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OBJECTIVE: To determine minimum alveolar concentration (MAC) of isoflurane in green iguanas and effects of butorphanol on MAC. DESIGN: Prospective randomized trial. ANIMALS: 10 healthy mature iguanas. PROCEDURE: in each iguana, MAC was measured 3 times: twice after induction of anesthesia with isoflurane and once after induction of anesthesia with isoflurane and IM administration of butorphanol (1 mg/kg [0.45 mg/lb]). A blood sample was collected from the tail vein for blood-gas analysis at the beginning and end of the anesthetic period. The MAC was determined with a standard bracketing technique; an electrical current was used as the supramaximal stimulus. Animals were artificially ventilated with a ventilator set to deliver a tidal volume of 30 mL/kg (14 mL/lb) at a rate of 4 breaths/min. RESULTS: Mean +/- SD MAC values during the 3 trials (2 without and 1 with butorphanol) were 2.0 +/- 0.6, 2.1 +/- 0.6, and 1.7 +/- 0.7%, respectively, which were not significantly different from each other. Heart rate and end-tidal partial pressure of CO2 were also not significantly different among the 3 trials. Mean +/- SD heart rate was 48 +/- 10 beats/min; mean end-tidal partial pressure of CO2 was 22 +/- 10 mm Hg.There were no significant differences in blood-gas values for samples obtained at the beginning versus the end of the anesthetic period. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the MAC of isoflurane in green iguanas is 2.1% and that butorphanol does not have any significant isoflurane-sparing effects.  相似文献   

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OBJECTIVE: To determine the minimum alveolar concentration (MAC) of isoflurane (ISO) in llamas. STUDY DESIGN: Prospective study. ANIMALS: Eight adult neutered male llamas (9 +/- 1 years [x +/- SD], 177 +/- 29 kg). METHODS: Anesthesia was induced and maintained in otherwise unmedicated llamas with a mixture of ISO in oxygen administered through a standard small-animal, semi-closed circle system using an out-of-circle, agent-specific vaporizer. The time from mask placement to intubation was recorded. Inspired and end-tidal (ET) ISO was sampled continuously. At each anesthetic concentration, a constant ET ISO was maintained for at least 20 minutes before application of a noxious electrical stimulus (50 volts, 5 Hz, 10 ms for up to 1 minute). A positive or negative response to the stimulus was recorded, and ET ISO then increased (if positive response) or decreased (if negative response) by 10% to 20%. Individual MAC was the average of multiple determinations. Body temperature was maintained at 37 +/- 1 degrees C. Selected cardiopulmonary variables (heart rate [HR], respiratory rate [RR], arterial blood pressure [ABP]) and ET ISO were recorded at hourly intervals from first ISO. Arterial blood was collected for pH, PCO2, PO2 analysis and measurement of packed cell volume (PCV) and total protein (TP) at 2 hour intervals. Following MAC determination, the anesthetic was discontinued and llamas were allowed to recover. Duration and quality of recovery were noted. RESULTS: The time from start of induction by mask to completion of intubation took 19.1 +/- 4.8 minutes. The MAC of ISO corrected to one atmosphere at sea level (barometric pressure 760 mm Hg) in these llamas was 1.05 +/- 0.17%. Mean ABP increased from 70 +/- 26 mm Hg at the end of the first hour of anesthesia to 102 +/- 7 mm Hg measured at the end of the sixth hour of anesthesia. ET ISO decreased from 2.06 +/- 0.10% to 1.27 +/- 0.07% over the same time period, but MAC did not change with time. The duration from first ISO to discontinuation of ISO averaged 6.19 +/- 0.9 hours. Animals were able to support their heads in a sternal posture at 23 +/- 10 minutes, and stood 62 +/- 26 minutes following discontinuation of the anesthetic. CONCLUSION: The MAC for ISO is similar to, but slightly lower than, values reported for other species. CLINICAL RELEVANCE: Knowledge of MAC may facilitate appropriate clinical use and provide the basis for future investigation of ISO in llamas.  相似文献   

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Objective

To characterize the isoflurane-sparing effects of a high and a low dose of fentanyl in dogs, and its effects on mean arterial pressure (MAP) and heart rate (HR).

Study design

Prospective, randomized crossover trial.

Animals

Eight healthy male Beagle dogs weighing 12.1 ± 1.6 kg [mean ± standard deviation (SD)] and approximate age 1 year.

