Minimum Alveolar Concentration Of Isoflurane Research Articles

The effect of oral pregabalin on the minimum alveolar concentration of isoflurane in cats

ObjectiveTo investigate the effect of three different doses of oral pregabalin on minimum alveolar concentration of isoflurane (MACISO) in cats. Study designProspective, randomized, placebo controlled, blinded, crossover trial. AnimalsA group of eight healthy adult cats (24–48 months old). MethodsCats were randomly assigned to three oral doses of pregabalin (low dose: 2.5 mg kg-1, medium dose: 5 mg kg-1, high dose: 10 mg kg-1) or placebo 2 hours before MACISO determination, with the multiple treatments administered with a minimum 7 day washout period. Anesthesia was induced and maintained with isoflurane in oxygen until endotracheal intubation was achieved, and maintained with isoflurane with volume-controlled ventilation. MACISO was determined in triplicate using the bracketing technique and tail clamp method 120 minutes after pregabalin or placebo administration. Physiologic variables (including heart rate and blood pressure) recorded during MACISO determination were averaged and compared between the pregabalin and placebo treatments. One-way analysis of variance and the Friedman test were used to assess the difference for normally and non-normally distributed data, respectively. The Tukey test was employed as a post hoc analysis. Values of p < 0.05 were considered significant. ResultsThe MACISO with the medium and high dose pregabalin treatments were 1.33 ± 0.21% and 1.23 ± 0.17%, respectively. These were significantly lower than MACISO after placebo treatment (1.62 ± 0.13%; p = 0.014, p < 0.001, respectively), representing a decrease of 18 ± 9% and 24 ± 6%. The mean plasma pregabalin concentration was negatively correlated with MACISO values. Physiologic variables did not differ significantly between treatments. Conclusion and clinical relevanceDoses of 5 or 10 mg kg-1 pregabalin, given orally 2 hours before determining MACISO, had a significant isoflurane-sparing effect in cats.

Effects of trazodone and dexmedetomidine on fentanyl-mediated reduction of isoflurane minimum alveolar concentration in cats

ObjectiveTo screen modulators of biogenic amine (BA) neurotransmission for the ability to cause fentanyl to decrease isoflurane minimum alveolar concentration (MAC) in cats, and to test whether fentanyl plus a combination of modulators decreases isoflurane MAC more than fentanyl alone. Study designProspective, experimental study. AnimalsA total of six adult male Domestic Short Hair cats. MethodsEach cat was anesthetized in three phases with a 1 week washout between studies. In phase 1, anesthesia was induced and maintained with isoflurane, and MAC was measured in duplicate using a tail clamp stimulus and standard bracketing technique. A 21 ng mL–1 fentanyl target-controlled infusion was then administered and MAC measured again. In phase 2, a single cat was administered a single BA modulator (buspirone, haloperidol, dexmedetomidine, pregabalin, ramelteon or trazodone) in a pilot drug screen, and isoflurane MAC was measured before and after fentanyl administration. In phase 3, isoflurane MAC was measured before and after fentanyl administration in cats co-administered trazodone and dexmedetomidine, the two BA modulator drugs associated with fentanyl MAC-sparing in the screen. Isoflurane MAC-sparing by fentanyl alone, trazodone–dexmedetomidine and trazodone–dexmedetomidine–fentanyl was evaluated using paired t tests with p < 0.05 denoting significant effects. ResultsThe MAC of isoflurane was 1.87% ± 0.09 and was not significantly affected by fentanyl administration (p = 0.09). In the BA screen, cats administered trazodone or dexmedetomidine exhibited 26% and 22% fentanyl MAC-sparing, respectively. Trazodone–dexmedetomidine co-administration decreased isoflurane MAC to 1.50% ± 0.14 (p < 0.001), and the addition of fentanyl further decreased MAC to 0.95% ± 0.16 (p < 0.001). Conclusions and clinical relevanceFentanyl alone does not affect isoflurane MAC in cats, but co-administration of trazodone and dexmedetomidine causes fentanyl to significantly decrease isoflurane requirement.

