Patients who are scheduled for surgery should have a preoperative evaluation by the surgeon and the anesthesiology, especially if general anesthesia is to be administered. These patients should have some baseline laboratory assessment that should include at a complete blood count. In patients with coexisting disease, an evaluation of other function is necessary. Patients over the age of 50 years should also have an ECG as should patients with heart disease. A preoperative pulmonary function assessment in patients with pulmonary disease is also warranted. These tests may determine postoperative care requirements and assess if preoperative treatment may reduce the perioperative risks. In this section a review of the current functional tests for cardiac and pulmonary function is presented. While in a high percentage of cases a cardiac or pulmonary consultant will be involved with the assessment of the patients, it is important for the otolaryngologist to understand some of the functional tests that will be ordered.
Assessment of Patient with Cardiac Disease
Patients over the age of 50 years and patients with cardiac disease should have an ECG prior to surgery. The preoperative ECG can provide important information on the status of the patient's cardiac and coronary circulation. Patients with abnormal Q waves seen on their ECG suggest a past myocardial infarction. These patients may be at increased risk of a perioperative cardiac event and may need further preoperative assessment. In fact about 30% of infarctions are silent and only detected on routine ECG, most notably in patients with diabetes or hypertension. In addition to the ECG, history taking can provide important information with regards to the patient's cardiac status. Assessing the patient's functional status by knowing the patient's exercise tolerance may determine the need for a cardiac evaluation. The information from cardiovascular testing may allow for optimization of preoperative medications, provide information on perioperative monitoring, or determine the need for coronary revascularization. There are several tests for assessing functional status (Table 5–5). These include the following:
Table 5–5. Sensitivity and Specificity of Noninvasive Testing. ||Download (.pdf)
Table 5–5. Sensitivity and Specificity of Noninvasive Testing.
|Test||Sensitivity (%)||Specificity (%)||Cost ($)|
|Ambulatory ECG (24 hours)||70||85||280|
|ECG stress test||65||80||450|
This ECG requires the placement of a Holter monitor, which records a continuous 12-lead ECG for 24 hours. This will detect arrhythmias and ischemic changes during a 24-hour period. This test will often require further testing, particularly if ischemic changes are noted.
Essentially, in an exercise ECG stress test where a patient is asked to exercise with the ECG, heart rate and blood pressure monitored. The presence of ECG signs of myocardial ischemia and/or the patient complaints of chest pain or dyspnea, and clinical signs of left ventricular dysfunction, are considered positive. Even more important is a decrease in blood pressure in response to exercise. This may be associated with global ventricular dysfunction. Syncope during the test also signifies decreased cardiac output. A positive exercise ECG stress test should alert the anesthesiologist that the patient is at risk for ischemia, within a wide range of heart rates, which may occur during surgery. These patients may require further workup and optimization of medical management.
The sensitivity and specificity of the noninvasive stress test can be increased by nuclear imaging techniques. Thallium-201 (Tl-201) is a radioactive compound that mimics potassium uptake by viable myocardial cells. The sensitivity of exercise Tl-201 imaging depends upon the imaging technique. Qualitative visual Tl-201 imaging has an average sensitivity of 84% and specificity of 87% for detecting coronary artery disease (CAD), although these numbers are improved with better imaging techniques. The drawback is that patients have to remain stationary for imaging to avoid artifact. Thallium defects are reported as normal, fixed, and/or reversible. Other measures of importance, particularly during stress Tl-201 imaging, are size of defect, lung uptake, and left ventricular cavity size. A large lung uptake of isotope has been associated with myocardial ischemia that produces left ventricular dysfunction that may result in pulmonary edema. The presence of a distended left ventricular cavity on the immediate post-stress image is another marker of severe CAD, presumably as a result of myocardial ischemia.
