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Anesthetic management can contribute to the success or failure of ophthalmic surgery. A closed claims analysis by Gild and colleagues[1] found that 30% of eye injury claims associated with anesthesia were characterized by patient movement during ophthalmic surgery. Blindness was the outcome in all cases. Although most problems occurred during general anesthesia, one of every four took place under monitored anesthesia care. Accordingly, clinical strategies to ensure patient immobility during ophthalmic surgery are essential.
Patient selection, preoperative evaluation, preparation, monitoring, sedation, and local anesthesia techniques are especially important for safe outpatient cataract surgery in the elderly (also see Chapter 62 and Chapter 68 ). An understanding of eye anatomy and the effect of anesthetics on intraocular pressure (IOP) and eye physiology is important when making anesthetic management decisions concerning such situations as strabismus, open eye injuries, performance of local anesthetic techniques, intravitreal gas injections, electroretinographic studies, oculocardiac reflex (OCR), and retinopathy of prematurity (ROP).[2]
Many ophthalmic procedures, such as cataract extraction, corneal transplants, trabeculectomy, lid surgery, and even vitrectomy or repair of a detached retaina, can be performed safely in an outpatient setting with regional anesthesia and mild sedation (see also Chapter 14 and Chapter 44 ). The number of outpatient ophthalmic procedures will increase as health care costs are contained and the population continues to age. The elderly constitute a large percentage of the 4 million people in the United States who have vision problems related to cataracts. For example, 46% of people older than 75 years have cataracts. [3]
These elderly ophthalmologic patients also frequently have associated diseases of concern to the anesthesiologist. Congestive heart failure, hypertension, diabetes, angina, chronic lung disease, senility, parkinsonism, and arthritis are all clinical conditions that can disrupt a smooth procedure.
Successful local anesthesia for eye surgery begins with preoperative screening, patient selection, and preparation for anesthesia. Although the general principles of preoperative evaluation and medication are standard (see Chapter 25 ), specific considerations are important for ophthalmic surgery and anesthesia. Patients with chronic spontaneous cough, shortness of breath while lying flat, parkinsonian head tremor, Alzheimer's disease, or claustrophobia may be very difficult to manage with regional anesthesia and light sedation. These patients may best be managed with a general anesthetic. Every effort must be made to help the
Whenever possible, the patient's usual medication regimens should not be interrupted. Treatment of asthma, hypertension, angina, congestive heart failure, or diabetes should be continued throughout the day of surgery. Patients with postnasal drip should be given a drying agent before surgery, and those with gastroesophageal reflux should receive at least metoclopramide (0.15 mg/kg intravenously [IV]).
A thorough explanation of the technique, monitoring, and safety precautions involved in regional anesthesia for eye surgery will allay patient anxiety and increase acceptance and cooperation in most cases. Thus, the preoperative anesthesia interview is most important in obtaining cooperation and patient acceptance. Still, premediation can be helpful in lessening anxiety and enhancing amnesia during injection for peribulbar block. The patient must be calm, cooperative, and aware during the operation; reflexes should not be obtunded; and the airway should not be obstructed. Intramuscular premedication is unnecessary in the outpatient setting, but proper sedation levels can be achieved by intravenous titration while monitoring the effect of the sedative. The patient should be monitored and provided with supplemental oxygen during the block process.
The ideal sedating drug before eye block would ensure amnesia for the block, decrease the discomfort of the injection, and limit patient motion while producing no cardiovascular or significant respiratory side effects.
Many drugs and combinations have been used for sedation during monitored anesthesia care, including alfentanil, remifentanil, midazolam, and propofol. [4] [5] [6] [7] [8] Benzodiazepines are synergistic with narcotics and increase the risk of apnea.[9] Altered pharmacodynamics with age requires decreased narcotic doses in the elderly. [10]
Propofol in small (20 mg) incremental intravenous doses has been used to achieve amnesia for regional eye blocks.[11] However, propofol provides no analgesia for insertion of the block needle, so semiconscious patients may have a startle response to needle insertion.
Remifentanil (0.3 to 0.6 µg/kg IV) has a 30- to 60-second onset time and a 5- to 10-minute duration.[12] The patient is clam and cooperative, though aware during the eye block and does not move or startle. A small supplement of midazolam (0.5 to 1.0 mg IV) may be added to this sedation regimen, but midazolam is synergistic with narcotics and increases the risk of temporary apnea. Midazolam has a 2- to 3-minute onset and 45- to 60-minute duration of action.[13]
Infusions of propofol or narcotic are not necessary during eye surgery. The eye block should provide the necessary analgesia and akinesia. The patient should remain awake and aware, but calm and cooperative during the procedure.
