and remifentanil effectively reduced the requirement of sevoflurane during anesthesia in dogs.

Effect of anesthesia on motor responses evoked by spinal neural prostheses during intraoperative procedures

OBJECTIVE

The overall goal of this study was to investigate the effects of various anesthetic protocols on the intraoperative responses to intraspinal microstimulation (ISMS). ISMS is a neuroprosthetic approach that targets the motor networks in the ventral horns of the spinal cord to restore function after spinal cord injury. In preclinical studies, ISMS in the lumbosacral enlargement produced standing and walking by activating networks controlling the hindlimb muscles. ISMS implants are placed surgically under anesthesia, and refinements in placement are made based on the evoked responses. Anesthesia can have a significant effect on the responses evoked by spinal neuroprostheses; therefore, in preparation for clinical testing of ISMS, we compared the evoked responses under a common clinical neurosurgical anesthetic protocol with those evoked under protocols commonly used in preclinical studies.

APPROACH

Experiments were conducted in seven pigs. An ISMS microelectrode array was implanted in the lumbar enlargement and responses to ISMS were measured under three anesthetic protocols: (1) isoflurane, an agent used pre-clinically and clinically, (2) total intravenous anesthesia (TIVA) with propofol as the main agent commonly used in clinical neurosurgical procedures, (3) TIVA with sodium pentobarbital, an anesthetic agent used mostly preclinically. Responses to ISMS were evaluated based on stimulation thresholds, movement kinematics, and joint torques. Motor evoked potentials (MEP) and plasma concentrations of propofol were also measured.

MAIN RESULTS

ISMS under propofol anesthesia produced large and functional responses that were not statistically different from those produced under pentobarbital anesthesia. Isoflurane, however, significantly suppressed the ISMS-evoked responses.

SIGNIFICANCE

This study demonstrated that the choice of anesthesia is critical for intraoperative assessments of motor responses evoked by spinal neuroprostheses. Propofol and pentobarbital anesthesia did not overly suppress the effects of ISMS; therefore, propofol is expected to be a suitable anesthetic agent for clinical intraoperative testing of an intraspinal neuroprosthetic system.

Healing of chronic venous ulcer with topical sevoflurane

The present study assesses the efficacy and safety of topical sevoflurane in chronic venous ulcers and its impact on analgesia and healing. This retrospective study included 30 patients older than 65 years with painful refractory chronic venous ulcers. Patients were treated with topical sevoflurane prior to the usual ulcer cleaning every 2 days for a period of 1 month. Treatment was initiated with a saline solution, followed by direct irrigation of 1 ml of liquid sevoflurane over the wound size, which was measured as cm2 . Sevoflurane had a fast, intense and long-lasting analgesic effect. Latency time ranged from 2 to 7 minutes (3·9 ± 1·5 minutes), and duration varied from 8 to 18 hours (12 ± 2·9). The mean ulcer size was 8·4 ± 9·7 cm2 . There was a progressive decrease in size in all patients, with a mean size of 4·2 ± 5·4 cm2 at the end of the study. There were no adverse systemic effects. Local adverse effects were mild and transient, including pruritus, erythema and heat. Topical sevoflurane is a new, efficient and safe therapeutic alternative in painful chronic venous ulcers, refractory to usual analgesic treatment. It can improve the ulcer-healing process that shortens the cicatrisation period.

Propofol Protects Rat Hypoglossal Motoneurons in an In Vitro Model of Excitotoxicity by Boosting GABAergic Inhibition and Reducing Oxidative Stress

In brainstem motor networks, hypoglossal motoneurons (HMs) play the physiological role of driving tongue contraction, an activity critical for inspiration, phonation, chewing and swallowing. HMs are an early target of neurodegenerative diseases like amyotrophic lateral sclerosis that, in its bulbar form, is manifested with initial dysphagia and dysarthria. One important pathogenetic component of this disease is the high level of extracellular glutamate due to uptake block that generates excitotoxicity. To understand the earliest phases of this condition we devised a model, the rat brainstem slice, in which block of glutamate uptake is associated with intense bursting of HMs, dysmetabolism and death. Since blocking bursting becomes a goal to prevent cell damage, the present report enquired whether boosting GABAergic inhibition could fulfill this aim and confer beneficial outcome. Propofol (0.5 µM) and midazolam (0.01 µM), two allosteric modulators of GABA_A receptors, were used at concentrations yielding analogous potentiation of GABA-mediated currents. Propofol also partly depressed NMDA receptor currents. Both drugs significantly shortened bursting episodes without changing single burst properties, their synchronicity, or their occurrence. Two hours later, propofol prevented the rise in reactive oxygen species (ROS) and, at 4 hours, it inhibited intracellular release of apoptosis-inducing factor (AIF) and prevented concomitant cell loss. Midazolam did not contrast ROS and AIF release. The present work provides experimental evidence for the neuroprotective action of a general anesthetic like propofol, which, in this case, may be achieved through a combination of boosted GABAergic inhibition and reduced ROS production.

