This was a prospective, randomized, single-center, double-blind study conducted adhering to the principles of the Declaration of Helsinki. Institute ethics committee approval was taken and the study was conducted from September 2020 to September 2021. Written informed consent was obtained from each patient to participate in this study.

Fifty-four patients of ASA (American Society of Anaesthesiologists) physical status I or II, aged between 18 and 65 years undergoing elective laparoscopic cholecystectomy under general anesthesia were enrolled in the study. One patient from group A was converted to laparotomy because of bleeding and one patient from group B could not be followed postoperatively. So these two were excluded from the study and a total of 52 patients, 26 in each group were analyzed (Fig. 1).

CONSORT diagram showing the progress of participants through the study

Patients with severe cardiac, respiratory, hepatic, renal, or endocrine disease, patients with a neurological disorder, electrolyte disorders, with a history of alcohol or any drug addiction, who were on analgesics pre-operatively, pregnant/breastfeeding females, and those who had known allergic to local anesthetic were excluded from the study.

To estimate the group size needed to show statistical significance, assuming a between-group difference in VAS pain score of 1.3 (mean difference) and standard deviation of 1.7 as reported by Gallagher et al. with a two-tailed α = 0.05 and power of 80%, it was calculated that a minimum of 24 patients per group were required (Gallagher et al. 2001). We increased the total number of patients to 27 per group to compensate for the dropouts.

Simple randomization was done using computer-generated random numbers. The Anaesthesia technician was assigned the role of group assignment using a computer-based randomization list, which was secured in sequentially numbered sealed envelopes concealed till enrollment of the patient. At the time of pre-anesthetic evaluation, all patients were explained about the study and briefed about the use of a visual analog scale (VAS) for pain assessment. VAS is a pain assessment tool in which pain is assessed by asking the patient to indicate on a 10-cm line the point that corresponds to the level of pain intensity they felt, where 0 is “no pain” and 10 is “worst imaginable pain”. Patients were advised to remain fasting for 8 h before surgery.

On arrival in the operation theatre, peripheral venous access was secured with 20 G intravenous cannula. Patients were shifted to operation theatre and a multipara monitor was connected for monitoring ECG, pulse rate, noninvasive blood pressure (NIBP), and pulse oximetry. It was a double-blinded study and attempts were made to maintain allocation concealment from patients and anesthetists. One anesthetist was responsible for the preparation of the medication, and the other anesthetist who infused the medication was not aware of the strength of the infused medication. Patients in group A received an IV bolus of lidocaine 1.5 mg/kg slowly over 10 min, prior to induction followed by a continuous infusion at the rate of 1.5 mg/kg/h via infusion pump. Patients in group B patients received an IV lidocaine bolus of 1.5 mg/kg slowly over 10 min followed by infusion at the rate of 2 mg/kg/h.

Induction was done with Inj. propofol 2 mg/kg and Inj. fentanyl 2 µg/kg, followed by Inj. atracurium 0.5 mg/kg intravenously and the airway was secured by endotracheal tube. Maintenance of anesthesia in both groups was with 50% N2O in O2, isoflurane, and intermittent atracurium as required. Fentanyl 0.5 µg/kg was repeated every hour after the first hour. Fifteen minutes prior to the end of surgery, all patients received intravenous paracetamol 1 gm infusion and ondansetron 4 mg. The lidocaine infusion was continued throughout the surgery and was terminated just after the last suture. Neuromuscular blockade was reversed with IV neostigmine and glycopyrrolate and the patients were extubated after regaining consciousness and were transferred to the post-anesthesia care unit (PACU). Local anesthetic was not given in any other form. During the whole perioperative period heart rate, systolic blood pressure, diastolic blood pressure, mean arterial pressure, and ECG were monitored and documented. Bradycardia was defined as HR < 60 bpm or less than 20% of the baseline and was treated with atropine 0.6 mg (may repeat up to a total of 3 mg). Hypotension was defined as a fall in mean arterial pressure (MAP) of more than 20% of the baseline and was treated with an injection of mephenteramine 6 mg iv.

VAS score was evaluated in the PACU and the surgical ward by the investigator who was unaware of the study medication given, immediately after surgery, then at intervals of 30 min, 1 h, 2 h, 4 h, and thereafter every 4 hourly till 24 h. Postoperatively all the patients were given injection paracetamol 1gm IV 8 hourly. Patients having VAS scores of more than 3 were treated with diclofenac sodium 75 mg IV in 100 ml of saline to be repeated not less than 8-h intervals. If the patient’s VAS remained more than three even after 30 min of inj. diclofenac sodium then injection tramadol 2 mg/kbw was given as an infusion. The time to the first dose and total consumption of inj. diclofenac in 24 h was noted. Adverse effects of lidocaine, i.e., lightheadedness, perioral numbness, nausea and vomiting, sedation, arrhythmias, hypotension, and bradycardia were monitored and documented if present.

The data was tabulated in MS Excel and statistical analysis was done using SPSS software, version 19.0 (Statistical Package for the Social Sciences Inc., Chicago, IL, USA. Mean and standard deviation were used for descriptive analysis. An unpaired t test was used to compare the mean difference of VAS scores at different time points, mean time to demand for the first rescue analgesic (in minutes), and mean total analgesic requirement between the two groups. Demographic and other background characteristics were compared between the two groups using suitable statistical tests. For all statistical tests p < 0.05 was considered statistically significant.