Final answer:
The absence of occult blood in the stools is the best indicator of propranolol's effectiveness in a patient with cirrhosis and esophageal varices because it suggests reduced bleeding risk, which is a direct benefit of the medication in this context.
Step-by-step explanation:
The best indicator to the nurse that propranolol has been effective for a patient with cirrhosis and esophageal varices is C. Stools test negative for occult blood. Propranolol is a beta-blocker used to treat conditions related to the cardiovascular system, including high blood pressure and heart failure, and it is also used in the prevention of variceal bleeding in patients with portal hypertension related to cirrhosis. The fact that stools test negative for occult blood suggests that the esophageal varices are less likely to be bleeding, which is a direct benefit of the beta blocker in reducing portal hypertension and therefore strain on varices. While a normal blood pressure and apical pulse rate may also indicate the effectiveness of propranolol in general, the absence of occult blood specifically addresses the complication related to varices. Reports of no chest pain, while positive, do not directly correlate with the risk of variceal bleeding.