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ophthalmic anesthesia more than meets the eye


ophthalmic anesthesia more than meets the eye

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Ophthalmic Anesthesia: More Than Meets the Eye Steven I. Gayer, M.D., M.B.A. Miami, Florida

Ophthalmic surgery patients may be anesthetized via general anesthesia (GA), retrobulbar block (RBB), peribulbar injection (PBB), sub-tenon’s block (STB), intracameral injection, or topical application of anesthetic drops and gels. The choice of anesthesia technique should be individualized based upon specific patient needs, the nature and extent of eye surgery, and the anesthesiologist’s and surgeon’s preferences and skills. Most anesthesiologists provide monitored anesthesia care (MAC) for their ophthalmic surgical patients; allowing the ophthalmologist to perform the regional anesthetic. This is probably due to the fact that less than 25% of anesthesiology residency programs provide training in ophthalmic regional anesthesia.1 In private practice, anesthesiologists may balk at learning these procedures because of a perceived increased risk of eye injury while learning these new techniques. Additionally, the rationalization that no additional fees are generated related to the enhanced risk may propagate the tradition of avoiding anesthesiologist-rendered blocks. This logic avoids acknowledging the efficiencies that occur when patients are anesthetized and immediately ready for surgery as soon as (or prior to) the conclusion of the previous eye surgery case. Additionally, anesthesiologists tend to perform peribulbar eye blocks that may have fewer untoward sequelae than traditional RBBs. These blocks have a longer latency of onset, a disadvantage for the ophthalmologist blocking a patient between cases, but a variable not necessarily significant to the anesthesiologist who can place the anesthetic farther in advance of surgery while the ophthalmologist is in the operating room with the previous patient. Many ophthalmologists and administrators advocate anesthesiologist-provided ophthalmic anesthesia as a means toward diminishing turn-over time, providing excellent operating akinesia/analgesia, and allowing more cases to be done per-room per-day, thus enhancing operating room efficiency. Preoperative Considerations Due to geriatric age and prevalence of co-morbidities, cataract patients have a high incidence of abnormalities in preoperative medical tests. A large multicenter study found that the number of intraoperative and postoperative events were similar for patients independent of whether or not routine preoperative labs were obtained.2 Routine testing conferred no additional benefits. Some physicians have misinterpreted these results, believing that patients for cataract surgery need no preoperative evaluation. This is most certainly not the case. All patients in this trial received regular care by primary-care providers and were evaluated by a physician prior to surgery. Patients whose medical status indicated a need for specific tests were excluded from the study. Thus, cataract surgery patients require assessment by a physician who should determine the need for indicated laboratory testing. The routine cessation of antiplatelet and anticoagulation medications prior to eye surgery is an area of controversy. Many eye surgery patients receive anticoagulant medications for concomitant diseases. Traditionally, such medicines were withheld prior to ophthalmic surgery in order to minimize the likelihood of perioperative bleeding into the orbit or eye. On the other hand, discontinuing anticoagulant therapy may increase the risk of perioperative stroke, myocardial ischemia, and deep venous thrombosis. Investigations of this conundrum have produced equivocal results. A recent multicenter study of almost 20,000 patients for cataract surgery found that those who continued their aspirin or coumadin therapy did not have significantly more serious ocular bleeding, while those patients that discontinued taking anticoagulants prior to surgery did not have significantly greater incidence of medical events.3 We need more data to resolve this issue. Ophthalmic patients with hypertension should not receive pupilary-dilating drops such as phenylephrine prior to surgery without consultation with the anesthesiologist. Phenylephrine drops are available in two concentrations- 2.5% and 10%. Systemic absorption can occur via passage of drops through the nasolacrimal duct to the nasal mucosa. Bioavailability from nasally absorbed medications is quite high. Improperly instilled mydriatic agents can precipitate a transient hypertensive crisis with potential devastating consequences.4 Beta blockers and calcium channel blockers may exacerbate the hypertensive response. Additionally, treatment with long acting antihypertensive agents can produce profound hypotension once the short-lived effect of phenylephrine has passed.5 The best strategy is to limit the use of ocular phenylephrine, otherwise ensure the smallest dose of the 2.5% concentration with concomitant occlusion of the puncta when administering the drug. One of the most important preoperative decisions relates to the likelihood of patient movement during surgery. Inability to remain supine or still may have devastating visual consequences should marked patient movement result in eye injury. Two strategies seem prudent: GA or postponement of elective surgery until such time

