Anesthesia and the Eye

From the 22nd Annual Scientific Meeting of the Ophthalmic Anesthesia Society,
jointly sponsored by the Cleveland Clinic Foundation and the Ophthalmic Anesthesia Society

Educational Objectives

   The goal of this program is to improve the efficiency of preoperative evaluations and the perioperative management of anticoagulant therapy in patients undergoing ophthalmic procedures.  After hearing and assimilating this program, the clinician will be better able to:

1.   Choose laboratory evaluations with the greatest significance for a patient’s management.

2.   Identify cardiovascular, pulmonary, and endocrine risk factors that require management or observation in a pa­tient scheduled for ophthalmic surgery.

3.   Recognize the factors that influence the pharmacokinetics of warfarin.

4.   Calculate a patient’s international normalized ratio (INR) and explain the importance of maintaining it within the therapeutic range.

5.   Evaluate the risks and benefits of discontinuing anticoagulation before ophthalmic surgery.

Faculty Disclosure

In adherence to ACCME Standards for Commercial Support, Audio-Digest requires all faculty and members of the planning committee to disclose relevant financial relationships within the past 12 months that might create any per­sonal conflicts of interest. Any identified conflicts were resolved to ensure that this educational activity promotes quality in health care and not a proprietary business or commercial interest. For this program, the faculty and the planning committee reported nothing to disclose.

Acknowledgments

This program was recorded at the 22nd Annual Scientific Meeting of the Ophthalmic Anesthesia Society, held Septem­ber 26-28, 2008, in Chicago, IL, and jointly sponsored by the Cleveland Clinic Foundation and the Ophthalmic Anes­thesia Society. The Audio-Digest Foundation thanks the speakers and the sponsors for their cooperation in the production of this program.

Preoperative Preparation for Ophthalmic Surgery

Marc Allan Feldman, MD, MHS, Head, Section of Anesthesia, Cole Eye Institute, Cleveland Clinic Founda­tion, Cleveland, OH

Defining risk: unacceptable  —  presence of condition indicating acute inpatient admission and treatment, or revers­ible condition that could result in perioperative complication

Results of multicenter study of 19,557 cataract procedures: patients randomized to one group with  preoperative electrocardiography (ECG) and blood testing, and other group without; perioperative data collected for 7 days; rate of adverse events 31.3/1000 in both groups

Adverse events studied: hypertension, hypotension, arrhythmias, myocardial ischemia or infarction, stroke, respira­tory failure, hospitalization, and death; >50% of all events hypertensive or bradycardic events

Elements of preoperative evaluation: medical history; record of allergies, including latex allergy; patient question­naire on day of evaluation or surgery helpful; look for conditions that might impair patient’s ability to lie still during surgeries requiring wakefulness; surgeons should know before surgery whether patient affected by de­mentia, deafness, or inability to understand English; restless legs syndrome may worsen under sedation, espe­cially with propofol infusion; administer ropinirole (Requip) or carbidopa-levodopa (Sinemet) 45-60 min before surgery; other potential issues include claustrophobia and obstructive sleep apnea

Physical examination: evaluate for cardiac or pulmonary decompensation, and positioning issues such as scoliosis, spondylosis, or orthopnea

Cardiovascular evaluation: determine whether surgery urgent (then “do the best you can”); ask whether patient has undergone coronary artery bypass grafting within last 5 yr; further cardiac work-up indicated if patient under­went coronary evaluation (including stress test) <2 yr ago, with detection of major risk predictors, or of inter­mediate risk factors with low functional capacity, or if noninvasive testing had “worrisome” results

Major risk predictors: recent (within 30 days) or ongoing myocardial infarction (MI); unstable or severe angina; decompensated heart failure; high-grade atrioventricular block; symptomatic arrhythmias with heart disease; uncontrolled arrhythmia (eg, atrial fibrillation >100 beats per minute [bpm]); or severe or symptomatic valvu­lar disease; if patient had recent MI, postpone surgery 4-6 wk; with stage III hypertension (systolic pressure consistently >180 mm Hg or diastolic pressure >110 mm Hg), postpone surgery until patient on antihyperten­sive therapy for few weeks; evaluate patient with valvular disease for repair or replacement before cataract sur­gery; stabilize symptomatic regurgitating valves; treat arrhythmias or conduction abnormalities as in nonsurgical patients; frequent premature ventricular contractions and asymptomatic nonsustained ventricular tachycardia not considered risk factors (Holter monitoring not necessary)

