Perioperative Approach to the High-Risk Cardiac Patient

Ambulatory Surgery

A challenging triage decision is identifying which surgical patients are best cared for in hospital-based versus ambulatory settings. Adequate preoperative patient assessment is important in determining the appropriate surgical environment. Criteria associated with increased hospital admission after outpatient surgery include age 65 years or older, cardiac diagnoses, peripheral vascular disease, surgery lasting more than 2 hours, cerebrovascular disease, malignancy, HIV diagnosis, and general anesthesia. Data evaluating 5 years of common ambulatory-eligible surgical procedures (≈250,000 procedures) suggest the following risk factors are associated with an increase in morbidity and mortality: previous cardiac surgical intervention (percutaneous coronary intervention [PCI] or cardiac surgery), overweight or obese body mass index, chronic obstructive pulmonary disease, prior transient ischemic attack or stroke, hypertension, and prolonged surgical time ( Table 2.1 ). Patients with stable coronary artery disease (CAD) may not be at higher risk for perioperative complications after ambulatory surgery. Additionally, patients with cardiac pacemakers or implantable cardioverter-defibrillators can be evaluated for ambulatory surgical cases. Important information includes the type and function of these devices before proceeding with surgery. Similarly, it is appropriate to develop a definitive perioperative plan for the management of these devices (in terms of electromagnetic interference and follow-up) (see Chapter 4 ).

Critical Care Services

Triaging healthy and moribund patients away from critical care services (excluding palliative services and services to those who are brain dead) seems to be relatively straightforward. However, healthcare providers are challenged by a scarcity of intensive care unit (ICU) beds and an inherent cost in determining which patients will truly benefit from intensive care. Improving preoperative evidence-based strategies to identify which patients are at highest risk for postoperative complications may aid in determining patient need. Similarly, reducing hospital variability in managing these patients when they develop postoperative complications is also paramount to reducing morbidity and mortality. Approximately 30% of patients accepted for ICU services have cardiac diseases.

Observational studies also outline the potential benefit of ICU admission for older adult patients, suggesting a greater mortality reduction in older adult patients admitted to ICUs compared with younger patients. Based on these findings, intensivists may consider accepting even older adults who appear “well.”

Studies evaluating intraoperative events such as blood loss have shown a reduction in mortality rate with ICU admission. Intraoperative hemodynamics and blood loss should indeed influence ICU triage.

Triaging Patients With Coronary Stents for Noncardiac Surgery

One of the largest observational studies to date reported an approximately 23% rate of noncardiac surgery 1 year after PCI. Multiple guidelines report that elective surgery should be delayed for at least 4 to 6 weeks after bare-metal stent (BMS) placement and 6 to 12 months after drug-eluting stent (DES) placement, depending on the type of stent. The major challenge is determining the risk of perioperative surgical hemorrhage versus dual antiplatelet therapy (DAPT) interruption, and its relation to subsequent coronary stent thrombosis (see Chapter 3 ).

A safe time period for antiplatelet therapy interruption has yet to be clearly defined. Still, the continuation of aspirin is often recommended throughout the perioperative period. In the absence of guidelines supported by strong evidence, it may be important for the care team (primary care doctor, cardiologist, perioperative physicians) to collaborate and develop a definitive perioperative plan regarding continuation of DAPT, type and timing of stent placement, and disposition. Risk factors such as those mentioned may lead the perioperative team to suggest hospital-based surgery with the potential for an overnight stay and monitoring.

Coronary Artery Disease

Patients with or at risk for CAD present significant challenges to anesthesiologists in the perioperative period. As many as 5% of patients with CAD undergoing noncardiac surgery may develop cardiac complications. Risk factors include a history of ischemic heart disease, HF, stroke, diabetes mellitus, or renal insufficiency. Preoperative risk stratification is discussed in detail in Chapter 1 . Perioperative acute coronary events may range from myocardial ischemia or myocardial injury to myocardial infarction (MI). MI is universally defined as an elevation of cardiac biomarkers such as troponin, electrocardiographic (ECG) changes, new regional wall motion abnormalities seen on echocardiography, or coronary catheterization findings consistent with acute blockages.

The perioperative management of acute coronary syndrome (ACS), unstable angina, or acute MI presents a unique challenge because these patients under anesthesia or sedated postoperatively may not have the same signs and symptoms often seen in nonoperative patients. In fact, one large study found that 65% of patients with perioperative MI did not have symptoms. Thus the diagnosis is often confirmed only when clinical suspicion leads to further laboratory testing or investigation. When patients do complain of symptoms or clinical suspicion exists, clinicians should obtain a 12-lead ECG and serial cardiac biomarkers (e.g., troponin). Cardiology consultation for risk stratification, further testing, and therapy may be warranted.

Unlike nonsurgical patients with ACS or MI, care pathways for perioperative patients are not well studied. Unique concerns such as bleeding risk, surgical stressors, and perioperative physiologic changes make protocols for therapy very challenging. Management must be considered in context for each patient and the relative risk-to-benefit ratio of therapies applied uniquely.

