Approximately 27 million patients undergo surgery each year in the United States, and an estimated 8 million have known coronary artery disease (CAD) or risk factors for cardiovascular disease. A substantial number of all deaths in patients undergoing noncardiac surgery are caused by cardiovascular complications. It is estimated that almost 1 million patients will have perioperative cardiovascular complications. Approximately 50,000 of these patients will experience perioperative myocardial infarction (MI), and about 40% will die. The incidence of perioperative MI is increased 10- to 50-fold in patients who have previously experienced coronary events. When considering a patient for non-cardiac surgery, it is important to approximate the risk for postoperative cardiovascular complications. The preoperative evaluation is meant not to “clear” the patient for surgery but to identify obvious or hidden cardiovascular risk and therefore reduce the occurrence of complications.
In the following sections are some very common examples of patients whom a maxillofacial surgeon may see on a daily basis. This chapter is meant to clarify certain cardiovascular scenarios and provide recommendations on how to approach patients with common cardiovascular disorders.
Clinical Cases
Case 1
Mr. H. is a 68-year-old white man with diabetes, hypertension, dyslipidemia, and previous tobacco use. He suffered a small MI two years ago and occasionally has chest discomfort with exertion. Oropharyngeal cancer has recently been diagnosed and he is now scheduled to undergo maxillectomy. Does he need further evaluation before his elective surgery? What can be done to minimize his risk for perioperative complications?
Case 2
Mrs. W. is a 45-year-old African American woman. She has non-ischemic chronic heart failure (HF) with a left ventricular ejection fraction (LVEF) of 25%. She has been maintained on a stable regimen of a beta blocker, angiotensin converting enzyme inhibitor, spironolactone, and a diuretic and had an implantable cardioverter-defibrillator (ICD) placed 3 years ago. She has had no hospitalizations for HF in the past two years. On her way home from work one evening, she was struck head-on in a motor vehicle accident. She was rushed to the local trauma center and found to have extensive maxillofacial trauma. She needs to undergo semi-urgent surgery. How should her cardiac condition be managed?
Case 3
Mr. A. is a 75-year-old Asian-American being seen for preoperative evaluation. He is scheduled for a dental implant in one week. While auscultating his chest, you hear a murmur. When you question Mr. A. about this murmur, he produces an echocardiogram report revealing that he has moderate aortic stenosis. Should you proceed with surgery next week?
Etiology
Perioperative MI is a complex entity that can be precipitated by a number of different pathophysiologic mechanisms. The cardiovascular system of patients who undergo general anesthesia and noncardiac surgical procedures is subject to multiple strains and complications. Patients who were previously stable can decompensate postoperatively, thus leading to significant postoperative morbidity and mortality. Mechanisms by which patients may deteriorate include increases in myocardial oxygen consumption, alterations in coagulation that precipitate thrombosis, and changes in vascular tone and endothelial function. Furthermore, most postoperative MIs are associated with either no chest pain or atypical chest pain. This can be a result of pain medications, residual anesthesia, or other postoperative painful stimuli that may mask angina pectoris.
Most experts agree that the anesthesiologist should choose the type of anesthesia, but there can be risks involved with each type. General anesthesia has been shown to cause changes in arterial and central venous pressure, alter cardiac output, and contribute to the development of arrhythmias. Decreased systemic vascular resistance, a decline in myocardial contractility, a reduction in stroke volume, and an increase in myocardial irritability are all possible mechanisms for these cardiovascular shifts. Induction of general anesthesia lowers systemic arterial pressure by 20% to 30%, endotracheal intubation increases blood pressure by 20 to 30 mmHg, and agents such as nitric oxide lower cardiac output by 15%.
Nongeneral anesthesia can also play a role in cardiovascular compromise. Opioid-based drugs are widely used because of their cardiac safety profile, but increased doses may lead to respiratory depression and the need for mechanical ventilation. Postoperative weaning from mechanical ventilation is associated with myocardial ischemia. Although the use of fentanyl, sufentanil, or alfentanil usually causes less myocardial depression than inhaled anesthetics do, many of these intravenous agents still cause venodilation, which in turn may lead to reduced preload and a further decrease in cardiac output. Other sedatives, including propofol, may compromise cardiac contractility and increase afterload on the right ventricle.
