Impact of Propofol Dose Reduction in Relation to the Time Since Administration of Fentanyl During Anesthesia Induction

A minimum of 162 patients were required, considering an expected Mean Difference of 5 with expected Standard Deviation of 22, confidence level of 95% and power of 80%. Estimating a possible loss of 15%, it was raised to 192. Consecutive identification numbers were assigned and the sample was randomized in six groups of 32 patients according to time and dose of propofol.

Pre-oxygenation was performed until the expired oxygen fraction exceeded 80% and 2 µg/kg of intravenous fentanyl were administered. Depending on the study group, 1 or 2 minutes were allowed to pass and 1, 1.5 or 2 mg/kg of propofol were supplied (prior administration of intravenous lidocaine 0.5 mg/kg). The time in which the BIS dropped below 60 was recorded. If it did not reach that level after two minutes or when it exceeded it but then rose above 60 again, an extra dose of propofol of 0.5 mg/kg was administered. Muscle relaxation was performed with rocuronium 0.6 mg/kg. The patient was manually ventilated until endotracheal intubation was performed by the same experienced anaesthesiologist and connected to mechanical ventilation.

Data were collected manually. Statistical analysis was performed using SPSS ver. 22. Inferential statistics were performed using t-test for quantitative variables, chi-square for qualitative and ANOVA for qualitative and quantitative comparisons. Non-parametric statistical tests were used when necessary. Confidence intervals were estimated at a level of 95% and a P value of <.05 was considered statistically significant.