Regional Anesthesia in Ophthalmology

van Zundert, André; Kumar, Chandra; Jankovic, Danilo

doi:10.1007/978-3-319-05131-4_6

André van Zundert MD, PhD, FRCA, EDRA, FANZA³,
Chandra Kumar FFARCS, FRCA, MSc⁴ &
Danilo Jankovic MD⁵

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1 Citations

Abstract

The pioneering work of Carl Koller (1884) on the anesthetic effect of cocaine in the context of ophthalmic surgery was the historical starting point for local and regional anesthesia. Local anesthesia is commonly used today for majority of ophthalmic surgical procedures. Cataract surgery is the most common surgery and local anesthesia is the norm, but the provision of anesthesia varies worldwide but exact frequency of the use of a particular technique is not known. Patient comfort, safety, and low complication rates are the essentials of local anesthesia. The technique is chosen to provide anesthesia with or without reduction of eye movements. Ophthalmic blocks can be achieved by inserting a needle or a blunt cannula.

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Recognizing and Mitigating Risk of Ophthalmic Regional Anesthesia

Anesthesia for Ophthalmologic Surgery

Karl Koller: The Introduction of Local Anesthesia

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The pioneering work of Jankovic [1] on the anesthetic effect of cocaine in the context of ophthalmic surgery was the historical starting point for local and regional anesthesia. Local anesthesia is commonly used today for majority of ophthalmic surgical procedures. Cataract surgery is the most common surgery and local anesthesia is the norm, but the provision of anesthesia varies worldwide but exact frequency of the use of a particular technique is not known. Patient comfort, safety, and low complication rates are the essentials of local anesthesia. The technique is chosen to provide anesthesia with or without reduction of eye movements. Ophthalmic blocks can be achieved by inserting a needle or a blunt cannula.

Orbital Anatomy

The globe or bulbus oculi lies in front of the orbit and is covered by eyelids. The orbit is an irregular four-sided pyramid with its apex pointing posteromedially and its base facing anteriorly (Figs. 6.1, 6.2, and 6.3). The base is formed by the surface of the cornea, the conjunctiva, and the lids. The medial wall of orbit is parallel to the sagittal plane, but the lateral wall is angled inward at 45°. The roof is horizontal but the floor slopes upward, front to back by 10°. The globe is closer to the roof than the floor of the orbit. The length of orbit varies from 42 to 54 mm. One-fourth of the orbit is filled by the globe (7 ml), and the remainder is filled with fatty tissue, vessels, lacrimal gland, connective tissue, nerves, and extraocular muscles. The transparent cornea lies on the anterior surface of the eyeball (Fig. 6.4).

Underneath this lies the crystalline lens which is located in front of the iris, with its central opening, the pupil. The conjunctiva covers relatively the tough sclera. The optic nerve enters the globe on the hind surface of the globe slightly medial to the axis. The anterior chamber of the eye is bounded by the cornea, the iris, and the lens. The posterior chamber of the eye encircles the lens in a ringlike shape, and the posterior chamber of the eye contains the vitreous body.

The movements of the globe are made possible by four straight muscles, inferior rectus (oculomotor nerve), lateral rectus (abducent nerve), medial rectus (oculomotor nerve), and superior rectus (oculomotor nerve), and two oblique, superior oblique muscle (trochlear nerve) and inferior oblique muscle (oculomotor nerve) (Figs. 6.2, 6.3, and 6.5). The rectus muscles arise from the annulus of Zinn near the apex of the orbit and insert anterior to the equator of the globe thus forming an incomplete cone. Thus, the orbit is divided into two compartments although not completely separate, an extraconal compartment and an intraconal compartment. Injected local anesthetics are easily able to cross the barrier between two compartments by diffusion. Within the annulus and the muscle cone lie the optic nerve (II), the oculomotor nerve (III containing both superior and inferior branches), the abducent nerve (VI nerve), the nasociliary nerve (a branch of V nerve), the ciliary ganglion, and vessels.

