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Inotrope use at separation from cardiopulmonary bypass and the role of prebypass TEE

2004; Elsevier BV; Volume: 18; Issue: 4 Linguagem: Inglês

10.1053/j.jvca.2004.05.033

1532-8422

Hani Jneid, Roberto Bolli,

Cardiac Structural Anomalies and Repair

LOW CARDIAC OUTPUT syndrome (LCOS) occurring during or shortly after cardiovascular (CV) surgery is characterized by cardiac and/or circulatory failure and results in a spectrum of clinical entities ranging from the inability to wean from cardiopulmonary bypass (CPB) to postcardiotomy cardiogenic shock. Although the latter represents a dreadful postoperative clinical complication occurring in 1% to 2% of adult cardiac procedures and carries a substantial morbidity and in-hospital mortality, cardiogenic shock remains the strongest indication for mechanical circulatory support.1Goldstein D.J. Oz M.C. Mechanical support for postcardiotomy cardiogenic shock.Semin Thorac Cardiovasc Surg. 2000; 12: 220-228Abstract Full Text PDF PubMed Scopus (62) Google Scholar, 2Kouchoukos N.T. Oberman A. Kirklin J.W. et al.Coronary bypass surgery Analysis of factors affecting hospital mortality.Circulation. 1980; 62: I84-89PubMed Google Scholar Inability to wean from CPB and use of inotropes to this end may potentially be associated with adverse events such as increased rates of perioperative myonecrosis, longer intensive care unit stay, prolonged mechanical ventilation and, particularly, increased arrhythmias. Supraventricular and ventricular arrhythmias produce challenging CV problems in the early perioperative period. LCOS may occur secondary to abnormalities in heart rate (tachyarrhythmias or bradyarrhythmias), hypovolemia, inappropriately elevated afterload, or myocardial dysfunction. Myocardial dysfunction or “stunning” describes a phenomenon of transient global biventricular dysfunction that may occur even in the presence of normal preoperative cardiac function and that usually dissipates within 24 to 48 hours postoperatively.3Breisblatt W.M. Stein K.L. Wolfe C.J. et al.Acute myocardial dysfunction and recovery A common occurrence after coronary bypass surgery.J Am Coll Cardiol. 1990; 15: 1261-1269Abstract Full Text PDF PubMed Scopus (260) Google Scholar Initial treatment of LCOS aims at addressing surgically correctable causes (graft occlusion, bleeding, valve malfunction, and so on) and then initiating inotropes for circulatory support followed by mechanical support, if needed, of which the intra-aortic balloon pump is a first-line modality.4Gorman 3rd, J.H. Gorman R.C. Milas B.L. et al.Circulatory management of the unstable cardiac patient.Semin Thorac Cardiovasc Surg. 2000; 12: 316-325Abstract Full Text PDF PubMed Scopus (6) Google Scholar, 5Doyle A.R. Dhir A.K. Moors A.H. et al.Treatment of perioperative low cardiac output syndrome.Ann Thorac Surg. 1995; 59: S3-11Abstract Full Text PDF PubMed Scopus (37) Google Scholar In this context, cardiac imaging during CV surgery can provide substantial insights into the mechanisms of perioperative LCOS and help guide therapy. Since the initial introduction of echocardiography as an intraoperative imaging modality,6Goldman M.E. Mindich B.P. Intraoperative two-dimensional echo-cardiography New application of an old technique.J Am Coll Cardiol. 1986; 7: 374-382Abstract Full Text PDF PubMed Scopus (26) Google Scholar, 7Matsumoto M. Oka Y. Strom J. et al.Application of transesophageal echocardiography to continuous intraoperative monitoring of left ventricular performance.Am J Cardiol. 1980; 46: 95-105Abstract Full Text PDF PubMed Scopus (158) Google Scholar intraoperative transesophageal echocardiography (TEE) has progressively become an essential tool in CV surgery with various applications, including evaluation of valvular anatomy and function, ischemic wall motion abnormalities, ventricular function, hemodynamics, thoracic aortic anatomy, identification of intracardiac shunts, monitoring of pericardial procedures, and other miscellaneous uses.8Gillam L.D. Intraoperative transesophageal echocardiography.Cardiol Rev. 2000; 8: 269-278Crossref PubMed Scopus (5) Google Scholar Routine intraoperative TEE use has become especially widespread with the increasing number of anesthesiologists adequately trained to perform and evaluate these procedures and with its proven safety; in 1 series of 7,200 cardiac surgical patients, 0% mortality and only 0.2% morbidity (mostly postoperative dysphagia) due to TEE were observed.9Kallmeyer I.J. Collard C.D. Fox J.A. et al.The safety of intraoperative transesophageal echocardiography A case series of 7200 cardiac surgical patients.Anesth Analg. 