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  • Author or Editor: Regula Bettschart-Wolfensberger x
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Abstract

Objective—To determine the minimal infusion rate of propofol in combination with medetomidine for longterm anesthesia in ponies and the effects of atipamezole on recovery.

Animals—12 ponies.

Procedure—Ponies were sedated with medetomidine (7 µg/kg of body weight, IV). Ten minutes later, anesthesia was induced with propofol (2 mg/kg, IV). Anesthesia was maintained for 4 hours, using an infusion of medetomidine (3.5 µg/kg per hour, IV) and propofol at a rate sufficient to prevent ponies from moving after electrical stimulation. Arterial blood pressures and blood gas analysis, heart rates, and respiratory rates were monitored. For recovery, 6 ponies were given atipamezole (60 µg/kg, IV). Induction and recovery were scored.

Results—Minimal propofol infusion rates ranged from 0.06 to 0.1 mg/kg per min. Mean arterial blood pressure was stable (range, 74 to 86 mm Hg), and heart rate (34 to 51 beats/min) had minimal variations. Variable breathing patterns were observed. Mean Pao2 (range, 116 to 146 mm Hg) and mean Paco2 (range, 48 to 51 mm Hg) did not change significantly with time, but hypoxemia was evident in some ponies (minimal Pao2, 47 mm Hg). Recovery was fast and uneventful with and without atipamezole (completed in 20.2 and 20.9 minutes, respectively).

Conclusion and Clinical Relevance—Infusion of a combination of medetomidine and propofol was suitable for prolonged anesthesia in ponies. Recovery was rapid and uneventful. A combination of propofol and medetomidine may prove suitable for long-term anesthesia in horses. Monitoring of blood gases is essential because of potential hypoxemia. (Am J Vet Res 2001;62:500–507)

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in American Journal of Veterinary Research

Abstract

Objective—To evaluate effects of racemic ketamine and S-ketamine in gazelles.

Animals—21 male gazelles (10 Rheem gazelles [Gazella subgutturosa marica] and 11 Subgutturosa gazelles [Gazella subgutturosa subgutturosa]), 6 to 67 months old and weighing (mean±SD) 19 ± 3 kg.

Procedures—In a randomized, blinded crossover study, a combination of medetomidine (80 μg/kg) with racemic ketamine (5 mg/kg) or S-ketamine (3 mg/kg) was administered IM. Heart rate, blood pressure, respiratory rate, rectal temperature, and oxygen saturation (determined by means of pulse oximetry) were measured. An evaluator timed and scored induction of, maintenance of, and recovery from anesthesia. Medetomidine was reversed with atipamezole. The alternate combination was used after a 4-day interval. Comparisons between groups were performed with Wilcoxon signed rank and paired t tests.

Results—Anesthesia induction was poor in 2 gazelles receiving S-ketamine, but other phases of anesthesia were uneventful. A dominant male required an additional dose of S-ketamine (0.75 mg/kg, IM). After administration of atipamezole, gazelles were uncoordinated for a significantly shorter period with S-ketamine than with racemic ketamine. Recovery quality was poor in 3 gazelles with racemic ketamine. No significant differences between treatments were found for any other variables. Time from drug administration to antagonism was similar between racemic ketamine (44.5 to 53.0 minutes) and S-ketamine (44.0 to 50.0 minutes).

Conclusions and Clinical Relevance—Administration of S-ketamine at a dose 60% that of racemic ketamine resulted in poorer induction of anesthesia, an analogous degree of sedation, and better recovery from anesthesia in gazelles with unremarkable alterations in physiologic variables, compared with racemic ketamine.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of inhalation of isoflurane at end-tidal concentrations greater than, equal to, and less than the minimum anesthetic concentration (MAC) on bispectral index (BIS) in chickens.

Animals—10 chickens.

Procedures—For each chicken, the individual MAC of isoflurane was determined by use of the toe-pinch method. After a 1-week interval, chickens were anesthetized with isoflurane at concentrations 1.75, 1.50, 1.25, 1.00, and 0.75 times their individual MAC (administered from higher to lower concentrations). At each MAC multiple, a toe pinch was performed and BIS was assessed and correlated with heart rate, blood pressure, and an awareness score (derived by use of a visual analogue scale).

Results—Among the chickens, mean ± SD MAC of isoflurane was 1.15 ± 0.20%. Burst suppression was detected at every MAC multiple. The BIS and awareness score were correlated directly with each other and changed inversely with increasing isoflurane concentration. Median (range) BIS values during anesthesia at 1.75, 1.50, 1.25, 1.00, and 0.75 MAC of isoflurane were 25 (15 to 35), 35 (25 to 45), 35 (20 to 50), 40 (25 to 55), and 50 (35 to 65), respectively. Median BIS value at extubation was 70 ± 9. Values of BIS correlated with blood pressure, but not with heart rate. Blood pressure changed with end-tidal isoflurane concentrations, whereas heart rate did not.

Conclusions and Clinical Relevance—Assessment of BIS can be used to monitor the electrical activity of the brain and the degree of unconsciousness in chickens during isoflurane anesthesia.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine cardiopulmonary effects of total IV anesthesia with propofol and medetomidine in ponies and effect of atipamezole on recovery.

