Handbook of Clinical Anesthesia
Anesthesia for Ophthalmologic Surgery
Anesthesia for ophthalmic surgery presents unique anesthetic challenges and requirements (Table 51-1) (McGoldrick KE, Gayer SI: Anesthesia for ophthalmologic surgery. In Clinical Anesthesia. Edited by Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC. Philadelphia: Lippincott Williams & Wilkins, 2009, pp 1321–1345). Patients undergoing ophthalmic surgery may represent extremes of age (macular degeneration is the leading cause of blindness in individuals older than 65 years of age) and coexisting medical diseases.
- Ocular Anatomy
- The supraorbital notch, infraorbital foramen, and lacrimal fossa are clinically palpable and function as important landmarks for performance of regional anesthesia (Fig. 51-1).
- The coat of the eye is composed of three layers: the sclera, uveal tract, and retina.
- Whereas the fibrous outer layer of the sclera is protective, providing sufficient rigidity to maintain the shape of the eye, the anterior portion of the sclera, the cornea,is transparent, permitting light to enter the internal ocular structures.
- The uveal tract consists of the iris, ciliary body, and choroid.
- The pupil is part of the iris that controls the amount of light that enters by dilation (sym-pathetic innervation) or constriction (parasym-pathetic innervation).
- The ciliary body produces aqueous humor.
- The retina is a neurosensory membrane that converts light impulses to neural impulses that travel via the optic nerve to the brain.
Table 51-1 Requirements for Ophthalmic Surgery
- Six intraocular muscles move the eye within the orbit.
- The conjunctivais a mucous membrane (where topical ophthalmic drugs are administered) that covers the globe and serves as a lining of the eyelids.
Figure 51-1. Diagram of the ocular anatomy.
- Blood supply to the eye is from branches of the internal and external carotid arteries.
- Ocular Physiology
- Formation and Drainage of Aqueous Humor
- Aqueous humor is formed in the posterior chamber by the ciliary body in an active secretory process involving carbonic anhydrase as well as by passive filtration from the vessels on the anterior surface of the iris.
- Drainageof aqueous humor is via a network of connecting venous channels (including Schlemm's canal) that empty into the superior vena cava. (Any obstruction between the eye and right atrium impedes aqueous drainage and increases intraocular pressure [IOP].)
- Maintenance of Intraocular Pressure
- IOP normally varies between 10 and 21.7 mm Hg but becomes atmospheric when the globe is opened. The major determinant of IOP is the volume of aqueous humor.
- Any sudden increase in IOP when the globe is open may lead to prolapse of the iris and lens, extrusion of the vitreous, and blindness.
- Straining, vomiting, or coughing (as during laryngoscopy and tracheal intubation) greatly increases venous pressure and IOP.
- Glaucomais characterized by increased IOP, resulting in impairment of capillary blood flow to the optic nerve.
- Treatment consists of topical medication to produce miosis and trabecular stretching.
- Atropine premedication in the dose range used clinically has no effect on IOP in patients with glaucoma. Scopolamine may have a greater mydriatic effect, and its use may be avoided.
III. Effects of Anesthesia and Adjuvant Drugs on Intraocular Pressure (Table 51-2)
- Intravenous (IV) injection of succinylcholine (SCh) transiently increases IOP by about 8 mm Hg with
return to baseline in 5 to 7 minutes. This reflects the cycloplegic action of SCh and is not reliably prevented by pretreatment with nondepolarizing muscle relaxants or IV administration of lidocaine.
Table 51-2 Events That Alter Intraocular Pressure
- Etomidate-induced myoclonus may be hazardous in the setting of an open globe.
- Oculocardiac Reflex
- This reflex manifests as bradycardia (and occasionally cardiac dysrhythmias) that is elicited by pressure on the globe and by traction on the extraocular muscles (strabismus surgery), especially the medial rectus.
- Monitoring of the electrocardiogram is useful for early recognition of this reflex.
- Atropine given IV within 30 minutes of surgery is thought to lead to a reduced incidence of the reflex (controversial). Atropine as administered intramuscularly for preoperative medication is not effective for preventing this reflex.
- Anesthetic Ramifications of Ophthalmic Drugs
- Echothiophateis a long-acting anticholinesterase miotic that decreases IOP and prolongs the duration of action of SCh.
- Cyclopentolateis a mydriatic that may produce central nervous system toxicity.
- Phenylephrineis a mydriatic that may produce cardiovascular effects.
- Acetazolamide,when administered chronically to lower IOP, may be associated with renal loss of bicarbonate and potassium ions.
