Pediatric emergency medicine trisk 128

shunting of oxygenated blood through the ductus arteriosus may present with the
rare findings of an upper body that is blue and the lower body pink.
The need for laboratory evaluation is determined based on the historical
features and physical findings established on initial encounter ( Fig. 21.1 ). All
patients, except very well-appearing newborns and well-appearing cold-exposed
patients with peripheral cyanosis only, require measurement of PaO2 . Oxygen
saturation by pulse oximetry may be helpful in determining if hypoxemia is the
cause of cyanosis, but it may also be misleading when abnormal forms of Hb
such as methemoglobin or carboxyhemoglobin are present.
If the PO2 is normal, further laboratory evaluation is determined by the degree
of ill appearance. Well-appearing cyanotic children with normal PO2 usually have
less urgent conditions, such as polycythemia, mild methemoglobinemia, cold
exposure, newborn acrocyanosis, or dermatologic findings. In this case,
laboratory evaluation might include a methemoglobin level and complete blood
count (CBC), or no further investigation may be warranted. Despite a normal PO2
, an ill-appearing cyanotic patient may have a more emergent condition such as
severe methemoglobinemia or septic or cardiogenic shock and may require more
aggressive laboratory investigation. This might include CBC, co-oximetry
including methemoglobin level, blood cultures, and blood chemistry. Blood with
high methemoglobin content may appear very dark or “chocolate brown” and
fails to turn red on exposure to air, such as in a drop on filter paper.
Methemoglobinemia may improve with intravenous methylene blue.
If the PO2 is decreased, oxygen therapy should be instituted. In general,
cyanosis caused by decreased alveolar ventilation or diffusional abnormalities
often improves with delivery of 100% O2 . However, hypoxemia caused by
decreased pulmonary perfusion or shunt will have minimal response to oxygen
therapy and can be assessed objectively with the hyperoxia test during which
administration of 100% O2 for 10 minutes will increase the PaO2 to over 150 mm
Hg in primary pulmonary deficiency but will fail to increase past 100 mm Hg in
shunting due to congenital heart disease. A chest radiograph should be obtained
for evaluation. Abnormalities of the lungs may confirm pulmonary disease, and

changes in the cardiac size or silhouette may suggest cardiac causes. If the chest
radiograph is normal, other reasons for diminished PaO2 , such as CNS- or chest
wall–related respiratory depression, upper airway obstruction, or pulmonary
perfusion abnormalities, must be entertained. If a concomitant murmur or other
concern for cardiac disease exists, an electrocardiogram (ECG) is essential.


Abnormal ECGs may suggest cardiac etiologies, either congenital or acquired (
Table 21.1 ). Echocardiography will help establish the definitive diagnosis.
Suggested Readings and Key References
Cortazzo JA, Lichtman AD. Methemoglobinemia: a review and recommendations
for management. J Cardiothorac Vasc Anesth 2014;28(4):1043–1047.
Hall JE. Principles of gas exchange; diffusion of oxygen and carbon dioxide
through the respiratory membrane. In: Guyton and Hall Textbook of Medical
Physiology . 13th ed. Philadelphia, PA: Elsevier; 2016:517–526.
Lundsgaard C, Van Slyke DD. Cyanosis. Medicine 1923;2:15.
Roche SL, Greenway SC, Redington AN. Tetralogy of Fallot with pulmonary
stenosis, pulmonary atresia, and absent pulmonary valve. In: Allen HD, ed.
Moss and Adams’ Heart Disease in Infants, Children, and Adolescents:
Including the Fetus and Young Adult . 9th ed. Philadelphia, PA: Wolters
Kluwer; 2016:1039–1040.
Strobel AM, Lu LN. The critically ill infant with congenital heart disease. Emerg
Med Clin North Am 2015;33(3):501–518.

Additional Resources Online


e-FIGURE 21.1 Acrocyanosis. Note blueness of the hands. (Reprinted with permission from
Kyle T, Carman S. Essentials of Pediatric Nursing . 2nd ed. Philadelphia, PA: Lippincott
Williams & Wilkins; 2012.)

e-FIGURE 21.2 Acrocyanosis. This commonly appears on the feet and hands of babies shortly
after birth. This infant is a 32-week newborn. (Reprinted with permission from Fletcher M.
Physical Diagnosis in Neonatology . Philadelphia, PA: Lippincott-Raven Publishers; 1998.)