What must be documented when performing anesthesia on an animal?

Documenting the method used, vital signs, and any complications encountered during anesthesia is essential because this information directly affects the welfare and safety of the animal. This documentation serves multiple purposes: it provides a clear record of the anesthetic protocols followed, allows for monitoring of the animal's physiological status during the procedure, and ensures that any complications can be tracked and addressed appropriately.

In anesthesia, keeping detailed records of vital signs is critical to detect any adverse reactions or changes in the animal's condition in real-time. If a complication arises, having this comprehensive documentation can help in assessing the situation and determining the next steps for treatment. Furthermore, this information is vital for continuity of care, particularly if the animal needs further treatment or monitoring post-anesthesia.

While owner consent and payment agreements, medical history and dietary restrictions, and the procedure's duration and recovery plan are all important aspects of veterinary practice, they do not directly relate to the specifics of monitoring and managing anesthesia itself. Thus, option C stands out as the most relevant and crucial documentation required during anesthesia procedures.