**13. Summary**

The evaluation of the cyanotic neonate should be done in an algorithmic manner that focuses on evaluation and management of the most life-threatening disease processes first.The hyperoxia test should be utilized early in the evaluation of these patients to assist in the differentiation and categorization of the cyanotic event. Be careful to obtain a detailed history of the prenatal, birth, and postnatal periods, as physicians will often be able to narrow the differential by the history alone. Neonates may decompensate very quickly, and preparations for a life-saving emergency should be made as soon as possible.
