Tuesday, March 23, 2021

Basic MAC/Anesthesia for Cataract Surgery Case File

Posted By: Medical Group - 3/23/2021 Post Author : Medical Group Post Date : Tuesday, March 23, 2021 Post Time : 3/23/2021
Basic MAC/Anesthesia for Cataract Surgery Case File
Lydia Conlay, MD, PhD, MBA, Julia Pollock, MD, Mary Ann Vann, MD, Sheela Pai, MD, Eugene C. Toy, MD

Case 49
An 82-year-old woman presents for cataract surgery. She has a history of hypertension, and an MI some 10 years ago. She reports no change in her health recently, and her functional capacity is excellent for her age. She is an avid gardener. As is custom at your institution, this patient did not visit the preoperative clinic. The ophthalmologist did provided a recent note from the patient’s physician stating that her medical conditions were stable, and “clearing her for surgery.” Her ECG and laboratory tests from 3 months ago were attached to his note.

➤ What is this patient’s suitability for cataract surgery?

➤ What are the most likely complications which may be observed during the case?

➤ What factors influence the need for sedation?

ANSWERS TO CASE 49:
Basic MAC/Anesthesia for Cataract Surgery

Summary: An 82-year-old patient with stable medical conditions presents for cataract surgery.

➤ Suitability for surgery: This patient is stable, followed by her primary physician, and ready to proceed with monitored anesthesia care (MAC) for her cataract surgery.

➤ Most common complications: During a case performed under MAC, there is always the danger that patients will move inappropriately. During eye procedures, this is especially perilous because the procedure is performed using a microscope. The most likely medical events are hypertension, and an arrhythmia, usually bradycardia.

➤ Amount of sedation: The amount of sedation depends on the type of anesthesia for the eye, topical anesthesia versus an eye block, as well as the method of removing the cataract.


ANALYSIS

Objectives
1. Understand how the preparation of patients having cataract surgery differs from other surgical procedures.
2. Become familiar with the anesthetic techniques used for cataract surgery and many eye procedures.


Considerations
Since this patient’s medical condition is stable and she is followed by a primary physician, she is ready for cataract surgery. She does not need any additional medical testing prior to surgery, although it is helpful to have access to any tests which have been recently performed. In particular, a recent baseline ECG is helpful since arrhythmias may occur in eye surgery.

Once it is determined that the patient is ready for cataract surgery, a small intravenous is started, and standard monitors are placed. The need for sedation is determined by the type of anesthesia provided to the eye during the case. This patient’s cataract is suitable for PHACO extraction, and she is cooperative and able to lie still without the need for sedation. Thus, her surgery can be safely performed using topical anesthesia administered in the form of eye drops.


APPROACH TO
Basic MAC/Anesthesia for Cataract Surgery

DEFINITIONS
MONITORED ANESTHESIA CARE (MAC): The care of a patient by an anesthesiologist, during which time the patient is monitored, and sedative, hypnotic, opioid, or anxiolytic medications may be administered.

TOPICAL ANESTHESIA: Local anesthesia applied as drops or gels to the surface of the eye.

EYE BLOCK: Method of administering local anesthesia to the eye so as to block nerve conduction, both motor and sensory, to the eye.

RETROBULBAR BLOCK: Local anesthesia injected into the muscle cone behind the globe.

PERIBULBAR BLOCK: Local anesthesia injected outside the muscle cone.

SUB-TENONS BLOCK: Local anesthesia injected into the Tenons capsule below the surface of the globe.


CLINICAL APPROACH
Cataract extraction is the most common surgical procedure in the United States today. These procedures are done very quickly, and often, almost in an “assembly line” fashion. Since this type of surgery is so common, the costs of any associated care are multiplied many times over. In a study of over 18,000 patients, Schein et al demonstrated that preoperative testing did not change outcomes in patients undergoing cataract surgery under MAC anesthesia. However, this study cohort was associated with one significant caveat: all of the study subjects were followed by a primary physician for their medical conditions, and had received testing for these conditions when appropriate. So unlike all other surgical procedures, patients followed by a primary physician may undergo cataract extraction without further preoperative evaluation.

During the course of an eye operation, there are several reasons why a patient may benefit from the care of an anesthetist. The patient may be anxious, and require medication to calm or relax them so they can lie still for the procedure; he or she may need medication to treat pain or fright during the surgery; or the patient may experience arrhythmias, hypertension, or tachycardia necessitating a medical intervention.

It is imperative that the patient remain quiet, cooperative, and still during the procedure. In a recent review of closed malpractice insurance claims for MAC cases, 11% of claims involved injury due to movement or inadequate anesthesia during eye surgery. Elderly patients, especially those with medical conditions and ASA III or IV classification, made up a higher percentage of the MAC claims, but were no different from the population as a whole receiving other types of anesthesia. Eye procedures may also pose some additional risk, since the patient is draped around the head and neck making detection of any impairment in respiratory movements difficult, or even a buildup of carbon dioxide may occur under the drapes, which is more difficult to detect. For this reason, when available, measurement of end-tidal CO2 levels is desirable. Otherwise, standard monitors are all that are necessary for this type of case.