Pacemakers and defibrillators: considerations include bipolar or unipolar devices, relative distance from electro­cautery to pacemaker leads, and patient’s dependence on pacemaker; cautery used during most ophthalmic procedures will not interfere with pacemaker function; monitoring respiration with impedance plethysmogra­phy may cause certain pacemakers to behave as if patient exercising (may increase heart rate); in those cases, turn off respiratory rate monitor; general recommendations under optimal circumstances  —  know device; eval­uate device before and after surgery; determine patient’s underlying cardiac rhythm; check battery function; turn off rate-response mode during surgery; determine pacing threshold for pacemaker-dependent patients; turn off implantable cardioverter defibrillator immediately before surgery, and turn it back on immediately af­ter

Laboratory studies: based on history and physical examination; choose only tests that might change management; manage conditions found; ECG recommended if patient has new chest pain, exercise intolerance, palpitations, syncope, tachycardia, bradycardia, or irregular pulse on examination; if routine ECG not performed, check pulse periodically; check ECG for signs of acute ischemia or injury, malignant arrhythmias, heart block, new atrial fibrillation, or atrial fibrillation >100 bpm; serum electrolytes  —  indications include prolonged vomiting or diarrhea, poor oral intake, recent changes in diuretic management, and arrhythmia

Panic values: established by Society of Laboratory Medicine as guide for further follow-up; include sodium <120 mmol/L or >158 mmol/L; potassium <2.8 mmol/L or >6.2 mmol/L; serum urea nitrogen >100 mg/dL; glucose <50 mg/dL or >400 mg/dL; hematocrit <20% or >60% (correlates with hemoglobin <7 g/dL or >20 g/dL)

Pulmonary evaluation: determine whether patient can lie flat; assess for obstructive sleep apnea; encourage smoking cessation; prescribe bronchodilators, steroids, or antibiotics if necessary

Endocrine evaluation: diabetes  —  recommended blood glucose range, 150 mg/dL to 250 mg/dL; check for auto­nomic neuropathy; “stress-dose” steroids rarely indicated

Anticoagulation: weigh thrombotic against hemorrhagic risks; cessation of warfarin therapy not recommended

Ophthalmic evaluation: check visual acuity in both eyes; measure axial length; glaucoma raises risk for subcho­roidal hemorrhage

The Anticoagulated Patient and Ophthalmic Surgery

Gary L. Fanning, MD, Former Director of Anesthesiology and Medical Director, Hauser-Ross Eye Institute, Sycamore, IL

Common anticoagulants: warfarin, aspirin, ticlopidine (Ticlid), dipyridamole, and clopidogrel (Plavix)

Warfarin (Coumadin): indications include deep venous thrombosis (DVT), atrial fibrillation, and prosthetic heart valves; prevention of stroke or MI (less common)

Pharmacokinetics: inhibits reduction of vitamin K to vitamin K epoxide, leading to diminished production of vita­min K-dependent clotting factors (prothrombin and factors VII, IX, and X); may take 4 days after discontinua­tion of warfarin for international normalized ratio (INR) to return to normal; also interferes with production of anticoagulant proteins C, S, and Z, resulting in paradoxical procoagulant effect; S form of warfarin »5 times more potent than R form; rapidly absorbed; peak levels appear within »90 min of administration; 99% protein-bound; half-life 36 to 42 hr; mostly metabolized through hepatic P₄₅₀ system; drugs that enhance or inhibit P₄₅₀ enzymes change effectiveness of warfarin accordingly; other factors influencing pharmacokinetics  —  age (older patients need lower doses) and sex (women need less medication than men in all age groups); risks for complications increase with age; genetics  —  certain mutations increase or decrease warfarin sensitivity, result­ing in widely varying response among patients; environmental factors  —  drugs, diet, and disease; prolonged diarrhea may diminish gut bacteria producing vitamin K and thereby potentiate effect of warfarin; warfarin inhibitor  —  bosentan (treats pulmonary hypertension)

