Multiple factors can contribute to difficulty separating a patient from CPB. The adequacy of myocardial preservation should be considered. LVH without or with accompanying coronary artery disease increases myocardial oxygen demand and predisposes to demand/supply imbalance. The prolonged cross-clamp time necessitated by dual-valve replacement can lead to inadequate and/or inhomogeneous myocardial protection. In addition, there may be residual effects from the cardioplegia solution. Therefore, some degree of post-bypass LV dysfunction can be anticipated, and inotropic support required.

Although obstruction to LV ejection is acutely relieved by replacement of the stenotic valve, LV compliance is largely unchanged. Adequate preload still depends on sinus rhythm and sufficient LV filling pressures (PA occlusion pressure [PAOP] or LVEDP). Elevations in pulmonary vascular resistance can render estimation of left atrial pressure through the PA catheter inaccurate. In this setting, placement of a left atrial catheter can be useful.

TEE can be invaluable in identifying surgically correctable causes for inability to wean from CPB. Evaluation of LV filling and contractility can help resolve the situation of low cardiac output and high filling pressures. A small underfilled LV with hyperdynamic contractility and a dilated, overfilled, hypokinetic LV can both give the same hemodynamic parameters but require different pharmacologic interventions. Abnormal valve seating can compromise flow into the coronary ostia, and return to CPB might be indicated for valve inspection, repositioning or coronary artery bypass grafting. Similarly, paravalvular leaks or aortic dissection can be readily identified.

Iatrogenic injury to the circumflex artery, although rare, can occur during MV annuloplasty or replacement. The course of the circumflex artery along the posterior path of the MV annulus makes it a potential target for errant valve stitches. New regional wall motion abnormalities in the inferior-lateral territory help make this unusual diagnosis or influence the decision to pursue diagnostic testing, such as emergent cardiac catheterization. The coronary sinus can also be damaged during MV repair and replacement because the suture line is placed in the lateral mitral annulus. TEE can demonstrate abnormal echodensities in the area of the atrioventricular groove, and color flow Doppler can demonstrate high-velocity flow jets from the chambers to the sinus.

References

• Ender J, Selbach M, Borger MA, et al. Echocardiographic identification of iatrogenic injury of the circumflex artery during minimally invasive mitral valve repair. Ann Thorac Surg. 2010;89:1866-1872.
• Monaco F, Di Prima AL, Kim JH, et al. Management of challenging cardiopulmonary bypass separation. J Cardiothorac Vasc Anesth. 2020;34:1622-1635.
• Nguyen L, Roth DM, Shanewise JS. Discontinuing cardiopulmonary bypass. In: Kaplan JA, Augustides J, Maneck GR, Maus T, eds. Kaplan's Cardiac Anesthesia. 7th ed. Elsevier; 2017:1291-1310.