Repeated Administration of the Cannabinoid WIN Alters the Isoflurane-Sparing Effect of Morphine and Dexmedetomidine.

Prior to the administration of morphine, the MAC was measured in both untreated rats (MAC (ISO)) and those treated with a cannabinoid (MAC (ISO + CANN)). The effects of morphine (MAC (ISO + MOR)) and dexmedetomidine (MAC (ISO + DEX)) on untreated rats and rats treated for 21 days with the cannabinoids (MAC (ISO + CANN + MOR)) and (MAC (ISO + CANN + DEX) were also studied. MAC (ISO) was 1.32 ± 0.06, and MAC (ISO + CANN) was 1.69 ± 0.09. MAC (ISO + MOR) was 0.97 ± 0.02 (26% less than MAC (ISO)). MAC (ISO + CANN + MOR) was 1.55 ± 0.08 (8% less than MAC (ISO + CANN)), MAC (ISO + DEX) was 0.68 ± 0.10 (48% less than MAC (ISO)), and MAC (ISO + CANN + DEX) was 0.67 ± 0.08 (60% less than MAC (ISO + CANN)). Medication with a cannabinoid for 21 days augmented the MAC of isoflurane. The sparing effect of morphine on isoflurane is lower in rats constantly medicated with a cannabinoid. The sparing effect of dexmedetomidine on the minimum alveolar concentration of isoflurane is greater in rats repeatedly medicated with a cannabinoid.

TREK-1 and TREK-2 knockout mice are not resistant to halothane or isoflurane.

A variety of molecular targets for volatile anesthetics have been suggested including the anesthetic-sensitive K+ leak channel, TREK-1. Knockout of TREK-1 is reported to render mice resistant to volatile anesthetics, making TREK-1 channels compelling targets for anesthetic action. Spinal cord slices from mice, either wildtype or an anesthetic-hypersensitive mutant, Ndufs4, display an isoflurane-induced outward K+ leak that correlates with their minimum alveolar concentrations (MAC) and is blocked by norfluoxetine. We hypothesized that TREK-1 channels conveyed this current and contribute to the anesthetic hypersensitivity of Ndufs4. Our results led to evaluation of a second TREK channel, TREK-2, in control of anesthetic sensitivity. We measured anesthetic sensitivities of mice carrying knockout alleles of Trek-1 and Trek-2, the double knockout Trek-1;Trek-2, and Ndufs4;Trek-1. Neurons from spinal cord slices from each mutant were patch clamped to characterize isoflurane-sensitive currents. Norfluoxetine was used to identify TREK-dependent currents. We compared mean values for MAC (+/- SD) between wildtype and two Trek-1 knockout alleles in mice (p-values, Trek-1 compared to wildtype). Wildtype: (MAC(Hal), 1.30%(0.10); MAC(Iso), 1.40%(0.11): Trek-1tm1Lex (MAC(Hal), 1.27%(0.11); p=0.387; MAC(Iso), 1.38%(0.09); p=0.268): Trek-1tm1Lzd (MAC(Hal); 1.27%(0.11); p=0.482: MAC(Iso); 1.41%(0.12); p=0.188). Neither allele was resistant for loss of righting reflex. The EC50s of Ndufs4;Trek-1tm1Lex did not differ from Ndufs4. Ndufs4: (EC50(Hal), 0.65%(0.05); EC50 (Iso), 0.63%(0.05): Ndufs4;Trek-1tm1Lex (EC50(Hal), 0.58%(0.07); p=0.004; EC50(Iso); 0.61%(.06); p=0.442). Loss of TREK-2 did not alter anesthetic sensitivity in a wildtype or Trek-1 genetic background. Loss of TREK-1 or TREK-2, or both, did not alter the isoflurane-induced currents in wildtype cells but did cause them to be norfluoxetine-insensitive. Loss of TREK channels did not alter anesthetic sensitivity in mice, nor did it eliminate isoflurane-induced transmembrane currents. However, the isoflurane-induced currents are norfluoxetine-resistant in Trek mutants indicating that other channels may function in this role when TREK channels are deleted.