Effects on coagulation: measured in prothrombin time (PT); thromboplastins assessed according to international sensitivity index (ISI); permits comparisons between laboratories; INR calculated by dividing patient’s pro­thrombin time by prothrombin time of control sample, taken to power of ISI; example  —  if patient’s PT 24 sec, control sample PT 12 sec, and ISI 1, then INR = 2; if ISI 2, with other values same, then INR = 4; desired INR is 2 to 3 (3.5 INR units in some cases); no additional therapeutic benefit and increased risk for complications with INR >3.5; individuals on warfarin have »50% risk for mortality associated with intracranial hemorrhage; risk for warfarin-associated intracranial hemorrhage »0.47 per 100 yr of treatment, compared to 0.29 among patients not taking warfarin

Caveats: narrow therapeutic window; variable dose response; interacts with multiple drugs and environmental factors; difficult to find laboratory controls; good physician-patient and physician-physician communication essential

Antiplatelet drugs: aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), dipyridamole, and clopidogrel; indications  —  prevention of coronary events, stroke, and thromboembolism; pain relief (for NSAIDs); aspirin  — inhibits cyclooxygenase (COX)-1, which mediates thromboxane-induced platelet aggregation; aspirin destroys platelets’ ability to produce COX-1; effect lasts for 7 to 10 days (time required to produce new platelets); 81 mg/day sufficient for most individuals; clopidogrel and ticlopidine  —  block platelet receptors for adenosine di­phosphate (ADP; potent stimulator of platelet aggregation); patient must be off drug »7 days for complete rever­sal of effect

Dilemma of anticoagulant drugs: if continued, patient at risk for “disastrous” intraocular or retrobulbar hemor­rhage; if discontinued, patient at increased risk for stroke, MI, DVT, or pulmonary embolism

Evidence: in 2001 study, discontinuing anticoagulant for 4 to 6 days in patient with atrial fibrillation associated with risk for stroke of 0.012-0.3 (3 per 1000); risk slightly higher among patients with prosthetic heart valves; in other studies, discontinuing warfarin after DVT increased risk for new DVT 1% per day after 1 mo; drops to 0.2% per day within 2 to 3 mo and to 0.04% per day at >3 mo (“still fairly risky”); study involving 46 derma­tologic surgery patients showed lower risk for adverse events after withholding of anticoagulants, but study de­sign less rigorous; authors concluded that discontinuing anticoagulants potentially catastrophic, even fatal

Effects in ophthalmic patients: in study of 41 patients on warfarin who underwent 50 ophthalmic procedures (in­cluding 39 cataract procedures), immediate preoperative INR was 1.1 to 4.9; no hemorrhagic complications; however, study small and range of INR values wide; another study of 61 patients taking aspirin showed no dif­ference in postoperative outcomes and little difference in postoperative bleeding between patients who stayed on aspirin or discontinued it 2 to 5 days or 7 to 10 days preoperatively; in multicenter study of 1842 patients undergoing >2200 cataract procedures (53% on anticoagulants), only 2 cases of hyphema and 17 cases of mi­nor bleeding; in multicenter study including 19,000 patients (72% on no anticoagulant, 24% on aspirin, 4% on warfarin, and 0.4% on both), no significant differences in outcomes seen among those who remained on anti­coagulants, those who discontinued them, and those who never took them; in report of 2 patients on clopido­grel plus another anticoagulant who underwent vitreoretinal surgery, both sustained severe intraocular hemorrhages and bad visual outcomes; message  —  type of eye surgery has significance; author of study ad­vises patients on aspirin and clopidogrel to discontinue anticoagulation 1 wk before surgery; patients on only 1 anticoagulant not required to discontinue