Although Gold and associates[6] noted a 13% incidence of nausea and vomiting associated with continuous intravenous remifentanil infusion, low-dose (30 µg IV) bolus injections of remifentanil rarely cause nausea or vomiting.
If a narcotic must be used, an antiemetic drug such as ondansetron (0.08 mg/kg IV) or dolasetron (0.20 mg/kg IV) may also be given to counteract the tendency of narcotics to cause nausea and vomiting.
Standard monitoring for regional anesthesia during ophthalmic surgery (see Chapter 43 and Chapter 44 ) includes observation of arterial blood pressure, the electrocardiogram (ECG), and the pulse oximeter. If possible, peribulbar block should be performed in a special block area at least 20 minutes before the start of surgery. This interval allows time for the block to become effective, for the use of a Honan cuff to lower IOP, and for the patient to begin to recover from sedation. The Honan cuff pressure or the block injection may induce an OCR vagal response that causes bradycardia and nausea. Open eye surgery should not proceed if nausea is present; this complaint should be treated and allowed to subside before proceeding.
Monitoring in the operating room is also standard (see Chapter 43 and Chapter 44 ), but special precautions must be taken because the patient's face is covered by drapes. Respiration may be monitored by direct vision and placing a carbon dioxide sampler near the mouth. A facemask delivering an air-oxygen mixture at a total flow rate of at least 10 L/min should be used to supplement oxygen and prevent accumulation of carbon dioxide under the drapes surrounding the face. These drapes should be tented away from the patient to prevent claustrophobia and to permit free flow of air. Because high oxygen concentrations near the face increase the risk of fire in the presence of cautery, the air-oxygen mix should be kept to at least a 4:1 ratio.
Postoperative care and discharge are standard (see Chapter 68 and Chapter 71 ). The patient is discharged into the care of a responsible adult who provides help when the patient is walking and eating, as well as home care the night after surgery. Moreover, written instructions from the surgeon are provided. Regional anesthesia for eye surgery is generally safe, even for elderly patients with a history of myocardial infarction,[14] However, 26% of high-risk (diabetes, hypertension) ambulatory patients undergoing retina surgery with local anesthesia had at least one silent myocardial ischemic event within 18 hours of surgery.[15] These events were usually associated with an increased heart rate. Therefore, cardiac medication regimens should be continued in the perioperative period and the use of prophylactic β-blockers considered.[16]
Wong[17] and Troll[18] reviewed regional anesthesia techniques for intraocular surgery in detail and presented an excellent description of important orbital anatomy. Kumar and Fanning discussed techniques for peribulbar/retrobulbar blocks and sub-Tenon blocks, including the choice of anesthetic mixture and types of needles.[19]
Hamilton and coworkers[22] have shown that safe, comfortable, and effective analgesia and akinesia of the eye can be obtained with a peribulbar block, or injection of local anesthetic outside the muscle cone. Hamilton and colleagues used their "customized peribulbar block" in more than 10,000 patients without the occurrence of complications (brainstem anesthesia, retrobulbar hemorrhage, atrophy of the optic nerve, or spread of anesthetic to the contralateral orbit).
Davis and Mandel[23] reviewed 16,225 peribulbar blocks and found them to be effective with a very low complication rate. Perforation of the globe occurred in a patient with an eye axial length of 23.5 mm when a sharp needle was inserted through a superonasal approach. Akinesia was achieved in 95% of patients, and the reinjection rate was about 10%. Amaurosis is not usually expected with peribulbar blocks.
Disadvantages of peribulbar blocks versus retrobulbar blocks include larger injected volumes (6 to 8 mL) causing a possible increase in IOP,[24] slower onset (5 to 10 minutes), the potential for perforation of the globe, and vertical diplopia as a result of myotoxicity of the inferior rectus muscle by the local anesthetic. [25] [26] [27] [28] [29]
The customized peribulbar block described by Hamilton and coworkers [22] requires attention to detail to maximize patient comfort and good analgesia and to minimize complications. Dull, short-beveled, 25- to 27-gauge, 22-mm needles (Atkinson) are usually recommended to minimize the risk of bleeding and perforation of the globe. Careful placement of the needle in the lateral aspect of the inferotemporal quadrant and checking for aspiration of blood decrease the risk of vessel perforation. Hamilton and coworkers[22] recommend topical application of 0.5% proparacaine followed by an initial injection of local anesthetic through the inferior fornix of the conjunctiva rather than transcutaneously. The needle is never inserted beyond 25 mm because large vessels and the optic nerve are more likely to be encountered with deeper retrobulbar penetration. No attempt is made to pierce the muscle cone.
