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Retrospective analysis of detomidine infusion for standing chemical restraint in 51 horses
Veterinary Anaesthesia and Analgesia, 2002, 29, 54^57
B R I E F C O M M U N I C AT I O N
Retrospective analysis of detomidine infusion for standing chemical restraint in 51 horses DV Wilson BVSc, MS, Dipl ACVA, GV Bohart DVM, AT Evans DVM, MS, Dipl ACVA, S Robertson BVMS, PhD, Dipl ACVA, Dipl ECVA, Y Rondenayy DVM College of Veterinary Medicine, Michigan State University, East Lansing, MI.
Correspondence: Dr DV Wilson, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824^1314, USA.
Abstract Objective To assess the e¡ectiveness of a detomidine infusion technique to provide standing chemical restraint in the horse. Design Retrospective study. Animals Fifty-one adult horses aged 9.5 6.9 years (range1^23 years) and weighing 575 290.3 kg. Methods Records of horses presented to our clinic over a 3-year period in which a detomidine infusion was used to provide standing chemical restraint were reviewed. Information relating to the types of procedure performed, duration of infusion, drug dosages and adjunct drugs administered was retrieved. Results Detomidine was administered as an initial bolus loading dose (mean SD) of 7.5 1.87 mg kg1. The initial infusion rate was 0.6 mg kg1 minute1, and this was halved every 15 minutes. The duration of the infusion ranged from 20 to 135 minutes. Twenty horses received additional detomidine or butorphanol during the procedure. All horses undergoing surgery received local anesthesia or epidural analgesia in addition to the detomidine infusion. A wide variety of procedures were performed in these horses.
Dr Robertson’s present address is the College of Veterinary Medicine, University of Florida. yDr Rondenay’s current address is the Department of Clinical Sciences, University of Montreal.
54
Conclusions Detomidine administered by infusion provides prolonged periods of chemical restraint in standing horses. Supplemental sedatives or analgesics may be needed in horses undergoing surgery. Clinical relevance An e¡ective method that provides prolonged periods of chemical restraint in standing horses is described. The infusion alone did not provide su⁄cient analgesia for surgery and a signi¢cant proportion of animals required supplemental sedatives and analgesics. Keywords chemical restraint, detomidine, horse, infusion, standing surgery.
Introduction Infusions of sedative or anesthetic drugs generally provide more consistent levels of sedation/anesthesia while using less drug than intermittent bolus techniques. Infusions of both medetomidine (Bettschart^Wolfensberger et al. 1999) and detomidine (Wertz et al. 1994) for standing chemical restraint in the horse have been described, and the authors of the second report were the source of the initial dose rates used in this study (Wertz et al.1994). Detomidine is an unscheduled a2-adrenergic drug with potent tranquilizing, analgesic and sedative properties. These e¡ects can be achieved by bolus administration of detomidine but this is usually accompanied by prolonged ataxia, marked cardiovascular changes and prolonged recovery times (Kamerling et al. 1988; England et al. 1992). Ataxia and cardiovascular e¡ects peak 5 minutes after intravenous administration (England et al.1992).
Detomidine infusion for standing chemical restraint DV Wilson et al.
The sedative and cardiovascular e¡ects of various steady-state plasma concentrations of detomidine in standing horses have been described using a computer-controlled infusion (Daunt et al. 1993). The successful use of detomidine infusion as an anesthetic adjunct in halothane-anesthetized horses has also been described (Wagner et al. 1992) The purpose of the study reported here was to describe and assess the protocol utilized when providing chemical restraint in standing horses with detomidine infusion. Procedures successfully performed using this protocol are also described.
Methods and Results
Signalment The anesthetic records of 51 horses that received a detomidine infusion during the course of their treatment at the MSU VTH were reviewed. There were ¢ve stallions, 18 mares and 28 geldings in the group. Our patient population included nine Quarterhorses, seven Thoroughbreds, seven Belgians, ¢ve Percherons, ¢ve Standardbreds, ¢ve mixed breeds, three Arabs, two Appaloosas, two Paints, two Foxtrotters, one Morgan, one Pony, one Trakhener and one Saddlebred. Average age was 9.5 6.9 years and weight was 575 290.3 kg.
