Final answer:
If a nurse cannot hear sounds through the stethoscope during BP measurement, the initial action should be to ensure the stethoscope is properly plugged in and operational.
Step-by-step explanation:
When a nurse cannot hear the sounds through the stethoscope during blood pressure (BP) measurement, the first action they should take is to check if the stethoscope is plugged and functioning properly before attempting further measurements. A proper functioning stethoscope is essential for detecting Korotkoff sounds that are crucial for determining systolic and diastolic pressures. If after checking the stethoscope the issue persists, other actions such as retaking the BP with the same or an electronic cuff may follow.