Cardiopulmonary effects and induction and recovery characteristics of isoflurane and sevoflurane in foals

OBJECTIVE: To compare induction and recovery characteristics and cardiopulmonary effects of isoflurane and sevoflurane in foals. DESIGN: Prospective crossover study. ANIMALS: 6 healthy foals. PROCEDURE: Foals were anesthetized twice (once at 1 month of age and again at 3 months of age). Anesthesia was induced by administration of the agent in oxygen through a nasotracheal tube. During maintenance of anesthesia, foals were positioned in dorsal recumbency; intermittent positive-pressure ventilation was performed. Characteristics of induction and recovery were recorded. Cardiopulmonary variables were recorded 10 minutes after anesthetic induction and 15, 30, 45, and 60 minutes later. RESULTS: All 6 foals were successfully anesthetized with isoflurane and sevoflurane. There were no significant differences between the 2 drugs in regard to characteristics of induction or recovery, and induction and recovery were generally smooth and unremarkable. There were no significant differences between drugs in regard to measured cardiopulmonary variables; however, both drugs caused initial hypotension that resolved over time. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that isoflurane and sevoflurane can both be used for general anesthesia of 1- to 3-month-old foals. Significant differences between the 2 agents were not detected for any of the variables measured, suggesting that quality of anesthesia with these 2 agents was comparable.     

Temporal effects of halothane and isoflurane in laterally recumbent ventilated male horses

Cardiopulmonary function was monitored in 6 non-medicated, healthy male horses, anesthetized with halothane or isoflurane in O2 at a constant dose (1.2 times the minimum alveolar concentration). Horses were exposed once to each anesthetic agent, and a minimum of 2 weeks separated anesthetic exposures. All horses were studied in left lateral recumbency, and ventilation was mechanically controlled to induce a PaCO2 of 35 to 45 mm of Hg and an inspiratory peak airway pressure of 18 to 22 cm of H2O. After 1 hour of horse preparation, constant conditions were begun. With duration of anesthesia, cardiac output increased (P less than 0.05) with both anesthetic agents, because of an increase in stroke volume (P less than 0.05). Heart rate did not change from initial values with either agent. Mean arterial blood pressure also increased (P less than 0.05) with both agents. With both anesthetics, respiratory rate (P less than 0.05) was increased progressively to maintain acceptable PaCO2 values. Arterial O2 tension did not change with time.     

Atrial fibrillation in halothane- and isoflurane-anesthetized dogs

Programmed electrical stimulation techniques were used to evaluate the effects of halothane and isoflurane on induction of atrial fibrillation in anesthetized dogs. Experiments were performed in 16 dogs anesthetized with alpha-chloralose. Critically timed premature stimuli were applied to the right atrial appendage and Bachmann bundle to determine the atrial fibrillation threshold, defined as the minimal current required to induce rapid, irregular atrial electrical activity of at least 8 seconds' duration. Atrial fibrillation thresholds were determined at baseline (0.0% inhalational anesthetic), 0.5 minimal alveolar concentration (MAC), and 1.0 MAC of halothane (n = 8) and isoflurane (n = 8). In the absence of inhalation anesthetic, it was significantly (P less than 0.01) easier to induce atrial fibrillation at the Bachmann bundle vs the right atrial appendage. Atrial fibrillation threshold at the Bachmann bundle was not affected by increasing concentrations of halothane, but was increased by 1.0 MAC of isoflurane (P less than 0.05). It was concluded that at 1.0 MAC isoflurane, but not halothane, has antifibrillatory effects in atrial tissue.     

Effects of Halothane, Enflurane, and Isoflurane on Supraventricular and Ventricular Rate in Dogs With Complete Atrioventricular Block

Complete atrioventricular (AV) block was produced in 32 chloralose-anesthetized autonomically intact dogs to determine the effects of halothane, enflurane, and isoflurane on supraventricular and ventricular rate. Halothane (n = 17), enflurane (n = 6), and isoflurane (n = 9) were administered in three separate experiments in sequential minimum alveolar concentration (MAC) multiples of 0.5, 1.0, 1.5, 2.0, 1.5, and 1.0. Supraventricular rate, ventricular rate, and mean arterial blood pressure (MAP) were measured and recorded at baseline and after a 20-minute equilibration period of each inhalation anesthetic at each MAC multiple. Increasing concentrations of enflurane and isoflurane significantly decreased supraventricular rate ( P < .05). Ventricular rate was not significantly changed by sequential MAC multiples of halothane, enflurane, and isoflurane. Increasing concentrations of halothane, enflurane, and isoflurane significantly decreased MAP with enflurane producing the most significant decrease ( P < .05). Ventricular arrhythmias occurred in 5 of 17 dogs anesthetized with halothane and 1 of 9 dogs anesthetized with isoflurane. Inhalation anesthesia can significantly decrease supraventricular rate and MAP, does not alter ventricular rate, and can produce ventricular arrhythmias in dogs with complete AV block.     