Procedures
Data were obtained from the medical records of horses that received detomidine infusion as part of their treatment at the Michigan State University Veterinary Teaching Hospital (MSU VTH) between 1996 and1999. All horses were monitored for clinical signs of sedation. Pulse and respiratory rates were measured and recorded at variable intervals before and during the procedure. All data are listed as mean ( SD) unless otherwise indicated.
Fifty-one procedures were performed. The average duration of these standing procedures was 40 (range 10^90) minutes. The horses presented for a wide range of procedures which are listed in Table 1 with the relative frequencies of occurrence of those procedures.
Detomidine and adjunctive drugs A 14-gauge catheter was placed in the jugular vein and sutured in position following local anesthesia
Table 1 A list of the procedures performed, relative frequencies and numbers of cases with additional drugs administered when using detomidine by infusion to provide standing chemical restraint in 51horses
Total cases
(No. horses) additional drugs administered
13
1 d, 6 b
10
3 b, 1 b þ d
7
2b
4
1 b, 1 b þ d
3 3
1 b, 1 b þ d
3 2 2 1 1 1 1
1b
1b 1b
Procedure
Skin surgery, cryosurgery Sarcoids, other masses, abscesses, lacerations, scrotal hematoma Throat/neck surgery Laryngeal ventriculectomy, sternothyrohyoid myectomy, permanent tracheostomy Perineal surgery Cervical laceration, urethrostomy, removal peri-anal melanoma Nasal, sinus surgery Flush and pack nasal, frontal sinuses, remove packing Cast change, removal Intra-abdominal procedures Ovariectomy, laparoscopy, uterine torsion correction Eye and eyelid procedures Distichiasis – excision and debride corneal ulcer, eyelid mass removal, third eyelid mass removal Joint lavage Extensor tenectomy – stringhalt, patellar desmotomy Esophageal obstruction Explore draining tract in tongue Bone biopsy Endoscopy: Bronchial biopsy
d ¼ detomidine, b ¼ butorphanol.
Veterinary Anaesthesia and Analgesia, 2002, 29, 54^57
55
Detomidine infusion for standing chemical restraint DV Wilson et al.
and a surgical preparation of the site. The detomidine infusion was prepared by adding a dose of 24 mg kg1 of detomidine (Dormosedan, P¢zer Animal Health, West Chester, PA, USA) to a 250-mL bag of 0.9% saline solution. Final average concentration was 33 19.7 mg mL1. Detomidine was administered to these horses as a bolus loading dose of 7.5 1.87 mg kg1. The median interval between the bolus dose of detomidine and the start of the infusion was 0 minutes (range 0^20 minutes). The starting infusion rate was 8 mL minute1 (0.6 0.19 mg kg1 minute1) for the ¢rst 15 minutes, and this was serially halved every 15 minutes of the infusion. The average duration of the detomidine infusion in these horses was 62 (range 20^135) minutes. A period of at least 20 minutes elapsed after the termination of the infusion before the horse was released from the stocks, or encouraged to walk. The total dose of detomidine infused was12 6.2 mg kg1. Any responses to surgical stimuli were treated by administering a small additional bolus of detomidine, doubling the infusion rate, administering a bolus of butorphanol or a combination of the above. Twenty of these horses received additional detomidine, butorphanol (Torbugesic, Fort Dodge Animal Health, Ft. Dodge, IA, USA), or both drugs at the start of or during the surgical procedure. Additional doses of detomidine (6 2.4 mg kg1) were administered to four horses during the procedure. Supplemental butorphanol was administered to 19 horses (dose 19 16.5 mg kg1). Half of the horses undergoing surgical procedures of the skin required additional supplemental drugs, as did four of the 10 throat surgery cases. The surgical procedures associated with administration of additional drugs are indicated in Table 1. Local anesthesia (mepivacaine) or epidural analgesia (xylazine in six horses) was used in addition to the detomidine infusion to facilitate surgery, and was performed after sedation had reached its peak e¡ect.
