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Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
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PLACEMENT

Anatomy.

Sensation to the eye is provided by the ophthalmic nerve via the long and short posterior ciliary nerves. Autonomic innervation is provided by the same nerves, and sympathetic fibers traveling with the arteries and parasympathetic fibers carried by the inferior branch of the oculomotor nerve provide additional autonomic innervation. Because the innervation of the orbicularis oculi muscle is via the facial nerve, blockade of these fibers is required to ensure a quiet eye during ophthalmic operations. The ciliary ganglion, approximately 2 to 3 mm in length, lies deep within the orbit just lateral to the optic nerve and medial to the lateral rectus muscle. The long and short ciliary nerves from this ganglion extend forward in the orbit. Immediately posterior to the ciliary ganglion, the ophthalmic artery can be found at the lateral side of the optic nerve as it crosses superior to it and passes forward in a medial direction ( Fig. 24-1 ).

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Figure 24-1  Orbital anatomy.


Position.

Patients are placed in the supine position and are instructed to maintain their primary gaze directly ahead, not “up and in,” as in earlier recommendations. With the globe in primary gaze, the optic nerve position minimizes potential intraneural injection. The anesthesiologist is positioned for the injection as illustrated in Figure 24-2 .

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Figure 24-2  Retrobulbar (peribulbar) block: technique.


Needle Puncture.

While the patient is looking cephalad and opposite the site of injection, a 27-gauge, 31 mm long, sharp-beveled needle is inserted at the inferolateral border of the bony orbit and directed toward the apex of the orbit, as illustrated in Figure 24-3 . The needle should be oriented so the bevel opening faces toward the globe. A “pop” may be appreciated as the needle tip traverses the bulbar fascia and enters the orbital muscle cone. Before injecting 2 to 4 mL of local anesthetic, the needle should be carefully aspirated. After retrobulbar block, 5 to 10 minutes should be allowed to pass before the operation is started. This helps avoid operating on patients who develop retrobulbar hematomas. During these 5 to 10 minutes, the anesthesiologist can apply gentle pressure on the globe, principally to facilitate lowering the intraocular pressure. If a peribulbar technique is chosen, needle insertion begins like that used for retrobulbar (inferotemporal) injection; however, the needle is inserted parallel and lateral to the lateral rectus muscle and bulbar fascia rather than making an effort to puncture it. Many practitioners also now suggest making a second injection of 3 to 5 mL for a peribulbar block either in the superomedial orbit or at the extreme medial side of the palpebral fissure. To complete the local block for ocular surgery, the orbicularis oculi muscle must be blocked to produce an immobile eye. This is accomplished by blocking the facial nerve fibers that innervate the muscle.

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Figure 24-3  Retrobulbar (peribulbar) block: technique.


There are many ways to perform blocks of these facial nerve fibers, and the method illustrated in Figure 24-4 is that of Van Lint. For this block, a 25-gauge, 4-cm needle is inserted at needle position 1 until the lower inferolateral orbital rim is reached. When the needle tip contacts bony surface, 1 mL of local anesthetic is injected. Through this skin wheal, the needle is repositioned along the lateral and inferior margins of the orbit (needle positions 2 and 3), and 2 to 3 mL of local anesthetic is injected at each point along the needle path.

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Figure 24-4  Regional block of the orbicularis oculi muscle: Van Lint method.


Potential Problems.

The most common complication that accompanies retrobulbar block is hematoma formation. It can be minimized by using a needle shorter than 31 mm. Hematoma formation is more likely if a longer needle is used and if the needle tip rests in the vicinity of the ophthalmic artery as it crosses the optic nerve. Hematoma can also be avoided by utilizing a peribulbar approach. Other complications that can accompany retrobulbar block include local anesthetic toxicity, development of the oculocardiac reflex, and cases of sudden apnea and obtundation after retrobulbar injection. The latter two results are probably related to injection within the optic nerve sheath, resulting in unexpected spinal anesthesia or intravascular injection affecting the respiratory centers in the midbrain, as illustrated in Figure 24-5 .

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Figure 24-5  Orbital functional anatomy.


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