Final answer:
When performing a physical examination of a newborn with Down syndrome, the nurse should prioritize examining for cardiac abnormalities due to the common association with congenital heart disease, which requires early identification and management.
Step-by-step explanation:
During the physical examination of a newborn with Down syndrome, the nurse should prioritize examining for cardiac abnormalities. Down syndrome is often associated with congenital heart disease, among other health issues such as intellectual disability and a predisposition to certain medical conditions. Since cardiac problems can have a significant impact on the health and wellbeing of the child, it is essential for these to be identified and managed as early as possible.
While assessments for cognitive development and cleft lip are also relevant, they are typically conducted later in a child's development. Furthermore, signs of jaundice, while important, are not specific to Down syndrome and are a common condition that can occur in many newborns. Therefore, in terms of immediate health concerns, assessing the heart is most critical.