|I. Exclusion of other causes of cardiovascular failure (e.g. sepsis or congenital heart defect)|
II. Clinical findings of cardiovascular failure secondary to significant ductal left-to-right shunting:|
a. Signs of systemic hypoperfusion (refractory systemic hypotension and/or elevated serum lactate concentration (> 2.5 mmol/L)) and/or;
b. Signs of pulmonary hyperperfusion (prolonged ventilator dependency).
III. Echocardiographic findings of significant ductal left-to-right shunting|
a. Diameter of PDA > 1.5 mm, and;
b. Unrestricted ductal left-to-right shunting (‘pulsatile pattern’): end-diastolic flow velocity < 50% of peak flow velocity, and/or;
c. End-diastolic flow velocity left pulmonary artery > 0.3 m/s, and/or;
d. Left atrial to aortic ratio > 1.5.
a. Severe left ventricular failure (mitral regurgitation), and/or;
b. Disturbed end-organ perfusion (retrograde diastolic blood flow in descending aorta).