Final answer:
New onset of chest pain warrants follow-up nursing actions after an air leak into the closed chest drainage system (CDS) following a thoracotomy.
Step-by-step explanation:
An air leak into the closed chest drainage system (CDS) after a thoracotomy can be a concerning situation. Out of the given options, the assessment that would warrant follow-up nursing actions is B) New onset of chest pain. Chest pain can indicate a worsening condition or complications such as pneumothorax or infection. It is essential to assess and monitor the patient closely, notify the healthcare provider, and initiate appropriate interventions.