Comparison Between Peribulbar And Sub-tenon Blocks on Oculocardiac Reflex (OCR) During Pediatric Strabismus Surgery

120 children, American Society of Anaesthesiology (ASA) I or II, aged 6 to 13 years, scheduled for elective squint surgery under GA will be included in the study. Children with tumors or infections of the orbit, raised intraocular pressure, eye injury, airway abnormalities or who are blind in the eye other than that which will to be operated, will be excluded. Other exclusion criteria will include known allergy to local anaesthetics or nonsteroidal anti-inflammatory drugs (NSAIDS), steroid therapy, those with significant cardiac, respiratory, renal, hepatic, or neurological disorders, mentally challenged children, or parental refusal to participate.

All children will undergo a detailed preanesthetic evaluation including previous history of operations, drug history, physical examination (cardiovascular and respiratory systems, blood pressure, oxygen saturation, airway and dentition, body weight and height). During the pre-anesthesia evaluation, children will be encouraged to report postoperative pain, if present. All children will be fasted for a minimum of 4 hours and premedicated with oral midazolam 0.5 mg/kg 30 minutes before anaesthesia. Anesthesia will be induced with sevoflurane 6% in oxygen or intravenous (i.v.) propofol (2mg/kg), as appropriate for the child's age and preference. Following inhalational induction, an intravenous line will be placed. The airway will be secured using an appropriately sized endotracheal tube (ETT) following intravenous atracurium(0.5 mg.kg) and 1 to 3 min of mask ventilation using isoflurane 1.5% in oxygen.Anesthesia will then be maintained with isoflurane in air-oxygen and end tidal minimal alveolar concentration maintained at 1 to 1.3. ventilation will be established at 6-8ml per kg with a target PECO2 of 32 - 34 and will be adjusted accordingly.

Children will then be randomly allocated to one of three groups; by a nurse who will not participate in the study, reads the number contained in the envelope and makes group assignment.

Children in the control group (group C, n_20) will receive IV paracetamol (20mg/kg).

Children in the sub-tenon group (sub-tenon group (S), n _ 20) will receive a sub-tenon block. Sub-Tenon's anesthesia will be performed with 5% bupivacaine (0.08 ml/kg). Under sterile conditions, a 19-gauge curved, blunt metallic cannula (25 mm) will be inserted into sub-Tenon's space and the local anesthetic will be injected by the ophthalmologist.

The peribulbar group (P group _ 20) will receive peribulbar block with 0.25 mL/kg of a 1:1 mixture of 0.5% bupivacaine and 2% lignocaine containing hyaluronidase (500 IU hyaluronidase has been premixed with 30 mL 2% lignocaine). Peribulbar block using a two-injection technique will be performed by a second anaesthetist.

The children will not be aware to as which group they will be allocated into. Digital oculopression will be performed for 5 minutes. All blocks will be performed by one of the investigators. LAM will be injected both inferotemporallly and superonasally using a 26-G needle. Haemodynamic variables; electrocardiography (ECG), pulse oximetry, noninvasive blood pressure (NIBP) and end tidal carbon dioxide (PECO2); will be monitored continuously and Occurrence of oculocardiac reflex (OCR) will be recorded (either in the form of bradyarrhythmias mostly sinus bradycardia or o) . bradyarrhythmias which is the most common presentation of Oculocardiac reflex (OCR) will be considered as an acute decrease in heart rate below 60 beats/min and will be treated by asking the surgeon to stop stimulation and giving intravenous atropine (0.01 mg.kg), whereas other less common presentations of oculocardiac reflex (OCR) will be managed accordingly. All children will receive Dexamethasone (0.125mg/kg) 30 minutes before the end of surgery. At the end of the procedure, the ETT will be removed after reversing residual neuromuscular blockade with 50 μg·kg-1 neostigmine and 20 μg·kg-1 atropine and adequate spontaneous ventilation established.

Children will then be transferred to the recovery room, where they will be kept for 2 to 3 hours. On arrival in the recovery room, the child's' behavior and postoperative pain level will be assessed at 30 min by the recovery room nurse who will not be aware of the block using the modified objective pain scale (MOPS) [10] which assess pain via 5 points (crying, facial expressions, posture of the trunk, posture of the legs, and motor restlessness) with a minimum score of 0 and a maximum score of 10. 0-1 (no pain), 2-5 (mild), 6-7 (moderate), and 8-10 (severe) out of 10.

For pain judged as moderate or severe (MOPS > 5), ibuprofen 10mg/kg will be administered orally. After 2 hours in the recovery area, the children's pain will be assessed by Modified objective pain scale (MOPs) at 2 and 4 hours. Requirement of postoperative analgesia will be recorded. The incidence of PONV will be recorded. Numeric scoring will be used for PONV (0 = no nausea; 1 = nausea is present, but no vomiting; 3 = vomiting once within 30 min; 4 = vomiting two or more times within 30 min). Ondansetron (0.1 mg/kg, i.v.) will be given in cases of vomiting. The data collector will not be aware of the intervention the child will receive