Patients with ACS preoperatively must first be clinically stabilized. Therapies to augment cardiac output may be needed. Administration of β-adrenergic agonists (e.g., dobutamine [2.5–5 µg/kg per minute] or epinephrine [1–2 µg/min]) can be effective. Mechanical augmentation with devices such as an intraaortic balloon pump or axial-flow pumps may be considered in severe cases. Arrhythmias may occur and should be managed, but prophylactic lidocaine is not indicated.

Medical therapy with aspirin (162–325 mg) should be initiated if not contraindicated. Additional antiplatelet therapy with a P2Y ₁₂ receptor blocker is indicated in ACS, but may not be safe in the perioperative period. In patients with non–ST segment elevation ACS or MI (non-STEMI), systemic anticoagulation (i.e., heparin infusion) may be indicated, but the risk of surgical bleeding must be weighed against the risk of advancing ACS. Oxygen should be administered to all hypoxemic patients in concentrations needed to achieve normoxia. There are no data to support the use of oxygen in patients with MIs and normal oxygen saturation. Nitroglycerin may be administered to patients with angina, but should be avoided in patients with severe aortic stenosis (AS), right ventricular infarction, hypotension, or a history of phosphodiesterase inhibitor use in the previous 24 hours. Caution should also be used with this vasodilator in patients under neuraxial anesthesia because this could precipitate hypotension. Pain control with opioid analgesics may be considered; however, evidence suggests that morphine may be detrimental in patients with ACS. Proposed mechanisms include a morphine-induced impaired absorption or effectiveness of certain antiplatelet therapies. Statin therapy is indicated as soon as possible ( Box 2.1 ).

Box 2.1

Management of Acute Myocardial Infarction/Acute Coronary Syndrome

• Oxygen to maintain normoxia

• Aspirin 162–325 mg

• P2Y ₁₂ antiplatelet therapy

• Systemic anticoagulation (if no contraindication)

• Nitroglycerin for pain (if no contraindication)

• Opioid analgesics as needed

• β-Blockers if stable

• Statin therapy as soon as possible

β-Blocker therapy is perhaps the most controversial perioperative cardiac therapy. Although several studies have shown improved cardiac morbidity and mortality with the administration of perioperative β-blockers, concern for increased stroke risk and all-cause mortality has been noted. Current guidelines recommend that patients on chronic β-blocker therapy continue this perioperatively. In the setting of perioperative ACS, β-blocker therapy may decrease demand ischemia by improving oxygen supply and demand imbalance and is indicated in stable patients with ACS. The use of β-blockers in unstable patients or patients with acute cocaine intoxication should be cautioned.

Angiotensin-converting enzyme (ACE) inhibitor therapy should be considered in ACS after patients are stabilized. Angiotensin receptor blockers (ARBs) may be substituted in patients with HF with a left ventricular ejection fraction (LVEF) less than 40% or significant kidney dysfunction (creatinine >2.5 mg/dL for men or >2.0 mg/dL for women).

The optimum hemoglobin level in patients with perioperative ACS or MI is not known. Routine red blood cell transfusion in stable, nonbleeding patients may not be indicated when the hemoglobin is above 8 g/dL.

More aggressive interventional therapy with cardiac catheterization or fibrinolytics is dependent on the type of myocardial injury and risk of surgical bleeding. STEMI presents a high mortality rate if left untreated. In the nonsurgical setting, patient outcome is clearly related to time to reperfusion with a recommended “door to reperfusion time” of less than 90 minutes. The mainstays of reperfusion therapy include (1) cardiac catheterization and angioplasty or stent placement or (2) fibrinolytic therapy. Multiple studies have shown an improved survival rate, fewer bleeding complications, and reduced recurrent MI with catheterization and PCI. These interventions present significant concerns in the perioperative period because of an increased risk of bleeding.

Fibrinolytic therapy is often reserved for centers without PCI capabilities. It is recommended when symptom onset is less than 12 hours before presentation and PCI would not be available within 120 minutes. However, in the perioperative setting, fibrinolytics are almost universally contraindicated because of bleeding risk. PCI may be better suited for the treatment of perioperative STEMI. This is not without risk, however, because angioplasty or stent placement often requires DAPT and anticoagulation. Finally, emergent coronary artery bypass graft (CABG) surgery is an option, although this is associated with increased mortality rate when performed in the first 7 days after STEMI. Close consultation with cardiology and surgery is needed to weigh the risks and benefits of therapeutic options in perioperative STEMI patients.

Patients with NSTEMI may be managed more conservatively. However, in patients with a low cardiac output syndrome or arrhythmias, emergent PCI and reperfusion may be warranted. In stable NSTEMI patients, noninvasive studies may be the first approach. Again, close consultation with cardiology will aid in risk stratification and management.

Patients with significant chronic stable CAD also can present for noncardiac surgery. These patients may have either severe multivessel disease or left main CAD. Both portend an increased risk in the perioperative period. Significant left main disease or its equivalent is an indication for CABG. Occasionally, however, emergency noncardiac surgery may be needed before definitive CAD treatment. The risks and benefits of noncardiac surgery in these patients should be considered carefully in consultation with a cardiologist or cardiac surgeon.

