A nurse is caring for a client with a newly inserted left subclavian central line. What assessment finding one hour after insertion warrants immediate action by the nurse?

Choice A reason: Mild discomfort near the insertion site is an expected finding after central line placement due to local tissue irritation. This can be managed with routine comfort measures and does not require immediate intervention. Choice B reason: The presence of blood return when checking catheter patency indicates that the line is properly positioned within the vascular system. This is an expected and desired finding, not a complication. Choice C reason: An antimicrobial disk at the insertion site is a preventive measure used to reduce the risk of catheter-related bloodstream infections. Its presence is appropriate and does not indicate a problem. Choice D reason: Absent breath sounds on the same side as a recently inserted subclavian central line strongly suggest a pneumothorax, a potentially life-threatening complication caused by accidental puncture of the lung. This finding requires immediate action to prevent respiratory compromise.