Why do doctors tell you not to smoke after midnight when getting your gallbladder removed?

Cigarette Smoke can cause respiratory problems while under and upon waking up from anesthesia. Making the lungs more suceptiable to filling with fluid and potentially causing pnumonia. Cigarette smoke also makes it harder for the individual to get proper oxygenation throughout the body. This can cause the person to bleed more during the procedure, making it harder to complete the procedure without complications. All of these puts the person being operated on at higher risk for things to go wrong. This is true with every surgery not just gall bladder operations.