Electrophysiological responses to noxious stimuli in the anaesthetised child

In the UK, more than 235,000 children admitted to hospital each year receive an operation or investigation under general anaesthesia. It is not known whether nociceptive stimulation evokes a change in cortical brain activity in the anaesthetised child. The aim of this thesis is to determine whether noxious stimulation administered to anaesthetised children results in a measurable change in brain activity and whether this evoked activity is altered in children who have been born prematurely and experienced a high level of pain in early life. Changing patterns of neuronal activity evoked by noxious and non-noxious stimuli were 'time locked' to electrophysiological recordings by means of a novel high-speed camera and an event detection interface developed during this thesis. Changes in band power were examined pre- and post-stimuli and across the different stimulus modalities. In all children, background EEG activity was dominated by delta (<3 Hz) and alpha (8-12 Hz) band frequencies, consistent with previously reported anaesthetic literature. Clinical and experimental noxious stimulation, and tactile stimulation evoked a significant increase in delta activity (p<0.05) with no changes in average heart rate or ipsilateral EMG activity observed between pre- and post-stimulus. The application of local anaesthetic to the stimulation site diminished the evoked increase in delta activity. The response to noxious stimulation in the children born prematurely was not significantly different from the age-matched control group (p>0.05) but they had striking differences in their background EEG activity. Prematurely born children had significantly lower alpha and beta band activity. The electrophysiological recordings we have obtained show that it is possible to measure evoked brain activity following a variety of noxious and non-noxious stimuli to investigate how the paediatric human brain processes sensory information under anaesthesia. The EEG measures were more sensitive to nociception than changes in autonomic activity and reflex withdrawal activity. Noxious stimulation caused a significant increase in delta activity, representing an increase in cortical synchronisation. While the children who were born prematurely did not respond differently to the noxious stimulation they had dramatically different background activity, which could have clinical relevance when using brain-derived patterns of EEG activity to help establish anaesthetic depth.