2001; 92: 1126-1130Crossref PubMed Scopus (358) Google Scholar More importantly, TEE proved to be an important tool to guide intraoperative therapy such as fluid administration, inotropic use, and anti-ischemic therapy. In 1 report of 75 cardiac surgical procedures, TEE was the single most important guiding factor for intraoperative intervention in 17% of cases,10Bergquist B.D. Bellows W.H. Leung J.M. Transesophageal echocardiography in myocardial revascularization: II. Influence on intraoperative decision making.Anesth Analg. 1996; 82: 1139-1145PubMed Google Scholar and resulted in at least one major anesthetic or hemodynamic change in up to 51% of another cohort of 82 patients undergoing high-risk coronary artery bypass graft (CABG) surgery.11Savage R.M. Lytle B.W. Aronson S. et al.Intraoperative echo-cardiography is indicated in high-risk coronary artery bypass grafting.Ann Thorac Surg. 1997; 64 (discussion 373–374): 368-373Abstract Full Text PDF PubMed Scopus (86) Google Scholar In a large prospective analysis of 5,016 CV surgical procedures, prebypass TEE helped guide hemodynamic interventions in 38% of patients (similar to postbypass TEE use) in the presence of invasive hemodynamic monitoring and was associated with no complications.12Mishra M. Chauhan R. Sharma K.K. et al.Real-time intraoperative transesophageal echocardiography—How useful? Experience of 5,016 cases.J Cardiothorac Vasc Anesth. 1998; 12: 625-632Abstract Full Text PDF PubMed Scopus (115) Google Scholar Interestingly, in this particular study, an 87% concordance was observed between the echocardiographic interpretation of anesthesiologists and a later analysis by a cardiologist. Multiple guidelines have recently been published to facilitate the perioperative use of TEE.13Practice guidelines for perioperative transesophageal echocardiography. A report by the American Society of Anesthesiologists and the Society of Cardiovascular Anesthesiologists Task Force on Transesophageal Echocardiography.Anesthesiology. 1996; 84: 986-1006Crossref PubMed Scopus (517) Google Scholar, 14Cheitlin M.D. Armstrong W.F. Aurigemma G.P. et al.ACC/AHA/ASE 2003 Guideline Update for the Clinical Application of Echocardiography Summary article. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/ASE Committee to Update the 1997 Guidelines for the Clinical Application of Echocardiography).J Am Soc Echocardiogr. 2003; 16: 1091-1110Abstract Full Text Full Text PDF PubMed Scopus (252) Google Scholar, 15Shanewise J.S. Cheung A.T. Aronson S. et al.ASE/SCA guidelines for performing a comprehensive intraoperative multiplane transesophageal echocardiography examination Recommendations of the American Society of Echocardiography Council for Intraoperative Echocardiography and the Society of Cardiovascular Anesthesiologists Task Force for Certification in Perioperative Transesophageal Echocardiography.J Am Soc Echocardiogr. 1999; 12: 884-900Abstract Full Text Full Text PDF PubMed Scopus (302) Google Scholar In this issue of the Journal of Cardiothoracic and Vascular Anesthesia, McKinlay et al report their findings from a retrospective analysis of 1,009 patients who underwent “on-pump” CABG with or without valve surgery at Duke University Medical Center (DUMC). They aimed to derive predictors associated with inotropic use at separation from CPB. After excluding patients pretreated with inotropes and those not undergoing prebypass TEE, the authors studied 8 demographic and clinical characteristics and 9 TEE variables. They found that 39% of patients required inotropic or intra-aortic balloon pump support at separation from CPB. Using multivariate analysis, 6 variables remained significantly associated with inotropic therapy, which were by decreasing order of importance: wall motion score index (odds ratio [OR] = 4.22), combined CABG and mitral valve (MV) surgery (OR = 1.28), reoperation (OR = 2.38), left ventricular ejection fraction <35% (OR = 2.38), moderate-to-severe mitral regurgitation (OR = 2.28), and increasing cross-clamp time (OR = 1.01). The authors are to be congratulated on their well-designed analysis, which carries a particular