Anesthesia for Elective Eye Surgery
Anesthesia for cataract surgery — Cataract surgery is one of the most common procedures requiring anesthetic care. Most cataract surgery is performed with a topical or regional anesthetic technique. Surgical procedure — During monitored anesthesia care (MAC) for the surgical procedure, the following considerations apply:
•Sedation is minimized to reduce the risk of side effects (eg, restlessness, confusion, unresponsiveness, or airway obstruction) that may jeopardize the patient’s ability to cooperate during surgery. Patient cooperation is necessary throughout the procedure to avoid any head movement. Even minor movement, which is highly magnified under a microscope, may result in eye injury.
•If the patient experiences eye pain, the ophthalmologist is alerted to request administration of additional local anesthetic. Heavy sedation should not be used as a substitute for inadequate analgesia.
•Compressed room air (21 percent oxygen concentration) is delivered under the surgical drapes. If supplemental oxygen is required during the procedure, an air/oxygen mixture (with an oxygen concentration 30 percent) is used. Minimizing oxygen concentration reduces the risk of fire during surgery with use of a heat source (eg, electrocautery).
•The gas (room air or an air/oxygen mixture 30 percent oxygen) is delivered under the surgical drapes at a rate of 10 L/minute. Otherwise, completely covering the face with drapes may cause rebreathing of clinically significant amounts of carbon dioxide (CO2). Another option is use of a vacuum line to remove expired CO2.
Anesthetic techniques — Most cataract operations are performed with MAC and a topical or regional anesthetic technique. In the United States, topical analgesia is the most common technique, followed by peribulbar (extraconal) block or, less commonly, retrobulbar (intraconal) block. Sub-Tenon blocks are most popular in the United Kingdom. Typically, general anesthesia is reserved for adults who are unable to communicate, cooperate, or remain stationery during eye surgery, and for children.
•General principles – Topical anesthesia is a good choice for short, uncomplicated procedures in which the surgeon does not require complete akinesia (eg, cataract surgery with phacoemulsification through a small corneal incision), as well as in the following situations:
•Fully anticoagulated patients, due to concerns regarding the risk of bleeding during needle insertion to perform a regional technique.
•Patients with monocular vision (ie, unilateral blindness), due to concerns regarding the risk of vision loss in the remaining eye because of perforation or penetration of the globe during performance of a regional eye block.
•Technique – The anesthesiologist or the ophthalmologist applies local anesthetic eye drops or gels on the cornea and conjunctiva (eg, lidocaine 2% jelly, proparacaine 0.5% solution, or tetracaine 0.75% solution) . Anesthetic gels produce greater levels of drug in the anterior chamber than equal doses of drops and may provide superior surface analgesia. However, gels may form a barrier to bactericidal agents; thus, they are administered after antiseptic solutions.
•Benefits – Topical analgesia may be used as the sole anesthetic technique. The risk of complications may be lower than with other anesthetic techniques since no needle is used. Vision is quickly regained in the postoperative period.
•Drawbacks – Topical analgesia cannot provide akinesia of the eye. Since the patient must voluntarily remain motionless for the entire procedure, appropriate patient selection is important. Anxious patients with a low pain threshold would fare better with a regional anesthetic technique or general anesthesia.
Risks of topical anesthesia are minimal, but very rarely, an allergic reaction or infection may occur.
Regional anesthesia — Profound anesthesia and akinesia of the eye are provided with a successful regional anesthesia technique (ie, eye block).
ANESTHESIA FOR INTRAOCULAR GLAUCOMA SURGERY — Anesthetic techniques for intraocular glaucoma surgery (eg, trabeculectomy) are the same as those for cataract surgery.
Topical anesthesia can be the choice for patients for glaucoma surgery to avoid any transitory increase in intraocular pressure (IOP) during injection of local anesthetic for a regional anesthetic.
Outcomes after glaucoma surgery appear to be similar regardless of the anesthetic technique used. In a randomized study of 120 consecutive glaucoma patients undergoing combined phacotrabeculectomy with either a regional technique (peribulbar local anesthesia) or topical anesthesia with 2% lidocaine jelly, there were no differences in pain control and satisfaction during or shortly after the procedure, and no differences in intraocular pressure (IOP) or the incidence of bleb leakage at follow-up after one year. Similarly, anesthetic technique did not influence the success of trabeculectomy surgery during a longer follow-up period (4.2 years) in 57 patients receiving either a regional or topical anesthetic technique.
However, some surgeons prefer general endotracheal anesthesia in patients undergoing trabeculectomy, due to specific concerns regarding increased risk of damage to the optic nerve due to injections of local anesthetic in glaucoma patients, as well as concerns regarding poor healing after administration of subconjunctival lidocaine.
