💔 Chapter 57: Low Cardiac Output Syndrome (LCOS) in Postoperative Cardiac Surgery

Nadir 6-12 hours Post-CPB · Inodilators · Milrinone · Afterload Reduction · ECMO · Ventricular Interdependence

💔 Low Cardiac Output Syndrome: Transient but Life-Threatening Reduction in CO After Cardiac Surgery

📊 Definition & Time Course
Transient reduction in CO with decreased systemic O2 delivery after congenital heart surgery. Nadir occurs 6-12 hours post-CPB, returns to baseline by 24 hours. Most common in infants after complex repairs.
🩸 Pathophysiology
CPB inflammatory response + myocardial ischaemia/reperfusion + ventriculotomy + residual lesions + hypothermia → decreased contractility, increased SVR, diastolic dysfunction. 25% of neonates develop LCOS.
📋 Clinical & Biochemical Markers
• Rising lactate (failing to normalise)
• Decreasing ScvO2 (<70%)
• Widening arterial-venous O2 gradient (>27)
• Metabolic acidosis
• Tachycardia, poor perfusion, oliguria, hepatomegaly
💊 Pharmacological Management
• Optimise preload (CVP 8-12)
• Inodilators: Milrinone (PDE3 inhibitor) — first-line for LCOS
• Dobutamine for inotropy + afterload reduction
• Adrenaline for hypotension with LCOS
• Afterload reduction: Milrinone, nitroprusside, phenoxybenzamine
⚙️ Mechanical Support
• Delayed sternal closure (reduces myocardial compression)
• VA-ECMO for refractory LCOS
• VAD or IABP (older children)
📋 Metabolic & Hormonal Support
• Maintain ionised Ca >1.2 (neonates depend on extracellular Ca)
• Levothyroxine (T3) 0.2 mcg/kg q8h
• Hydrocortisone stress dose for refractory shock
📌 Key Pearl: LCOS nadir 6-12 hours post-CPB. Aggressive afterload reduction is cornerstone — do not wait for hypotension. Milrinone is preferred inodilator (no chronotropy, lusitropy). Phenoxybenzamine (alpha-blocker) for Norwood.

🩺 Step-by-Step: Low Cardiac Output Syndrome Management

1
Recognise LCOS — early signs
Rising lactate, decreasing ScvO2 (<70%), widening AVO2 gap, metabolic acidosis, poor perfusion, oliguria. Occurs predictably 6-12 hours post-CPB.
2
Exclude residual anatomical lesions and tamponade
Emergency ECHO to rule out residual VSD, outflow obstruction, valvular regurgitation, pericardial effusion. If present — return to OR.
3
Optimise preload (cautious fluid management)
Target CVP 8-12 mmHg (higher for Fontan/Glenn). Use slow continuous infusion. Avoid fluid overload — worsens diastolic dysfunction.
4
Start inodilator therapy — Milrinone first-line
Milrinone 0.25-0.75 mcg/kg/min (no loading dose if hypotensive). Provides inotropy + afterload reduction + lusitropy. Avoid pure vasopressors (increase afterload).
5
Add afterload reduction (cornerstone of LCOS management)
After BP stabilises: milrinone (already on), nitroprusside 0.5-5 mcg/kg/min, or phenoxybenzamine (alpha-blocker, long-acting, for Norwood).
6
Metabolic & hormonal support
Maintain ionised Ca >1.2 (neonates). Levothyroxine (T3) 0.2 mcg/kg q8h for low T3 syndrome. Hydrocortisone for refractory catecholamine-resistant shock.
7
Optimise rhythm and pacing
Treat JET with cooling/amiodarone. AV sequential pacing if bradycardia or loss of atrial kick (increases CO by 20-25%).
8
Mechanical support for refractory LCOS
If rising lactate and ScvO2 <55% despite maximal therapy → VA-ECMO. Delayed sternal closure should already be considered.