Year : 2007 | Volume
| Issue : 1 | Page : 2
Administration of extraconal anesthesia: What care providers should know?
Department of Anesthesia, King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia
Department of Anesthesia, King Khaled Eye Specialist Hospital, P.O. Box 7191, Riyadh 11462
Source of Support: None, Conflict of Interest: None
|Date of Web Publication||5-Oct-2009|
|How to cite this article:|
Riad W. Administration of extraconal anesthesia: What care providers should know?. Saudi J Anaesth 2007;1:2
| Introduction|| |
The introduction of modern regional ophthalmic anesthesia can be traced back to both Knapp and Koller, who in 1884 described not only topical anesthesia using 5% cocaine, but also an early attempt at retrobulbar anesthesia . Since that time, various local anesthetic techniques have been developed and refined, including retrobulbar , peribulbar , subconjunctival , deep fornix , sub-Tenon's  and topical anesthesia . Provision of ophthalmic regional anesthesia varies worldwide. The choice of anesthetic technique depends on several factors including the type of surgical procedure, provision of high therapeutic index, painless injection, speed of onset, production of combined motor and sensory block together with care givers preference and experience. Extraconal anesthesia is the most common technique used in Saudi Arabia. It can provide adequate anesthesia for different ophthalmic procedures including lengthy retinal surgery. This article conveys the necessary information for anesthesiologist in order to perform safe and effective anesthesia.
| Applied ocular anatomy|| |
In order to perform periocular block, it is extremely important to understand thoroughly the anatomy of the orbit and its content. The bony orbit has a volume of about 30 ml. An average globe is close to 7 ml in volume, the rest of the orbit being filled with blood vessels, nerves, muscles, fat, and connective tissue . The orbit is an irregular four-sided pyramid with its apex pointing posteromedially and its base facing anteriorly. The medial wall of the orbit is parallel to the sagittal plane, and the lateral wall lies at 45°to the medial wall. The posterior orbit is perforated by the superior and inferior orbital fissures, through which pass the nerves to the extraocular muscles, the branches of the ophthalmic division of the trigeminal nerve, and the superior ophthalmic vein. The medial wall of the orbit is composed of the thinnest portion of the ethmoid bone called the lamina papyracea, which separates it from the ethmoid sinus. It also contains foramina for the exit of the anterior and posterior ethmoid arteries and nerves from the orbit. Above the orbital cavity lie the anterior cranial fossa and frontal sinus. The maxillary sinus lies beneath the orbital floor. The lateral wall is bordered by the temporal fossa in front, and the middle cranial fossa at the back .
Globe movements are controlled by four rectus muscles (inferior, lateral, medial and superior) and two oblique muscles (superior and inferior).The rectus muscles originate from the annulus of Zinn, a fibrous ring encircling the optic canal and the medial aspects of the superior and inferior orbital fissures . The rectus muscles course forward toward their tendinous insertions on the sclera anterior to the equator of the globe. Four cranial nerves are responsible for the innervation of the extraocular muscles and the orbicularis oculi: the oculomotor nerve to the levator, superior rectus, medial rectus, inferior rectus, and inferior oblique; the trochlear nerve to the superior oblique; the abducens nerve to the lateral rectus and the facial nerve to the orbicularis oculi. Together, the four rectus muscles form a "cone" with the point at the orbital apex and the base at the equator of the globe. Within this cone lie the optic nerve, oculomotor nerve, abducent nerve, nasociliary nerve, the ciliary ganglion and optic vein and artery . The trochlear nerve runs outside and above the annulus . Nerves and vessels coming through the optic foramen and medial portion of the superior orbital fissure go through the annulus of Zinn to supply the structures within the muscle cone. The optic nerve, ophthalmic artery and ocular sympathetics pass through the optic canal and foramen. The dura is adherent to the optic canal and the optic nerve itself. Inadvertent needle penetration of the optic nerve sheath may result in depositing the local anesthetic directly in the subarachnoid space . There is an extensive system of orbital fascial membranes interconnecting the muscles and suspending them to the orbital wall.