There has been conflicting evidence surrounding the differences or decrease in cardiac risk when using general versus local anesthesia. Both epidural and spinal anesthesia may cause decreases in preload and afterload by sympathetic blockade. Many studies have reported no significant differences in complication rates for regional versus general anesthesia, but two studies have demonstrated lower rates of MI in patients who received regional or spinal anesthesia.
Thus, it is crucial to identify and optimize medical therapy in patients with chronic HF because such patients are extremely sensitive to these hemodynamic changes. Recognizing this condition before surgery and increasing preoperative volume status helps in applying the Frank-Starling principle, which can offset a potential decrease in cardiac output. Moreover, other inhalational and intravenous anesthetics, when combined with muscle relaxants, frequently sensitize the myocardium to circulating catecholamines, which along with the stress of the surgical procedure, often increases the risk for ventricular arrhythmias.
Etiology
Perioperative MI is a complex entity that can be precipitated by a number of different pathophysiologic mechanisms. The cardiovascular system of patients who undergo general anesthesia and noncardiac surgical procedures is subject to multiple strains and complications. Patients who were previously stable can decompensate postoperatively, thus leading to significant postoperative morbidity and mortality. Mechanisms by which patients may deteriorate include increases in myocardial oxygen consumption, alterations in coagulation that precipitate thrombosis, and changes in vascular tone and endothelial function. Furthermore, most postoperative MIs are associated with either no chest pain or atypical chest pain. This can be a result of pain medications, residual anesthesia, or other postoperative painful stimuli that may mask angina pectoris.
Most experts agree that the anesthesiologist should choose the type of anesthesia, but there can be risks involved with each type. General anesthesia has been shown to cause changes in arterial and central venous pressure, alter cardiac output, and contribute to the development of arrhythmias. Decreased systemic vascular resistance, a decline in myocardial contractility, a reduction in stroke volume, and an increase in myocardial irritability are all possible mechanisms for these cardiovascular shifts. Induction of general anesthesia lowers systemic arterial pressure by 20% to 30%, endotracheal intubation increases blood pressure by 20 to 30 mmHg, and agents such as nitric oxide lower cardiac output by 15%.
Nongeneral anesthesia can also play a role in cardiovascular compromise. Opioid-based drugs are widely used because of their cardiac safety profile, but increased doses may lead to respiratory depression and the need for mechanical ventilation. Postoperative weaning from mechanical ventilation is associated with myocardial ischemia. Although the use of fentanyl, sufentanil, or alfentanil usually causes less myocardial depression than inhaled anesthetics do, many of these intravenous agents still cause venodilation, which in turn may lead to reduced preload and a further decrease in cardiac output. Other sedatives, including propofol, may compromise cardiac contractility and increase afterload on the right ventricle.
There has been conflicting evidence surrounding the differences or decrease in cardiac risk when using general versus local anesthesia. Both epidural and spinal anesthesia may cause decreases in preload and afterload by sympathetic blockade. Many studies have reported no significant differences in complication rates for regional versus general anesthesia, but two studies have demonstrated lower rates of MI in patients who received regional or spinal anesthesia.
Thus, it is crucial to identify and optimize medical therapy in patients with chronic HF because such patients are extremely sensitive to these hemodynamic changes. Recognizing this condition before surgery and increasing preoperative volume status helps in applying the Frank-Starling principle, which can offset a potential decrease in cardiac output. Moreover, other inhalational and intravenous anesthetics, when combined with muscle relaxants, frequently sensitize the myocardium to circulating catecholamines, which along with the stress of the surgical procedure, often increases the risk for ventricular arrhythmias.
