How I Do a Retrobulbar Block
Retrobulbar block is a regional anesthetic technique for ophthalmic surgery that is more commonly practiced by ophthalmologists than anesthesiologists. Placement of the local anesthetic within the muscular cone of the eye can provide faster onset, denser block, and require less anesthetic than other regional techniques such as peribulbar or sub Tenon's blocks.
Anatomy The extraocular muscles form a cone about the globe, with the apex at the optic foramen. Passing through this foramen are the ophthalmic artery, ciliary ganglion, ophthalmic division of the trigeminal nerve, cranial nerves supplying the extraocular muscles (III, IV, and VI) and the optic nerve. When the globe is in its primary (neutral, straight forward) gaze, the optic nerve, sheathed in dura as it exits the optic foramen, passes closer to the medial rectus than lateral rectus muscles. Also, the primary gaze allows easier access to the cone via the relatively avascular inferotemporal area of the orbit. Thus, two of the more serious risks, retrobulbar hemorrhage and central spread through dural puncture, can be reduced if an inferotemporal approach is used.
Technique This neutral gaze, of course, can be easily obtained by adequately sedating the patient with IV propofol. Once sedated, the inferotemporal area of the lower eyelid is wiped with isopropyl alcohol and the upper eyelid manually retracted to reveal the globe. A 27-gauge 1 1/4 inch flat grind needle with a 3cc syringe of local anesthetic is introduced into the inferotemporal orbit just above the inferior rim of the orbit and just lateral to the border of the iris (Figure 1) at an initially perpendicular angle until the tip passes the level of the globe's equator. Once at that depth, the needle is angled superiorly and medially as if aiming for the center of the pupil (but never crossing midline) and slowly advanced with the bevel pointed toward the globe. Advancing the needle in this fashion can reduce the risk of global or optic nerve penetration. As the needle passes through the inferior rectus muscle, the globe is tethered and the gaze turns downward (Figure 2a). Once the muscle's posterior fascia is traversed the globe then pops back into its neutral gaze and the needle tip is now positioned inside the cone (Figure 2b). Without this return of primary gaze, the needle could be tethering the globe or still be within the muscle and therefore should be withdrawn and redirected. After negative aspiration, 3cc of local anesthetic is injected and the needle withdrawn. Gentle intermittant pressure on the globe can help the intraconal spread of the anesthetic.
The retrobulbar block is often supplemented with topical anesthetic (such as 0.5% ophthalmic tetracaine solution) and with a facial nerve block (such as the Van Lint or Nadbath approaches) to provide akinesis of the orbicularis oculi muscles.
Local Anesthetics Typically, we have used 2% lidocaine mixed in equal portions with 0.75% bupivacaine to create a 1% lidocaine: 0.375% bupivacaine mix in a 3cc volume. The lidocaine provides the anesthesia in a less myotoxic concentration, and the bupivacaine for longer analgesia. Other local anesthetics including ropivacaine, mepivacaine, and etidocaine have been used as well.
When it was widely available, we found the addition of hyaluronidase (7.5-10 units/ ml) hastened the spread of local anesthetic and provided a faster onset and better motor and sensory block. Postoperative diplopia after peribulbar block has been blamed on the lack of hyaluronidase presumably caused by the lack of local anesthetic spread causing focal myotoxicity. Clonidine is another adjunct that has been described for the retrobulbar block to provide longer analgesia. The addition of atracurium and vecuronium has been studied in peribulbar block for enhancing the motor block but should not be necessary in retrobulbar block. Epinephrine is generally not used because of risk of retinal artery vasoconstriction.
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Figure 1. Needle placement for inferotemporal approach to the retrobulbar block. Line represents inferior rim of the orbit. "X" is optimal location for needle placement. |
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Figure 2. The needle is advanced through the inferior rectus, the gaze turns outward and down (2a). One through the muscle, the gaze returns to neutral. (2b). |
Risks Risks can result from local anesthetic being deposited in undesirable places: 1) in the cerebrospinal fluid of optic nerve's dural sheath, 2) intravascularly in the ophthalmic artery or its branches, 3) in the globe itself, or 4) within the extraocular muscle causing myotoxicity. Risk of global perforation is increased in patients with significant myopia due to longer axial length and thinner sclera. Retrobulbar hemorrhage can result in permanent loss of vision if the pressure is not immediately relieved; patients taking anticoagulants may be at an increased risk. These adverse events can be kept rare with careful advancement of the needle and with injection of anesthetic only after negative aspiration and if no resistance is encountered.
Susan McDonald, MD
Virginia Mason Medical Center
Seattle, WA
References:
1. Kallio H, Paloheimo M, Maunuksela EL. Hyaluronidase as an adjuvant in bupivacaine-lidocaine mixture for retrobulbar/peribulbar block. Anesth Analg, 2000; 91(4):934-7.
2. Mjahed K, el Harrar N, Hamdani M, Amraoui M, Benaguida M. Lidocaine-clonidine retrobulbar block for cataract surgery in the elderly. Reg Anesth, 1996; 21(6):569-75.
3. Kucukyavuz Z, Arici MK. Effects of atracurium added to local anesthetics on akinesia in peribulbar block. Reg Anesth Pain Med, 2002; 27(5):487-90.
4. Troll G, Borodic G. Diplopia after cataract surgery using 4% lidocaine in the absence of Wydase (sodium hyaluronidase). J Clin Anesth, 1999; 11(7):615-6.
5. Batra MS. Anesthesia for ophthalmic surgery. In: Cole D, Schlunt M, eds. Requisites in Anesthesiology: Adult Perioperative Anesthesia. Mosby, Inc; in press.
