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Anesth Analg 2004;99:12-16 © 2004 International Anesthesia Research Society doi: 10.1213/01.ANE.0000117284.25696.64
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Abstract |
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Pulmonary embolism (PE) is associated with significant perioperative morbidity and mortality. Transesophageal echocardiography (TEE) may permit direct visualization of PE or secondary signs of pulmonary artery (PA) obstruction. However, its utility in diagnosing PE in the intraoperative setting has yet to be defined. Therefore, we performed intraoperative TEE examinations in 46 patients immediately before pulmonary embolectomy. TEE examinations were reviewed for signs of thromboemboli within the right, left, and main PA, and secondary signs of acute PA obstruction (right ventricular dysfunction, moderate-to-severe tricuspid regurgitation, leftward bowing of the interatrial septum). The definitive location of thromboemboli was determined from the surgical record. Echocardiographic evidence for the presence of PE was correctly demonstrated in 46% of all patients (n = 21 of 46). However, the sensitivity for direct visualization of thromboemboli at any specific location was only 26%. TEE was least sensitive for thromboemboli in the left PA (17%). TEE evidence of right ventricular dysfunction was observed in 96%, tricuspid regurgitation in 50%, and leftward interatrial septal bowing in 98% of examinations. Therefore, the use of intraoperative TEE to diagnose acute PE via direct visualization is limited. Indirect TEE evidence of PA obstruction may be helpful in supporting a diagnosis of PE.
IMPLICATIONS: Intraoperative pulmonary embolism is associated with frequent morbidity and mortality. A reliable diagnosis is crucial to initiate therapeutic intervention. Despite its practicality and utility for revealing indirect signs of pulmonary artery obstruction, intraoperative transesophageal echocardiography is limited in diagnosing pulmonary embolism via direct visualization.
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Introduction |
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Pulmonary embolism (PE) is often associated with significant morbidity and mortality (1,2). For example, the incidence of intraoperative PE in patients undergoing hip surgery is approximately 2% and has been associated with a fatal outcome in almost half of the cases (3). Conservative treatment of PE includes the administration of thrombolytics. However, placement of an inferior vena caval filter may be required to prevent further embolic events (4). In hemodynamically unstable patients with severe PE, surgical embolectomy may be necessary. A recent study of patients undergoing pulmonary embolectomy for severe PE demonstrated a survival rate of 89% and suggested that survival is related to early diagnosis and surgical intervention (5). Thus, the survival of perioperative PE patients is critically dependent on early recognition and diagnosis.
Over the past decade, the importance of transesophageal echocardiography (TEE) as a diagnostic and monitoring tool for the perioperative management of surgical patients has become increasingly more evident (6). For example, TEE has been shown to influence the management of cardiac surgery patients in >20% of cases (7). Several previous studies have investigated the utility of TEE as a primary technique to diagnose hemodynamically significant PE via direct visualization of thromboemboli (8,9) or using indirect signs of pulmonary artery (PA) obstruction such as right ventricular (RV) dysfunction, tricuspid regurgitation (TR), or leftward bowing of the interatrial septum (10,11). In a study using pulmonary angiography as a "gold standard," the global sensitivity of TEE (80%) and spiral computed tomography (CT) for directly visualizing central PE was comparable (9). Secondary echocardiographic signs of severe PE associated with acute PA obstruction are relatively nonspecific and may be difficult to differentiate from other sources of acute RV failure, including protamine reaction or previously undiagnosed pulmonary hypertension (12). Although practice guidelines recently introduced by the American Society of Echocardiography and Society of Cardiovascular Anesthesiologists strongly recommend TEE for diagnosis and management of acute, life-threatening intraoperative hemodynamic collapse, the utility of TEE for intraoperative diagnosis of acute PE in this setting has not been specifically investigated (13,14).
The utility of TEE for diagnosing acute PE in the perioperative setting may be limited for several reasons. In comparison to the hemodynamically stable patient with suspected chronic pulmonary thromboembolism who presents for a diagnostic transthoracic echocardiographic (TTE) examination, patients with massive acute PE requiring immediate continuous resuscitation and imminent surgical intervention are usually unstable and often on the verge of cardiovascular collapse. Consequently, optimal conditions for performing a thorough intraoperative TEE examination in this emergent clinical setting cannot be anticipated. In addition, the sensitivity of TEE for diagnosing PE based on direct visualization of thrombus may be low because of the distal location of the thrombus within the pulmonary circulation (15). Furthermore, echocardiographic evidence of chronic adaptive changes to the pulmonary circulation including PA dilation may not be identified after acute, severe PE. Finally, although TEE may generally provide superior echocardiographic windows and resolution for visualizing PE in comparison to TTE, the location of the air-filled trachea and left mainstem bronchus may interfere with the ability to image PE, especially in the left PA (LPA) (16). Despite these limitations, anesthesiologists trained in perioperative TEE may frequently be asked to confirm the clinical suspicion of intraoperative PE by means of TEE in the setting of acute persistent hypotension. Therefore, we performed a study in patients undergoing pulmonary embolectomy to determine the utility of intraoperative TEE in diagnosing severe PE.