During general anesthesia for intraocular surgery, complete akinesia is necessary. Therefore, a nondepolarizing neuromuscular blocking agent (eg, rocuronium or vecuronium) is administered and titrated according to monitoring of muscle relaxation with a peripheral nerve stimulator, and a deep plane of anesthesia is maintained.
ANESTHESIA FOR VITREORETINAL SURGERY — Patients undergoing vitreoretinal surgery (eg, a detached retina) usually receive a regional anesthetic block and/or general anesthesia (without the use of nitrous oxide), rather than topical anesthesia. Topical anesthesia alone is avoided because surgery may be quite lengthy, and it is imperative that the patient does not move.
If general anesthesia is used, patients should not receive nitrous oxide when injection of gas (eg, SF6 or C3F8) is planned, or when gas was previously used to create a “bubble” to internally tamponade the detached retina, unless an ophthalmologist has documented that the bubble has been completely absorbed. Although SF6 is usually completely absorbed by 10 days, and C3F8 by six weeks, there are case reports of blindness due to use of nitrous oxide after 25 days for SF6 and after 41 days for C3F8.
Retinal detachment operations are basically extraocular, but may become intraocular if the surgeon elects to perforate and drain subretinal fluid. Hence, patients are managed in the same manner as those having intraocular surgery. Furthermore, rotation of the globe with traction on the extraocular muscles during retinal detachment operations may elecit the oculocardiac reflex. Thus, vigilance must be maintained to detect bradycardia and other arrhythmias.
ANESTHETIC COMPLICATIONS — The complications of anesthesia for ophthalmic surgery can be both vision- and life-threatening. An acronym to remember the serious complications of eye surgery is OPHTS. “O” stands for optic nerve perforation (very rare and extremely unlikely with needles 1.25 inches or less), “P” for globe perforation, “H” for hemorrhage (eg, retrobulbar hemorrhage), “T” for toxic reactions to local anesthetics (eg, injury to extraocular muscles caused by injection of these agents), and “S” for systemic adverse effects (eg, spread of local anesthetic into the central nervous system or intravascular injection with resultant cardiorespiratory depression or arrest).
Ophthalmologic complicationsGlobe or optic nerve perforation — Globe perforation is a rare but serious complication of ocular regional anesthesia. It is more common in myopic patients with long axial eye length (>25 mm). Symptoms of ocular perforation are variable, ranging from intense ocular pain with abrupt loss of vision and hypotonus, to no signs or symptoms. The clinician performing the block may have a sense of increased resistance, particularly if a blunt needle is used.
If ocular perforation is suspected, the ophthalmologist must be notified immediately to perform ophthalmoscopy or ultrasound in order to assess the damage. Usually the planned surgery must be cancelled, and the patient is referred to a retinal surgeon. Occasionally, the damage can be managed with cryosurgery, laser treatment, or mere observation. More commonly, however, proliferative vitreoretinopathy occurs, often accompanied by retinal detachment, and this is managed with vitrectomy and retinal reattachment surgery.
A devastating scenario occurs when the ocular perforation is undetected and an intraocular injection of local anesthetic occurs. Less than 2 mL of solution injected into the globe can produce an ocular explosion and permanent blindness in the affected eye.
Hemorrhage — Bleeding secondary to needle-based techniques is not uncommon. Bleeding may be superficial or deep, arterial, or venous. Superficial hemorrhage, while not vision-threatening, may produce an unsightly circumorbital hematoma. In contrast, retrobulbar hemorrhage, when arterially based, may cause sudden bleeding and a palpable, dramatic increase in IOP, as well as globe proptosis and upper lid entrapment. This can jeopardize the globe’s vascular supply, with a potentially devastating effect on vision. The incidence of retrobulbar hemorrhage has been reported to be 0.03 to 3 percent.
If hemorrhage is suspected, immediate consultation with an ophthalmologist is indicated, and fundoscopic examination, tonometric determination of IOP, ultrasound assessment, and even a lateral canthotomy or paracentesis may be required. Continuous ECG monitoring is necessary because the oculocardiac reflex may occur as blood extravasates from the muscle cone.
If the hemorrhage is mild or moderate, the decision to proceed with surgery depends on several factors, including the amount of bleeding, the nature of the proposed ophthalmic surgery, and the patient’s condition. In cases of severe hemorrhage, surgery should be cancelled.
Intramuscular injection — Intramuscular injection of local anesthetics may cause injury to extraocular muscles. This is thought to be a cause of postoperative strabismus. Oculocardiac reflex manifestations — Manifestations of the oculocardiac reflex can occur when pressure is applied to extraocular muscles. These include bradycardia (a decrease of 10 to 20 percent in the basal heart rate), junctional rhythms, hypotension, and, rarely, asystole. This reflex can occur during injection of local anesthesia or during the surgical procedure itself. Management includes stopping the stimulus (eg, release of traction or manipulation of the extraocular muscles). If this is ineffective, an anticholinergic medication (eg, atropine or glycopyrrolate) is administered.