Pain, Quality of Life, and Functional Capacity With Topical Sevoflurane Application for Chronic Venous Ulcers: A Retrospective Clinical Study

Introduction

Chronic venous ulcers (CVU) commonly have poorly controlled pain.

Report

Thirty patients older than 65 years of age with painful CVU were reviewed. At the initial visit, cleaning without sevoflurane was performed. Cleaning visits with sevoflurane every 2 days for 1 month were scheduled. The results of subsequent treatment with sevoflurane at the first, second, seventh, and twelfth cleanings were analysed. Pain was measured using a visual analog scale (VAS), quality of life by the Charing Cross Venous Leg Ulcer Questionnaire, and functional capacity by the Barthel Index.

Discussion

Initial VAS was 8.8 ± 1.3 points and at the twelfth cleaning VAS was 0.8 ± 1 points (p = .001). Latency time ranged between 2 and 7 m and duration ranged between 8 and 18 h. It improved quality of life (83 ± 14 points before treatment vs. 50 ± 14 at the twelfth cleaning) and functional capacity (82 ± 13.3 before treatment vs. 91 ± 11.6 points at the twelfth cleaning) (p = .001). The safety profile was favourable with mild and self limited local cutaneous adverse effects, including pruritus, erythema, and heat. No systemic toxicity was detected. Topical sevoflurane may be a therapeutic alternative for painful CVU with a fast, intense, and long-lasting analgesic effect.

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

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

Spinal Reflexes and Windup In Vitro: Effects of Analgesics and Anesthetics

The spinal cord is the first relay center for nociceptive information. Following peripheral injury, the spinal cord sensitizes. A sign of spinal sensitization is the hyper-reflexia which develops shortly after injury and can be detected in the isolated spinal cord as a "memory of pain." In this context, it is easy to understand that many analgesic compounds target spinally located sites of action to attain analgesia. In vitro isolated spinal cord preparations have been used for a number of years, and experience on the effects of compounds of diverse pharmacological families on spinal function has accumulated. Recently, we have proposed that the detailed study of spinal segmental reflexes in vitro may produce data relevant to the evaluation of the analgesic potential of novel compounds. In this review, we describe the main features of segmental reflexes obtained in vitro and discuss the effects of compounds of diverse chemical nature and pharmacological properties on such reflexes. Our aim was to compare the different profiles of action of the compounds on segmental reflexes in order to extract clues that may be helpful for pharmacological characterization of novel analgesics.

Effects of centrally acting analgesics on spinal segmental reflexes and wind-up

BACKGROUND

The spinal cord is a prime site of action for analgesia. Here we characterize the effects of established analgesics on segmental spinal reflexes. The aim of the study was to look for the pattern of action or signature of analgesic effects on these reflexes.

METHODS

We used a spinal cord in vitro preparation of neonate mice to record ventral root responses to dorsal root stimulation. Pregabalin, clonidine, morphine and duloxetine and an experimental sigma-1 receptor antagonist (S1RA) were applied to the preparation in a cumulative concentration protocol. Drug effects on the wind-up produced by repetitive stimulation of C-fibres and on responses to single A- and C-fibre intensity stimuli were analysed.

RESULTS

All compounds produced a concentration-dependent inhibition of total spikes elicited by repetitive stimulation. Concentrations producing ∼50% reduction in this parameter were (in μM) clonidine (0.01), morphine (0.1), pregabalin (1), duloxetine (10) and S1RA (30). At these concentrations clonidine, pregabalin and S1RA had significant effects on the wind-up index and little depressant effects on responses to single stimuli. Morphine and duloxetine did not depress wind-up index and showed large effects on responses to single stimuli. None of the compounds had strong effects on the amplitude of the non-nociceptive monosynaptic reflex.

CONCLUSIONS

morphine and duloxetine had general depressant effects on spinal reflexes, whereas the effects of clonidine, pregabalin and S1RA appeared to be restricted to signals originated by strong repetitive activation of C-fibres. Results are discussed in the context of reported behavioural effects of the compounds studied.