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Methods |
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Subject Population
The study population consisted of 46 consecutive patients who underwent emergent pulmonary embolectomy at the Brigham and Women’s Hospital between January 1995 and December 2002. Approval for reviewing the patients’ medical records was obtained from the IRB.
TEE Examination
Comprehensive intraoperative echocardiographic examinations were performed using multiplane TEE probes (Acuson, Mountain View, CA) after the induction of general anesthesia and before the institution of cardiopulmonary bypass (CPB). All TEE examinations were performed, videotaped, and concurrently interpreted by cardiac anesthesiologists experienced in perioperative echocardiography. Echocardiographic evidence documenting the specific location of any visualized PE, as well as secondary signs of PA obstruction (RV dysfunction, TR, and leftward bowing of the interatrial septum), were confirmed upon review of the videotaped study by a cardiac anesthesiologist blinded to the written TEE report. Masses were qualified as thromboemboli if they were mobile or immobile, homogenous or heterogeneous with clear central areas. Any discrepancies regarding thromboemboli localization or secondary signs of PA obstruction between the off-line analysis of the TEE videotape and written report were resolved by a second cardiac anesthesiologist who was a member of the study team.
Secondary echocardiographic signs of PA obstruction were assessed using standardized criteria. RV dysfunction was defined by the presence of hypokinesis and a diastolic diameter that exceeded the left ventricular diastolic diameter in the transgastric mid short-axis view (17). TR was evaluated by colorflow Doppler and graded according to the ratio of the regurgitant jet to right atrial area as mild: <30%; moderate: >30%–50%; or severe: >50% (18,19). Bowing of the interatrial septum was defined as a leftward curvature of the interatrial septum that persisted throughout the cardiac cycle, thereby suggesting the presence of right atrial pressures that exceeded left atrial pressures (20).
Review of Surgical Operative Notes
The surgical operative records were reviewed for documentation of the distribution of extracted emboli from different locations within the pulmonary arterial circulation (main [MPA], right [RPA], and LPA). Foreign bodies or tumors were not found during surgical exploration of the MPA, RPA, or LPA.
The sensitivity of TEE for identifying PE globally, and the sensitivity, specificity, and predictive values at specific locations within the pulmonary circulation (MPA, RPA, and LPA) were calculated from confirmation of the diagnosis during surgical exploration.
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Results |
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Study Population
The medical records, intraoperative TEE reports (written and videotape), and surgeon’s operative notes of 46 patients (28 men, 18 women), median age 60 (range, 31–86) yr, undergoing emergent pulmonary embolectomy were reviewed. Preoperative diagnosis was made using a variety of techniques in 96% of the patients (Table 1). Magnetic resonance imaging was not used as a diagnostic technique in any of the patients. Two patients were taken to the operating room based on clinical presentation and urgency, which precluded further diagnostic evaluation. CPB was emergently initiated in 10 patients (22%) who experienced significant intraoperative hypotension, including 6 patients (13%) who required cardiopulmonary resuscitation. Seven patients (15%) died postoperatively.
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Direct Visualization of Pulmonary Thromboemboli
There were no discrepancies in the on-line and off-line diagnoses of location, presence or absence of PE in any patient. Intraoperative echocardiographic diagnosis of thromboemboli identified anywhere within the proximal PA circulation was confirmed by surgical findings in 21 of the 46 patients, thus providing a sensitivity of 46% (Table 2). The sensitivity of intraoperative TEE for locating thromboembolism within a particular PA location was only 26% with a range of 17% (LPA) to 35% (RPA) (Table 3 and Fig. 1). TEE was most specific for excluding thromboembolism in the LPA (100%) and least specific for the RPA (89%) (Fig. 1).
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Secondary Signs of PE
Discrepancies between the TEE written and off-line assessment were noted in four patients. After consultation with a second cardiac anesthesiologist who reviewed the intraoperative TEE examination on videotape, the TR grade was increased by 1 grade in 2 patients, and 2 other patients were considered to have RV dysfunction. Bowing of the interatrial septum, RV dysfunction, and at least moderate TR were present in 45 (98%), 44 (96%), and 23 (50%) patients, respectively.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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PE can occur in a variety of perioperative scenarios, and is frequently associated with significant morbidity and mortality. Reliable and timely diagnosis of PE before the institution of specific treatment options is crucial to ensure limited morbidity and mortality. TEE is often considered a primary diagnostic technique to identify patients with intraoperative PE because of its availability and practicality in the operating room, safety, lack of interference with resuscitation efforts, and previously reported diagnostic utility in nonoperative settings (8,21). However, the diagnostic accuracy of TEE for diagnosing PE in the intraoperative setting has not been specifically investigated. In the present series of 46 patients undergoing emergent pulmonary embolectomy, echocardiographic evidence of PE was confirmed during surgical exploration in only 46% of the patients. The specificity of TEE to exclude PE was not determined because all patients were known to have severe PE requiring surgical exploration. Secondary signs of acute PA obstruction such as leftward bowing of the interatrial septum, or acute RV dysfunction may be helpful in supporting a clinical diagnosis of PE in conjunction with other clinical signs. However, the present study does not specifically address whether these signs alone have predictive value.