The traditional practice of having the patient look upward and in to make the muscle cone more accessible also brings the optic nerve and vascular structures closer to the tip of the needle, thus increasing the risk of retrobulbar hemorrhage, optic nerve injury, or central nervous system (CNS) tracking of local anesthetic along the optic nerve sheath. A safer maneuver is to have the patient look straight ahead (neutral gaze position) to avoid entering the cone. All injections should be performed slowly to ensure patient comfort and promote even spread of local anesthetic within the orbit.
The use of an orbital compression balloon facilitates the block by lowering IOP and promoting the periorbital spread of local anesthetic to achieve akinesia of the periorbital muscles. In this way, the need for a separate and painful facial nerve block is avoided. Any complications that occur (vasovagal reactions, retrobulbar hemorrhage, spread of the local anesthetic to the CNS) are usually obvious within 10 to 15 minutes of injection.
This procedure is virtually pain free because of use of the peribulbar approach, careful placement of fine needles (25 to 27 gauge), slow injection of local anesthetic, and avoidance of a separate block of the facial nerve. As a result, the elderly outpatient population usually needs minimal premedication and, consequently, has fewer drug side effects (e.g., somnolence, hypotension, emesis). The local anesthetic mixture advocated by Hamilton and colleagues[22] consists of equal portions of 2% lidocaine (rapid onset and penetration) and 0.75% bupivacaine (prolonged duration and postoperative comfort). The addition of hyaluronidase (3 U/mL) promotes the spread of local anesthetic, and the addition of epinephrine (in a final concentration of 1:400,000) reduces bleeding, promotes vasoconstriction, and prolongs orbital akinesia.
The peribulbar technique requires a total of approximately 6 mL of injectate. The total amount of epinephrine injected is small and should pose no problem to patients with angina, hypertension, or irritable myocardium.
Direct injection of local anesthetic into the posterior sub-Tenon space with the use of blunt dissection and a blunt probe avoids many of the complications of peribulbar and retrobulbar injections.[30] [31] [32] [33]
Tenon's capsule is a dense fibrous layer of connective tissue surrounding the globe and extraocular muscles. Local anesthetic in the posterior aspect of this space spreads along the extraocular muscles and diffuses into the retrobulbar space.
This technique uses a blunt probe (curved lacrimal cannula) to instill local anesthetic into the posterior sub-Tenon space, thereby avoiding sharp needles blindly placed in the orbit or retrobulbar space. It is painless to perform and provides reliable anesthesia with minimal risk of serious complications.[31]
Ripart and associates[30] have shown by computed tomography that a sub-Tenon medial canthus injection is episcleral and allows the local anesthetic to spread over the extraocular muscles and provide akinesia. A volume of 4 mL is sufficient to surround the globe and produce analgesia.
The sensitivity of the eye is provided by the ciliary nerves, which cross the episcleral space after they emerge from the globe.[30]
Hamilton has recently reviewed the complications of ophthalmic regional anesthesia in detail, including oculocardiac reflex (OCR), hemorrhage, brainstem anesthesia, globe perforation, myotoxicity, optic nerve damage, anticoagulant therapy, and allergic responses.[34]
The complications associated with eye block techniques, though rare (approximately 1 in 500 blocks), generally occur within 15 minutes of injection and are the result of
OCR is a trigeminal-vagal reflex response that is manifested as cardiac arrhythmias and hypotension and may be elicited by pain, pressure, or manipulation of the eyeball. The afferent pathway follows the long and short ciliary nerves to the ciliary ganglion and then to the gasserian ganglion along the ophthalmic division of the trigeminal nerve (the fifth cranial nerve). These afferent pathways terminate in the main trigeminal sensory nucleus in the floor of the fourth ventricle. The efferent impulses start in the muscles of the vagal cardiac depressor nerve and cause negative inotropic and conduction effects.
OCR occurs most often during strabismus surgery in children but also occasionally during retinal surgery at the time of injection for retrobulbar block; it can even occur during nonophthalmic surgery if pressure is placed on the eyeball. The reported incidence of OCR varies considerably (from 32% to 90%), depending on the intensity of observation and the definition of arrhythmias. Transient cardiac arrest may occur as frequently as 1 in 2200 strabismus surgeries.