Effect of oral administration of gabapentin on the minimum alveolar concentration of isoflurane in cats.

To determine if oral gabapentin decreases the minimum alveolar concentration (MAC) of isoflurane in cats. Prospective, randomized, blinded, crossover, and experimental study. A total of six healthy adult cats (three male, three female) aged 18-42 months, weighing 3.31 ± 0.26 kg. Cats were randomly given oral gabapentin (100 mg cat-1) or placebo 2 h before starting MAC determination, with the crossover treatment given at least 7 days apart. Anesthesia was induced and maintained with isoflurane in oxygen. Isoflurane MAC was determined in duplicate using an iterative bracketing technique and tail clamp method. Hemodynamic and other vital variables were recorded at each stable isoflurane concentration and were compared between gabapentin and placebo treatments at lowest end-tidal isoflurane concentration when cats did not respond to tail clamping. A paired t-test was used to compare normally distributed data, and a Wilcoxon signed-rank test was applied for non-normally distributed data. Significance was set at p < 0.05. Data are mean ± standard deviation. Isoflurane MAC in the gabapentin treatment was 1.02 ± 0.11%, which was significantly lower than that in the placebo treatment (1.49 ± 0.12%; p < 0.001), decreasing by 31.58 ± 6.94%. No significant differences were found in cardiovascular and other vital variables between treatments. Oral administration of gabapentin 2 h before starting MAC determination had a significant isoflurane MAC-sparing effect in cats with no observed hemodynamic benefit.

Effect of atracurium and rocuronium on the state and response entropy during isoflurane anesthesia: randomized prospective study

BackgroundSeveral researches have examined the impact of inhalation anesthetics, intravenous anesthetics, and muscle relaxants on spectral entropy, but many did not evaluate the extent of neuromuscular block. Besides, they did not inspect the impact of distinct degrees of neuromuscular blockade on spectral entropy under dissimilar saturations of isoflurane inhalation. Hence, this study has evaluated variant degrees of minimum alveolar concentration (MAC) to estimate the isoflurane concentration, along with various levels of neuromuscular blockade.This study aims to evaluate the effect of muscle relaxants (atracurium and rocuronium) on entropy readings (state, response entropy, and response-state difference) during isoflurane anesthesia.This is a prospective randomized study, as forty patients have been included and divided into two study groups: patients in group A received atracurium, while patients in group R received rocuronium. Under 50% and 100% neuromuscular blockage, state and response entropy were observed at MACs of 0.8% and 1%, respectively.ResultsThere was a positive correlation between state (SE) and response entropy (RE) at baseline, different MACs, and different trains of four (TOF) for both atracurium and rocuronium. State and response entropy decreased with increasing MAC of isoflurane (P < 0.001), while atracurium and rocuronium at TOF 50% and 100% showed no effect on SE, RE, or RE-SE (P > 0.05).ConclusionsState and response entropy can be used effectively to evaluate the depth of anesthesia at different isoflurane MAC and atracurium or rocuronium doses.Registration numberClinicalTrials.gov identifier: NCT 05097508, Registered October 5, 2021 (prospectively registered), http://www.ClinicalTrial.gov

Development of NMDA receptors contributes to the enhancement of electroencephalogram oscillations under volatile anesthetics in rats.

Volatile anesthetics including sevoflurane and isoflurane enhance oscillations of cortical electroencephalogram (EEG), partly by their modulations on glutamate-mediated excitatory synaptic transmission. Expression of NMDA receptors is increased during neonatal development. However, how the development of NMDA receptors influences EEG under volatile anesthesia remains unclear. Expressions of NMDA receptor subtypes (NR1, NR2A, and NR2B) during neonatal development were measured by Western blotting. MAC (minimal alveolar concentration) of isoflurane and sevoflurane that inducing loss of righting reflex (LORR) and no response to tail-clamp (immobility) were measured to verify the effect of NR1 expression on anesthetic potency during neonatal development. Cortical electroencephalogram recording was used to examine the influence of NR1 expression on the power density of EEG. The expressions of GluNR1, GluNR2A and GluNR2B receptors were gradually increased during neonatal development in cortex, hippocampus and thalamus of rats. Knockdown of NR1 enhanced the sedative potency of volatile anesthetics but not on immobility potency in postnatal day 14 (P14)-P17 rats. For cortical EEG, along with the increased concentration of volatile anesthetics, cortical slow-delta oscillations of P5 rats were inhibited, theta and alpha oscillations were not changed significantly; while these oscillations were enhanced until high anesthetic concentrations in P21 rats. Knockdown of NR1 in forebrain suppressed the enhancement of cortical EEG oscillations in P21 rats. The development of NMDA receptors may contribute to the enhancement of cortical EEG oscillations under volatile anesthetics.

