Bradycardia during critical care intubation: mechanisms, significance and atropine.

Bradycardia occurs during the intubation of some critically ill children as a result of vagal stimulation due to hypoxia and/or laryngeal stimulation; such 'stable' bradycardia is accompanied by selective vasoconstriction. Some induction drugs also induce bradycardia which may be accompanied by vasodilatation which is also a feature of certain pathologies, which influence the progression to 'unstable' bradycardia, which does not respond to re-oxygenation and a pause in laryngoscopy. Preintubation atropine diminishes the overall incidence of stable bradycardia during routine anaesthesia. However, clinical studies of critical care intubation show that atropine does not prevent all episodes of bradycardia and specifically cannot affect vasodilatation. As such, there is insufficient evidence to support a recommendation for the indiscriminate use of atropine for intubation during critical care illness, including simple neonatal respiratory distress. Atropine is appropriate during septic or late stage hypovolaemic shock where abnormal vasomotor tone and bradycardia may potentially set up a negative feedback loop of cardiac hypo-oxygenation and hypoperfusion and during premedication when using suxamethonium.