A Comparison Between The Effects Of Peribulbar And Sub-tenon Blocks Combined With General Anesthesia On The Incidence Of Oculocardiac Reflex (OCR) During Pediatric Strabismus Surgery: A Double Blinded Randomised Control Study

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.