Final answer:
During a thoracentesis, a patient should remain still and avoid coughing or deep breathing as the catheter/needle is withdrawn.
Step-by-step explanation:
During a thoracentesis, a patient should remain still and avoid coughing or deep breathing as the catheter/needle is withdrawn. This is important to prevent damage to the lungs or disruption of the procedure. The clinician may provide instructions to the patient on how to maintain a relaxed posture or breathing pattern during the process.