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Pregabalin produces similar effects as gabapentin for preanesthetic sedation in cats. J Am Vet Med Assoc 2024; 262:359-363. [PMID: 38134455 DOI: 10.2460/javma.23.09.0493] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Accepted: 11/10/2023] [Indexed: 12/24/2023]
Abstract
OBJECTIVE To compare the effects of oral pregabalin versus gabapentin on sedation quality and anesthesia recovery times in cats in a typical perioperative setting. ANIMALS 50 healthy cats with > 1 kg body weight presenting for elective surgery. METHODS In this randomized, prospective clinical trial, cats presenting to the University of California-Davis Veterinary Medical Teaching Hospital were assigned to receive buprenorphine 0.02 mg/kg IM followed by 1 of 2 oral sedation treatments: pregabalin 4 mg/kg or gabapentin 10 mg/kg. Cats were then anesthetized using a standardized protocol. Physical examination parameters and behavioral scores were measured by 2 treatment-blinded veterinarians to compare sedation levels before and after drug administration. Inadequate sedation for handling or IV catheter placement was addressed by dexmedetomidine administration. After surgery was completed, anesthesia recovery times and quality were assessed by the same veterinarians. The effects of pregabalin versus gabapentin on body temperature, respiratory rate, and heart rate were analyzed using Student t tests; behavioral assessments were analyzed using Wilcoxon signed-rank tests; and drug treatment effects on dexmedetomidine sedation rescue and frequency of delirium during anesthetic recovery were analyzed using Fisher exact tests. A P < .05 indicated statistical significance. RESULTS There was no significant difference in change of physiologic parameters or sedation scores before and after sedation between groups. The need for rescue sedation for IV catheter placement and the incidence of emergence delirium were infrequent and similar for both treatments. CLINICAL RELEVANCE At the doses studied, oral pregabalin and gabapentin produced indistinguishable effects as adjunctive perioperative sedation agents in cats.
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Effects of trazodone and dexmedetomidine on fentanyl-mediated reduction of isoflurane minimum alveolar concentration in cats. Vet Anaesth Analg 2024; 51:80-89. [PMID: 37926586 DOI: 10.1016/j.vaa.2023.09.130] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 09/16/2023] [Accepted: 09/30/2023] [Indexed: 11/07/2023]
Abstract
OBJECTIVE To 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 DESIGN Prospective, experimental study. ANIMALS A total of six adult male Domestic Short Hair cats. METHODS Each 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. RESULTS The 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 RELEVANCE Fentanyl alone does not affect isoflurane MAC in cats, but co-administration of trazodone and dexmedetomidine causes fentanyl to significantly decrease isoflurane requirement.
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Feline herpesvirus-1-related multiple respiratory eosinophilic nodules in an adult cat receiving long-term oral prednisolone. JFMS Open Rep 2024; 10:20551169231220291. [PMID: 38299191 PMCID: PMC10829494 DOI: 10.1177/20551169231220291] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2024] Open
Abstract
Case summary A 10-year-old male castrated domestic shorthair cat was presented for evaluation of a 3-day history of increased inspiratory effort. The cat had received prednisolone 1 mg/kg PO q24h for 1 year due to chronic diarrhea. On physical examination, the patient exhibited severe stridor, intermittent open-mouth breathing and bilateral mucopurulent nasal discharge. Subcutaneous emphysema was palpated over the dorsal cervical region. Mild hypoventilation (PvCO2 55.1 mmHg; approximate reference interval 35-45 mmHg) was identified. Cervicothoracic radiographs showed marked gas tracking within cervical soft tissues with concurrent laryngeal thickening, pulmonary nodules, a bronchial pulmonary pattern, pneumomediastinum and aerophagia. The cat was hospitalized and treated overnight with oxygen and intravenous fluid therapy before anesthesia the next day. On laryngoscopy, a large tracheal mass was observed arising from the right subglottic region and was removed using biopsy forceps. CT revealed an additional mass at the level of the tracheal bifurcation causing marked luminal narrowing of the trachea and proximal main bronchi. The cat made a good initial recovery, although moderate stridor persisted. Five days later, the cat was re-examined due to recurrence of respiratory distress and orthopnea, and the owner elected euthanasia. Histopathology revealed severe nodular obstructive eosinophilic plasmacytic laryngotracheitis with intranuclear inclusion bodies positive for feline herpesvirus-1 on immunohistochemistry. Relevance and novel information This report describes the presentation and management of a cat with respiratory distress secondary to intratracheal eosinophilic masses caused by feline herpesvirus-1. Although the outcome was ultimately unsatisfactory, to the authors' knowledge, this clinical presentation has not been previously reported.
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Analgesic effect of the mint terpenoid L-carvone in sheep. Vet Anaesth Analg 2023; 50:459-465. [PMID: 37500407 DOI: 10.1016/j.vaa.2023.06.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Revised: 06/23/2023] [Accepted: 06/26/2023] [Indexed: 07/29/2023]
Abstract
OBJECTIVE To determine whether L-carvone increases the voltage threshold response to a noxious electrical stimulus in sheep. STUDY DESIGN Prospective, blinded, randomized, crossover experimental study. ANIMALS A group of six healthy adult sheep. METHODS Sheep were instrumented with cranial dorsothoracic subcutaneous copper electrodes. A stimulator delivered a 10 ms square-wave stimulus at 50 pps starting at 0.1 V with a 0.2 V second-1 ramp. The stimulus stopped once two observers who were blinded to treatment noted a behavioral pain response or when a 15 V cut-off was reached. Next, 0.15 mL kg-1 of either a 50% L-carvone solution or a saline-vehicle control was administered intramuscularly, and electrical threshold responses were measured every 5-15 minutes over a 6 hour period using methods identical to the baseline. One week following the first treatment (L-carvone or control), sheep were studied using identical methods with the second treatment (control or L-carvone). Drug and time effects were evaluated using a two-way repeated measures analysis of variance, and pairwise comparisons were evaluated with Holm-Sidák tests with values of p < 0.05 considered significant. RESULTS L-carvone significantly increased voltage threshold responses for most time points up to 75 minutes compared with baseline and with saline control. The last time point with a significantly different response between L-carvone and saline treatments was 5 hours after drug administration. The saline-vehicle control decreased voltage threshold responses at several time points after 3 hours. CONCLUSIONS AND CLINICAL RELEVANCE Intramuscular L-carvone is analgesic in sheep, although the ethanol-propylene glycol vehicle may cause mild hyperalgesia. This study demonstrates that a food-derived compound can be used to relieve pain in a food-producing animal.
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Anesthetic Pharmacology of the Mint Extracts L-Carvone and Methyl Salicylate. Pharmacology 2022; 107:167-178. [PMID: 35100605 DOI: 10.1159/000520762] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Accepted: 11/04/2021] [Indexed: 11/19/2022]
Abstract
INTRODUCTION Hydrocarbons with sufficient water solubility allosterically modulate anesthetic-sensitive ion channels. Mint extracts L-carvone and methyl salicylate water solubility exceeds modulation cutoff values for γ-amino butyric acid type A (GABAA) receptors, N-methyl-D-aspartate (NMDA) receptors, and type-2 voltage-gated sodium (Nav1.2) channels. We hypothesized that mint extracts modulate these channels at concentrations that anesthetize rats. METHODS Channels were expressed separately in frog oocytes and studied using 2-electrode voltage clamp techniques at drug concentrations up to 10 mM. Normalized current effects were fit to Hill equations. Mint compounds were formulated in a lipid emulsion and administered IV to rats. When unresponsive to the tail clamp, rats were exsanguinated, and plasma drug concentrations were measured. RESULTS Both mint compounds caused concentration-dependent inhibition of all channels except for methyl salicylate which inhibited GABAA receptors at low concentrations and potentiated at high concentrations. Plasma drug concentrations in anesthetized rats were 7.9 mM for L-carvone and 2.7 mM for methyl salicylate. This corresponded to ≥53% NMDA receptor inhibition and ≥78% Nav1.2 channel inhibition by both compounds and 30% potentiation of GABAA receptors by methyl salicylate. CONCLUSION L-Carvone and methyl salicylate allosterically modulate cell receptor targets important to molecular actions of conventional anesthetics at concentrations that also induce general anesthesia in rats.
