If a patient develops shortness of breath and unilateral distension after placing a central venous catheter, what should be done first?

In situations where a patient experiences shortness of breath and unilateral distension after the placement of a central venous catheter, the most appropriate initial action is to immediately stop treatment. This is critical because the symptoms suggest a possible complication, such as a pneumothorax or catheter-related thrombosis.

Stopping treatment helps to prevent further harm and allows for a safer evaluation of the situation. Continuing treatment could worsen the patient's condition, especially if air has entered the vascular system or the catheter has migrated to an incorrect position.

Following the cessation of treatment, it is essential to conduct a thorough evaluation including assessing the catheter site. This step can help determine the cause of the patient's symptoms, guide further interventions, and ensure patient safety. Providing oxygen or notifying the family may become relevant later but does not address the immediate potential for harm caused by continuing treatment. Hence, stopping treatment is the priority in this scenario.