Perioperative Transesophageal Echocardiography

From near the time of its introduction in 1980, two-dimensional transesophageal echocardiography (TEE) has been employed by anesthesiologists to monitor patients in the operating room. TEE provides direct visual information about ventricular filling 1 and performance and is also a sensitive monitor for detection of myocardial ischemia 2. With the advent of Doppler color flow imaging, rapid assessment of valvular function and cardiac flow patterns became possible and led to widespread use of TEE to improve surgical outcome during cardiac valve replacement and repair 3,4 and correction of congenital defects 5,6. However, as documented in the three case reports 7-9 in this issue of Anesthesia & Analgesia, TEE is capable of providing a wide range of precise information about cardiac structure and function in the perioperative period, which greatly exceeds that which is available from other monitoring modalities commonly employed by anesthesiologists. Sophisticated echocardiographic equipment is already in place in many operating rooms, and many anesthesiologists are interested in using this equipment. As a result, some anesthesiologists find themselves in a new role as cardiac diagnosticians. With this new role come new responsibilities, which require collaboration, completeness, and competence on the part of the anesthesiologist-echocardiographer. The case report by Swenson and Bailey 7 describes a 37-yr-old woman who suffered an acute left middle cerebral artery stroke and then the sudden onset of a cold pulseless leg. General anesthesia was induced for an emergency femoral embolectomy, and intraoperative TEE was performed to search for a cardiac source of embolism. A definitive source of embolism was discovered, a left atrial myxoma, which was resected during the same anesthetic. In this case, TEE was undertaken as part of the sequential diagnostic evaluation of this patient, which occurred during general anesthesia for emergency surgery. The authors appropriately emphasize the need for immediate collaboration with cardiologists and surgeons, as well as consultation with family members, prior to the major decision to proceed directly with curative cardiac surgery. The next case report, by Brooker et al. 8, presents a different perspective on the diagnostic role of TEE. Their patient was undergoing general anesthesia for thrombectomy and possible revascularization of an occluded popliteal artery. Angiography had disclosed a femoral artery aneurysm, the presumed source of embolism in this case. Intraoperative hypoxemia and hypotension did not respond to the usual treatment, and, rather than place a pulmonary artery catheter to evaluate cardiac preload and ventricular function, the authors chose TEE. Echocardiographic monitoring provided the answer to their question and guided the specific treatment of the cardiac and pulmonary problems faced by the authors. However, Brooker et al. made another serendipitous diagnosis during the TEE examination--a 2-cm left atrial myxoma! Not only did the echocardiographic examination fulfill its monitoring role in this instance, but it also allowed the authors to make an important, additional diagnostic observation. Had these authors not performed a complete examination with TEE, but instead sought only the transgastric short-axis view to "monitor" the left ventricle, the diagnosis of atrial myxoma would have been missed. The third case report, by Jacka and Oxorn 9, provides an example of the diagnostic power of TEE in the critical care setting. This patient had dyspnea and peripheral edema, and a ventilation/perfusion scan suggested massive right pulmonary artery embolism. Hypoxemic respiratory failure ensued, requiring mechanical ventilation. Attempts to float a pulmonary artery catheter were unsuccessful because the catheter would not pass beyond the right ventricle. Pulmonary angiography suggested extrinsic compression of the main pulmonary artery, and a computed tomography scan demonstrated contained rupture of an ascending aortic aneurysm. Finally, TEE examination confirmed the presence of the aortic aneurysm and revealed paradoxical right-to-left shunting through a patent foramen ovale. The authors present this case as an unusual cause of proximal pulmonary artery obstruction which mimicked massive pulmonary embolism. They emphasize the diagnostic role of TEE in this critical care setting, not only to confirm the primary diagnosis, but also to provide a clear pathophysiologic explanation for the severe hypoxemia caused by an anatomic right-to-left shunt in patients with pulmonary hypertension. This case also highlights the advanced level of proficiency or competence required to interpret correctly such unusual echocardiographic findings, particularly when the results of other invasive diagnostic tests, such as angiography, remain equivocal. These case reports underscore the diagnostic power of TEE in evaluating cardiac sources of embolism 10, abnormalities of the thoracic aorta 11,12, and causes of hypoxemia and hypotension. Of greater importance, however, are the issues emerging from these reports which provide three lessons for the growing number of anesthesiologists undertaking perioperative TEE. First, successful diagnostic-quality TEE is best performed when anesthesiologists performing the studies work in close collaboration with their colleagues in cardiology. This point has been emphasized by the American Society of Echocardiography, in their recent published practice guideline for physician training in TEE 13: "The noncardiologist who needs to perform TEE studies as the primary operator … needs to develop a close, functional, working relationship with an experienced echocardiographer who can provide relatively immediate consultation and help in the event of unsuspected or confusing findings." As changes in our health care system occur, diagnostic testing (including TEE) may be deferred intentionally to the intraoperative setting for the sake of convenience or economy. Post hoc cardiology "overreading" of intraoperative TEE studies performed by anesthesiologists is not sufficient when important immediate decisions must be made. Cardiologists and anesthesiologists must collaborate effectively if we are to best serve the patient, a point illustrated by Swenson and Bailey 7 in their case report. Second, all TEE examinations must be complete. A complete examination is one in which all cardiac valves and chambers are evaluated in sequential fashion and viewed in orthogonal planes when multiplane transducers are employed. It is not sufficient to subject the patient to the real, albeit small risk of perioperative TEE, and then restrict the examination to the specific chamber of interest, which is often the left ventricle. Had a cursory and limited examination been performed by Brooker et al. 8, the diagnosis of left atrial myxoma would not have been made until another, potentially more catastrophic systemic embolism occurred. Finally, diagnostic TEE interpretation requires an advanced level of training to achieve proficiency and ongoing experience to maintain competence. The recommended training for the anesthesiologist-echocardiographer has not been defined, but, in 1993, the American Society of Anesthesiologists and the Society of Cardiovascular Anesthesiologists established an Ad Hoc Task Force on Practice Parameters for Transesophageal Echocardiography. We hope that indications for perioperative TEE will be addressed by the task force and that they will offer a guide to the technical and cognitive skills required for proficiency in TEE, including the ability to make diagnostic quality echocardiographic observations in surgical and critically ill patients. In a number of institutions like ours, anesthesiologists are trained in echocardiography along similar pathways as cardiologists, but with a special emphasis on TEE and perioperative applications. If anesthesiologists performing perioperative TEE are to fulfill new responsibilities as cardiac diagnosticians, the lessons learned from these case reports provide a valuable starting point. Maintaining effective collaboration with cardiologist-echocardiographers, performing careful and complete examinations, and achieving and maintaining a high level of competence are sound principles on which we should base our practice. Our patients deserve no less from us.