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Continuous measurement of arterial oxygenation in mechanically ventilated horses. Equine Vet J 2021; 54:1144-1152. [PMID: 34797580 DOI: 10.1111/evj.13542] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Revised: 11/01/2021] [Accepted: 11/11/2021] [Indexed: 11/29/2022]
Abstract
BACKGROUND The possibility of accurately and continuously measuring arterial oxygen partial pressure (PaO2 ) in horses may facilitate the management of hypoxaemia during general anaesthesia. OBJECTIVES The aim of this study was to evaluate the ability of a novel fibreoptic sensor to measure PaO2 (PaO2Sensor ) continuously and in real time in horses undergoing ventilatory manoeuvres during general anaesthesia. STUDY DESIGN In vivo experimental study. METHODS Six adult healthy horses were anaesthetised and mechanically ventilated in dorsal recumbency. A fibreoptic sensor was placed in one of the facial arteries through a catheter to continuously measure and record PaO2Sensor . After an alveolar recruitment manoeuvre, a decremental positive end-expiratory pressure (PEEP) titration using 20-minute steps of 5 cm H2 O from 20 to 0 cm H2 O was performed. An arterial blood sample was collected at 15 minutes of ventilation at each PEEP level for PaO2 measurement using an automated blood gas machine (PaO2Ref ). The agreement between PaO2Sensor and PaO2Ref was assessed by Pearson's correlation, Bland-Altman plot and four-quadrant plot analysis. In the last minute of ventilation at each PEEP level, a slow tidal inflation/deflation manoeuvre was performed. RESULTS The mean relative bias between PaO2Sensor and PaO2Ref was 4% with limits of agreement between -17% and 29%. The correlation coefficient between PaO2Sensor and PaO2Ref was 0.98 (P < .001). The PaO2Sensor and PaO2Ref concordance rate for changes was 95%. Measurements of PaO2Sensor during the slow inflation/deflation manoeuvre at PEEP 15 and 10 cm H2 O were not possible because of significant noise on the PaO2 signal generated by a small blood clot. MAIN LIMITATIONS Small sample size. CONCLUSION The tested fibreoptic probe was able to accurately and continuously measure PaO2Sensor in anaesthetised horses undergoing ventilatory manoeuvres. A heparinised system in the catheter used by the fibreoptic sensor should be used to avoid blood clots and artefacts in the PaO2 measurements.
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Evaluation of whether acepromazine maleate causes fentanyl to decrease the minimum alveolar concentration of isoflurane in cats. Am J Vet Res 2021; 82:352-357. [PMID: 33904805 DOI: 10.2460/ajvr.82.5.352] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE 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. ANIMALS 5 healthy male purpose-bred cats. PROCEDURES 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. RESULTS 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. CONCLUSIONS AND CLINICAL RELEVANCE 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.
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Pharmacokinetics and pharmacodynamics of a high concentration of buprenorphine (Simbadol) in conscious horses after subcutaneous administration. Vet Anaesth Analg 2021; 48:585-595. [PMID: 33934992 DOI: 10.1016/j.vaa.2021.02.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Revised: 01/27/2021] [Accepted: 02/17/2021] [Indexed: 10/21/2022]
Abstract
OBJECTIVE To determine the pharmacokinetics and pharmacodynamics of high-concentration formulation of buprenorphine (1.8 mg mL-1; Simbadol) following subcutaneous (SC) administration in horses. STUDY DESIGN Prospective, randomized, crossover trial. ANIMALS A group of six healthy adult horses weighing 521-602 kg. METHODS On three occasions, Simbadol (0.005 mg kg-1; treatment S5), (0.0025 mg kg-1; treatment S2.5) or saline (treatment SAL) were administered SC at least 7 days apart in random order. Electrical nociceptive threshold (ENT) measured on the neck region, physiologic variables, locomotor activity, degree of restlessness and presence of excitatory signs were measured at baseline and for up to 48 hours after injection. Blood was collected for pharmacokinetic analysis at the same time intervals and plasma buprenorphine concentration (Cp) measured using liquid chromatography-tandem mass spectrometry. RESULTS Buprenorphine was quantifiable in all horses from 15 minutes after administration up to 8-12 hours. ENT was significantly increased in treatment S2.5 compared with treatment SAL at 0.75-6 hours after treatment. Increase in locomotor activity and compulsive behavior were recorded in all horses after Simbadol, and degree of restlessness was significantly higher in treatment S5 than SAL for a sustained time. Gastrointestinal motility significantly decreased in all horses after Simbadol and returned to baseline by 16 hours after treatment. CONCLUSIONS AND CLINICAL RELEVANCE In horses, SC Simbadol was rapidly absorbed and Cp decreased rapidly. Side effects commonly seen in horses after opioids were observed in both Simbadol treatments, but degree of opioid-induced excitement lasted significantly longer in treatment S5. Simbadol (0.0025 mg kg-1) SC has the potential to be used clinically to treat pain in horses. However, at this dose, duration of antinociceptive effects was not longer than that reported for conventional buprenorphine, and side effects, including reduction in gastrointestinal motility and increased locomotor activity, were documented.
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Phenylpiperidine opioid effects on isoflurane minimum alveolar concentration in cats. J Vet Pharmacol Ther 2020; 43:533-537. [PMID: 32557697 DOI: 10.1111/jvp.12886] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Revised: 05/12/2020] [Accepted: 05/27/2020] [Indexed: 12/01/2022]
Abstract
Different structurally related phenylpiperidine opioids exhibit different isoflurane-sparing effects in cats. Because minimum alveolar concentration (MAC) in cats is affected only by very high plasma concentrations of some phenylpiperidine opioids, we hypothesized these effects are caused by actions on nonopioid receptors. Using a prospective, randomized, crossover design, six cats were anesthetized with isoflurane, intubated, ventilated, and instrumented. Isoflurane MAC was measured in triplicate using a tail-clamp and bracketing technique. A computer-controlled intravenous infusion using prior pharmacokinetic models targeted plasma concentrations of 60 ng/ml fentanyl, 10 ng/ml sufentanil, or 500 ng/ml alfentanil, and isoflurane MAC was measured in duplicate. Next, naltrexone 0.6 mg/kg was administered to cats hourly during the opioid infusion, and isoflurane MAC was measured in duplicate. Blood was collected during MAC determinations to measure opioid concentrations. Responses were analyzed using repeated measures ANOVA with significance at p < .05. Alfentanil and sufentanil decreased isoflurane MAC by 16.4% and 6.4%, respectively, and these effects were completely reversed by naltrexone. Fentanyl had no significant effect on isoflurane MAC. Alfentanil and sufentanil modestly reduce isoflurane MAC via agonist effects on opioid receptors. However, these effects are too small to justify clinical use of phenylpiperidine opioids as single agents to reduce MAC in cats.
