Final answer:
The nurse should immediately notify the client's practitioner due to the low blood pressure reading, which could be indicative of postpartum hemorrhage or other complications.
Step-by-step explanation:
When the fundus remains firm and four fingerbreadths above the umbilicus after urinary catheterization, and the bladder is known to be empty, the current data suggest that the bladder is no longer causing uterine displacement. Given that the client's blood pressure (BP) is significantly low at 86/40, which could indicate postpartum hemorrhage (PPH) or other forms of hypovolemia, the most immediate concern is the client's stability. The nurse should C. Notify the client's practitioner immediately to address the potential of PPH or other complications. While routinely palpating the fundus and checking vital signs are important aspects of postpartum care, the priority in this scenario is the client's low blood pressure and ensuring timely medical evaluation and intervention.