Objective: Determine if, by reducing the dose of propofol and increasing the time elapsed between fentanyl and propofol administration, hemodynamic response is improved.

Methods: Patients were randomized into time groups (2 and 1 minute) and each subdivided into dose groups (1, 1.5 and 2 mg kg-1) obtaining six time-dose groups. After receiving 2 μg kg-1 of fentanyl, propofol was administered after the predetermined time. Time to hypnosis (BIS<60) and hemodynamic parameters at pre-induction, pre-intubation and postintubation were registered.

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.

Inclusion Criteria:

• Adults who required general anesthesia
• General anesthesia with endotracheal intubation (no supraglottic devices)
• Signed informed consent
• Non-cardiac surgery
• Same anesthesiologist

Exclusion Criteria:

• Hemodynamic instability (systolic BP < 90 mmHg with clinical signs of low cardiac output: impaired consciousness, diuresis <0.5 ml/kg/h, central venous saturation <60% with normal arterial saturation or lactate >3 mmol/l)
• Increased risk of bronchoaspiration (absence of fasting, stomach retention, intestinal obstruction, pregnancy, etc.)
• Suspected difficult airway
• Known allergy to anesthetic drugs

Baseline until 60 seconds after endotracheal tube positioned

Extreme bradicardia (HR<40) Extreme hypotension (SBP <60)

Pediatric population not included. BMI not registrated. Type of surgery not registered.

aleatory assignation, time measured by nurses, drugs administrated by principal investigator