The type of surgery, expected blood loss, duration of anesthesia, and anticipated fluid shifts each contribute to surgical stress. Surgical approaches in the same general category may have a broad range of risk (e.g., among intraperitoneal surgeries, the laparoscopic band surgery likely has lower risk than a complex open abdominal surgery). Procedures with prolonged anesthesia (especially >8 h) and cases with extensive fluid shifts or blood loss are higher risk for perioperative complications.
Functional Capacity/Exercise Tolerance
Clarifying an individual patient’s functional capacity is critical to estimating surgical risk and to decision-making regarding further evaluation. A metabolic equivalent (MET) is a measure of degree of oxygen uptake of sitting at rest and has been used in many studies to help assess functional capacity (Table 6.1) [3]. Patients who are able to achieve four METs without limiting cardiopulmonary symptoms can usually proceed to surgery without further cardiac evaluation. Self-reported reduced exercise tolerance (inability to walk four blocks or climb two flights of stairs) predicts perioperative complications [4].
Table 6.1
Examples of estimated metabolic equivalents
METs | Activity |
|---|---|
1–3 | Care of self (eating, dressing, using toilet) |
4 | Climbing a flight of stairs, walking up a hill, walking on level ground at 4 mph |
6 | Moderate recreational activity, e.g., dancing, doubles tennis, moderate cycling |
Estimation of Cardiac Risk
There are several clinical tools to estimate perioperative cardiovascular risk, though none have ideal predictive performance. These tools are helpful when used in combination with a traditional medical evaluation and clinical gestalt. When documenting and discussing risk with patients, avoid quoting exact percentage estimates from these tools; rather, indicating that a patient is at low, moderate, or high risk for cardiac complications is more useful (and accurate). Keep in mind that the specific cardiac complications predicted by these tools may be different. Two commonly used calculators include:
MICA / Gupta Perioperative Cardiac Risk Calculator
The MICA (perioperative myocardial infarction or cardiac arrest) risk calculator was created using the American College of Surgeons’ 2007 National Surgical Quality Improvement Program (NSQIP) database and evaluated over 200,000 surgical patients for perioperative cardiac complications [5]. The risk model was then validated, and the predictive performance surpassed the commonly used Revised Cardiac Risk Index (RCRI) risk calculator (below). Five major predictors for perioperative myocardial infarct or cardiac arrest were determined: type of surgery, functional status, American Society of Anesthesiologists class, elevated creatinine, and advanced age. The online calculator is available at: http://www.surgicalriskcalculator.com/miorcardiacarrest.
Revised Cardiac Risk Index
The Revised Cardiac Risk Index (Table 6.2) is an older, well-validated, and easy to use tool, though it may overstate risk in part because anesthesia and surgical techniques have improved since its publication [6]. Patients in the study were 50 years or older and underwent major noncardiac surgery. Note that the RCRI estimates risk of pulmonary edema and heart block, in addition to MI and cardiac arrest.
Table 6.2
Revised cardiac risk index
Risk factors (1 pt for each) | # Of risk factors | Risk class | % Major cardiac complications (95 % confidence interval) |
|---|---|---|---|
“High-risk” surgery | 0 | I | 0.4 (0.05–1.5) |
Intraperitoneal | 1 | II | 0.9 (0.3–2.1) |
Intrathoracic | 2 | III | 6.6 (3.9–10.3) |
Suprainguinal vascular | 3 or more | IV | 11 (5.8–18.4) |
History of myocardial ischemia (pathologic Q’s, angina, nitrates, prior MI, positive stress test) | |||
History of heart failure | Major cardiac complications = MI, pulmonary edema, cardiac arrest, complete heart block | ||
History of CVA or TIA | |||
Preoperative insulin use | |||
Creatinine > 2.0 | |||
Preoperative Cardiac Testing
ACC/AHA guidelines recommend the following preoperatively:
12-Lead Electrocardiogram
Do not obtain routine electrocardiogram (ECG) in asymptomatic patients undergoing low-risk surgical procedures.
It is reasonable to obtain an ECG (within 3 months of surgery) for patients with known coronary artery disease, significant arrhythmia, peripheral arterial disease, cerebrovascular disease, or significant structural heart disease, except for those undergoing low-risk surgery.
Consider ECG in patients without above conditions, but undergoing higher risk surgery.
ACC/AHA guidelines do not support routine ECG based on advanced age alone. However, we consider an ECG in patients age 70 and older in some clinical situations, because finding an abnormality may change our prediction of risk, and will provide a baseline to help interpret changes postoperatively, should the patient develop cardiac complications.
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