Ординатура / Офтальмология / Английские материалы / Glaucoma Surgery_Trope_2005

of glaucoma medications with general anesthetics should be considered. Complications such as tachycardia, extra systoles, hypertension, and syncope have been reported in patients on therapy with topical epinephrine (6,7). Special precautions should also be taken with patients on chronic acetazolamide therapy, as patients may be hypokalemic and hyponatremic and therefore at risk of significant arrhythmias especially under general anesthesia.

. Preanesthetic assessment with an anesthesiologist or a member of the anesthesia care team is advisable. This evaluation should include: a review of the patient’s medical history, a decision regarding further laboratory tests or consultations, development of an anesthetic plan, and discussion with the patient.

. The role of pre-operative blood tests and electrocardiogram on post-operative outcome is controversial. Evidence from a large, multi-centre trial reported no benefit of pre-operative tests on post-operative outcome (8 10). Our pre-operative testing and consultation protocol for patients scheduled for glaucoma surgery in Toronto is guided by each patient’s particular anesthetic risk provided by the patient’s medical history, that is, if under 65 with no history of heart, respiratory, or other problems, routine x-ray chest and electrocardiogram are not done.

. The risks associated with anesthesia and the procedure itself should be carefully discussed with the patient and detailed informed consent should be completed.

Guidelines to encourage consistency of care and to minimize disruption to patients have been published by the British Ophthalmic Anesthesia Society, specifically addressing pre-operative management of patients with cardiovascular disease (8).

Adequate pre-operative evaluation is a medical, ethical, and legal duty of the ophthalmic medical care team.

3.GENERAL ANESTHESIA

Many ophthalmic procedures including filtration surgery traditionally performed under general anesthesia (GA) are now routinely performed under topical anesthesia with monitored anesthesia care. There are, however, occasions when local anesthesia is not appropriate and GA is still the best option. Although a discussion on the details of general anesthetic technique and medications are beyond the scope of this chapter, we will briefly describe the indications, contraindications, risks, and goals of GA.

Indications for GA include:

. Inability of the patient to cooperate with monitored local anesthesia care (e.g., children, adults with mental or psychological deficits, nystagmus, general movement disorders, excessive anxiety or claustrophobia, tremor, inability to lie supine).

. Surgeons or patient preference.

. Surgical field not amenable to regional, local, or topical anesthesia.

. Regional block technically difficult or contraindicated (e.g., large globe from myopia or congenital glaucoma, coagulopathy).

. Allergy or sensitivity to topical anesthesia.

. Following intrathecal or intravascular injection of local anesthetic.

. Previous retrobulbar hemorrhage.

General anesthesia should be avoided in the following cases:

. Patients with Marfan’s syndrome as they have a high prevalence of cardiovascular and pulmonary abnormalities (11).

. Myotonic dystrophy patients as they may develop significant bradycardia and respiratory complications (12).

. Patients with previous severe reactions to general anesthesia or a family history of malignant hyperthermia.

It is prudent to avoid general anesthesia in patients with severe cardiovascular or pulmonary disease, and those who are particularly prone to post-operative nausea and vomiting.

Ocular complications of GA include:

. Retinal or optic nerve ischemia from profound hypotony (rare) (13).

. Retinal or suprachoroidal hemorrhages due to vomiting and straining on the endotracheal tube. These are of importance in filtration surgery.

. Exposure keratitis in the fellow eye (incidence as high as 44%) (14).

4.LOCAL ANESTHESIA FOR GLAUCOMA SURGERY

4.1.Monitored Anesthesia Care with Local Anesthesia

In Toronto, virtually all filtration surgery is done under local anesthesia with monitored anesthesia care (MAC) utilizing a respiratory therapist under the supervision of an anesthesiologist to monitor the patient. The patient should ideally be awake or rousable during the procedure and able to communicate.

The level of monitoring required during local anesthesia depends on the anesthetic technique and the medical condition of the patient. Appropriate facilities for monitoring in the post-operative period must be available.

