Review Articles Complications of Ophthalmologic Nerve Blocks: A Review Shireen Ahmad, MD,* Afzal Ahmad, MD† Department of Anesthesiology, Northwestern University Feinberg School of Medicine, Chicago, IL; and Midwest Eye Center, Calumet City, IL

Complications of ophthalmologic nerve blocks are rare, but they can have serious life- and sight-threatening consequences. Knowledge of the potential complications is essential for the anesthesiologist who performs ophthalmologic nerve blocks. However, most anesthesiologists are unfamiliar with these complications because the majority have been reported in the ophthalmology literature. We review the complications that may occur during the placement of ophthalmologic blocks and their appropriate prompt treatment. © 2003 by Elsevier Inc. Keywords: Anesthesia; ophthalmologic; eye surgery; ophthalmologic nerve blocks.

Introduction

*Assistant Professor of Anesthesiology †Medical Director Address correspondence to Dr. Shireen Ahmad at the Department of Anesthesiology, Northwestern University Feinberg School of Medicine, 251 East Huron St., F5-704, Chicago, IL, USA. E-mail: sah704@ northwestern.edu Received for publication September 3, 2002; revised manuscript accepted for publication January 14, 2003. Journal of Clinical Anesthesia 15:564⫺569, 2003 © 2003 Elsevier Inc. All rights reserved. 360 Park Avenue, South, New York, NY 10010

More than one million ophthalmologic nerve blocks are performed each year in the United States. Traditionally these blocks were done by ophthalmologists, but over the last decade anesthesiologists have started performing an increasing number of these procedures. The majority of academic programs do not have a formal program to teach these nerve blocks but there is ample description of the techniques in the literature.1–7 Complications are rare but can have serious consequences. A prior knowledge of the possible complications of the procedure, together with a thorough knowledge of orbital anatomy, will lead the anesthesiologist to exert care to avoid them.8 The ability to recognize the complication and provide suitable therapy promptly can be life-saving and sight-saving. Unfortunately, most anesthesiologists are unaware of these complications because the majority are documented only in the ophthalmologic literature. The complications of ophthalmologic nerve blocks fall into the following two major categories:

A. Life-Threatening Brain stem anesthesia Seizures Cranial nerve block 0952-8180/03/$–see front matter doi:10.1016/j.jclinane.2003.01.003

Ophthalmologic nerve block complications: Ahmad and Ahmad

B. Sight-Threatening Retrobulbar, peribulbar hemorrhage Ocular penetration/perforation Retinal vascular occlusion Ocular myotoxicity Direct nerve trauma Corneal injury

Brain Stem Anesthesia This complication has also been referred to as “retrobulbar apnea syndrome”, and it is potentially life-threatening. It has been reported by several authors who used various local anesthetic drugs.8 –10 The frequency noted by Wittpenn et al.,8 at the Wilmer Eye Institute, where they evaluated 3,123 patients who had received ophthalmologic blocks, was 0.79%. This complication is more likely to occur during the placement of retrobulbar block than peribulbar injection. The symptoms vary from focal signs such as nausea, vomiting, dysphagia, contralateral amaurosis, facial paralysis, aphasia and hemiplegia; to bradycardia and cardiac and respiratory arrest.11–14 The onset is gradual, ranging from 2 to 8 minutes, and the duration ranges from 5 to 55 minutes. It usually resolves without any long-term sequelae if appropriate supportive measures are instituted. The mechanism is felt to be the entry of the local anesthetic into the subarachnoid space as a result of direct injection into the optic nerve sheath. Subsequent spread centrally to the cistern in the middle cranial fossa results in brain stem anesthesia.15 By injecting cadavers with methylene blue solution and using contrast radiography inpatients, it has been demonstrated that the optic nerve sheath is composed of meninges that are continuous with those of the neurocranium. The outer sheath consists of dura mater, while the inner sheath is composed of arachnoid and pia mater.*16 –19 Increased resistance to injection has been described in association with this complication and following respiratory arrest local anesthetic has been obtained by lumbar puncture.20 Direct application of local anesthetics to specific areas of the brain in animals can have profound cardiac effects,21 and is the most likely cause of the hypotension and bradycardia noted in these patients. Cadaver experiments have shown that the position of the eye during the injection is a contributing factor and the upward and inward gaze described by Atkinson is no longer advocated. Instead, the neutral position, with the gaze directed straight ahead, is recommended, because this position will move the nerve away from the needle being inserted into the muscle cone when performing the retrobulbar block.22 Furthermore, a study of 60 skulls found that the length of the needle is also a factor. The distance from the inferolateral orbital rim to the optic foramen is 42 to 54 mm. The standard Atkinson needle is 35 mm (11⁄2 inches) and has an 11% chance of perforating *Wang BC, Bogart BI, Hillman DE, Turndorf H: Subarachnoid injection—a potential complication of retrobulbar block [Abstract]. Anesthesiology 1988;69:A369.

