A comparison of risk of hypotension using standard doses of remifentanil versus dexmedetomidine infusions in adult patients undergoing surgery under general anaesthesia at the Aga Khan University Hospital, Nairobi

Abstract

Background: Remifentanil and dexmedetomidine are common agents used in general anaesthesia, monitored anaesthesia care and critical care. When combined with inhaled or intravenous anaesthetic agents intra-operatively, they provide analgesia, lower general anaesthetic requirements and provide sedation and analgesia in the peri-operative period if indicated. Pharmacodynamically, they cause hypotension and bradycardia which are reversible if well managed. Past studies of these drugs have shown a significant proportion of patients with hypotension when compared with similar agents or in isolation. This study compares these two drugs on the effect of hypotension when used as adjuncts to general anaesthesia at low dose standard rate of infusions.  
Objective: To compare the proportion of hypotension episodes in a group of adult patients receiving dexmedetomidine infusion at 0.4mcg/kg/hr versus a group receiving remifentanil infusion at 0.2mcg/kg/min, severity of hypotension and physician interventions in each group.
Methods: One hundred and four patients scheduled for elective surgery under general anaesthesia were randomized into two groups:
Control group; received remifentanil infusion at 0.2mcg/kg/min Intervention group; received dexmedetomidine at 0.4mcg/kg/hr.
General anaesthesia was standardized in both groups. The patients were blinded to the study. Baseline blood pressures of all patients were determined prior to induction. The patient’s demographic characteristics were recorded. The number of patients who developed hypotension, the frequency of hypotension and the physician interventions were recorded and analysed.  
Results: The age and gender characteristics were different between the two groups (p values <0.023 and 0.05 respectively) however they did not affect the proportion of patients with hypotension. The weight, baseline pressures and ASA status of the patients within the groups were similar. The operative procedures varied within the groups. General surgery did not influence the outcome of hypotension in both arms.  The duration of surgery in remifentanil group exceeded that of Dexmedetomidine p value<0.0005 however the time to the first episode of hypotension was similar between the groups. The episodes of hypotension were fewer in the dexmedetomidine arm and the proportion of patients with hypotension were higher in the remifentanil arm, p value<0.001, R.R 0. = 0.5938, 95% C.I=   0.329-0.819  
The physician interventions administered were similar between the two groups except the use of ephedrine between the groups.  
Conclusion: Among this population, at standard infusion rates, the proportion of patients that risk hypotension was greater in those undergoing elective surgery receiving remifentanil at 0.2mcg/kg/min than in dexmedetomidine at 0.4mcg/kg/hr under isoflurane based anaesthesia.

Keywords:  Risk of hypotension, remifentanil versus dexmedetomidine infusions, general anaesthesia, Aga Khan University Hospital, Nairobi.