4.1.1.Intravenous Medications

An intravenous ultra short hypnotic such as propofol and very small doses of a short-acting narcotic such as alfentanyl, remifentanyl, fentanyl, or sufentanyl can be combined to accomplish most of the goals of MAC (15). Propofol provides sedation, decreased awareness, antiemesis (counteracting the pro-emetic effects of the narcotic), and amnesia. The narcotic provides a brief period of intense analgesia. This combination yields cardiopulmonary stability during stress and painful stimuli and return to baseline mental status within 10 min. Intravenous benzodiazepines such as midazolam can be used as an alternative anesthetic providing adequate sedation for patients who require anxiolysis or a small amount of sedation after the application of topical anesthesia.

4.1.2.Technique

At the University Health Network, Toronto, intravenous sedation is, virtually, always used in conjunction with topical anesthesia for glaucoma surgery. Our sedation protocol includes a combination of:

. Fentanyl 1 2 mg/kg I.V. (1 or 2 bolus depending on each patient).

Doses should be individualized. Patients generally do not need any further sedation and are ready for discharge when they leave the recovery room.

4.1.3.Adverse Effects

. Sudden movement and restlessness.

. Airway obstruction.

. Lack of response to command and mild stimulation.

. Induction of anesthesia.

4.2.Local Anesthesia

Local anesthesia is the procedure of choice for most anterior segment ophthalmic surgeries. The use of local anesthesia in United Kingdom has risen from around 20% in 1991 (16,17) to 86% in 1997 (18).

4.2.1.Advantages

. Less post-operative nausea and vomiting.

. Greater cardiopulmonary stability.

. Morbidity and mortality lower than with GA.

. Quick return to ambulation.

. Prolonged post-operative analgesia.

. Cost.

Local anesthesia includes:

. Retrobulbar anesthesia.

. Peribulbar anesthesia.

. Sub-Tenon’s or subconjunctival anesthesia.

. Topical and peribulbar anesthesia.

. Topical and intraocular anesthesia.

. Topical anesthesia.

In this chapter, only the most frequently used anesthesia techniques for filtration and Seton surgery are described including retrobulbar, sub-Tenon’s, and topical anesthesia with lidocaine jelly.

Ophthalmic regional anesthesia can be nonakinetic and akinetic. Akinetic blocks include retrobulbar, peribulbar, and combined retro/peribulbar techniques (19 23). Motor, sensory, and autonomic fibers are all blocked, resulting in regional motor paralysis and anesthesia.

4.3.Local Anesthetics

Clinicians who use local anesthetics must be familiar with three different groups: short-acting local anesthetics (20 45 min), including procaine and chlorprocaine; inter- mediate-acting anesthetics (60 120 min, longer with epinephrine), including lidocaine (xylocaine) and mepivacaine; and long-acting anesthetics (400 450 min or longer), including bupivacaine, etidocaine, and ropivacaine (24,25) (Table 3.2).

4.4.Retrobulbar Anesthesia

4.4.1.Technique

. For retrobulbar anesthesia, light general sedation and analgesia should be started before the retrobulbar is started. It is important that the patient remains cooperative during the retrobulbar. After the retrobulbar, more sedation can be supplied.

. A 1:1 mixture of lidocaine (2%, 1.5 mL) without epinephrine and bupivacaine (0.5%, 1.5 mL) should be used, with or without hyaluronidase (5 U/mL). There is poor evidence that adding hyaluronidase increases the effectiveness of these blocks at producing akinesia (26). We do not use hyaluronidase in our unit.

. A maximum of 3 mL retrobulbar injection is administered with the globe in primary position preferably via a short blunt 25 27-gauge (31 mm) needle on a 5 10 mL syringe. This provides consistent tactile feedback for both insertion of the needle and injection of the anesthetic, which in turn, provides reliable and safe blocks. Several techniques for the administration of retrobulbar block have been described, however, no single method has established a striking advantage in safety or efficacy. We recommend an entry site through the lower lid at the junction of the lateral and middle third of the inferior orbital rim with the eye in the primary position with the needle initially directed parallel to the floor of the orbit aimed at the opposite mandibulary process.

. It is very important to feel the lower border of the globe through the lid prior to needle insertion. The globe size is determined and only then the needle inserted 1 2 mm below the lowest edge of the globe. Once passed the equator the needle can be tilted 208 with the tip towards superior orbit to facilitate entry to the muscle cone. A slight “give” from the inferior rectus can sometimes be felt. The hub of the needle should not go beyond the inferior orbital rim. Any pain reported by the patient may signal contact with the sclera and should prompt partial withdrawal and redirection of the needle.

