Since this patient in the question has developed respiratory distress while inseing a central venous catheter, the most likely cause is pneumothorax. Pneumothorax is the most frequently repoed acute complication of subclan vein catheterization. Complications of subclan vein catheterization can be acute or chronic. Acute complications occur within 30 days of procedure, it includes: failure of placement of catheter, pneumothorax, hemothorax, hemopneumothorax, hemorrhage, misplacement of catheters, aerial injury, air embolism, injury to veins, cardiac chambers and neural structures. Ref: Venous Catheters: A Practical Manual By Philip C. Pieters, Page 250 ; Critical Care Study Guide: Text and Review By Gerard J. Criner, Pages 55-6