Once volume, rate and rhythm have been addressed, one is left with contractility as the only remaining determinant of cardiac output which is possible to manipulate.
The choice of inotrope in this situation has never been a topic for which there is a widespread consensus.
Luckily, there are only a few to chose from.
Dobutamine and milrinone seem to be the two popular choices. A comparison of the hemodynamic effects of milrinone with dobutamine has found that they are essentially the same when hemodynamic outcomes are concerned.
Milrinone and dobutamine are important enough to have their own pages, and in the table below I will summarise their distinct advantages and disadvantages.
Dobutamine | Milrinone | |
Contractility increase | Equipotent | Equipotent |
Heart rate increase | Significantly increased | Mildly increased, mainly as a response to vasodilation |
Myocardial relaxation | Unchanged; thus a poor choice for severe diastolic failure | Mildly increased |
Pulmonary artery pressure and right ventricular afterload | Unchanged; thus a poor choice for severe pulmonary hypertension | Potent pulmonary vasodilator |
Systemic vascular resistance, left ventricular afterload | MAP and SVR remain largely unchanged over a range of doses | Moderately potent arterial and venous vasodilator |
Myocardial oxygen consumption | At least moderately increased | Mildly increased, and sometimes not at all (due to vasodilation and decreased myocardial workload) |
Cardiac output | Significantly increased (due to increase in heart rate) | Moderately increased |
Change in pharmacodynamics post cardiopulmonary bypass | Decreased catecholamine sensitivity, thus decreased dobutamine effect | Unchanged sensitivity to milrinone |
Clearance | Hepatic, very rapid | Renal; prolonged |
Historically, IABP has also been offered to this sort of hemodynamically unstable patient. The abovementioned textbook recommends its use as a means of ameliorating the effects of inotropes on the oxygen demand of the stressed ventricle, and as a technique for improving coronary flow in situations where there is evidence of post-operative ischaemia. Certainly there seems to be at least physiological data that good diastolic augmentation improves coronary flow.
As for empirical outcomes data - most of it comes from the period spanning the late 1970s to mid 1990s.
There was a lot of early interest in this, and initially favourable outcomes were achieved, particularly in patients who failed to separate from bypass postoperatively (the mortality in this group being notoriously high at this stage). Today, this recommendation remains, largely because of inertia in this field. Strong evidence is lacking. However, some evidence is available for the preoperative use of IABP in patients with poor systolic function; in a retrospective audit the mortality of these patients halved (from 20% to 10%) in association with pre-operative IABP use.
Frederick A. Hensley, Jr., M.D., Donald E. Martin, M.D., Glenn P. Gravlee, M.D. A Practical Approach to Cardiac Anaesthesia, 3rd ed. Sibylle A. Ruesch and Jerrold H. Levy. CHAPTER 9. The Postcardiopulmonary Bypass Period: A Systems Approach. 2003 by LIPPINCOTT WILLIAMS & WILKINS
André, Arthur C. St, and Anthony DelRossi. "Hemodynamic management of patients in the first 24 hours after cardiac surgery." Critical care medicine 33.9 (2005): 2082-2093.
Eagle, Kim A., et al. "ACC/AHA 2004 guideline update for coronary artery bypass graft surgery: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1999 Guidelines for Coronary Artery Bypass Graft Surgery)." Circulation 110.14 (2004): e340.
Goepfert, Matthias SG, et al. "Goal-directed fluid management reduces vasopressor and catecholamine use in cardiac surgery patients." Intensive care medicine 33.1 (2007): 96-103.
Marik, Paul E. "Hemodynamic parameters to guide fluid therapy." Transfusion Alternatives in Transfusion Medicine 11.3 (2010): 102-112.
Almassi, G. Hossein, et al. "Atrial fibrillation after cardiac surgery: a major morbid event?." Annals of surgery 226.4 (1997): 501.
Maisel, William H., James D. Rawn, and William G. Stevenson. "Atrial fibrillation after cardiac surgery." Annals of Internal Medicine 135.12 (2001): 1061-1073.
BUCKLEY, MORTIMER J., et al. "Intra-aortic balloon pump assist for cardiogenic shock after cardiopulmonary bypass." Circulation 48.1S3 (1973): III-90.
Licker, Marc, et al. "Clinical Review: Management of weaning from cardiopulmonary bypass after cardiac surgery." Annals of cardiac anaesthesia15.3 (2012).
Lavana JD, Fraser JF, Smith SE, Drake L, Tesar P, Mullany DV. Influence of timing of intraaortic balloon placement in cardiac surgical patients. J Thorac Cardiovasc Surg 2011;140(1):80-5.
Maas, Jacinta J., et al. "Cardiac Output Response to Norepinephrine in Postoperative Cardiac Surgery Patients: Interpretation With Venous Return and Cardiac Function Curves*." Critical care medicine 41.1 (2013): 143-150.
Hajjar, L., et al. "Vasopressin Versus Norepinephrine for the Management of Shock After Cardiac Surgery (VaNCS study): a randomized controlled trial." Critical Care17.Suppl 2 (2013): P222.