The profound augmentation of the oculocardiac reflex by fast acting opioids.

BACKGROUND

Trigemino-vagal bradycardia elicited by tension on an extraocular muscles (oculocardiac reflex; OCR) is a hazard for strabismus surgery patients. OCR can be reduced by anticholinergic medications and regulating the depth of anesthesia. We investigated the influence of narcotic agents as a routine part of general anesthesia for strabismus surgery in adults and children.

METHOD

From August, 1992 through September, 2000, 1275 patients undergoing extraocular muscle surgery were prospectively studied during 10 second, 200 gram square wave tension on gently isolated rectus muscles. The anesthetic agents, gas concentrations, and patient age were recorded. Patients receiving an anticholinergic agent and reoperated cases were excluded, yielding 1029 study cases. 849 received no narcotic as a part of induction. Two groups of patients were given no opiate before the first inferior rectus muscle was pulled. A narcotic was administered IV 5 minutes before the second inferior rectus was pulled. One group of 49 received fentanyl 0.15 uL/Kg and the second group of 12 received meperidine 1 mg/kg.

RESULTS

Faster acting intravenous induction opioids had a profound augmenting effect on the degree of oculocardiac reflex. Compared to no narcotic, the OCR was increased most by remifentanyl (p less than .0001), then sufenta (p=.02), and fentanyl (p less than .0001). Induction morphine had no appreciable effect on the OCR (p=.9). For the 49 patients with IV fentanyl delivered between the first OCR and second OCR, a significant increase occurred (p=.003). This increase in %OCR was not correlated with a change in inhalational gas concentration (p=.9), CO2 concentration (p=.6) or age (p=.12). For the 12 patients given demerol between the first and second rectus tension, no significant OCR change occurred (p=.7). The OCR was greatest for inferior rectus, then superior rectus, then medial rectus, and least for lateral rectus. (See text for details.)

CONCLUSION

In the absence of anticholinergic blockade, rapidly acting narcotics enhance the degree of bradycardia due to the OCR elicited by controlled extraocular muscle tension during strabismus surgery. Some opioids had the same augmenting magnitude as the blocking effect of IV anticholinergic medication. Meperidine, which has some anticholinergic characteristics, neither blocked nor augmented the OCR.