Retrobulbar dexmedetomidine decreases the MLAC of ropivacaine in vitreoretinal surgery in children

PURPOSE

Dexmedetomidine can prolong the duration of local anesthetics, but the effect of retrobulbar dexmedetomidine on the potency of ropivacaine for retrobulbar block has not been investigated. Our study was designed to determine the effect of retrobulbar dexmedetomidine on ropivacaine for retrobulbar block in children.

METHODS

A group of 90 children aged 10-16 years scheduled for vitreoretinal surgery who received retrobulbar block were randomly assigned to 1 of 3 groups: group L (retrobulbar ropivacaine), group LD1 (ropivacaine plus 0.5 µg.kg-1 dexmedetomidine), or group LD2 (ropivacaine plus 1 µg.kg-1 dexmedetomidine). The minimum local anesthetic concentration (MLAC) was determined according to a Dixon-Massey protocol. The primary endpoint of the study was MLAC. Secondary outcomes were duration of postoperative analgesia, postoperative pain scores, dexmedetomidine side effects, and time to hospital discharge.

RESULTS

The MLAC values of retrobulbar ropivacaine were 0.314%, 0.259%, and 0.246% in groups L, LD1, and LD2, respectively. The median (interquartile range) durations of analgesia in the postoperative period were 66 (54-117), 89 (40-157), and 168 (120-194) minutes in groups L, LD1, and LD2, respectively (L vs LD1 or LD2, p&lt;0.05). Wake-up time was significantly increased in groups LD1 and LD2.

CONCLUSIONS

Retrobulbar dexmedetomidine reduces the MLAC values of ropivacaine and improves postoperative analgesia in children without any neurologic side effects.

Caudal dexmedetomidine decreases the required concentration of levobupivacaine for caudal block in pediatric patients: a randomized trial

BACKGROUND AND OBJECTIVES

Dexmedetomidine (D) can prolong the duration of local anesthetics, but the effect of caudal dexmedetomidine on the potency of levobupivacaine (L) for caudal block has not been investigated. This study was designed to determine the effect of caudal dexmedetomidine on levobupivacaine for caudal block in pediatric patients.

METHODS

Eighty-nine children scheduled for elective inguinal hernia repair or hydrocele were randomly assigned to one of the three groups: Group L (caudal levobupivacaine), Group LD1 (levobupivacaine plus 1 μg·kg(-1) dexmedetomidine), or Group LD2 (levobupivacaine plus 2 μg·kg(-1) dexmedetomidine). The primary endpoint was the minimum local anesthetic concentration (MLAC), which was determined using the Dixon up-and-down method. The secondary endpoints were the duration of analgesia and sedation.

RESULTS

The MLAC values (sd) of caudal levobupivacaine were 0.103 (0.01)%, 0.068 (0.02)%, and 0.055 (0.03)% in Groups L, LD1, and LD2, respectively. The values of EC50 and EC95 (95% CI) of caudal levobupivacaine from logistic regression analysis were 0.094 (0.083-0.105)% and 0.129 (0.1-0.159)%, 0.058 (0.044-0.072)% and 0.106 (0.067-0.144)%, and 0.046 (0.033-0.059)% and 0.091 (0.055-0.127)% in Groups L, LD1, and LD2, respectively. The mean durations of analgesia in the postoperative period were 141, 378, and 412 min in Groups L, LD1, and LD2, respectively (L vs LD1 or LD2, P < 0.001). The mean durations of sedation in both Groups LD1 and LD2 also were significantly prolonged, compared with Group L (P < 0.01).

CONCLUSIONS

Caudal dexmedetomidine reduces the MLAC values of levobupivacaine and improves postoperative analgesia in children without any neurological side effects.

Effects of sevoflurane postconditioning on cell death, inflammation and TLR expression in human endothelial cells exposed to LPS

Background

Sevoflurane is an anesthetic agent which also participates in protective mechanisms in sepsis, likely due to anti-inflammatory properties. A key tissue in sepsis is the endothelium, which expresses TLR2 and TLR4 receptors, known regulators of inflammatory mechanisms and potential therapeutic targets for this pathology. In this context, we explored the effect of sevoflurane postconditioning in an in vitro sepsis model.

