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Retrobulbar Blocks

(Originally posted 18 January 1999 on About Anesthesiology)

INTRODUCTION
Many ophthalmologic procedures can be performed with retrobulbar blockade. This block can provide adequate anesthesia, akinesia and control of introcular pressure as well as postoperative analgesia. Most anesthesiologists do not perform these blocks, preferring to let the ophthalmologist place the block prior to beginning of surgery. In these cases, the anesthesiologist often provides sedation to make the block more tolerable/comfortable for the patient. In some centers, however, the anesthesiologists are the ones actually placing the blocks. In any case, it is a handy technique to be familiar with.

ANATOMY:
The ciliary ganglion, a parasympathetic ganglion, lies approximately 1 cm from the posterior boundary of the orbit between the lateral surface of the optic nerve and the ophthalmic artery. Parasympathetic fibers originating in the oculomotor nerve and postganglionic fibers supply the ciliary body and pupillary sphincter muscles.

The nasociliary nerve, a branch of the ophthalmic nerve, supplies sensory innervation of the cornea, iris, and ciliary body by way of the short ciliary nerves (these short viliary nerves are 6-10 small filaments that run with the ciliary arteries).

Retrobulbar block is aimed at blocking the ciliary ganglion, ciliary nerves, and cranial nerves II, II and VI. Cranial nerve IV is not affected since it lies outside the muscle cone. When the block is performed, the local anesthetic is delivered within the muscle cone itself.

TECHNIQUE OF RETROBULBAR BLOCK:
In the adult, the distance to the ciliary ganglion from the skin is about 3.5cm. Most commonly, a 25 gauge, 35mm needle is used to reduce the risk of passage beyond the ciliary ganglion. Advancement too far can result in puncture of the vessels in the apex of the orbit.

Steps in the blockade are as follows:

1. Palpate the inferolateral margin of the orbit and make a skin wheal.

2. Ask the patient to look straight ahead. (Note: it used to be common to ask the patients to look upward and inward and some ophthalmologists may still do this. However, this seems to put the needle path close to the optic nerve, ophthalmic artery and ophthalmic vein. Looking forward seems to be better.)

3. The injection is at the junction of the lateral and middle thirds of the inferior orbital rim.

4. Advance slowly. The needle should only penetrate retrobulbar fat and intermuscular septum. If you feel resistance, the needle may be in muscle, optic nerve or wall of the eye and it should be withdrawn and redirected.

5. Advance to 35 mm (depth of the needle).

6. Inject approximately 1cc of local anesthetic at this depth and then another 1cc of local anesthetic while withdrawing the needle.

CHOICE OF LOCAL ANESTHETIC:
The most commonly used local anesthetic agents are a 1:1 mixture of 2% lidocaine with 0.5 or 0.75% bupivicaine. Some like to use epinephrine or hyaluronidase.

OOCULOCARDIAC REFLEX
Bradycardia, junctional rhythm, or asystole can occur secondary to traction on the eye and ocular muscles. This is called the oculocardiac reflex (OCR). Better knowledge and aggressive treatment has decreased serious morbidity from this reflex from 1 in 3,500 to less than 1 in 100,000.

Atropine of glycopyrrolate can be used to treat this reflex (some recommend that it be given prophylactically). OCR can occur in an empty orbit from extraocular muscle stimulation.

The afferent pathway is ciliary ganglion to ophthalmic division of trigeminal nerve to gasserian ganglion to main trigeminal sensory nucleus fourth ventricle. The efferent pathway is the vagus nerve.

Hypoxia, hypercarbia and light anesthesia potentiate this reflex and should be avoided. Retrobulbar block does not guarantee attenuation of this reflex, so use caution when massaging the eye after placing the block. (The eye is commonly massaged with light pressure after the local anesthetic is injected to promote onset and completeness of the block.

PERIBULBAR ANESTHESIA:
Another technique that will produce orbital anesthesia has been described that involves injections above and below the orbit, with local anesthetic deposited in the orbicularis oculi muscle, behind it, and beneath, above and behind the globe. The potential for intraocular or intradural injection is decreased because the anesthetic is deposited outside the muscle cone. The risk of intraconal hemmorhage and direct optic nerve injury is also decreased.

