IV. EXTRACONAL BLOCK (SOMETIMES CALLED PERIBULBAR BLOCK)
Several decades ago, when anesthesiologists began performing eye blocks more commonly, a technique was reported for placing local anesthetic purposely outside the EOM cone.Proponents of extraconal block suggest that it would be safer to routinely keep the tip of the needle further from the globe and intraconal components. These blocks were called “peribulbar” blocks, although extraconal is perhaps a more accurate term.
A. Additional Indications for Extraconal Block
Extraconal blocks may be safer in situations in which intraconal blocks are contraindicated (eg, AL > 25 to 26 mm). Extraconal blocks should also be considered for patients with a scleral buckle or severe enophthalmos. Initially, 2 needles were placed in the extraconal space, one in the inferior lateral orbit, and the other in the superior orbit. Over time evidence has shown that one injection may be as effective as two.In addition, a second injection in the superior orbit may increase the risk of globe perforation due to the proximity of the globe to the superior orbital wall.
B. Single Injection and Supplementary Technique
Most practitioners now routinely use only a single inferior lateral extraconal injection. If an additional medial or superior block is required, many practitioners now use a “median orbital block,” a technique for administering local anesthetic in the avascular space medial to the globe. Readers are referred to the original article for those interested in learning this technique.
C. Success Rate
Although the reported success rates of 83% to 84% with extraconal block are not quite as high as with retrobulbar technique, it is adequate to warrant use of an extraconal block when a retrobulbar block is contraindicated. Some practitioners use extraconal blocks as their primary block.
D. Local Anesthetic Requirements
The inferior lateral extraconal block requires a larger volume of local anes- thetic (5 to 8 mL are commonly used), and takes slightly longer to be effective. These blocks are usually effective because there are no discrete septal barriers defining the intraconal space.Local anesthetic placed near the intraconal space can diffuse into the intraconal space and anesthetize the sensory and motors nerves within the intraconal space.
The technique of extraconal block is similar to an intraconal block (see Intraconal Blocks Sections III F and G mentioned previously). Again the authors recommend a needle ≤1 inch in length with the bevel of the needle facing the globe. The insertion site is 0.25 to 0.5 inch below the lateral canthus just above the inferior orbital rim. The needle is directed below the inferior- lateral aspect of the globe and parallel to the floor of the orbit. Once through the skin, the needle is directed posteriorly, parallel to the intraconal space, without entering it. There will be some resistance as the needle pierces the skin and sometime a small “pop” is felt as the needle penetrates the orbital fascia a few millimeters posterior to skin. Care is taken to avoid the lateral and inferior wall of the globe as the needle is advanced. Further, 6 to 8 mL of local anesthetic are injected outside but in close proximity to the EOM cone.
V. SUPPLEMENTARY TECHNIQUES
If patients experience eye pain in the operating room despite a preoperative attempt(s) to obtain adequate analgesia or receive supplemental topical anesthesia, the surgeon can place a small amount of local anesthetic in the subconjunctival or anterior sub-Tenon space (STB). A fine gauge needle (eg, 30-gauge needle) is used. Care must be taken not to perforate the globe if this technique is used.
VI. SUB-TENON BLOCK
Turnbull introduced the concept of STB block in 1884.Classic articles about its preoperative use appeared in the early 1990s.Its use has increased rapidly in the United Kingdom and several other countries. It has been promoted by its practitioners, largely because they believe that STB reduces the risk of serious injury to the eye.
Minor complications, such as chemosis and subconjuntival hemorrhage, occur more frequently than with needle blocks. However, as the popular- ity of this technique has increased, occasional case reports have appeared describing many of the same serious injuries that occur with needle techniques.
The technique involves administering local anesthetic eye drops, followed by 5% povidone-iodine eyedrops. The conjuntiva is picked up with toothless forceps, usually in the inferior-medial quadrant 3 to 5 mm from the limbus. At this point, the conjunctiva and sub-Tenon capsule are fused. Using blunt scissors, a 1- to 2-mm incision is made in the conjunctiva. A curved blunt cannula (eg, a 1-inch Steven cannula) is inserted through the incision, and ad- vanced posteriorly between the sclera and sub-Tenon capsule. Then, 3 to 5 mL of local anesthesia is injected into sub-Tenon space. Analgesia and akinesia of the EOM occur within minutes after the injection.
Absolute contraindications include infection and prior scleral buckle. (Scleral buckle prevents the posterior spread of local anesthetic.) Relative contraindications include coagulopathy, prior retinal surgery (can cause scarring and ineffective block), and glaucoma surgery (STB can interfere with the lifting of a flap required for some glaucoma operations).
*Dikutip dari Buku Essentials of Cataract Surgery 2nd Ed, halaman 37-40