Isoflurane has no effect on cognitive or behavioral performance in a mouse model of early-stage Alzheimer's disease.

Patients with Alzheimer's disease show a sex-dependent decline of cognitive and behavioral performance. It is controversially discussed whether general anesthesia itself can aggravate or even cause this neurocognitive decline. Therefore, we investigated the effect of general anesthesia on neurocognitive and behavioral function and amyloidopathy in a mouse model of early-stage Alzheimer's disease with respect to sex. After governmental approval 10 months old Tg2576 mice and wild type (total 85 mice) either underwent general anesthesia with 1.0 minimal alveolar concentration of isoflurane for 2 h or were not exposed to isoflurane (controls). Following cognitive and behavioral testing using the modified hole board test (mHBT), brains were investigated regarding amyloidopathy, inflammation, and apoptosis. Data were analyzed using repeated measure analysis of variance (ANOVA) and univariate analysis of variance (UNIANOVA). Tg2576 mice showed a decline in memory function (p < 0.001), less anxiety (p = 0.022 and p = 0.024), increased locomotor activity (p = 0.025), and impaired fine motor skills (p < 0.001). Amyloid precursor protein (p < 0.001), soluble amyloid-beta (p < 0.001) and insoluble amyloid deposits (p < 0.001) were increased in Tg2576 animals. Neither sex nor exposure to isoflurane had an effect on cognitive or behavioral testing or expression of amyloid-related biomarkers. We found that 10 months old Tg2576 showed typical signs of early-stage Alzheimer's disease and corresponding histopathological alterations. Relevant sex-specific differences or an effect of isoflurane anesthesia could not be detected at this early stage of the disease.

Use of Ketamine or Xylazine to Provide Balanced Anesthesia with Isoflurane in C57BL/6J Mice.

Balanced anesthesia-the use of a combination of drugs to achieve a desired anesthetic plane-offers many benefits, including smoother induction and recovery and fewer adverse effects than occur with individual drugs. Although premedication prior to inhalant anesthesia is routine in other species, mice are commonly induced with gas anesthesia alone. The hypothesis of this study was that premedication with ketamine or xylazine would safely reduce the stress of isoflurane induction and lower the minimum alveolar concentration (MAC) of isoflurane. Young adult male and female C57BL/6J mice were premedicated with ketamine (100 mg/kg), xylazine (4 mg/kg), or isotonic crystalloid (0.1 mL) and were used in 4 experiments. First, isoflurane induction was video recorded under all test conditions, and the videos were scored according to a behavioral ethogram to identify signs of distress. Mice in the ketamine group experienced tremors and ataxia before and dur- ing induction. Therefore, ketamine was given after induction with isoflurane in subsequent experiments. Second, the MAC value for each anesthetic protocol was determined by using quantal and bracketing analysis. Third, mice were anesthetized according to the 3 protocols, and vital parameters were monitored for 60 min. Finally, anesthetized mice were challenged with hypoxia and hypovolemia, and vital parameters were monitored. Premedication with xylazine significantly reduced the stress scores for isoflurane induction (control, 7.3 ± 1.5; ketamine, 6.0 ± 3.0; xylazine, 3.1 ± 1.0). Ketamine and xylazine both reduced the MAC of isoflurane (control, 1.89%; ketamine, 0.96%; xylazine, 1.20%). All mice survived 60 min of anesthesia and the hypoxia-hypovolemia challenge. Premedication with xylazine reduced the stress of induction and lowered the necessary dose of isoflurane in C57BL/6J mice to maintain a surgical plane of anesthesia. We recommend administering xylazine before isoflurane induction and anesthesia of healthy mice that are undergoing procedures in which 100% oxygen is provided and anticipated blood loss is less than 10% to 15% of the total blood volume.