Methods

Primary cultures of human umbilical vein endothelial cells were used for two different experiments. In the first set, cultures were placed in an airtight incubation chamber and exposed to different concentrations of sevoflurane (0,1,3 or 7% vol,) for 1 hour. In the second set, lipopolysaccharide from Escherichia coli 0111:B4 (1 μg/mL) was added to culture medium for 3 hours and cells were subsequently exposed to sevoflurane (0,1,3 or 7% vol,) for 1 hour as explained before. In both cases, cell viability was measured by MTT and Trypan blue assays, TLR2 and TLR4 expression were analyzed by flow cytometry, and TNFα and IL-6 levels were quantified in cell culture media by an immunoassay immediately after exposure, at 6 and 24 hours.

Results

Exposure to 3% sevoflurane decreased TLR2 at 24 hours and TLR4 at 6 and 24 hours (both p<0.05), whereas exposure to 7% decreased TLR4 expression at 6 hours (p<0.05). Both 3 and 7% sevoflurane decreased TNF-α and IL-6 levels at 24 hours (both p<0.05). In LPS-stimulated cultures, exposure to 3% sevoflurane was cytoprotective at 6 and 24 hours (p<0.05) compared with control, and decreased TLR2 and TLR4 expression at 24 hours (p<0.05); whereas 7% decreased TLR4 expression at 24 hours (p<0.05). Both 3% and 7% sevoflurane decreased TNF-α and IL-6 levels at 24 hours (both p<0.05).

Conclusions

Postconditioning with the halogenated anesthetic agent sevoflurane after LPS stimulation shows a cytoprotective effect in an in vitro model, decreasing cell death and reducing TLR2 and TLR4 expression as well as levels of the inflammatory mediators TNF-α and IL-6 in human endothelial cells.

Esmolol versus ketamine-remifentanil combination for early postoperative analgesia after laparoscopic cholecystectomy: a randomized controlled trial

PURPOSE

Controversy surrounds the optimal technique to moderate pain after laparoscopic cholecystectomy (LC). Opioid analgesics, sympatholytic drugs, and adjuvants, such as ketamine, have all been used. We compared esmolol with a combination of remifentanil plus ketamine in patients undergoing LC to determine the impact of these drugs on morphine requirements and pain control.

METHODS

Sixty American Society of Anesthesiologists physical status I-II patients undergoing LC and anesthetized with sevoflurane were randomized to one of two groups. Group E patients received a bolus of esmolol 0.5 mg·kg(-1) iv at induction followed by an infusion of 5-15 μg·kg(-1)·min(-1), and Group R-K patients received a bolus of ketamine 0.5 mg·kg(-1) iv and remifentanil 0.5 μg·kg(-1) iv at induction followed by a remifentanil infusion titrated over a range of 0.1-0.5 μg·kg(-1)·min(-1). All patients received paracetamol, dexketoprofen, and levobupivacaine via infiltration of laparoscopic port sites. After surgery, a predetermined bolus of morphine was administered according to a verbal numerical rating scale (VNRS) for pain intensity. The primary outcome of interest was postoperative morphine requirement.

RESULTS

Median consumption of morphine was higher in Group R-K than in Group E (5 mg [4-6] vs 0 mg [0-2], respectively; P < 0.001). In the postanesthesia care unit, patients in Group R-K had higher pain scores than patients in Group E (difference in maximum VNRS, -11; 95% confidence interval (CI), -19 to -3). The concentration of sevoflurane to maintain a bispectral index~40 was higher in Group E than in Group R-K (between-group difference 0.3%; 95% CI, 0.15 to 0.40). The incidence of postoperative nausea and vomiting was similar between the two groups.

CONCLUSION

Intraoperative esmolol infusion reduces morphine requirements and provides more effective analgesia compared with a combination of remifentanil-ketamine given by infusion in patients undergoing LC.

Effects of anesthetic propofol on release of amino acids from the spinal cord during visceral pain

As one of general anesthetics, propofol, has been used for surgical procedures of visceral organs. However, the mechanisms underlying the action of propofol on visceral nociception remain controversial. The aim of this study is to test whether the antinociception of systemic administration of propofol against visceral stimuli is related to the changes in release of excitatory and inhibitory amino acids in the spinal cord. The spinal microdialysis catheters were implanted subarachnoidally via the atlanto-occipital membrane in healthy SD rats. The rats received an intraperitoneal injection of acetic acid for visceral pain induction 10min after intraperitoneal pretreatment with vehicle or propofol (100mg/kg). The acetic acid-induced writhing assay was used to determine the degree of antinociception. Cerebrospinal fluid dialysate was collected by microdialysis from the spinal subarachnoid space before pretreatment and after visceral pain induction. Visceral pain-induced release of amino acids into the dialysate, including glutamate, aspartate, and γ-amino butyric acid was evaluated by measuring the changes in the concentrations of these amino acids. Acetic acid increased release of aspartate and glutamate, and decreased release of γ-amino butyric acid in the cerebrospinal fluid as measured by microdialysis. Pretreatment with propofol significantly decreased writhing responses induced by visceral pain, suppressed the visceral pain-induced aspartate and glutamate release, and reversed the decreased release of γ-amino butyric acid in the cerebrospinal fluid. These data provide evidence for a potential mechanism for the antinociceptive effects of propofol on visceral nociception.

