Peribulbar Block for Prevention of Oculocardiac Reflex

Strabismus is a common ophthalmic problem in Egypt that usually requires surgical correction. This surgery primarily aims to improve alignment of visual axis but may be required only for cosmetic reasons. General anesthesia is mandatory for most cases however a concomitant local anesthetics administration is preferable to improve patient satisfaction, decrease postoperative analgesic requirements and reduce post-operative pain. Oculocardiac reflex is a noted serious complication that accompanies such surgeries and may be life threatening. Oculocardiac reflex (OCR) is one of the main challenges that face anesthesiologists during strabismus surgery. The incidence of OCR varies from 16 to 82 % in strabismus surgeries and this wide range does depend on the anesthetic agents, premedications, and the definition of OCR being used. Maintenance of adequate depth of anesthesia and the use of anti-cholinergic is the mainstay to reduce this risk. OCR is usually defined as a decrease in heart rate of more than 20 % from the baseline. This reflex is triggered by the pressure on the extra ocular muscles (EOM) or eyeball, orbital hematoma or trauma, the afferent limb is from orbital contents to ciliary ganglion then to the sensory nucleus of the trigeminal nerve near the fourth ventricle through the ophthalmic division of the trigeminal nerve. The main response of this reflex is transmitted through the vagus to the heart. This vagal stimulation leads to a decrease in heart rate (sinus bradycardia), contractility and arrhythmias such as atrioventricular block, ventricular fibrillation up to cardiac arrest.

The incidence of the OCR decreases with age and tends to be more pronounced in young healthy patients. It has been suggested that the anesthetic agents used during surgery influence the incidence of OCR. To date, the only successful method to interrupt an OCR is to stop the EOM traction, and then proceed with caution as surgery continues. Depth of anesthesia is another presumed factor having an impact on reducing of OCR incidence.

The response to surgical stimulus can be minimized or stopped with the help of peribulbar block.

The study will be performed from July 2019 to February 2020 at Fayoum University hospital after approval of the local institutional ethics committee and local institutional review board. The study design will be prospective, randomized, parallel groups, controlled clinical trial. A detailed informed consent will be signed by the eligible participants before recruitment and randomization.

Randomization \& blinding:

It will be done by using computer-generated random numbers that will be placed in separate opaque envelopes that will be opened by study investigators just before the surgery. Neither the participants, the study investigators, the attending clinicians, nor the data collectors will be aware of groups' allocation till the study end. The Consolidated Standards of Reporting Trials (CONSORT) recommendations for reporting randomized, controlled clinical trials will be followed. This is the randomized case-control study. 30 patients will be randomly divided into 2 study groups .each group contains 15 patients; Group GA: Total 15 cases who will receive general anesthesia only, i.e., without peribulbar block.

Group GB: Total 15 cases who will receive general anesthesia with peribulbar block.

Anesthetic technique:

Preoperative preparations:

History taking, physical examination and investigation will be done according to local protocol designed to evaluate the patients which include complete blood count and coagulation profile. All cases will have a routine pre-operative check-up, starve for 6 h for solids and 2 hours for clear fluids and water. Written informed consent will be signed by adult patients or parents of pediatric participants.

Intraoperative technique and management:

Upon arrival to the operating room standard monitors (Pulse oximeter, Noninvasive blood pressure monitoring, and Electrocardiogram) will be applied and continued all over the operation and a peripheral intravenous (IV) cannula (20G) will be inserted.

After adequate pre-oxygenation, Induction will be accomplished with the injection of propofol 2 mg/kg and Fentanyl 1 µg/kg IV. Endotracheal intubation will be facilitated by the intravenous injection of 0.5 mg/kg atracurium. General anesthesia will be maintained by mechanical ventilation with oxygen and air (50:50), isoflurane.

Patients in peribulbar block group will receive lidocaine 2%, bupivacaine 0.5% and hyaluronidase with total volume 0.06 ml/kg keeping the ratio 1: 1 between lidocaine combined with hyaluronidase and bupivacaine by 24 Gauge needle after induction of general anesthesia and before start of surgery.

Intraoperative OCR with decrease of heart rate more than 20% from baseline. If happened it will be managed by asking the operator to stop the surgical traction and giving 0.01 mg/kg of atropine. If cardiac arrest was identified, resuscitation will be according to advanced cardiac life support (ACLS) protocols.

Perioperative Nausea and vomiting will be treated by ondansetron 0.15 mg/kg intravenously over 15 min.

Postoperative monitoring, Pain control and follow up:

At the end of surgery, Participant will be transferred to postoperative anesthesia care unit (PACU) with standard monitoring applied. Pain will be evaluated by visual analog score (VAS) score from (0_ 100) (where; zero = no pain, 100=worst imaginable pain) assessed at 2 ,4, 6 ,12 ,24 and after 24 h.

Eligibility Criteria:
Inclusion Criteria:

* Patients aged 10 years to 50 years
* American society association (ASA) physical status I, II
* Patient scheduled for a unilateral strabismus surgery.

Exclusion Criteria:

* Refusal of local anesthesia.
* Contraindications of local anesthesia e.g. allergy or hypersensitivity to local anesthetics or orbital inflammation .
* Pregnancy
* Glaucoma
* Communication barrier between physician and patient e.g. impaired hearing, impaired mental status