- Timolollowers IOP, but systemic absorption may result in cardiac depression and increased airway resistance. Betaxolol may be more oculo specific and has minimal systemic effects.
- Sulfur hexafluoride (SF6)is injected into the vitreous to mechanically facilitate retinal reattachment. Nitrous oxide (N2O) (blood/gas solubility, 0.47) should be avoided for 10 days after intravitreous injection of SF6 (blood/gas solubility, 0.004). A Medic-Alert bracelet may be helpful to identify patients at risk.
- Preoperative Evaluation
- Establishing Rapport and Assessing Medical Conditions
- Preoperative testing should be based on the history and physical examination.
- Many elderly adult candidates for ophthalmic surgery are on antiplatelet or anticoagulant therapy owing to a history of coronary or vascular pathology.
- Despite the possibility of eye injury from patient movement in the event of implanted cardiac defibrillator activation, there are no reports of activation during ophthalmic surgery, and magnets to inactivate the device before surgery are rarely used.
- Perioperative movement is a possible cause of patient eye injury and potential anesthesiologist liability. Inadequate sedation during monitored anesthesia care (MAC) may be associated with unpredictable movement that results in blindness or poor visual outcome. Intraoperative movement during general anesthesia may also result in adverse visual consequences.
- Anesthesia Options.A commonly selected regional anesthetic technique for cataract surgery is peribulbar block, which has a better safety profile than retrobulbar block. Topical anesthesia is also effective for cataract surgery.
Table 51-3 Factors That Influence the Choice of Anesthesia
- Side Effects of Anesthesia and Surgery.Ophthalmologic surgery and regional anesthesia confer greater risk than many other surgical procedures because of the potential for laterality errors.
VII. Anesthesia Techniques
Most ophthalmic procedures in adults can be performed with either local or general anesthesia. Data have failed to demonstrate a difference in complications between local and general anesthesia for cataract surgery (Table 51-3).
- Retrobulbar and Peribulbar Blocks.Retrobulbar block may be associated with significant complications, emphasizing that local anesthesia does not necessarily involve less physiologic trespass than general anesthesia (Table 51-4). Elevations of IOP after a retrobulbar block can be minimized by application of gentle noncontinuous digital pressure or use of an ocular decompressive device. Akinesia of the eyelids is obtained by blocking the branches of the facial nerve supplying the orbicularis muscle.
Table 51-4 Complications of Needle-Based Ophthalmic Anesthesia
Table 51-5 General Principles of Monitored Anesthesia Care
- Topical analgesiacan be achieved with local anesthetic drops or gels.
- Choice of Local Anesthetics, Block Adjuvants, and Adjuncts.Anesthetics for ocular surgery are selected based on the onset and duration needed (local anesthetics should be mixed to obtain the desired onset and duration). Osmotic agents (mannitol, glycerin, carbonic anhydrase) may be administered intravenously to reduce vitreous volume and IOP.
- General Principles of Monitored Anesthesia Care (MAC)(Table 51-5). Cataract surgery, which is the top Medicare expenditure, is most commonly performed with the patient under some form of regional anesthesia plus monitoring equipment and often with the presence of an anesthesiologist with MAC. MAC should reflect “maximum anesthesia caution” rather than “minimal anesthesiology care.”
VIII. Anesthetic Management of Specific Situations
- Open Eye, Full Stomach.Anesthesiologists must balance the risk of aspiration against the risk of blindness in an injured eye that may result from an acute increase in IOP and extrusion of ocular contents.
- Rocuronium (1.2 mg/kg IV) may be useful for rapid control of the airway, but its intermediate duration of action is a disadvantage compared with succinyl-choline. Sugammadex may provide a solution.
Table 51-6 Considerations for Strabismus Surgery
- When confronted with a patient whose airway anatomy or anesthetic history suggests potential difficulties, the anesthesiologist should consult with the ophthalmologist concerning the probability of saving the injured eye.
- Strabismus surgeryis the most common pediatric ocular operation and may introduce unique concerns (Table 51-6).
- The laryngeal mask airway has the potential advantage of not requiring the use of muscle relaxants and being associated with less straining or coughing with its removal.
- The incidence of postoperative nausea and vomiting may be decreased by use of an IV anesthetic technique with propofol, avoidance of opioids (ketorolac 750 µg/kg IV an alternative), and prophylactic administration of an antiemetic (250 µg/kg IV of metoclopramide or 150 µg/kg IV of ondansetron) immediately after induction of anesthesia.
- Intraocular surgery(glaucoma drainage surgery, open-eye vitrectomy, corneal transplants, cataract extraction) introduces unique concerns and requirements (Table 51-7).