Animals—10 ponies.

Procedure—After sedation was induced by IV administration of medetomidine (7 μg/kg of body weight), anesthesia was induced by IV administration of propofol (2 mg/kg) and maintained for 4 hours with infusions of medetomidine (3.5 μg/kg per hour) and propofol (0.07 to 0.11 mg/kg per minute). Spontaneous respiration was supplemented with oxygen. Cardiopulmonary measurements and blood concentrations of propofol were determined during anesthesia. Five ponies received atipamezole (60 μg/kg) during recovery.

Results—During anesthesia, mean cardiac index and heart rate increased significantly until 150 minutes, then decreased until cessation of anesthesia. Mean arterial pressure and systemic vascular resistance index increased significantly between 150 minutes and 4 hours. In 4 ponies, PaO2 decreased to < 60 mm Hg. Mean blood propofol concentrations from 20 minutes after induction onwards ranged from 2.3 to 3.5 μg/ml. Recoveries were without complications and were complete within 28 minutes with atipamezole administration and 39 minutes without atipamezole administration.

Conclusions and Clinical Relevance—During total IV anesthesia of long duration with medetomidine-propofol, cardiovascular function is comparable to or better than under inhalation anesthesia. This technique may prove suitable in equids in which prompt recovery is essential; however, in some animals severe hypoxia may develop and oxygen supplementation may be necessary. (Am J Vet Res 2001;62:1428–1435)

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in American Journal of Veterinary Research

Abstract

Objective—To determine whether inhaled nitric oxide (NO) prevents pulmonary hypertension and improves oxygenation after IV administration of a bolus of dexmedetomidine in anesthetized sheep.

Animals—6 healthy adult sheep.

Procedure—In a crossover study, sevoflurane-anesthetized sheep received dexmedetomidine (2 µg/kg, IV) without NO (DEX treatment) or with inhaled NO (DEX-NO treatment). Cardiopulmonary variables, including respiratory mechanics, were measured before and for 120 minutes after bolus injection of dexmedetomidine.

Results—Dexmedetomidine induced a transient decrease in heart rate and cardiac output. A short-lived increase in mean arterial pressure (MAP) and systemic vascular resistance (SVR) was followed by a significant decrease in MAP and SVR for 90 minutes. Mean pulmonary arterial pressure (MPAP) and pulmonary vascular resistance increased transiently after dexmedetomidine injection. The PaO2 was significantly decreased 3 minutes after injection and reached a minimum of (mean ± SEM) 13.3 ± 7.8 kPa 10 minutes after injection. The decrease in PaO2 was accompanied by a sudden and prolonged decrease in dynamic compliance and a significant increase in airway resistance, shunt fraction, and alveolar dead space. Peak changes in MPAP did not differ between the 2 treatments. For the DEX-NO treatment, PaO2 was significantly lower and the shunt fraction significantly higher than for the DEX treatment.

Conclusions and Clinical Relevance—Inhalation of NO did not prevent increases in pulmonary arterial pressures induced by IV administration of dexmedetomidine. Preemptive inhalation of NO intensified oxygenation impairment, probably through increases in intrapulmonary shunting. (Am J Vet Res 2005;66:1496–1502)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To compare anesthesia recovery quality after racemic (R-/S-) or S-ketamine infusions during isoflurane anesthesia in horses.

Animals—10 horses undergoing arthroscopy.

Procedures—After administration of xylazine for sedation, horses (n = 5/group) received R-/S-ketamine (2.2 mg/kg) or S-ketamine (1.1 mg/kg), IV, for anesthesia induction. Anesthesia was maintained with isoflurane in oxygen and R-/S-ketamine (1 mg/kg/h) or S-ketamine (0.5 mg/kg/h). Heart rate, invasive mean arterial pressure, and end-tidal isoflurane concentration were recorded before and during surgical stimulation. Arterial blood gases were evaluated every 30 minutes. Arterial ketamine and norketamine enantiomer plasma concentrations were quantified at 60 and 120 minutes. After surgery, horses were kept in a padded recovery box, sedated with xylazine, and video-recorded for evaluation of recovery quality by use of a visual analogue scale (VAS) and a numeric rating scale.

Results—Horses in the S-ketamine group had better numeric rating scale and VAS values than those in the R-/S-ketamine group. In the R-/S-ketamine group, duration of infusion was positively correlated with VAS value. Both groups had significant increases in heart rate and mean arterial pressure during surgical stimulation; values in the R-/S-ketamine group were significantly higher than those of the S-ketamine group. Horses in the R-/S-ketamine group required slightly higher end-tidal isoflurane concentration to maintain a surgical plane of anesthesia. Moderate respiratory acidosis and reduced oxygenation were evident. The R-norketamine concentrations were significantly lower than S-norketamine concentrations in the R-/S-ketamine group.

Conclusions and Clinical Relevance—Compared with R-/S-ketamine, anesthesia recovery was better with S-ketamine infusions in horses.

Full access
in American Journal of Veterinary Research