Methods

Dogs were anesthetized using isoflurane and minimum alveolar concentration (MAC) was determined in duplicate by the bracketing method using an electrical stimulus on the tarsus. Animals were administered fentanyl: low dose (33 μg kg?1 loading dose, 0.2 μg kg?1 minute?1) or high dose (102 μg kg?1 loading dose, 0.8 μg kg?1 minute?1) and MAC was re-determined (MACISO-F). Blood was collected for analysis of plasma fentanyl concentrations before administration and after MACISO-F determination. All values are presented as mean ± SD.

Results

Isoflurane MAC (MACISO) was 1.30 ± 0.23% in the low dose treatment, which significantly decreased to 0.75 ± 0.22% (average MAC reduction 42.3 ± 9.4%). MACISO was 1.30 ± 0.18% in the high dose treatment, which significantly decreased to 0.30 ± 0.11% (average MAC reduction 76.9 ± 7.4%). Mean fentanyl plasma concentrations were 6.2 and 29.5 ng mL?1 for low and high dose treatments, respectively. MAP increased significantly only in the high dose treatment (from 81 ± 8 to 92 ± 9 mmHg). HR decreased significantly in both treatments from 108 ± 25 to 61 ± 14 beats minute?1 with the low dose and from 95 ± 14 to 42 ± 4 beats minute?1 with the high dose.

Conclusions and clinical relevance

Fentanyl administration resulted in a dose-dependent isoflurane MAC-sparing effect with bradycardia at both doses and an increase in MAP only at high dose. Further evaluation is needed to determine the effects of fentanyl on the overall cardiovascular function.  相似文献   

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ObjectiveTo determine the minimum alveolar concentration (MAC) of sevoflurane in Holstein steers using electric stimulation.Study designProspective experimental study.AnimalsA total of 15 Holstein steers aged 7.3 ± 1.2 months and weighing 121 ± 25 kg.MethodsAnimals were anesthetized with sevoflurane at 8% in oxygen at 5 L minute–1 via facemask and were intubated with an orotracheal tube of a compatible size. After 15 minutes of stabilization of the initial expired concentration of sevoflurane (Fe′Sevo) at 2.6%, electrical stimulation on the thoracic limb was initiated with a sequence of 2 × 10 ms followed by 2 × 3 second electrical currents of 50 V and 50 Hz, 5 seconds apart. Following each stimulus with a negative response, the Fe′Sevo was decreased by 0.2% and a 15 minute interval was awaited before the next stimulus. The procedure was repeated until the first Fe′Sevo value with a positive motor response was obtained. The Fe′Sevo was then increased by 0.1%, followed by a new stimulus, until a negative response was obtained. The value of MAC was calculated as the arithmetic mean between the lowest Fe′Sevo associated with a negative motor response and the highest Fe′Sevo associated with a positive response.ResultsThe mean MAC for the 15 steers was 2.0 ± 0.3%, which corresponds to 2.1 ± 0.3% at sea level.ConclusionsBased on the proposed methodology, the MAC of sevoflurane for healthy Holstein steers is 2.1 ± 0.3% at sea level.Clinical relevanceThis Fe′Sevo value can be used to guide depth of anesthesia in steers weighing approximately 120 kg in clinical practice.  相似文献   

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ObjectiveTo 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 designRandomized, crossover, placebo-controlled, blinded experimental design.AnimalsSix healthy adult cats weighing 4.9 ± 0.7 kg.MethodsThe 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.ResultsIsoflurane MAC was 2.03 ± 0.12% and was unchanged from baseline following saline or naltrexone administration.Conclusion and clinical relevanceMinimum 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.  相似文献   

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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.  相似文献   

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Pigs are important animal models in veterinary and medical research and have been widely used in experiments requiring surgical anesthesia. Sevoflurane is an inhalant anesthetic with unique properties that make it an ideal anesthetic for mask induction and anesthesia maintenance. However, there are relatively few studies reporting the anesthetic requirements for sevoflurane in juvenile swine, an age group that is commonly used in research experiments. Therefore the objective of this study was to determine the Minimum Alveolar Concentration (MAC) for sevoflurane in juvenile swine. Sevoflurane anesthesia was induced in six Yorkshire-cross pigs of approximately 9 weeks-of-age and MAC for sevoflurane was determined. The sevoflurane MAC value was determined to be 3.5+/-0.1% which is notably higher than values reported in the literature for pigs. This discrepancy in MAC values may represent changes in anesthetic requirements between different age groups of pigs and differences in the type of stimulus used to determine MAC.  相似文献   