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that the patient is in a condition that would not predispose them to significant intraoperative movement. The ASA Closed Claims Project found that the anesthesiologist was often cited in blindness-due-to-movement cases done via GA. All but one of those cases could have been conducted with regional anesthesia. On the other hand, both the number of claims with payment and the size of payments were significantly lower for those patients that had permanent injury due to movement while under MAC.6 Needle-Based Ophthalmic Regional Anesthesia Regional anesthesia for ophthalmic surgery is divided into two categories: Needle-based blocks and cannula-based anesthesia. The retrobulbar block (RBB) has traditionally been the most commonly used needle-based regional anesthesia technique for eye surgery. A purportedly safer approach is the peribulbar block. Sub-tenon’s blocks are commonly placed with a blunt cannula instead of a needle. The anatomical basis of RBB rests upon the notion of the orbital cone. It is comprised of four ocular rectus muscles, extending from their origins at the Annulus of Zinn up to their attachment into the globe anteriorly, and connective tissue surrounding and investing these muscles, forming an impermeable compartment behind the globe akin to the brachial plexus sheath in the axilla.7 A RBB is performed by inserting a needle into the orbit with appropriate depth and angulation through the cone such that the tip of the needle is behind (retro) the globe (bulbar). A more appropriate terminology is intraconal block. See Figure 1.

Figure 1. Traditional Retrobulbar Block (left) versus Peribulbar Block (right) Cadaver dissections have shown that the concept of the cone is more theoretical than actual and clearly demonstrated that intraconal injections of dye into cadaveric orbits diffused into the extraconal space, while solutions placed just outside of the cone penetrated into the intraconal space.8 Thus one can accomplish peribulbar orbital anesthesia by placing a needle with less depth and less angulation, parallel to the globe. This is theoretically safer since the needle is ultimately directed toward the greater wing of the sphenoid bone rather than towards the apex of the orbit, keeping the needle tip further from key intraorbital structures. A RBB deposits local anesthetics deep within the orbit close to nerve and muscle origins, therefore it requires a low volume, has quick onset, and yields intense anesthesia. Due to distance and need for diffusion the peribulbar (PBB), or extraconal, block requires larger volumes of local anesthetic and has a longer latency of onset. Some of the increased volume of anesthetic injected with the peribulbar technique diffuses peripherally and blocks branches of the facial nerve innervating the eyelid’s orbicularis oculi muscle. This serves to attenuate eyelid squeezing intraoperatively; a distinct advantage for patients undergoing corneal transplant surgery. Use of RBB requires a separate lid block to limit eyelid squeezing. The conventional needle-entry point for both blocks has been the junction of the medial two-thirds and lateral one-third of the inferior orbital rim. Shifting the entry site more laterally along the orbital rim may diminish the likelihood of block-induced postoperative strabismus thought to be caused by injecting local anesthetic into the inferior rectus muscle.9 Other entry sites include medially at the caruncle as well as superiorly, above the globe. One should avoid superonasal needle placement as the superior oblique muscle and the trochlear apparatus are vulnerable to injury here. The commonly used 1.5” (38mm) needle can reach the apex of the orbit in one-of-five RBBs, thus a shorter needle, ≤1.25” (31 mm), is more prudent.10 Some anesthesiologists believe that dull needles are safer because

