Ординатура / Офтальмология / Английские материалы / The Art and the Science of Cataract Surgery_Boyd, Barraquer_2000

PREPARATION, SEDATION AND ANESTHESIA

Preparation of Patient

Unless the patient is scheduled for general anesthesia or is likely to be operated under very heavy sedation (non-airway supported) it is unnecessary to keep these usually older, fragile patients fasting for a large number of hours. This only contributes to fatigue and anxiety. It is also contraindicated to have the patients remove all their clothes. This interferes with the patient's sense of privacy and contributes to further anxiety as to what is to come.

The patient is made comfortable in the holding area, where he or she is met by the attending nurse, who then explains what is going to transpire. Presurgical checks are conducted, and the nurse instills Neosinephrine 10% and tropicamide 1% two drops each in order to dilate the pupil and one drop of antibiotic and of Betadine solution, depending on the surgeon's preference. This subject is discussed in Chapter 4. Long acting pupillary dilating agents such as cyclopentolate, atropine, homatropine or scopolamine have no role in today`s small incision surgery.

The patient is then transported to another holding area in the operating room suite either by walking or on a lounge chair on wheels. There the patient is met by the anesthesiologist, who explains that an intravenous line will be started and administers sedative

agents which vary according to the anesthesiologist's and surgeon's choice. In the holding area, Jack Dodick, M.D. in New York, applies a prudent amount of ocular compression to the eye and orbit for 10-15 minutes. He finds this very beneficial in lowering the intraocular pressure. This maneuver lowers the volume of the fluid inside of the eye and orbits thereby leading to a hypotensive eye. This creates a more favorable surgical environment. This maneuver was previously done using Honan's ballon in conjunction with peribulbar or retrobulbar injection of local anesthetic, procedures no longer used in small incision cataract surgery. The patient is made comfortable in the reclining chair which is very much like a first class seat on an airplane that reclines in an almost 180 degree position. Other surgeons prefer to place the patient on an operating table specially adapted to their needs and whether they operate from above or on the side.

Sedation

What sedation to administer depends on the individual patient's emotional profile, which the surgeon should have detected during his preoperative evaluation. In most cases, 5 mg of Valium per mouth on arrival to the clinic leads to sufficient relaxation so that he or she feels comfortable during surgery. Dodick prefers for the anesthetist to administer a small dose, 1 mg, of Versed intravenously. Versed, like Valium, is a member of the benzodiazepine family, but it has a much

shorter half-life. Whereas valium takes up to 24 hours to be metabolized by the liver, Versed is totally out of the body in less than 2 hours. The patient is totally sedated for about 10 minutes and the patient is wide awake and alert after 10-15 minutes, which is the time the operation lasts. The drug is gone from the system within 2 hours. With valium, on the other hand, patients sometimes feel groggy for a day or two.

Pupillary Dilation

Pupillary dilation is critical to the success of ECCE, especially phacoemulsification. Cycloplegic/mydriatic drops, administered preoperatively, effectively dilate the pupil, while topical nonsteroidal antiinflammatory drops can help to maintain dilation during surgery. These medications are instilled topically at the time of preparation of the patient before entering the operating room.

ANESTHESIA

Topical

All patients have two or three drops of proparacaine or tetracaine instilled in the eye, regardless of the type of anesthesia the surgeon decides to use. One drop every minute x 3 is a standard protocol (Fig. 35).

Selection of Anesthetic Method

There are a variety of anesthetic methods known to all of you. We will list them here and proceed to identify those that no longer have a place in small incision cataract surgery. They are:

1) Blocks by Injection Anesthesia with Sharp Metal Needles

a)Retrobulbar: no longer used except in exceptional cases.

b)Peribulbar: no longer used.

c)Parabulbar: no longer used.

d)Van Lint, O'Brien, Nadbath for controlling lid contraction: no longer used.

e)Hyaluronidase: after many years of recommending its use, it has been finally shown that hyaluronidase is not an important factor in obtaining akinesia more promptly or having a more lasting effect.

2) SubTenon's with a Flexible Needle

This is a highly effective anesthesia mostly used in combination with topical anesthesia by surgeons who are either beginning or already are in the transition period of ECCE to phacoemulsification. This combination is also the procedure of choice by surgeons who perform extracapsular extraction or small incision manual extracapsular. Prospective, randomized studies have concluded that single-quadrant, direct subTenon`s injection of anesthetic is as rapid and effective as retrobulbar injection for cataract surgery (Figs. 33 and 34). It provides better anesthesia with comparable akinesia.

