Patient Position: Supine, eyes closed in a central position.
Indications: Anterior eye segment surgery—cataract, trabeculectomy; posterior eye segment surgery—vitreoretinal surgery; conjunctival surgery, scleral buckle.
Needle Size: 22-gauge, 25-mm, normal bevel.
Local Anesthetic Solution: Half 0.5% or 0.75% bupivacaine, half 2% lidocaine, plus 100 to 150 IU/10 mL hyaluronidase.
Volume: 8 to 12 mL.
Anatomic Landmarks: Inferotemporal orbit injection—third inferolateral border of the orbit; superonasal orbit injection—third superomedial border of the orbit.
Approach and Technique: For an inferotemporal periconal injection, the needle is introduced perpendicular to the skin. After contact with the bony rim, the needle is moved slightly in the cranial direction to lose this bone contact, angled 30°, and introduced another 5 mm to a new periosteum contact. The needle is then moved back to the perpendicular position and progressively inserted to its full extent. After a negative blood aspiration, 6 to 8 mL of local anesthetic solution is injected. A good sign is a relative protrusion of the eye with a downward movement of the superior eyelid during the injection. Ocular tonicity must be checked continuously during the procedure (Fig. 17-1).
For a superonasal periconal injection, the technique is similar to the one described for the inferotemporal injection. The needle is moved slightly in the caudal direction, and 2 to 4 mL of local anesthetic solution is injected (Fig. 17-2).
After these injections, the globe is compressed for 5 to 10 minutes with a special device such as a Hoonan balloon. The low-pressure cuff allows for ocular compression of less than 30 mm Hg (Fig. 17-3).
Figure 17-1. Inferotemporal periconal injection.
Evaluation of the Block
The potency of the motor block is evaluated using the akinesia score: the patient is asked to open his or her eye (0 to 2), to look up (0 to 2), to look down (0 to 2), and to move laterally on one side (0 to 2) and on the other side (0 to 2). The total score varies from 0 to 10. A block with a score of at least 8 is considered satisfactory. The quality of the sensory blockade can be verified by testing conjunctival sensitivity to touch or topical drugs.
Patients with large eyes are at an increased risk of ocular perforation. In addition, in patients with a small orbital cavity, the risk of ocular perforation is especially increased during the superonasal injection.
Figure 17-2. Superonasal periconal injection.
Figure 17-3. Low-pressure cuff.
The risk for retrobulbar hemorrhage is increased in elderly patients treated with steroids or aspirin and other nonsteroidal anti-inflammatory drugs.
The risk of infection after peribulbar block is minimal because of the bacteriostatic property of the local anesthetic solution and the use of aseptic technique.
There is a slight risk of paresis of the upper eyelid with the superonasal approach.
Central Nervous System Side Effects
The risk of injection into the optic nerve sheath (resulting in unexpected intradural injection, requiring general anesthesia and tracheal intubation) or intravascular injection (producing centrally mediated cardiovascular or respiratory depression) is minimal with this approach.
1. The peribulbar block allows for most types of intraocular surgery to be performed with a lower risk of neural optic damage or intradural or intravascular injection than the retrobulbar block. Use of the retrobulbar block should be reserved to ophthalmologists.
2. Sedation: The use of sedation before injection is indicated to decrease anxiety and minimize recall. During the procedure, patient cooperation is important, and therefore excessive use of sedative drugs is not advisable. However, in patients with major respiratory or neuromuscular diseases, sedation is contraindicated. In this instance, the use of topical anesthesia with a transconjunctival injection represents an alternative.
3. Needle: (a) The normal bevel increases the penetration power of the needle (less painful) and does not increase the risk of ocular perforation. In addition, in case of perforation, the damage done to the globe is decreased. (b) The length of the needle must be less than 30 mm to lower the risk of neural optic damage (unexpected retrobulbar injection).
4. Drugs: Mepivacaine 2% results in a good motor block and can be used alone instead of the mixture of lidocaine and bupivacaine. When a prolonged sensory block is required (vitreoretinal surgery), 1 mg/kg clonidine can be added to the solution of local anesthetic. Ropivacaine 0.75% can also be used as a long-acting local anesthetic.
5. Medial canthus (caruncula) approach: This approach can be used to complement an incomplete peribulbar block. The puncture is done just above the caruncula, in the semilunaris fold. The needle is directed primarily to the nose and is inserted perpendicular to the eye with a constant pressure, producing a slight attraction of the eye. During the introduction of the needle, a loss of resistance is indicated by the eye returning to a central position. After a negative blood aspiration, 6 to 10 mL of the local anesthetic solution is injected. The caruncula approach can also be used as the sole approach for a peribulbar block. However, there is an increased risk of paresis of the medial rectus muscle, which is temporary most of the time but requires physical therapy in a few cases.
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