The force and type of stimulus seem to influence the incidence of OCR.[35] The more acute the onset and the stronger and more sustained the traction, the more likely OCR is to occur. Although the medial rectus muscle is commonly believed to be the most sensitive in eliciting OCR, Blanc and associates[35] did not find this to be necessarily true. This misconception may result from two lines of reasoning. The medial rectus muscle is less accessible and may therefore require more pulling for exposure. In addition, the medial rectus is the muscle manipulated most often in strabismus surgery and may thus be more refractory to fatigue.
Hypoventilation and increased arterial carbon dioxide partial pressure significantly increase the incidence of bradycardia during strabismus surgery. Intramuscular administration of atropine, gentle manipulation of the extraocular muscles, and control of ventilation to maintain normocapnia should reduce the incidence and severity of OCR.[35]
The intravenous administration of atropine to prevent or treat OCR is controversial. Atropine may cause bigeminy and increase ectopic beats, especially when halothane is the primary anesthetic. These arrhythmias are more persistent than the OCR. Although intramuscular premedication with atropine reduced the incidence of OCR from 90% to 50%, Mirakuhr and coauthors[36] noted that intravenous administration of atropine or glycopyrrolate was even more effective in preventing OCR. Although the peak effect of glycopyrrolate did not occur for 3 to 4 minutes, glycopyrrolate did not produce as great a tachycardic response as atropine did.
Bradycardia is the most common manifestation of OCR, but other abnormal rhythms (nodal, junctional, ectopic atrial, or even serious ventricular arrhythmias) are possible. Therefore, the ECG should always be monitored continuously during ophthalmic surgery. The OCR ceases when stimulation (pressure or traction) ends, so the surgeon and anesthesiologist should not hesitate to communicate during procedures in which an OCR may develop.
The first step in treating OCR is to stop stimulation by the surgeon before the arrhythmia progresses to sinus arrest. Fortunately, sustained and repeated stimulation usually causes the OCR to fatigue. If arrhythmias persist, treatment with atropine (0.007 mg/kg IV) and a local injection of lidocaine near the eye muscle may be necessary. If the patient still seems unusually sensitive to manipulation of the extraocular muscles, the anesthesiologist should ensure that the depth of general anesthesia is adequate, the patient is normocapnic, and surgical manipulation is gentle.
Retrobulbar hemorrhage varies in onset and intensity but has been reported to occur in 1 in 700 retrobulbar blocks [37] ; it is usually noted during injection as the eye tenses and pushes forward and proptosis occurs. Treatment includes the application of gentle pressure for 20 to 30 minutes and, if necessary, lateral canthotomy to relieve optic nerve compression. Surgery should be rescheduled. This complication is less likely with peribulbar or sub-Tenon blocks. Most orbital blood vessels are located posteriorly in the medial and superior aspects of the orbit. The lateral area of the inferotemporal quadrant is the least vascular of the orbit. The risk of retrobulbar hemorrhage may be minimized by using a lateral inferotemporal approach, avoiding deep needle placement (less than 32 mm), using fine-gauge needles (25 to 30 gauge), and applying some pressure to the eye for 1 minute after injection.
Direct trauma to the eye (optic nerve damage, scleral perforation) occurs rarely (<1 in 1000 retrobulbar injections). Possible risk factors for needle penetration include increased axial length (>26 mm) as a result of high myopia or a previous scleral buckle procedure and poor patient cooperation during the injection. In one study, 70% of globe perforations involved sharp, full-beveled needles. Birch and colleagues demonstrated by ultrasonic localization that 56% of retrobulbar needle shafts indent the globe.[38] Optic nerve damage and retrobulbar hemorrhage may be minimized by having the patient look straight ahead and avoiding deep penetration into the orbit. Katsev and coworkers [39] recommend using needles no longer than 32 mm.
Shivering occurs in approximately 0.64% of patients, probably because of absorption of local anesthetic along the optic nerve sheath into the CNS (see Chapter 14 and Chapter 43 or Chapter 45 ).
