There are several commonly used techniques for providing analgesia, sedation, and anesthesia for patients undergoing cataract surgery. Anesthetists and ophthalmologists caring for these patients should be familiar with the benefits, risks, and technical considerations of these techniques.
II. TOPICAL ANESTHESIA
Topical anesthesia involves placing a local anesthetic eyedrop(s) on the cornea and conjunctiva, thereby anesthetizing that area. Topical anesthesia is best suited for patients who are having brief procedures in or near the anterior chamber. Topical anesthesia may be used as the sole anesthetic for cataract surgery or to supplement another anesthetic technique (eg, an incomplete block or a block that has worn off).
A. Patient Requirements
Patients receiving topical anesthesia must be able to cooperate, communicate, and lie supine and motionless during surgery. Surgeons must be able to tolerate some eye movement, as topical anesthesia will not provide akinesia of the extraocular muscles (EOM).
B. Common Usage
Topical anesthesia is a widely used form of analgesia in the United States for cataract surgery.1 Commonly used local anesthetics include lidocaine 2% jelly, proparacaine 0.5%, and tetracaine 0.75%.
To facilitate patient cooperation, it is wise to give sedatives only to patients who require them for anxiety and cannot be relaxed by verbal reassurance. For many anxious patients, holding their hand has a calming effect. It is important to remember that no amount of sedation, short of general anesthesia (GA), will compensate for inadequate analgesia. Therefore, it is necessary to ensure that the eye is anesthetized during the entire operation.
D. Sedative Requirements
If sedatives are required, they should be used in the smallest dose needed (eg, midazolam 0.5 to 1 mg intravenously). If sedatives (or regional blocks) are administered, pulse oximetry, blood pressure, and electrocardiogram monitors should be used by appropriately trained personnel. Supplementary oxygen and appropriately trained resuscitation personnel and equipment must be immediately available. If oxygen is administered, starting it at a concentration of 30% and increasing it to the lowest concentration clinically required will reduce the rare but serious risk of fire. If >30% oxygen is required, the surgeon should be warned not to use any heat source for at least 60 seconds after discontinuing oxygen to allow the high concentration of oxygen to dissipate.
Topical anesthesia has the lowest local complication rate of any anesthet- ic technique. Rarely serious systemic complications such as arrhythmias or pulmonary edema can occur. Eke and Thompson reported a 0.2% serious systemic complication rate of patients undergoing eye surgery with topical anesthesia.2 Interestingly, this rate was similar to the serious systemic compli- cation rate of most other anesthetic techniques in their review.
III. INTRACONAL BLOCK (RETROBULBAR BLOCK)
Intraconal block was first described over 125 years ago and has been the predominant technique of providing regional anesthesia to the globe during the 20th century.3 The goal of the block is to deposit about 5 mL of local anes- thetic in the anterior half of the muscle cone formed by the 4 recti muscles (the intraconal space). From this location, it spreads and anesthetizes the sensory and motor nerves to the eye. Patient requirements to undergo surgery with sedation and an intraconal block are similar to those of topical anesthesia.
A. Commonly Used Anesthetics
Commonly used local anesthetics include lidocaine 2%, bupivacaine 0.75%, and equal ratio mixtures of the two. Lidocaine can be myotoxic in concentrations greater than 2% and should not be used.4 Epinephrine is not usually required to prolong the duration of lidocaine if bupivacaine and lidocaine are combined. For patients with vascular disease, epinephrine might increase the risk of inadequate blood flow to the eye.5 Analgesia from intraconal block usually lasts 1 hour to several hours, depending on the local anesthetic(s) used.
The bulk of evidence suggests hyaluronidase increases the speed of onset of ophthalmic blocks and reduces the chance of EOM injuries.6-8 Several phar- maceutical companies now manufacture hyaluronidase that is approved for use by the US FDA. Although higher concentrations of hyaluronidase had been suggested in the past,9 there is evidence that it is effective in concentrations as low as 0.75 unit/mL.10
C. Effects of Intraconal Block
Unlike topical anesthesia, an intraconal block is effective in anesthetizing the posterior chamber of the eye and causing akinesis of EOM. In experi- enced hands, intraconal block has a success rate of >90%.11 Intraconal blocks may occasionally require supplementation with a Van Lint block (a peripheral facial nerve block) if blinking interferes with surgery.
D. Long Axial Lengths
Patients with long axial lengths (ALs) are at significantly higher risk of globe perforation if an intraconal block is performed.Therefore, the AL (obtained from the preoperative ultrasound report) should be determined be- fore attempting an intraconal block on cataract patients. If the AL is greater than 25 to 26 mm, other techniques (eg, topical, extraconal block, sub-Tenon block [STB], or GA) should be considered.