Ophthalmic anesthesiologists divide the orbit into three spaces (anterior, mid and posterior) for better appreciation of the relationship of injection site. The anterior orbit is the space between the lids and the sites of attachment of the extraocular muscles to the periorbital and sclera 2-5 mm anterior to the equator of the globe and is filled primarily with connective tissue and minor adipose compartments. The mid-orbit followed and ends posterioly about 10-12 mm behind the hind surface of the globe. It contains primarily muscle bellies and adipo-connective tissue. The posterior orbit consists mainly of muscles origin and collection of arteries, nerves and veins and end at the optic canal . From this classification, it is obvious that insertion of needle deeply increases the potentials to injury important structures. Needles entering the anterior orbit must be placed in avascular sites to avoid blood vessels in the lid and conjunctiva. The adipose tissue compartments (ATCs) are the standard entrance sites. In the right eye the ATCs are at 12:30-1:30, 2:30, 4:30, 7:30-8:00 and 10:45 and show bilateral symmetry . Coronal section of the orbit  perpendicular to the optic nerve through the mid portion of the globe [Figure 1] based on a recent MRI study  showed the safe areas to insert the needle. The circle in the diagram indicates the recommended and commonly used places to insert the needle. These are at the extreme inferotemporal corner of the orbit and in the medial area. The superior oblique muscle, trochlear pulley, terminal branches of ophthalmic artery, superior ophthalmic vein, supraorbital artery and terminal branches of the nasociliary nerve are all found in the superonasal quadrant of the orbit . Currently it is not recommended to use this site for extraconal block.
Details of the orbital anatomy and description of subtenon's space are beyond the scope of this article. Interested readers can refer to the cited references for more anatomical information.
| Nomenclature|| |
Anatomically the orbit can be divided into two major compartments, extraconal and intraconal spaces. Extraocular (Peribulbar) anesthesia is the introductions of the needle outside the muscle cone with the risks of trauma to orbital structures are much reduced. It is based on the tissue compartment principle. The needle is inserted into a compartment and the local anesthetic injected diffuses easily by of its pressure and volume throughout the compartment. The local anesthetic injected into the extraconal space must spread to the intraconal space to provide adequate anesthesia and akinesia of the globe . A relatively high volume of local anesthetic is injected into the extraconal space (usually 8-12 ml). This technique has a slower onset and sometimes requires multiple injections .
There is controversy regarding the terminology of this block. Many authors use the terms Extraocular or Peribulbar , Periocular  and Periconal  interchangeably way. In our practice at King Khaled Eye Specialist Hospital, extraocular (Peribulbar) anesthesia is classified into Periocular which is placement of the injectate within the anterior orbit using short (15 mm) needles and Periconal which is placement of the injectate within the mid orbit using medium length (25 mm) needles .
| Preoperative evaluation|| |
Most of the ophthalmic procedures are performed for elderly patients who usually have a significant comorbidity. All patients scheduled for eye surgery under local anesthesia should be examined thoroughly by the attending anesthesiologist at least one day prior to surgery. Apart from the routine preoperative assessment, an ophthalmic evaluation should take place. Elements of ophthalmic evaluation which are important to the anesthesiologist include, the visual acuity of both eyes, previous ophthalmic surgery, axial length, presence of staphyloma and glaucoma history. Extraocular movements and external examination to rule out any acute infectious process should be noted. Recording of the preoperative visual acuity is of great importance and patients with poor vision in the non-operative eye should be anesthetized by a well trained ophthalmic anesthesiologist as any complication from anesthesia to the operative eye may be devastating. A history of previous scleral buckling surgery for correction of retinal detachment is of utmost importance. Buckling surgery alters globe dimensions, contour and results in significant scarring within the orbit and so increases the potential of perforation . B-scan echography for intraocular lens diopter power calculation is usually done before cataract surgery. It also determines the axial length (the distance from the corneal surface to the retina), the presence and location of staphyloma (outpouching of the globe resulting from the pathological thinning of sclera, choroid and retina). If no ultrasound available, the myopic patient should be assumed to have an increased axial length. The risk of globe perforation is greatly increased in patients whose axial length is greater than 26 mm and in the presence of staphyloma . Preoperative glaucoma history, increased intraocular pressure and increased axial length are important risk factors for suprachoroidal hemorrhage .
| Technique of extraocular block|| |
There are numerous forms of extraocular anesthesia. All the ATCs entry points are used with great success worldwide. The current article restricts the description to the most popular techniques used in Saudi Arabia.
