Antagonism of detomidine sedation in the horse using intravenous tolazoline or atipamezole

REASONS FOR PERFORMING STUDY

The ability to shorten the duration of sedation would potentially improve safety and utility of detomidine.

OBJECTIVES

To determine the effects of tolazoline and atipamezole after detomidine sedation.

HYPOTHESIS

Administration of tolazoline or atipamezole would not affect detomidine sedation.

METHODS

In a randomised, placebo-controlled, double-blind, descriptive study, detomidine (0.02 mg/kg bwt i.v.) was administered to 6 mature horses on 4 separate occasions. Twenty-five mins later, each horse received one of 4 treatments: Group 1 saline (0.9% i.v.) as a placebo control; Group 2 atipamezole (0.05 mg/kg bwt i.v.); Group 3 atipamezole (0.1 mg/kg bwt i.v.); and Group 4 tolazoline (4.0 mg/kg bwt i.v.). Sedation, muscle relaxation and ataxia were scored by 3 independent observers at 9 time points. Horses were led through an obstacle course at 7 time points. Course completion time was recorded and the ability of the horse to traverse the course was scored by 3 independent observers. Horses were videotaped before, during and after each trip through the obstacle course.

RESULTS

Atipamezole and tolazoline administration incompletely antagonised the effects of detomidine, but the time course to recovery was shortened.

CONCLUSIONS AND POTENTIAL RELEVANCE

Single bolus administration of atipamezole or tolazoline produced partial reversal of detomidine sedation and may be useful for minimising detomidine sedation.

Atipamezole in the management of detomidine overdose in a pony

OBSERVATIONS

A pony undergoing elective castration accidentally received an overdose of IV detomidine (200 microg kg(-1)) before anaesthesia was induced with ketamine and midazolam. A further 100 microg kg(-1) IV dose of detomidine was administered during anaesthesia. The mistake was recognized only when the animal failed to recover from anaesthesia in the expected time. The overdose (300 microg kg(-1) in total) was treated successfully with atipamezole, initially given IV and subsequently IM and titrated to effect to a total dose of 1100 microg kg(-1). The pony regained the standing position. A further injection of atipamezole (76 microg kg(-1) IM) was given 5 hours later to counteract slight signs of re-sedation.

CONCLUSIONS

Atipamezole proved an effective antagonist for detomidine in a pony at an initial dose 3.65 x and a final total dose 3.9 x greater than the alpha2 agonist.

Detomidine-diazepam-ketamine anaesthesia in buffalo (Bubalus bubalis) calves

Eight buffalo calves (8-12 months, 70-100 kg) were randomly assigned to two groups of four animals each. Animals of group I were given detomidine (100 micrograms/kg), whereas animals of group II received a mixture of detomidine (100 micrograms/kg), diazepam (100 micrograms/kg) and ketamine (3 mg/kg) (DDK) intravenously. Various clinical parameters, such as weak time, down time, pedal and pinprick reflexes, muscle relaxation and extent of sedation, as well as heart and respiratory rates and electrocardiograms were measured before (time 0) and 15, 30, 45, 60, 75 and 90 min after treatment. In all the animals of group II (DDK), the pedal reflex was completely abolished (score: 3.00 +/- 0.00) within 5 min, the pinprick response was either very weak or it was completely abolished at this interval. Muscle relaxation and sedation were excellent within 5 min of DDK administration. The depth of sedation and analgesia was maximum from 5 to 15 min postinjection. Detomidine alone, however, failed to produce appropriate depression of the pedal and pinprick reflexes, sedation was mild and muscle relaxation was inadequate. Heart rate showed a significant (P < 0.05) decrease in group I, but the decrease was non-significant in group II. A more pronounced increase in respiratory rate was observed in group I as compared to group II. Animals of both groups recovered within 90 min without any complication. Minimal changes in the cardiovascular system in the group given the DDK combination were an advantage over the group given detomidine. The results indicated that DDK combination is safe and suitable for 15 min of anaesthesia with excellent muscle relaxation and has only limited cardiorespiratory effects in buffaloes.

Sedation and antisedation as tools in equine lameness examination

A kinematic study was performed to establish the locomotion pattern of horses under detomidine sedation and the effects of antagonization for possible use during lameness examinations in uncooperative horses. The kinematics of 17 Warmblood horses (9 sound, 8 lame with chronic forelimb lameness) were recorded on 2 days using a high-speed video system while trotting (3.9 m/s) on a treadmill. On each day a control measurement was carried out prior to sedation with detomidine (10 micrograms/kg bwt) and repeated recordings at 15, 25, 35, 45 and 60 min after sedation. On the second day, sedation was antagonized using atipamezole (100 micrograms/kg bwt) after the 15 min recording. Head height and pulse rate documented the level of sedation. The head dropped from mean 1.23 m (s.d. 0.13) to 0.50 m (0.26) following sedation to reach again 1.06 m (0.19) after 60 min. Antagonization reversed the height significantly at the 25 min recording to 1.06 m (0.11). Walking and trotting were possible in all sedated horses in response to voice commands only. Forelimb lameness symmetry parameter (Head Acceleration Asymmetry: HAAS) in 8 lame horses did not change significantly due to sedation. Stride length increased significantly from mean 2.53 m (0.18) to 2.66 m (0.20) 15 min after sedation and reversed to 2.56 (0.17) m after antagonization. Stride and stance durations changed accordingly. In conclusion, sedation did not change the degree of lameness, but did alter the general locomotion pattern. Antagonization diminished most of these effects, but small differences to the unsedated pattern remained.

The effect of detomidine and its antagonism with tolazoline on stress-related hormones, metabolites, physiologic responses, and behavior in awake ponies

Six ponies were used to investigate the effect of tolazoline antagonism of detomidine on physiological responses, behavior, epinephrine, norepinephrine, cortisol, glucose, and free fatty acids in awake ponies. Each pony had a catheter inserted into a jugular vein 1 hour before beginning the study. Awake ponies were administered detomidine (0.04 mg/kg intravenously [i.v.]) followed 20 minutes later by either tolazoline (4.0 mg/kg i.v.) or saline. Blood samples were drawn from the catheter 5 minutes before detomidine administration (baseline), 5 minutes after detomidine administration, 20 minutes before detomidine administration which was immediately before the administration of tolazoline or saline (time [T] = 0), and at 5, 30, and 60 minutes after injections of tolazoline or saline (T = 5, 30, and 60 minutes, respectively). Compared with heart rate at T = 0, tolazoline antagonism increased heart rate 45% at 5 minutes. There was no difference in heart rate between treatments at 30 minutes. Blood pressure remained stable after tolazoline, while it decreased over time after saline. Compared with concentrations at T = 0, tolazoline antagonism of detomidine in awake ponies resulted in a 55% increase in cortisol at 30 minutes and a 52% increase in glucose at 5 minutes. The change in free fatty acids was different for tolazoline and saline over time. Free fatty acids decreased after detomidine administration. Free fatty acids did not change after saline administration. After tolazoline administration, free fatty acids increased transiently. Tolazoline tended to decrease sedation and analgesia at 15 and 60 minutes postantagonism. Antagonism of detomidine-induced physiological and behavioral effects with tolazoline in awake ponies that were not experiencing pain appears to precipitate a stress response as measured by cortisol, glucose, and free fatty acids. If antagonism of an alpha-agonist is contemplated, the potential effect on hormones and metabolites should be considered.