Comparing the haemodynamic effects of high- and low-dose opioid anaesthesia: a secondary analysis of a randomised controlled trial

UNLABELLED: Post-induction hypotension (MAP < 65 mmHg) occurs frequently and is usually caused by the cardiovascular adverse effects of the anaesthetic induction drugs used. We hypothesize that a clinically significant difference in the incidence and severity of hypotension will be found when different doses of propofol and remifentanil are used for induction of anaesthesia.

METHODS: This is a secondary analysis of a randomised controlled trial wherein four groups (A-D) of patients received one out of four different combinations of propofol and remifentanil, titrated to a predicted equipotency in probability of tolerance to laryngoscopy (PTOL) according to the Bouillon interaction model. In group A, a high dose of propofol and a low dose of remifentanil was administered, and across the groups this ratio was gradually changed until it was reversed in group D. Mean and systolic arterial blood pressure (MAP, SAP) were compared at four time points (T baseline, T post-bolus, T 3min, T nadir) within and between groups Heart rate, bispectral index (BIS) and the incidence of hypotension were compared.

RESULTS: Data from 76 patients was used. At T post-bolus a statistically significant lower MAP and SAP was found in group A versus D (p = 0.011 and p = 0.002). A significant higher heart rate was found at T 3min and T nadir between groups A and B when compared to groups C and D (p = < 0.001 and p = 0.002). A significant difference in BIS value was found over all groups at T 3min and T nadir (both p < 0.001). All other outcomes did not differ significantly between groups.

CONCLUSION: Induction of anaesthesia with different predicted equipotent combinations of propofol and remifentanil did result in statistically different but clinically irrelevant differences in haemodynamic endpoints during induction of anaesthesia. Our study could not identify preferable drug combinations that decrease the risk for hypotension after induction, although they all yield a similar predicted PTOL.