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This study reports the effects of dexmedetomidine on the minimum alveolar concentration of isoflurane (MAC(iso) ) in cats. Six healthy adult female cats were used. MAC(iso) and dexmedetomidine pharmacokinetics had previously been determined in each individual. Cats were anesthetized with isoflurane in oxygen. Dexmedetomidine was administered intravenously using target-controlled infusions to maintain plasma concentrations of 0.16, 0.31, 0.63, 1.25, 2.5, 5, 10, and 20 ng/mL. MAC(iso) was determined in triplicate at each target plasma dexmedetomidine concentration. Blood samples were collected and analyzed for dexmedetomidine concentration. The following model was fitted to the concentration-effect data: [Formula in text] where MAC(iso.c) is MAC(iso) at plasma dexmedetomidine concentration C, MAC(iso.0) is MAC(iso) in the absence of dexmedetomidine, I(max) is the maximum possible reduction in MAC(iso), and IC(50) is the plasma dexmedetomidine concentration producing 50% of I(max). Mean ± SE MAC(iso.0), determined in a previous study conducted under conditions identical to those in this study, was 2.07 ± 0.04. Weighted mean ± SE I(max), and IC(50) estimated by the model were 1.76 ± 0.07%, and 1.05 ± 0.08 ng/mL, respectively. Dexmedetomidine decreased MAC(iso) in a concentration-dependent manner. The lowest MAC(iso) predicted by the model was 0.38 ± 0.08%, illustrating that dexmedetomidine alone is not expected to result in immobility in response to noxious stimulation in cats at any plasma concentration.  相似文献   

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OBJECTIVE: To determine the effect of IV administration of perzinfotel on the minimum alveolar concentration (MAC) of isoflurane in dogs. Animals-6 healthy sexually intact male Beagles. PROCEDURES: Dogs were instrumented with a telemetry device that permitted continuous monitoring of heart rate, arterial blood pressure, and body temperature. Dogs were anesthetized with propofol (4 to 6 mg/kg, IV) and isoflurane for 30 minutes before determination of MAC of isoflurane. Isoflurane MAC values were determined 4 times, separated by a minimum of 7 days, before and after IV administration of perzinfotel (0 [control], 5, 10, and 20 mg/kg). Bispectral index and percentage hemoglobin saturation with oxygen (SpO(2)) were monitored throughout anesthesia. RESULTS: Isoflurane MAC was 1.32 +/- 0.14%. Intravenous administration of perzinfotel at 0, 5, 10, and 20 mg/kg decreased isoflurane MAC by 0%, 24%, 30%, and 47%, respectively. Perzinfotel significantly decreased isoflurane MAC values, compared with baseline and control values. The bispectral index typically increased with higher doses of perzinfotel and lower isoflurane concentrations, but not significantly. Heart rate, body temperature, and SpO(2) did not change, but systolic, mean, and diastolic arterial blood pressures significantly increased with decreases in isoflurane MAC after administration of perzinfotel at 10 and 20 mg/kg, compared with 0 and 5 mg/kg. CONCLUSIONS AND CLINICAL RELEVANCE: IV administration of perzinfotel decreased isoflurane MAC values. Improved hemodynamics were associated with decreases in isoflurane concentration.  相似文献   

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ObjectiveTo evaluate the effect of tramadol on sevoflurane minimum alveolar concentration (MACSEVO) in dogs. It was hypothesized that tramadol would dose-dependently decrease MACSEVO.Study designRandomized crossover experimental study.AnimalsSix healthy, adult female mixed-breed dogs (24.2 ± 2.6 kg).MethodsEach dog was studied on two occasions with a 7-day washout period. Anesthesia was induced using sevoflurane delivered via a mask. Baseline MAC (MACB) was determined starting 45 minutes after tracheal intubation. A noxious stimulus (50 V, 50 Hz, 10 ms) was applied subcutaneously over the mid-humeral area. If purposeful movement occurred, the end-tidal sevoflurane was increased by 0.1%; otherwise, it was decreased by 0.1%, and the stimulus was re-applied after a 20-minute equilibration. After MACB determination, dogs randomly received a tramadol loading dose of either 1.5 mg kg?1 followed by a continuous rate infusion (CRI) of 1.3 mg kg?1 hour?1 (T1) or 3 mg kg?1 followed by a 2.6 mg kg?1 hour?1 CRI (T2). Post-treatment MAC determination (MACT) began 45 minutes after starting the CRI. Data were analyzed using a mixed model anova to determine the effect of treatment on percentage change in baseline MACSEVO (p < 0.05).ResultsThe MACB values were 1.80 ± 0.3 and 1.75 ± 0.2 for T1 and T2, respectively, and did not differ significantly. MACT decreased by 26 ± 8% for T1 and 36 ± 12% for T2. However, there was no statistically significant difference in the decrease between the two treatments.Conclusion and clinical relevanceTramadol significantly reduced MACSEVO but this was not dose dependent at the doses studied.  相似文献   

