Kirby's Rule of 20 is a patient checklist including 20 parameters that should be checked daily in the critically ill patient. It reviews the established evidence-based information regarding patient checklist use in veterinary emergency and critical care medicine. The list of 20 will be discussed over a four-part series to give an appropriate level of information and attention to each patient parameter. Part 3 includes: renal function, gastrointestinal motility and integrity, nutrition, glucose and immune status.