the optic nerve.23 Based on this finding, use of shorter needles, such as the 31 mm (11⁄4 inches) in length, is advisable so as to avoid this complication. If resistance to injection of a small volume (0.1 mL) of local anesthetic is encountered while performing a retrobulbar block, the needle should be withdrawn a 1⁄4 inch before completing the injection.

Seizures Grand mal seizures following inadvertent intravascular injection of local anesthetic are the result of the selective depression of inhibitory centers in the amygdala.24 Retrograde flow in the arterial system allows direct access to the cerebral circulation,25 and, under those circumstances, accidental intra-arterial injection of a very small dose of local anesthetic can cause seizures. While the orbit is a highly vascular region, studies of orbital anatomy reveal several avascular adipose tissue compartments where needle placement is relatively safe.26 The two safest areas are at the inferotemporal and superonasal quadrants, which correspond to the two most common injection sites for placement of ophthalmologic blocks. It has been suggested that the superior nasal angle be avoided since inadvertent injection of local anesthetic into the superior oblique muscle tendon may result in Brown’s syndrome, or inability to elevate the eye in the adducted position.27 Injection in the adipose tissue areas at the midsuperior location of the orbit may result in injury to the supraorbital artery or the superior ophthalmic and the superior orbital veins. At the inferotemporal and superonasal quadrants, the palpebral arteries may be injured resulting in lid hematomas. The medial collateral vein may be damaged by injection at the inferonasal quadrant. Careful aspiration and use of a small test dose before injection of the total volume of local anesthetic will prevent this complication.

Cranial Nerve Block Facial nerve blocks are combined with ophthalmologic nerve blocks so as to block the orbicularis oculi muscle and prevent the patient from squeezing the eyelids, thereby elevating intraocular pressure (IOP) intraoperatively. The Nadbath Rehman block consists of an injection of local anesthetic over the main trunk of the facial nerve, in the region of the stylomastoid foramen.28 Because of their close proximity, the vagus, glossopharyngeal, and spinal accessory nerves may become anesthetized, resulting in hoarseness, dysphagia, and laryngospasm.29,30 For this reason, the more selective facial blocks such as the Atkinson and Van Lint blocks are more commonly performed.31–33

Retrobulbar/Peribulbar Hemorrhage The reported incidence of hemorrhage associated with ophthalmologic blocks varies from 1% to 3%.34 It varies in severity, from mild ecchymosis to major hemorrhage with proptosis, conjunctival, and palpebral ecchymosis and J. Clin. Anesth., vol. 15, November 2003

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elevated IOP. Major hemorrhage occurs less frequently with the peribulbar technique and rarely results in elevated IOP. Retrobulbar hemorrhage has been associated with visual loss, which may be related to the increased orbital pressure and resultant impaired circulation in the ophthalmic artery,35 or compromise of the small nutrient blood vessels in the optic nerve causing late optic atrophy and visual loss.36 The treatment is based on the severity of the hemorrhage and the risk to the blood supply of the eye. Intraocular pressure must be measured promptly, as treatment will be necessary in the event of a marked elevation. Immediate intermittent digital pressure at the bedside is beneficial in reducing IOP and reducing further hemorrhage. Intravenous (IV) mannitol may be used to lower IOP but the onset of action is slow. Lateral canthotomy, incision of the conjunctiva, and Tenon’s capsule in the appropriate quadrant, can promptly reduce the orbital pressure. Anterior chamber paracentesis may be necessary, but this procedure carries the risk of intraocular hemorrhage.37 If the pressure is not reduced by these measures, orbital decompression through a transantral approach38 or through the medial orbital floor has been advocated.39

