From the Guidelines
The best next step in evaluation of this patient's symptoms is to pass a catheter through the nares (option D). This newborn is presenting with cyanosis that occurs specifically during feeding but resolves with crying, which strongly suggests choanal atresia, as the symptoms are consistent with intermittent obstruction of the nasal passages during feeding 1. Choanal atresia is a congenital blockage of the nasal passages that causes respiratory distress in obligate nasal breathers like newborns, particularly during feeding when the mouth is occupied. The normal pulse oximetry readings when not feeding and the normal chest radiograph support this diagnosis rather than cardiac or pulmonary pathology. Passing a catheter through the nares would confirm the diagnosis by demonstrating the obstruction. This is preferred over the other options because it directly addresses the most likely cause of the intermittent cyanosis during feeding. Blood cultures would be appropriate for suspected infection, methemoglobin measurement for persistent cyanosis, echocardiogram for suspected cardiac defects, and head ultrasound for neurological concerns - none of which fit this clinical picture as well as choanal atresia. Measurement of blood methemoglobin level (option B) could be considered if choanal atresia is ruled out, as methemoglobinemia can cause cyanosis not associated with hypoxemia, cold exposure, or other known explanation, with MetHb levels typically >10% if blue discoloration is present 1. However, given the clinical presentation of cyanosis during feeding that resolves with crying, choanal atresia is the more likely diagnosis.
From the Research
Evaluation of the Patient's Symptoms
The patient's symptoms, such as blue tinge on the face during feeding, suggest a possible condition of methemoglobinemia. The key findings in this case include:
- The patient's face develops a blue tinge during feeding, which improves with crying
- Pulse oximetry readings are 97% and 96% on room air, measured from the right hand and left foot, respectively
- The palate appears intact, and lung examination shows equal sounds bilaterally
- There are no murmurs or gallops, and peripheral pulses are strong
Possible Causes and Diagnostic Tests
The possible causes of methemoglobinemia include oxidizing reactions to certain medications or substances. Diagnostic tests for methemoglobinemia include:
- CO-oximetry, which is superior to standard pulse oximetry in detecting methemoglobinemia 2
- Measurement of blood methemoglobin level, which can help confirm the diagnosis
Best Next Step in Evaluation
Based on the patient's symptoms and the possible causes of methemoglobinemia, the best next step in evaluation would be to:
- Measure blood methemoglobin level to confirm the diagnosis of methemoglobinemia 2, 3, 4, 5 This test can help determine if the patient has methemoglobinemia and guide further treatment. Other options, such as drawing blood cultures or obtaining an echocardiogram, may not be directly relevant to the patient's symptoms and the possible diagnosis of methemoglobinemia.