The sensory supply of the orbit is provided by lacrimal, frontal, and nasociliary branches of the ophthalmic division of the trigeminal nerve. (See Chap. 10 Trigeminal Nerve, pp. 135–7) Autonomic fibers run from the ciliary ganglion situated within the cone near to the orbital apex (Figs. 6.2 and 6.3). The ciliary ganglion, a tiny collection of nerve cells, lies in the posterior part of the orbit between the optic nerve and the lateral rectus muscle. The sensory and sympathetic roots of the ciliary ganglion are provided by the nasociliary nerve and the neural network around the internal carotid artery but do not always connect to the ciliary ganglion. Their fibers can reach the eye directly via the ciliary nerves. The sympathetic fibers which are already postganglionic after they have switched to the cervical sympathetic trunk ganglia can accompany the ophthalmic artery and its branches on the way to their destination. Stimuli from the cornea, iris, choroid, and intraocular muscles are conducted in the sensory fibers.

The eye and orbital contents receive their main arterial supply from the ophthalmic artery (Fig. 6.6). The ophthalmic artery is a branch of the internal carotid artery. In the orbital cavity, the artery runs forward for a short distance lateral to the optic nerve and medial to the lateral rectus muscle, the abducent and oculomotor nerves, and the ciliary ganglion. The artery then turns medially and crosses above the optic nerve, accompanied by the nasociliary nerve. The venous blood of the orbit is drained by the superior and inferior ophthalmic veins which in turn drain into the cavernous sinus. The superior ophthalmic vein crosses the optic nerve with the ophthalmic artery. The veins of the orbit are tortuous and freely anastomose with one another, and they have no valves. These vessels are known to be damaged when a long needle is inserted deep into the apex.

Tenon capsule (fascial sheath) is a thin membrane that envelops the eyeball and separates it from the orbital fat. The inner surface is smooth and shiny and is separated from the outer surface of the sclera by a potential space the sub-Tenon space. Crossing the space and attaching the fascial sheath to the sclera are numerous delicate bands of connective tissue (Fig. 6.7). Anteriorly, the fascial sheath is firmly attached to the sclera about 3–5 mm posterior to the corneoscleral junction. Posteriorly, the sheath fuses with the meninges around the optic nerve and with the sclera around the exit of the optic nerve. The tendons of all six extrinsic muscles of the eye pierce the sheath as they pass to their insertion on the globe. At the site of perforation, the sheath is reflected back along the tendons of these muscles to form a tubular sleeve. The local anesthetic is injected beneath this part of the sub-Tenon space.

Anatomy Relevant to Blocks

The terminology used for regional orbital blocks is controversial. An intraconal (retrobulbar) block involves the injection of a local anesthetic agent into the muscle cone behind the globe formed by four recti muscles and the superior and inferior oblique muscles. An extraconal (peribulbar) block involves the injection of local anesthetic outside the muscle cone. Many studies confirm that there are multiple communications between two compartments, and it is sometimes difficult to differentiate if the injection is intraconal or extraconal. A combination of intraconal and extraconal blocks is described as combined retroperibulbar block.

The average distance between the orbital margin and the ciliary ganglion is approximately 38 mm (range 32–44 mm). If a 38-mm needle is used, it may reach the optic nerve in a large number of patients leading to serious catastrophic events. A needle <31 mm must be used to protect the globe, optic nerve, and other major structures behind the globe during both extraconal and intraconal blocks. In cadaver studies, Karampatiakis et al. found that when a retrobulbar block was carried out with a needle 40 mm long, the needle tip would reach the posterior optic nerve in 100 % of cases; even with needles 35 mm long, the covering of the optic nerve would be touched [2].

Average axial length (anteroposterior distance of the globe) of the eye varies from 22 to 24 mm. Eye with axial lengths >26 mm are more prone to globe damage. The axial length measurement is available during cataract surgery. If a patient is scheduled for non-cataract surgery, spherical power of the spectacles may offer some clue. If a patient has very thick prescription glasses, it indicates high myopia. The risk of damage to the globe and optic nerve is also greater when the globe is rotated during injection. Therefore, it is recommended that the globe should be in the neutral gaze during the injection. It is safer to introduce a needle as far lateral as possible because if it is introduced at the junction of medial 2/3rd and lateral 1/3rd of the inferior orbital rim, the inferior rectus and inferior oblique muscles and their nerves may be damaged.

In sub-Tenon block, local anesthetic agent is injected under the Tenon capsule. This block is also known as parabulbar block, pinpoint anesthesia, and medial episcleral block.

Physiology

The physiological pressure (intraocular pressure) interior of the eye is between 10 and 20 mmHg. It is higher in patients with a large-diameter eyeball and in the recumbent position. It is higher in the morning than in the evening. It increases during coughing, physical exertions, and vomiting. An increase in the plasma concentration of carbon dioxide and decrease in oxygen concentration increase the intraocular pressure. Intraocular pressure increases after the needle technique, and this is due to increase in the volume behind the globe. There is little or no increase in intraocular pressure after sub-Tenon block. The anterior and posterior chambers of the eye contain 250 μl of an aqueous liquid (rate of synthesis ca. 2.5 μl/min).

