Jones, PR; (2012) Haemodynamic instability during the intubation of critically-ill children. Doctoral thesis , UCL (University College London).

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Abstract

Haemodynamic instability is common during critical illness when homeostatic mechanisms are attenuated or already at the limit of their efficacy. Intubation is a crucial life-saving intervention which seeks to stabilize respiratory and cardiovascular function, but itself represents an additional, short-term haemodynamic challenge. This thesis aimed to investigate changes in heart rate during intubation of critically ill children. Heart rate was chosen as a crude measure of haemodynamic stability because it is most readily available even in time-critical pre-hospital settings. Focusing on heart rate also raised the question of the benefits of atropine pre-medication The first study was an international survey of Paediatric Intensivists using the Delphi methodology. There was agreement that there is a risk of death during intubation. There was no agreement about the capacity of atropine to reduce the incidence of bradycardia, hypotension or death. An observational study of 414 intubations in critically ill children was used to provide data for the thesis. Reductions in heart rate were common amongst first intubations in neonates, children between 28 days of age and eight years and further intubations in both groups. The limitations of using the minimum heart rate as a measure of haemodynamic disturbance were considered. An alternative measure of the change in heart rate, or ‘lost-beats’, was proposed and investigated. Atropine use was associated with less of a fall in heart rate and fewer lost heart beats during intubation. There was a strong association between a low heart rate and an increased incidence of arrhythmias and conduction abnormalities during intubation. Arrhythmias and conduction abnormalities were reduced, but not eliminated, by atropine pre-medication. Sinus tachycardia was not observed to convert to ventricular tachycardia or fibrillation when atropine was used. Mortality during critical care intubation was low (<0.5%). Atropine could not be statistically proven to have an effect on mortality during intubation although was associated with reduced intensive care mortality in children over 28 days of age but not in neonates. The association of atropine pre-medication with reduced PICU mortality in children over one month is unexpected and requires further investigation. A rabbit model of endotracheal intubation was used to investigate the consequences of vagal activation on blood pressure in hypovolaemia and endotoxaemia. Hypovolaemic rabbits observed a significantly smaller decrease in blood pressure after vagal stimulation than that in control rabbits. The relative change in blood pressure after vagal stimulation was similar between the endotoxaemic rabbits and controls. This finding suggests that different disease states may influence the haemodynamic function during intubation.

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