Pediatric emergency medicine trisk 1706 1706
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Less severe forms of ductal dependency for PBF present with varying degrees
of cyanosis at the time of ductal closure. The degree of cyanosis is determined by
the amount of blood flow to the lungs. These infants feed and grow well initially,
have normal respiratory rate and effort, and normal vital signs. Defects such as
TOF and some forms of tricuspid atresia and double outlet right ventricle
(DORV) present in this manner.
Ductal Dependent Systemic Blood Flow
Patients with severe left ventricular outflow tract obstructive (LVOTO) lesions
depend on blood flow from the pulmonary artery via the DA to supply the
descending aorta. By definition, this is a right-to-left shunt that causes desaturated
blood to be circulated systemically, and it is necessary to provide systemic blood
flow. Cyanosis is usually mild. Early symptoms include mild tachypnea or
cyanosis, which can quickly progress to cardiogenic shock when the ductus
closes. Cardiovascular collapse may be the first indication that there is a heart
defect. Resulting acidosis and pressure loading of the ventricle accelerate
decompensation and end-organ failure rapidly follows. LVOTO lesions such as
hypoplastic left heart syndrome (HLHS), critical aortic stenosis, and severe
coarctation of the aorta present in this way.
Shunt Lesions
Left-to-Right Shunts
Left-to-right shunt lesions allow oxygenated blood to pass from the systemic
circulation to the pulmonary circulation. The amount of flow is determined by the
size of the defect and the relative PVR compared to systemic vascular resistance
(SVR). If the PVR is high or if the defect is small, left-to-right shunting is limited
and the patient is relatively asymptomatic. As PVR drops, left-to-right shunting
increases causing increased PBF, which results in pulmonary overcirculation.
Overcirculation of the lungs presents as tachypnea, sinus tachycardia, poor
feeding, sweating with feeds, and failure to thrive, which may be mistaken for a
respiratory illness. Typical examples of left-to-right shunt lesions include
ventricular septal defect (VSD) and PDA.
Patients with left-to-right shunts usually present between 6 and 8 weeks of life.
They present with tachypnea (not cyanosis) and have a history of poor feeding
and/or weight gain. They may also have started out life feeding well and
asymptomatic, but their feeding has worsened as their PVR dropped and
pulmonary overcirculation increased. On physical examination, the provider may
or may not appreciate a murmur. A large, nonrestrictive VSD will not produce a