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Anesthetic-sensitive ion channel modulation is associated with a molar water solubility cut-off. BMC Pharmacol Toxicol 2018; 19:57. [PMID: 30217234 PMCID: PMC6137927 DOI: 10.1186/s40360-018-0244-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Accepted: 08/22/2018] [Indexed: 12/31/2022] Open
Abstract
Background NMDA receptor modulation by hydrocarbons is associated with a molar water solubility cut-off. Low-affinity phenolic modulation of GABAA receptors is also associated with a cut-off, but at much lower molar solubility values. We hypothesized that other anesthetic-sensitive ion channels exhibit distinct cut-off effects associated with hydrocarbon molar water solubility, and that cut-off values are comparatively similar between related receptors than phylogenetically distant ones. Methods Glycine or GABAA receptors or TREK-1, TRESK, Nav1.2, or Nav1.4 channels were expressed separately in frog oocytes. Two electrode voltage clamp techniques were used to study current responses in the presence and absence of hydrocarbon series from eight functional groups with progressively increasing size at saturated aqueous concentrations. Null response (cut-off) was defined by current measurements that were statistically indistinguishable between baseline and hydrocarbon exposure. Results Ion channels exhibited cut-off effects associated with hydrocarbon molar water solubility in the following order of decreasing solubility: Nav1.2 ≈ Nav1.4 ≳ TRESK ≈ TREK-1 > GABAA >> glycine. Previously measured solubility cut-off values for NMDA receptors were intermediate between those for Nav1.4 and TRESK. Conclusions Water solubility cut-off responses were present for all anesthetic-sensitive ion channels; distinct cut-off effects may exist for all cell surface receptors that are sensitive to volatile anesthetics. Suggested is the presence of amphipathic receptor sites normally occupied by water molecules that have dissociation constants inversely related to the cut-off solubility value. Poorly soluble hydrocarbons unable to reach concentrations sufficient to out-compete water for binding site access fail to modulate the receptor.
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Investigation of perioperative and anesthetic variables affecting short-term survival of horses with small intestinal strangulating lesions. Vet Surg 2017; 46:345-353. [PMID: 28152199 DOI: 10.1111/vsu.12618] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 09/26/2016] [Indexed: 11/29/2022]
Abstract
OBJECTIVE To determine if preoperative and intraoperative physiologic variables, and surgical factors correlate with survival to anesthetic recovery or hospital discharge, repeat celiotomy, and postoperative nasogastric intubation (NGT) in horses undergoing exploratory celiotomy for small intestinal (SI) strangulating lesions. STUDY DESIGN Retrospective case series. ANIMALS Horses that had surgical correction of SI strangulating lesions (n = 258). METHODS Medical records (January 2000-December 2014) of horses that had surgical correction of SI strangulating lesions were reviewed. Data collection included signalment, preoperative physical examination variables, hematologic values, presence of gastric reflux, peritoneal fluid analysis, intraoperative physiologic variables, intraoperative findings/treatments, and arterial blood gas values. Risk factors for survival to anesthetic recovery and hospital discharge were determined using exact logistic regression. RESULTS Survival to anesthetic recovery was 76% and survival to discharge after anesthetic recovery was 79%. The difference between abdominal and peripheral lactate concentrations and intraoperative tachycardia were associated with not surviving to anesthetic recovery or hospital discharge. Intraoperative hypotension, hypocapnia, and low intraoperative packed cell volume (PCV) were negative predictors of survival to anesthetic recovery. Low intraoperative PCV was also associated with NGT postoperatively. Performing resection-anastomosis and jejunocecostomy were associated with repeat celiotomy and with not surviving to hospital discharge. CONCLUSION Several hematological and cardiorespiratory variables show good correlation with short-term survival in horses undergoing surgery for SI strangulating lesions. These variables are easily measured and could be useful for prognosticating survival in horses presenting with SI strangulating lesions.
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Anesthetic synergy between two n-alkanes. Vet Anaesth Analg 2017; 44:577-588. [PMID: 28583773 DOI: 10.1016/j.vaa.2016.07.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2016] [Revised: 06/28/2016] [Accepted: 07/03/2016] [Indexed: 11/17/2022]
Abstract
OBJECTIVE N-butane and n-pentane can both produce general anesthesia. Both compounds potentiate γ-aminobutyric acid type A (GABAA) receptor function, but only butane inhibits N-methyl-d-aspartate (NMDA) receptors. It was hypothesized that butane and pentane would exhibit anesthetic synergy due to their different actions on ligand-gated ion channels. STUDY DESIGN Prospective experimental study. ANIMALS A total of four Xenopus laevis frogs and 43 Sprague-Dawley rats. METHODS Alkane concentrations for all studies were determined via gas chromatography. Using a Xenopus oocyte expression model, standard two-electrode voltage clamp techniques were used to measure NMDA and GABAA receptor responses in vitro as a function of butane and pentane concentrations relevant to anesthesia. The minimum alveolar concentrations (MAC) of butane and pentane were measured separately in rats, and then pentane MAC was measured during coadministration of 0.25, 0.50 or 0.75 times MAC of butane. An isobole with 95% confidence intervals was constructed using regression analysis. A sum of butane and pentane that was statistically less than the lower-end confidence bound isobole indicated a synergistic interaction. RESULTS Both butane and pentane dose-dependently potentiated GABAA receptor currents over the study concentration range. Butane dose-dependently inhibited NMDA receptor currents, but pentane did not modulate NMDA receptors. Butane and pentane MAC in rats was 39.4±0.7 and 13.7±0.4 %, respectively. A small but significant (p<0.03) synergistic anesthetic effect with pentane was observed during administration of either 0.50 or 0.75×MAC butane. CONCLUSIONS Butane and pentane show synergistic anesthetic effects in vivo consistent with their different in vitro receptor effects. CLINICAL RELEVANCE Findings support the relevance of NMDA receptors in mediating anesthetic actions for some, but not all, inhaled agents.
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Pharmacokinetics and pharmacodynamics of intravenous romifidine and propranolol administered alone or in combination for equine sedation. Vet Anaesth Analg 2017; 44:86-97. [DOI: 10.1111/vaa.12410] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Accepted: 03/08/2016] [Indexed: 12/01/2022]
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GABAA Receptor Modulation by Phenyl Ring Compounds Is Associated with a Water Solubility Cut-Off Value. Pharmacology 2016; 98:13-9. [PMID: 26986632 DOI: 10.1159/000444935] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 02/22/2016] [Indexed: 11/19/2022]
Abstract
BACKGROUND The modulation of N-methyl-D-aspartate receptors is associated with a molar water solubility cut-off effect of approximately 1.1 mmol/l and hence are unaffected by significantly less soluble compounds. However, compounds with this molar water solubility are still able to modulate x03B3;-aminobutyric acid type A (GABAA) receptors. We hypothesized that GABAA receptor modulation by phenolic compounds would exhibit cut-off at a molar water solubility value less than 1.1 mmol/l. METHODS GABAA receptors consisting of human α1 and rat β2 and x03B3;2s subunits were expressed in Xenopus laevis oocytes, and drug responses were measured using standard 2-electrode voltage clamp techniques. Twenty substituted phenols and benzenes of similar size and molecular volume were studied at saturated aqueous concentrations. Reversible and statistically significant change in GABAA receptor current that was 10% or greater in magnitude from the baseline response defined a positive drug effect. RESULTS All phenyl ring compounds with a molar water solubility value equal to or greater than 0.46 mmol/l positively modulated GABAA receptor currents. No compounds with a molar water solubility value equal to or less than 0.10 mmol/l had any effect on GABAA receptor currents. Saturated solutions of phenols with 2,6-dimethyl and 2,6-diisopropyl substituents also caused channel opening in the absence of GABA. CONCLUSIONS The molar water solubility cut-off for GABAA receptor modulation by phenyl ring compounds lies between 0.10 and 0.46 mmol/l. Data suggest that hydrocarbons, perhaps including inhaled anesthetics, might modulate GABAA receptors by displacing water from one or more low-affinity amphipathic binding sites to induce conformational changes that increase ion conductance.
