Neonatal CCRN Exam

This chapter organizes congenital heart defects by physiology, because the CCRN exam asks what to do, not how to draw the anatomy. It also covers screening for critical congenital heart disease (CCHD), the hyperoxia test, prostaglandin E1 and hypercyanotic spells.

Most critical lesions fit one of four patterns. Ductal-dependent pulmonary flow lesions need the ductus to get blood to the lungs, so the infant is cyanotic and becomes more cyanotic as the duct closes. Ductal-dependent systemic flow lesions need the ductus to get blood to the body, so the infant presents with shock, poor perfusion and acidosis as the duct closes. Mixing lesions depend on blood crossing between parallel or common circulations. Left-to-right shunts cause pulmonary over-circulation and heart failure weeks later as PVR falls.

Ductal-Dependent Pulmonary Blood Flow

Ductal-Dependent Systemic Blood Flow

Mixing Lesions

Left-to-Right Shunts

d-Transposition of the great arteries is the most common cyanotic lesion presenting in the first day. The infant is often a well-grown term baby with marked cyanosis but little respiratory distress. The chest radiograph may show a narrow mediastinum ("egg on a string"). Survival depends on mixing at the atrial, ductal or ventricular level. PGE1 keeps the duct open, but if the atrial septum is restrictive, the infant needs an urgent balloon atrial septostomy. Definitive repair is the arterial switch operation, usually in the first weeks of life.

Obstructed TAPVR is the lesion that most often fools clinicians. The pulmonary veins drain through a narrowed channel (often below the diaphragm), causing severe pulmonary venous congestion. The infant has severe cyanosis, respiratory distress and a chest radiograph with diffuse pulmonary edema or a "white-out" pattern with a normal-sized heart. It can look like severe lung disease or PPHN. PGE1 does not help and can worsen pulmonary edema by increasing pulmonary flow. It is a surgical emergency.

Hypoplastic left heart syndrome often appears well at birth. As the duct closes in the first days, the infant develops tachypnea, poor perfusion, gray color, weak pulses, oliguria and severe metabolic acidosis. Once PGE1 is running, the goal is to balance pulmonary flow (Qp) and systemic flow (Qs). Too much oxygen or hyperventilation lowers PVR and steals flow from the body. Target saturations are typically about 75% to 85% per cardiology orders, and supplemental oxygen is usually avoided unless ordered.

Critical coarctation may present at days 3 to 10 with shock when the ductus closes. Look for weak or absent femoral pulses, a right arm systolic pressure more than about 10 to 20 mm Hg higher than the leg pressure, and differential saturations. Four-extremity blood pressures help identify it.

Tetralogy of Fallot includes a VSD, overriding aorta, right ventricular outflow obstruction and right ventricular hypertrophy. The degree of outflow obstruction determines cyanosis. Chest radiograph may show a boot-shaped heart with reduced pulmonary markings.

Memory Aid: Systemic ductal-dependent lesions (the left-sided obstructions) present with shock; pulmonary ductal-dependent lesions (the right-sided obstructions) present with cyanosis. Left lesion, low output. Right lesion, rising blue.

PGE1 relaxes ductal smooth muscle and keeps the ductus arteriosus open, or reopens it if it recently closed. It is started for any suspected ductal-dependent lesion before the diagnosis is confirmed, because delay can be fatal. Typical starting doses are 0.05 to 0.1 mcg/kg/min, then reduced to the lowest effective dose (often 0.01 to 0.05 mcg/kg/min), per order and unit protocol.

Adverse effects and nursing actions:

Cutaneous flushing, especially with peripheral infusions.

Hypotension and bradycardia from vasodilation; monitor BP and have volume ready.

Long-term effects: cortical hyperostosis (bone changes), gastric outlet obstruction from antral hyperplasia, and jitteriness or seizures.

Infuse through a dedicated line or a compatible line with no interruption; an interruption may let the ductus close within minutes to hours. Label clearly and avoid flushing the line.

Worked calculation: A 3.2 kg infant is ordered PGE1 at 0.05 mcg/kg/min. Dose per minute = 0.05 × 3.2 = 0.16 mcg/min. Dose per hour = 0.16 × 60 = 9.6 mcg/h. If the pharmacy concentration is 10 mcg/mL, the rate = 9.6 ÷ 10 = 0.96 mL/h.

Exam Tip: When a term neonate develops shock or profound cyanosis in the first week and a cardiac lesion is possible, the best answer is usually to start PGE1 while preparing for an echocardiogram, not to wait for the echo.

The hyperoxia test helps separate cardiac from pulmonary causes of cyanosis. An arterial blood gas from the right radial artery (preductal) is obtained in room air and again after about 10 minutes of 100% oxygen. A PaO2 above about 150 mm Hg makes cyanotic heart disease unlikely. A PaO2 that stays below about 100 mm Hg (often under 50) suggests a fixed intracardiac right-to-left shunt or mixing lesion. Results in between can occur with lung disease or PPHN. Because it requires high oxygen exposure, many units now rely on early echocardiography instead, but the logic still appears on the exam.

Pulse oximetry screening for CCHD is done after 24 hours of age (or before discharge if earlier) in well newborns. Measure the right hand (preductal) and one foot (postductal). Under the current AAP-endorsed algorithm:

A failed screen needs a full evaluation for hypoxemia, including cardiac, respiratory and infectious causes. The screen can miss lesions, especially coarctation, so a normal screen never overrides clinical signs.

Worked example: Right hand 96%, foot 92%. The difference is 4 points, which is more than 3, so the screen is repeated in 1 hour rather than passed.

A hypercyanotic spell occurs when right ventricular outflow obstruction worsens or SVR falls, increasing right-to-left shunting across the VSD. Triggers include crying, feeding, defecation, dehydration and procedures. The infant becomes deeply cyanotic, irritable then lethargic, hyperpneic, and the murmur may soften or vanish because less blood crosses the obstructed outflow.

Priority actions in order:

Calm the infant and place in a knee-chest position (hips flexed to the chest), which increases SVR and venous return.

Give supplemental oxygen.

Give morphine as ordered to reduce agitation and hyperpnea.

Give an IV fluid bolus as ordered to improve preload.

If spells continue, anticipate phenylephrine to raise SVR and a beta-blocker such as esmolol or propranolol to relax the infundibulum, per order.

Prepare for urgent surgical consultation; a spell is often the indication for earlier repair or a shunt.

Common Trap: Choosing an inotrope such as dopamine or epinephrine for a tet spell. Increasing contractility worsens infundibular obstruction. The goal is to raise SVR and relax the outflow tract.

Clinical Scenario: A 4-day-old term infant brought back to the emergency area is gray, tachypneic and mottled, with a capillary refill of 5 seconds, absent femoral pulses and a pH of 7.08. The nurse anticipates and prepares for PGE1 at the ordered dose, establishes access, prepares for intubation because of the apnea risk, supports ventilation, and obtains four-extremity BPs. Absent femoral pulses with shock on day 4 suggest closure of the ductus in critical coarctation or interrupted arch.

Classify lesions by physiology: ductal-dependent pulmonary flow (cyanosis), ductal-dependent systemic flow (shock), mixing, and left-to-right shunts.

Start PGE1 for suspected ductal dependence without waiting for an echocardiogram; anticipate apnea, fever, flushing and hypotension.

Obstructed TAPVR mimics lung disease, does not respond to PGE1 and needs emergency surgery.

CCHD screening fails with any value under 90%; repeat for 90% to 94% or a difference over 3 points.

Tet spell care: calm, knee-chest, oxygen, morphine, fluid, then phenylephrine; avoid inotropes.