Emergency and intensive care is a special branch of veterinary medicine that deals with the diagnosis and treatment of life - threatening conditions. Receiving and treating patients who are in a life-threatening condition is a tremendous clinical challenge that requires precision as well as speed. Rule of 20, combined with laboratory diagnostics, provides great assistance to every clinician as it serves as a pattern of behavior with very detailed and organized methods of approach when receiving a critically ill patient. Anticipation is perhaps the most important step in successfully managing the fate of a critically ill patient. The rule of 20 serves as a reminder to clinicians to always monitor the status of critical organ systems, clinical and laboratory parameters and to always try to choose the most appropriate individual form of treatment for each and every patient because critically ill patients need this "package" in order to survive. Although the cause of critical illness will vary from patient to patient, almost every single one of them will develop symptoms of systemic inflammation such as increased capillary permeability, altered heart function or symptoms of shock. Damage to only one organ can very quickly result in a "domino effect" and damage, i.e result in dysfunction of several organs or organ systems. Animals should be accurately, efficiently and continuously monitored to detect and prevent potential organ failure in a timely manner. Working with such high-risk group of patients often requires an aggressive approach and continuous ongoing resuscitation, aggresive fluid replacement and detailed monitoring. The list of these 20 parameters should be evaluated at least on a daily basis, and in some patients several times a day. This list ensures that the clinical status and treatment strategy for each animal is comprehensive and meets all current animal needs. The rule of 20 is a dynamic concept, whose parameters will change with each laboratory test, with each greater understanding of the pathologies of the disease and with an effort to always be up to date with the latest tricks in medicine. It is very important to understand that this list is not used separately for each parameter, and that the most parameters are interreleted and should be perceived as one big whole.