Research Paper| Volume 33, ISSUE 3, P149-157, May 2006

The effect of hyoscine on dobutamine requirement in spontaneously breathing horses anaesthetized with halothane



      To determine whether hyoscine has a sparing effect on the volume of dobutamine required to maintain mean arterial pressure (MAP) at 70 mmHg in horses anaesthetized with halothane.

      Study design

      Prospective, randomized, controlled clinical trial.


      Twenty adult horses weighing 507 ± 97 kg (mean ± SD), aged 10 ± 5 years.

      Materials and methods

      Pre-anaesthetic medication in all horses was intramuscular (IM) acepromazine (40 μg kg−1) and intravenous (IV) detomidine (0.02 mg kg−1). Anaesthesia was induced with ketamine (2.2 mg kg−1 IV) and diazepam (0.02 mg kg−1 IV), and maintained with halothane in oxygen. Horses breathed spontaneously. Flunixin (1.1 mg kg−1 IV) was given to provide analgesia. Heart rate, ECG, invasive arterial pressure, respiratory rate, percentage end-tidal carbon dioxide, percentage end-tidal halothane and partial pressure of oxygen and carbon dioxide in arterial blood and blood pH were monitored. Dobutamine was infused by an infusion pump to maintain MAP at 70 mmHg. Horses were randomly assigned to receive saline or hyoscine (0.1 mg kg−1) IV 30 minutes after induction. The heart rate, MAP and volume of dobutamine infused over 30-minute periods were measured and analysed statistically using a one-way anova.


      After administration of hyoscine, heart rate increased for 10 minutes (p < 0.01) and MAP for 5 minutes (p < 0.01). There was no difference in the volume of dobutamine infused over 30 minutes between horses given hyoscine or saline, although there was a wide individual variation in dobutamine requirements. No side effects of hyoscine were seen.


      The increase in heart rate and blood pressure that occurs after 0.1 mg kg−1 hyoscine is given IV in anaesthetized horses, is of short duration and does not significantly alter the amount of dobutamine required to maintain arterial pressure over the next 30 minutes.

      Clinical relevance 

      The short duration of action of 0.1 mg kg−1 hyoscine IV may limit its usefulness for correction of hypotension in horses anaesthetized with halothane. Further work is necessary to investigate the effects of higher or repeated doses or constant rate infusions of hyoscine.


      To read this article in full you will need to make a payment

      Purchase one-time access:

      Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
      One-time access price info
      • For academic or personal research use, select 'Academic and Personal'
      • For corporate R&D use, select 'Corporate R&D Professionals'


      Subscribe to Veterinary Anaesthesia and Analgesia
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect


        • Adams SB
        • Lamar CH
        • Masty J
        Motility of the distal portion of the jejunum and pelvic flexure in ponies: effects of six drugs.
        Am J Vet Res. 1984; 45: 795-799
        • Alibhai HIK
        • Clarke KW
        • Lee YH
        • et al.
        Cardiopulmonary effects of combinations of medetomidine hydrochloride and atropine sulphate in dogs.
        Vet Rec. 1996; 138: 11-13
        • Alitalo I
        • Vainio O
        • Kaartinen L
        • et al.
        Cardiac effects of atropine premedication in horses sedated with detomidine.
        Acta Vet Scand Suppl. 1986; 82: 131-136
        • Boatwright CE
        • Fubini SLF
        • Grohn YT
        • et al.
        A comparison of N-butylscopolammonium bromide and butorphanol tartrate for analgesia using a balloon model of abdominal pain in ponies.
        Can J Vet Res. 1996; 60: 65-68
        • Clark ES
        • Thompson SA
        • Becht JL
        • et al.
        Effects of xylazine on cecal mechanical activity and cecal blood flow in healthy horses.
        Am J Vet Res. 1988; 49: 720-723
        • Clarke KW
        • Hall LW
        ‘Xylazine’- a new sedative for horses and cattle.
        Vet Rec. 1969; 85: 512-517
        • Clarke KW
        • Taylor PM
        Detomidine: a new sedative for horses.
        Equine Vet J. 1986; 18: 366-370
        • Davies JV
        • Gerring EL
        Effect of spasmolytic analgesic drugs on the motility patterns of the equine small intestine.
        Res Vet Sci. 1983; 34: 334-339
        • Donaldson LL
        Retrospective assessment of dobutamine therapy for hypotension in anesthetized horses.
        Vet Surg. 1988; 17: 53-57
        • Ducharme NG
        • Fubini SL
        Gastrointestinal complications associated with the use of atropine in horses.
        J Am Vet Med Assoc. 1983; 182: 229-231
        • Dyson DH
        • James-Davies R
        Dose effect and benefits of glycopyrrolate in the treatment of bradycardia in anesthetized dogs.
        Can Vet J. 1999; 40: 327-331
        • Freeman SL
        • England GCW
        Effect of romifidine on gastrointestinal motility, assessed by transrectal ultrasonography.
        Equine Vet J. 2001; 33: 570-576
        • Gasthuys F
        • De Moor A
        • Parmentier D
        Haemodynamic changes during sedation in ponies.
        Vet Res Commun. 1990; 14: 309-327
        • Gasthuys F
        • Parmentier D
        • Goossens L
        • et al.
        A preliminary study on the effects of atropine sulphate on bradycardia and heart blocks during romifidine sedation in the horse.
        Vet Res Commun. 1990; 14: 489-502
        • Geimer TR
        • Ekström PM
        • Ludders JW
        • et al.
        Haemodynamic effects of hyoscine-N-butylbromide in ponies.
        J Vet Pharmacol Ther. 1995; 18: 13-16
        • Grandy JL
        • Steffey EP
        • Hodgson DS
        • et al.
        Arterial hypotension and the development of postanesthetic myopathy in halothane-anaesthetized horses.
        Am J Vet Res. 1987; 48: 192-197
        • Hall LW
        • Gillespie JR
        • Tyler WS
        Alveolar-arterial oxygen tension differences in anaesthetized horses.
        Br J Anaesth. 1968; 40: 560-567
        • Lee Y-HL
        • Clarke KW
        • Alibhai HIK
        • et al.
        Effects of dopamine, dobutamine, dopexamine, phenylephrine, and saline solution on intramuscular blood flow and other cardiopulmonary variables in halothane-anesthetized ponies.
        Am J Vet Res. 1998; 59: 1463-1472
        • Light GS
        • Hellyer PW
        Effects of atropine on the arrhythmogenic dose of dobutamine in xylazine-thiamylal-halothane-anesthetized horses.
        Am J Vet Res. 1993; 54: 2099-2103
        • Lindsay WA
        • Robinson GM
        • Brunson DB
        • et al.
        Induction of equine postanesthetic myositis after halothane-induced hypotension.
        Am J Vet Res. 1989; 50: 404-410
        • Marques JA
        • Teixeira Neto FJ
        • Campebell RC
        • et al.
        Effects of hyoscine-N-butylbromide given before romifidine in horses.
        Vet Rec. 1998; 142: 166-168
        • Nyman G
        • Funkquist B
        • Kvart C
        • et al.
        Atelectasis causes gas exchange impairment in the anaesthetised horse.
        Equine Vet J. 1990; 22: 317-324
        • Parks C
        • Manohar M
        • Lundeen G
        Regional myocardial blood flow and coronary vascular reserve in unanesthetized ponies during pacing induced ventricular tachycardia.
        J Surg Res. 1983; 35: 119-131
        • Raisis AL
        • Young LE
        • Blissitt KJ
        • et al.
        Effect of a 30-minute infusion of dobutamine hydrochloride on hind limb blood flow and hemodynamics in halothane-anesthetized horses.
        Am J Vet Res. 2000; 61: 1282-1288
        • Roberts MC
        • Argenzio A
        Effects of amitraz, several opiate derivatives and anticholinergic agents on intestinal transit in ponies.
        Equine Vet J. 1986; 18: 256-260
        • Roelvink MEJ
        • Goossens L
        • Kalsbeek HC
        • et al.
        Analgesic and spasmolytic effects of dipyrone, hyoscine-N-butylbromide and a combination of the two in ponies.
        Vet Rec. 1991; 129: 378-380
        • Singh S
        • McDonell WN
        • Young SS
        • et al.
        Cardiopulmonary and gastrointestinal motility effects of xylazine/ketamine-induced anesthesia in horses previously treated with glycopyrrolate.
        Am J Vet Res. 1996; 57: 1762-1770
        • Singh S
        • McDonell W
        • Young S
        • et al.
        The effect of glycopyrrolate on heart rate and intestinal motility in conscious horses.
        J Vet Anaesth. 1997; 24: 14-19
        • Singh S
        • Young SS
        • McDonell WN
        • et al.
        Modification of cardiopulmonary and intestinal motility effects of xylazine with glycopyrrolate in horses.
        Can J Vet Res. 1997; 61: 99-107
        • Steffey EP
        • Howland Jr, D
        Cardiovascular effects of halothane in the horse.
        Am J Vet Res. 1978; 39: 611-615
        • Steffey EP
        • Kelly AB
        • Hodgson DS
        • et al.
        Effect of body posture on cardiopulmonary function in horses during five hours of constant-dose halothane anesthesia.
        Am J Vet Res. 1990; 51: 11-16
        • Teixeira Neto FJ
        • McDonell WN
        • Black WD
        • et al.
        Effects of a muscarinic type-2 antagonist on cardiorespiratory function and intestinal transit in horses anesthetized with halothane and xylazine.
        Am J Vet Res. 2004; 65: 464-472
        • Weil AB
        • Keegan RD
        • Greene SA
        Effect of low-dose atropine administration on dobutamine dose requirement in horses anesthetized with detomidine and halothane.
        Am J Vet Res. 1997; 58: 1436-1439
        • Young LE
        • Blissitt KJ
        • Clutton RE
        • et al.
        Temporal effects of an infusion of dobutamine hydrochloride in horses anesthetized with halothane.
        Am J Vet Res. 1998; 59: 1027-1032