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, which results in bi-ventricular systolic and diastolic dysfunction. Although transient, subsequent hemodynamic deterioration can be associated with poor prognosis and, in extreme cases, emergency conversion to on-pump surgery, which is associated with high morbidity and mortality. Thus, appropriate decision-making regarding whether the surgery can be proceeded based on objective hemodynamic targets is essential before coronary arteriotomy. For adequate hemodynamic management, avoiding myocardial oxygen supply-demand imbalance, which includes maintaining mean arterial pressure above 70 mmHg and preventing an increase in oxygen demand beyond the patient's coronary reserve, must be prioritized. Maintaining mixed venous oxygen saturation above 60%, which reflects the lower limit of adequate global oxygen supply-demand balance, is also essential. Above all, severe mechanical cardiac displacement incurring compressive syndromes, which cannot be overcome by adjusting major determinants of cardiac output, should be avoided. An uncompromising form of cardiac constraint can be ruled out as long as the central venous pressure is not equal to or greater than the pulmonary artery diastolic (or occlusion) pressure, as this would reflect tamponade physiology. In addition, transesophageal echocardiography should be conducted to rule out mechanical cardiac displacement-induced 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 grafting. Finally, the ascending aorta should be carefully inspected for gas bubbles to prevent hemodynamic collapse caused by a massive gas embolism obstructing the right coronary ostium.

Keywords: Cardiac tamponade; Hemodynamic monitoring; Mixed venous oxygen saturation; Off-pump coronary artery bypass; Swan-ganz catheterization; Transesophageal echocardiography..

Fig. 1.

Continuous-wave Doppler assessment of the pulmonary artery. Note that the Doppler beam is aligned parallel to the main pulmonary artery (arrow) in this upper-esophageal aortic arch short axis view. Peak flow velocity (dotted line, 1.5 m/s) indicates mild degree of stenosis.

Fig. 2.

Changes in the pulmonary artery waveform resulting from myocardial ischemia. (A) Pulmonary artery occlusion pressure waveform. (B) Superimposition of the accentuated A, C, and V waves by decreased LV compliance with or without mitral regurgitation on the normal pulmonary artery waveform.

Fig. 3.

Management algorithm based on monitoring targets following mechanical cardiac displacement. PAC: pulmonary artery catheter, CVP: central venous pressure, PADP: pulmonary artery diastolic pressure, PAOP: pulmonary artery occlusion pressure, TEE: transesophageal echocardiography, MR: mitral regurgitation, LVOTO: left ventricular outflow tract obstruction, SvO₂: mixed venous oxygen saturation, MAP: mean arterial pressure, ECG: electrocardiography, IVC: inferior vena cava, bpm: beats per minute. ^*Consider continuation depending on the expertise of the team if SvO₂ is above 50% but below 60% after repeated efforts for optimization.