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they require more force in order to accidentally puncture the eye. Purportedly, one can redirect the needle path if the globe appears to be impinged by the dull tip. On the other hand, dull needles are more painful to insert and often cause greater injury with inadvertent globe puncture.11 The most dreaded complication for anesthesiologists doing orbital regional anesthesia is accidental needle penetration of the globe. Aside from the potentially devastating outcome of blindness, it is the one complication of orbital anesthesia that we must rely upon others to diagnose and manage. By definition, a RBB requires angling of the needle tip steeply and deeply within the orbit behind the globe. If the globe is longer than average, or recessed deeply, it is at greater risk of accidental injection by the needle. Eyes are most commonly penetrated posteriorly. Some globes have abnormal outpouched areas called staphylomata, frequently situated posteriorly at the junction of the eye and the optic nerve. While a recessed eye may be apparent upon examination of the surface anatomy, longerlength globe and staphylomata are not.12 There is some correlation between prescription glasses’ spherical equivalent and eye length, therefore, eliciting a history of near-sightedness may indicate longer than ordinary eye length. Additionally, scleral buckle surgery increases the A-P distance of an eye, so prior retina surgery may imply long eye length. Optimally, one would like to have the length and shape of the eye measured by ultrasound prior to performing a needle-based regional anesthetic. Fortunately, an ultrasound is a prerequisite for the ophthalmologist in order to determine the appropriate lens implant to insert and is done on every patient scheduled for cataract surgery. Due to the outpatient nature of cataract surgery, this information rarely is placed on patients’ surgical charts. Be aware: it exists. If one intends to perform an eye block, ask the ophthalmologist for the ultrasound data. Confirm that the eye length is normal (< 26 mm) and that there are no staphylomata. Remember that for normal eyes, the retrobulbar needle tip is often closer to the posterior portion of the globe than physicians presume.13 The PBB approach involves shallower needle placement and minimal angulation, thus may be associated with less chance of posterior globe puncture. It is still possible, though, to pierce the globe laterally.14 Risk Factor Long Eye Length Abnormal Eye Shape (Staphyloma) Recessed Globe Indicator History of Near-Sightedness History of Prior Scleral Buckle Surgery Ultrasound Report (Axial Length >26 mm) Ultrasound Report Exam of Surface Anatomy

Table 1. Risk Factors and Indicators for Inadvertent Globe Puncture Another potential complication of needle-based blocks is retrobulbar hemorrhage. The vast majority are superficial, with little consequence other than circumorbital discoloration. On rare occasion, arterially-based retrobulbar hemorrhage may produce precipitous bleeding and retinal perfusion may be compromised by the increased ocular pressure. An ophthalmologist should be immediately consulted to measure the globe pressure and assess adequacy of perfusion via fundoscopic exam. Continuous monitoring for bradydysrhythmia due to oculocardiac reflex is warranted. An urgent surgical incision along the outer margin of the orbit, a lateral canthotomy, may be needed in order to relieve the pressure, improve perfusion, and preserve vision. The decision to proceed with surgery in light of a mild or moderate hemorrhage is dependant upon numerous factors including degree of bleeding, nature of the ophthalmologic surgery, and stability of vital signs. Brainstem anesthesia results from direct spread of local anesthetic to the brain along the optic nerve’s meningeal sheaths. Symptoms may be slow to develop and continuous monitoring of consciousness, particularly en route from a holding area to an operating room is essential. Loss of consciousness, apnea, seizures, dysphagia, and cardiovascular instability may occur. Personnel skilled in airway maintenance and ventilatory/circulatory support should be immediately available. One prospective study of over 3000 RBBs reported an almost tenfold greater incidence of respiratory arrest with the use of a 4% lidocaine / 0.75% bupivacaine mixture (0.79%) versus 2% lidocaine / 0.75% bupivacaine (0.089%).15 Brainstem anesthesia is less likely with PBB rather than RBBB.16 Anesthesiologists and ophthalmologists often disagree as to etiology when a patient loses consciousness or becomes apneic shortly after an eye block. One key means of establishing a definitive diagnosis of brainstem anesthesia as opposed to oversedation is the presence of a dilated pupil, loss of eye mobility and/or diminished

