Walsh: Perinatal and Pediatric Respiratory Care, 3rd Edition

Chapter 30: Congenital Cardiac Defects

Answers to Assessment Questions and Clinical Scenarios

1.	C
Rationale: Once the umbilical vessels are clamped, the low-pressure system of the placenta is removed from the fetal circulation. Pressures in the right side of the heart decrease and pressures in the left side increase. During this time, the pressure in the aorta increases and becomes greater than the pressure in the pulmonary artery, thus decreasing the amount of shunting through the ductus arteriosus and foramen ovale.
2.	D
See Box 30-2
Rationale: Interventions that affect PVR
Increase
•	 pH
o	 Minute ventilation (VE) to  Paco2 to 45 mm Hg
o	 Inhale CO2 to  pH
•	 FiO2 < 0.21, as needed
•	 Mean arterial pressure (MAP)
o	 Peak inspiratory pressure (PIP),  PEEP,  F,  Freq,  I/E ratio
•	Treatment with adrenergic agents
o	Dopamine (high dose)
o	Epinephrine
o	Norepinephrine
o	Phenylephrine
Decrease 
•	 pH
o	 VE to  Paco2 to <45 mm Hg
•	 FiO2
•	 PEEP
•	 MAP
•	Pharmacology
o	Prostaglandin E1 (PGE1)
o	iNO
o	Prostacyclin
3.	C
Rationale: In discussions of congenital cardiac anomalies, two categories have typically been used to classify these lesions—cyanotic and acyanotic—referring to whether the principal direction of extrapulmonary shunting is right to left (cyanotic) or left to right (acyanotic).
4.	B
Rationale: With a PDA blood flows from left to right, from the aorta to the pulmonary artery, causing an increase in pulmonary blood flow.
5.	A
Rationale: The preoperative stability of patients with certain types of cardiac defects often depends partially on maintaining an elevated PVR. FiO2 of less than 0.21 may be administered to patients with ductal-dependent lesions to limit the pulmonary vasodilatory effect of oxygen, thus maintaining a high PVR. This prevents pulmonary overcirculation and helps to balance pulmonary and systemic blood flow.
6.	A
Rationale: Increasing PVR limits blood flow to the lungs, increasing blood flow to the left side of circulation and increasing cardiac output. Reducing PVR has the opposite effect, decreasing cardiac output.
7.	B
Rationale: Tetralogy of Fallot consists of four concomitant conditions:
1.	Overriding aorta
2.	Pulmonary stenosis
3.	Ventricular septal defect (VSD)
4.	Right ventricular hypertrophy
8.	B
Rationale: In complete transposition of the great arteries, the aorta and pulmonary artery circulation run in parallel.
9.	D
Rationale: For second- and third-phase repairs of hypoplastic left heart syndrome (HLHS) (Glenn and Fontan procedures), a low-rate, high tidal volume approach is recommended. This allows for the longest expiratory phase possible, which keeps mean intrathoracic pressure low, thus improving venous drainage from the superior and inferior vena cavae (SVC/IVC) into the pulmonary arteries.
10.	B
Rationale: End-tidal CO2 technology is remarkably reliable and increasing gradients are rarely a result of a loss of calibration or other equipment malfunction. An increasing P(et–a)CO2 (difference between end-tidal and arterial CO2 concentration) gradient can be caused by noncardiogenic derangements in the ventilation–perfusion relationship in the lung or by cardiac failure.