- Epinephrine 1:200,000 may be infused into the anterior chamber of the eye to produce mydriasis. Systemic absorption and the resulting cardiac dysrhythmias in the presence of volatile anesthetics have not been recognized as problems.
Table 51-7 Considerations for Intraocular Surgery
- Nondepolarizing muscle relaxants administered to provide akinesia and facilitate performance and interpretation of the forced duction test (which can be used to differentiate between a paretic muscle and a restrictive force preventing ocular motion) can be safely antagonized, even in patients with glaucoma, because in conventional doses, the combination of anticholinesterase and anticholinergic drugs has minimal effects on pupil size and IOP.
- Retinal Detachment Surgery
- Internal tamponade of the retinal break may be accomplished by injecting the expandable gas SF6into the vitreous. Owing to the blood/gas partition coefficient differences, the concomitant administration of N2O may enhance the internal tamponade effect of SF6 intraoperatively, resulting in increases in IOP and interference with retinal circulation. For this reason, N2O probably should be discontinued for at least 15 minutes before injection of SF6, and likewise N2O probably should not be administered for 10 days after the injection.
- Decrease in IOP is often provided by IV administration of acetazolamide or mannitol.
- Akinesia is not critical, and inhalation anesthetics need not be accompanied intraoperatively by nondepolarizing muscle relaxants.
- Principles of Laser Therapy
- Lasers are used to treat a wide spectrum of eye conditions, including three of the most common causes of visual loss: diabetic retinopathy, glaucoma, and macular degeneration.
- An excimer laser is a form of high-power ultraviolet chemical laser used in refractive surgery (LASIK).
- Postoperative Ocular Complications (Table 51-8)
The incidence of eye injuries associated with nonocular surgery is very low (0.056%). Certain types of surgery, including complex spinal surgery in the prone position, operations involving extracorporeal circulation, and nasal
or sinus surgery may increase the risk of serious postoperative visual complications. Injuries associated with regional anesthesia for ophthalmic surgery are typically permanent and related to the block technique.
Table 51-8 Postoperative Ocular Complications
- Corneal abrasionis the most common ocular complication after general anesthesia. Patients complain of pain and a foreign body sensation that is exacerbated by blinking. An ophthalmology consultation is appropriate, and treatment is prophylactic topical application of antibiotic ointment and patching of the injured eye. Healing usually occurs within 24 to 48 hours.
- Ischemic optic neuropathyis the most common cause of visual loss in patients older than 50 years of age. The incidence of postoperative vision loss after spine surgery performed in the prone position may be as high as 1%. (It is prudent to discuss this potential
complication before surgery as part of the informed consent process.)
- Anterior ischemic optic neuropathyis thought to reflect temporary hypoperfusion or nonperfusion of the vessels supplying the anterior portion of the optic nerve.
- Male patients undergoing prolonged spine surgery in the prone position and operations requiring cardiopulmonary bypass may be at increased risk for development of anterior ischemic optic neuropathy.
- The cause is very likely multifactorial, although intraoperative anemia, controlled hypotension, and increased IOP or orbital venous pressure (in the prone and head-down positions) may contribute to the ischemia of the optic nerve.
- Patients typically experience painless visual loss in the early postoperative period that is associ-ated with an afferent pupillary defect and optic disc edema or pallor. Magnetic resonance imaging initially shows enlargement of the optic nerve followed by optic atrophy. Visual loss is usually permanent.
- Posterior ischemic optic neuropathyis produced by decreased oxygen delivery to the optic nerve.
- Male patients undergoing surgery involving the neck, nose, or spine may be at increased risk for development of posterior ischemic optic neuropathy.
- Patients typically experience a symptom-free period that often precedes the loss of vision associated with a nonreactive pupil. Bilateral blindness is more common than after anterior ischemic optic neuropathy. Disc edema is not a feature of posterior ischemic optic neuropathy because of its retrobulbar location.
- Patients undergoing spinal surgery who are at greatest risk for ischemic optic neuropathy include those undergoing surgery exceeding 6 hours and those with blood loss greater than 1 L. Based on current information, there is no established “transfusion threshold,” and deliberate intraoperative hypotension during surgery has not been proven as contributory to postoperative vision loss.
Editors: Barash, Paul G.; Cullen, Bruce F.; Stoelting, Robert K.; Cahalan, Michael K.; Stock, M. Christine
Title: Handbook of Clinical Anesthesia, 6th Edition
Copyright ©2009 Lippincott Williams & Wilkins
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