Indications and Contraindications

Both intraocular procedures (cataract extraction, vitrectomy) and extraocular procedures (strabismus surgery, retinal detachment) can be carried out under local anesthesia in suitable patients. There are only a few absolute contraindications such as patient refusal to accept local anesthesia, allergy to local anesthetic agent, local infection, excessive abnormal body movements, severe breathlessness, psychiatric conditions, and in situations where it is difficult to establish a good communication between patients and health-care workers, but the list is shrinking and local anesthesia is increasingly used even in the above group.

Patient’s Assessment and Preparation

Most ophthalmic surgical procedures are carried out as outpatient basis. There is debate as to the degree of preoperative assessment and investigation required and they vary worldwide. In the UK, the Joint Colleges Working Party Report recommended that routine investigations are unnecessary and the patients are not fasted [3]. Routine investigation of patients undergoing cataract surgery under regional anesthesia is not essential because it neither improves the health nor improves the outcome of surgery, but tests can be done to improve the general health of the patient if required [4].

The preoperative assessment should always include a specific enquiry about bleeding disorders and related drugs. There is an increased risk of hemorrhage, and this requires that a clotting profile is available (and recorded) prior to injection (see later) [5, 6]. Patients receiving anticoagulants are advised to continue their medications. Clotting results should be within the recommended therapeutic range. Currently, there is no recommendation for patients receiving antiplatelet agents. Blood pressure should be controlled in hypertensive patients. Diabetic patients are allowed to take their usual medications, and active control of blood sugar is not necessary. There is no need for antibiotic prophylaxis in patients with valvular heart disease, and surgery is not performed if patient has suffered myocardial infarction during the last 3 months [3]. The presence of a long eye, staphyloma, or enophthalmos, the use of faulty technique, a lack of appreciation of risk factors, an uncooperative patient, and the use of unnecessarily long needles are some of the contributing causes. Knowledge of axial length measurement is essential. A precise axial length measurement is usually available for intraocular lens diopter power calculation before cataract surgery [7]. If the block is performed for other surgery and the axial length measurement is not known, close attention to the diopter power of patients’ spectacles or contact lenses may provide valuable clues to globe dimension (patients usually provide this history).

General Considerations and Preparation Before Block

The patient and the person performing the block must be involved in full discussion of the proposed technique. The anesthetic and surgical procedures are explained to the patients. Patient is placed in a comfortable position, and oxygen is administered via a suitable device. All monitoring and anesthetic equipments in the operating environments should be fully functional. Blood pressure, oxygen saturation, and ECG leads are connected, and baseline recordings are obtained. Insertion of an intravenous line is a prerequisite for needle block, but its use has been questioned during sub-Tenon injections [2]. It is not unusual to observe adverse medical events in elderly patient, and a working intravenous line could only be a good clinical practice.

Sedation and Analgesia During Ophthalmic Blocks

The use of sedation varies in different parts of the world and may or may not be used. Sedation is used during block procedure, surgical procedure, or during block and surgery. However, sedation is common during topical anesthesia. Selected patients, in whom explanation and reassurance have proved inadequate, may benefit from sedation. Short-acting benzodiazepines, opioids, and small doses of intravenous anesthetic induction agents are favored, but the dosage must be minimal. An increased incidence of adverse intraoperative events is anticipated with sedation in elderly [6].

It is recommended that one of the following drugs is given immediately before carrying out regional anesthesia:

Midazolam 1 mg (+ remifentanil 0.33 μg/kg)
Propofol 0.5 mg/kg

Deep sedation should not accompany regional anesthesia; the patient should be capable of cooperating.

Conduction and Infiltration Block

Needle Techniques

Atkinson’s classical retrobulbar block involves insertion of a 38-mm-long needle through the skin at the junction of the medial 2/3rd and lateral 1/3rd of the inferior orbital margin in a rotated eye toward the orbital apex. A facial nerve block (7th nerve block) is essential (see Chap. 7).

The classical retrobulbar block has now been superseded by a higher-volume modern retrobulbar and peribulbar blocks.

