The effect of remifentanil on cardiovascular dynamics during anaesthesia

Alterations in cardiovascular parameters are common during general anaesthesia, owing to the combined effects of anaesthetic drugs, surgical stimuli, changes in intravascular volume and baroreflex activity. In healthy patients, these changes may be well tolerated with minimal morbidity. However, in patients with limited cardiovascular function, hypotension, hypertension and tachycardia may lead to cardiac arrhythmias, myocardial ischaemia and infarction. Certain phases of anaesthesia and surgery are associated with particular increased risk for cardiovascular instability, especially induction of anaesthesia, instrumentation of the airway, skin incision, emergence and awakening from anaesthesia. Therefore specific measures may be required to attenuate cardiovascular responses to noxious stimuli. Remifentanil is a new opioid introduced into clinical practice in 1996, whose pharmacokinetic and pharmacodynamic properties suggested it might be useful to attenuate adverse autonomic and cardiovascular responses. This thesis describes studies of these possible effects of remifentanil. Remifentanil attenuated the cardiovascular and plasma catecholamine responses to laryngoscopy and tracheal intubation in healthy young adults. However, bradycardia and hypotension were observed in some individuals, and further studies confirmed that lower doses than originally recommended were effective. Remifentanil was also effective in elderly patients, and hypertensive patients, but observations of myocardial ischaemia confirmed that these groups are at risk. There was significant inter-individual variation in cardiovascular responses, confirming that remifentanil and other drugs used during anaesthesia should be titrated to effect. Remifentanil administered as a bolus attenuated the cardiovascular responses to emergence from anaesthesia and tracheal extubation, without compromising clinical recovery. Future studies should also address its place as an analgesic/sedative outside the operating room, for example in Intensive Care. This thesis details the effects of remifentanil on responses to noxious stimuli during anaesthesia and adds to our collective understanding of cardiovascular responses during anaesthesia in different groups of patients.