Does trazodone reduce anaesthetic agent requirement in dogs?

PICO question&#x0D; In dogs undergoing anaesthesia, does the use of oral trazodone given 2 hours before induction of anaesthesia reduce injectable or inhalant anaesthetic agent requirements?&#x0D; &#x0D; Clinical bottom line&#x0D; Category of research question&#x0D; Treatment&#x0D; The number and type of study designs reviewed&#x0D; Two randomised controlled trials were critically appraised&#x0D; Strength of evidence&#x0D; Moderate&#x0D; Outcomes reported&#x0D; Trazodone was shown to have a significant isoflurane minimum alveolar concentration (MAC) sparing effect for isoflurane. There is also evidence to suggest trazodone has a similar effect on the cardiovascular system as acepromazine&#x0D; Conclusion&#x0D; Trazodone should be considered as part of a multimodal approach to anaesthesia in dogs to reduce the injectable and inhalant anaesthetic agent requirements&#x0D; &#x0D; How to apply this evidence in practice&#x0D; The application of evidence into practice should take into account multiple factors, not limited to: individual clinical expertise, patient’s circumstances and owners’ values, country, location or clinic where you work, the individual case in front of you, the availability of therapies and resources.&#x0D; Knowledge Summaries are a resource to help reinforce or inform decision making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care.&#x0D; &#x0D;

An Entropy-Based Prospective Randomized Controlled Trial to Evaluate the Analgesic and Hypnotic Effects of Equipotent Doses of Sevoflurane and Isoflurane in Patients Presenting for Spine Surgeries.

Objectives Minimal alveolar concentration (MAC) of anesthetic agents has been considered a suitable measure of the potency of inhalational anesthetics. Furthermore, it is assumed that equi-MAC concentrations of different anesthetic agents have a similar potency in suppressing responses to painful stimuli. Isoflurane and sevoflurane are two commonly used volatile anesthetic agents in spine surgeries. Therefore, these agents' hypnotic and analgesic potencies should be distinguished and comprehended for the optimal administration of anesthesia. Consequently, we undertook this study to compare the analgesic and hypnotic potencies between these agents at equi-MAC concentrations, using the entropy monitor. Materials and Methods Forty patients undergoing lumbar spine surgery were randomly assigned to two groups receiving either isoflurane ( n = 20) or sevoflurane ( n = 20). After induction, maintenance of anesthesia was done with age-corrected 1.0 MAC of either isoflurane or sevoflurane. A standardized noxious stimulus was provided to all the patients after achieving a steady state of 1.0 MAC. The state entropy (SE), response entropy (RE), and RE–SE were recorded at baseline, prestimulus, and poststimulus time points in both groups. Statistical Analyses Data are presented as frequency and percentages for categorical variables and mean ± standard deviation for continuous variables. The comparison of categorical variables between the two groups was made using the Fisher's exact test, and the Student's t -test was used for continuous variables. A p -value of < 0.05 was considered to be statistically significant. Results At age-corrected 1.0 MAC, there was no significant difference in the SE, RE, and RE–SE in both the groups at any time point. Conclusion Our study shows that during a steady state of age-corrected 1.0 MAC single-agent anesthesia, sevoflurane and isoflurane have comparable analgesic and hypnotic potencies as measured by entropy indices when a standardized nociceptive stimulus is provided.

Determination of the minimum alveolar concentration of isoflurane in donkeys.

