Pediatric Examination and Board Review Read Free Page A

in distal capillary beds and is commonly seen in normal neonates. The clinical detection of cyanosis occurs when approximately 3-5 g/dL of desaturated hemoglobin is present in the systemic circulation. The most common causes of central cyanosis in the neonate include cyanotic heart disease, hemoglobinopathies, and respiratory distress.
    11. (A) The test most likely to help differentiate cyanotic heart disease from respiratory disease is the hyperoxia test. In this test, 100% oxygen is administered to the patient and the partial pressure of oxygen is measured. In patients with cyanotic heart disease, the partial pressure of oxygen rarely increases above the level of 100 mm Hg, whereas in lung disease there is usually some change from the baseline PO 2 with administration of oxygen. The lack of response to oxygen in cyanotic heart disease is a result of fixed right-to-left shunting of desaturated blood to the systemic circulation. Although the other tests mentioned may be helpful in the evaluation of the cyanotic neonate, they are not as sensitive in differentiating cardiac from respiratory etiologies.
    12. (A) Cardiac lesions associated with cyanosis include
• transposition of the great arteries (the most common)
• tetralogy of Fallot
• truncus arteriosus
• tricuspid atresia
• pulmonary atresia
• total anomalous pulmonary venous return
    Other lesions include single-ventricle physiology such as hypoplastic left heart syndrome, or Ebstein anomaly of the tricuspid valve with right-to-left shunting across an atrial septal defect.
    13. (A) In patients with cyanosis because of heart disease, there is either obligate mixing of saturated and desaturated blood reaching the systemic circulation (eg, truncus arteriosus) or decreased effective pulmonary blood flow. In either situation, promotion of increased pulmonary blood flow or improved mixing of desaturated and saturated blood would increase the systemic oxygen saturation. This is acutely achieved by infusion of prostaglandin E 1 to reestablish (or maintain) patency of the ductus arteriosus. Therefore, in situations where cyanosis because of heart disease is suspected, infusion of prostaglandin E 1 should be instituted as soon as possible.
    14. (D) Patients with tetralogy of Fallot are at risk for a hypercyanotic “tet” spell. This usually occurs in patients older than 2 years of age, although it has been reported at younger ages. The mechanism of a hypercyanotic spell is acute and progressive pulmonary stenosis, with increased right-to-left shunting of desaturated blood to the systemic circulation. This is precipitated by an increase in circulating catecholamines, anxiety, hypoxia, or dehydration. Interventions to break this cycle include administration of oxygen, morphine, propranolol, or phenylephrine, placing the child in a knee-chest position. In extreme cases, muscle relaxation and intubation are required. Rectal stimulation would serve to worsen the crisis by increasing the catecholamine levels ( Figure 1-2 ).

    FIGURE 1-2. Tetralogy of Fallot. There are infundibular and pulmonary stenoses. There is also right-to-left shunting at the atrial level. (1) Superior vena cava, (2) inferior vena cava, (3) right atrium, (4) right ventricle, (5) right pulmonary vein, (6) left atrium, (7) left ventricle, (8) aorta.
     
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    15. (E) Complications in patients with chronic cyanosis include polycythemia (compensation for decreased systemic oxygen tension), and risk of strokes because of an increased propensity for forming blood clots and increased blood viscosity. This is particularly concerning when the hematocrit is higher than 70%. A relative anemia may be seen in patients with cyanosis with low hemoglobin indexes. Some have suggested that this increases the risk of stroke because of increased blood viscosity. Another complication is brain abscess formation because of poor venous blood flow and increased susceptibility to infection. Impaired cognitive function is