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vision in the contralateral, unblocked eye. These findings are pathognomonic for flow of local anesthetic across the optic chiasm to the other eye. Intravascular injection of local anesthetic occurs via retrograde flow through the ophthalmic artery into the internal carotid artery and then to the Circle of Willis. Rapid redistribution produces abrupt onset of convulsions. Symptoms tend to resolve quickly. Personnel skilled in airway maintenance and ventilatory/circulatory support should be immediately available. Traditionally, regional anesthesia has been shunned in the setting of open-eye injuries due to the concern that pressure generated by local anesthetic placed behind the globe may precipitate extrusion of intraocular contents. Recognizing that open-eye injuries can vary by degree and extent, regional anesthesia techniques to safely block select injured eyes have been established.17 Suitable eyes tend to have smaller, well defined, linear, more anterior wounds. In two studies there was no difference in visual outcomes between eyes repaired with regional versus GA.17-18 Additionally, TA for patients with minor open-globe injuries has also been employed.19 Cannula-Based Ophthalmic Regional Anesthesia The sub-tenon’s (STB) or episcleral block has been rediscovered and popularized over the past few years. Cannula techniques are another practical means to achieve analgesia and akinesia of the globe. They are accomplished by instilling local anesthetic via a blunt tube inserted through a small incision in the episcleral membrane (tenon’s capsule). See Figure 3. Radiology studies have proven that anesthetics injected in this manner diffuse behind the eye.20 A prospective study of 6000 patients found this technique to be safe and effective.21 There is less likelihood of perforating the posterior globe due to the fact that cannulae are placed anteriorly and this is a needle-less technique. The STB is particularly useful for those patients with very long globes, markedly recessed eyes, or staphylomata as well as for intraoperative supplementation of anesthesia. Equipment for STB includes the cannula, blunt scissors, and forceps. Additional optional equipment are hand-held cautery to manage minor conjunctival bleeding and a lid speculum to hold the eyelids open during the procedure. After applying topical anesthetic drops, one can access the episcleral space after raising Tenon’s Capsule with the forceps and cutting/dissecting a hole. The cannula is then threaded through the dissected opening and local anesthetic is injected. Retrograde efflux of anesthetic around the tube and out of the incision is not uncommon. Additionally, some local anesthetic may diffuse under the conjunctiva, causing unsightly swelling of tissues. Subconjunctival bleeding and “red eye” are not uncommon. These issues are usually of minimal consequence. A video of the procedure will be shown during the lecture. Significant complications are rare. They include globe perforation, major retrobulbar hemorrhage, and muscle trauma with resulting strabismus.22-26 One case of brainstem anesthesia has been reported.27 A greater number of significant complications seem to be associated with longer, more rigid cannulae; while the incidence of minor bleeding and conjunctival swelling is more common with shorter, flexible tubes.28 Some variations on STB techniques include the use of an ultra-short (<6mm) cannula and needle-based episcleral injections.28-29 Topical Anesthesia Topical anesthesia (TA) was pioneered by Koller in the 1880’s. Recent advances in surgical techniques have made reintroduction of TA feasible. Ideal candidates may include monocular patients who would otherwise be rendered transiently blind by a block in the operative eye, markedly anticoagulated individuals, and those with other pronounced risk factors for needle-based techniques. Appropriate candidates are mature, cooperative patients who can constrain eye movements, focus on bright light, resist lid squeezing, and remain relatively still. TA is associated with more patient discomfort during surgery than other techniques.30 Inappropriate patient selection may lead to a session of “vocal local!” TA can be obtained via anesthetic drops or gels. Gels yield significantly greater levels of drug in the anterior chamber than equal doses of anesthetic drops.31 There are theoretical concerns of endophthalmitis with gelbased topical anesthetics as they may form a barrier to bactericidal agents, thus they should only be applied after

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antiseptic agents are instilled. Bactericidal preps should be preceded by anesthetic drops in order to prevent patient discomfort. Injection of 0.1 cc of 1% preservative-free lidocaine into the anterior chamber adds to the analgesic effects of topical anesthetics, but may have adverse effects on corneal endothelium.32 Monitored Anesthesia Care Eye surgery is often performed on the elderly and those with significant systemic comorbidities Perioperative care by anesthesiologists, particularly preoperative evaluation, is essential. Intravenous sedation is less predictable in the elderly. Surgery via TA may be more uncomfortable and patients may require more sedation. For both ethical and technical reasons the ophthalmologist’s attention must not be distracted from the microsurgical field.33 Several recent studies have shown intervention by anesthesia personnel is required in approximately 30 to 40% of cataract cases.34-36 Intraoperative medical issues are not predictable by preoperative criteria, thus one cannot discern which patients to monitor intraoperatively and which to disregard.37-38 A host of potential adverse events, including angina, arrhythmias, hypertension, apnea, hypoxia, hypercarbia, confusion, seizures and more, can occur. Personnel with airway and resuscitation skills must be immediately available. Mortality rates are lower when anesthesiologists direct Medicare patients’ care.39 At Bascom Palmer Eye Institute anesthesia staff are present for every case. MAC by anesthesia personnel is reasonable and justified and contributes to the quality of the ophthalmic surgery patient’s experience. General Anesthesia GA is most often reserved for pediatric patients and those adults who are unable to remain relatively still. Oculoplastic surgery, retina procedures and open globe injuries are also frequently done via GA. Patients with marked abnormalities of the orbit, staphylomata, extremely long eyes, gross infection and significant bleeding diathesis may not be suitable for regional anesthesia. Although endotracheal anesthesia is necessary for patients at significant risk of aspiration, the laryngeal mask airway (LMA) has been increasingly accepted for patients without risk factors for aspiration who are having eye surgery via GA.40 The LMA is safe and effective in this setting and confers the additional advantage of less increase in intraocular pressure upon insertion and removal than is encountered with laryngoscopy and endotracheal intubation.41 Similarly, there is less coughing on emergence and during recovery.42 For oculoplastic surgery, the FlexibleTM LMA can be positioned to allow superior access to facial and oral structures. Craniomandibulofacial dystoses, although rare in the general population, are more common in pediatric ophthalmic surgery patients. The LMA and the FastrachTM LMA are frequently used in case of difficult airway. Additional Resources for More Information 1. Ophthalmic Anesthesia Society 20th Annual Scientific Meeting - September, 2006 in Chicago, Illinois 2. ASA Workshops on Ophthalmic Regional Anesthesia 3. British Ophthalmic Anaesthesia Society Annual Conference - October, 2006 4. 14th Video-Conference Meeting: Anaesthesia for Ophthalmic Surgery February, 2006 in Middlesbrough, England

