Hemodynamic management during off-pump coronary artery bypass surgery: a narrative review of proper targets for safe execution and troubleshooting

Abstract

Off-pump coronary surgery requires mechanical cardiac displacement yielding bi-ventricular systolic and diastolic dysfunction. Although transient, subsequent hemodynamic deterioration can bear dismal prognosis and at the extreme, emergent on-pump conversion may be needed, which is associated with undesirably high morbidity and mortality rates. Thus, proper decisions should be made based on objective hemodynamic targets whether surgery can be proceeded before opening the coronary artery.Hemodynamic management should prioritize the avoidance of perplexing myocardial oxygen-supply demand balance, which include maintenance of mean arterial pressure above 70 mmHg while avoiding increase in oxygen demand beyond the patient's coronary reserve. Maintenance of mixed venous oxygen saturation above 60%, which reflects the lower limit of the adequacy of global oxygen-supply demand balance, seems also important not to jeopardize the patient's prognosis. Above all, severe mechanical cardiac constraint incurring compressive syndromes that cannot by overcome by manipulating major determinants of cardiac output should be avoided. To rule out uncompromising form of cardiac constraint, central venous pressure should not equal or exceed the pulmonary artery diastolic (or occlusion) pressure, which would reflect tamponade physiology. In addition, transesophageal echocardiography should rule out mechanical cardiac displacementinduced ventricular interdependence, dyskinesia, severe mitral regurgitation, and left ventricular outflow tract obstruction with or without systolic motion of the anterior leaflet of the mitral valve, which cannot be tolerated during the period of grafting. Also, careful inspection for gas bubbles in the ascending aorta should be performed to prevent rare causes of hemodynamic collapse by massive gas embolism obstructing the right coronary ostium.