Final answer:
The critical care nurse should promptly report the absence of drain output to the physician when monitoring a patient following renal surgery.
Step-by-step explanation:
The critical care nurse should promptly report the absence of drain output to the physician when monitoring a patient following renal surgery. A lack of drain output may indicate a blockage or malfunction in the drainage system, which could lead to complications such as infection or urinary retention. It is important for the nurse to promptly notify the physician so that appropriate interventions can be taken to address the issue and ensure the patient's optimal recovery.