This study was designed to investigate pre-operatively measured parameters of various anaesthetic regimes, iris color, sex, age, surgical time, severity of Marcus-Gunn Pupil (MGP), type of mechanical stimulation of eye, and number of extraocular muscle (EOM) under tension as predictors of significant OCR in pediatric strabismus surgery.

Objectives: Despite various proposed maneuver, successfully predicting an oculocardiac reflex (OCR) is difficult to achieve. This study was designed to investigate pre-operatively measured parameters of various anaesthetic regimes, iris color, sex, age, surgical time, severity of Marcus-Gunn Pupil (MGP), type of mechanical stimulation of eye, and number of extraocular muscle (EOM) under tension as predictors of significant OCR in pediatric strabismus surgery.

Methods: Three hundred patients were randomized to one of three anesthetic regimes: group P: propofol (2 mg/kg), alfentanil 0.02 mg/kg, and atracurium 0.5 mg/kg at induction; group K: ketamine (2mg/kg), alfentanil 0.02 mg/kg, and atracurium 0.5 mg/kg at induction; group T: thiopental (5mg/kg), alfentanil 0.02 mg/kg, and atracurium 0.5 mg/kg at induction. OCR was defined as a 10% change in heart rate induced by traction.

Results: Incidence of OCR was significantly lower in patients in group k compared with patients in group T or P. Chi-square test results showed that the occurrence of OCR was significantly associated with difference of iris color (P=0.01). The occurrence of the OCR did not correlate with sex, age, duration of surgery, iris color, severity of MGP, number of EOM under tension, and type of mechanical stimulation of eye. Type of mechanical stimulation of eye or number of EOM under tension increased risk of developing OCR by 0.81 (95% CI, 0.66-0.98) and 1.29 (95% CI; 1.12-1.63) respectively.

Conclusions: Induction of anesthesia with ketamine is associated with least hemodynamic changes induced by OCR during strabismus surgery. The prediction of oculocardiac reflex propensity remains elusive.

Inclusion Criteria:

• 300 ASA physical status I or II patients, aged 2-18 years, who candidate for elective strabismus surgery

Exclusion Criteria:

• trauma to eye, ASA III or IV, who had contraindication for using thiopental, ketamine, or propofol, had cardiovascular diseases or had taken cardiovascular drugs