Modern Retrobulbar Block

The needle is deliberately directed toward the apex and within the muscle cone (see above) while the globe is in neutral gaze.

Indications

Both intraocular and extraocular surgery may include cataract surgery, vitreoretinal surgery, panretinal photocoagulation, trabeculectomy, optic nerve sheath fenestration, delivery of drugs (steroids, neurolytic agents), and sometimes strabismus surgery in willing patients. Retrobulbar block is also performed for the delivery of neurolytic agents for the treatment of chronic orbital pain.

Preparation

See above.

Materials

Equipments such as local anesthetic eyedrop, local anesthetic agent, needle, and syringe (Fig. 6.8) are essential for needle block. Other materials such as syringe, small needle, oculocompression device, gauge swab, hyaluronidase, epinephrine, and balanced salt solution (BSS) may be required.

The short and sharp needles are favored because they reduce the discomfort on insertion but at the expense of a reduced tactile feedback, hence a higher risk of failing to recognize a globe perforation. The blunt or dull needles are favored because it is believed that blood vessels are pushed rather traumatized and tissue planes could be more accurately defined, but these are more likely to cause greater damage when misplaced [8].

Patient Positioning

The best position for the patient is a semi-recumbent position (45°).

Injection Technique

Topical local anesthetic drops and antiseptic drops are instilled to obtain surface anesthesia (Fig. 6.9). A dilute local solution (add 2 ml of concentrated local anesthetic agent to 13 ml of BSS) is helpful before the injection of concentrated local anesthetic agent. Of this dilute solution, 1.5–2 ml is injected through the conjunctiva under the inferior tarsal plate in the inferotemporal quadrant.

A 27-gauge, 1-cm-long needle (Fig. 6.10) is inserted under the inferior tarsal plate through the conjunctiva to deliver dilute local anesthetic. The needle can be introduced through the skin or conjunctiva. A 25-G, 31-mm-long needle is inserted through the skin in the inferotemporal quadrant as far lateral as possible (7 o’clock position on the right eye or the 5 o’clock position on the left eye) below the lateral rectus muscle (Fig. 6.11) while the patient’s eye is in the neutral gaze position. It is important that the needle hub is visible and the skin is not indented. The initial direction of the needle is tangential to the globe, then passed below the globe, and, once passed the equator as gauged by axial length of the globe, is allowed to go upward and inward along the floor of the orbit to enter the central space just behind the globe (Figs. 6.12 and 6.13). The globe is continuously observed during the needle placement.

Motility testing of the eye must be carried out before the procedure.

Dosage

Oxybuprocaine HCl 0.4 % for surface anesthesia if the transconjunctival access route is chosen.
3–5 ml local anesthetic (e.g., 0.75 % ropivacaine, 0.5 % bupivacaine, 2 % prilocaine, 2 % mepivacaine, 2 % lidocaine) or combinations of these.
Possible adjuncts to the local anesthetic:
- Epinephrine (5 μg/ml or 1:200,000)
- Hyaluronidase (150 IU) [7]

The addition of hyaluronidase to local anesthetics leads to improved diffusion and thus to a faster onset. This provides very good conditions for surgical procedures in the eye. Akinesia and anesthesia usually follow but they are dose dependent. If the amount injected is small, anesthesia may follow but akinesia may not occur at all. On the other hand, higher volume can generally guarantee anesthesia and akinesia, but intraocular pressure rises and other complications such as chemosis may occur. Sometimes a supplementary injection such as a medial peribulbar block is required (see later).

Advantages

Anesthesia and akinesia are very predictable and quick. It is easy to learn the technique provided knowledge of basic sciences relevant to block are achieved.

Disadvantages

There are reports of serious complications both sight- and life-threatening.

Side Effects and Complications

1.
Hemorrhage in the very well-vascularized orbit, with a frequency of 0.7–1.7 % (known as “compartment syndrome”), can lead to blindness.
2.
Conjunctival hemorrhage (20–100 %).
3.
Retinal detachment and vitreous hemorrhage after perforation of the eyeball can lead to loss of vision.
4.
Subperiosteal hemorrhage due to contact between the needle and the orbital floor.
5.
Chemosis (25–40 %) due to fast injection of larger volumes of a local anesthetic.
6.
Perforation of the eyeball and intraocular injections can occur, particularly in severely myopic patients. To avoid these, patients should gaze straight ahead throughout the block procedure.
7.
Injury to the optic nerve or intraneural injection (immediate blindness).
8.
Subarachnoid injection is a severe complication.
9.
Intravascular injection, with serious CNS intoxication. See Chap. 1.
10.
Oculocardiac reflex: bradycardia due to the vasovagal reflex is observed in younger and frail patients and may be seen both during the block procedure and also intraoperatively.
11.
Injury to the extraocular muscles (usually the inferior oblique muscle or inferior rectus muscle) can lead to muscle necrosis, contractions, or disturbances of healing.