Anesthetic management in these patients should be geared toward preventing, monitoring, and detecting myocardial ischemia. Careful monitoring of the ECG and hemodynamic status is important. Hemodynamic goals include a low-normal heart rate, normal to high BP, and normothermia. Left ventricular distention caused by fluid overload should be avoided because increased wall tension may increase myocardial oxygen demand and decrease myocardial perfusion. Additional monitoring may be considered, including perioperative TEE. Medications with more favorable hemodynamic profiles (e.g., etomidate) should be considered for anesthetic induction and maintenance. Pharmacologic therapy in the form of inotropic support may be needed. Mechanical support of the heart with an aortic balloon pump or axial flow devices may help maintain coronary perfusion in the setting of severe disease. Additional anesthetic considerations must be based on patient- and procedure-specific needs.

Hypertension

Hypertension is a common perioperative illness that has included roughly one third of all noncardiac surgery patients in the past. The new 2017 guidelines on hypertension define a normal BP as less than 120/80 mm Hg. Elevated BP is systolic BP between 120 and 129 mm Hg and diastolic BP less than 80 mm Hg. Stage I hypertension is now a systolic BP between 130 and 139 or diastolic BP between 80 and 89 mm Hg. Stage II hypertension is systolic BP greater than 140 and diastolic BP greater than 90 mm Hg. These new guidelines state that BP should be treated earlier to avoid complications, and with these new definitions, nearly half of the U.S. population will be considered to be hypertensive. Chronic hypertension is associated with an increased risk of stroke, heart disease, and renal failure.

Patients presenting on the day of surgery with high BP represent a clinical challenge. Safe systolic BP cutoffs for elective surgery are not well established. Uncontrolled hypertension is listed as a “minor” risk factor by the American College of Cardiology/American Heart Association (ACC/AHA), and it remains unclear if postponing surgery for uncontrolled hypertension improves patient outcome. Diastolic BP is better studied, with the preponderance of evidence suggesting safely proceeding with elective surgery if the diastolic BP is below 110 mm Hg. The relative risks and benefits of surgery in the setting of hypertension should be considered by the care team on a patient-by-patient basis.

Most preoperative antihypertensive medication can be continued in the perioperative period. Renin–angiotensin system blockers are associated with intraoperative hypotension and vasoplegia. Therefore many centers hold ACE inhibitors or ARBs for 24 hours before surgery, although this practice is controversial. A decrease in intraoperative hypotension is noted when these medications are held. On the other hand, failure to restart ACE inhibitor or ARBs has been associated with an increased 30-day mortality rate. The initiation of new medications immediately before surgery, such as β-blockade, may increase the risk of stroke or death. These medications should not be started preoperatively unless there is sufficient time for the patient to acclimate to the new medication before surgery. Patients taking β-blocker or sympatholytic agents should continue these medications perioperatively because acute withdrawal symptoms can occur if these agents are stopped.

Appropriate BP monitoring must be considered on a case-by-case basis with patient and surgical considerations in mind. Patients with chronic hypertension are at increased risk for hemodynamic lability. Anesthetic goals, therefore, include maintenance of hemodynamic stability within a range of BP. A reasonable goal is to maintain the BP within 20% of a patient's baseline. In addition, blunting of the sympathetic response to anesthetic (laryngoscopy) and surgical stimuli should be attempted with anesthetic agents or adjunct medications. Relative hypotension can be treated with vasopressors with the goal of maintaining BP within a predefined range.

Severe hypertension must be managed expeditiously if end-organ complications are to be avoided (i.e., neurologic, cardiac, renal). First-line therapy with intravenous antihypertensive medications (e.g., calcium channel blocker, nitrates, β-blockers) is recommended. Postoperative complications related to elevated BP, such as surgical bleeding, must also be considered when determining the level of urgency in BP therapy.

Hypotension unresponsive to standard therapy may require further investigation. Surgical bleeding or manipulation of the vasculature may induce low BP and communication with the surgical team is vital. Myocardial ischemia or arrhythmias should be considered. Less common, but an important consideration, is the vasoplegic syndrome (VS), which is defined as severe hypotension refractory to catecholamine therapy without clear cause. The incidence of VS is highest in cardiac surgical patients, but it may be seen in noncardiac surgery as well. Exogenous vasopressin (dose of 1–2 units) may improve hypotension when conventional therapy has failed (i.e., decreasing anesthetic agent, volume expansion, and routine vasopressors). Alternatively, methylene blue (MB) is a well-described treatment. It is believed to interfere with the nitric oxide–cyclic guanylate monophosphate pathway, decreasing its vasorelaxant effect on smooth muscle. A bolus dose of 1 to 2 mg/kg over 10 to 20 minutes followed by an infusion of 0.25 mg/kg per hour for 48 to 72 hours is typical. Recently, the use of hydroxocobalamin (vitamin B _12a ; dose of 125–250 mg) has been recommended in the occasional complex patient who does not respond to the above treatments.