Thallium Imaging in Patients WHO Cannot Exercise
The use of pharmacologic agents to induce cardiac stress in patients who cannot exercise can also detect CAD. These agents can be divided into two categories: those that result in coronary artery vasodilatation, such as dipyridamole and adenosine, and those that increase myocardial oxygen demand, such as dobutamine and isoproterenol. Coronary artery vasodilators are useful for defining myocardium at risk by causing differential flows in normal coronary arteries compared with those with a stenosis. The use of dolbutamine is an alternative method of increasing myocardial oxygen demand without exercise. The goal is to increase heart rate and blood pressure.
The use of echocardiography for preoperative cardiac evaluation has increased in the last few years. Left ventricular function, pulmonary vascular pressures, and valvular competence can be evaluated. In most cases, a transthoracic approach has been used. Transesophageal echocardiography may provide better measurement of valvular abnormalities and left ventricular function. Echocardiography can also be performed with exercise, and in patients unable to exercise, dolbutamine has been used to mimic the stress effects of exercise.
Coronary angiography has been called the gold standard for defining coronary anatomy. In addition, angiography also can assess valvular function and hemodynamic indices, including ventricular pressure and gradients across valves. In most cases, angiography is performed after a positive stress test to determine if coronary revascularization will improve cardiac function and reduce perioperative cardiac morbidity after noncardiac surgery. One major difference between stress tests described previously and coronary angiography is that the latter provides the clinician with anatomic, not functional, information. It is also an expensive test with potential complications.
Patient with Drug-Eluting Stents (DES)
In the last several years, percutaneous vascular interventions have replaced open surgical procedures (coronary artery bypass graft [CABG]) in a number of situations. One such situation is percutaneous placement of DES for coronary revascularization in patients with CAD. DES, unlike their counterparts, the bare metal stents (BMS), are coated with slow-release chemicals that prevent thrombus formation with the help of antiplatelet drugs such as clopidogrel. As the number of patients with DES who present for head and neck surgery increases, it is imperative that surgeons and anesthesiologists be aware of guidelines for stopping antiplatelet medications. The current recommendation for patients with DES is that elective surgery should be postponed if the duration between stent placement and noncardiac surgery is less than 6 months. For semi-emergent procedures, both aspirin and clopidogrel should be continued during surgery unless clearly contraindicated by the nature of the surgery. If the risk of bleeding is high, then modification of antiplatelet medications should be considered on a case-by-case basis.
Patients with Pacemakers and Aicds
With the advances in pacemaker technology, the placement of pacemakers in patients with both cardiac conduction defects and arrhythmias has dramatically increased. Hence some basic knowledge of pacemakers must be known. In addition to patients with pacemakers, some patients who present for surgery may have automated implantable cardioverter defibrillators (AICDs). Both groups of patients benefit from a careful preoperative evaluation and device interrogation by a cardiologist specializing in electrophysiology. It is important to know the type of the device; in the case of the pacemaker, the configuration should be known and then also the reaction of either device to “inhibition” by placing a magnet over the implanted device. Most of the problems encountered with pacemakers and AICD devices are due to electrocautey. Several measures can be made to avoid potential adverse effects. These include the use of bipolar cautery. If unipolar cautery is needed, then the grounding pad should be placed away from the pacemaker and close to the operative site. It is recommended that electrocautery not be used at a distance less than 15 cm from the pacemaker or AICD device; if this is unavoidable, then use of cautery with short bursts and long pauses will reduce adverse events. The pacemaker may be programmed to an asynchronous mode by a magnet or by a programmer. The magnet will place the pacemaker in a backup-pacing mode. Reprogramming of the device should be instituted after the surgery.
Patients with Drug-Eluting Stents
In the last few years, percutaneous coronary intervention by placement of coronary stents has surpassed CABG for revascularization due to CAD. This is due primarily to the introduction of DES. In the past, patients with multi-vessel CAD requiring revascularization would often undergo CABG surgery instead of stent placement because of concerns regarding re-stenosis with BMS. Nevertheless, patients with DES merit special consideration if they are scheduled for surgery. Because of the risk of thrombus formation during the period of re-endothelialization of the stent, antiplatelet drugs are given particularly in the first 6 months to prevent thrombus formation. Aspirin and clopidogrel are the two most common drugs used. In most patients with DES, antiplatelet drugs should be used in the first 6 months, and stopping these medications puts patients at risk for thrombus formation in the stents. Hence, in patients with a DES, a preoperative cardiology consultation is essential. Elective surgery should be postponed if the duration between DES placement and noncardiac surgery is less than 6 months. For semi-emergent procedures, both aspirin and clopidogrel should be continued during surgery unless clearly contraindicated by the nature of the surgery. If the risk of bleeding is high, then modification of antiplatelet medications should be considered on a case-by-case basis.