PE is often diagnosed by pulmonary angiography, spiral CT, or ventilation-perfusion scintigraphy (22). However, these diagnostic techniques may not be practical in the setting of severe intraoperative PE. Even though laboratory data such as increased levels of D-dimers may be highly specific for diagnosing PE (23), the time required to perform such tests may be a limiting factor. Although acute changes in arterial-alveolar carbon dioxide tension (24) may also be useful in establishing the diagnosis of intraoperative PE, commonly encountered signs, such as oxygen desaturation or hypotension, are not specific for the diagnosis. Thus, obtaining a definitive diagnosis of PE may be challenging, especially in the intraoperative period.
TEE has been recommended as a diagnostic technique for rapidly confirming the diagnosis of PE (8). Current practice guidelines for the perioperative use of TEE proposed by the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists consider pulmonary embolectomy as a Class II indication (13). However, a comprehensive TEE examination may demonstrate additional criticalinformation that may directly influence patient management, even if a diagnosis of PE cannot be confirmed. Accordingly, the same set of practice guidelines classify acute, life-threatening intraoperative hemodynamic disturbances (including PE) as "Category 1 indications," which include clinical scenarios that may receive the greatest benefit from TEE in improving outcomes (13).
Despite the apparent advantages for using TEE in the setting of acute hemodynamic collapse, the present study demonstrates that TEE is not reliable for directly visualizing PE in the intraoperative setting of pulmonary embolectomy. In more than two-thirds of the patients, TEE did not reveal a PE at the subsequently verified location within the pulmonary circulation. Moreover, in 54% of patients, TEE did not reveal thromboembolism despite confirmation of PE during pulmonary arteriotomy. In contrast to these findings, Vieillard-Baron et al. (8) reported that compared with spiral CT and/or pulmonary angiography, TEE had a sensitivity of 84% for the diagnosis of PE in intensive care unit patients. All TEE examinations were performed under sedation without the need for general anesthesia. The difference in reported sensitivities between the finding of Vieillard-Baron et al. and the present study could be related to the circumstances under which the TEE examinations were performed. In the present study, all patients were undergoing emergent pulmonary embolectomy, including 21% of the population who experienced significant, acute hypotension requiring emergent institution of CPB. Consequently, the operative environment during a critical emergency may not provide optimal conditions for performing an echocardiographic interrogation. In addition, all previous studies that have investigated the utility of TEE in diagnosing PE have relied on alternate imaging techniques such as CT or pulmonary angiography as gold standards to confirm the diagnosis of PE. In the present study, the definitive diagnosis was indisputably determined by direct inspection during surgery. Thus, differences between our results and previously published data may reflect differences in the populations, clinical setting, and comparative diagnostic techniques. In addition, the echocardiographic findings described might not be the same in patients who have less serious PE, which, nevertheless carry risks and for which the diagnosis is also very important.
In the present study, TEE was least sensitive for diagnosing thromboembolism in the LPA. Thromboemboli located in the LPA could only be visualized in 17% of patients. Other investigations have confirmed this finding, suggesting that the position of the left main bronchus anterior to the esophagus produces an ultrasonographic "blind spot" that may obscure TEE imaging of the LPA. In a study of pediatric patients undergoing cardiac surgery for congenital heart disease, complete TEE imaging of the LPA was only possible in 10% of patients (16). Thus, TEE cannot reliably be used to exclude the presence of thromboembolism in the LPA.
Indirect echocardiographic evidence of PA obstruction may support the diagnosis of PE in the absence of direct visualization. However, these secondary echocardiographic signs are not specific for PE, and do not permit reliable differentiation from other possible etiologies of RV dysfunction. In contrast, patients with PE may exhibit a specific pattern of RV regional wall motion abnormality characterized by relatively normal contraction and "sparing" of the apex, despite moderate or severe RV free-wall hypokinesis, also known as the "McConnell sign" (25). This pattern of regional wall motion is reportedly specific for PE and can be used to differentiate RV dysfunction associated with primary pulmonary hypertension (26). Unfortunately, compared with TTE, echocardiographic imaging of the RV apex using TEE is often difficult and evaluation for the McConnell sign is not always possible with TEE. Thus, indirect echocardiographic evidence may support the diagnosis of PE, but is relatively nonspecific.
In conclusion, the present data suggest that unequivocal TEE evidence of thromboembolism within the pulmonary circulation is highly predictive for PE and may be sufficient to exclude the need for further diagnostic testing and to initiate specific therapeutic interventions. However, the limited sensitivity of intraoperative TEE for identifying PE may restrict its utility as a primary diagnostic tool. Thus, failure of TEE to directly demonstrate a PE within the PA circulation should not exclude a patient from undergoing further diagnostic testing or therapeutic intervention when a PE is suspected. Therefore, intraoperative TEE may be more important as a monitoring tool of PE-induced hemodynamic compromise than as a primary diagnostic technique for obtaining a definitive diagnosis of PE.
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Acknowledgments |
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Support was provided solely from institutional and/or departmental sources.
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