1) Inferotemporal injection:
With the patient's eye in the neutral position, the needle is inserted transcutanously in the extreme inferotemporal corner approximately 1- 11/2 cm below the lateral canthus [Figure 2] . Traditionally the needle used to be inserted at the junction of the lateral third and medial two-thirds of the lower lid. This area contains the neurovascular bundle to the inferior oblique and the belly of the inferior rectus [Figure 1] which are potentially at risk for needle penetration. These are the two most commonly injured muscles from orbital blocks . The bevel of the needle should be facing the globe in order to keep the tip of the needle away from the sclera. The needle should be inserted perpendicular to the skin then advanced in a sagittal plane, parallel to the orbital floor, thereby reducing the risk of globe perforation. When the needle tip is judged to be past the equator of the globe (this can be estimated from the axial length), the direction is changed to point slightly up and medially by 20 degrees, to avoid the bony orbital margin. The needle should not be directed to the orbital apex to avoid injury of the extraocular muscles. During needle insertion, the globe should be carefully observed for any movement. If the globe moves this indicates that the needle has contract with the sclera and it should be immediately removed. The standard needle used is a 25mm, 25 gauge needle, however some authors demonstrated a similar result a with 15mm needle . After negative aspiration to rule out any intravascular injection, approximately 7-10 ml of anesthetic solution is injected. Total upper eyelid drop to cover the cornea  and measurement of intraocular pressure (IOP) by digital palpation periodically during injection to ensure that the globe does not become too tight are the end points to stop injection. An excessive increase in IOP during administration of the block may cause severe pain, triggering of oculocardiac reflex and acute ischemic optic neuropathy .
2) Medial canthal injection:
A 25 or 27 gauge, sharp needle is inserted in the blind pit between the caruncula and the medial canthal angle [Figure 2] . The needle should be 45o to the saggital plane aiming for medial orbital wall, displacing the caruncule medially away from the globe. Extreme caution should be applied as the medial wall in this area is very thin (lamina papyracea) and easily to be perforated. The needle is then redirected posteriorly parallel to the medial orbital wall. The needle should be close to the wall and should not be inserted too deep to avoid injury of medial rectus muscle . In contrast to the inferotemporal approach, the globe may directed slightly medially by the needle. This movement possibly corresponds to the passage through the medial check ligament, at a mean depth of 15-20 mm . In our practice, it is used as a supplementary block if the inferotemporal injection fails to produce satisfactory anesthesia, and the recommended volume of anesthetic solution is 3-5 ml. The volume injected is increased until conjunctival edema (chemosis), proptosis, and lid fullness appears, which are predictive of a successful blockade. Some practitioners use the medial canthal injection as a primary injection point for extraconal anesthesia and inject 8-10 ml of anesthetic solution after topical anesthesia drops . The author believes that a 15mm needle length is the best choice regarding safety. Needles longer than 25mm should not be used because of possible injury of optic nerve and/or ophthalmic artery .
3) Superonasal injection:
The superior nasal ATCs are less safe to pass the needle [Figure 1]. Its use should be discouraged. The needle can be introduced through the upper eyelid at about 2 mm below and medial to the supraorbital notch (at 2:30) or lateral and inferior to the supraorbital notch (at 12:30-1:30) [Figure 2]. It is advanced in a sagittal plane under the roof of the orbit for a maximal depth of 25 mm, injecting 3-5 ml of anesthetic solution. The needle hub should just touch the skin; if the skin is indented this can increase the incidence of injury of the important structures located deeply in this orbital quadrant. It is best to avoid deeper than anterior orbit , the author recommends the use of a 15mm needle. Currently, this ATCs are used only for a supplementary block in order to achieve full akinesia if it is required by the surgeon. Anesthesia injected there will directly affect the levator, superior rectus, superior oblique and medial rectus muscles.