Cardiovascular changes Baseline heart rates were 42 6 beats minute1 (n ¼ 32), and had decreased to 32 6 (range 20^43) beats minute1 by 20 minutes after initiation of the infusion.
Sedation All but three horses were restrained by stocks. All horses lowered their head and exhibited reduced 56
response to external stimuli following the start of the infusion. Some horses swayed or leaned heavily on the side bars of the restraining stocks. Pronounced muscle relaxation was commonly observed.
Complications All procedures but one were completed satisfactorily with no adverse sequelae noted as being associated with the restraint technique. In one horse the restraint provided was not adequate for the desired procedure (removal of lingual foreign body) and general anesthesia was elected the next day. Other less obvious complications were not speci¢cally recorded so the incidence may have been higher than reported here.
Discussion Detomidine infusion very e¡ectively produces extended periods of chemical restraint in the horse. A wide variety of procedures were completed using this form of chemical restraint. The horses became very tractable and tolerated signi¢cant manipulations. Pharmacokinetic data from these horses would have been interesting. Our delivery system utilized an exponentially decreasing dose of detomidine to produce a clinically constant level of sedation. The degree of sedation shown by our patients matches that described by Daunt et al. (1993) as occurring at plasma detomidine concentrations of between 19 and 43 ng mL1 (Daunt et al.1993). At these concentrations horses were markedly sedated with profound head lowering, limited response to environmental stimuli, and leaning on the side and rear bars of the stocks (Daunt et al.1993). As a reference, serum levels of detomidine half an hour following intravenous administration of 80 mg kg1 to horses have been shown to be approximately 100 ng mL1 (Salonen et al.1989). A plasma detomidine level of 25 ng mL1 (infusion rate of 0.18 mg kg1 minute1) has been shown to reduce the MAC of halothane in horses by 33% (Dunlop et al.1991;Wagner et al.1992) Horses undergoing surgery of the sinus, throat and abdominal cavity were likely to require additional doses of detomidine or butorphanol. This implies that the infusion dose of detomidine was not su⁄cient to mask any de¢ciencies in local anesthesia of these surgical sites. One author suggests that detomidine is a more potent sedative than analgesic (Kamerling et al.1988) and our clinical experience would support this. Veterinary Anaesthesia and Analgesia, 2002, 29, 54^57
Detomidine infusion for standing chemical restraint DV Wilson et al.
One potential source of variability in the e¡ect of the infusion in these horses arises from the use of gravity to in£uence infusion rate. A gravity-based drip delivery system may have variations in actual £ow of 20% (Davis & Parbrook 1995). To minimize these e¡ects we closely monitored the infusion, and adjusted the rate where appropriate. Cardiovascular alterations induced by infusions of detomidine have been shown to be similar in magnitude to those in which bolus administration of detomidine was used (Daunt et al. 1993). In one report, heart rate was decreased by 38%, second-degree atrioventricular block was reported in 83% of horses, and cardiac index decreased by a third as plasma detomidine concentrations increased to 43 ng mL1 during an infusion (Daunt et al. 1993). Mean arterial pressure increased by 23% above baseline values at this detomidine plasma concentration (England et al. 1992; Daunt et al. 1993). The decrease in cardiac output caused by a2-adrenergic agonists is believed to be largely due to a reduction in heart rate and to an increase in afterload. This cardiovascular change may also be related to stimulation of central imidazoline receptors (Hamilton1992). In conclusion, a detomidine infusion was an e¡ective method for providing prolonged periods of chemical restraint in standing horses. However, this method alone did not provide su⁄cient analgesia for surgery and a signi¢cant proportion of animals required supplemental sedatives and analgesics.
Acknowledgements The authors would like to thank Drs Wertz, Dunlop and Daunt for suggestions concerning the dosage pattern described herein.