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ObjectiveTo investigate the effects of methadone on the minimum alveolar concentration of isoflurane (ISOMAC) in dogs.Study designProspective, randomized cross-over experimental study.AnimalsSix adult mongrel dogs, four males and two females, weighing 22.8 ± 6.6 kg.MethodsAnimals were anesthetized with isoflurane and mechanically ventilated on three separate days, at least 1 week apart. Core temperature was maintained between 37.5 and 38.5 °C during ISOMAC determinations. On each study day, ISOMAC was determined using electrical stimulation of the antebrachium (50 V, 50 Hz, 10 mseconds) at 2.5 and 5 hours after intravenous injection of physiological saline (control) or one of two doses of methadone (0.5 or 1.0 mg kg?1).ResultsMean (±SD) ISOMAC in the control treatment was 1.19 ± 0.15% and 1.18 ± 0.15% at 2.5 and 5 hours, respectively. The 1.0 mg kg?1 dose of methadone reduced ISOMAC by 48% (2.5 hours) and by 30% (5 hours), whereas the 0.5 mg kg?1 dose caused smaller reductions in ISOMAC (35% and 15% reductions at 2.5 and 5 hours, respectively). Both doses of methadone decreased heart rate (HR), but the 1.0 mg kg?1 dose was associated with greater negative chronotropic actions (HR 37% lower than control) and mild metabolic acidosis at 2.5 hours. Mean arterial pressure increased in the MET1.0 treatment (13% higher than control) at 2.5 hours.Conclusions and clinical relevanceMethadone reduces ISOMAC in a dose-related fashion and this effect is lessened over time. Although the isoflurane sparing effect of the 0.5 mg kg?1 dose of methadone was smaller in comparison to the 1.0 mg kg?1 dose, the lower dose is recommended for clinical use because it results in less evidence of cardiovascular impairment.  相似文献   

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Objective  To investigate the effects of a low-dose constant rate infusion (LCRI; 50 μg kg−1 minute−1) and high-dose CRI (HCRI; 200 μg kg−1 minute−1) lidocaine on arterial blood pressure and on the minimum alveolar concentration (MAC) of sevoflurane (Sevo), in dogs.
Study design  Prospective, randomized experimental design.
Animals  Eight healthy adult spayed female dogs, weighing 16.0 ± 2.1 kg.
Methods  Each dog was anesthetized with sevoflurane in oxygen and mechanically ventilated, on three separate occasions 7 days apart. Following a 40-minute equilibration period, a 0.1-mL kg−1 saline loading dose or lidocaine (2 mg kg−1 intravenously) was administered over 3 minutes, followed by saline CRI or lidocaine LCRI or HCRI. The sevoflurane MAC was determined using a tail clamp. Heart rate (HR), blood pressure and plasma concentration of lidocaine were measured. All values are expressed as mean ± SD.
Results  The MAC of Sevo was 2.30 ± 0.19%. The LCRI reduced MAC by 15% to 1.95 ± 0.23% and HCRI by 37% to 1.45 ± 0.21%. Diastolic and mean pressure increased with HCRI. Lidocaine plasma concentration was 0.84 ± 0.18 for LCRI and 1.89 ± 0.37 μg mL−1 for HCRI. Seventy-five percent of HCRI dogs vomited during recovery.
Conclusion and clinical relevance  Lidocaine infusions dose dependently decreased the MAC of Sevo, did not induce clinically significant changes in HR or arterial blood pressure, but vomiting was common during recovery in HCRI.  相似文献   

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OBJECTIVE: To determine the influence of a low-dose constant rate infusion (LCRI; 50 microg kg(-1) minute(-1)) and high-dose CRI (HCRI; 200 microg kg(-1) minute(-1)) lidocaine infusion on the minimum alveolar concentration (MAC) of isoflurane (I) in dogs. STUDY DESIGN: Prospective experimental study. ANIMALS: Ten mongrel dogs (four females, six males), weighing 20-26.3 kg. METHODS: Dogs were anesthetized with I in oxygen and their lungs mechanically ventilated. Baseline MAC was determined using mechanical or electrical stimuli. Lidocaine (2 mg kg(-1) IV) was administered over 3 minutes, followed by the LCRI and MAC determination commenced 30 minutes later. Once MAC was determined following LCRI, the lidocaine infusion was stopped for 30 minutes. A second bolus of lidocaine (2 mg kg(-1), IV) was administered, followed by the HCRI and MAC re-determined. Concentrations of lidocaine and its metabolites were measured at end-tidal I concentrations immediately above and below MAC. Heart rates and blood pressures were measured. RESULTS: Minimum alveolar concentration of I was 1.34 +/- 0.11 (%; mean +/- SD) for both types of stimulus. The LCRI significantly reduced MAC to 1.09 +/- 0.13 (18.7% reduction) and HCRI to 0.76 +/- 0.10 (43.3% reduction). Plasma concentrations (ng mL(-1), median; value below and above MAC, respectively) for LCRI were: lidocaine, 1465 and 1537; glycinexylidide (GX), 111 and 181; monoethylglycinexylidide (MEGX), 180 and 471 and for HCRI were: lidocaine, 4350 and 4691; GX, 784 and 862; MEGX, 714 and 710. Blood pressure was significantly increased at 30 minutes after high dose infusion. CONCLUSION AND CLINICAL RELEVANCE: Lidocaine infusions reduced the MAC of I in a dose-dependent manner and did not induce clinically significant changes on heart rate or blood pressure.  相似文献   