. After aspiration to rule out intravascular placement, 1 3 mL of anesthetic solution is injected slowly (1 mL/10 s) (27). It is important not to deliver a large bolus into the muscle cone, as the increased pressure around an atrophic glaucomatous nerve can damage it. There should be little resistance to injection.

. Fullness and mild ptosis of the upper lid will be evident towards the end of the injection. The tension in the orbit should be monitored manually. On no account

should pressure be applied to the glaucomatous eye to disperse the anesthetic. Pressure from a Honan’s balloon with orbital pressure from the injection bolus can cause dangerous reduction in optic nerve head perfusion possibly leading to “wipe out” of remaining field.

. On withdrawal, orbicularis akinesia is achieved with injection of 1.5 mL of the same anesthetic solution slowly (1 mL/s) anterior to the septum orbitale.

Supplementary injections may be needed in 10% of cases. It takes around 10 min for most retrobulbar injections to exert their maximal effect.

Evaluation of the block involves:

. Paralysis in all positions of gaze and ptosis help you to decide whether there is adequate anesthesia.

If there is excessive movement or if more than two muscles are still active at 10 min, a further 1.0 mL of the anesthetic mixture should be given in the same manner. Some activity of the superior oblique persists after the recti are completely blocked, probably from incomplete spread of the anesthetic to the superonasal/posterior aspect of the orbit where cranial nerve IV supplies the superior oblique (28).

4.4.2.Complications

As the retrobulbar technique involves blind insertion of a needle into a space occupied by a number of neural and vascular structures, significant complications can and do threaten the patient’s vision or life. Complications can be divided into systemic and ocular.

Systemic Complications. The systemic toxicity of local anesthetics on the central nervous and cardiovascular systems are often due to inadvertent intravascular or subarachnoid injection of the drug via the sheaths of the optic nerve or via the superior orbital fissure, with immediate transit via the bloodstream to brain or heart, or due to systemic absorption of an excess dose of the drug. This can result in brainstem anesthesia (incidence as high as 0.79%), respiratory depression, apnea, and even death (25,29 31).

The development of toxic blood levels depends, to some degree, on the total dose, location of the block, the addition of epinephrine to the anesthetic, and the skill of the physician administering the anesthetic. Within the central nervous system, toxicity is a spectrum, extending from “excitation” to convulsions. This can serve as a warning of impending local anesthetic-induced cardiovascular collapse, characterized by profound hypotension, cardiac arrhytmias, and even death (32). It is therefore crucial that resuscitation equipment be on hand when this form of anesthesia is used. Also an experienced member of the anesthetic team should be available on short notice if retrobulbar anesthesia is to be performed. It is important to remember the maximum dosage for each anesthetic when considering local anesthesia. Table 3.3 shows the maximum dosage for local anesthetics.

Ocular Complications. Rare but serious complications including amaurosis, akinesia, retinal vascular occlusion, scleral perforation, sight-threatening retrobulbar hemorrhage (incidence of 1 5%), and even “ocular explosion” (35 37) have all been reported (38 40). Post-operative ptosis, diplopia, and transient loss of vision in both eyes have also been described. Although these are less serious and transient, they are disturbing to patient and physician (41,42).

Methods to reduce complications include:

. Using a short needle with a blunted tip.

. Aspirating the syringe prior to injection.

Table 3.3 Maximum Doses for Local Anesthetics (Illustrated in the Case of a 70 kg Patient) (24,33,34)

. Reducing the bolus volume.

. Reducing the force with which the local anesthetic is injected.

In Toronto, we never use retrobulbar blocks for trabeculectomy surgery, but we do use them in selected Seton cases.

4.5.Subconjunctival/Sub-Tenon’s Anesthesia

4.5.1.Introduction

Sub-Tenon’s local anesthesia, an alternate to retrobulbar anesthesia, has the advantage of being performed under direct observation potentially reducing the numerous complications associated with retrobulbar anesthesia (43 49). Parabulbar block, pinpoint anesthesia, single quadrant injection, episcleral block, and subconjunctival injection are different names or modifications of this technique (50 53). A recent survey of the members of United Kingdom and Ireland Cataract and Refractive Society (UKISCRS) suggests that the sub-Tenon’s block is now practiced in 51% units (23). This suggests that large numbers of surgeons still use retrobulbar or general anesthesia, methods we stopped using many years ago.