| Ocular Compression|| |
After local anesthetic injection, the eye is closed by adhesive tape and covered with gauze. The increased IOP after injections may lead to vitreous loss during intraocular surgery . The ocular compression device we use is a Honan's balloon applied for 10-20 min and set at 30 mm Hg. In addition to softening the globe, compression also helps to spread the anesthetic solution posteriorly, decrease conjuctival oedema and promote akinesia. The use of pressure reducing devices depends on the type of procedure and surgeon preference. In conditions when impairment of blood flow to the retina and optic nerve can take place such as in glaucoma and retinal surgery, it has been recommended to maintain ocular perfusion and refrain from using continuous compression . If it is necessary, intermittent digital pressure is applied .
| Double injection technique|| |
Extraocular block is usually established using a single or double injection technique (9, 23). Generally the Inferotemporal site is the preferred entry point. The choice between single or double injection techniques is based on the volume of the orbit, degree of akinesia required, experience of the ophthalmologist, type and duration of the procedure and preference of the anesthesiologist. Although the inferotemporal plus medial canthus combination produces rapid ocular akinesia with less need for supplementation, it results in less efficient lid akinesia and more subconjuctival hemorrhage . The latter minor complication is considered by some surgeons as an obstacle to perform glaucoma filtration procedures and hence the survival of the inferotemporal and superonasal combination.
| Block assessment|| |
Akinesia (immobility) of the globe is used as the main index of the quality of anesthesia. A Simple Akinesia score is commonly used, for assessment of the block. . Assessment is made by comparing the ability of the patient's blocked and unblocked eye to follow the movement of a light. Eye movement in four directions is assessed - inferior, superior, medial& lateral. Normal movement is scored at 2, reduced movement at 1 and flickering or no movement is scored at zero. Using this scale, an ocular mobility of 3 or less is an indicative of a successful block in most institutions . In author hospital, we attempt to achieve akinesia to assist the teaching of surgical techniques to ophthalmology residents. Younger adult patients present more of a challenge in achieving total akinesia than the elderly because of more dense connective tissues hindering access of anesthetics to the oculomotor nerves .
| Anesthetic mixture|| |
The ideal local anesthetic drug for ophthalmic blocks should provides adequate analgesia and akinesia. In ophthalmic regional anesthesia a variety of agents may be mixed to provide a rapid onset of dense motor and sensory block. A mixture of lidocaine and bupivacaine is the most popular preparation used . Lidocaine produces a fast onset and reduces the potential toxicity of the relatively large volume of local anesthetic, while bupivacaine covers the prolonged duration for surgery and extends its effect to the postoperative period. The standard practice at our institute is to mix bupivacaine 0.5% with lidocaine 2% in a ratio of 3:2 with hyaluronidase 5unit/ml. Hyaluorinidase, breaks down hyaluronic acid in the connective tissue, which normally obstructs intercellular diffusion. It has been suggested that hyaluronidase increases the permeability of the fibrous septa which compartmentalize the orbital contents . It is commonly added to local anesthetic solutions to improve the speed of onset and spread of anesthetic block, and to prevent a sustained rise in orbital pressure .
| Complications|| |
Although the administration of extraconal anesthesia is generally a safe procedure, complications do occur. Complications are related to the insertion of a needle into the orbit with potential trauma to orbital structures or secondary to the local anesthetic mixture. They may be divided into minor and major complications. Major complications include; retrobulbar hemorrhage, globe penetration or perforation, central spread of local anesthetic producing brain stem anesthesia, rectus muscle paresis which leads to postoperative diplopia, optic nerve damage, intravascular injection of anesthetic mixture, oculocardiac reflex and orbital cellulites. Minor complications include; conjuctival hemorrhage, lid chemosis and corneal abrasions.
| Conclusion|| |
Ophthalmic regional anesthesia evolved into a sophisticated art. Administration of extraocular anesthesia requires a sound knowledge of orbital anatomy, physiology and pharmacology of anesthesia and ophthalmic drugs. The technique is not without complications. Adequate training under expert supervision is a prerequisite to perform a safe technique.
| Acknowledgment|| |
The author thanks Dr. Mark Schreiber chairman of anesthesia department, King Khaled Eye Specialist Hospital for his valuable advice with the manuscript.
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