The use of hyoscine N‐butylbromide to treat intraoperative bradycardia during isoflurane anaesthesia in three horses

Abstract

Intraoperative bradycardia is not an uncommon complication in anaesthetised horses and it has been recommended that severe bradycardia (defined as heart rate (HR) <25 beats/min) during general anaesthesia, when associated with hypotension (mean arterial pressure (MAP) <70 mmHg) and other signs of inadequate tissue perfusion, should be treated with anticholinergics. Muscarinic antagonists, such as atropine and glycopyrrolate, cause positive chronotropism and dromotropism (improved atrioventricular conduction) by competitively blocking the effects of acetylcholine at muscarinic receptors in the heart. However, in horses, prolonged intestinal hypomotility and colic have been associated with the use of atropine and glycopyrrolate which has led to the investigation of the use of hyoscine Nbutylbromide (hyoscine NBB) to treat alpha 2 agonist-induced bradycardia in horses. This report describes the successful use of hyoscine NBB to treat symptomatic intraoperative bradycardia in three isoflurane-anaesthetised horses. Case 1 Case historyA 3-year-old 555 kg Warmblood gelding presented for bilateral stifle arthroscopy under general anaesthesia. Preanaesthetic examination identified a second-degree atrioventricular (AV) block which disappeared after trot up. Physical examination was otherwise unremarkable.