After receiving approval from Ain Shams University, Faculty of Medicine, Research Ethics Committee (REC), FWA 000,017,585 (FAMASU M D 236/2019) and obtaining written informed consent, the interventional, randomized, and double-blinded trial was conducted in the institute hospital. Registration number is PACTR202109892575291.

One hundred and forty patients with American Society of Anesthesiologists (ASA) I and II, aged 21–55 years scheduled for elective open abdominal surgery having body mass index (BMI) between 18 and 25 kg/m2 with adequate cognitive state (able to understand and collaborate). The study exclusion criteria were hypersensitivity to any of the used drugs, pregnancy, and lactating mothers, chronic pain requiring daily use of opioid medication or chronic alcohol abuser, sleep apnea syndrome, bradycardia (heart rate of less than 50 beats per min at rest), or patients on beta-blockers or alpha 2 agonists, epilepsy or chronic daily use of psychiatric medication, patients received any other regional anesthesia technique (epidural, transverse abdominis plane (tap) or plexus block), and re-exploration cases were also excluded from the study.

Study groups

The patients were randomized into two groups by using computer-generated random sequences to prevent skewing or deliberate manipulation of results. Patients were given a random number from 1 to 140 and were allocated into one of two parallel groups with a ratio of 1:1 between the two groups. The dexmedetomidine group (group D) received 1 μg/kg loading dose over 10 min, followed by 0.5 μg/kg/h. and the lidocaine group (group L) received 1.5 mg/kg loading dose over 5 min (lidocaine 2%), followed by 1 mg/kg/h. The infusions were continued 24 h post-bolus dose. Blinded solutions were prepared by the pharmacist to be of the same volume and to the targeted doses of which is started immediately after intubation.

After full history was obtained, including age, history of chronic diseases, previous surgeries, drug allergies, and regular drug intake, the patients were fully examined, and vital data were measured and recorded.

Preoperatively, patients were taught how to evaluate their pain intensity using the VAS score, scored from 0 to 10 (where 0 = no pain and 10 = worst imaginable pain) (Cachemaille et al. 2020).

On arrival at the operating room, two intravenous lines were inserted in both upper limbs and all patients were premeditated with 2 mg of IV midazolam. Intraoperative monitoring included standard ASA monitors; electrocardiography (ECG), non-invasive blood pressure (NIBP), arterial oxygen saturation (SpO2), end-tidal carbon dioxide (EtCO2), body temperature using nasopharyngeal probe. Blood loss assessment was done throughout the surgeries as well.

All patients received general anesthesia, induction was done by 2 μg/kg fentanyl, 2–3 mg/kg propofol and endotracheal intubation was facilitated by 0.5 mg/kg atracurium.

All weight-based dosing was calculated on ideal body weight (IBW).

Anesthesia was maintained by 1–1.5 MAC isoflurane (according to the patient’s age) in 50% oxygen/air mixture (no nitrous oxide), and 0.1 mg/kg atracurium every 20 min, and ventilation parameters that maintain normocapnia (CO2 between 35 and 40 mmHg). [volume control mode, tidal volume 6–8 ml/kg, RR 12–14 b/min, peak respiratory pressure < 30 mmhg]. IV crystalloids (in the form of ringer lactate) were used for maintenance and to replace the deficit as needed according to a fluid chart. Fentanyl (0.5–1.5 μg/kg) was used as a rescue for pain suggested by A 20% increase in heart rate and /or arterial blood pressure from the preoperative baseline.

At the end of the surgery, reversal of muscle relaxant was done by using neostigmine (0.04 mg/kg) and atropine (0.01 mg/kg). After extubation, all patients were transmitted to the post-anesthesia care unit (PACU). Patients were discharged from the recovery unit based on modified Aldrete score.

Post-operative analgesia was in form of:

Regular dose of Ketorolac 30 mg per dose for a maximum 60 mg per day.

Pethidine 50 mg intravenous bolus once the pain is expressed by the patient or if VAS was ≥ 3.

Outcome’s measurements

All patients were followed up and assessed at baseline (time of administration of studying drug intraoperatively, (on arrival to PACU, 1 h, 2 h, 4 h, and every 6 h up to 24 h post-operatively for hemodynamics (blood pressure, heart rate), VAS score, total consumption of narcotics and post-operative occurrence of side effect as episodes of nausea and vomiting and time of the return of bowel movement. While the primary outcome was total dose consumption of intraoperative opioids.

Sample size calculation

Using G power program, setting alpha error at 5% and power at 80% after reviewing of literature, no previous similar study was done comparing between the two study groups (dexmedetomidine and lidocaine in 24 h) as regards the mean post-operative dose of analgesia. So, assuming an effect size of 0.5 (Cohen d) between the two groups regarding mean dose produced a sample size of 64 cases per group (128 total) taking an account 10% drop out rate, Sample Size will be 140 patients (70 patients in each group.

Data management and analysis

Data were analyzed using Statistical Package for Social Science (SPSS) version 18.0. Quantitative data were expressed as mean ± standard deviation (SD). Qualitative data were expressed as frequency and percentage.

The following tests were done:

Independent-samples ANOVA-test of significance was used when comparing between two means and variance.

Chi-square (χ2) test of significance will compare used to compare proportions between two qualitative parameters.

Probability (p value): p value < 0.05 is considered significant.