Most cataracts today are removed by PHACO emulsification. The cataract is broken into small pieces by ultrasound waves which are suctioned out through a cannula, requiring only very tiny incisions in the eye. The older technique of extracapsular cataract extraction removes the lens intact through a larger incision. The PHACO procedure is quicker and easier and allows more rapid recovery for the patient.

In many centers, cataract surgeries are now done under topical anesthesia, during which local anesthesia is administered via drops or gels to the surface of the eye. An additional intracameral injection of local anesthesia improves the quality of the anesthesia for the topicalized eye. The patient does not require sedation for the administration of topical anesthesia. However, the emulsification of the lens can cause images that may be frightening. Since the patient’s vision is intact, they may see the bright light of the microscope and the surgeon’s hands and instruments. They may also feel pain during placement of the speculum on the eyelids, iris manipulation, globe expansion by injection of solution into the eye, and introduction of the new lens. Since the patient’s extra-ocular movements are intact, they need to be sufficiently awake to cooperate with the surgeon’s instructions during the case.

Many older patients tolerate topical anesthesia for cataract surgery without any sedation. Education for the patient on what to expect during the procedure and careful patient selection results in greater success with topical anesthesia. After cataract surgery under topical anesthesia, patients may have their vision restored immediately, since taping and protective shielding of the eye is not always necessary.

Eye blocks provide anesthesia, analgesia, and motor blockade to the eye. Eye blocks are administered in the operating room as with any regional block, or they may be placed prior to the patient coming into the OR in a holding area or block room where the patient can be sedated and monitored consistent with the same standards applied in the operating room. Although these blocks can be done without sedation, more commonly, the patient is sedated briefly for block placement, often with a small dose of propofol. This practice of doing the block ahead of time ensures that the patient is well recovered from any sedation prior to the start of surgery.

For a retrobulbar block, local anesthesia is injected through the skin of the lower eyelid at the inferior aspect of the orbit, and into the muscle cone behind the globe. Entrance into the muscle cone is confirmed by downward movement of the eye, as the needle travels through the inferior rectus muscle.
After a negative aspiration, a small amount of local anesthesia is injected, and travels along the nerves and blood vessels to block nerve transmission at the ciliary ganglion.

The peribulbar technique is similar, but requires a larger volume of local anesthesia and a longer time to work since the drug needs to diffuse further to reach the ganglion. To perform a peribulbar block, the local anesthetic is injected outside the muscle cone, inferior and/or superior to the globe. It is important that the patient does not move during the injection of an eye block due to the proximity of the needle to nerves and blood vessels, as well as to the globe itself.

The sub-Tenons eye block is typically performed by the surgeon after prepping and draping the eye. A small incision is made on the surface of the globe under local anesthesia, then a small blunt cannula is inserted into this space and local anesthesia travels to the retrobulbar space via Tenons capsule.

A patient’s extra-ocular movements indicate the quality of all eye injection blocks. All blocks provide superior pain relief during and after cataract surgery as compared to topical anesthesia. Injection blocks prevent the occulocardiac reflex, which causes bradycardia during manipulation of the globe. Major complications that may occur after injection blocks include retrobulbar hemorrhage, globe perforation, and brain stem anesthesia if the local anesthesia tracks back along the nerves all the way to their origin.

There are several drugs commonly used for sedation during cataract surgery. Midazolam, a short-acting benzodiazepine, is useful for patients undergoing either topical anesthesia or injection blocks. It provides sedation, anxiolysis, and amnesia. A dose of 0.5 to 2 mg total should be administered slowly in elderly patients to avoid respiratory depression or over dosage. One must avoid oversedation since patient cooperation is necessary to prevent unintentional movement during surgery. Midazolam may cause prolonged psychomotor impairment in the elderly, especially those with pre-existing cognitive dysfunction.

Propofol, an induction agent, is used in smaller doses for sedation during administration of an eye block. The rapid onset and quick recovery profile allow the patient to be awake and cooperative prior to starting the surgery. Propofol can be administered in a dose from 0.3 to 1.0 mg/kg prior to the eye block. The patient will have sedation and amnesia for the eye block but little analgesia is expected. Movement during the block is frequent and sneezing may also occur. This technique is useful for the patient who wants to be “asleep” for the block.

Remifentanil, an opioid agonist, is the newest drug frequently administered to eye surgery patients. This drug displays both fast onset and rapid clearance by the plasma via ester hydrolysis. Given in a dose of 0.3 to 0.5 mcg/kg the patient feels no pain for the injection block. However, respiratory depression and chest wall rigidity can occur when remifentanil is bolused quickly. Also, like any other opiate, remifentanil is not a hypnotic, so patients frequently have recall for the block. Nausea and vomiting may occur, although rarely.