The most common complications are chemosis and subconjunctival hemorrhage, but no major complications are encountered. The dispersion of anesthetic fluid under Tenon's is effective enough to substantially diminish lid discomfort. For these reasons, Sub-Tenon's anesthesia using a flexible cannula has replaced retrobulbar and peribulbar except in very unusual cases.

Technique for Performing SubTenon's

When performing a Sub-Tenon's local anesthesia, 1.5 ml of lidocaine is injected. Under topical anesthesia, a small incision is made in the fused conjunctiva/Tenon's capsule 3 mm from the limbus (Fig. 33). If the surgeon is right handed, it is easier to perform the incision at the inner lower quadrant between the rectus muscles in the right eye and at the lower temporal quadrant in the left eye. If the surgeon is left handed, it would be the opposite. The surgical plane of Tenon's attachment to the sclera is carefully dissected and the cannula is advanced through this apperture (Fig. 34). It is very important that the cannula is always in sub-Tenon's plane. Otherwise, if it is only under the conjunctiva, the flushed anesthetic solution will backflush or will infiltrate all throughout the subconjunctival space, where it becomes ineffective and creates chemosis.

The cannula is advanced under Tenon's until the conjunctiva/Tenon's fits snugly over the hub of the 3 cc syringe. 1.5 cc of the local anesthetic is infused using the "bolus" technique. The anesthetic is infused quickly creating a gush of fluid that spreads throughout the retro and parabulbar spaces (Fig. 34).

Unassisted Topical Anesthesia

Most ophthalmic surgeons, when using unassisted topical anesthesia, in which only drops are administered, use it only when performing phacoemulsification and IOL implantation through a clear cornea tunnel incision. The increased acceptance of topical anesthesia is directly related to the somewhat

wider popularity of the clear corneal tunnel incision as first emphasized by I. Howard Fine, M.D., (Oregon, USA).

Most surgeons who use this incision now do it from the temporal side, which requires a series of readjustments in the operating room. This procedure requires the use of a foldable IOL. A corneal tunnel sutureless valve incision no larger than 3.0mmis recommended. Otherwise, corneal complicationsmay ariseandtheincisionwould not be self-sealing.

Advantages of Unassisted Topical

Anesthesia

This term refers to the use only of anesthetic drops to obtain sufficient anesthesia to perform the cataract operation. Edgardo Carreño, M.D., Professor of Ophthalmology at the Funcacion Los Andes, Santiago, Chile and a phacoemulsification expert, considers that the use of topical anesthesia using a clear corneal tunnel self-sealing valve incision is a significant advance in cataract surgery. With topical anesthesia, visual recovery is immediate. Other advantages as outlined by Carreño:

1)It prevents the well-known complications of retrobulbar and peribulbar injections

2)It lowers the time of operating room use thereby lowering costs.

3)There is no immediate postoperative ptosis, which with retrobulbar or peribulbar and Van-Lint-O'Brien infiltrations lasts from 6-8 hours due to temporary akinesia of the lids (as contrasted with the late postoperative ptosis which is related to the bridle suture on the superior rectus). It provides for immediate postoperative visual recovery which, again, is its main advantage.

DisadvantagesofUnassisted Topical Anesthesia

Many surgeons who have performed cataract surgery utilizing "unassisted" topical anesthesia, that is, topical drops alone, agree with Paul S. Koch, M.D., that pure, unassisted topical anesthesia is fairly disappointing. He estimates that one out of four patients have some sensation during the operation. Sometimes, patients feel pressure build up in the eye during injection of viscoelastic. Some feel iris manipulation. Others are aware of the sensation of the lens being implanted into the eye. Koch found that he felt uncomfortable operating on these people, because he never knew in advance who would be comfortable and who would not.

Other disadvantages and limitations as outlined by Carreño are:

1)Only a highly experienced surgeon should operate with topical anesthesia. The eyecanmove,whichmakestheoperationmore difficult. If the eye movement occurs while capsulorhexis is being done, an undesirable capsular tear may take place leading to failure of this important stage of the operation.

2)The most controversial argument against topical anesthesia is an intraoperative complication. Consequently,thesurgeonmust be highly skilled so as to:

a)expectasfewintraoperativecomplications as possible. b) be able to convert to another method of anesthesia during the intraoperative stage. Topical anesthesia by itself may be insufficient for the surgeon to adequately handle intraoperative complications.

3)Topical anesthesia is not indicated in

all patients. This is particularly true in anxious, stressed patients, people with hearing limitations, children and very young patients.

