What is the typical cardiac output equivalent achieved in patients undergoing heart surgery who are on cardiopulmonary bypass (CPB)?

From the Guidelines

The typical cardiac output equivalent achieved in patients undergoing heart surgery on cardiopulmonary bypass is approximately 2.2 to 2.5 L/min/m² of body surface area. This flow rate is generally maintained throughout the bypass period to ensure adequate perfusion of vital organs while the heart is stopped. The perfusionist typically adjusts the pump flow based on the patient's body surface area, with a target of about 50-60 mL/kg/min in adults, which translates to roughly 4-6 L/min for an average-sized adult 1. This flow rate is lower than the normal cardiac output of 4-8 L/min (or 2.5-4.0 L/min/m²) in awake patients because hypothermia during bypass reduces metabolic demands, and anesthesia decreases oxygen consumption.

Key Considerations

• The adequacy of perfusion is monitored through various parameters including mixed venous oxygen saturation, arterial blood pressure (typically maintained at 50-80 mmHg), acid-base status, and lactate levels 1.
• Flow rates may be adjusted based on these parameters to ensure optimal tissue perfusion while minimizing the risk of hemolysis or excessive shear stress that can occur at higher flow rates.
• Targeting sufficient mean arterial blood pressure during CPB is of importance in order to maintain appropriate perfusion pressures in all end-organs, particularly the kidneys, the brain and the gastrointestinal tract 1.

Adjusting Flow Rates

• The use of vasopressors to force the MAP during CPB at values higher than 80 mmHg is not recommended 1.
• It is recommended to adjust the MAP during CPB with the use of arterial vasodilators (if MAP >80 mmHg) or vasoconstrictors (if MAP <50 mmHg), after checking and adjusting the depth of anaesthesia and assuming sufficiently targeted pump flow 1.

From the Research

Cardiac Output Equivalent in Heart Surgery Patients on Cardiopulmonary Bypass

• The typical cardiac output equivalent achieved in patients undergoing heart surgery who are on cardiopulmonary bypass can vary depending on several factors, including the patient's preoperative cardiac index and the use of inotropic agents 2, 3, 4, 5, 6.
• Studies have shown that patients with a low preoperative cardiac index (<2.5 L/min/m2) may require higher doses of inotropic agents, such as dopamine and dobutamine, to achieve adequate cardiac output after cardiopulmonary bypass 2, 3.
• The use of milrinone, a phosphodiesterase inhibitor, has been shown to improve cardiac output and reduce systemic vascular resistance in patients with a low preoperative cardiac index 2.
• Epinephrine, an alpha- and beta-adrenergic receptor agonist, has also been shown to increase cardiac output, but its effects on systemic vascular resistance and pulmonary vascular resistance may be less desirable than those of milrinone 4.
• The combination of amrinone and epinephrine has been shown to have complementary actions in improving myocardial function after cardiopulmonary bypass, with significant increases in cardiac output, stroke volume, and left ventricular stroke work 4.
• Echocardiography-guided pacemaker optimization has been shown to increase cardiac output and reduce total isovolumic time in patients after cardiac surgery, with individualized heart rate optimization resulting in significant improvements in cardiac output 5.
• Milrinone has been shown to improve left ventricular compliance after cardiopulmonary bypass, whereas epinephrine does not have this effect 6.