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American Society of Anesthesiologists (ASA) Physical Status Scale

Class I 

Minimal Risk

Normal healthy animal, no underlying disease

Working Definition: “Young, healthy patient for elective procedure”


Class II

Slight risk, minor disease present

Animal with slight to mild systemic disturbance, animal able to compensate

Examples: neonate or geriatric animals, obesity

Working Definition: “Healthy patient that needs a procedure”


Class III

Moderate risk, obvious disease present

Animal with moderate systemic disease or disturbances

Examples:  systemic disease or condition that is compensated

Working Definition: “Systemic disease complicates anesthesia”


Class IV

High risk, significantly compromised by disease

Animals with preexisting systemic disease or disturbances of a severe nature

Examples:  systemic disease or condition that is uncompensated

Working Definition: “Systemic disease jeopardizes anesthesia”


Class V

Extreme risk, moribund

Surgery often performed in desperation on animal with life threatening systemic disease

Examples:  advanced systemic disease or condition (e.g. cardiac failure, renal failure, hepatic failure, cerebral insult, end stage endocrine disease, etc.), uncompensated shock, severe trauma, terminal malignancy or infection that is a constant threat to life.

Working Definition: “Patient will likely die with or without the procedure”

denotes emergency and can be added to any of the above classes that require immediate intervention or surgery.