Is there a cholinergic and an adrenergic phase of the oculocardiac reflex during strabismus surgery?

We investigated the counterregulatory effect of the oculocardiac reflex (OCR) in 25 infants and children during strabismus surgery under three experimental conditions. In group 1, a series of measurements were recorded when the OCR was elicited by traction. The beat-to-beat heart rate reduction ranged from -26 to -64 beats/min (median: -46 beats/min). Constant traction increased heart rate in all patients from +23 to +50 beats/min (median: +30.5; P < 0.001). After a sudden release of the stimulation, heart rate rose further from +6 to +40 beats/min (median: +15; P < 0.001). In group 2, atropine (0.01 mg/kg) was administered 3-4 min prior to the same manipulations as in group 1. Constant traction changed heart rate from -1 to +20 beats/min (median: +4.5; P < 0.01). In group 3, a retrobulbar blockade suppressed the OCR and the counterregulation completely. These findings indicate that there is an active counterregulatory process which maintains heart rate during traction at the extraocular muscles after the bradycardic reflex has been initiated. The bradycardia and the counterregulation may be referred to as cholinergic and adrenergic phrases of the OCR. Atropine eliminates the cholinergic phase. Our study indicates that there may be receptors and afferent fibres for both phases, which can be blocked by local anaesthetics.