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Qualitative and Quantitative Characteristics of the Electroencephalogram in Normal Horses during Administration of Inhaled Anesthesia. J Vet Intern Med 2015; 30:289-303. [PMID: 26714626 PMCID: PMC4913671 DOI: 10.1111/jvim.13813] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Revised: 08/27/2015] [Accepted: 11/17/2015] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND The effects of anesthesia on the equine electroencephalogram (EEG) after administration of various drugs for sedation, induction, and maintenance are known, but not that the effect of inhaled anesthetics alone for EEG recording. OBJECTIVE To determine the effects of isoflurane and halothane, administered as single agents at multiple levels, on the EEG and quantitative EEG (qEEG) of normal horses. ANIMALS Six healthy horses. METHODS Prospective study. Digital EEG with video and quantitative EEG (qEEG) were recorded after the administration of one of the 2 anesthetics, isoflurane or halothane, at 3 alveolar doses (1.2, 1.4 and 1.6 MAC). Segments of EEG during controlled ventilation (CV), spontaneous ventilation (SV), and with peroneal nerve stimulation (ST) at each MAC multiple for each anesthetic were selected, analyzed, and compared. Multiple non-EEG measurements were also recorded. RESULTS Specific raw EEG findings were indicative of changes in the depth of anesthesia. However, there was considerable variability in EEG between horses at identical MAC multiples/conditions and within individual horses over segments of a given epoch. Statistical significance for qEEG variables differed between anesthetics with bispectral index (BIS) CV MAC and 95% spectral edge frequency (SEF95) SV MAC differences in isoflurane only and median frequency (MED) differences in SV MAC with halothane only. CONCLUSIONS AND CLINICAL IMPORTANCE Unprocessed EEG features (background and transients) appear to be beneficial for monitoring the depth of a particular anesthetic, but offer little advantage over the use of changes in mean arterial pressure for this purpose.
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Electroencephalogram of Healthy Horses During Inhaled Anesthesia. J Vet Intern Med 2015; 30:304-8. [PMID: 26376458 PMCID: PMC4913644 DOI: 10.1111/jvim.13613] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Revised: 07/23/2015] [Accepted: 08/05/2015] [Indexed: 11/27/2022] Open
Abstract
Background Previous study of the diagnostic validity of electroencephalography (EEG) to detect abnormalities in equine cerebral cortical function relied on the administration of various drugs for sedation, induction, and maintenance of general anesthesia but used identical criteria to interpret recordings. Objectives To determine the effects of 2 inhalation anesthetics on the EEG of healthy horses. Animals Six healthy horses. Methods Prospective study. After the sole administration of one of either isoflurane or halothane at 1.2, 1.4, and 1.6 times the minimum alveolar concentration, EEG was recorded during controlled ventilation, spontaneous ventilation, and nerve stimulation. Results Burst suppression was observed with isoflurane, along with EEG events that resembled epileptiform discharges. Halothane results were variable between horses, with epileptiform‐like discharges and bursts of theta, alpha, and beta recorded intermittently. One horse died and 2 were euthanized as the result of anesthesia‐related complications. Conclusions and Clinical Importance The results of this study indicate that the effects of halothane and isoflurane on EEG activity in the normal horse can be quite variable, even when used in the absence of other drugs. It is recommended that equine EEG be performed without the use of these inhalation anesthetics and that general anesthesia be induced and maintained by other contemporary means.
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Equivalence between invasive and oscillometric blood pressures at different anatomic locations in healthy normotensive anaesthetised horses. Equine Vet J 2015; 48:357-61. [PMID: 25790220 DOI: 10.1111/evj.12443] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Accepted: 03/07/2015] [Indexed: 11/30/2022]
Abstract
REASONS FOR PERFORMING STUDY Accurate blood pressure measurement is essential for effective clinical assessment and appropriate interventions in anaesthetised horses. Information on the accuracy of oscillometry for blood pressure measurement on the appendages of mature horses is limited. OBJECTIVES To assess equivalence between invasive and oscillometric blood pressures at different anatomic locations in horses. STUDY DESIGN Prospective experimental study using 6 healthy mature horses. METHODS Blood pressure was measured invasively in the right transverse facial artery and noninvasively by oscillometry in nondependent limbs and tail of laterally recumbent sevoflurane- or desflurane-anaesthetised horses. Cuff widths of 5-12 cm were tested on the tail, metatarsus, metacarpus and distal radius/ulna. Equivalence between mean arterial pressure (MAP) oscillometric and MAP invasive was assessed using a linear mixed effects model with a significance level of P≤0.05. RESULTS Twenty paired measurements were obtained for each cuff size in each of the locations, totalling 340 measurements. There was only one location (tail) and one cuff width (6 cm; cuff width-to-tail circumference ratio of 0.25) that resulted in equivalence between MAP measured with the oscillometric and the invasive methods (P = 0.8). All other locations (metacarpus, radius/ulna, metatarsus) and cuff widths were not equivalent (P≤0.01). CONCLUSIONS A cuff width-to-tail circumference ratio of 0.25 is recommended for accurate oscillometric blood pressure measurement in mature, laterally recumbent anaesthetised normotensive horses. Studies with variable haemodynamics are warranted. Oscillometric measurements at other extremities and/or with other cuff sizes cannot be recommended for clinical use.
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Desflurane and sevoflurane elimination kinetics and recovery quality in horses. Am J Vet Res 2015; 76:201-7. [DOI: 10.2460/ajvr.76.3.201] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Hydrocarbon molar water solubility predicts NMDA vs. GABAA receptor modulation. BMC Pharmacol Toxicol 2014; 15:62. [PMID: 25410726 PMCID: PMC4247779 DOI: 10.1186/2050-6511-15-62] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Accepted: 11/13/2014] [Indexed: 12/02/2022] Open
Abstract
Background Many anesthetics modulate 3-transmembrane (such as NMDA) and 4-transmembrane (such as GABAA) receptors. Clinical and experimental anesthetics exhibiting receptor family specificity often have low water solubility. We hypothesized that the molar water solubility of a hydrocarbon could be used to predict receptor modulation in vitro. Methods GABAA (α1β2γ2s) or NMDA (NR1/NR2A) receptors were expressed in oocytes and studied using standard two-electrode voltage clamp techniques. Hydrocarbons from 14 different organic functional groups were studied at saturated concentrations, and compounds within each group differed only by the carbon number at the ω-position or within a saturated ring. An effect on GABAA or NMDA receptors was defined as a 10% or greater reversible current change from baseline that was statistically different from zero. Results Hydrocarbon moieties potentiated GABAA and inhibited NMDA receptor currents with at least some members from each functional group modulating both receptor types. A water solubility cut-off for NMDA receptors occurred at 1.1 mM with a 95% CI = 0.45 to 2.8 mM. NMDA receptor cut-off effects were not well correlated with hydrocarbon chain length or molecular volume. No cut-off was observed for GABAA receptors within the solubility range of hydrocarbons studied. Conclusions Hydrocarbon modulation of NMDA receptor function exhibits a molar water solubility cut-off. Differences between unrelated receptor cut-off values suggest that the number, affinity, or efficacy of protein-hydrocarbon interactions at these sites likely differ.
