Which of the following is classified as a post-operative complication?

The classification of post-operative complications encompasses various issues that may arise after a surgical procedure, impacting the recovery and overall health of the patient. Infection is a notable example of a post-operative complication because it can occur at the surgical site or systemically following the operation. Infections can result from bacteria entering the body during surgery, and they can lead to significant morbidity if not identified and treated promptly.

Post-operative infections may manifest as wound infections, pneumonia, urinary tract infections, or other types of infections, and usually come after the initial recovery period. This emphasizes the importance of monitoring patients closely for signs of infection following surgery, as early intervention can prevent more severe complications.

In considering the other options, while hemorrhage can certainly occur post-operatively, it is typically classified as an intraoperative complication if identified during the surgery. Anesthesia reactions, though serious, are generally addressed under perioperative complications, whereas allergic reactions are treated more broadly, not specific to the post-operative phase. Hence, infection stands out clearly as a definitive post-operative complication that requires vigilant assessment and management.