Preanaesthetic use of atropine in small animals.

Although it is unwise to recommend any preanaesthetic drug or regimen to be used routinely without consideration for the individual patient, the procedure being undertaken or the other drugs that will be used during the anaesthetic, of all anaesthetic-related drugs that might be under review, atropine is probably one of the least 'toxic' and least likely to cause life-threatening complications when used correctly. In most small veterinary practices there isn't the luxury of a dedicated anaesthetist available to monitor and manage each anaesthetised patient and the best form of cardiac monitor available may be an audible rate monitor. In this situation the advantages combined with the usual indications probably far outweigh the disadvantages of using atropine prophylactically. If a choice must be made, a sinus tachycardia under anaesthesia is probably preferable to a profound bradyarrhythmia. Absolute contraindications for using atropine are rare; the drug, when used alone, has low incidence of toxicity at clinically recommended doses in dogs and cats. Further, the new inhalation agents available to veterinarians (enflurane and isoflurane) do not sensitise the heart to the effect of catecholamines, so that the predominance of sympathetic tone produced when atropine is used is unlikely to precipitate dysarrthythmias during gaseous anaesthesia. Rhythm disturbances that occur under halothane anaesthesia when atropine is used, suggest there is some other cause, or agent, that is arrhythmogenic, such as an alpha 2 agonist, excessively deep level of anaesthesia, hypercapnia or hypoxaemia. Notwithstanding the above arguments, my preference, as a specialist anaesthetist, is that a drug is given only as required (not before) and that when, for example, any unusual heart rhythm occurs, all possible reasons for the occurrence (such as excessively deep anaesthesia or hypoventilation) are eliminated before other drugs like atropine or antiarrhythmics are administered.