4.5.2.Advantages

. Provides prolonged anesthesia and adequate akinesia for filtration surgery.

. Smaller volume of local anesthetic is required compared with retrobulbar block.

. No risk of retrobulbar hemorrhage and minimizing the risk of ocular perforation.

. Reduced surgical time. No need to wait for the retrobulbar to work.

. Excellent patient and surgeons acceptance of the technique.

. Allows the surgeons to check for conjunctival mobility in filtration and Seton surgery in cases of re-operation as the infiltration of anesthetic fluid separates Tenon’s capsule and conjunctiva from episclera.

. Easy and safe anesthetic technique not only for trabeculectomy (49,54) but also for cataract surgery (46,55,56).

4.5.3.Technique

There are many variations of this block but they have similar principles. The techniques differ in access to the sub-Tenon’s space, cannula used, local anesthetic agent, volume and the use of adjuvant.

Our technique (49) involves the following steps:

. Insertion of tetracaine eyedrops 5 min before prepping and draping and one drop before the anesthetic injection followed by insertion of the lid speculum.

. For virtually painless anesthesia place a tetracaine soaked cotton bud tip on the proposed injection site for 3 5 min prior to injecting subconjunctival lidocaine.

. The most commonly used agent is 2% lidocaine without epinephrine. With the patient looking down, 0.5 1 cc of 2% lidocaine is injected under direct vision into the sub-Tenon’s or subconjunctival space utilizing the operating microscope via a 30-gauge needle (with a length of 0.5 in.) 8 mm from the limbus to avoid buttonholing the surgical area. With a fornix-based flap insert the needle 3 4 mm from the limbus outside the area operation site. Insert enough anesthetic to elevate the conjunctiva over the planned operation site.

. It is essential to ensure that the needle tip is visualized by the surgeon throughout the procedure; this avoids the possibility of scleral perforation. Excellent globe anesthesia for trabeculectomy is usually provided by 0.25 0.5 mL, but larger volumes (using cannulae) are required if akinesia is required (4 5 mL). Akinesia is not a prerequisite in our hands.

. Prior to final conjunctival closure, a further injection of anesthetic is administered into the conjunctival wound edges. This considerably reduces closure discomfort.

Different sub-Tenon’s anesthetic techniques have been described as follows:

. Fukasaku reported rapid, complete anesthesia with no akinesia utilizing placement of a specially designed curved 24-gauge blunt, metal cannula through an incision in conjunctiva and Tenon’s capsule 8 12 mm posterior to the limbus in the superotemporal quadrant. The cannula is introduced into the subTenon’s space and advanced posteriorly along the eye wall to its fullest extent and 1 mL of 2% lidocaine is infused. As the incision is made far from the limbus, this technique is used by some during limbal-based filtration surgery (51).

. Another technique described by Greenbaum involves performing an incision 2 mm behind the limbus followed by sub-Tenon’s infusion of anesthetic through a specially designed, flexible cannula (50). This conjunctival limbal incision can be eventually enlarged to incorporate a fornix-based conjunctival flap.

Cannulae for sub-Tenon’s anesthesia are either made of metal or plastic. Metal cannulae come in various sizes ranging from 19 to 23 gauges. The selection of a cannula depends on the availability and the preference of the surgeon and anesthetist. SubTenon’s anesthesia with a retained polyethylene catheter has been described for surgery of long duration (57).

Access to sub-Tenon’s space has been described from the superotemporal quadrant (51), medial canthus (52), and via inferonasal quadrant dissection (58).

4.5.4.Complications

. Pain during injection (reported in up to 44% of patients) (53,59).

. Subconjunctival hemorrhage (incidence: 20 100%) (49,53).

. Trauma by metal cannula to inferior and medial rectus muscles leading to fibrosis and diplopia (61).

Other blocks not involving blind use of sharp needles include intracameral, deep fornix nerve block, and various combinations of two or more of these. These are usually performed by surgeons only and do not provide akinesia.

