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FIG 15.7 (A) Two-dimensional echocardiographic representation of a large patent ductus arteriosus from a parasternal short-axis view (B) Pulsed wave Doppler interrogation at the mid ductal level reveals unrestrictive laminar transductal flow Ao, Aorta; MPA, main pulmonary artery; PDA, patent ductus arteriosus ▪ The pattern of transductal flow, estimated using pulse wave Doppler interrogation from a suprasternal short-axis view, can also be used to characterize ductal significance High-velocity, continuous left-toright flow is predictive of imminent functional closure, whereas a low-velocity pulsatile left-to-right flow pattern is likely to be clinically significant (see Fig 15.7B).125 ▪ Cross-sectional echocardiography has also been used to quantify the degree of volume overload Specifically, estimates of left atrial or left ventricular size have been used as surrogates of pulmonary overcirculation and/or volume loading Although the measurement is standardized, it is not very specific and is prone to error dependent on the operator.76 The presence of a large atrial septal defect permitting leftto-right shunting will lead to further augmentation of pulmonary flow, potentially overestimating the magnitude of the ductal shunt ▪ Left ventricular output is significantly higher in preterm infants with a hemodynamically significant ductal shunt.123,126 Minimal angle of insonation with the left ventricular outflow tract in the apical fivechamber view is important to ensure accurate measurement ▪ Interrogation of descending thoracic aorta diastolic flow at the level of the diaphragm has been investigated using cardiac magnetic resonance imaging.126 Flow reversal during diastole is highly associated with shunt volume Evidence of end-organ hypoperfusion may be also inferred from Doppler assessment of the patterns of flow in the mesenteric, cerebral, or renal arteries Specifically, reversal or absence of diastolic perfusion is pathognomonic of a hemodynamically significant duct.127,128 Management of the Hemodynamically Significant Duct The aims of treatment are to reduce pulmonary overcirculation and improve systemic blood flow The decision to treat is based on both clinical and echocardiographic findings, although the optimal time and method of ductal closure remain uncertain Treatment should be classified as supportive intensive care strategies and therapeutic interventions aimed at closing the duct Focused Intensive Care Ventilation Strategies that minimize pulmonary overcirculation in a fashion comparable to that used for congenital cardiac defects should be considered This can be achieved by accepting PCO2 between 45 and 55 mm Hg, arterial pH of 7.25 to 7.35, and oxygen saturations between 88% and 93% Improvements in oxygenation and lung compliance may also be achieved by increasing the positive end-expiratory pressure to levels that maintain optimal recruitment, minimize atelectasis-induced lung injury, and lead to improvements in myocardial performance and cardiac output by reducing left ventricular afterload.129,130 Reduced hematocrit is associated with both lower pulmonary vascular resistance and decreased oxygen delivery to the tissues which may result in a compensatory increase in cardiac output and peripheral vasodilation.131 Avoidance of anemia in the presence of a hemodynamically significant ductus arteriosus may be beneficial Cardiotropic support The optimal treatment for hypotension and/or systemic hypoperfusion is strategies aimed at increasing pulmonary vascular resistance and closure of the duct and, in the absence of left ventricular dysfunction, not cardiotropic support Excessive α-adrenergic stimulation, by agents such as dopamine or epinephrine, should be avoided because the increased systemic vascular resistance may lead to increased left-to-right shunting or may further compromise an already dysfunctional left ventricle Dobutamine or newer inodilators currently under investigation, such as milrinone, may be preferred if there is associated left ventricular dysfunction, although medications that reduce systemic vascular resistance (e.g., milrinone) should be avoided in neonates with low diastolic arterial pressure because further reduction may compromise coronary artery perfusion pressure Fluid management and diuretic therapy Fluid restriction, which has historically been a cornerstone of ductal management, should not be routinely recommended This strategy may lead to preload-reduced left ventricular stroke volume and cardiac output which may further compromise systemic blood flow without improving ductal shunt.132 Fluid restriction may be considered in patients who become oliguric and/or volume overloaded during treatment with indomethacin The evidence for routine diuretic therapy to promote ductal closure is also limited.133,134 This may relate to excessive new production of prostaglandin E2 by the kidneys in babies