Introduction

Low cardiac output syndrome is one of the complication in post op cardiac surgeries in adult as well as paediatric surgeries.

Myocardial function generally decline after 6-8hrs of post CPB/post revascularization surgery because of ischaemic reperfusion injury.

Definition – Low cardiac output state can be defined as cardiac index below 2 lits/min/m2,associated with lt. sided filling pressure exceeding 20 mm HG.and SVR exceeding 1500 dynes-sec/cm5.

Haemodynamic goal for postop cardiac surgery are-

• Cardiac index-2.5L/min/m2
• LA/PCW pressure below 20 mmhg
• Heart rate < 100/min
• Patient should have warm,well perfused extremities with good urine output

Marginal ventricular functionleads to sympathetic stimulation and endogenous catecholamine production.this increases heart rate, contractility, arterial and venous tone elevating afterload and preload. All these factors improve cardiac output blood pressure and also increasing myocardial oxygen demand.

Manifestations of  Low cardiac output syndrome-

• Poor peripheral perfusion with pale and cool extremities and diaphoresis.
• Pulmonary congestion and poor oxygenation.
• Impaired renal perfusion and oligouria.
• Metabolic acidosis.

 

Etiology of Low cardiac output state

• decreased Lt. ventricular preload– in
  1. Hypovolemia[bleeding,vasodilatation,narcotics,sedatives]
  2. Carduiac tamponade
  3. Positive pressure ventilation.
  4. ventricular dysfunction[rt.infarction,pulmonary hypertention]
  5. Tension pneumothorax.
• decreased contractility
  1. Low ejection fraction
  2. Myocardial “stunning”.-ischaemia or infarction
  3. Poor intra-op myocardial protection.
  4. Incomplete myocardial revascularization
  5. Anastomotic stenosis.
  6. Coronary artery spasm.
  7. Hypoxia ,hypercarbia,acidosis.
• Arrhythmias-
  1. Tachycardia with reduced cardiac filling time.
  2. Bradycardia
  3. Atrial arrhythmias with loss of atrial contraction
  4. Ventricular arrhythmias
• Increased afterload–
  1. Vasoconstriction
  2. Fluid overload.
• Diastoloic dysfunction.
• Syndromes associated with cardiovascular instability and hypotension.
  1. sepsis
  2. anaphylactic reactions[blood ,drugs].
  3. adrenaline insufficiency.
  4. protamine reaction.

 

Assesment

1. Clinical examination-breath sounds,murmur.extremities.
2. Obtain haemodyanamic measurement-filling pressure,cvp/LAP/PWCP/SVR/Svo2.
3. ABGs
4. ECG-Ischaemia, arrhythmias.
5. CHEST X RAY.
6. Urine output
7. Chest tube drainaige
8. -asses cardiac chamber function.

 

Management

1. Look for noncardiac correctable cause.[respiratory ,acid base and electrolyte derangements.
2. Treat ischaemia or coronary spasm.
3. Optimise preload [PCWP/LA pressure-15-18 mm Hg]
4. Optimise heart rate [90-100 / min with pacing.
5. Controll arrhythmias,asses cardiac output and start ionotropes if cardiac index is less than 2 lits/min/m2.choice of drug,if low svr-dopamine if high dobutamine.epinephrine if no arrhythmias.
6. If svr is high start vasodilator
7. SVR is less –epinephrine,nor epinephrine if marginal cardiac output.
8. Blood transfusion if Hct- less than 26%.