Low cardiac output syndrome

Definition: oxygen delivery provided by CO does not meet oxygen demand (or CI < 2.1 L/min/m2) due to inflammatory response of CPB, myocardial ischaemia from aortic crossclamp, hypo-/hyperthermia, reperfusion injury and surgical treatment (ventriculotomy).

Lowest CO usually 6-18 hrs post cross clamp removal, return to baseline after 24 hrs; approximately 25% of all children undergoing CHD have critical LCOS.

Monitoring cardiac output:

• Arterial blood pressure, but MAP ~ CO x SVR
• Cardiac filling pressures: CVP 9-12 mmHg, MPAP < 1/3 MAP, LAP 9-15 mmHg in biventricular heart without shunt
• Peripheral perfusion (capillary refill time)
• Core – peripheral temperature difference
• Urine output
• Base deficit
• Lactate trend
• Mixed venous saturation (aim SmvO2 >70% in biventricular heart without shunt)
• ECHO (EF, wall motion abnormality, valve dysfunction)
• Thermodilution (gold standard)
• Others: NIRS, oesophageal Doppler, bioimpedance measurement, arterial pulse pressure

Management strategies in LCOS:

• Exclusion of residual defects which compromise CO (ECHO)
• Pre-bypass strategies (methylprednisolone 10 mg/kg)
• Pre-surgical strategies (e.g. PFO/ASD in compromised RV function after biventricular repair, baffle fenestration in Fontan circulation)
• Post-surgical strategies: delayed sternal closure or chest reopening
• Ensure appropriate analgesia and sedation
• Consider muscle paralysis (to reduce oxygen demand)
• Preload adjustement: monitor filling pressures in regards to underlying lesion: optimise Hb (100-140 mg/dl in non-cyanotic, 140-160 mg/dl in cyanotic lesions), NaCl 0.9% bolus or albumin 4% bolus
• Pharmacological support: inodilator therapy (milrinone 0.5-1 mcg/kg/min) or phenoxybenzamine (0.5 mg/kg 8hrly) to reduce afterload; β-adrenergic drugs (dopamine 5-10 mcg/kg/min, dobutamine 5-10 mcg/kg/min, adrenaline 0.05-0.1 mcg/kg/min), but can increase diastolic dysfunction; short-term use of vasoconstrictors to maintain appropriate perfusion pressure (noradrenaline 0.05-0.1 mcg/kg/min, vasopressin 0.02-0.05 U/kg/hr) (see inotropes)
  
• Exclude rhythm abnormality
• Cardio-pulmonary interaction: aim for early extubation in Fontan circulation, TOF, Glenn Shunt if feasible
• Hypothermia: cooling to 34-35°C to reduce oxygen consumption
• Calcium-infusion (CaCl2 2-10 mg/kg/hr or 0.01-0.07 mmol/kg/hr), aim for Ca⁺⁺ : 1.4-1.6 mmol/l
• Triiodothyronine substitution in selected cases  in cardiac surgery
  
• Steroid replacement (hydrocortisone 1 mg/kg every 6 hrs)
• Consider PD
• ECLS: ECMO or VAD

References:

[1] Circulation. 1995 Oct 15;92(8):2226-35: Wernovsky et al: Postoperative course and hemodynamic profile after the arterial switch operation in neonates and infants. A comparison of low-flow cardiopulmonary bypass and circulatory arrest

[2] Eur J Cardiothorac Surg. 1999 Apr;15(4):515-8: Dalrymple-Hay et al: Induced hypothermia as salvage treatment for refractory cardiac failure following paediatric cardiac surgery

[3] Pediatr Crit Care Med. 2005 Nov;6(6):655-9: Suominen et al: Hemodynamic effects of rescue protocol hydrocortisone in neonates with low cardiac output syndrome after cardiac surgery

[4] Am Heart J. 2002 Jan;143(1):15-21: Hoffmann, Wernovsky et al: Prophylactic intravenous use of milrinone after cardiac operation in pediatrics (PRIMACORP) study. Prophylactic Intravenous Use of Milrinone After Cardiac Operation in Pediatrics

[5] J Cardiothorac Surg. 2010 Nov 17;5:112: Coskun et al: Extracorporeal life support in pediatric cardiac dysfunction

[6] Cardiology in the Young (2009), 19, 573-579: Vojitovic et al: Haemodynamic changes due to delayed sternal closure in newborns after surgery for congenital cardiac malformations

[7] Pediatr Crit Care Med. 2009 May;10(3):313-22: Bronicki et al: Cardiopulmonary interaction

[8] Curr Opin Cardiol. 2010 Mar;25(2):77-9: Absi et al: Noninvasive cardiac output monitoring in the pediatric cardiac Intensive Care Unit

[9] Crit Care Med. 2001 Oct;29(10 Suppl):S220-30: Wessel et al: Managing low cardiac output syndrome after congenital heart surgery

[10] Arch Dis Child. 2003 Jan;88(1):46-52: Tibby et al: Monitoring cardiac function in intensive care

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