Veterinary Anaesthesia and Analgesia, 2002, 29, 54^57
References Bettschart-Wolfensberger R, Clarke KW,Vainio O et al. (1999) Pharmacokinetics of medetomidine in ponies and elaboration of a medetomidine infusion regimen which provides a constant level of sedation. ResVet Sci 67,41^46. Daunt DA, Dunlop CI, Chapman PL et al. (1993) Cardiopulmonary and behavioral responses to computer-driven infusion of detomidine in standing horses. Am J Vet Res 54, 2075^2082. Davis PD, Parbrook GD (1995) Basic Physics and Measurement. In: Anaesthesia,4th edn. Butterworth Heinemann, Oxford, p. 40. Dunlop CI, Daunt DA, Chapman PL et al. (1991) The anesthetic potency of 3 steady-state plasma levels of detomidine in halothane anesthetized horses. Abstracts from the 4th International Congress of Veterinary Anaesthesia, Utrecht,The Netherlands, p.7. England GC, Clarke KW, Goossens L (1992) A comparison of the sedative e¡ects of three a2-adrenoceptor agonists (romi¢dine, detomidine and xylazine) in the horse. J Vet Pharmacol Ther15,194^201. Hamilton CA (1992) The role of imidazoline receptors in blood pressure regulation. Pharmacol Ther 54, 231^248. Kamerling SG, Cravens WMT, Bagwell CA (1988) Objective assessment of detomidine-induced analgesia and sedation in the horse. Eur J Pharmacol151,1^8. Salonen JS, Vaha-Vahe T, Vainio O et al. (1989) Single dose pharmacokinetics of detomidine in the horse and cow. J Vet Pharmacol Ther12,65^72. WagnerAE, Dunlop CI, Heath RB et al. (1992) Hemodynamic function during neurectomy in halothane-anesthetized horses with or without constant dose detomidine infusion.Vet Surg 21, 248^255. Wertz EM, Dunlop CI,Wagner AE et al. (1994) Three chemical restraint techniques for mares undergoing standing colpotomy surgery. Proceedings of the 5th International Congress onVeterinaryAnesthesia, Guelph Canada, p.133. Received12 October1999; accepted18 December 2000.
57
B R I E F C O M M U N I C AT I O N
Retrospective analysis of detomidine infusion for standing chemical restraint in 51 horses DV Wilson BVSc, MS, Dipl ACVA, GV Bohart DVM, AT Evans DVM, MS, Dipl ACVA, S Robertson BVMS, PhD, Dipl ACVA, Dipl ECVA, Y Rondenayy DVM College of Veterinary Medicine, Michigan State University, East Lansing, MI.
Correspondence: Dr DV Wilson, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824^1314, USA.
Abstract Objective To assess the e¡ectiveness of a detomidine infusion technique to provide standing chemical restraint in the horse. Design Retrospective study. Animals Fifty-one adult horses aged 9.5 6.9 years (range1^23 years) and weighing 575 290.3 kg. Methods Records of horses presented to our clinic over a 3-year period in which a detomidine infusion was used to provide standing chemical restraint were reviewed. Information relating to the types of procedure performed, duration of infusion, drug dosages and adjunct drugs administered was retrieved. Results Detomidine was administered as an initial bolus loading dose (mean SD) of 7.5 1.87 mg kg1. The initial infusion rate was 0.6 mg kg1 minute1, and this was halved every 15 minutes. The duration of the infusion ranged from 20 to 135 minutes. Twenty horses received additional detomidine or butorphanol during the procedure. All horses undergoing surgery received local anesthesia or epidural analgesia in addition to the detomidine infusion. A wide variety of procedures were performed in these horses.
Dr Robertson’s present address is the College of Veterinary Medicine, University of Florida. yDr Rondenay’s current address is the Department of Clinical Sciences, University of Montreal.
54
Conclusions Detomidine administered by infusion provides prolonged periods of chemical restraint in standing horses. Supplemental sedatives or analgesics may be needed in horses undergoing surgery. Clinical relevance An e¡ective method that provides prolonged periods of chemical restraint in standing horses is described. The infusion alone did not provide su⁄cient analgesia for surgery and a signi¢cant proportion of animals required supplemental sedatives and analgesics. Keywords chemical restraint, detomidine, horse, infusion, standing surgery.