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References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. Miller-Meeks MJ, Bergstrom T, Karp KO. Prevalent attitudes regarding residency training in ocular anesthesia. Ophthalmology. 101(8):1353-1356; 1994 Schein OD, Katz J, Bass EB, et al. The value of routine preoperative medical testing before cataract surgery. N Engl J Med 342: 168, 2000. Katz J, Feldman MA, Bass EB, et al. Risks and benefits of anticoagulant and antiplatelet medication use before cataract surgery. Ophthalmology 110:1784, 2003 Fraunfelder FT, Scafidi AF. Possible adverse effects from topical ocular 10% phenylephrine. Am J Ophthalmol 85:447-453, 1978 Groudine SB, Hollinger I, Jones J, et al. New York State Guidelines on the topical use of phenylephrine in the operating room. Anesthesiology 92(3):859-864, 2000 Gild WM, Posner KL, Caplan RA, Cheney FW. Eye injuries associated with anesthesia. Anesthesiology 76:204-208, 1992 Korneef L. The architecture of the musculo-fibrous apparatus in the human orbit. Acta Morphol Neerl Scand 15:35-64, 1977 Ripart J, Lefrant J, de la Coussaye J, et al. Peribulbar versus retrobulbar anesthesia for ophthalmic surgery. Anesthesiology 94:56-62, 2001 Brown SM, Coats DK, Collins MLZ, et al. Second cluster of strabismus cases after periocular anesthesia without hyaluronidase. J Cataract Refract Surg 27:1876, 2001 Katsev DA, Drews RC, Rose BT: An anatomic study of retrobulbar needle path length. Ophthalmology 96:1221, 1989 Waller SG, Taboada J, O’Connor P: Retrobulbar anesthesia risk: Do sharp needles really perforate the eye more easily than blunt needles? Ophthalmology 100:506, 1993 Edge R, Navon S. Axial length and posterior staphyloma in Saudi Arabian cataract patients. Journal of Cataract and Refractive Surgery 25:91-95, 1999 Birch A, Evans M, Redembo E: The ultrasonic localization of retrobulbar needles during retrobulbar block. Ophthalmology 102:824, 1995 Vohra SB, Good PA. Altered globe dimensions of axial myopia as risk factors for penetrating ocular injury during peribulbar anesthesia. British Journal of Anaesthesia 85:242-243, 2000 Wittpenn JR, Rapoza P, Sternberg P, et al. Respiratory arrest after retrobulbar anesthesia. Ophthalmology 93:867-870, 1986 Hamilton RC, Gimbel HV, Strunin L. Regional anesthesia for 12,000 cataract extractions and intraocular lens implantation procedures. Can J Anaesth 35:615, 1988 Scott IU, McCabe CM, Flynn HW Jr, Gayer S, et al. Local anesthesia with intravenous sedation for surgical repair of selected open globe injuries. Am J Ophthalmol 134:707-711, 2002 Scott IU, Gayer S, Voo I, et al. Regional anesthesia with monitored anesthesia car for surgical repair of select open globe injuries. Ophthalmic Surg Lasers Imaging 36:122-128, 2005 Boscia F, La Tegola MG, Columbo G, et al. Combined topical anesthesia and sedation for open-globe injuries in selected patients. Ophthalmology 110:1555-1559, 2003 Niemi-Murola L, Krootila K, Kivisaari R, et al. Localization of local anesthetic solution by magnetic resonance imaging. Ophthalmology 111(2):342-347, 2004 Guise PA. Sub-Tenon Anesthesia. A prospective study of 6,000 blocks. Anesthesiology 98(4):964-968, 2003 Frieman BJ, Friedberg MA. Globe perforation associated with subtenon’s anesthesia. American Journal of Ophthalmology. 131:520-521, 2001 Olitsky SE, Juneja RG. Orbital haemorrhage after the administration of sub-Tenon’s infusion anaesthesia. Ophthalmic Surg Lasers 28:145-146, 1997 Jaycock PD, Mather CM, Ferris JD, et al. Rectus muscle trauma complicating sub-Tenon’s local anaesthesia. Eye 15:583-586, 2001 Spierer A, Schwalb E. superior oblique muscle paresis after sub-Tenon’s anesthesia for cataract surgery. J Cataract Refract Surg 25:144-145, 1999