The risk of inducing this reflex may be reduced by an effective regional anesthetic block or general anesthesia with adequate depth.
Systemic complications — Emergency equipment must be immediately available, including resuscitation drugs and emergency airway equipment (eg, bag and mask, airways, and intubation equipment), even though serious systemic complications due to regional or general anesthetic techniques are rare during eye surgery.
Spread of local anesthetic into the central nervous system (ie, the brainstem) is possible, with resultant cardiorespiratory depression or arrest requiring airway management and cardiopulmonary resuscitation.
As with all nerve blocks, accidental intravascular injection of local anesthetic may lead to systemic toxicity. Treatment consists of IV administration of 20% lipid emulsion 1.5 mL/kg bolus followed by 0.25 mL/kg/min infusion, and supportive airway and hemodynamic management. Calcium channel blockers, beta blockers, and local anesthetics (eg, lidocaine, procaine) should be avoided; vasopressin is not recommended, and initial doses of epinephrine should be small (10 to 100 mcg IV). If, after 30 minutes, there is no clinical improvement, the bolus dose of 1.5 mL/kg lipid emulsion should be repeated, and the continuous infusion should be increased to 0.5 mL/kg/min.
•Preanesthesia consultation for elective eye surgery with sedation and monitored anesthesia care (MAC) includes assessment of ability to communicate, cooperate, and lie supine comfortably.
•Patients with a high risk of clotting and embolic complications who are receiving aspirin, clopidogrel, or warfarin in therapeutic doses may continue these medications before cataract surgery with minimal risk of intraocular bleeding.
•The ophthalmologist’s measurement of axial eye length on the preoperative ultrasound is reviewed, since long eyes (axial length >25 mm) have an increased risk of needle injury during retrobulbar (intraconal) block.
•Sedatives (eg, midazolam) and opioids (eg, remifentanil) with a short duration are administered to reduce or eliminate pain during needle insertion and injection of local anesthetic for a regional block. An alternative technique is administration of 10 to 20 mg increments of propofol until the patient briefly loses consciousness while the block is performed. Supplemental oxygen is administered to reduce the risk of hypoxemia.
•During the surgical procedure itself, sedation is minimized to reduce the risk of side effects that may jeopardize the patient’s ability to cooperate during surgery.
Compressed room air or an oxygen concentration 30 percent (to minimize fire risk) is delivered at a rate of 10 L/minute under the surgical drapes to minimize rebreathing of expired carbon dioxide.
•Anesthetic techniques for cataract surgery include the topical and regional techniques, as well as general anesthesia:
•Use of topical analgesia as the sole anesthetic technique avoids the potential complications of both needle insertion and local anesthetic injection. A drawback is that topical analgesia will not provide akinesia of the eye.
•Regional anesthesia may be provided by peribulbar, retrobulbar, or sub-Tenon block. Peribulbar (extraconal) regional blocks are most commonly used in the United States.
•General anesthesia is reserved for patients who cannot communicate or cooperate or who have severe anxiety or claustrophobia, as well as some patients who are unable to lie supine comfortably (eg, congestive heart failure, chronic obstructive pulmonary disease, or severe back pain), and also for children. Either endotracheal intubation with a nondepolarizing neuromuscular blocking agent or a laryngeal mask airway (LMA) may be used during cataract surgery. Maintenance of a deep plane of anesthesia is necessary to avoid laryngospasm, coughing, or other movement.
•For intraocular glaucoma surgery, anesthetic techniques are the same as those for cataract surgery. Some surgeons prefer general anesthesia for trabeculectomy; in these cases, complete akinesia is ensured by titration of a nondepolarizing neuromuscular blocking agent according to monitoring of muscle relaxation with a peripheral nerve stimulator and maintenance of a deep plane of anesthesia.
•For vitreoretinal surgery (eg, detached retina), a regional anesthetic technique or general anesthesia (without nitrous oxide) is preferred, rather than topical anesthesia.
Nitrous oxide is contraindicated when injection of gas (eg, SF6 or C3F8) is planned or was previously used to create a “bubble” to tamponade a detached retina, unless complete bubble absorption is documented.
•Serious eye complications of regional blocks include globe or optic nerve perforation, and retrobulbar hemorrhage.
•Rare serious systemic complications include inadvertent administration of local anesthetic into a blood vessel or the central nervous system, with resultant cardiorespiratory depression or arrest.
•The oculocardiac reflex can occur when pressure is applied to extraocular muscles and may result in bradycardia, junctional rhythms, hypotension, or asystole. Management includes discontinuing manipulation of the extraocular muscles and administration of an anticholinergic medication (eg, atropine or glycopyrrolate).