Atropine and succinylcholine: beliefs and controversies in paediatric anaesthesia.

Atropine was isolated in pure form in 1831. l One century and sixty-three years later, understanding of its complex pharmacology has yet to be achieved. Suceinylcholine was introduced into clinical practice in 1951. 2 Forty-three years later, we can only explain partly its mechanism of action at the neuromuscular junction, the duality of its neuromuscular block, and the diversity of its neurovegetative effects. Information on neuromuscular physiology, on neurohumoral transmission, and on the locations of different sub-types o f cholinergic receptors remains fragmentary. 3 In such a context, it is not surprising that issues of anticholinergics and succinylcholine in paediatric anaesthesia remain controversial. Atropine elicits two opposite cardiac effects, according to the dose used: (a) slowing of the heart rate, following 1.8 ~tg. kg -~ /v in adults, or 3.6 ~g-kg' /v in infants and children; and (b) acceleration of the heart rate, following a minimum of 7.2-14.3 ~tg. kg-' /v in infants, children, and adults. 4 It was thought that atropine and scopolamine caused cardioinhibition by central vagal stimulation. 5 However, cardiac slowing is also seen with -uaternary antimuscarinics which hardly cross the bloodrain barrier (atropine methylbromide, glycopyrrolate, and pirenzepine). 1.6-7 As a small dose of pirenzepine, an Ml-antagonist, can abolish the cardioinhibitory effect of atropine, it is now realized that atropine and other nonselective antimuscarinics can also produce bradycardia by blocking peripheral Mi-autoreceptors which normally inhibit or modulate the liberation of acetylcholine. 7 Cardioacceleration results from blockade of M2-receptors on the SA nodal pacemaker, t Intravenous atropine is commonly used in paediatric anaesthesia to (1) prevent and treat myocardial depression (bradycardia with hypotension) induced by halothane, (2) prevent and treat cardioinhibidon associated with potent opioids (fentanyl and congeners), (3) reduce the incidence of the oculocardiac