Final answer:
The nurse is most concerned about the complication of cardiac decompensation for a postpartum client with known cardiac disease. This is because postpartum recovery demands can lead to decompensation, particularly in those with pre-existing cardiac conditions.
Step-by-step explanation:
The nurse instructs a client with known cardiac disease who has been admitted to the postpartum care unit to use the call button for assistance when getting out of bed or caring for her infant. The postpartum complication of greatest concern for this client would be D. Cardiac decompensation. This is because the stress of labor and delivery followed by the demands of postpartum recovery can be significant, and in someone with pre-existing cardiac issues, this can lead to decompensation, where the heart is unable to maintain adequate blood circulation.
While postpartum hemorrhage, thrombophlebitis, and infection are also concerns in the postpartum period, the nurse's specific instructions suggest concern for the client's cardiac status. The stress and physical effort required to move around and care for a newborn could potentially exacerbate symptoms of cardiac disease and put the client at risk for complications such as heart failure or arrhythmias, which would require immediate medical attention.