Comparison of effects of thiopental, propofol or ketamine on the cardiovascular responses of the oculocardiac reflex during strabismus surgery

BACKGROUND: The oculocardiac reflex (OCR), which is most often encountered during strabismus surgery in children, may cause bradycardia, arrhythmias and cardiac arrest following a variety of stimuli arising in or near the eyeball. The main purpose of this study was to evaluate the effects of various anesthetic regimens on modulation of the cardiovascular effects of the OCR during strabismus surgery. METHODS: Three hundred ASA physical status I-II patients, scheduled for elective strabismus surgery under general anesthesia, randomly allocated in a double blind fashion to one of the three anesthetic regimens: group P: propofol (2 mglkg), alfentanil 0.02 mg/kg and atracurium 0.5 mglkg at induction; group K: ketamine racemate (2 mglkg), alfentanil 0.02 mg/kg and atracurium 0.5 mglkg at induction; group T: thiopental (5 mg/kg), alfentanil 0.02 mglkg, and atracurium 0.5 mglkg at induction. Mean arterial pressure (MAP) and heart rate (HR) were recorded just before induction, at 1, 15,30,45 and 60 minutes after induction. OCR was defined as a 20 beats/minute change in HR induced by traction compared with basal value. RESULTS: Mean HR ((PLUS-MINUS) SD) during total period of surgery in group P was significantly slower than that in group K (111.90(PLUS-MINUS) 1.10 vs. 116.7 (PLUS-MINUS) 0.70, respectively; P(LESS THAN)0.05). Mean HR changes ((PLUS-MINUS) SD) in group K was significantly higher than that in group P (11.2 (PLUS-MINUS) 1.44 vs. 8.7 (PLUS-MINUS) 1.50 respectively, P(LESS THAN)0.05). MAP changes ((PLUS-MINUS) SD) was significantly lower in patients in group P compared with patients in group K or T (12.5 (PLUS-MINUS) 1.13 vs. 19.3 (PLUS-MINUS) 0.80 or 18.9 (PLUS-MINUS) 0.91, respectively; P(LESS THAN)0.05). Incidence of OCR was significantly lower in patients in group K compared with patients in group T or P (9% vs. 16% and 13%. Respectively; P(LESS THAN)0.05). CONCLUSIONS: Induction of anesthesia with ketamine is associated with the least cardiovascular changes induced by OCR during strabismus surgery.