Concerning the oculocardiac reflex, all of the following are true EXCEPT:
A. The medical rectus is the most sensitive of the extra ocular muscles in terms of triggering the OCR
B. The OCR may occur without the presence of a globe
C. The OCR is defined as a HR decrease by 10% following the stimuli
D. The stimuli is associated with a oculo-respiratory reflex and oculo-emetic reflex
E. Short term opioids (remifentanil) reliably ablate the OCR
The answer is E. The OCR is defined clinically as a decrease in heart rate by 10% following pressure to the globe or traction of the ocular muscles. The reported incidence of the oculocardiac reflex varies from 14% to 90%. The OCR is usually triggered by traction on the extraocular muscles (especially medial rectus), direct pressure on the globe, ocular manipulation, or ocular pain. This reflex may also be triggered by a retrobulbar block (pressure associated with local infiltration), or even manipulation of ocular tissue after an enucleation. The globe does not need to be in place and the OCR can occur with an orbital hematoma after enucleation. The OCR is known to fatigue with repeated stimulation. The OCR most often leads to bradycardia but may also include junctional escape beats or even asytole. The OCR occurs more often in younger patients and is most pronounced in strabismus surgery. Hypoxia, hypercarbia, acidosis, and light anesthesia can worsen the OCR. As the oculocardiac reflex is a vagal response atropine may decrease the incidence of the OCR. Deepening the anesthetic will also decrease the OCR. Some have tried use short acting opioid narcotics such as remifentanil to decreased the OCR, however, the use of these agents has been associated with an increase severity of the OCR. The retrobulbar block may prevent arrythmias by blocking the afferent limb, but may also stimulate the OCR with pressure of local injection.