• E L M Pimenta, F J Teixeira Neto, P A Sá, W Pignaton, and N A Garofalo.
• Faculdade de Medicina Veterinária e Zootecnia, Universidade Estadual Paulista, São Paulo, Brazil.
• Equine Vet. J. 2011 May 1; 43 (3): 332-40.

Reasons For Performing StudyBradycardia may be implicated as a cause of cardiovascular instability during anaesthesia.HypothesisHyoscine would induce positive chronotropism of shorter duration than atropine, without adversely impairing intestinal motility in detomidine sedated horses.MethodsTen minutes after detomidine (0.02 mg/kg bwt, i.v.), physiological saline (control), atropine (0.02 mg/kg bwt) or hyoscine (0.2 mg/kg bwt) were randomly administered i.v. to 6 horses, allowing one week intervals between treatments. Investigators blinded to the treatments monitored cardiopulmonary data and intestinal auscultation for 90 min and 24 h after detomidine, respectively. Gastrointestinal transit was assessed for 96 h via chromium detection in dry faeces.ResultsDetomidine significantly decreased heart rate (HR) and cardiac index (CI) from baseline for 30 and 60 min, respectively (control). Mean ± s.d. HR increased significantly 5 min after atropine (79 ± 5 beats/min) and hyoscine (75 ± 8 beats/min). After this time, HR was significantly higher after atropine in comparison to other treatments, while hyoscine resulted in intermediate values (lower than atropine but higher than controls). Hyoscine and atropine resulted in significantly higher CI than controls for 5 and 20 min, respectively; but this effect coincided with significant hypertension (mean arterial pressures >180 mmHg). Auscultation scores decreased from baseline in all treatments. Time to return to auscultation scores ≥12 (medians) did not differ between hyoscine (4 h) and controls (4 h) but atropine resulted in significantly longer time (10 h). Atropine induced colic in one horse. Gastrointestinal transit times did not differ between treatments.ConclusionHyoscine is a shorter acting positive chronotropic agent than atropine, but does not potentiate the impairment in intestinal motility induced by detomidine. Because of severe hypertension, routine use of anticholinergics combined with detomidine is not recommended.Potential RelevanceHyoscine may represent an alternative to atropine for treating bradycardia.© 2010 EVJ Ltd.

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