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Rabbit model of chest wall rigidity induced by fentanyl and the effects of apomorphine. Respir Physiol Neurobiol 2014; 202:50-2. [DOI: 10.1016/j.resp.2014.07.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2014] [Revised: 07/26/2014] [Accepted: 07/28/2014] [Indexed: 11/17/2022]
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Effects of acetylcholinesterase inhibition on quality of recovery from isoflurane-induced anesthesia in horses. Am J Vet Res 2014; 75:223-30. [PMID: 24564307 DOI: 10.2460/ajvr.75.3.223] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To compare effects of 2 acetylcholinesterase inhibitors on recovery quality of horses anesthetized with isoflurane. ANIMALS 6 horses in phase 1, 7 horses in phase 2A, and 14 horses in phase 2B. PROCEDURES The study comprised 3 phases (2 randomized, blinded crossover phases in horses undergoing orthopedic procedures and 1 prospective dose-determining phase). In phase 1, horses were anesthetized with isoflurane and received neostigmine or saline (0.9% NaCl) solution prior to anesthetic recovery. Phase 2A was a physostigmine dose-determining phase. In phase 2B, horses were anesthetized with isoflurane and received neostigmine or physostigmine prior to recovery. Objective recovery events were recorded and subjective visual analogue scale scores of recovery quality were assigned from video recordings. RESULTS Recovery measures in phase 1 were not different between horses receiving neostigmine or saline solution. In phase 2A, 0.04 mg of physostigmine/kg was the highest cumulative dose that did not cause clinically relevant adverse behavioral or gastrointestinal effects. Horses receiving physostigmine had higher mean ± SD visual analogue scale recovery scores (70.8 ± 13.3 mm) than did horses receiving neostigmine (62.4 ± 12.8 mm) in phase 2B, with fewer attempts until sternal and standing recovery. Incidence of colic behavior did not differ among groups. CONCLUSIONS AND CLINICAL RELEVANCE Inhibition with physostigmine improved anesthetic recovery quality in horses anesthetized with isoflurane, compared with recovery quality for horses receiving neostigmine. Inhibition of central muscarinic receptors by inhalation anesthetics may underlie emergence delirium in horses recovering from anesthesia.
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Cardiopulmonary effects of butorphanol in sevoflurane-anesthetized guineafowl (Numida meleagris). Vet Anaesth Analg 2014. [DOI: 10.1111/vaa.12108] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Pharmacokinetics and physiological effects of repeated oral administrations of tramadol in horses. J Vet Pharmacol Ther 2013; 37:269-78. [PMID: 24180699 DOI: 10.1111/jvp.12086] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Accepted: 09/19/2013] [Indexed: 11/28/2022]
Abstract
This study evaluated the pharmacokinetics and physiological effects of tramadol during repeated oral administrations in horses. Nine adult healthy horses were administered tramadol at 5 and 10 mg/kg orally every 12 h for 5 days in a randomized, crossover design with a 3-week washout between treatments. Plasma concentrations of tramadol, O- and N-desmethyltramadol (M1 and M2) were measured using Liquid-Chromatography-Mass Spectrometry at predetermined time points following each tramadol administration. Cardiovascular, respiratory and gastrointestinal physiological variables were monitored and adverse events were recorded. Data were analysed with two-way repeated measures anova or Kruskal-Wallis one-way anova on ranks with P < 0.05 considered statistically significant. There were no significant effects of tramadol on the physiological variables. One horse receiving 10 mg/kg tramadol developed mild colic. Following tramadol at 5 and 10 mg/kg, respectively, maximum plasma concentrations (Cmax ) of tramadol ranged from 82-587 and 127-1280 ng/mL, nonconjugated M1 ranged from 2.51-26.7 and 4.88-34.3 ng/mL, and nonconjugated M2 from 12.5-356 and 35.4-486 ng/mL. Corresponding minimum plasma concentrations (Cmin ) of tramadol at 12 h following each dose ranged from 0.8-24 and 3-117 ng/mL. Tramadol accumulated considerably over time, more markedly when given at 10 mg/kg than at 5 mg/kg (accumulation indexes of 3.51 and 1.73 respectively). There was no accumulation of M1 but substantial accumulation of M2. In conclusion, there was accumulation and increase in exposure to tramadol and M2, but not M1, during repeated oral administrations in horses.
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Effects of ketamine, propofol, or thiopental administration on intraocular pressure and qualities of induction of and recovery from anesthesia in horses. Am J Vet Res 2013; 74:1070-7. [PMID: 23879844 DOI: 10.2460/ajvr.74.8.1070] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To assess the effects of ketamine hydrochloride, propofol, or compounded thiopental sodium administration on intraocular pressure (IOP) and qualities of induction of and recovery from anesthesia in horses. ANIMALS 6 healthy adult horses. PROCEDURES Horses were sedated with xylazine hydrochloride (0.5 mg/kg), and anesthesia was induced with guaifenesin followed by ketamine (2 mg/kg), propofol (3 mg/kg), or thiopental (4 mg/kg) in a crossover study with ≥ 1 week between treatments. For each horse, IOP in the right eye was measured with a handheld applanation tonometer before and after xylazine administration, at the time of recumbency, and every 3 minutes after induction of anesthesia until spontaneous movement was observed. Cardiorespiratory responses and venous blood measurements were recorded during anesthesia. Induction of and recovery from anesthesia were subjectively evaluated by investigators who were unaware of the anesthetic treatment of each horse. Data were analyzed via a repeated-measures ANOVA with Holm-Ŝidák post hoc comparisons. RESULTS Compared with findings after xylazine administration (mean ± SD, 17 ± 3 mm Hg), thiopental decreased IOP by 4 ± 23%, whereas propofol and ketamine increased IOP by 8 ± 11% and 37 ± 16%, respectively. Compared with the effects of ketamine, propofol and thiopental resulted in significantly lower IOP at the time of recumbency and higher heart rates at 3 minutes after induction of anesthesia. No other significant differences among treatments were found. CONCLUSIONS AND CLINICAL RELEVANCE These findings support the use of thiopental or propofol in preference to ketamine for horses in which increases in IOP should be minimized.
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Sensory nerve conduction and somatosensory evoked potentials of the trigeminal nerve in horses with idiopathic headshaking. J Vet Intern Med 2013; 27:1571-80. [PMID: 24107198 DOI: 10.1111/jvim.12191] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Revised: 06/20/2013] [Accepted: 08/06/2013] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND Idiopathic headshaking (HSK) in horses is a distressing disorder in which the etiology and pathophysiology are unknown. HYPOTHESIS Differences in sensory function of the trigeminal nerve exist between healthy and affected horses. ANIMALS Six healthy mature geldings and 6 mature geldings with idiopathic HSK. METHODS Prospective study. Sensory nerve action and somatosensory evoked potentials studies were performed. The stimulus site comprised the gingival mucosa dorsal to the maxillary canine. A pair of recording electrodes was placed along the sensory pathway of the trigeminal complex at the infraorbital nerve (R1), maxillary nerve (R2), spinal tract of trigeminal (R3), and somatosensory cortex (R4). Sensory nerve action potential latency (ms), amplitude (μV), duration (ms), area under the curve (μVms), and conduction velocity (m/s) were calculated. RESULTS Threshold for activation of the infraorbital branch of the trigeminal nerve was significantly different between 5 affected (≤ 5 mA) and 6 control horses (≥ 10 mA). After initiation of an action potential, there were no differences in all parameters measured and no differences between left and right sides. A horse with seasonal HSK tested during a time of no clinical manifestations showed a threshold for activation similar to control horses. CONCLUSIONS AND CLINICAL IMPORTANCE This study confirms involvement of the trigeminal nerve hyperexcitability in the pathophysiology of disease. Further, results might support a functional rather than a structural alteration in the sensory pathway of the trigeminal complex that can be seasonal. The horse could serve as a natural animal model for humans with idiopathic trigeminal neuralgia.
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Effects of postanesthetic sedation with romifidine or xylazine on quality of recovery from isoflurane anesthesia in horses. J Am Vet Med Assoc 2013; 242:533-9. [DOI: 10.2460/javma.242.4.533] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Abstract
Inhaled agents represent an important and useful class of drugs for equine anesthesia. This article reviews the ether-type anesthetics in contemporary use, their uptake and elimination, their mechanisms of action, and their desirable and undesirable effects in horses.