Introduction Infusions of sedative or anesthetic drugs generally provide more consistent levels of sedation/anesthesia while using less drug than intermittent bolus techniques. Infusions of both medetomidine (Bettschart^Wolfensberger et al. 1999) and detomidine (Wertz et al. 1994) for standing chemical restraint in the horse have been described, and the authors of the second report were the source of the initial dose rates used in this study (Wertz et al.1994). Detomidine is an unscheduled a2-adrenergic drug with potent tranquilizing, analgesic and sedative properties. These e¡ects can be achieved by bolus administration of detomidine but this is usually accompanied by prolonged ataxia, marked cardiovascular changes and prolonged recovery times (Kamerling et al. 1988; England et al. 1992). Ataxia and cardiovascular e¡ects peak 5 minutes after intravenous administration (England et al.1992).
Detomidine infusion for standing chemical restraint DV Wilson et al.
The sedative and cardiovascular e¡ects of various steady-state plasma concentrations of detomidine in standing horses have been described using a computer-controlled infusion (Daunt et al. 1993). The successful use of detomidine infusion as an anesthetic adjunct in halothane-anesthetized horses has also been described (Wagner et al. 1992) The purpose of the study reported here was to describe and assess the protocol utilized when providing chemical restraint in standing horses with detomidine infusion. Procedures successfully performed using this protocol are also described.
Methods and Results
Signalment The anesthetic records of 51 horses that received a detomidine infusion during the course of their treatment at the MSU VTH were reviewed. There were ¢ve stallions, 18 mares and 28 geldings in the group. Our patient population included nine Quarterhorses, seven Thoroughbreds, seven Belgians, ¢ve Percherons, ¢ve Standardbreds, ¢ve mixed breeds, three Arabs, two Appaloosas, two Paints, two Foxtrotters, one Morgan, one Pony, one Trakhener and one Saddlebred. Average age was 9.5 6.9 years and weight was 575 290.3 kg.
Procedures
Data were obtained from the medical records of horses that received detomidine infusion as part of their treatment at the Michigan State University Veterinary Teaching Hospital (MSU VTH) between 1996 and1999. All horses were monitored for clinical signs of sedation. Pulse and respiratory rates were measured and recorded at variable intervals before and during the procedure. All data are listed as mean ( SD) unless otherwise indicated.
Fifty-one procedures were performed. The average duration of these standing procedures was 40 (range 10^90) minutes. The horses presented for a wide range of procedures which are listed in Table 1 with the relative frequencies of occurrence of those procedures.
Detomidine and adjunctive drugs A 14-gauge catheter was placed in the jugular vein and sutured in position following local anesthesia
Table 1 A list of the procedures performed, relative frequencies and numbers of cases with additional drugs administered when using detomidine by infusion to provide standing chemical restraint in 51horses
Total cases
(No. horses) additional drugs administered
13
1 d, 6 b
10
3 b, 1 b þ d
7
2b
4
1 b, 1 b þ d
3 3
1 b, 1 b þ d
3 2 2 1 1 1 1
1b
1b 1b
Procedure
Skin surgery, cryosurgery Sarcoids, other masses, abscesses, lacerations, scrotal hematoma Throat/neck surgery Laryngeal ventriculectomy, sternothyrohyoid myectomy, permanent tracheostomy Perineal surgery Cervical laceration, urethrostomy, removal peri-anal melanoma Nasal, sinus surgery Flush and pack nasal, frontal sinuses, remove packing Cast change, removal Intra-abdominal procedures Ovariectomy, laparoscopy, uterine torsion correction Eye and eyelid procedures Distichiasis – excision and debride corneal ulcer, eyelid mass removal, third eyelid mass removal Joint lavage Extensor tenectomy – stringhalt, patellar desmotomy Esophageal obstruction Explore draining tract in tongue Bone biopsy Endoscopy: Bronchial biopsy
d ¼ detomidine, b ¼ butorphanol.