Sevoflurane for central catheter placement in neonatal intensive care: a randomized trial

OBJECTIVE

To compare the efficacy and safety of sevoflurane deep sedation with glucose and nonnutritive sucking (GNNS) in reducing the duration of the procedure and in preventing pain-related effects during peripherally inserted central catheter (PICC) placement.

BACKGROUND

PICC placement in neonatal intensive care is a delicate and stressful procedure that requires pain prevention. GNNS has been recommended in this situation but remain often inefficient.

METHODS

We designed a randomized controlled study in a sixteen-bed pediatric and neonatal unit in a tertiary hospital. Fifty-nine neonates at >28 weeks of gestation with continuous positive airway pressure or invasive mechanical ventilation and requiring PICC placement were included. Patients were randomized to receive inhaled sevoflurane (IS) or glucose and non-nutritive sucking (GNNS). Procedural duration and conditions, hemodynamic and respiratory parameters, occurrence of movements and complications were compared (http://clinicaltrials.gov trial register no. NCT00420693).

RESULTS

The two groups had similar demographics. There were no between-group differences in procedural duration (P = 0.84) despite greater immobility in IS group (P = 0.017). IS was also associated with fewer episodes of hypertension (P = 0.003), tachycardia (P < 0.001), and bradycardia (P = 0.02). Occurrences of hypotension were not different between the groups (P = 0.06). The GNNS group showed more desaturation during the 4 h after the procedure (P = 0.03). Complications during intensive care stay did not differ between groups.

CONCLUSION

Inhaled sevoflurane does not make easier catheters placement but prevent pain-related symptoms. Because sevoflurane is responsible for hypotension, it requires careful monitoring and treatment adaptation.

Effects of general anesthetics on visceral pain transmission in the spinal cord

Current evidence suggests an analgesic role for the spinal cord action of general anesthetics; however, the cellular population and intracellular mechanisms underlying anti-visceral pain by general anesthetics still remain unclear. It is known that visceral nociceptive signals are transmited via post-synaptic dorsal column (PSDC) and spinothalamic tract (STT) neuronal pathways and that the PSDC pathway plays a major role in visceral nociception. Animal studies report that persistent changes including nociception-associated molecular expression (e.g. neurokinin-1 (NK-1) receptors) and activation of signal transduction cascades (such as the protein kinase A [PKA]-c-AMP-responsive element binding [CREB] cascade)-in spinal PSDC neurons are observed following visceral pain stimulation. The clinical practice of interruption of the spinal PSDC pathway in patients with cancer pain further supports a role of this group of neurons in the development and maintenance of visceral pain. We propose the hypothesis that general anesthetics might affect critical molecular targets such as NK-1 and glutamate receptors, as well as intracellular signaling by CaM kinase II, protein kinase C (PKC), PKA, and MAP kinase cascades in PSDC neurons, which contribute to the neurotransmission of visceral pain signaling. This would help elucidate the mechanism of antivisceral nociception by general anesthetics at the cellular and molecular levels and aid in development of novel therapeutic strategies to improve clinical management of visceral pain.

Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors participate in the analgesic but not hypnotic effects of emulsified halogenated anaesthetics

The present study was designed to investigate the role of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in hypnosis and analgesia induced by emulsified inhalation anaesthetics. After having established the mice model of hypnosis and analgesia by intraperitoneally injecting appropriate doses of emulsified enflurane, isoflurane or sevoflurane, we intracerebroventricularly or intrathecally injected different doses of AMPA and then observed the effects on the sleep time using hypnosis test and the tail-withdrawal latency using the tail-withdrawal test. In hypnosis test, AMPA (50, 75 and 100 ng, intracerebroventricularly) had no distinctive effects on the sleep time of the mice treated with emulsified inhalation anaesthetics (P > 0.05). In tail-withdrawal test, AMPA (0.25, 0.5 and 1.0 ng, intrathecally) significantly and dose-dependently decreased the tail-withdrawal latency (P < 0.05 or P < 0.01) in the mice treated with emulsified anaesthetics. These results suggest that AMPA receptors may participate in the analgesic but not in the hypnotic effects induced by emulsified enflurane, isoflurane or sevoflurane.