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Naltrexone does not affect isoflurane minimum alveolar concentration in cats. Vet Anaesth Analg 2012; 40:225-8. [PMID: 23279646 DOI: 10.1111/vaa.12004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2011] [Accepted: 09/23/2011] [Indexed: 12/20/2022]
Abstract
OBJECTIVE To test whether naltrexone, an opioid receptor antagonist, affects the minimum alveolar concentration (MAC) of isoflurane in cats, a species that is relatively resistant to the general anesthetic sparing effects of most opioids. STUDY DESIGN Randomized, crossover, placebo-controlled, blinded experimental design. ANIMALS Six healthy adult cats weighing 4.9 ± 0.7 kg. METHODS The cats were studied twice. In the first study, baseline isoflurane MAC was measured in duplicate. The drug (saline control or 0.6 mg kg(-1) naltrexone) was administered IV every 40-60 minutes, and isoflurane MAC was re-measured. In the second study, cats received the second drug treatment using identical methods 2 weeks later. RESULTS Isoflurane MAC was 2.03 ± 0.12% and was unchanged from baseline following saline or naltrexone administration. CONCLUSION AND CLINICAL RELEVANCE Minimum alveolar concentration was unaffected by naltrexone. Because MAC in cats is unaffected by at least some mu-opioid agonists and antagonists, spinal neurons that are directly modulated by mu-opioid receptors in this species cannot be the neuroanatomic sites responsible for immobility from inhaled anesthetics.
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Use of Physiologic and Arterial Blood Gas Variables to Predict Short-Term Survival in Horses with Large Colon Volvulus. Vet Surg 2012; 42:107-13. [DOI: 10.1111/j.1532-950x.2012.01081.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Effects of butorphanol on the minimum anesthetic concentration for sevoflurane in guineafowl (Numida meleagris). Am J Vet Res 2012; 73:183-8. [PMID: 22280376 DOI: 10.2460/ajvr.73.2.183] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To determine the minimum anesthetic concentration (MAC) for sevoflurane and measure the dose and temporal effects of butorphanol on the MAC for sevoflurane in guineafowl. ANIMALS 10 healthy adult guineafowl (Numida meleagris). PROCEDURES Each bird was anesthetized with sevoflurane, and a standard bracketing method was used to measure the MAC in response to a noxious electrical stimulus. Subsequently, conditions were adjusted so that each bird was anesthetized with sevoflurane at a fraction of its respective MAC (eg, 0.7 times the MAC for that bird). Butorphanol tartrate (2 mg/kg, IV) was administered, and a noxious stimulus was applied every 15 minutes until the bird moved in response. The reduction in MAC was estimated with logistic regression by use of a standard quantal method. After an interval of ≥ 1 week, the MAC reduction experiment was repeated with an increased butorphanol dosage (4 mg/kg). RESULTS Individual mean ± SE MAC for sevoflurane was 2.9 ± 0.1%. At 15 minutes after administration of 2 mg of butorphanol/kg, estimated reduction in the MAC for sevoflurane was 9 ± 3%. At 15 and 30 minutes after administration of 4 mg of butorphanol/kg, estimated reduction in the MAC for sevoflurane was 21 ± 4% and 11 ± 8%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE In guineafowl, the MAC for sevoflurane was similar to values reported for other species. Increasing the butorphanol dosage decreased the MAC for sevoflurane, but the effect was small and of short duration for dosages up to 4 mg/kg.
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Increased NMDA receptor inhibition at an increased Sevoflurane MAC. BMC Anesthesiol 2012; 12:9. [PMID: 22672766 PMCID: PMC3439310 DOI: 10.1186/1471-2253-12-9] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2011] [Accepted: 06/06/2012] [Indexed: 11/10/2022] Open
Abstract
Background Sevoflurane potently enhances glycine receptor currents and more modestly decreases NMDA receptor currents, each of which may contribute to immobility. This modest NMDA receptor antagonism by sevoflurane at a minimum alveolar concentration (MAC) could be reciprocally related to large potentiation of other inhibitory ion channels. If so, then reduced glycine receptor potency should increase NMDA receptor antagonism by sevoflurane at MAC. Methods Indwelling lumbar subarachnoid catheters were surgically placed in 14 anesthetized rats. Rats were anesthetized with sevoflurane the next day, and a pre-infusion sevoflurane MAC was measured in duplicate using a tail clamp method. Artificial CSF (aCSF) containing either 0 or 4 mg/mL strychnine was then infused intrathecally at 4 μL/min, and the post-infusion baseline sevoflurane MAC was measured. Finally, aCSF containing strychnine (either 0 or 4 mg/mL) plus 0.4 mg/mL dizocilpine (MK-801) was administered intrathecally at 4 μL/min, and the post-dizocilpine sevoflurane MAC was measured. Results Pre-infusion sevoflurane MAC was 2.26%. Intrathecal aCSF alone did not affect MAC, but intrathecal strychnine significantly increased sevoflurane requirement. Addition of dizocilpine significantly decreased MAC in all rats, but this decrease was two times larger in rats without intrathecal strychnine compared to rats with intrathecal strychnine, a statistically significant (P < 0.005) difference that is consistent with increased NMDA receptor antagonism by sevoflurane in rats receiving strychnine. Conclusions Glycine receptor antagonism increases NMDA receptor antagonism by sevoflurane at MAC. The magnitude of anesthetic effects on a given ion channel may therefore depend on the magnitude of its effects on other receptors that modulate neuronal excitability.
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Effects of hypercapnic hyperpnea on recovery from isoflurane or sevoflurane anesthesia in horses. Vet Anaesth Analg 2012; 39:335-44. [PMID: 22574839 DOI: 10.1111/j.1467-2995.2012.00727.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE To test the hypothesis that hypercapnic hyperpnea produced using endotracheal insufflation with 5-10% CO(2) in oxygen could be used to shorten anesthetic recovery time in horses, and that recovery from sevoflurane would be faster than from isoflurane. STUDY DESIGN Randomized crossover study design. ANIMALS Eight healthy adult horses. METHODS After 2 hours' administration of constant 1.2 times MAC isoflurane or sevoflurane, horses were disconnected from the anesthetic circuit and administered 0, 5, or 10% CO(2) in balance O(2) via endotracheal tube insufflation. End-tidal gas samples were collected to measure anesthetic washout kinetics, and arterial and venous blood samples were collected to measure respiratory gas partial pressures. Horses recovered in padded stalls without assistance, and each recovery was videotaped and evaluated by reviewers who were blinded to the anesthetic agent and insufflation treatment used. RESULTS Compared to isoflurane, sevoflurane caused greater hypoventilation and was associated with longer times until standing recovery. CO(2) insufflation significantly decreased anesthetic recovery time compared to insufflation with O(2) alone without significantly increasing PaCO(2) . Pharmacokinetic parameters during recovery from isoflurane with CO(2) insufflation were statistically indistinguishable from sevoflurane recovery without CO(2). Neither anesthetic agent nor insufflation treatment affected recovery quality from anesthesia. CONCLUSIONS AND CLINICAL RELEVANCE Hypercapnic hyperpnea decreases time to standing without influencing anesthetic recovery quality. Although the lower blood gas solubility of sevoflurane should favor a shorter recovery time compared to isoflurane, this advantage is negated by the greater respiratory depression from sevoflurane in horses.