To determine the minimum alveolar concentration (MAC) of isoflurane in donkeys and characterize recovery from anesthesia. 7 healthy castrated male adult donkeys. Anesthesia was induced with propofol and maintained under mechanical ventilation with 1.3% isoflurane end-tidal concentration (ETiso). The MAC of isoflurane was determined after a 60-minute propofol washout period using the bracketing method. A continuous noxious electrical stimulation was applied to the oral mucosa for 1 minute or until the donkey moved. The ETiso was increased or decreased by 10% depending on the response, and MAC was defined as the average of 2 ETiso values allowing and preventing movement in response to stimulation. Arterial blood gases were measured during anesthesia and the recovery period. Unassisted recovery was timed, and a quality score was assigned from 1 (very poor) to 5 (excellent). The mean dose of propofol required for induction was 3.0 ± 0.6 mg/kg. The MAC of isoflurane was 1.44 ± 0.13%. One donkey was excluded from the study because it was still responsive when stimulated at ETiso of 2.8%. Immediately after extubation, the median (range) partial pressure of oxygen in the arterial blood was 63 (minimum to maximum, 46 to 72) mm Hg and 3 donkeys were hypoxemic (partial pressure of arterial oxygen < 60 mm Hg). The median time to standing was 13 (7 to 38) minutes, while the recovery score was 3 (2 to 5). The MAC of isoflurane in donkeys is similar to that reported in other species. Oxygen support should be provided to donkeys during recovery from isoflurane anesthesia to prevent hypoxemia.

Minimum Alveolar Concentration of Isoflurane in Rats Chronically Treated with the Synthetic Cannabinoid WIN 55,212-2.

Simple SummaryThe minimum alveolar concentration of isoflurane (inhaled anesthetic required to prevent movement in 50% of subjects exposed to a supramaximal noxious stimulus) was determined in 24 male rats chronically treated with the synthetic cannabinoid WIN 55,212-2 to evaluate the interaction of isoflurane with chronically administered cannabinoid agonist. The minimum alveolar concentration was determined in one group without treatment, in rats treated for 21 days with WIN 55,212-2, and another group 8 days after stopping treatment for 21 days with cannabinoid. We believe it is necessary to study the effects of chronic consumption of these substances on the requirements of inhalation anesthetics in patients that will be submitted to general anesthesia. The administration for 21 days of WIN 55,212-2 increases the minimum alveolar concentration of isoflurane in rats; this effect does not disappear after 8 days of discontinuing treatment with the synthetic cannabinoid.The minimum alveolar concentration MAC of isoflurane was measured in rats chronically treated with WIN 55,212-2. Methods: The MAC of isoflurane was determined in 24 male rats from expiratory samples at time of tail clamping under the following conditions: without treatment MAC(ISO), in rats treated for 21 days with WIN 55,212-2 MAC(ISO + WIN55), and in rats 8 days after stopping treatment with WIN 55,212-2 (MACISO + WIN55 + 8D). Results: The MAC(ISO) was 1.32 ± 0.06. In the MAC(ISO + WIN55) group, the MAC increased to 1.69 ± 0.09 (28%, p-value ≤ (0.0001). Eight days after stopping treatment with WIN55, the MAC did not decrease significantly, 1.67 ± 0.07 (26%, p-value ≤ 0.0001). Conclusions: The administration of WIN 55,212-2 for 21 days increases the MAC of isoflurane in rats. This effect does not disappear 8 days after discontinuation of treatment with the synthetic cannabinoid.

Anesthesia and Braquial Plexus Block in Nine-Banded Armadillo (Dasypus novemcinctus)-Case Report

The nine-banded armadillo (Dasypus novemcinctus) is the most common species of armadillos in North, Central and South Americas. This case report is about an anesthetic procedure of a male armadillo received for rehabilitation with a radioulnar fracture. For the anesthesia, we use methadone, midazolam, s-ketamine and isoflurane. We also use a human laryngeal mask for secure airway and brachial plexus block with a peripheral nerve stimulator. There is a little information about anesthesia of these species in the literature and the aim of this work is to contribute to this knowledge. Though it is unknown the minimum alveolar concentration of isoflurane in nine-banded armadillo, we concluded that, with the blockage of the brachial plexus, we saw cardiovascular stability and a decrease in isoflurane use. The reversal of midazolam added to a quick recovery. The human laryngeal mask is effective for inhalation anesthesia in nine-banded armadillo.

