How to manage difficult weaning from cardiopulmonary bypass (CPB)?

Management of Difficult Weaning from Cardiopulmonary Bypass

Positive inotropic and/or vasopressor agents are recommended as first-line medical treatment to reduce mortality in patients with hemodynamic instability during difficult weaning from CPB. 1

Systematic Pre-Weaning Assessment

Before attempting separation from CPB, implement a structured checklist approach to prevent critical omissions that could lead to hemodynamic instability and organ injury: 1

• Verify adequate reperfusion time following aortic cross-clamping to allow myocardial recovery 1
• Confirm rhythm and rate are appropriate (sinus rhythm preferred, heart rate 80-100 bpm) 1
• Assess temperature (core temperature >36°C) 1
• Evaluate ventilation and oxygenation adequacy 1
• Check metabolic parameters (potassium, calcium, acid-base status) 1
• Ensure de-airing procedures are complete 1

The use of simulation-based training with checklists significantly improves performance, with studies showing better completion of 5 of 9 designated tasks (P < 0.01) when checklists are employed. 1

Diagnostic Monitoring During Weaning

Transoesophageal echocardiography (TOE) should be considered in all open-heart and thoracic aortic procedures to assess cardiac performance, identify structural problems, detect retained intracardiac air, and evaluate preload, afterload, and biventricular contractility. 1, 2

Additional monitoring considerations:

• Pulmonary artery catheter (PAC) may be indicated in selected high-risk cases to measure cardiac output, pulmonary artery pressures, and mixed venous oxygen saturation, though evidence shows no mortality benefit and potential increased risk in octogenarians (OR 1.24, P = 0.024) 1
• Pulse contour analysis may be considered as a less invasive alternative for cardiac output monitoring 1

First-Line Pharmacological Management

Phosphodiesterase Inhibitors (Preferred Initial Agent)

Phosphodiesterase inhibitors should be considered to increase weaning success and are particularly effective in patients with pulmonary hypertension and right ventricular dysfunction. 1

Milrinone dosing protocol:

• Loading dose: 20-25 μg/kg administered 15 minutes before anticipated weaning 3, 4
• Maintenance infusion: 0.2-0.25 μg/kg/min 3, 4

Milrinone demonstrates superior efficacy in patients with low pre-CPB cardiac index (<2.5 L/min/m²), improving cardiac index and reducing systemic vascular resistance without the tachycardia associated with catecholamines. 3 In patients with mitral stenosis and pulmonary hypertension, low-dose milrinone significantly reduces pulmonary artery pressure, capillary wedge pressure, and central venous pressure during weaning. 4

Critical caveat: Milrinone causes vasodilation; approximately 50% of patients require concurrent norepinephrine to maintain adequate systemic blood pressure. 3 This combination (milrinone + norepinephrine) is a superior alternative to epinephrine for myocardial dysfunction after CPB. 3

Catecholamines (Alternative or Adjunctive)

When phosphodiesterase inhibitors are insufficient or contraindicated:

• Dobutamine and epinephrine both improve stroke volume and increase heart rate, though they increase myocardial oxygen consumption 1
• Norepinephrine is essential when low blood pressure results from vasoplegia to maintain adequate perfusion pressure 1, 5
• Epinephrine may be used but has less favorable coronary vasodilatory reserve compared to dobutamine 1

Levosimendan for Refractory Cases

Evidence-Based Indications

Levosimendan may be considered as a therapeutic strategy in selected difficult-to-wean patients when conventional inotropic therapy proves inadequate, particularly in patients with reduced left ventricular ejection fraction. 1

The 2025 EACTS/EACTAIC/EBCP guidelines provide nuanced recommendations:

• Perioperative levosimendan should be considered (Class IIa, Level A) to reduce risk of low cardiac output syndrome in patients with reduced LVEF undergoing isolated CABG 1, 6
• Levosimendan may be considered (Class IIb, Level B) to improve survival in patients with poor LV function and perioperative low cardiac output syndrome 1, 6

Dosing for difficult weaning:

• Loading dose: 12-24 μg/kg over 10 minutes 6, 7
• Maintenance infusion: 0.1-0.2 μg/kg/min for 24 hours 6, 7

In a series of 15 patients failing conventional therapy, levosimendan achieved successful weaning in 93.3% of cases, with 53.3% experiencing significant increases in cardiac index and blood pressure allowing reduction of catecholamine support. 7

Important Contraindications

Prophylactic levosimendan infusion to reduce adverse events and mortality is NOT recommended (Class III, Level A) in general cardiac surgery populations. 1, 6

Adding levosimendan to other inotropes/vasopressors in patients requiring hemodynamic support after cardiac surgery is NOT recommended (Class III, Level B). 1, 6 This means levosimendan should replace, not supplement, existing inotropic therapy when used.

Mechanical Circulatory Support

When pharmacological interventions fail:

• Intra-aortic balloon pump (IABP) should be considered before attempting levosimendan or as adjunctive therapy 7
• Ensure stable hemodynamics with minimal inotropic support before attempting IABP weaning; monitor for systolic blood pressure <80 mmHg and/or cardiac index <1.8 L/min/m² as signs of dependency 8
• Advanced mechanical circulatory support (ECMO, ventricular assist devices) must be available and considered early in persistent failure-to-wean scenarios 1, 9

Critical Pitfalls to Avoid

• Premature weaning attempts lead to rapid hemodynamic deterioration and organ injury; ensure adequate reperfusion time and metabolic stability first 1, 8
• Failure to identify structural problems (incomplete surgical repair, retained air, tamponade) before initiating pharmacological support; TOE is essential 1, 2
• Using levosimendan prophylactically or adding it to existing inotropes rather than as replacement therapy contradicts high-quality evidence 1
• Inadequate vasopressor support when using vasodilating inotropes (milrinone, levosimendan); have norepinephrine immediately available 3
• Ignoring right ventricular failure, which requires specific management including reduction of RV afterload and consideration of PAC-guided therapy 1