SPINAL ?-AMINO-3-HYDROXY-5-METHYL-4-ISOXAZOLEPROPIONIC ACID RECEPTORS MAY MEDIATE THE ANALGESIC EFFECTS OF EMULSIFIED HALOGENATED ANAESTHETICS

1. The present study was designed to investigate the relationship between spinal cord alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and the analgesic effects of emulsified halogenated anaesthetics. 2. After having established the mouse model of analgesia by intraperitoneal or subcutaneous injections of appropriate doses of emulsified enflurane, isoflurane or sevoflurane, we injected different doses of AMPA intrathecally and observed effects on the pain threshold using the hot-plate and acetic acid-induced writhing tests. 3. The results showed that intrathecal injection of AMPA (0.25, 0.5 and 1.0 ng) did not affect the pain threshold on the hot-plate test or the writhing times in conscious mice. In contrast, AMPA (0.25, 0.5 and 1.0 ng intrathecally) significantly and dose-dependently decreased the pain threshold on the hot-plate test and increased the writhing times in mice treated with emulsified anaesthetics. 4. These results suggest that spinal AMPA receptors may be important targets for the analgesic effects of emulsified enflurane, isoflurane and sevoflurane.

Bupivacaine caudal epidural anesthesia: assessing the effect of general anesthetic technique on block onset

BACKGROUND

The primary objective of this prospective, randomized trial was to compare the effect of propofol and sevoflurane on effectiveness of regional anesthesia. As a secondary objective, we aimed at evaluating the influence of age on neuraxial block profile.

METHODS

One hundred and thirteen healthy children aged <10 years, scheduled for general or urological surgical procedures were randomly allocated to receive either propofol or sevoflurane induction and maintenance. Children received caudal or lumbar epidural block depending on their weight and expected surgery. Time to onset of surgical anesthesia, intraoperative analgesic effectiveness, residual motor blockade, postoperative pain, and adverse effects were evaluated. To assess the influence of age on these measures children were further divided into three age groups: 0-24, 25-60 and >60 months.

RESULTS

The mean time to onset of surgical anesthesia was significantly shorter in the sevoflurane group than the propofol group (3.1 vs 4.7 min, P < 0.01), independent of the type of regional technique employed. Distress on arousal in recovery was increased in children receiving sevoflurane (P = 0.03). There was no significant difference in residual motor blockade between the groups but children between 0 and 24 months receiving sevoflurane had a higher incidence of residual motor blockade 3 h after local anesthetic injection (P = 0.01).

CONCLUSIONS

This study has demonstrated that general anesthesia with sevoflurane decreases the time to onset of surgical anesthesia relative to propofol anesthesia. This effect was most marked when sevoflurane anesthesia preceded caudal epidural blockade. The basis for this effect is most likely to be related to differential binding of the two anesthetic agents to receptors in the spinal cord that mediate immobility in response to surgical stimuli.

Isoflurane and Propofol Have Similar Effects on Spinal Neuronal Windup at Concentrations that Block Movement

BACKGROUND

We investigated the actions of isoflurane and propofol on neuronal windup in the spinal cord of intact rats. We hypothesized that propofol would depress windup more than isoflurane.

METHODS

In a cross-over design, rats received 0.8 and 1.2 minimum alveolar concentration (MAC) isoflurane and 0.8 and 1.2 ED50 (effective dose(50%)) of propofol, as recordings were made from single units in the lumbar cord (n = 13). Electrical stimuli were applied (20 stimuli at 0.1, 1, and 3 Hz). Neuronal responses were analyzed for those occurring in the C-fiber range (100-400 ms after each stimulus), combined C-fiber and afterdischarge range (100-1000 ms) and the 100-333 ms range for the 3 Hz stimuli. Absolute windup was also calculated (the sum of action potentials for 20 stimuli - 20 x response to the first stimulus).