Closed System Delivery of Halothane and Isoflurane with a Vaporizer in the Anesthetic Circle

Forty-four healthy dogs undergoing elective ovariohysterectomy were anesthetized with halothane or isoflurane delivered with an in-circuit vaporizer with closed system flow rates or an out-of-circuit vaporizer with semi-closed system flow rates. When dogs were anesthetized with halothane, there were no differences in heart rate, blood pressure, body temperature, respiratory rate, or lingual venous pH, PCO2, or PO2 during induction and maintenance. Lingual venous PO2 was significantly less but still within a clinically acceptable range when isoflurane was used in an in-circuit vaporizer. Recovery times tended to be longer with in-circuit vaporizers. The amount of anesthetic used was not affected by vaporizer location. In-circuit vaporizers were suitable for delivery of halothane or isoflurane to healthy dogs.     

Comparison of cardiopulmonary effects of isoflurane and halothane after atropine-guaifenesin-thiamylal anesthesia for rumenotomy in steers

Cardiopulmonary effects were assessed in 12 yearling steers anesthetized with guaifenesin and thiamylal sodium, intubated, and allowed to breathe isoflurane or halothane in oxygen spontaneously. Light surgical anesthesia, determined using eye position as a clinical indication of anesthetic depth, was maintained during surgical placement of a rumen cannula. Heart rate and respiratory rate were measured while the steers were standing quietly (baseline). Atropine (0.06 mg/kg of body weight, IM) was given after baseline measurements were taken. Heart rate, respiratory rate, arterial blood pressures, pHa, PaCO2, PaO2, arterial [HCO3-], esophageal temperature, and end-tidal anesthetic concentration were measured every 15 minutes for 90 minutes after induction of anesthesia. Mean heart rate increased significantly (P less than 0.05) above baseline in the isoflurane group at 15 and 30 minutes. Mean respiratory rate increased significantly (P less than 0.05) above baseline in the halothane group at 45 minutes. At 45 minutes, mean respiratory rate was lower (P less than 0.05) in the isoflurane group, compared with that in the halothane group. Mean values for arterial blood pressures and arterial gases were similar for both agents at comparable times. Mean end-tidal isoflurane concentrations were less than mean end-tidal halothane concentrations at each comparable time during maintenance of similar anesthetic depth. Maintenance of anesthesia with isoflurane resulted in higher heart rates and lower respiratory rates, compared with maintenance of anesthesia with halothane in these steers.     

Comparisons of Sevoflurane, Isoflurane, and Halothane Anesthesia in Spontaneously Breathing Cats

The clinical effects of sevoflurane, isoflurane, and halothane anesthesia with or without nitrous oxide, were compared in healthy, premedicated cats breathing spontaneously during 90 minutes of anesthesia. The effect of nitrous oxide in accelerating the induction of and recovery from anesthesia was more evident for halothane than for sevoflurane or isoflurane. The cats recovered more rapidly from sevoflurane-oxygen than from either halothane- or isoflurane-oxygen. Heart rates did not significantly change during anesthesia with any of the anesthetics. Arterial blood pressures during sevoflurane-oxygen anesthesia were somewhat higher than those with either isoflurane- or halothane-oxygen. There were no significant differences in arterial blood pressures among sevoflurane, isoflurane, and halothane anesthesia when combined with nitrous oxide. The respiration rate during sevoflurane-oxygen was similar to that during halothane-oxygen. There were no significant differences in respiration rate among sevoflurane, isoflurane, and halothane anesthesia when combined with nitrous oxide. The degree of hypercapnia and acidosis during sevoflurane anesthesia was similar to that observed during isoflurane anesthesia and less than during halothane anesthesia. The three anesthetic regimens, with or without nitrous oxide, induced a similar degree of hyperglycemia and hemodilution during anesthesia. Serum biochemical examination did not reveal any hepatic or renal injuries after each anesthesia.     