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OBJECTIVE: To evaluate the effects of ketamine, magnesium sulfate, and their combination on the minimum alveolar concentration (MAC) of isoflurane (ISO-MAC) in goats. ANIMALS: 8 adult goats. PROCEDURES: Anesthesia was induced with isoflurane delivered via face mask. Goats were intubated and ventilated to maintain normocapnia. After an appropriate equilibration period, baseline MAC (MAC(B)) was determined and the following 4 treatments were administered IV: saline (0.9% NaCl) solution (loading dose [LD], 30 mL/20 min; constant rate infusion [CRI], 60 mL/h), magnesium sulfate (LD, 50 mg/kg; CRI, 10 mg/kg/h), ketamine (LD, 1 mg/kg; CRI, 25 microg/kg/min), and magnesium sulfate (LD, 50 mg/kg; CRI, 10 mg/kg/h) combined with ketamine (LD, 1 mg/kg; CRI, 25 microg/kg/min); then MAC was redetermined. RESULTS: Ketamine significantly decreased ISOMAC by 28.7 +/- 3.7%, and ketamine combined with magnesium sulfate significantly decreased ISOMAC by 21.1 +/- 4.1%. Saline solution or magnesium sulfate alone did not significantly change ISOMAC. CONCLUSIONS AND CLINICAL RELEVANCE: Ketamine and ketamine combined with magnesium sulfate, at doses used in the study, decreased the end-tidal isoflurane concentration needed to maintain anesthesia, verifying the clinical impression that ketamine decreases the end-tidal isoflurane concentration needed to maintain surgical anesthesia. Magnesium, at doses used in the study, did not decrease ISOMAC or augment ketamine's effects on ISOMAC.  相似文献   

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OBJECTIVES: To quantify the change in the minimum alveolar concentration (MAC) of isoflurane (ISO) associated with oxymorphone (OXY) or hydromorphone (HYDRO) in dogs. DESIGN: Randomized crossover study with at least 1 week between assessments. ANIMALS: Six young, healthy, mixed-breed dogs (1-3 years old), weighing 24.7 +/- 4.70 kg. METHODS: Following mask induction, anesthesia was maintained with ISO in 100% O(2) using mechanical ventilation. The dogs received 0.05 mg kg(-1) OXY, 0.1 mg kg(-1) HYDRO, or 1 mL saline (control) IV. Following equilibration (15 minutes) at each percentage ISO tested, a supramaximal electrical stimulus was applied to the toe web and the response was assessed. Two separate MAC determinations were carried out during 4.5 hours of anesthesia, with completion of the evaluations at 1.5-2 and 4-4.5 hours after drug administration. A two-factor anova was used to determine whether there was a time or treatment effect on MAC and a Tukey test compared the drug effects at each time. Significance is reported at p < 0.05. RESULTS: The mean MAC values (+/-SD) were 1.2 +/- 0.18 and 1.2 +/- 0.16% for control, 0.7 +/-0.15 and 1.0 +/- 0.15% for OXY, and 0.6 +/- 0.14 and 0.8 +/- 0.17% for HYDRO. The initial MAC with OXY and the MAC determined at both times with HYDRO were significantly different from the control MAC values. CONCLUSIONS: Both OXY and HYDRO significantly reduced the MAC of ISO in dogs at 2 hours. At approximately 4.5 hours, HYDRO had a significant MAC-sparing effect, whereas OXY did not. CLINICAL RELEVANCE: Although both OXY and HYDRO resulted in a significant reduction in the MAC of ISO at approximately 2 hours, HYDRO may be preferred for procedures of long duration and rarely needs repeated dosing before 4.5 hours.  相似文献   

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