RESULTS

At 1 Hz, total action potentials (mean, standard error) summed across the 20 stimuli (100-1000 ms range) were 571 +/- 106 and 742 +/- 214 for isoflurane (at 0.8 and 1.2 MAC) and 586 +/- 148 and 641 +/- 143 for propofol (at 0.8 and 1.2 ED50), respectively (P = NS); corresponding values for the 0.1 Hz stimuli were 345 +/- 104, 370 +/- 108, 430 +/- 86, and 403 +/- 106 (P = NS), and for the 3 Hz stimuli (100-333 ms range) were 266 +/- 66, 333 +/- 76, 343 +/- 85, and 252 +/- 72 (P = NS). Absolute windup in the 100-1000 ms range was greater for 1.2 MAC isoflurane at 1 Hz (445 +/- 82, P < 0.01), when compared with absolute windup at 0.8 MAC isoflurane and 0.8 and 1.2 ED50 propofol (232 +/- 31, 88 +/- 65, and 210 +/- 41, respectively).

CONCLUSIONS

These data suggest that isoflurane and propofol have similar effects on neuronal windup in the spinal cord, although there was enhanced absolute windup at 1.2 MAC isoflurane for the 1 Hz stimulus.

The effect of anesthetic technique on early postoperative gastric emptying: comparison of propofol-remifentanil and opioid-free sevoflurane anesthesia

PURPOSE

A postoperative decrease in the gastric emptying (GE) rate may delay the early start of oral feeding and alter the bioavailability of orally administered drugs. The aim of this study was to compare the effect on early gastric emptying between two anesthetic techniques.

METHODS

Fifty patients (age, 19-69 years) undergoing day-case laparoscopic cholecystectomy were randomly assigned to received either total intravenous anesthesia with propofol/remifentanil/rocuronium (TIVA; n = 25) or inhalational opioid-free anesthesia with sevoflurane/rocuronium (mask induction; GAS; n = 25). Postoperative gastric emptying was evaluated by the acetaminophen method. After arrival in the recovery unit, acetaminophen (paracetamol) 1.5 g was given through a nasogastric tube, and blood samples were drawn during a 2-h period. The area under the serum-acetaminophen concentration curve from 0-60 min (AUC60), the maximal concentration (Cmax), and the time to reach C-max (Tmax) were calculated.

RESULTS

Twelve patients were excluded due to surgical complications (e.g., conversion to open surgery) and difficulty in drawing blood samples (TIVA, n = 7; GAS, n = 5). Gastric emptying parameters were (mean +/- SD): TIVA, AUC60, 2458 +/- 2775 min.micromol.l(-1); Cmax, 71 +/- 61 micromol.l(-1); and Tmax, 81 +/- 37 min; and GAS, AUC60, 2059 +/- 2633 min.micromol.l(-1); Cmax, 53 +/- 53 micromol.l(-1); and Tmax, 83 +/- 41 min. There were no significant differences between groups.

CONCLUSION

There was no major difference in early postoperative gastric emptying between inhalation anesthesia with sevoflurane versus total intravenous anesthesia with propofol-remifentanil. Both groups showed a pattern of delayed gastric emptying, and the variability in gastric emptying was high. Perioperative factors other than anesthetic technique may have more influence on gastric emptying.

Level of consciousness affects the excitability of spinal motor neurones during propofol sedation in humans

BACKGROUND

To investigate the relationship between the depression of spinal motor neuronal excitability and the sedative level induced by propofol infusion, we simultaneously analysed the suppressive effect of propofol on the F wave and the sedative level during propofol infusion.

METHODS

After spinal anaesthesia, sedation was achieved using a propofol target-controlled infusion (TCI) system to achieve a score of 4 on the Wilson sedation scale. The excitability of spinal motor neurones was determined by measuring the left median nerve F wave. F-wave persistence and the F/M ratio were recorded at pre-sedation as the control, during sedation, at arousal by mild physical stimulation and at post-sedation.

RESULTS

Wilson sedation scores increased significantly corresponding to the increase in the target propofol concentration (Cpt), and a Cpt-producing Wilson sedation scale 4 ranged between 1.2 and 1.8 microg ml(-1). The F-wave persistence and F/M ratio before propofol infusion were 80.7 (8.6)% and 9.5 (3.9)%, respectively. At Wilson sedation scale 4, F-wave persistence and F/M ratio were 17.6 (12.8)% (0-37.5%) and 4.3 (4.1)%, and, at return of consciousness by mild physical stimulation, significantly increased to 71.3 (7.9)% and 10.0 (5.0)%, respectively.

CONCLUSION

We demonstrated that the excitability of spinal motor neurones was suppressed during sedation by propofol TCI, but this suppressive effect vanished at return of consciousness by mild physical stimulation even at a constant Cpt. Our data suggested that the effect of propofol on the excitability of spinal motor neurones might be affected by consciousness level rather than propofol Cpt in humans.