4) The presence of a very opaque cataract is a contraindication to the use of topical anesthesia (Fig. 1-B). This is because the surgeon depends on the patient's capacity to visually concentrate on the operating microscope light in order to avoid eye movement during the operation. If he/she cannot fixate well on the microscope light and maintain that fixation, the eye will move. This may lead to complications.

Inessence,adequateselectionofpatients is fundamental when considering the use of topical anesthesia.

The Anesthetic Procedure of

Choice

It is the general consensus today among surgeons experienced with phacoemulsification that a combination of topical anesthesia (proparacaine 1% or tetracaine 1%) and 0.5 cc of 1% unpreservedlidocaine irrigated into the anterior chamber through a 30-gauge cannula (Figs. 35 and 36) is the anesthetic procedure of choice for small incision cataract surgery, particularlyphacoemulsification. Thisimportant breakthrough in ophthalmic anesthesia was introduced by James Gills, M.D. in 1997.

Technique forIrrigation of Lidocaine

in AC

Dodick first makes a clear cornea incisionusing a2.7mmdiamondknife.Hebelieves that the non-preserved lidocaine irrigated into the anterior chamber anesthetizes the nerves of the iris and the ciliary body. The pressure waves that ensue during irrigation and aspiration in the midst of the phaco operation can sometimes impinge upon those nerve fibers and lead to discomfort. In addition, Dodickhas

observed that this anesthesia inside the eye helps dull the patient’s sensitivity to the bright light of the microscope by temporarily blocking some photoreceptor cells. The rest of the operation is continued through the same clear cornea incision.

Intraocular unpreserved lidocaine irrigated into the anterior chamber as outlined has been proven safe and convenient.

Eventhoughafewresearchers(i.e.Gillow et al, Boulton et al) have concluded that the routineuseofintracamerallidocaineasasupplement to topical anesthesia in routine phacoemulsification does not have a clinically useful role, these experiences constitute a significantminorityandarebasedonpostoperative questioning of patients concerning discomfort or by well documented trials but in medium

number of patients and by different surgeons. In papers published based on monitoring patient discomfort, not by a subjective questionaire, but by objectively measuring vital signs during surgery. the data support the conclusion that patients operated with anterior chamber irrigation of unpreserved lidocaine feel comfortable during the procedure, despite having had no intravenous sedation and regardlessofsexorageanddismissthesubjective nature of postoperative questioning patients concerning discomfort. In view of the small controversyexisting,wemustrelyontheproven extensive experience of well known, prestigious, cataract surgeons such as James Gills, M.D., and Paul Koch,M.D., herepresented.

An alternative technique for intracameral irrigation of 0.5 cc of 1% lidocaine is the

Figure 36: Use of Intracameral Anesthesia

After instilling anesthetic drops on the conjunctiva and cornea (Fig. 35) the surgeon enters the anterior chamber through the ancillary incision (I) (Fig. 41-A) using an insulin syringe with a 30 gauge cannula (C). This maneuver is

done with the aid of fine toothed forceps (F) in the contralateral side of the ancillary incision acting as counterpressure. One dose of 0.5 ml of 1% unpreserved lidocaine is irrigated into the anterior chamber. The preliminary marking of the main incision is shown in (A).

one proposed by Paul S. Koch, M.D (Fig. 36). He uses a 15º blade in his left hand and .12 forceps in the right hand. The blade is placed where he wants the sideport entry incision and the forceps 180º away from that, resting on the peripheral cornea (Fig. 36). The forceps are only pressed against the cornea. They do not grab it, because the purpose of the forceps is only to provide counter pressure for the incision. Thebladeisthenusedtomakeanincision approximately 1 mm wide and 1 mm long, beginning in the peripheral clear cornea.

That incision is completely comfortable, because it is no more than a corneal manipulation, and the cornea is still anesthetized from the original drops given in the holding unit.

Then,0.5ccof1%unpreservedlidocaine is irrigated into the anterior chamber through a

30-gauge cannula (Fig. 36). Most of the time, the patient does not feel anything, but sometimes, either because of intraocular pressure changesortheeffectofdirectflowontotheiris, the patient may feel a little discomfort. This is not a matter of concern because in a matter of seconds the discomfort dissapears.

Koch squirts the little extra lidocaine that remains in the syringe on the surface of the cornea,providingadditionaltopicaleffect. The eye is not paralyzed, and an occasional patient may move it, but this is not nearly the problem that it is with topical anesthesia. The lack of discomfortmakesitunnecessaryforthepatient to want to move the eye, and Koch as well as Gills have found that cooperation in keeping the eye still is excellent.