Staphylomas are outpouches of a weakened sclera. They are usually located posteriorly and inferiorly on the globe. The presence of a staphyloma dramati- cally increases the risk of globe perforation from an intraconal block.15,16 The incidence of staphylomas increases with AL. In one study, 15% of patients with AL of 27 mm had a staphyloma. The incidence increased to 60% of patients who had AL >31 mm.16
F. Preparation and Sedation
At our institution we administer a topical anesthetic, then swab a 10% povidone-iodine solution over the injection site. The solution is wiped off several minutes after application for optimal antibacterial effect. The patient is usually lightly sedated. Common adult dosages of medications administered are 0.5 to 1 mg of midazolam, followed by 30 mcg of remifentanil. Patients who are <60 years of age will usually receive larger doses (up to 2 mg of midazolam and 60 mcg of remifentanil). Patients older than 80 years of age usually receive only remifentanil 0.5 to 1 mcg/mL. We think remifentanil has advantages over other narcotics because of its intense but brief effect, and the fact that patients given the drug can usually cooperate during the block. Our pharmacy will dilute a 1-mg vial of remifentanil to make about 33 syringes, each containing 30 mcg of the drug (10 mcg/mL).
G. Technique Continued and Complications
We request patients to look straight ahead during the block (primary gaze position). Looking up and in (Atkinson position) brings the optic nerve closer to the midline and increases the risk of injury from the needle tip.We promote the use of needles 1 inch (25 mm) or less instead of traditionally used long needles. Using needles ≤1.25 inches seems to reduce the risk of several complications including central nervous system spread of local anesthesia,injury to the optic nerve, injury to the superior rectus muscle,20 and retrobulbar hemorrhage2 (Figure 4-1). The success rate of intraconal blocks seems to be similar whether inserting needles 1 inch, or 1.5 inches, from the inferiolateral orbit to the intraconal space.
H. Insertion Point of Needle
A palpating finger identifies the lower part of the globe, the inferior orbital rim, and pushes the globe slightly up. The needle is inserted, bevel toward the globe, 0.25 to 0.5 inch below the lateral canthus, and just above the inferior orbital rim. There is evidence the insertion at this “modified” insertion point, instead of the “traditional” insertion point at the junction of the middle and lateral third of the orbital rim, reduces the risk of injury to the inferior rectus, and possibly the inferior oblique muscle (Figure 4-2).
I. Direction of Needle Approach
The needle is initially directed perpendicular to all planes of the skin. In order to minimize the chance of entering the globe one of the authors (AG) attempts to visualize the lower rim of the eyeball by displacing the lower lid caudally. Simultaneous retraction of the upper eyelid by an experienced as- sistant helps to achieve better exposure of the field.
To reduce the chance of inadvertently perforating the globe, one of the authors (JB) wiggles the needle when the needle is through the skin, parallel to the globe at a frequency of about 3 times per second, to help identify if the sclera is inadvertently encountered. (If so, the globe would be expected to move at the same frequency as the wiggling motion.) If this occurs, the needle is withdrawn and redirected slightly more inferiorly.
The needle is advanced under the most inferior aspect of the globe (the inferior equator). One author (JB) directs the tip of the needle directed to lie, when fully inserted, in the plane projecting posterior from the lateral limbus (the junction of the colored part of the lateral iris and the white of the sclera; Figure 4-3). The other author (AG) directs the needle tip, when fully inserted, to be in a plane projected backward from the center of the iris. There may be slight resistance as the needle pierces the skin and a slight “pop” after penetration through the orbital septum several millimeters below the skin (Figure 4-4).
J. Reducing Risk of Complications
To reduce the chance of the needle injuring the optic nerve, the tip should not cross the midline. When the tip of the needle is thought to be in the intraconal space, aspirate for signs of blood. If blood is identified, withdraw the needle, apply intermittent digital pressure and reevaluate the orbit before attempting to proceed. Injection into the globe of <2 mL of local anesthesia will cause the globe to rupture, a devastating injury.
K. Intraconal Block With Shorter Needles
It is of note that many anesthetists perform orbital blocks using a 7/8-inch or 1-inch “peribulbar” needle, an inferior-lateral insertion point and aim for the intraconal space. Despite the “peribulbar” needle name, we should be aware that with this technique the tip of the needle is likely to be in the ante- rior intraconal space.
*Dikutip dari Buku Essentials of Cataract Surgery 2nd Ed, halaman 31-37