Effectiveness of Low Dose Dexmedetomidine for an Oligaemic Field in Middle Ear Surgery: A Randomised Control Trial

Introduction: Microscopic middle ear surgeries are best done under hypotensive anaesthesia to provide an oligaemic field. Dexmedetomidine is an α2 agonist which produces hypotension by sympathetic response blockade. Aim: To study the effectiveness of low dose dexmedetomidine in providing an oligaemic field. The additional requirement of inhalational agent required to maintain the oligaemic field in the control group, intubation response and postoperative analgesia were also assessed. Materials and Methods: The randomised, placebo-controlled double-blind study was conducted by recruiting 48 patients in the study, who were divided into two groups i.e, study group (n=24) and placebo group (n=24). The study group received low dose dexmedetomidine infusion (0.5 μg/kg loading dose followed by 0.2 μg/kg/hr) and placebo group received weightadjusted saline. The quality of the surgical field was assessed on a score of 0-5. The Minimum Alveolar Concentration (MAC) of inhalational agent needed, postoperative sedation score and pain score were noted. All the data were recorded in Statistical Package for Social Sciences (SPSS) software, version 22.0. Results: The mean score of quality of the surgical field in the study group was 2.00±0.59, compared to 3.50±0.88 in the placebo group. The mean MAC of isoflurane was 1.32±0.31 in the placebo group and 0.85±0.23 in the study group (p-value=0.03). The study group had a Ramsay sedation score of 3.08±0.65 compared to 2.29±0.75 in the placebo group at 5 minutes after extubation (p-value &lt;0.001). The mean pain score in the dexmedetomidine group in 10 minutes postoperative period was 1.83±2.25, while in placebo group it was 3.25±1.96 (p-value=0.025). However, over the next 20-60 minutes postoperative period the pain score between the two groups were comparable, with no significant difference in analgesia, postoperative shivering and other side-effects. Conclusion: A low dose dexmedetomidine can effectively provide a bloodless field for middle ear microsurgical procedures.

Effect of intravenous butorphanol infusion on the minimum alveolar concentration of isoflurane in cats

ObjectiveTo determine the effect of butorphanol, administered by intravenous (IV) infusion, on the minimum alveolar concentration of isoflurane (MACISO) in cats and to examine the dosage dependence of this effect. Study designRandomized, placebo-controlled, crossover experimental study. AnimalsA group of six healthy adult male neutered cats. MethodsCats were anesthetized with isoflurane in oxygen. A venous catheter was placed for fluid and drug administration, and an arterial catheter was placed for measurement of arterial pressure and blood sampling. Four treatments were administered at random with at least 2 week interval between treatments: saline (control), butorphanol low dosage (treatment LD; 0.25 mg kg–1 IV bolus followed by 85 μg kg–1 minute–1 for 20 minutes, then 43 μg kg–1 minute–1 for 40 minutes, then 19 μg kg–1 minute–1), medium dosage (treatment MD, double the dosages in LD) and high dosage (treatment HD, quadruple the dosages in LD). MACISO was determined in duplicate using the bracketing technique and tail clamping. Pulse rate, arterial pressure, hemoglobin oxygen saturation, end-tidal partial pressure of carbon dioxide and arterial blood gas and pH were measured. ResultsButorphanol reduced MACISO in a dosage-dependent manner, by 23 ± 8%, 37 ± 12% and 68 ± 10% (mean ± standard deviation) in treatments LD, MD and HD, respectively. The main cardiopulmonary effect observed was a decrease in pulse rate, significant in treatment HD compared with control. Conclusions and clinical relevanceButorphanol caused a dosage-dependent MACISO reduction in cats. IV infusion of butorphanol may be of interest for partial IV anesthesia in cats.

Determination of the minimum alveolar concentration of isoflurane in donkeys

Introduction: The minimum alveolar concentration (MAC) of volatile anesthetic agents provides important clinical information. The MAC of isoflurane in donkeys is unreported.