Risks of anticoagulation and peribulbar block: in study of 1383 patients, 76 on warfarin; mild eyelid hemorrhage occurred in 55 (4%); no association with anticoagulant therapy

Sub-Tenon’s anesthesia: in 255 patients undergoing cataract surgery, including 75 controls, 65 patients on warfa­rin, 40 on clopidogrel, and 75 on aspirin, no sight-threatening hemorrhagic complications observed; no post­ponements or cancellations of surgery due to anesthetic complication; incidence of significant subconjunctival hemorrhage among control and aspirin groups, 20%, and nearly 40% in other anticoagulant groups

Glaucoma surgery: in study of 794 patients (50% taking warfarin or antiplatelet drugs), incidence of hemorrhagic complications 10% in anticoagulant group, compared to 4% in control group; of patients on warfarin, 23% ex­perienced complications, compared to 8% on antiplatelet drugs; 32% of patients who remained on warfarin at time of surgery had complications which compromised surgery; similar results obtained in patients undergoing trabeculectomy

Study conclusions: advisable to continue most antiplatelet drugs for cataract surgery, but discontinue clopidogrel 5 to 10 days before noncardiac procedures in patients at high risk for cardiac events (new recommendation); exception  —  if patient requires surgery within 6 wk of placement of bare metal coronary stent, or within 12 mo of placement of drug-eluting stent, continue aspirin and clopidogrel perioperatively

Speaker’s recommendations: exercise caution if patient on  >1 anticoagulant, especially if undergoing noncataract eye surgery; cataract surgery  —  do not discontinue warfarin, but determine patient’s INR during immediate peri­operative period

Risks of elevated INR: in study of 121 outpatients who had intracranial or subdural bleeding while on warfarin, el­evated INR was major risk factor for nontraumatic intracranial hemorrhage; other risk factors included age, history of cerebrovascular disease, prosthetic heart valve, and elevated INR; risk for intracranial hemorrhage increased dramatically with INR >4; authors concluded INR should be <4, and extreme caution necessary for use of warfarin in elderly patients;  when possible, ask primary care physician to measure INR 3 to 5 days be­fore surgery, then follow up with measurement on day of surgery; INR within therapeutic range may lower risk for hemorrhagic complications

Suggested Reading

Backer CL et al: Myocardial reinfarction following local anesthesia for ophthalmic surgery. Anesth Analg 59:257, 1980; Douketis JD et al: The perioperative management of antithrombotic therapy: American College of Chest Physicians Evidence-based Clinical Practice Guidelines (8th Edition). Chest 133:299S, 2008; du Breuil Al, Umland EM: Outpatient management of anticoagulation therapy. Am Fam Physician 75:1031, 2007; Eagel KA et al: ACC/AHA Guideline Update for Perioperative Cardiovascular Evaluation for Noncardiac Sur­gery—Executive Summary. Anesth Analg 94:1052, 2002; Gayer S, Zuleta J: Perioperative management of the elderly undergoing eye surgery. Clin Geriatr Med 24:687, 2008; Herbert EN et al: Haemorrhagic vitreoretinal complications associated with combined antiplatelet agents. Br J Ophthalmol 90:1209, 2006; Hirschman DR, Morby LJ: A study of the safety of continued anticoagulation for cataract surgery patients. Nurs Forum 41:30, 2006; Jacobs LG: Warfarin pharmacology, clinical management, and evaluation of hemorrhagic risk for the el­derly. Cardiol Clin 26:157, 2008; Jafri SM: Periprocedural thromboprophylaxis in patients receiving chronic anticoagulation therapy. Am Heart J 147:3, 2004; Kumar N et al: Sub-Tenon’s anesthesia with aspirin, warfa­rin, and clopidogrel. J Cataract Refract Surg 32:1022, 2006; Law SK et al: Hemorrhagic complications from glaucoma surgery in patients on anticoagulation therapy or antiplatelet therapy. Am J Ophthalmol 145:736, 2008; Sweitzer BJ: Preoperative medical testing and preparation for ophthalmic surgery. Ophthalmol Clin North Am 19:163, 2006.