Peribulbar Block

Inferotemporal Peribulbar Block

This block is used as a main injection alternative to modern retrobulbar block.

Indications, Preparation, and Materials

See above

Patient Positioning

See above.

Injection Technique

Possible approaches of peribulbar injection are presented in Fig. 6.14.

A 25-G, 31-mm-long needle is inserted through the conjunctiva as far laterally as possible in the inferotemporal quadrant. Once the needle is under the globe, it is not directed upward and inward, but it is directed along the orbital floor. Five milliliter of local anesthetic agent of choice is injected. Many patients require a supplementary injection [8, 9].

Medial Peribulbar Injection: The Medial Canthus (Caruncular) Single Injection

A medial peribulbar block is usually performed to supplement inferotemporal, retrobulbar, or peribulbar injection, when akinesia is not adequate. A 27-G, 2.5-cm-long needle is inserted in the blind pit between the caruncle and the medial canthus (Figs. 6.14, 6.15, 6.16, and 6.17) to a depth of 15–20 mm. The needle is inserted at the medial side of the caruncle, at the extreme medial side of the palpebral fissure, and directed at a 5° angle away from the sagittal plane toward the medial orbital wall. The needle should never be introduced more than 20 mm for the caruncular puncture. This technique may require supplementary injection [10]. A medial peribulbar with a 25-G, 31-mm-long needle is used as primary technique in patients with long axial length which may be associated with higher incidence of staphyloma [11].

Dosage

Three to five milliliter of local anesthetic agent of choice is injected if this technique is used as a supplementary injection. However, if this technique is used as a primary injection technique, a volume of 8 ml may be required and this may be very painful during injection.

Advantages of the Caruncular Technique

1.
The medial canthus single injection of peribulbar anesthesia is less painful as -efficient as the classic double-injection peribulbar technique.
2.
Less local anesthetic agent is required.
3.
Reduce the number of punctures and, thus, reduce the risk of injuring an important structure of the eye.
4.
Short onset of block.
5.
Less volume acquired, less ocular pressure.
6.
The diffusion space of anesthetic agents around the globe is segmented by a network of numerous tiny aponeuroses, which may be less dense in the medial canthus region, and this might explain better diffusion and low-volume requirement. Further extraconal space in this compartment is relatively large and avascular, and this may reduce the risk of hematoma or intravascular injection.

Disadvantages

Multiple injections are required during peribulbar block. Caution is required during supplementary injection as the first injection is likely to alter the position of the globe in the orbit.

Complications of Needle Blocks

There are many complications of needle blocks, ranging from simple to serious, that have been reported and published [7]. The complications may be limited to the orbit or may be systemic. Orbital complications include failure of the block, corneal abrasion, chemosis, conjunctival hemorrhage, vessel damage leading to retrobulbar hemorrhage, globe perforation, globe penetration, optic nerve damage, and extraocular muscle damage. The systemic complications, such as local anesthetic agent toxicity, brain stem anesthesia, and cardiorespiratory arrest, may be due to intravenous or intrathecal injections or the spread or misplacement of drug in the orbit during or immediately after injection.

Sub-tenon Block

This block was introduced as a simple, safe, and effective alternative to needle blocks. The technique involves gaining access to the sub-Tenon space, the insertion of a blunt cannula, and the administration of local anesthetic agent into the sub-Tenon space [12].

Anatomy Relevant to Block

Orbital blocks are performed to achieve anesthesia and akinesia during orbital regional blocks. Injection of local anesthetic agent under the Tenon capsule diffuses into the intraconal space. Anesthesia is obtained when the branches of short ciliary nerve are blocked as they pass through the Tenon capsule to the globe. Akinesia occurs when branches of the motor nerves are blocked in the intraconal compartment.

The sub-Tenon space can be accessed from all four quadrants, but the inferonasal quadrant is the most commonly reported site of access in the published studies as the placement of cannula in this quadrant allows good fluid distribution superiorly while avoiding the area of access for surgery and damage to the vortex veins.