COMPLICATIONS OF RETROBULBAR BLOCK:

Retrobulbar Hemmorhage: This is the most common complication seen and is due to inadvertant puncture of vessels within the retrobulbar space. It is evidenced by the simultaneous appearance of an excellent motor block of the globe, closing of the upper lid, proptosis and a palpable increase in intraocular pressure. Subconjunctival blood and eyelid ecchymosis may be seen as the hemmorhage extends anteriorly. Retrobulbar hemmorhage can lead to other complications such as central retinal artery occlusion and stimulation of the oculocardiac reflex. That said, many are minimal or even subclinical. On a rare occasion, surgery may be continued. However, it is usually considered the best course of action to postpone surgery for 2-4 days after hemmorhage because of the risk of repeat hemmorhage.

Oculocardiac Reflex: As discussed above. Note that this can occur several hours later in the event of an expanding hemmorhage. Thus, the patient should be closely monitored for several hours following a hemmorhage. If the OCR develops, surgical stimulation should stop and intravenous atropine is the treatment of choice (0.007 mg/kg).

Central Retinal Artery Occlusion: This can result from retrobulbar hemmorhage and may result in total loss of vision if not treated. If retrobulbar hemmorhage occurs, the patient's intraocular pressure and central retinal artery pulsations should be monitored. If external pressure on the globe is high enough to result in compression of the retinal arteries, then the surgeon will perform a deep lateral canthotomy or an anterior chamber paracentesis to decompress the orbit. This complication can also occur if the dura is penetrated and the local anesthetic is injected into the subarachnoid space.

Puncture of the Posterior Globe: Use of a blunted needle is common in an attempt to reduce this complication. However, this puncture can still occur and is more likely in patients with severely myopic eye ("long eye") or requiring repeated anesthetic injections. The patient experiences immediate ocular pain and restlessness following perforation. Intraocular hemmorhage and retinal detachment may occur.

Penetration of the Optic Nerve: Direct injury to the nerve, injection into the nerve sheath with compression ischemia and intramural sheath hemmorhage can result in optic atrophy and loss of vision even without retrobulbar hemmorhage. (See previous discussion concerning asking the patient to look forward during blockade)

Inadvertant Brain Stem Anesthesia: Accidental injection into the CSF can occur during the block due to perforation of the meningeal sheaths that surround the optic nerve. The patient may experience disorientation, amaurosis fugax, aphasia, hemiplegia, unconsciousness, convulsions, and respiratory or cardiac arrest. The incidence of this is estimated in studies to be 0.13%. Direct injection intravascularly via the optic nerve sheath or local anesthesia carried by the ophthalmic and internal carotid artery by retrograde flow to the thalamus and midbrain can also present the same way. This situation requires prompt recognition and treatment (including airway control, respiratory support, possible cardiac intervention, etc.)

Epinephrine Toxicity: In patients with hypertension, angina, or arryhthmias, the amount of epinephrine injected with the local anesthetic should be reduced. Injections of a total of 0.05 mg (10cc of 1:200,000) of epinephrine does not contribute significantly to problems in these patients. In fact, the release of endogenous catecholamines in reponse to suboptimal analgesia may greatly exceed the small amount of exogenous epinephrine administered.

Other Complications: Allergic reactions may occur to the ester-type local anesthetics. Blocks usually last 2 to 3 hours. If the block wears off before surgery is complete, supplementation of the retrobulbar block may be risky when the eyeball is open. The volume of injected fluid, edema, or hemmorhage may distort original anatomy and make surgery difficult.

CONTRAINDICATIONS TO RETROBULBAR BLOCK:

  • Age less than 15 years old
  • Procedures lasting significantly more than 90 minutes
  • Uncontrolled cough, tremor or convulsive disorder
  • Disorientation or mental impairment
  • Excessive anxiety or claustrophobia
  • Language barrier or deafness
  • Bleeding or coagulation disorders (some surgeon will proceed despite mild coagulopathy)
  • Perforated globe
  • Inability to lie flat

 

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