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26. Dahlmann AH, Appaswamy S, Headon MP. Orbital cellulitis following sub-Tenon’s anaesthesia. Eye 16:200-201, 2002 27. Ruschen H, Bremner FD, Carr C. Complications after sub-Tenon’s eye block. Anesthesia and Analgesia 96:273-277, 2003 28. McNeela BJ, Kumar CM. Sub-Tenon’s block with an ultrashort cannula. J Cataract Refract Surg 30(4):858-862, 2004 29. Ripart J, Metge L, Prat-Pradal D, et al. Medial Canthus single-injection episcleral (sub-Tenon) anesthesia: computed tomography imaging. Anesthesia and Analgesia 87:42-45, 1998 30. Katz J, Feldman MA, Bass EB, et al. Injectable versus topical anesthesia for cataract surgery: Patient perceptions of pain and side effects. Ophthalmology 107(11):2054-2060, 2000 31. Bardocci A, Lofoco G, Perdicaro, et al. Lidocaine 2% gel versus lidocaine 4% unpreserved drops for topical anesthesia in cataract surgery: a randomized controlled trial. Ophthalmology 110(1):144-149, 2003 32. Eggeling P, Pleyer U, Hartman C, et al. Corneal endothelial toxicity of different lidocaine concentrations. J Cataract Refr Surg 26:1403-1408, 2000 33. Arbisser LB. MAC for cataracts: A question of ethics. Outpatient Surgery Magazine. March, 2003 34. Rosenfeld SL, Litinsky SM, Snyder DA, et al. Effectiveness of monitored anesthesia care in cataract surgery. Ophthalmology 106(7):1256-1260, 1999 35. Pecka SL, Dexter F. Anesthesia providers’ interventions during cataract extraction under monitored anesthesia care. JAANA 65(4):357-360, 1997 36. Romero Aroca P, Perena Soriano F, Salvat Serra M, et al. ¿Es necesaria la presencia del médico anestesista en la cirugía de la catarata? Arch Soc Esp Oftalmol 77:13-16, 2002 37. Katz J, Feldman MA, Bass EB, et al. Adverse intraoperative medical events and their association with management strategies in cataract surgery. Ophthalmology 108(10):1721-1726, 2001 38. Eke T, Thompson JR. The national survey of local anesthesia for ocular surgery. II. Safety profiles of local anesthesia techniques. Eye 13:196-204, 1999 39. Silber JH, Kennedy SK, Even-Shoshan O, et al. Anesthesiologist direction and patient outcomes. Anesthesiology 93:152-163, 2000 40. Wainwright AC: Positive pressure ventilation and the laryngeal mask airway in ophthalmic anaesthesia. Br J Anaesth 75:249, 1995 41. Duman A, Ogun CO, Okesli S. The effect on intraocular pressure of tracheal intubation without the use of muscle relaxants. Paediatric Anaesthesia 11(4):421-424, 2001 42. Thomson KD: The effect of the laryngeal mask airway on coughing after eye surgery under general anesthesia. Ophthalmic Surgery. 23(9):630-631, 1992

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