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Anesthetic Guidelines, Part 1 - Classification of Patient Status

This article is the first in a series intended to present technicians with guidelines for making sure their patient has the safest anesthetic experience it is within their power to provide. The information is based on 2011 AAHA guidelines.

There are no safe anesthetic agents, there are no safe anesthetic procedures. There are only safe anesthetists. – Robert Smith, MD

Prior to any anesthetic procedure, it is necessary for the veterinarian to evaluate a minimum data base which includes results of physical examination, history and diagnostic tests. Based on this evaluation, a status should be assigned to the patient before the anesthetic protocol is chosen. The most widely accepted classification system is that proposed by the American Society of Anesthesiologists (ASA), presented below. Patients assigned a higher ASA status are at a greater risk for complications and require additional precautions to help ensure an uneventful recovery. Record the status number on the patient’s anesthetic flow chart, or as a separate entry if computerized.


Physical Condition

Examples of Clinical Situations

Class I
Minimal risk

Normal healthy animal, no underlying disease

Ovariohysterectomy, castration, declaw, hip dysplasia radiograph

Class II
Slight risk

Animals with slight to mild systemic disturbances
Animals are able to compensate
No clinical sign of disease

Neonate or geriatric animal; obesity; fracture without shock; mild diabetes; parasites; mild malnourishment

Class III
Moderate risk

Animals with moderate systemic disease or disturbances
Mild clinical signs
Multiple signs

Anemia; anorexia; moderate dehydration; low-grade kidney disease; low-grade heart murmur or cardiac disease; moderate fever

Class IV
High risk

Animals with preexisting systemic disease or disturbances of a severe nature.

Severe dehydration; shock; uremia or toxemia; severe anemia; high fever; uncompensated heart disease

Class V
Grave risk

Surgery often performed in desperation on animals with life-threatening systemic disease or disturbances not often correctable by an operation; includes all moribund animals not expected to survive 24 hours

Advanced cases of heart, kidney, liver, lung or endocrine disease; profound shock; major head injury; severe trauma; pulmonary embolus; end stage heartworm