Veterinary Anaesthesia and Analgesia, 2002, 29, 54^57
55
Detomidine infusion for standing chemical restraint DV Wilson et al.
and a surgical preparation of the site. The detomidine infusion was prepared by adding a dose of 24 mg kg1 of detomidine (Dormosedan, P¢zer Animal Health, West Chester, PA, USA) to a 250-mL bag of 0.9% saline solution. Final average concentration was 33 19.7 mg mL1. Detomidine was administered to these horses as a bolus loading dose of 7.5 1.87 mg kg1. The median interval between the bolus dose of detomidine and the start of the infusion was 0 minutes (range 0^20 minutes). The starting infusion rate was 8 mL minute1 (0.6 0.19 mg kg1 minute1) for the ¢rst 15 minutes, and this was serially halved every 15 minutes of the infusion. The average duration of the detomidine infusion in these horses was 62 (range 20^135) minutes. A period of at least 20 minutes elapsed after the termination of the infusion before the horse was released from the stocks, or encouraged to walk. The total dose of detomidine infused was12 6.2 mg kg1. Any responses to surgical stimuli were treated by administering a small additional bolus of detomidine, doubling the infusion rate, administering a bolus of butorphanol or a combination of the above. Twenty of these horses received additional detomidine, butorphanol (Torbugesic, Fort Dodge Animal Health, Ft. Dodge, IA, USA), or both drugs at the start of or during the surgical procedure. Additional doses of detomidine (6 2.4 mg kg1) were administered to four horses during the procedure. Supplemental butorphanol was administered to 19 horses (dose 19 16.5 mg kg1). Half of the horses undergoing surgical procedures of the skin required additional supplemental drugs, as did four of the 10 throat surgery cases. The surgical procedures associated with administration of additional drugs are indicated in Table 1. Local anesthesia (mepivacaine) or epidural analgesia (xylazine in six horses) was used in addition to the detomidine infusion to facilitate surgery, and was performed after sedation had reached its peak e¡ect.
Cardiovascular changes Baseline heart rates were 42 6 beats minute1 (n ¼ 32), and had decreased to 32 6 (range 20^43) beats minute1 by 20 minutes after initiation of the infusion.
Sedation All but three horses were restrained by stocks. All horses lowered their head and exhibited reduced 56
response to external stimuli following the start of the infusion. Some horses swayed or leaned heavily on the side bars of the restraining stocks. Pronounced muscle relaxation was commonly observed.
Complications All procedures but one were completed satisfactorily with no adverse sequelae noted as being associated with the restraint technique. In one horse the restraint provided was not adequate for the desired procedure (removal of lingual foreign body) and general anesthesia was elected the next day. Other less obvious complications were not speci¢cally recorded so the incidence may have been higher than reported here.
Discussion Detomidine infusion very e¡ectively produces extended periods of chemical restraint in the horse. A wide variety of procedures were completed using this form of chemical restraint. The horses became very tractable and tolerated signi¢cant manipulations. Pharmacokinetic data from these horses would have been interesting. Our delivery system utilized an exponentially decreasing dose of detomidine to produce a clinically constant level of sedation. The degree of sedation shown by our patients matches that described by Daunt et al. (1993) as occurring at plasma detomidine concentrations of between 19 and 43 ng mL1 (Daunt et al.1993). At these concentrations horses were markedly sedated with profound head lowering, limited response to environmental stimuli, and leaning on the side and rear bars of the stocks (Daunt et al.1993). As a reference, serum levels of detomidine half an hour following intravenous administration of 80 mg kg1 to horses have been shown to be approximately 100 ng mL1 (Salonen et al.1989). A plasma detomidine level of 25 ng mL1 (infusion rate of 0.18 mg kg1 minute1) has been shown to reduce the MAC of halothane in horses by 33% (Dunlop et al.1991;Wagner et al.1992) Horses undergoing surgery of the sinus, throat and abdominal cavity were likely to require additional doses of detomidine or butorphanol. This implies that the infusion dose of detomidine was not su⁄cient to mask any de¢ciencies in local anesthesia of these surgical sites. One author suggests that detomidine is a more potent sedative than analgesic (Kamerling et al.1988) and our clinical experience would support this. Veterinary Anaesthesia and Analgesia, 2002, 29, 54^57
Detomidine infusion for standing chemical restraint DV Wilson et al.
