This study consists of a randomized, double blinded study. It was performed in the Bechir-Hamza Children’s Hospital, Tunis, Tunisia. It was approved by our institutional review board (Comité de protection des personnes, Hôpital, d’enfants Béchir-Hamza; # 123–2017, Chairman: Professor Said JLIDI). Informed written consent was obtained from all parents. Reporting of the current study follows the consort checklist, and the trial was registered (ClinicalTrials.gov Identifier: NCT03902249, registration on 04/04/2019).

The inclusion criteria selected patients aged < 18 years of age, American Society of Anesthesiologists health status (ASA) 1 to 2, undergoing surgical correction of hypospadias (all forms) and Snodgrass technique for surgery management. Exclusion criteria included: refusal of study participation and/or personal data use, coagulation disorder or skin infection at the puncture point (for regional anesthesia), preoperative administration of corticosteroids for other reasons, known allergic reactions to any medication used during the study (anesthetics agents, opioids and common non-opioid analgesics).

Patients were excluded from the study (and from the analyses) in case of failure of regional anesthesia or any intraoperative complication related to regional anesthesia (systemic toxicity, hematoma or regional infection).

The patients were assigned to the control or intervention groups using the opaque sealed envelope technique based on computer-generated randomized numbers in blocks of 5 patients per group.

Dexamethasone was prepared by hospital pharmacists. Four mg of dexamethasone was diluted in 8 ml of normal saline solution (final concentration 0.5 mg.ml− 1). The volume to be injected was 0.3.(weight in kg) ml. The control group received 0.9% saline solution presented in the same packaging. Patients and all healthcare professional involved in patients’ management were unaware of the assigned treatment.

Anesthesia was standardized in all patients. Pre-operatively, no premedication was administered; all patients were allowed to drink apple juice and water freely until 2 h before surgery. After preoxygenation, anesthesia induction was performed with sevoflurane 6% in an O2/air 50%/50% mixture. After securing intravenous access, fentanyl 3 mcg.kg− 1 and either dexamethasone or the control solution was administered. The airway was secured using a supraglottic device (igel, Intersurgical®, Wokingham, Berkshire, UK) and controlled ventilation was performed. A tidal volume of 7 to 9 ml.kg− 1 of an O2/Air mixture (50%/50%) was administered, an end-expiratory pressure 5 cmH2O was applied, and respiratory rate was adjusted to an end-tidal CO2 of 35 to 40 mmHg. The pudendal block was performed after the induction of anesthesia (and dexamethasone or the control solution adminitsration) and before incision. Hypnosis was achieved employing 1 age-adjusted minimal alveolar concentration of sevoflurane. Any increase in blood pressure or heart rate > 20% in comparison to preoperative values was treated by a fentanyl bolus of 3 mcg.kg− 1. Intraoperative maintenance fluid management consisted of Ringer’s Lactate administered according to the Holliday and Segar formula [15]. Body temperature was maintained between 36.5° and 37 °C using a simple warmer system on the upper part of the body.

The pudendal block was performed with a nerve stimulator under aseptic conditions [7, 8]. Patients were positioned in the lithotomy position. The point of injection was the medial side of the inferomedial ischial tuberosity, located at the 3- and 9-o’clock positions relative to the anus. With initial settings of 1.5 mA and 2 Hz, the nerve stimulator needle (22 gauge Stimuplex A, 50–100 mm; B. Braun, Melsungen, Germany) was inserted perpendicular to the skin, observing for the external anal sphincter contraction. The needle was advanced cranially, until obtaining penile movement. Maintenance of penile movement with reduction of stimulator current to 0.3 to 0.4 mA confirmed adequate proximity to the pudendal nerve. After negative blood aspiration, 0.1 ml.kg− 1 of 0.5% bupivacaine solution without epinephrine was injected per side. Adequate analgesia provided by the pudendal block was judged by the stability of the increase in heart rate or blood pressure < 20% in comparison to preoperative values during surgery.

Postoperatively, intravenous fluid administration consisted of a balanced crystalloid solution at 2 ml.kg− 1.h− 1 until the first postoperative day (24 h). Postoperative analgesia was standardized. Pain was evaluated using the CHEOPS score at arrival in the PACU (H0) at 30 min, and at 1, 2, 3, 4, 8 and 24 h after admission to PACU. In case of significant pain (CHEOPS > 7), a paracetamol bolus was administered (15 mg.kg− 1). In case of persistent pain 30 min after paracetamol administration, an intravenous bolus of nalbuphine (0.2 mg.kg− 1) was administered. All patients were managed in the hospital during 24 h and discharged the day after surgery.

All procedures were performed using the Snodgrass technique.

Data collected and analyzed consist of: age, weight, ASA status, type of hypospadias, the duration of the surgery, the time for the first rescue analgesia (paracetamol and nalbuphine), the number of boluses of each medication, the CHEOPS scores during the first 24 postoperative hours after surgery (admission to the PACU then 30 min, 1 h, 2 h, 3 h, 4 h, 8 h, 12 h and 24 h after admission to the PACU), the occurrence of vomiting during the 24 postoperative hours. The primary outcome was the proportion of patients needing any rescue analgesia during the first 24 postoperative hours. Secondary outcomes were: (a) the delay for the first administration of rescue analgesia, (b) postoperative CHOPS scores (c) opioid requirements during the first 24 postoperative hours and (d) the number of episodes of vomiting during the first 24 postoperative hours.

Long term follow-up after surgery explored surgical complications (urethrocutaneous fistula, meatal stenosis, urethral stricture, urethral diverticulum, glans dehiscence, breakdown, and cosmetic unfavorable outcome requiring redo-surgery) [16], Cometic result and micturition functions.

Data were expressed as median and [25–75 interquartile ranges] for continuous variables. Comparisons were performed using the Mann and Whitney test, the X², Fisher’s exact test and the Kaplan-Meyer survival curve.

The sample size for the current study was calculated according to previous studies on the efficacy of pudendal block during hypospadias surgery. Studies found rescue analgesia rates in pudendal block groups to range from 20% [8] to 7% [7]. Given that previous studies demonstrate a reduction in rescue analgesia with dexamethasone use [9, 11, 14], we hypothesized that rescue analgesia would be required in 20% of control group patients and 0% of dexamethasone group patients. Accordingly, 34 patients per group were necessary to ensure an alpha risk of 5% and a power of 80% Footnote 1. Taking into account for a small number of excluded patients for block failure, we designed for 36 patients per arm.

Statistical analyses were performed using SPSS 20.0 software (IBM Company, Chicago, Illinois, USA). P value was set to 0.05 and Bonferroni correction was applied to multiple comparisons. Results were expressed as N (%) or median [25; 75 interquartile ranges].