The suppression of spinal F-waves by propofol does not predict immobility to painful stimuli in humans †

BACKGROUND

The immobilizing effects of volatile anaesthetics are primarily mediated at the spinal level. A suppression of recurrent spinal responses (F-waves), which reflect spinal excitability, has been shown for propofol. We have assessed the concentration-dependent F-wave suppression by propofol and related it to the logistic regression curve for suppression of movement to noxious stimuli and the effect on the bispectral index (BIS). The predictive power of drug effects on F-waves and BIS for movement responses to noxious stimuli was tested.

METHODS

In 24 patients anaesthesia was induced and maintained with propofol infused by a target controlled infusion pump at stepwise increasing and decreasing plasma concentrations between 0.5 and 4.5 mg litre(-1). The F-waves of the abductor hallucis muscle were recorded at a frequency of 0.2 Hz. BIS values were recorded continuously. Calculated propofol concentrations and F-wave amplitude and persistence were analyzed in terms of a pharmacokinetic-pharmacodynamic (PK/PD) model with a simple sigmoid concentration-response function. Motor responses to tetanic electrical stimulation (50 Hz, 60 mA, 5 s, volar forearm) were tested and the EC(50tetanus) was calculated using logistic regression.

RESULTS

For slowly increasing propofol concentrations, computer fits of the PK/PD model for the suppression by propofol yielded a median EC50 of 1.26 (0.4-2.3) and 1.9 (1.0-2.8) mg litre(-1) for the F-wave amplitude and persistence, respectively. These values are far lower than the calculated EC(50) for noxious electrical stimulation of 3.75 mg litre(-1). This difference results in a poor prediction probability of movement to noxious stimuli of 0.59 for the F-wave amplitude.

CONCLUSIONS

F-waves are almost completely suppressed at subclinical propofol concentrations and they are therefore not suitable for prediction of motor responses to noxious stimuli under propofol mono-anaesthesia.

Clinical actions of subarachnoid sevoflurane administration in vivo : a study in dogs

BACKGROUND

Halogenated ethers produce clinical effects at spinal sites. Nevertheless, in vitro and in vivo studies have not determined whether the immobilizing effect in the spinal cord is due to inhibition of nociceptive or motor transmission or both. Our goal was to characterize the clinical effects of direct spinal sevoflurane administration.

METHODS

Five adult beagle dogs completed the study. In a randomized and blinded manner each animal received placebo (saline 0.1 ml kg(-1)) and three concentrations of pure sevoflurane administered intrathecally (0.05, 0.075 and 0.1 ml kg(-1)) by means of a permanent spinal catheter. Sensory and motor block and state of consciousness were determined at baseline and at predetermined regular intervals until at least 2 h after total recovery.

RESULTS

None of the dogs presented a decrease in consciousness with either 0.05 or 0.075 ml kg(-1) of sevoflurane. Administration of 0.1 ml kg(-1) produced light sedation (2 on a four-point sedation scale) in three of the five dogs. A comparison of the duration of the sensory and motor blocks among the three sevoflurane dosages shows a significant dose-dependent increase that is greater in all cases than that for the saline solution.

CONCLUSIONS

Spinal administration of pure sevoflurane resulted in a dose-related and totally reversible motor and sensory regional block without any signs of clinical neurotoxicity or significant decrease in consciousness. Therefore the model allows us to comment on the analgesic effects at the spinal level in addition to the direct immobilizing effects of sevoflurane.

Electrophysiological and pharmacological characterisation of ascending anterolateral axons in the in vitro mouse spinal cord

Here we describe a procedure to obtain electrophysiological recordings from cut ends of ascending axons of the spinal cord white matter. This procedure involves the use of an in vitro preparation of the neonate mouse spinal cord and suction microelectrodes of about 10 microm tip diameter. Using this procedure, we have recorded from axons of the anterolateral quadrant at the thoracic level which responded to electrical stimulation of a lumbar dorsal root. Using adequate stimulation parameters, we have identified axons responding exclusively to activation of C-fibres and axons responding to activation of A- and C-fibres. These axons are likely to originate at dorsal horn second order sensory neurons of different functional types. Simultaneous recordings from a lumbar ventral root and from ascending axons were used to assess the effects of noradrenaline and sevoflurane on motor and sensory pathways. The results obtained show that noradrenaline can potentiate responses of motor neurons to dorsal root stimulation while depressing responses of ascending axons to the same stimulus. In contrast both motor and sensory pathways were inhibited by sevoflurane. We believe that the procedures developed here may be of great interest to assess spinal nociceptive and antinociceptive mechanisms in vitro.