Isoflurane Anesthesia for Equine Colic Surgery Comparison with Halothane Anesthesia

Isoflurane was compared with halothane as an anesthetic agent for emergency colic surgery in a series of 38 juvenile and adult horses. After presurgical stabilization with fluids and supportive medications, anesthesia was induced by intravenous xylazine and/or diazepam followed by ketamine. Anesthesia was maintained with isoflurane or halothane in oxygen with controlled ventilation. Heart rates (HR), arterial blood gases, mean arterial pressures (MAP), rate pressure products (RPP), requirements for cardiovascular support medications, and recovery times to standing were compared using nonparametric methods. Cardiopulmonary responses to isoflurane and halothane anesthesia were generally comparable although some temporal differences were observed. Higher HR (p less than 0.02) and lower PaCO2 levels (p less than 0.01) were identified during the course of isoflurane anesthesia. Recovery times to standing were significantly shorter (0.02 less than p less than 0.05) after isoflurane than halothane anesthesia.     

Hemodynamic effects of ionized calcium in horses anesthetized with halothane or isoflurane

OBJECTIVES: To evaluate the effects of halothane and isoflurane on cardiovascular function and serum total and ionized calcium concentrations in horses, and to determine whether administration of calcium gluconate would attenuate these effects. ANIMALS: 6 clinically normal adult Thoroughbreds. PROCEDURE: Catheters were inserted for measurement of arterial blood pressures, pulmonary arterial blood pressures, right ventricular pressure (for determination of myocardial contractility), right atrial pressure, and cardiac output and for collection of arterial blood samples. Anesthesia was then induced with xylazine hydrochloride and ketamine hydrochloride and maintained with halothane or isoflurane. An i.v. infusion of calcium gluconate was begun 75 minutes after anesthetic induction; dosage of calcium gluconate was 0.1 mg/kg of body weight/min for the first 15 minutes, 0.2 mg/kg/min for the next 15 minutes, and 0.4 mg/kg/min for an additional 15 minutes. Data were collected before, during, and after administration of calcium gluconate. RESULTS: Halothane and isoflurane decreased myocardial contractility, cardiac index, and mean arterial pressure, but halothane caused greater depression than isoflurane. Calcium gluconate attenuated the anesthetic-induced depression in cardiac index, stroke index, and maximal rate of increase in right ventricular pressure when horses were anesthetized with isoflurane. When horses were anesthetized with halothane, a higher dosage of calcium gluconate was required to attenuate the depression in stroke index and maximal rate of increase in right ventricular pressure; cardiac index was not changed with calcium administration. CONCLUSIONS AND CLINICAL RELEVANCE: I.v. administration of calcium gluconate may support myocardial function in horses anesthetized with isoflurane.     

Surgical Correction of Uterine Torsion and Mare–Foal Survival in Advance Pregnant Equine Patients

This article describes the surgical management of uterine torsion by midline celiotomy and cesarean section on 12 mares presented with signs of colic to a teaching veterinary hospital. The mares were either in full term of gestation (n = 7) or in advanced stage of pregnancy (n = 5). Six mares were in first parity. Uterine torsion was diagnosed by per rectal and per vaginal examinations. For surgical intervention, mares were anesthetized using a combination of xylazine (1.1 mg/kg) and ketamine (2.2 mg/kg), intravenously. After intubation, the animals were maintained on halothane (n = 4) or isoflurane (n = 8) inhalation anesthesia. Midline celiotomy was performed, and foals were delivered by cesarean section. In 11 mares, before closing the abdominal wound, the uterus was detorted manually and confirmed for its normal position. Both anesthetic protocols using halothane and isoflurane were found satisfactory for surgical correction of uterine torsion. After long-term follow-up, the study reported 75.0% (9/12) survival rate for mares. One mare was euthanized because of devitalized, necrosed, and adhered uterus to the abdominal wall. Of the nine surviving mares, seven were successfully bred. Three foals were born alive, and only one could survive on long-term basis. Of the nine dead foals, two had umbilical cord torsion.     

Pharmacokinetics of inhaled anesthetics in green iguanas (Iguana iguana)

OBJECTIVE: To test the hypothesis that differences in anesthetic uptake and elimination in iguanas would counter the pharmacokinetic effects of blood:gas solubility and thus serve to minimize kinetic differences among inhaled agents. ANIMALS: 6 green iguanas (Iguana iguana). PROCEDURES: Iguanas were anesthetized with isoflurane, sevoflurane, or desflurane in a Latin-square design. Intervals from initial administration of an anesthetic agent to specific induction events and from cessation of administration of an anesthetic agent to specific recovery events were recorded. End-expired gas concentrations were measured during anesthetic washout. RESULTS: Significant differences were not detected for any induction or recovery events for any inhalation agent in iguanas. Washout curves best fit a 2-compartment model, but slopes for both compartments did not differ significantly among the 3 anesthetics. CONCLUSIONS AND CLINICAL RELEVANCE: Differences in blood:gas solubility for isoflurane, sevoflurane, and desflurane did not significantly influence differences in pharmacokinetics for the inhalation agents in iguanas.     