Sedative drugs are often used in combination. However, in the elderly these combinations may result in exaggerated sedation or respiratory depression. The Study of Medical Testing for Cataract Surgery found infrequent adverse medical events during cataract surgery in their study population. However, the
administration of a combination of drugs increased the odds ratio for an event significantly. The use of a short-acting hypnotic (such as propofol), combined with an opiate, a sedative, or both elevated the odds ratio for an adverse event from a low of 9.8 with a hypnotic alone to as high as 30.7 for a combination of all three categories. Fortunately, they did not identify any anesthetic regimen that increased the risk of death or unexpected hospitalization.

Patient satisfaction following eye surgery has been associated with specific factors such as surgeon skill and the length of operation. However, there is no evidence that any particular class of sedative or anesthetic improves satisfaction.

The postoperative course for the cataract surgery patient most often is very short and uneventful. The patients usually meet discharge criteria prior to leaving the OR, so it is customary for cataract patients to go directly to a phase 2 or step down unit rather than the main PACU. Since the injection block usually lasts much longer than the procedure, vision is limited and so the patient is instructed to wear an eye shield to protect the eye from injury. Significant postoperative pain is an unusual event. Pain in the cataract surgery patient that is unrelieved with an over-the-counter strength analgesic such as acetaminophen should be considered unusual and that patient should be seen by a physician. If nausea or vomiting occurs, they should be treated aggressively as both retching and vomiting can increase intra-ocular pressure and jeopardize the closure of the incisions.


Comprehension Questions

49.1. A 75-year-old man is being scheduled for an outpatient cataract extraction and lens placement. He is followed by his primary physician for coronary disease with congestive heart failure, which is stable. Which of the following tests are required prior to his anesthesia for cataract surgery?
    A. ECG
    B. Chest x-ray
    C. Hemoglobin
    D. Electrolytes
    E. No tests are required

49.2. Your patient expresses fear of the injection block for cataract surgery. Which drug or combination is most likely to be associated with recall of the block?
    A. Propofol
    B. Midazolam
    C. Remifentanil
    D. Midazolam and propofol

49.3. Which of these statements about topical anesthesia for cataract surgery is most accurate?
    A. Extra-ocular movements are a good way to check the quality of the block.
    B. Topical anesthesia renders the patient insensate during iris manipulation and lens placement.
    C. Patients cannot see instruments or light following topical anesthesia.
    D. Patients usually don’t require sedation for placement of the topical anesthetic.


ANSWERS
49.1. E. Patients who have stable medical conditions that are followed by a primary physician do not need additional testing prior to cataract surgery. An ECG is useful, especially if it is recent (within the last 6 months).

49.2. C. Remifentanil, an ultra short-acting opioid agonist, may allow recall of the injection block since it has no amnesic properties. During the block, the patient is analgesic, but not amnestic. He is aware of and remembers the block in many cases. Midazolam usually results in amnesia. Propofol administered prior to the block in small doses allows the patient to sleep through the block, and be unaware of its administration. One caution with propofol: a patient is more likely to move during the block placement.

49.3. D. Topical anesthesia is applied to the surface of the eye with drops or gels, providing less analgesia so a patient has more pain during the procedure as well as sensations of light and movement. The administration of the drops is sometimes associated with a burning sensation, but this does not usually require sedation. However, since there is no nerve block with topical anesthesia, movements of the extraocular muscles remain intact.


Clinical Pearls
➤ Elderly patients undergoing cataract surgery do not need additional preoperative testing as long as they are followed by a primary physician and receive care for any medical conditions.
➤ Monitored anesthesia care for the eye surgery patient varies greatly with the type of procedure, method of anesthesia for the eye, and the amount of pain or discomfort the patient may encounter.
➤ There are several methods to deliver anesthesia to the eye for cataract procedures. The patient’s sensations during cataract surgery may differ based on the type of block. Often eye blocks are administered by anesthesiologists; sometimes these are performed in the holding area.

References

Bhananker SM, Posner KL, Cheney FW, Caplar RA, Lee LA, Domino KB. Injury and liability associated with monitored anesthesia care: a closed claim analysis. Anesthesiology. 2006;104:228-234. 

Katz J, Feldman MA, Bass EB, Lubomski LH, et al. Adverse intraoperative medical events and their association with anesthesia management strategies in cataract surgery. Ophthalmology. 2001;108:1721-1726. 

Schein OD, Katz J, Bass EB, et al. The value of routine preoperative medical testing before cataract surgery. NEJM. 2000;342:168-175. 

Vann MA, Ogunnaike BO, Joshi GP. Sedation and anesthesia care for ophthalmologic surgery during local/regional anesthesia. Anesthesiology. 2007;107:502-508.

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