To maintain blinding, in the control group, the remifentanil infusion was replaced with 50 ml of normal saline in 50 ml syringe. The remifentanil (or saline) infusion was run until the pump indicated the target Ce had been achieved. Pharmacokinetic model for remifentanil was the Minto model (Height, Weight, and Age) Anesthesia in all patients was induced using 2 mg/kg of 2% propofol. The attending anesthesiologist asked the patients how they felt pain to evaluate pain severity of PIP while half -dose of propofol was administered. After the rest of the propofol was administered, the attending anesthesiologists asked the same question.

Remifentanil 1 mg was diluted into 50 ml of normal saline. A commercial TCI pump (Orchestra Base Primea, Fresenius Vial, France) was used for the effect-site TCI of remifentanil. The study groups received remifentanil to a target Ce of 4 ng/ ml. Pharmacokinetic model for remifentanil was the Minto model (Height, Weight, and Age) Anesthesia induction and the evaluation of pain were same as control group

V1 and V5 electrocardiographic positions as per the manufacturer's recommendations. The ANI was continuously recorded and displayed with a frequency of 1 Hz. ANI scores measured immediately before propofol administration, half-dose administration (1mg/kg), and full-dose administration (2mg/kg)of propofol.

The correlation of preanesthetic ANI scores and incidence of PIP.

Incidence and severity with numeric rating scales( 0= no pain, 100=worst pain) of propofol injection pain