Retrospective comparison of caffeine and doxapram for the treatment of hypercapnia in foals with hypoxic-ischemic encephalopathy

BACKGROUND: Despite a lack of data regarding their efficacy, both caffeine and doxapram have been recommended for treatment of hypercapnia in equine neonates with central nervous system damage. HYPOTHESIS: Caffeine and doxapram alleviate hypercapnia in foals with hypoxic-ischemic encephalopathy. ANIMALS: Sixteen foals treated with either caffeine (n = 8) or doxapram (n = 8). METHODS: Information on age, body temperature, heart rate, respiratory rate, arterial blood gas parameters, duration of therapy, and outcome was abstracted from each medical record. RESULTS: Therapy with doxapram resulted in a significant decrease in partial pressure of carbon dioxide (PaCO2 [P= .004]), bicarbonate concentration (P= .002), and base excess (P= .005) compared with baseline values but failed to correct acidemia. In contrast, administration of caffeine did not result in significant changes from baseline values. The percentage decrease in PaCO2 and bicarbonate concentration was significantly greater in foals treated with doxapram than in foals treated with caffeine (P= .004). The proportions of foals that achieved the targeted PaCO2 (< or = 50 mmHg) were significantly higher in foals treated with doxapram than in foals treated with caffeine (P= .029). The proportion of survivors in the 2 treatment groups was not significantly different. CONCLUSIONS AND CLINICAL IMPORTANCE: Doxapram is more effective than caffeine for rapid correction of hypercapnia in foals with hypoxic-ischemic encephalopathy.     

Comparison of isoflurane and halothane as inhalation anaesthetics in the dog

A number of clinically important features of isoflurane anaesthesia were studied in comparison to those of halothane. Two groups of dogs were used. After light premedication, anaesthesia was induced by mask, and both groups of dogs were maintained for 30 minutes at 1.5 X MAC value of either halothane or isoflurane in a combination of oxygen and nitrous oxide (50:50). All animals were ventilating spontaneously. There was no difference in the speed of induction of the halothane and isoflurane groups. Blood pressure in both groups dropped to approximately 7.5 kPa (56 mm Hg) during maintenance anesthesia (1.5 MAC), while the heart rate was significantly higher in the isoflurane group. Individual respiratory variables were not significantly different between the two groups, however the differences between the trends of the mean values were significant (Sign-test). In general, with isoflurane, respiration rates were lower, with the tidal volume and end tidal CO2 being greater. The trends in pH and arterial pCO2 showed a slightly more severe respiratory acidosis in the isoflurane group. However, neither group showed values corresponding to any expected clinical problems. Speed of recovery (determined by times to head-lift and righting-reflex) was greater in the isoflurane group. Previously known important features of isoflurane are low biodegradability, low blood: gas partition coefficient, and decreased myocardial sensitivity to catecholamines. It is concluded from this study that isoflurane deserves a place in canine anesthesia whenever these specific pharmacologic properties are desired.     

速眠新和异氟烷对蟒蛇的全麻效果研究

本试验通过使用速眠新和异氟烷两种常用全身麻醉剂对缅甸蟒的麻醉效果进行了研究。对15条蟒蛇肌肉注射和腹腔注射(0.1、0.2、0.4 mL/kg)速眠新麻醉剂和对6条蟒蛇使用异氟烷吸入性麻醉后,进行麻醉效果的评估。试验结果表明,常规动物2~4倍的速眠新Ⅱ注射剂对蟒蛇的麻醉效果不明显;4%的异氟烷吸入性麻醉剂可用于蟒蛇的诱导麻醉,2.5%的异氟烷可用于蟒蛇的维持麻醉,其麻醉效果显著,具有诱导麻醉迅速、维持麻醉稳定、肌松作用好、安全性高、可控性强、苏醒快、副作用小等优点。结果显示,异氟烷吸入性麻醉剂可运用于蟒蛇的临床麻醉保定中。     

Arterial to end-tidal CO2 tension and alveolar dead space in halothane- or isoflurane-anesthetized ponies

