Significance of the oculocardiac reflex during ophthalmic surgery in the dog

Antimuscarinic drugs were intentionally excluded from the anaesthetic protocol used in 72 dogs undergoing a variety of ophthalmic surgical procedures. Following premedication with acepromazine and morphine, anaesthesia was induced with thiopentone and maintained with halothane vaporised in oxygen and nitrous oxide. Muscle relaxation was achieved in all dogs using either vecuronium or atracurium and ventilation was controlled to produce mild hypocapnia. Only one patient showed electrocardiographic and arterial blood pressure changes that could be attributed to the oculocardiac reflex. This indicates that the reflex is of minor clinical importance when anaesthesia results in good muscle relaxation, mild hypocapnia and adequate unconsciousness. When these conditions are present the routine use of atropine or glycopyrrolate is unwarranted during ocular surgery in the dog.