The study will be conducted prospectively, using a randomized double-blinded design. Male patients scheduled for elective unilateral herniorrhaphy will be included in the study.
Patients will be randomly allocated into two groups using the sealed envelope technique. All patients will have inhaled induction of anesthesia by facemask using oxygen and 8% sevoflurane for 2 to 4 minutes followed by placement of an IV cannula. After performing PVB injections, the sevoflurane concentration will be decreased to 0.4% to 0.8% and maintained until completion of surgery.
Then, group I will receive one PVB injection at L1-L2 and placebo PVB injections at T12-L1 and L2-L3. Group III will receive three PVB injections at T12-L1, L1-L2 and L2-L3.
Paravertebral block technique After induction of anesthesia and placement of regular anesthetic monitors, three unilateral PVBs will be performed with the child lying in the lateral position with the operative side uppermost. The needle insertion sites will be 1.5-2.0 cm lateral to the midline depending on the age and the body mass index of the child.
After aseptic preparation of the skin, a nerve stimulator (Stimuplex, B Braun AG, Melsungen, Germany) is used to identify an evoked muscular contraction appropriate for the levels. A 50 mm 21G insulated needle (Stimuplex A, B Braun AG) will be introduced perpendicular to the skin using 5 mA and 1 Hz. Then, the stimulating needle is gently manipulated to allow for adequate muscle response with a stimulating current of 0.4-0.6 mA.
In order to preserve the double-blindness of this trial, an independent nurse will prepare three syringes. Each syringe is labeled with the corresponding level of injection i.e, T12-L1, L1-L2 and L2-L3. The T12-L1 and L2-L3 syringes that will be used for group I will contain 0.45 ml placebo (0.9% normal saline) per syringe. The syringe labeled L1-L2 will contain 0.45 ml local anesthesia. On the other hand, the three syringes that will be used for group III will contain 0.15 ml local anesthesia and 0.3 ml placebo. Consequently, all patients will receive a total of 0.45 ml anesthesia and 0.9 ml placebo.
Data collection Demographic data such as age, weight and height will be collected. Non-invasive mean arterial blood pressure and heart rate will be recorded preoperatively (baseline), intraoperatively (incision of skin, dissection of hernia, traction over the sac and closure of incision) and immediately postoperatively. During the operation, any hemodynamic changes in excess of 15% from baseline values will result in a step-wise increase or decrease of the sevoflurane concentration. Intra-operative sevoflurane concentration will be recorded.
Postoperative pain assessment and analgesia As for pain assessment, the Face, Legs, Activity, Cry, Consolability (FLACC) scale will be used to measure postoperative pain (0 indicating no pain and 10 maximum possible pain).
Patients with pain score greater than 4 are given 1-2 mg/kg Tramadol hydrochloride (Tramal drops, Laboratoire Grunenthal, Aachen, Germany) A 350 mg paracetamol suppository (Tylenol CILAG SA, Schaffhouse, Switzerland) will be prescribed in pain score is less than 5.
During hospitalization trained nurses, blinded to the randomization, will collect the pain scores. Following hospital discharge, pain scores will be assessed by parents through phone calls made by the same nurses during the first postoperative day at predetermined time intervals (0h, 6h, 12h, 24h).
