Literature shows fentanyl reduces the median effective concentration (EC50) of propofol when used for various noxious stimuli. However, fentanyl combined with propofol has a depressive effect on haemodynamics. We hypothesise that low dose dexmedetomidine will reduce the propofol requirement for induction with better haemodynamic profile compared with fentanyl.

120 ASA I/II adult patients, of age group 20 to 60 years, scheduled for elective day-care surgeries under general anaesthesia were randomised to three equally distributed groups as group D, group F and group S (control) of 40 patients each. They received infusions of dexmedetomidine 0.5 mcg/kg, fentanyl 1.5 mcg/kg and normal saline (control) respectively over 5 min prior to induction with propofol TCI (Marsh model). EC50 of propofol (primary objective) for I-gel insertion in each group was determined from the estimated effect site concentration (Ce), using Dixon's up-and-down method . Secondary objectives were propofol dose requirement and percentage change in haemodynamics during induction.

Our study demonstrates that low-dose dexmedetomidine premedication achieves more reduction in the EC50 (2.4 µg/ml, IQR 2.4 – 2.6 µg/ml, 95% CI 2.40 - 2.55 µg/ml) and dose of propofol (1.14 ± 0.28 mg/kg, 95% CI 1.05 - 1.23 mg/kg), for I-gel insertion, than that can be achieved by the use of fentanyl with propofol (EC50 of 3.0 µg/ml IQR 3.0 – 3.05 µg/ml, 95% CI 2.94 - 3.11 µg/ml; propofol dose 1.89 ± 0.55 mg/kg, 95% CI 1.72 - 2.07 mg/kg ) without any significant change in the haemodynamics.

Low-dose dexmedetomidine when compared with fentanyl significantly reduce the EC50 and dose of propofol required for I-gel insertion with propofol TCI, without much change in the haemodynamic profile.

Clinical trial registration number: CTRI/2019/03/018003.