Injection of Viscoelastic

The eye anesthetizes quickly, and the anesthesia is very profound. Usually in less than 10 seconds, the eye is already anesthetized,andtheviscoelasticinjectionisperformed quite comfortably.

What Can be Done with the Combined Anesthesia

Because the combination of topical and intracameral irrigation anesthesia is so effective, the surgeon can perform cataract surgery, lens implantation, iris manipulation, and even vitrectomy if a complication arises usually without any further injection of anesthetic. If a patient does feel some discomfort, a second irrigation may be performed. Patients with mental retardation and those with deafness havebeensuccessfullyoperatedwiththisanesthetic combination as long as the surgeon takes the time to explain prior to surgery that he wanted them to look at the light and keep looking at the light.

Side Effects of the Combined

Anesthesia

Lidocaine has an effective duration of up to 4 hours. Patients may not see very well immediately after the operation, but then a few hours later the vision really improves. Koch has concluded that patients have a temporary, neuro-sensory, retinal blockade causing transientblurringofvisionfollowingtheoperation. He has postulated that the anesthetic may diffuse back to the retina and perhaps has a direct effect on the ganglion cells. Gills had a patient withanopenposteriorcapsulewhohadsignificant vision loss for about 24 hours after the

operation. This clinical observation may supportKoch'shypothesis,becauseintheabsence of a posterior capsule the lidocaine could diffuse back toward the retina that much more easily. As the lidocaine wears off, the visual acuity and contrast sensitivities recover.

How to Manage Patients Who Feel Pain and Discomfort

Ifthepatientcontinuestoblinkorsqueeze the eyelids following the combined topical and intracameral anesthesia, you can control this with the sub-Tenon's injection of lidocaine as illustrated in Figs. 33 and 34. The effect is almost instantaneous, and surgery can continue without delay.

PHOTOTOXICITY IN CATARACT SURGERY

Since all cataract surgery is done under the microscope, we should clarify here the practical and clinical aspects of light or phototoxicity from the surgical microscope. It has been demonstrated that in some patients andunderspecificcircumstances,toxicityfrom thelightofthemicroscopecanaffectthemacula. This is seen with fluorescein angiography, which shows an area of pigment abnormality usually below the fovea. The visual field in these patients shows that in this area there is severe to moderate phototoxic damage to the photoreceptors. Without these tests, phototoxicity can be difficult to determine and to see.

The major factors involved with phototoxicity are the time of exposure, the tilt and the illumination intensity. (It is important to realize how hard it is to get away from the macular area if we are centered over the pupil).

The microscope has three light sources: the two side lights and the coaxial beam. Each of these light sources produces a focal point of illumination on the retina. It is not the time length of the operation that is important. It is the time the light is focused on one particular area of the retina which is critical.

In addition, within the period which any one operation lasts, sequential light exposure tothesameretinalarea isadditive. Ifweturn on the light on one spot for three minutes, turn it off and then turn it on that same spot for another four minutes, the effects of those exposures are additive. If, in a certain patient and with a certain intensity of light from the microscope, we expose one macular area during three minutes, we may have no lesion whatsoever but if the total exposure extends to seven and a half to eight minutes, a lesion may occur. In the human eye, with the standard surgical microscopes on maximum intensity of light, it probably only takes four to eight minutes to produce a retinal lesion. Most phototoxic burns are seen in the inferior part of the fovea.

We should leave the light source on the lowest setting.

The potential for trouble related to phototoxicity in cataract surgery is not often recognized. Thepatientmayhave20/25vision postoperatively and still complain that he does not see adequately. Only after fluorescein angiography and a visual field can we then explain why these patients complain. Even the most experienced of us need to be aware of the potential for phototoxicity and take the steps to avoid it.

BIBLIOGRAPHY

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Boyd, BF: Significant developments in local anes- thesia.HighlightsofOphthalmol.Bi-MonthlyJour- nal, Vol. 23, Nº 6, 1995 Series, pp 55-62.

Carreño E.: Phacoemulsification Sub-3 technique. Guest Expert, Boyd’s BF., The Art and the Science of Cataract Surgery, Highlights of Ophthalmology, 2001.

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Gills JP., Cherchio M., Raanan MG.: Unpreserved lidocaine to control discomfort during cataract surgery using topical anesthesia. J Cataract Refract Surg. 1997; 23:545-550.

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