Ocular Penetration or Perforation The reported incidence of ocular perforation during placement of ophthalmologic blocks varies from 1:1,00040 to 1:12,000.41 Patients at risk include myopics, who usually have a greater antero-posterior diameter and thinner sclera. The risk of perforation is 30 times greater in the myopic patient than in the normal population and, based on these statistics, some authors feel that general anesthesia is safer in this group of patients. However, this belief is controversial, since numerous peribulbar blocks have been performed by skilled physicians in myopic patients without any perforations. Patients with enophthalmos or posterior and inferior staphylomas are another group who are at increased risk for perforation. Patients who have undergone a previous scleral buckle procedure are at risk for this complication due to increased axial length as a result of the surgery.42– 45 Perforation is associated with pain, and vitreous hemorrhage will be present in all cases. Retinal detachment (55%) and hypotony (30%) or sudden increase in IOP (10%) has also been reported. Pain associated with this complication may be obscured by the use of the newer potent IV drugs such as remifentanil and propofol, which are used for sedation. In some instances, the complication may not be recognized until the time of the postoperative examination. In 50% of cases in the literature, the operating surgeon was unaware of the perforation at the time of surgery,45 and only detected the problem postoperatively. Intraocular injections of local anesthetics do not have any long-term toxic effects on the retina.46 – 48 However, it has been reported that the intraocular injection of local anesthetic has resulted in “explosion” of the eye, rupture of the globe at the limbus, a lens that was dislodged, and a detached retina. This injection requires 566

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that an unusual amount of force to be exerted–in the range of 3,000 mmHg!49 If ocular perforation is suspected, prompt evaluation by a retinal specialist is absolutely necessary. The final outcome of the eye is dependent on the location of the perforation and the presence or absence of a retinal detachment. If no retinal detachment is present, removal of vitreous hemorrhage, in conjunction with laser retinopexy or transceral cryotherapy of the perforation sites, is recommended. In these cases, the incidence of future detachment is only 11%. If treated with photocoagulation or cryotherapy, 56% of patients may have no significant impairment of visual activity. If retinal detachment is present, scleral buckle, vitrectomy, and intravitreal gas or silicone oil tamponade is performed. In these instances, the long-term reattachment rate is reduced to 64% due to proliferative vitreous retinopathy, and despite surgical repair visual acuity will be decreased.

Retinal Vascular Occlusion Retinal vascular occlusion is usually diagnosed following surgery. It may involve the central retinal artery or both the artery and vein. In some cases, there may be predisposing vascular or hematological disease.50,51 The artery may be injured by the needle as it runs inferior to the nerve before entering the nerve, or the artery may be compressed by hemorrhage within the optic nerve sheath.52 Injection of local anesthetic into the optic nerve sheath can result in central retinal vein occlusion initially and preretinal hemorrhage over the macula, followed by retinal artery occlusion from the pressure as increasing volume is injected.53 Retrobulbar injection of lidocaine with epinephrine causes a 50% reduction in ophthalmic artery pulse pressure.52 It has been recommended that epinephrine-containing local anesthetic solutions not be used inpatients with optic nerve disease since they may compromise blood flow in the posterior ciliary and ophthalmic arteries with resulting ischemic optic neuropathy. In patients with vascular disease, epinephrine-containing solutions may further compromise perfusion and thus should be avoided. Epinephrine is added to local anesthetic solutions to prolong the duration of anesthesia and to decrease absorption and toxicity of local anesthetics. However, bupivacaine is the most commonly used local anesthetic for ophthalmologic blocks, and epinephrine does not significantly prolong its effect. Furthermore, the doses used in ophthalmology are well within the safe limit, and therefore there is very little indication for the use epinephrine in these blocks. Retinal examination with an indirect ophthalmoscope is recommended if vascular injury is suspected. If the retinal vessels are not patent, a computed axial tomographic (CAT) scan of the optic nerve may reveal a dilated nerve sheath due to the hemorrhage, which will have to be surgically decompressed.50 Because, in most cases, the vascular occlusion is often detected a few days after the surgery, the visual loss may be permanent.

