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consequences are rare Other potentially important complications are disturbance to flow in the proximal left pulmonary artery or descending aorta from a protruding device, hemolysis from high-velocity residual shunting, femoral arterial or venous thrombosis related to vascular access, and infection Regardless of technique of closure, the clinical diagnosis should be confirmed noninvasively prior to catheterization by color Doppler echocardiography, with particular emphasis placed on the presence of associated lesions that could complicate the procedure, such as azygos continuation of the inferior caval vein, presence of an additional lesion that requires surgical intervention, or the presence of pulmonary vascular disease Special attention should also be directed to the transverse arch and isthmic region, to exclude unsuspected coarctation Although initially the procedure was best suited for patients weighing more than 6 kg, improved device design and operator experience has allowed application even to the very low birth weight infant (see later) Nevertheless, in smaller infants, difficulties in positioning, left pulmonary arterial stenosis, or aortic obstruction may occur There is considerable variation in procedural details as practiced among centers, such as the use of coincident arterial cannulation and the number and type of angiograms However, the majority of procedures can be performed in an outpatient setting, with discharge on the afternoon of insertion Patency of the Arterial Duct in the Premature Infant (see also Chapter 15) During the past 4 decades, there has been a marked increase in premature delivery in many, but not all, developed countries Although the reasons for this are obscure, the increase has been met by the development of neonatal intensive care units and, more recently, units for pregnancies considered to be at high risk The art and science of caring for the extremely premature infant have developed to the point where survival of infants weighing no more than 500 g is not uncommon Pathophysiology The presence of a patent arterial duct is a common clinical problem in the premature neonate and those of extreme low birth weight, being found in 65% of neonates with a birth weight less than 1000 g and often associated with various neonatal morbidities.163 There are several factors that tend to prevent closure of the arterial duct in the immature infant because both the sensitivity to oxygen and the action of prostaglandin are age dependent164 and the relaxant mechanism of prostaglandin is more active in the immature duct.164–166 The type and duration of ventilatory support, drug therapy, phototherapy, blood transfusions, and diuretics, undoubtedly account for the wide variations in incidence reported from different institutions The pulmonary vascular resistance is lower in the premature than the full-term child, due to the rapid increase in number of muscularized pulmonary vessels The vessels of the immature lung also constrict less for a given stimulus than at term Constrictive stimuluses include hypoxia, acidemia, and possibly circulating vasoactive peptides and prostaglandins, frequent comorbidities in the respiratory distress syndromes These factors render the immature infant especially liable to develop left-to-right shunting when the duct remains patent Systemic vasoconstriction, so often a feature of the sick premature infant, may further encourage the shunt and exacerbate the respiratory distress syndrome.167 The immature infant is further handicapped by its reduced cardiac reserve The increased volume overload secondary to a left-to-right shunt produces an inordinate rise in left ventricular end-diastolic pressure and a concomitant rise in pulmonary venous pressure With a large left-to-right shunt through the duct, systemic diastolic pressure falls, compromising the flow through the coronary arteries, which, combined with a shortened diastole because of tachycardia and raised ventricular end-diastolic pressures, predisposes to subendocardial ischemia Systemic hypoxia secondary to pulmonary problems, combined with a reduced capacity to carry and deliver oxygen due to anemia and fetal hemoglobin, further impairs myocardial function and is reflected in ischemic changes in the electrocardiogram frequently seen in the sick premature infant Other important circulations, such as those of the gut, kidneys, and brain, may be compromised by the hemodynamic changes related in part to the diastolic runoff from the aorta into the pulmonary arteries, with the duct an etiologic factor in necrotizing enterocolitis and cerebral hemorrhage Clinical Features The clinical picture of patency of the duct in the premature infant depends on the size of the left-to-right shunt, on the maturity of the heart and lungs to adjust to the increased volume load, and on the presence of other pathologies, which may obscure the more typical findings Because many premature infants have respiratory distress syndrome, the use of surfactant will modify the clinical expression of ductal shunting by influencing pulmonary vascular resistance The presence of a significant duct can often be difficult to recognize even by experienced clinicians, and echocardiography is of great value Three distinct patterns of clinical presentation may be observed.168 Absence of Pulmonary Disease These infants generally have birth weights exceeding 1500 g However, smaller infants may be encountered whose mothers may have received steroids or themselves received surfactant Sometimes a systolic murmur is detected in the first week of life This becomes louder and longer as pulmonary vascular resistance falls and eventually spills into early diastole The murmur is best heard in the second and third left interspaces It is associated with accentuation of pulmonary closure, with the typical continuous murmur as heard in older children usually not being present If the shunt becomes large, the precordium becomes hyperactive, the pulse pressure wide, and the peripheral pulses bounding An apical third sound may also occur associated with a diastolic flow murmur If the left ventricle fails, tachycardia and tachypnea develop, and moist sounds can be heard in the chest Apnea and bradycardia may complicate severe left ventricular failure Hepatomegaly may only develop late Most infants in this group do not develop massive shunts and can be managed by simple medical means The duct closes spontaneously in the majority at an age approximating to full term These older infants tend to respond less well to indomethacin than more immature infants do Infants Recovering From Lung Disease Left-to-right ductal shunting may develop in infants recovering from respiratory distress syndrome Usually they weigh between 1000 and 1500 g Most probably the duct is patent from birth, and left-to-right shunting develops only during recovery when pulmonary vascular resistance falls At this time, increased administration of fluids may further aggravate the loading effects of the shunt on left ventricular function Many of these infants are still maintained on mechanical ventilators or continuous positive airway pressure, when shunting first develops Because of this, the initial systolic murmur may be difficult to