An entropy based observational study to determine the effect of varying time intervals between fentanyl and propofol administration on propofol requirement for induction of anaesthesia

Written informed consent will be taken from all patients. All the patients will undergo a thorough pre anaesthetic evaluation and pre-operative orders will be given.

Then they will be assigned to three groups by convenience non probability sampling by the Anaesthesia consultant.

Group 1: patients who will be receiving propofol immediately after fentanyl injection.

Group 2: patients who will be receiving propofol 3 min after fentanyl injection.

Group 3: patients who will be receiving propofol 6 min after fentanyl injection.

In the operating room, standard pre induction monitors including electrocardiography, entropy monitor, pulse oximetry and non-invasive blood pressure will be attached and baseline heart rate, blood pressure, saturation, state entropy and response entropy will be recorded.

Intravenous fluid infusion will be started at a rate of 10 ml/kg/hour. Patients will be pre oxygenated with 100% oxygen. Intravenous fentanyl 2 mcg/kg will be administered as a bolus.

Subsequently, according to group, Group 1 patients will be administered propofol immediately after fentanyl injection, patients in Group 2 will receive propofol 3 minute after fentanyl injection, and

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those in group 3 will be receiving propofol 6 min after the fentanyl injection by anaesthesia consultant. Patient will be monitored during and after administration of fentanyl.

Propofol will be injected slowly while communicating verbally with the patient. Induction of anaesthesia will be considered as complete when there is loss of response to verbal commands. Entropy value at this time is noted and will be recorded every minute until 10-minute post intubation. Patient will be monitored during and after propofol injection.

Spo2, Heart rate and Non-invasive blood pressure will be recorded every 2 min by the Anaesthesia postgraduate, from the time of fentanyl administration for 10 min and after that vitals will be recorded every 3 minutes.

The dose of propofol required for induction is noted. If any movement, vocalisation or bucking is noted at the initiation of mask ventilation, additional doses of propofol in aliquots of 20 mg will be administered by Anaesthesia consultant. The total dose requirement (induction dose plus additional boluses) will be also noted by the postgraduate. After confirmation of mask ventilation, rocuronium 0.6 mg/kg will be administered by the Anaesthesia consultant to facilitate tracheal intubation.

In case of hypotension – which is defined as fall of blood pressure of more than 20% from the baseline - an intravenous bolus of 300 ml of Ringer’s lactate will be administered.

Hypotension not responding to fluid bolus will be treated with a 100 mcg bolus of intravenous phenylephrine. Bradycardia-which is defined as fall in heart rate <50 or a rapidly falling heart rate, will be treated by 0.6mg bolus of intravenous atropine.

Occurrences of hypotension, bradycardia, and requirement of fluid boluses and vasopressors for treatment of hypotension will be recorded.

The following demographic parameters will be noted: age, sex, and weight and ASA physical status.

The primary outcome measures will be the total dose of propofol and the dose of propofol required in milligram per kg body weight for induction of anaesthesia.

Secondary outcome measures will be entropy values, SPO2, Heart rate, Systolic blood pressure, Diastolic blood pressure, Mean arterial pressure of the groups.

All interventions and entropy value interpretation will be done by Anaesthesia consultant.

All the data will be recorded by Anaesthesia postgraduate.