American Society of Anesthesiologist (ASA) Physical Status Classification System

By: Rebecca S. Salazar, DVM, DACVAA

The ASA Physical Classification System has been in use in human medicine for over 60 years. The classification system has been adapted for veterinary patients. An ASA classification should be assigned to every patient undergoing sedation or general anesthesia.

The purpose of the ASA classification system is to provide the anesthetist with appropriate patient assessment and to communicate preanesthetic co-morbidities with staff and owners. Physical status classification alone does not predict surgical outcomes, but is a helpful way to predict perioperative and postoperative risk, mainly morbidity and mortality.

The definitions and examples given below are only guidelines. The classification system is subjective and assessment can vary among doctors and staff. The ASA classification system is to be used as a communication and assessment tool. Additionally, the chosen status is to be noted in the patient record prior to the anesthetic event. Different hospitals can choose specific examples to fit their hospital needs.

ASA I	Normal healthy patient that is not obese	Non-obese
ASA II	A patient with mild systemic disease, without substantial functional limitations	Obese, brachycephalic, asymptomatic congenital abnormalities, scheduled cesarean section
ASA III	A patient with severe systemic disease with substantial function limitations	One or more moderate co-morbidities not limited to ACVIM stage C cardiac disease, non-controlled diabetes, various stages of kidney disease
ASA IV	A patient with severe systemic disease that is a constant threat to life and will not survive without surgical intervention	One or more severe co-morbidities, not limited to severe cardiac disease, sepsis, shock, severe renal disease, uncontrollable hemorrhage, organ ischemia and or organ entrapment
ASA V	A moribund patient who is not expected to survive past surgical intervention	Massive trauma and or severe hemorrhage, multiple organ dysfunction, severely ischemic tissues causing further cellular apoptosis

Addition of the letter “E” denotes an emergency.
There is an ASA VI classification, for declared brain dead patients whose organs are being removed for donor purposes.
Pregnancy is not a disease, but the physiologic state is altered from a non-gravid animal, hence an uncomplicated scheduled cesarean section or simple procedure done on a healthy gravid patient should be considered an ASA II.
Age is not a disease, however most geriatric patients have some form of physiologic compensation, due to disease and or the aging process, therefore an uncomplicated procedure in a geriatric patient with no known co-morbidities is considered an ASA II.
Brachycephalic patients have overall increased morbidity and mortality during and following any anesthetic event. Brachycephalic patients going an elective uncomplicated procedure should be given an ASA II classification.

References:

Mayhew D, Mendonca V, Murthy BVS. A review of ASA physical status – historical perspectives and modern developments. Anaesthesia 2019; 74:373-9
ASA House of Delegates. ASA Physical Status Classification System: Committee of Oversight- Economics. First published Oct. 15 2014, amended Dec. 13, 2020.
Gruenheid M, Aarnes TK, McLoughlin MA, et al. Risk of anesthesia-related complications in brachycephalic dogs. Journal of Vet Med Am. Vol 253:3. Aug 2018.