Effect of fentanyl, with or without treatment of bradycardia, on the minimum alveolar concentration of isoflurane and cardiovascular function in dogs

ObjectiveTo determine the effect of fentanyl on the minimum alveolar concentration of isoflurane (MACISO) and cardiovascular variables in dogs, and how the treatment of bradycardia affects them. Study designProspective, randomized crossover-controlled trial. AnimalsA total of six male Beagle dogs weighing 9.9 ± 0.7 kg (mean ± standard deviation) and aged 13 months. MethodsTo each dog, two treatments were assigned on different days: fentanyl (FENTA) or fentanyl plus glycopyrrolate (FENTAglyco) to maintain heart rate (HR) between 100 and 132 beats minute−1. Determinations of MACISO were performed with 10 plasma fentanyl target concentrations ([Fenta]Target (0, 0.16, 0.32, 0.64, 1.25, 2.5, 5.0, 10.0, 20.0 and 40.0 ng mL−1) for FENTA and 5 [Fenta]Target (0, 1.25, 2.5, 5.0, 10.0 ng mL−1)) for FENTAglyco. During each MACISO determination, cardiovascular variables [mean arterial pressure (MAP), HR and cardiac index (CI)] were measured, and systemic vascular resistance index (SVRI) calculated. Pharmacodynamic models were used to describe the plasma fentanyl concentration [Fenta]–response relationship for the effect on MACISO and cardiovascular variables. A mixed-model analysis of variance followed by Dunnett’s or Tukey’s test, and the Bonferroni adjustment were used for comparisons within and between each treatment, respectively. Significance was set as p < 0.05. ResultsFentanyl decreased MACISO by a maximum of 84%. The [Fenta] producing 50% decrease in MAC, HR and CI were 2.64, 3.65 and 4.30 ng mL−1 (typical values of population model), respectively. The prevention of fentanyl-mediated bradycardia caused no significant effect on MACISO, but increased HR, MAP and CI, and decreased SVRI when compared with isoflurane alone. Conclusions and clinical relevanceFentanyl caused a plasma concentration-dependent decrease in MACISO, HR and CI and an increase in SVRI. Cardiovascular improvements associated with fentanyl in isoflurane-anesthetized dogs only occurred when the fentanyl-mediated bradycardia was prevented.

Science, Medicine, and the Anesthesiologist

Science, Medicine, and the Anesthesiologist

Evaluation of whether acepromazine maleate causes fentanyl to decrease the minimum alveolar concentration of isoflurane in cats.

To determine whether isoflurane-anesthetized cats with demonstrated resistance to the immobilizing effects of fentanyl would exhibit naltrexone-reversible sparing of the minimum alveolar concentration (MAC) of isoflurane when fentanyl was coadministered with the centrally acting catecholamine receptor antagonist acepromazine. 5 healthy male purpose-bred cats. Anesthesia was induced and maintained with isoflurane in oxygen. Baseline isoflurane MAC was measured by use of a standard tail clamp stimulus and bracketing study design. Afterward, fentanyl was administered IV to achieve a plasma concentration of 100 ng/mL by means of target-controlled infusion, and isoflurane MAC was remeasured. Next, acepromazine maleate (0.1 mg/kg) was administered IV, and isoflurane MAC was remeasured. Finally, isoflurane concentration was equilibrated at 70% of the baseline MAC. Movement of cats in response to tail clamping was tested before and after IV bolus administration of naltrexone. Physiologic responses were compared among treatment conditions. Isoflurane MAC did not differ significantly between baseline and fentanyl infusion (mean ± SD, 1.944 ± 0.111% and 1.982 ± 0.126%, respectively). Acepromazine with fentanyl significantly decreased isoflurane MAC to 1.002 ± 0.056% of 1 atm pressure. When isoflurane was increased to 70% of the baseline MAC, no cats moved in response to tail clamping before naltrexone administration, but all cats moved after naltrexone administration. Acepromazine caused fentanyl to decrease the isoflurane MAC in cats that otherwise did not exhibit altered isoflurane requirements with fentanyl alone. Results suggested that opioid-mediated increases in brain catecholamine concentrations in cats counteract the opioid MAC-sparing effect.