4.5.5.Recommendation

We recommend subconjunctival placement of local anesthetic. This works well, raises the conjunctiva, is safe (as long as the needle tip is visualized), and effectively controls pain during surgery (49).

4.6.Topical Anesthesia with Unpreserved Lidocaine 2% Jelly

4.6.1.Introduction

Topical jelly anesthesia has been used by us for over 5 years for patients needing filtration surgery (62). Lidocaine 2% jelly is a widely used agent for topical anesthesia in urogenital, laryngotracheal, and even skin anesthesia and has recently been described in cataract, trabeculectomy, and phacotrabeculectomy surgery (63 65). Recent evidence suggests that topical anesthesia with lidocaine 2% jelly is a safe and effective alternative for clear cornea cataract surgery (66), trabeculectomy (62), and phacotrabeculectomy, even without systemic sedation (67).

4.6.2.Advantages

. Pain control equal to sub-Tenon’s anesthesia (62).

. Provides adequate anesthesia and patient comfort (65 68).

. Excellent patient and surgeon acceptance (62).

. Compared with regional anesthetic techniques such as peribulbar anesthesia, this topical approach does not increase vitreous pressure and there is no effect on the optic nerve perfusion.

. Post-operative recovery is quick and post-operative pain is minimal.

. No subconjunctival hemorrhage. Eye look is cosmetically better.

. Promotes efficient use of operating time (62).

. Preserved ocular motility can be used to optimize the wound access.

. The gel formulation has an increased contact time with the ocular surface, providing prolonged release of lidocaine, thus creating a sustained effect.

We conducted a prospective randomized clinical trial comparing lidocaine 2% jelly vs. sub-Tenon’s injection in 59 trabeculectomy patients (62). Anesthesia with lidocaine 2% jelly was not associated with any significant complications. For trabeculectomy surgery, 2% jelly was found to be as effective as sub-Tenon’s anesthesia. In addition, it

(37%; range: 22 63%) according to a survey conducted by David Learning in 1998 (20). Topical anesthesia for ophthalmologic surgery has been successfully used by different authors for cataract surgery (69 71), trabeculectomy (62,72,73), vitrectomy (74), and phaco-trabeculectomy surgery (67,75). We find it possible to perform Seton surgery with topical jelly, but suggest addition of subconjunctival anesthesia for routine cases. A modified topical anesthesia technique has also been described for Ahmed valve placement surgery (Ayala R. Seven easy steps allow Ahmed glaucoma valve implantation under modified topical anesthesia. Ocular Surgery News 2003).

4.6.3.Disadvantages

. Slightly sticky jelly covering the surgical field.

. Possible increased expense.

4.6.4.Technique of Topical Jelly Anesthesia

. Lidocaine 2% jelly, 0.2 cc, is instilled into the conjunctival fornices 5 min before surgery. Use a 5 cc syringe with a size 20 angiocath on its end. The angiocath facilitiates application of the jelly.

. The Lidocaine jelly is directed over the operation site and cornea at the start of surgery and supplemented during surgery as required.

. Prior to final conjunctival closure, a further application of jelly must be administered to the edges of the open conjunctival wound to reduce pain.

4.7.Topical Anesthesia with Eye Drops

Topical anesthesia with eyedrops alone has been reported to be a safe and effective alternative for trabeculectomy surgery (72,73).

4.7.1.Technique

For topical anesthesia administration with eyedrops, use preservative-free single-dose unit (minims) of tetracaine containing 0.5 mL. For each case, the entire contents of a single unit should used and administered 5 10 min prior to surgery. One drop more should be additionally administered after draping the patient just before start of surgery and during the procedure as required (73).

4.7.2.Disadvantages of Local Drops

. Need for administration of several doses prior and during surgery.

. Short anesthetic effect without elimination of ocular movement.

. Potential for cumulative corneal toxicity.

5.CONCLUSION

Subconjunctival and, more recently, topical jelly anesthesia are rapidly replacing older forms of anesthesia for filtration surgery.

ACKNOWLEDGMENTS

The authors acknowledge the support of Dr. Frances Chung from the Department of Anesthesia, Toronto Western Hospital, University Health Network.

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