Ophthalmologic nerve block complications: Ahmad and Ahmad

Direct Nerve Injury Intraneural injection of local anesthetic resulting in blindness has been noted with retrobulbar blocks performed using the Atkinson method.54 For this reason, it is now recommended that the block be performed with the eye positioned in the neutral gaze. This complication can also be avoided by redirecting the needle if any resistance is encountered. Injury to the ciliary ganglion or parasympathetic fibers may occur during retrobulbar block placement and may result in a permanently dilated, nonreactive pupil.55

Ocular Myotoxicity Ptosis following ocular surgery has been widely reported.56 –59 The incidence ranges from 1% to 13.5%, and it is seen with retrobulbar and peribulbar blocks with equal frequency.60 Ptosis has also been reported following general anesthesia. Multiple factors have been implicated, including traction from the lid speculum or bridle suture, disinsertion of the levator aponeurosis, injury to the rectus muscle, and myotoxicity of the local anesthetic. It has been suggested that the addition of hyaluronidase to the local anesthetic solution may protect the extraocular muscles from the toxicity of the local anesthetic by facilitating diffusion of the drug.60 Ptosis is common within 24 to 48 hours after surgery; however, 25% of patients with postoperative ptosis may have permanent damage.§ The ocular myotoxic effect of local anesthetics has been studied in rats and rhesus monkeys.61,62 The local anesthetics cause severe damage of muscle fibers within minutes of contact, with regeneration starting at the end of 1 week and return to normal in 1 to 2 months. If the initial lesion is associated with ischemia, as seen with mepivacaine or lidocaine with epinephrine; regeneration is delayed since new blood vessels must grow into the area. This is not the case with bupivacaine, where a functional capillary bed is maintained. The severity of the deficit is dependent on several factors, such as location of the injection, volume and concentration of the local anesthetic, injury to the muscle, and possible intramuscular injection. To decrease the possibility of this complication, it has been recommended that the peribulbar injection be made medially or laterally to the vertical recti muscles and that the smallest volume and lowest concentration necessary be used. Repeated injections should be avoided.63

Corneal Injury To prevent damage to the anesthetized cornea because of exposure, the eyelids should be kept closed and covered following the placement of the ophthalmologic block. When closing the eye, it is important to make sure that the lids are completely approximated to prevent drying of the

§Tennant JL: Diplopia. Presented at the Fourth Annual Scientific Meeting of the Ophthalmic Anesthesia Society, San Antonio, TX, October 6, 1990.

cornea due to the absence of blinking and suppression of lacrimal gland function.

Conclusion When performing any regional anesthetic technique, the anesthesiologist must be aware of all possible complications and be prepared to treat them promptly. Ophthalmologic blocks should be performed only by individuals who have adequate training in the techniques. Knowledge of anatomy will increase the success and diminish the complication rate. To avoid the complications of injections, many ophthalmologists are performing cataract surgery successfully with topical anesthesia.64 However, not all patients are suitable candidates for this type of anesthesia. Contraindications to topical anesthesia include difficulty with communication, prolonged or complicated surgery, and the surgeon’s lack of comfort with the technique. For these reasons, there continues to be a need for ophthalmologic nerve blocks. The peribulbar block is the technique chosen by many clinicians who believe that the technique offers certain advantages over the retrobulbar injection, and that it provides adequate anesthesia for almost all ophthalmologic surgery. All patients should be closely monitored while the block is being performed, and appropriate resuscitation equipment must be readily available. Although significant patient anxiety can be controlled by communication, the administration of a short-acting opioid analgesic is advantageous so as to limit reflex movement of the head during block placement.㛳 Patients must be closely observed following the block placement, to detect the early symptoms of complications, such as altered mentation, extreme pain, or sudden loss of vision. Because of the fact that the needles used for ocular blocks are usually of a small gauge, it may not always be possible to detect blood or cerebrospinal fluid on aspiration. Therefore, it is essential for the anesthesiologist to maintain a high index of suspicion in any case of alterated resistance during block placement or injection. It is also important for the anesthesiologist to be cognizant of the condition of the eye that is to be anesthetized. Finally, if an ocular complication is suspected, the ophthalmologist must be notified immediately, since prompt surgical intervention may preserve vision.

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