One potential source of variability in the e¡ect of the infusion in these horses arises from the use of gravity to in£uence infusion rate. A gravity-based drip delivery system may have variations in actual £ow of 20% (Davis & Parbrook 1995). To minimize these e¡ects we closely monitored the infusion, and adjusted the rate where appropriate. Cardiovascular alterations induced by infusions of detomidine have been shown to be similar in magnitude to those in which bolus administration of detomidine was used (Daunt et al. 1993). In one report, heart rate was decreased by 38%, second-degree atrioventricular block was reported in 83% of horses, and cardiac index decreased by a third as plasma detomidine concentrations increased to 43 ng mL1 during an infusion (Daunt et al. 1993). Mean arterial pressure increased by 23% above baseline values at this detomidine plasma concentration (England et al. 1992; Daunt et al. 1993). The decrease in cardiac output caused by a2-adrenergic agonists is believed to be largely due to a reduction in heart rate and to an increase in afterload. This cardiovascular change may also be related to stimulation of central imidazoline receptors (Hamilton1992). In conclusion, a detomidine infusion was an e¡ective method for providing prolonged periods of chemical restraint in standing horses. However, this method alone did not provide su⁄cient analgesia for surgery and a signi¢cant proportion of animals required supplemental sedatives and analgesics.
Acknowledgements The authors would like to thank Drs Wertz, Dunlop and Daunt for suggestions concerning the dosage pattern described herein.
Veterinary Anaesthesia and Analgesia, 2002, 29, 54^57
References Bettschart-Wolfensberger R, Clarke KW,Vainio O et al. (1999) Pharmacokinetics of medetomidine in ponies and elaboration of a medetomidine infusion regimen which provides a constant level of sedation. ResVet Sci 67,41^46. Daunt DA, Dunlop CI, Chapman PL et al. (1993) Cardiopulmonary and behavioral responses to computer-driven infusion of detomidine in standing horses. Am J Vet Res 54, 2075^2082. Davis PD, Parbrook GD (1995) Basic Physics and Measurement. In: Anaesthesia,4th edn. Butterworth Heinemann, Oxford, p. 40. Dunlop CI, Daunt DA, Chapman PL et al. (1991) The anesthetic potency of 3 steady-state plasma levels of detomidine in halothane anesthetized horses. Abstracts from the 4th International Congress of Veterinary Anaesthesia, Utrecht,The Netherlands, p.7. England GC, Clarke KW, Goossens L (1992) A comparison of the sedative e¡ects of three a2-adrenoceptor agonists (romi¢dine, detomidine and xylazine) in the horse. J Vet Pharmacol Ther15,194^201. Hamilton CA (1992) The role of imidazoline receptors in blood pressure regulation. Pharmacol Ther 54, 231^248. Kamerling SG, Cravens WMT, Bagwell CA (1988) Objective assessment of detomidine-induced analgesia and sedation in the horse. Eur J Pharmacol151,1^8. Salonen JS, Vaha-Vahe T, Vainio O et al. (1989) Single dose pharmacokinetics of detomidine in the horse and cow. J Vet Pharmacol Ther12,65^72. WagnerAE, Dunlop CI, Heath RB et al. (1992) Hemodynamic function during neurectomy in halothane-anesthetized horses with or without constant dose detomidine infusion.Vet Surg 21, 248^255. Wertz EM, Dunlop CI,Wagner AE et al. (1994) Three chemical restraint techniques for mares undergoing standing colpotomy surgery. Proceedings of the 5th International Congress onVeterinaryAnesthesia, Guelph Canada, p.133. Received12 October1999; accepted18 December 2000.
57