The correlation between end-tidal partial pressure of CO2 (PETCO2) and arterial (PaCO2) was determined for spontaneously breathing ponies under halothane or isoflurane anesthesia. The PETCO2 was useful as a trend indicator of PaCO2 during the first 60 minutes of halothane or isoflurane anesthesia when PaCO2 values were less than 60 to 70 mm of Hg. Halothane anesthesia lasting greater than 90 minutes was associated with PaCO2 values in excess of 60 to 70 mm of Hg, a large arterial- to end-tidal PCO2 difference (PaCO2-PETCO2) and a significant increase in alveolar dead space. These effects were not seen during the same period of isoflurane anesthesia. Arterial blood gas analysis is therefore recommended during halothane anesthesia when the PETCO2 is greater than 60 to 70 mm of Hg. A decrease in alveolar capillary perfusion relative to alveolar ventilation is the most likely cause for the increase in alveolar dead space during halothane anesthesia. Based on these findings, isoflurane may be superior to halothane for prolonged anesthesia of spontaneously breathing horses.     

Comparison of recoveries from halothane vs isoflurane anesthesia in horses.

Recovery from isoflurane anesthesia was shorter, with no difference in quality, compared with halothane anesthesia in 2 groups of horses. In 1 group, 12 horses scheduled for elective arthroscopy were randomly assigned to receive halothane or isoflurane for maintenance of anesthesia during surgery. In the other group, 6 horses received anesthesia only, on 2 occasions, with halothane on 1 occasion, and isoflurane on the other. Difference in the quality of recovery was not seen between isoflurane and halothane anesthesia in either group. In the group that had surgery, recovery to sternal position was significantly shorter when isoflurane was used. In the group not treated surgically, recovery to sternal and standing positions was significantly shorter with isoflurane.     

Cardiovascular effects of halothane anesthesia after diazepam and ketamine administration in beavers (Castor canadensis) during spontaneous or controlled ventilation

Fourteen adult beavers (Castor canadensis) weighing 16.5 +/- 4.14 kg (mean +/- SD) were anesthetized for surgical implantation of radio telemetry devices. Beavers were anesthetized with diazepam (0.1 mg/kg) and ketamine (25 mg/kg) administered IM, which provided smooth anesthetic induction and facilitated tracheal intubation. Anesthesia was maintained with halothane in oxygen via a semiclosed circle anesthetic circuit. Values for heart rate, respiratory rate, esophageal temperature, direct arterial blood pressure, end-tidal halothane concentration, and end-tidal CO2 tension were recorded every 15 minutes during the surgical procedure. Arterial blood samples were collected every 30 minutes to determine pH, PaO2, and PaCO2. Values for plasma bicarbonate, total CO2, and base excess were calculated. Ventilation was spontaneous in 7 beavers and controlled to maintain normocapnia (PaCO2 approx 40 mm of Hg) in 7 others. Vaporizer settings were adjusted to maintain a light surgical plane of anesthesia. Throughout the surgical procedure, all beavers had mean arterial pressure less than 60 mm of Hg and esophageal temperature less than 35 C. Mean values for arterial pH, end-tidal CO2, PaO2, and PaCO2 were significantly (P less than 0.05) different in spontaneously ventilating beavers, compared with those in which ventilation was controlled. Respiratory acidosis during halothane anesthesia was observed in spontaneously ventilating beavers, but not in beavers maintained with controlled ventilation. All beavers recovered unremarkably from anesthesia.     

Effects of various anesthetic agents on laryngeal motion during laryngoscopy in normal dogs