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Use of naltrexone to antagonize high doses of remifentanil in cats: a dose-finding study. Vet Anaesth Analg 2011; 38:594-7. [DOI: 10.1111/j.1467-2995.2011.00649.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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GABA(A) receptor antagonism increases NMDA receptor inhibition by isoflurane at a minimum alveolar concentration. Vet Anaesth Analg 2011; 38:231-9. [PMID: 21492389 DOI: 10.1111/j.1467-2995.2011.00605.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
OBJECTIVE At the minimum alveolar concentration (MAC), isoflurane potentiates GABA(A) receptor currents and inhibits NMDA receptor currents, and these actions may be important for producing anesthesia. However, isoflurane modulates GABA(A) receptors more potently than NMDA receptors. The objective of this study was to test whether isoflurane would function as a more potent NMDA receptor antagonist if its efficacy at GABA(A) receptors was decreased. STUDY DESIGN Prospective experimental study. ANIMALS Fourteen 10-week-old male Sprague-Dawley rats weighing 269 ± 12 g. METHODS Indwelling lumbar subarachnoid catheters were surgically placed in isoflurane-anesthetized rats. Two days later, the rats were anesthetized with isoflurane, and artificial CSF containing either 0 or 1 mg kg(-1) picrotoxin, a GABA(A) receptor antagonist, was infused intrathecally at 1 μL minute(-1). The baseline isoflurane MAC was then determined using a standard tail clamp technique. MK801 (dizocilpine), an NMDA receptor antagonist, was then administered intravenously at 0.5 mg kg(-1). Isoflurane MAC was re-measured. RESULTS Picrotoxin increased isoflurane MAC by 16% compared to controls. MK801 significantly decreased isoflurane MAC by 0.72% of an atmosphere in controls versus 0.47% of an atmosphere in rats receiving intrathecal picrotoxin. CONCLUSIONS AND CLINICAL RELEVANCE A smaller MK801 MAC-sparing effect in the picrotoxin group is consistent with greater NMDA antagonism by isoflurane in these animals, since it suggests that fewer NMDA receptors are available upon which MK801 could act to decrease isoflurane MAC. Decreasing isoflurane GABA(A) potentiation increases isoflurane NMDA antagonism at MAC. Hence, the magnitude of an anesthetic effect on a given channel or receptor at MAC may depend upon effects at other receptors.
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Does anesthetic additivity imply a similar molecular mechanism of anesthetic action at N-methyl-D-aspartate receptors? Anesth Analg 2011; 112:568-73. [PMID: 21233494 DOI: 10.1213/ane.0b013e3182080599] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
BACKGROUND Isoflurane and carbon dioxide (CO(2)) negatively modulate N-methyl-d-aspartate (NMDA) receptors, but via different mechanisms. Isoflurane is a competitive antagonist at the NMDA receptor glycine binding site, whereas CO(2) inhibits NMDA receptor current through extracellular acidification. Isoflurane and CO(2) exhibit additive minimum alveolar concentration effects in rats, but we hypothesized that they would not additively inhibit NMDA receptor currents in vitro because they act at different molecular sites. METHODS NMDA receptors were expressed in frog oocytes and studied using 2-electrode voltage clamp techniques. A glycine concentration response for NMDA was measured in the presence and absence of CO(2). Concentration-response curves for isoflurane, H(+), CO(2), and ketamine as a function of NMDA inhibition were measured, and a Hill equation was used to calculate the EC(50) for each compound. RESULTS Binary drug combinations containing ½ EC(50) were additive if NMDA current inhibition was not statistically different from 50%. The ½ EC(50) binary drug combinations decreased the percentage baseline NMDA receptor current as follows (mean ± SD, n = 5 to 6 oocytes each): CO(2)+ H(+) (51% ± 5%), CO(2 )+ isoflurane (54% ± 5%), H(+) + isoflurane (51% ± 3%), CO(2)+ ketamine (67% ± 8%), and H(+) + ketamine (64% ± 2%). CONCLUSIONS In contrast to our hypothesis, NMDA receptor inhibition by CO(2) and isoflurane is additive. Possibly, CO(2) acidification modulates a pH-sensitive loop on the NMDA receptor that in turn alters glycine binding affinity on the GluN1 subunit. However, ketamine plus either CO(2) or H(+) synergistically inhibits NMDA receptor currents. Drugs acting via different mechanisms can thus exhibit additive or synergistic receptor effects. Additivity may not robustly indicate commonality between molecular anesthetic mechanisms.
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Use of propofol-xylazine and the Anderson Sling Suspension System for recovery of horses from desflurane anesthesia. Vet Surg 2010; 38:927-33. [PMID: 20017849 DOI: 10.1111/j.1532-950x.2009.00599.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
OBJECTIVE To characterize the behavior of horses recovering in the Anderson Sling Suspension System after 4 hours of desflurane anesthesia and postdesflurane intravenous (IV) administration of propofol and xylazine. STUDY DESIGN Experimental study. ANIMALS Healthy horses (n=6), mean+/-SEM age 12.3+/-1.8 years; mean weight 556+/-27 kg. METHODS Each horse was anesthetized with xylazine, diazepam, and ketamine IV and anesthesia was maintained with desflurane in O(2). At the end of 4 hours of desflurane, each horse was positioned in the sling suspension system and administered propofol-xylazine IV. Recovery events were quantitatively and qualitatively assessed. Venous blood was obtained before and after anesthesia for biochemical and propofol analyses. RESULTS Anesthetic induction and maintenance were without incident. Apnea commonly accompanied propofol administration. All horses had consistent recovery behavior characterized by a smooth, careful, atraumatic return to a standing posture. CONCLUSIONS Results of this study support careful, selective clinical use of desflurane, propofol-xylazine, and the Anderson Sling Suspension System to atraumatically transition horses with high anesthetic recovery risk to a wakeful standing posture. CLINICAL RELEVANCE Technique choices to facilitate individualized, atraumatic recovery of horses from general anesthesia are desirable. Use of IV propofol and xylazine to transition horses from desflurane anesthesia during sling recovery to standing posture may facilitate improved recovery management of high-injury risk equine patients requiring general anesthesia.
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Effect of administration of propofol and xylazine hydrochloride on recovery of horses after four hours of anesthesia with desflurane. Am J Vet Res 2009; 70:956-63. [PMID: 19645576 DOI: 10.2460/ajvr.70.8.956] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To compare characteristics of horses recovering from 4 hours of desflurane anesthesia with and without immediate postanesthetic IV administration of propofol and xylazine. Animals-8 healthy horses (mean +/- SEM age, 6.6 +/- 1.0 years; mean body weight, 551 +/- 50 kg). PROCEDURES Horses were anesthetized twice. Both times, anesthesia was induced with a combination of xylazine hydrochloride, diazepam, and ketamine hydrochloride and then maintained for 4 hours with desflurane in oxygen. Choice of postanesthetic treatment was randomly assigned via a crossover design such that each horse received an IV injection of propofol and xylazine or saline (0.9% NaCl) solution after the anesthetic episode. Recovery events were quantitatively and qualitatively assessed. Venous blood samples were obtained before and after anesthesia for determination of serum creatine kinase activity and plasma propofol concentration. RESULTS Anesthetic induction and maintenance were unremarkable in all horses. Compared with administration of saline solution, postanesthetic administration of propofol and xylazine resulted in an increased interval to emergence from anesthesia but improved quality of recovery-related transition to standing. Compared with administration of saline solution, administration of propofol also delayed the rate of decrease of end-tidal concentrations of desflurane and carbon dioxide and added to conditions promoting hypoxemia and hypoventilation. CONCLUSIONS AND CLINICAL RELEVANCE Propofol and xylazine administered IV to horses after 4 hours of desflurane anesthesia improved the quality of transition from lateral recumbency to standing but added potential for harmful respiratory depression during the postanesthetic period.