Preoperative Pulmonary Evaluation
Patients scheduled for head and neck surgery may present with coexisting pulmonary diseases. For patients with acute pulmonary disease scheduled for elective surgery, the surgery may be postponed until the pulmonary disease resolves. Postoperative pulmonary complications include atelectasis, pneumonia, respiratory failure, and exacerbation of chronic pulmonary disease. Patients with chronic pulmonary disease may merit from a preoperative pulmonary workup that includes an arterial blood gas, chest X-ray, and pulmonary function tests. The presence of pulmonary disease may increase perioperative morbidity and mortality. Preoperative pulmonary function tests measure the severity of lung disease, measure the efficacy of bronchodilator therapy to improve the pulmonary function, and can predict the need for the patient for postoperative mechanical ventilation.
In general, disease of the pulmonary system may be classified as obstructive or restrictive.
Obstructive Pulmonary Diseases
Obstructive pulmonary disease includes asthma, emphysema, chronic bronchitis, bronchiectasis, and bronchiolitis. These disorders are characterized by an increase in expiratory airflow resistance that results in an increase in the work of breathing. The most typical finding noted on pulmonary function tests is that both forced expiratory volume in 1 second (FEV1) and the FEV1/FVC (forced vital capacity) ratio are less than 70% of the predicted values. The expiratory airflow resistance results in air trapping. In addition, the residual volume (RV) and the total lung capacity (TLC) are increased. Wheezing is a common clinical finding and represents turbulent airflow. In mild obstructive disease, wheezing may be absent but can be elicited by prolonged exhalation.
Restrictive Pulmonary Diseases
Restrictive lung diseases may be acute or chronic intrinsic disorders that include pulmonary edema, ARDS, infectious pneumonia, or the interstitials lung diseases. Restrictive pulmonary disease may also represent extrinsic disorders involving the pleura, chest wall, diaphragm, or neuromuscular function.
The hallmark of this group of disorders is decreased lung compliance that increases the work of breathing due to a characteristic rapid-shallow breathing pattern. Lung volumes are typically reduced as well as the FEV1 and the FVC. There is a normal FEV1/FVC ratio. The expiratory flow rates are unchanged.
Management of Patients with Chronic Anticoagulation
As noted above, some patients who present for elective surgery often require chronic anticoagulation for conditions such as venous thromboembolism, mechanical valve implants, or chronic atrial fibrillation. The management of these patients requires careful consideration. Common medications used include vitamin K antagonists such as Coumadin and antiplatelet agents such as aspirin and clopidogrel. For patients undergoing a major surgical or invasive procedure, if the intent is to eliminate any effect of antithrombotic therapy, it should be stopped at a time before the procedure. Coumadin (warfarin) should be stopped approximately 5 days if the patient's INR is maintained between 2 and 3, with the goal of bringing the INR to 1.5 prior to surgery. If the INR persists between 1.8 or higher, then the option of administering a small dose (1 mg, subcutaneously) of vitamin K is an option for antagonism of anticoagulation. If the INR is maintained at greater than 3.0, then Coumadin should be stopped 10 days prior to surgery. In patients in whom there is concern for thrombus formation if the vitamin K antagonist is stopped, then “bridging therapy” with lower molecular weight Heparin given via subcutaneous means or unfractionated heparin given intravenously, can be used as bridging therapy.
In patients receiving an antiplatelet drug, clopidogrel, medication should be stopped 7–10 days prior to surgery. In patients who are receiving antiplatelet drugs alone, bridging anticoagulation is not typically administered.