Final answer:
A b. T-tube drain is the correct choice for a cholecystostomy performed during gallbladder surgery when there is an infection, as it allows bile to drain externally and prevents accumulation.
Step-by-step explanation:
In the case of Mr. Robertson's intraoperative change from a cholecystectomy to a cholecystostomy due to gallbladder infection, the type of drain used is instrumental for postoperative management. The appropriate drain for a cholecystostomy is a b. T-tube drain. This type of drain serves two purposes: it allows bile to flow out of the gallbladder and prevents the accumulation of bile within the gallbladder, which could happen due to inflammation or infection. The T-tube is typically placed during the surgical procedure into the common bile duct and the gallbladder. It provides a pathway for bile to drain externally into a collection bag, which is necessary when the normal flow into the duodenum is interrupted or needs to be bypassed.