post CABG hypotension cardiac causes

  • related: Cardiology
  • tags: #literature #cardiology

The patient has hypotension and low cardiac output after cardiac surgery. The differential diagnosis includes left ventricular dysfunction, which can result from perioperative myocardial infarction or myocardial stunning after cardioplegia; reduced preload, which can be due to blood loss or decreased venous tone; and mechanical complications. This question asks the reader to make a diagnosis based on clinical presentation and hemodynamics. A sudden decrease in chest tube output should raise the suspicion that the tube is clotted, and, when this occurs, blood that has been draining may produce a hemothorax that accumulates around the heart and inhibits venous return. This is associated with a decrease in cardiac output and elevation and equalization of cardiac pressures, as is seen in this case. Although chest tube patency can sometimes be restored, and other measures, such as fluid administration and increased vasopressor support may be used to temporize and raise BP, definitive therapy is exploration and potential mediastinal washout in the operating room. Diagnostic choices are not presented in the question, but early echocardiography can be very useful in diagnosis of postoperative hypotension.

Echocardiography can evaluate global and regional left ventricular function, right ventricular function, and valvular abnormalities and may identify mechanical complications. Transthoracic echocardiography can be technically challenging after cardiac surgery; echocardiographic windows can be difficult when bandages and tubes are present, and optimal patient positioning may not be achievable. In addition, pericardial effusions after cardiac surgery may not be circumferential but may be localized, often posterior and impinging on left ventricular filling. Such effusions may not be well visualized with transthoracic echocardiography. Many of these limitations can be overcome with the use of transesophageal echocardiography, if this can be performed and interpreted expeditiously. Presence of some pericardial and juxtacardiac fluid after cardiac surgery, however, is common; the decision to perform reexploration is based on hemodynamics. The problem in this case is decreased venous return, and sympathetic tone is increased in this setting, so increasing cardiac contractility with either dobutamine or epinephrine will not be very helpful. In addition, administration of dobutamine or epinephrine is challenging in this setting because they can exacerbate tachycardia. Stroke volume is decreased consequent to decreased venous return, so slowing heart rate down with esmolol is likely to further decrease cardiac output and worsen hypotension.1234

Footnotes

  1. SEEK Questionnaires ↩

  2. Pepi M, Muratori M, Barbier P, et al. Pericardial effusion after cardiac surgery: incidence, site, size, and haemodynamic consequences. Br Heart J. 1994;72(4):327-331. PubMed ↩

  3. Spodick DH. Pathophysiology of cardiac tamponade. Chest. 1998;113(5):1372-1378. PubMed ↩

  4. Wallen M, Morrison A, Gillies D, et al. Mediastinal chest drain clearance for cardiac surgery. Cochrane Database Syst Rev. 2004;(4):CD003042. PubMed ↩