OBJECTIVE: To evaluate the effects of various drugs and drug combinations conventionally used for anesthesia on arytenoid cartilage motion during laryngoscopy in normal dogs. STUDY DESIGN: Experimental study. ANIMALS: Six large breed healthy dogs with no previous history of respiratory dysfunction. METHODS: Each dog was randomly assigned to a different injectable anesthetic protocol once weekly for 6 weeks, then in the 7th week all dogs were anesthetized with isoflurane. Videolaryngoscopy was performed and recorded starting immediately after induction until dogs could no longer be safely restrained for endoscopy. Video was digitized and 3 still images of maximal inspiration and expiration from the first 15 seconds (induction) and the last 15 seconds (recovery) were captured and imported into an image analysis software program. The height and area of the laryngeal ostium were measured in pixels. Normalization of the glottal gap area was performed using the formula (normalized glottal gap area (NGGA)=area in pixels/height(2)). ANOVA was performed on the NGGA of images collected at inspiration and expiration during induction and recovery. Fischer's exact test was performed when significance (P<.05) was found. RESULTS: Within each protocol, laryngeal motion (defined as change in NGGA) at induction was not significantly different from laryngeal motion measured at recovery. Additionally, no significant differences were found in arytenoid motion immediately after induction when anesthetic protocols were compared. Arytenoid motion before recovery was significantly greater with thiopental when compared with propofol (P=.046), ketamine+diazepam (P=.0098), acepromazine+thiopental (P=.0021), and acepromazine+propofol (P=.0065). No significant difference in arytenoid motion was seen immediately after induction or before recovery when acepromazine+butorphanol+ isoflurane and thiopental were compared. CONCLUSION: We concluded that intravenous thiopental given to effect is the best choice for assessing laryngeal function in dogs. Dogs premedicated with acepromazine with or without opioids that require further anesthetic restraint for laryngoscopy should be anesthetized with isoflurane administered by mask. CLINICAL RELEVANCE: Misdiagnosis of laryngeal paralysis during laryngoscopy can be avoided by selecting the anesthetic regimens with the least effect on arytenoid motion.     

Comparison of isoflurane and halothane as inhalation anaesthetics in the dog

Summary

A number of clinically important features of isoflurane anaesthesia were studied in comparison to those of halothane. Two groups of dogs were used. After light premedication, anaesthesia was induced by mask, and both groups of dogs were maintained for 30 minutes at 1.5 × MAC value of either halothane or isoflurane in a combination of oxygen and nitrous oxide (50:50). All animals were ventilating spontaneously.

There was no difference in the speed of induction of the halothane and isoflurane groups. Blood pressure in both groups dropped to approximately 7.5 kPa (56 mm Hg) during maintenance anesthesia (1.5 MAC), while the heart rate was significantly higher in the isoflurane group. Individual respiratory variables were not significantly different between the two groups, however the differences between the trends of the mean values were significant (Sign‐test). In general, with isoflurane, respiration rates were lower, with the tidal volume and end tidal CO₂ being greater.

The trends in pH and arterial pCO₂ showed a slightly more severe respiratory acidosis in the isoflurane group. However, neither group showed values corresponding to any expected clinical problems. Speed of recovery (determined by times to head‐lift and righting‐reflex) was greater in the isoflurane group. Previously known important features of isoflurane are low biodegradability, low blood: gas partition coefficient, and decreased myocardial sensitivity to catecholamines. It is concluded from this study that isoflurane deserves a place in canine anesthesia whenever these specific pharmacologic properties are desired.     

The recovery of horses from inhalant anesthesia: a comparison of halothane and isoflurane

Objective— Recovery is one of the more precarious phases of equine general anesthesia. The quality and rate of recovery of horses from halothane and isoflurane anesthesia were compared to determine differences in the characteristics of emergence from these commonly used inhalant anesthetics. Experimental Design— Prospective, randomized blinded clinical trial. Sample Population— A total of 96 Thoroughbred and 3 Standardbred racehorses admitted for elective distal forelimb arthroscopy. Methods— All horses were premedicated with intravenous xylazine, induced with guaifenesin and ketamine, and maintained on a large animal circle system fitted with an out of the circle, agent specific vaporizer. Recoveries were managed by a blinded scorer with a standardized protocol. A 10 category scoring system was used to assess each horse's overall attitude, purposeful activity, muscle coordination, strength and balance from the time of arrival in recovery to standing. Times to extubation, sternal recumbency and standing were recorded. Median recovery scores and mean times to extubation, sternal and standing were compared using the Mann‐Whitney U test and student's t test, respectively. Results— The median score for horses recovering from halothane was lower (20.0; range, 10 to 57) than that for horses recovering from isoflurane (27.5; range, 10 to 55). Horses in the two groups were extubated at similar mean times (halothane, 11.3 ± 5.5 and isoflurane, 9.5 ± 5.2 minutes ) but horses recovering from isoflurane achieved sternal recumbency (halothane, 37.7 ± 12.1 and isoflurane, 24.7 ± 8.8 minutes ) and stood (halothane, 40.6 ± 12.9 and isoflurane, 27.6 ± 9.6 minutes ) sooner than those recovering from halothane. Conclusions— The recovery of horses from isoflurane anesthesia was more rapid but less composed than that from halothane. Clinical Relevance— The quality of recovery following isoflurane was worse than after halothane anesthesia using the criteria chosen for this study. However, the range of recovery scores was similar for both groups and all horses recovered without significant injury.