importance given their use of prebypass TEE criteria in the predictive models. Although only 53% (1,009/1,908) of all screened patients were included in the final study, it is important to note that intraoperative TEE has been routinely used during CV surgery at DUMC (KH McKinlay, personal communication, May 2004), which downplays the possibility of any selection bias related to TEE use. In addition, although prebypass TEE may not predict myocardial stunning or a new onset of regional ischemia (related to graft failure, coronary spasm, or emboli), the authors still showed a strong association between prebypass global/regional left ventricular function and inotropic therapy. This further highlights the importance of conducting prebypass TEE routinely during CV surgery rather than limiting its use solely to the complicated postoperative course or to the postbypass period. It is also interesting to note that age and sex were not significant predictors of inotropic drug use in the multivariate analysis and that cross-clamp time was barely predictive (OR = 1.01, confidence interval = 1.008–1.1019) because the lower limit of the confidence interval was nearly crossing the line of unity. The latter observation may possibly be attributed to the inclusion of other related variables (such as age, valve surgery, and reoperation) in the stepwise regression model. The authors also found that MV replacement, but not repair, was a significant predictor of inotropic use. Because this runs counterintuitive to multiple previous experimental and clinical reports showing the importance of maintaining the integrity of the MV apparatus in preserving LV function and improving outcomes,16David T.E. Uden D.E. Strauss H.D. The importance of the mitral apparatus in left ventricular function after correction of mitral regurgitation.Circulation. 1983; 68: II76, 82PubMed Google Scholar the authors correctly attributed their findings to the small number of MV replacement procedures in their study. A few words of caution are worth mentioning before using the findings of this analysis in clinical practice. First, the study was observational and retrospective in design. Therefore, it is possible that chance occurrences may explain some of the predictor-outcome relationships that, notably, reflect at best an association and not necessarily a causality. Second, the multivariate model has some shortcomings and is by no means comprehensive. Hemodynamic parameters, which can be readily measured during surgery (such as systemic and pulmonary arterial pressures), emergency operation, and the number of bypass grafts, were not included. Cardiac medications used preoperatively (which are modifiable factors) could possibly yield interesting findings in the model because some have clearly shown powerful cardioprotective effects. Diastolic dysfunction, with a prevalence of 74% at least in 1 study of cardiac surgical patients using transmitral flow Doppler measurements,17Lappas D.G. Skubas N.J. Lappas G.D. et al.Prevalence of left ventricular diastolic filling abnormalities in adult cardiac surgical patients An intraoperative echocardiographic study.Semin Thorac Cardiovasc Surg. 1999; 11: 125-133PubMed Scopus (21) Google Scholar was also inaccurately assessed and underreported. Finally, before drawing conclusions from this derivation analysis for clinical application, it is important to note that no unified or prespecified algorithms dictating inotropic drug use during separation from CPB were used during the study. Therapy was simply initiated based on the clinical judgment of the anesthesiologists, which, although emanating from a high-volume and renowned center, may not always reflect the ‘best’ clinical judgment or the “right” clinical decision. McKinlay et al’s findings shed light on an important topic in CV surgery; however, the findings should be regarded as hypothesis generating and require further work to define the predictors of “appropriate” inotropic therapy use during separation from CPB. More conclusive studies should have a prospective design, include derivation and validation studies, use more comprehensive models, use prespecified and accepted criteria for the initiation of inotropic therapy, and, most importantly, compare the use of a prebypass TEE-guided strategy to initiate inotropic support at separation from CPB to conventional strategies with respect to clinical outcomes.