Table 1

Clinical and echocardiographic measures of the haemodynamic significance of the patent ductus arteriosus (PDA)

Clinical signs (one or more)	Echocardiographic markers*
Mild: Need for supplemental oxygen (fraction of inspired oxygen (FiO₂)<30%) Need for non-invasive respiratory support or mechanical ventilation with mean airway pressure (MAP) <8 cm H₂0	Mild (A and one or more of B) PDA size: <1.5 mm shunting predominantly left right (>66% of the cardiac cycle)† Pulmonary and systemic shunt effects Left atrium: aortic root ratio <1.5 Transductal peak systolic velocity >2.0 m/s Left ventricular output (ml/kg/min) <200 Diastolic flow pattern in the descending aorta: Normal antegrade flow
Moderate: Need for supplemental oxygen (FiO₂ requirement 30–50%) Need for non-invasive respiratory support or mechanical ventilation with mean airway pressure (MAP) 8–12 cm H₂0 Oliguria (urine output <1 mL/kg/h) not explained by other clinical conditions (medications; birth asphyxia) Systemic hypotension (mean BP <gestational age in weeks at birth)	Moderate (A and one or more of B) PDA size: 1.5–2.5 mm shunting predominantly left right (>66% of the cardiac cycle)† Pulmonary and systemic shunt effects Left atrium: aortic root ratio 1.5–2.0 Transductal peak systolic velocity 1.5–2.0 m/s Left ventricular output (ml/kg/min) 200–400 Diastolic flow pattern in the descending aorta: Absent/retrograde
Severe: Need for supplemental oxygen (FiO₂ requirement>50%) Need for non-invasive respiratory support or mechanical ventilation with mean airway pressure (MAP) >12 cm H₂0 Profound or recurrent pulmonary haemorrhage Acute renal failure (oliguria with elevated creatinine levels) Haemodynamic instability requiring >1 cardiotropic agent	Severe (A and one or more of B) PDA size: >2.5 mm shunting predominantly left right (>66% of the cardiac cycle)† Pulmonary and systemic shunt effects Left atrium: aortic root ratio >2.0 Transductal peak systolic velocity <1.5 m/s Left ventricular output (ml/kg/min) >400 Diastolic flow pattern in the descending aorta: Retrograde

*In the event that PDA size criteria do not match with any of the corresponding B criteria during a particular echocardiographic assessment (ie, all B criteria indicate a higher or lower degree of haemodynamic significance as compared with A criteria), the higher of the two will be used to assign the degree of haemodynamic significance on echocardiography.
†PDA (of any size) shunting right-left for >33% of cardiac cycle is suggestive of persistent pulmonary hypertension; therefore, will not be classified under any category above and will not be considered for the treatment.