Furthermore, the superadded respiratory illness will result in more desaturated blood returning to the heart from the pulmonary veins, due to worsening ventilation and perfusion mismatch. The underlying anatomy and circulatory physiology results in increased systemic venous admixture as a result of inferior caval blood being directed into the systemic circulation, and pulmonary venous blood returning to the systemic venous circulation, via collateral circulation. In the setting of a child with cyanotic congenital heart disease with a pulmonary-to-systemic blood flow ratio of less than 1:1, presenting with an intercurrent lower respiratory illness, who may also have pulmonary arteriovenous collaterals, the cause of the respiratory distress and worsening hypoxemia can be multifactorial.
Following the institution of oxygen therapy, the saturation increases to 75%, with some resolution of the respiratory distress.
As part of the initial assessment of the child, the pulse oximeter is noted to read a saturation of 65% on room air and the child appears to have some perioral cyanosis as well as mild respiratory distress.
A 10-month-old child with a history of hypoplastic left heart syndrome, who has undergone a bidirectional cavopulmonary anastomosis four months earlier, presents with a three-day history of cough, rhinorrhea, and increased respiratory rate.
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