Approach To The Patient Undergoing Maxillofacial Surgery
Stepwise Approach
When planning surgery, it is important to approach the patient in a systematic fashion. The American College of Cardiology (ACC) and the American Heart Association (AHA) recommended a stepwise approach to cardiac evaluation in the 2007 Updated Guidelines on Perioperative Cardiovascular Evaluation for Noncardiac Surgery. One should evaluate a patient’s current medical conditions and risk-stratify, medically optimize, and monitor the patient perioperatively.
The first decision to consider is whether this is a surgery that can wait. If the answer is no, the surgery must proceed. The preoperative evaluation may need to be limited if the procedure is urgent. Rapid assessment of the 12-lead electrocardiogram (ECG), vital signs, volume status, hematocrit, electrolytes, renal function, and urinalysis should be performed. In this situation, a more complete assessment can be accomplished once the urgent surgery is completed.
If the surgery is elective and non-urgent, a stepwise approach to the patient should be pursued. The first step should be a thorough history. This will help stratify patients into low- or higher-surgical risk categories. The history should inquire about any past episodes of angina pectoris, MI, HF or HF symptoms, and symptomatic arrhythmias as well as whether the patient has a pacemaker or implantable cardiac defibrillator (ICD). Related illnesses such as diabetes mellitus, peripheral vascular disease, cerebrovascular disease, renal impairment, and chronic pulmonary disease should also be assessed and documented. If the patient has known CAD, a thorough assessment of any recent change in symptoms is essential. Precise doses of current medications and over-the-counter or herbal drugs are also extremely important.
Risk stratification includes assessment of the risk for complications associated with the individual patient and the patient’s co-morbid conditions and the risk for complications associated with the planned surgical procedure. Box 27-1 outlines symptoms or co-morbid conditions that make up the major-, intermediate- and low-risk patient categories.
Major
-
Unstable coronary syndromes
- •
Acute or recent myocardial infarction *
* The American College of Cardiology National Database Library defines recent MI as longer than 7 days but less than or equal to 1 month (30 days); acute MI is MI occurring within 7 days.
with evidence of important ischemic risk by clinical symptoms or noninvasive study
- •
Unstable or severe †
† May include “stable” angina in patients who are unusually sedentary.
angina (Canadian class III or IV) ‡
‡ Campeau L: Grading of angina pectoris, Circulation 54:522-523, 1976.
- •
-
Decompensated heart failure
-
Significant arrhythmias
- •
High-grade atrioventricular block
- •
Symptomatic ventricular arrhythmias in the presence of underlying heart disease
- •
Supraventricular arrhythmias with uncontrolled ventricular rate
- •
-
Severe valvular disease
Intermediate
-
Mild angina pectoris (Canadian class I or II)
-
Previous myocardial infarction by history or pathologic Q waves
-
Compensated or previous heart failure
-
Diabetes mellitus (particularly insulin dependent)
-
Renal insufficiency
Minor
-
Advanced age
-
Abnormal findings on electrocardiography (left ventricular hypertrophy, left bundle branch block, ST-T abnormalities)
-
Rhythm other than sinus (e.g., atrial fibrillation)
-
Low functional capacity (e.g., inability to climb one flight of stairs with a bag of groceries)
-
History of stroke
-
Uncontrolled systemic hypertension
Major risk is defined as patients with recent MI, unstable angina (defined as Canadian class III or IV), decompensated HF, significant arrhythmias, or severe valvular disease. Patients with major clinical predictors of increased risk may warrant further testing or intervention before surgery or at the least a delay in surgery until these symptoms can be adequately assessed.
Intermediate risk includes patients with previous MI by history or ECG, renal insufficiency, diabetes (especially insulin requiring), compensated HF, or mild angina (defined as Canadian class I or II). Intermediate-risk symptoms demand comprehensive questioning and careful evaluation regarding the patient’s functional status before further testing is needed.
Minor risk most often includes patients with advanced age, uncontrolled systemic hypertension, atrial fibrillation, low functional capacity, history of stroke, or findings on the ECG such as left ventricular hypertrophy, ST-T wave abnormalities, or left bundle branch block. These patients also need no further evaluation before surgery unless their functional capacity is very low.
