Retrobulbar block: Hemodynamic effect

A retrobulbar block is frequently used for various ophthalmologic procedures including surgeries of the cornea, anterior chamber, and lens. A local anesthetic is injected into the cone formed by the four rectus muscles of the eye, thereby providing akinesia and anesthesia to ocular and extraocular muscles, with the exception of the orbicularis oculi of the eyelid (the superior oblique muscle also has extraocular innervation and can be incompletely anesthetized with the block).

When the block is performed, the pain associated with the block frequently induces elevated heart rate and blood pressure in the minutes immediately following. With the passage of time, however, the patient usually has very few complaints of pain during the surgery and does not have subsequent hemodynamic changes stemming from the block unless complications occur.

Complications of retrobulbar block include orbital perforation or ischemia, vascular injury causing retrobulbar hemorrhage, brainstem anesthesia, and activation of the oculocardiac reflex. Of these complications, the oculocardiac reflex is the common. The oculocardiac reflex occurs when afferent nerve signals are sent via the trigeminal nerve to synapses with the vagus nerve on the floor of the fourth ventricle. These signals may induce bradycardia and occasionally arrhythmias, particularly in younger patients.

Brainstem anesthesia occurs when local anesthetic is accidentally injected in the subdural space, likely due to placement of the needle through the optic nerve sheath. This results in respiratory depression and even arrest requiring assisted ventilation. Hemodynamic changes are occasional and variable.