Javitt and coauthors[40] reported eight instances of brainstem anesthesia after retrobulbar block, six of which progressed to apnea requiring assisted ventilation. The clinical picture of brainstem anesthesia can include amaurosis, gaze palsy (ductional defects), dysphagia, cardiac arrest, shivering, apnea, tachycardia, hypertension, loss of consciousness, and dilatation of the contralateral pupil. Full recovery from brainstem anesthesia is the expectation, provided that the condition is detected early and proper treatment is instituted.[41]
Nicoll and coworkers[42] found that direct spread of local anesthetic to the CNS along the optic nerve sheath occurred in 1 of 750 retrobulbar blocks and caused severe, unpredictable, life-threatening complications. The onset of symptoms may be delayed 2 to 40 minutes after injection. If recognized early and treated promptly, patients usually recover within 1 to 3 hours and do well.
Access to the brainstem can occur as a result of direct injection of local anesthetic into the optic nerve sheath during a deep retrobulbar approach, with retrograde tracking to the midbrain and respiratory area of the brainstem. Javitt and colleagues[40] noted that communication between the optic nerve sheath and the subarachnoid space had been demonstrated and that contrast material is able to track along the optic nerve to the optic chiasm and into the subarachnoid space surrounding the pons and midbrain areas. Such an occurrence would be consistent with the signs and symptoms manifested by their patients. Javitt and coworkers also noted that a down-and-out gaze for retrobulbar block injection was safer than the traditional up-and-in gaze. Brainstem anesthesia has not yet been reported with the peribulbar method of eye anesthesia. Javitt and colleagues concluded that careful monitoring and the presence of an anesthesiologist during the administration of anesthesia for the eye are necessary to detect and treat these rare, but serious complications.
Another mechanism for CNS complications can be intra-arterial injection of local anesthetic with retrograde flow through the ophthalmic artery into the cerebral circulation and midbrain area. The onset is usually immediate and may be associated with seizure activity.
Life-threatening complications associated with regional eye blocks can occur quickly and therefore require the anesthesia care team to be prepared and vigilant. Treatment includes oxygen, assisted ventilation, intravenous fluids and pharmacologic circulatory support, suppression of convulsions, and if necessary, intubation and cardiopulmonary resuscitation.[43]
Vertical diplopia caused by degeneration of the muscle fibers of the inferior rectus muscle has been reported to occur at an incident rate of 1.4% after regional local anesthetic injection for cataract surgery.[25] The diplopia may be temporary or permanent. Possible etiologies include traumatic injection, myotoxicity of the local anesthetic solution, bridle sutures, surgical trauma, ocular compression, and pressure from the volume of injectate. Carlson and Raimin[27] noted muscle degeneration after the injection of bupivacaine, mepivacaine, or lidocaine near the extraocular muscles of rats. Damage reflected diffusion of the anesthetic into the muscle. General recommendations for preventing postinjection diplopia include the following: limiting the injected volume to 6 mL, injecting slowly, avoiding injection into the muscle body, injecting lateral to the inferior rectus muscle,[26] avoiding 4% lidocaine (Xylocaine) injection, and adding hyaluronidase (2 to 8 U/mL) to the injection solution.
Postoperative ptosis after cataract surgery is reported to have an incidence as high as 13%. It is usually associated with the levator palpebrae muscle. Feibel and associates[44] found no significant difference in the incidence of ptosis after either peribulbar or retrobulbar injection. Injection of a large volume of local anesthetic into the upper lid should be avoided when possible.
Modern cataract surgical techniques allow the use of smaller incisions without the necessity for total akinesia. It is now possible to perform cataract extractions in selected patients with a topical local anesthetic eyedrop technique. [45]
Fanning and Fichman[45] reviewed this technique in detail, including the anatomy, pharmacology, advantages, sedation, and patient selection. The cornea receives its sensory innervation through the long ciliary nerve, which forms an intraepithelial plexus. Terminal nerve endings are superficial, so topically applied local anesthetics are easily absorbed through the conjunctival membrane and effectively block the sensory innervation of the cornea.
Advantages of topical local anesthesia for eye surgery are virtually no risk of hemorrhage, brainstem anesthesia, optic nerve damage, or perforation of the globe.
Limitations of this method include lack of eye akinesis, treatment of uncomplicated cataracts only, and the need for cooperative, communicative patients who are not anxious, claustrophobic, or demented.
Local anesthetic eyedrops used for topical eye anesthesia include bupivacaine, lidocaine, proparacaine, and tetracaine. Proparacaine is the least irritating on application.[46] Usually, little or no sedation is necessary, especially when the patient has been well selected and prepared. The patient should be comfortably relaxed but remain aware and cooperative. If necessary, a small dose of midazolam (0.01 mg/kg IV) is generally sufficient. Oversedation, especially in the elderly, can lead to hypoventilation, hypoxia, and disorientation.
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