Risk Stratification
Functional capacity is an extremely useful tool in assessing risk. A patient’s functional capacity can be illustrated in metabolic equivalents (METs), which are defined as the oxygen consumption of a 70-kg, 40-year-old man in a resting state. By asking simple, straightforward questions, one can ascertain a patient’s ability to perform daily activities, which can correlate with cardiovascular health ( Box 27-2 ). For example, an inability to walk or dress oneself would indicate very low functional capacity at around 1 MET, but scrubbing floors or playing golf may indicate higher functioning individuals. Patients who fall into the lower MET group may need further testing before surgery. An increased incidence of cardiac complications in non-cardiac surgery is directly related to poor functional capacity.
* Data from Hlatky MA, Boineau RE, Higginbotham MB, et al: A brief self-administered questionnaire to determine functional capacity (the Duke Activity Status Index), Am J Cardiol 64:651-654, 1989; Fletcher GF, Balady G, Froelicher VF, et al: Exercise standards. A statement for healthcare professionals from the American Heart Association, Circulation 91:580-615, 1995; from Eagle KA, Berger PB, Calkins H, et al: ACC/AHA guideline update for perioperative cardiovascular evaluation for noncardiac surgery-executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1996 Guidelines on Perioperative Cardiovascular Evaluation for Noncardiac Surgery), J Am Coll Cardiol 39:542-553, 2002.
1 MET
-
Can you take care of yourself?
-
Eat, dress, or use the toilet?
-
Walk indoors around the house?
-
Walk a block or two on level ground at 2 to 3 mph or 3.2 to 4.8 km/h?
-
Do light work around the house such as dusting or washing dishes?
4 METs
-
Can you climb a flight of stairs or walk up a hill?
-
Walk on level ground at 4 mph or 6.4 km/h?
-
Run a short distance?
-
Do heavy work around the house such as scrubbing floors or lifting or moving heavy furniture?
-
Participate in moderate recreational activities such as golf, bowling, dancing, doubles tennis, or throwing a baseball or football?
Greater than 10 METs
-
Can you participate in strenuous sports such as swimming, singles tennis, football, basketball, or skiing?
METs, metabolic equivalents.
When assessing a patient before surgery, it is also important to classify the type of surgery that will be performed as high-, intermediate-, or low-risk surgery. Box 27-3 lists several common surgeries and the type of risk with which they are associated. These are stratified in the following manner:
- 1
High risk involves any type of emergency surgery, aortic or major vascular surgery, peripheral vascular surgery, or a procedure defined as prolonged or associated with large fluid shifts. The cardiac risk reported for these surgeries is usually defined as being greater than 5%.
- 2
Intermediate risk carries a reported cardiac risk of less than 5% and includes head and neck surgery, carotid endarterectomy, orthopedic surgery, prostate surgery, and intraperitoneal and intrathoracic surgery.
- 3
Low-risk surgeries typically do not require any further testing before the procedure. Such surgeries include cataract surgery, breast surgery, and superficial and endoscopic procedures.
* Combined incidence of cardiac death and non-fatal myocardial infarction.
High (Reported Cardiac Risk Often Greater than 5%)
-
Emergency major operations, particularly in the elderly
-
Aortic and other major vascular surgery
-
Peripheral vascular surgery
-
Anticipated prolonged surgical procedures associated with large fluid shifts, blood loss, or both
Intermediate (Reported Cardiac Risk Generally Less than 5%)
-
Carotid endarterectomy surgery
-
Head and neck surgery
-
Intraperitoneal and intrathoracic surgery
-
Orthopedic surgery
-
Prostate surgery
Low †
† Does not generally require further preoperative cardiac testing.
(Reported Cardiac Risk Generally Less than 1%)
-
Endoscopic procedures
-
Superficial procedure
-
Cataract surgery
-
Breast surgery
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