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Effects of remifentanil on measures of anesthetic immobility and analgesia in cats. Am J Vet Res 2009; 70:1065-71. [DOI: 10.2460/ajvr.70.9.1065] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Abstract
OBJECTIVE We hypothesized that propofol can produce rapidly-reversible, dose-dependent standing sedation in horses. STUDY DESIGN Prospective randomized, blinded, experimental trial. ANIMALS Twelve healthy horses aged 12 +/- 6 years (mean +/- SD), weighing 565 +/- 20 kg, and with an equal distribution of mares and geldings. METHODS Propofol was administered as an intravenous bolus at one of three randomized doses (0.20, 0.35 and 0.50 mg kg(-1)). Cardiovascular and behavioral measurements were made by a single investigator, who was blinded to treatment dose, at 3 minute intervals until subjective behavior scores returned to pre-sedation baseline values. Continuous data were analyzed over time using repeated-measures anova and noncontinuous data were analyzed using Friedman tests. RESULTS There were no significant propofol dose or temporal effects on heart rate, respiratory rate, vertical head height, or jugular venous blood gases (pH(v), P(v)O(2), P(v)CO(2)). The 0.35 mg kg(-1) dose caused mild sedation lasting up to 6 minutes. The 0.50 mg kg(-1) dose increased sedation depth and duration, but with increased ataxia and apparent muscle weakness. CONCLUSIONS AND CLINICAL RELEVANCE Intravenous 0.35 mg kg(-1) propofol provided brief, mild sedation in horses. Caution is warranted at higher doses due to increased risk of ataxia.
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Effect of administration of propofol and xylazine hydrochloride on recovery of horses after four hours of anesthesia with desflurane. J Am Vet Med Assoc 2009. [DOI: 10.2460/javma.235.3.298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Abstract
BACKGROUND Carbon dioxide (CO2) dose-dependently decreases minimum alveolar concentration (MAC) of anaesthetics in rats. CO2 also dose-dependently decreases cerebrospinal fluid pH. N-methyl-D-aspartate (NMDA) channels exhibit pH sensitivity and are putative targets for inhaled anaesthetics. We hypothesized that CO2 dose-dependently decreases rat NMDA channel current via an acidifying effect at concentrations relevant to CO2 MAC. METHODS To test this hypothesis, we studied rat NR1/NR2A glutamate receptors expressed in voltage-clamped Xenopus oocytes. To measure pH effects, we used perfusates adjusted between 7.3 and 5.3 with HCl. To measure CO2 effects, we used equimolar sodium perfusates containing either 0 or 24 mM NaHCO3 and CO2 between 0% and 87% atm. Solution compositions were measured using a blood gas analyser with values corrected using a calibrated pH meter and gas chromatograph with solutions at 37 degrees C. RESULTS We found that decreasing pH decreased NMDA current. Moreover, pH effects produced by adding CO2 to NaHCO3-containing perfusates were identical to those produced by adding HCl to normal perfusates. The pH inhibiting 50% of NMDA current was 6.52. The CO2 concentration inhibiting 50% of rat NMDA current was 63% for solutions with 24 mM NaHCO3. CO2 exhibited a linear dose-dependent NMDA response analogous to that observed for in vivo CO2 anaesthetic potency in rats. CONCLUSIONS CO2 and hydrogen ions act via the same mechanism to inhibit NMDA receptors. Moreover, CO2 inhibits rat NMDA receptors in a manner that is consistent with CO2 MAC-sparing effects in rats.
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Effects of head-down positioning on regional central nervous system perfusion in isoflurane-anesthetized horses. Am J Vet Res 2008; 69:737-43. [DOI: 10.2460/ajvr.69.6.737] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Pharmacokinetics of remifentanil in conscious cats and cats anesthetized with isoflurane. Am J Vet Res 2008; 69:531-6. [DOI: 10.2460/ajvr.69.4.531] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Abstract
BACKGROUND We tested the hypothesis that two metabolites that are elevated in ketosis (beta-hydroxybutyric acid, and acetone) modulate ion channels in a manner similar to anesthetics and produce anesthesia in animals. METHODS alpha1beta2gamma2sgamma-aminobutyric acid type A (GABA(A)), alpha1 glycine, NR1/NR2A N-methyl-d-aspartate, and two pore domain TRESK channels were expressed in Xenopus laevis oocytes and studied using two-electrode voltage clamping. The effect of beta hydroxybutyric acid and acetone on channel function was measured. The anesthetic effects of these drugs were measured in X. laevis tadpoles. RESULTS Both beta hydroxybutyric acid and acetone enhanced glycine receptor function in the concentration range that is obtained in ketoacidosis in humans. Beta hydroxybutyric acid also enhanced GABA(A) receptor function at these concentrations. Both acetone and beta-hydroxybutyric acid anesthetized tadpoles, with an EC50 for acetone of 264 +/- 2 mM (mean +/- se) and for beta-hydroxybutyric acid of 151 +/- 11 mM at pH 7.0. Acetone enhanced GABA(A) receptors at concentrations of 50 mM and above. Inhibition of TRESK channel function was seen with 100 mM acetone or larger concentration. N-methyl-D-aspartate receptor function was inhibited at concentrations of acetone of 200 mM and larger. CONCLUSIONS Beta hydroxybutyric acid and acetone are anesthetics. Both ketone bodies enhance inhibitory glycine receptors at concentrations observed clinically in ketoacidosis. In addition, beta-hydroxybutyric acid enhances GABA(A) receptor function at these concentrations. Subanesthetic concentrations of these drugs may contribute to the lethargy and impairment of consciousness seen in ketoacidosis.
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The plasticizer di(2-ethylhexyl) phthalate modulates gamma-aminobutyric acid type A and glycine receptor function. Anesth Analg 2007; 105:393-6. [PMID: 17646496 DOI: 10.1213/01.ane.0000267336.37735.d7] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
INTRODUCTION Intravenous (IV) fluid bags made of polyvinyl chloride (PVC) often contain the plasticizer di(2-ethylhexyl) phthalate (DEHP) to make the PVC flexible. Phthalate esters have been reported to inhibit neuronal nicotinic acetylcholine receptors, which are sensitive to many inhaled anesthetics. This raises the possibility that DEHP might modulate the function of other cys-loop receptors, such as gamma-amino butyric acid type A (GABA(A)) and glycine receptors, and that DEHP-plasticized PVC might interfere with electrophysiologic studies of anesthetic mechanisms on those receptors. METHODS alpha(1)beta(2) GABA(A) and alpha(1) glycine receptors were expressed in Xenopus laevis oocytes and studied using two-electrode voltage clamping. We then measured the effect of buffers from IV bags containing DEHP-plasticized PVC, and of buffers saturated with DEHP, on agonist-induced currents. RESULTS Agonist-induced currents from glycine receptors were enhanced by buffers from IV bags containing DEHP-plasticized PVC by 291.9% +/- 84.5% (mean +/- se) and from saturated solutions of DEHP by 70.8% +/- 16.7%. Agonist-induced currents from alpha(1)beta(2) GABA(A) receptors were inhibited by buffers from IV bags containing DEHP-plasticized PVC by 19.3% +/- 3.2% and by 31.7% +/- 7.0% from buffers saturated with DEHP. CONCLUSIONS The plasticizer DEHP modulates the function of both GABA(A) and glycine receptors. DEHP contamination can confound the results of electrophysiologic studies of anesthetic mechanisms on these receptors if DEHP-plasticized PVC is present in the experimental apparatus.
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Abstract
BACKGROUND Carbon dioxide decreases halothane minimum alveolar concentrations (MAC) in dogs when Paco(2) exceeds 95 mm Hg. We sought to confirm these findings for several potent inhaled anesthetics in rats. METHODS Groups of eight rats were anesthetized with halothane, isoflurane, or desflurane. MAC was determined for each anesthetic alone, and then with increasing concentrations of inspired CO(2). A fourth group was given CO(2) alone to determine the MAC of CO(2). RESULTS Increasing inspired CO(2) concentrations produced a linear dose-dependent decrease in MAC of each potent inhaled anesthetic. With elimination of CO(2), the MAC of isoflurane and desflurane returned to the original MAC. As determined by extrapolating these data to 0% of the inhaled anesthetic, the MAC of CO(2) was approximately 50% of 1 atm. Given alone, CO(2) proved lethal. CONCLUSIONS Unlike dogs, no threshold for the CO(2)-MAC response arose with halothane, isoflurane, or desflurane in rats. The ED(50) for CO(2) is also approximately 50% greater in rats than reported in dogs.
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