top of page

Assessing Physical Status Prior to Anesthesia

You are presented with a 12 year old, obese (BCS 8/9) Chihuahua with a cough attributable to collapsing trachea. How do you assess anesthesia-related risk? Do you use a stratification system such as the American Society of Anesthesiologist's Physical Status (ASA PS) score? If so, what ASA PS would you give him?

And, really, who cares if you use a pre-anesthetic physical status scoring system? What’s the point?

Hopefully, most veterinary anesthetists are assessing the cardiorespiratory fitness of the patient at hand - even if unconsciously and even in high volume or low resource settings. Anesthesia presents a challenge to homeostasis and a sick patient may not withstand that challenge as easily as a well patient. Assessing physical fitness can help you decide if anesthetizing a certain patient in your clinical setting is even advisable, as well as guide how you manage that patient in the perioperative time period.

This kitten with an upper respiratory infection will be classified with a higher Physical Status score (I would call her a 3) than she would if she were well and healthy. If she has to be anesthetized before resolution of the infection, she may need more intensive perioperative care, including close monitoring and possibly oxygen supplementation into the recovery period. If you work in a setting in which cats are not intubated during anesthesia, you should consider it for this kitten!

The ASA PS classification system is the gold standard in preoperative fitness assessment. Originally developed in 1941 “for the collection and tabulation of statistical data in anesthesia” (1), the ASA PS has been used for more than 50 years to establish the physical health of humans presenting for an anesthetic event. In the most recent revision, in 2014, the ASA added back in examples of patients who would be stratified into each category. There are 6 classifications in the current ASA PS, ranging from a systemically robust PS I to a PS VI brain-dead organ donor. An E is added if the procedure is emergent. The most current version can be found here:

Obesity increases the risk of anesthetic-related repiratory complications and may be accompanied by systemic inflammation.

The ASA PS is NOT an assessment of total perianesthetic or perioperative risk, since many things, including the surgical procedure planned, the skill & training of the anesthetist and the surgeon, as well as the the resources at hand, contribute to the entirety of operative risk. For example, a well controlled diabetic dog having a dental cleaning and the same dog undergoing a resection and anastamosis for intestinal adenocarcinoma could have similar preanesthetic ASA PS classification but a vastly different overall perioperative risk.

I strongly believe that the anesthetist should not come up with a perianesthetic management plan - or even anesthetic drug plan - without first evaluating the patient and assigning an ASA PS score. This can help you decide what approach to take with an anesthetic event: a patient who is sick to begin with may not tolerate the same drugs or doses that a healthy patient can handle just fine! In addition, a less physically healthy patient may need more intensive monitoring and supportive care. Assigning a preanesthetic physical status score can also improve communication among providers, help in assigning resources within the clinic, promote better record-keeping, and allow for statistical analysis of anesthetic events and outcomes (it’s original intent).

There is no universally accepted veterinary version of ASA PS. I think that veterinary patients often get classified with a higher ASA score than a similar human patient would receive. For example, mild anemia or a clinically silent heart murmur is not a PS III patient!

Here is the version I use:

The version of Physical Status assessment that I use to evaluate veterinary patients prior to anesthesia

A few big differences from the human version immediately stand out to me:

1) lifestyle diseases such alcoholism and smoking don’t have to be considered though obesity sure does and heavy second hand smoking may!

2) many fewer of our patients will be ASA PS IV and V due to the intensive, expensive, and potentially prolonged perioperative care required.

3) there is no PS VI classification in clinical veterinary medicine

One problem of the ASA PS classification is that it does have a hefty dose of subjectivity and many studies indicate only modest inter-rater consistency. (2, 3) Despite this inherent subjectivity, ASA physical status has been shown repeatedly to correlate with patient outcomes, including the risk of death. (2, 4, 5)

Do you use a version of the American Society of Anesthesiologists Physical Status score for your veterinary patients?

Do you find it helpful in thinking about case management?

Have you adapted the traditional score into something different? If so, why and what has this added for you?

1. Saklad M. Grading of patients for surgical procedures. Anesthesiology (1941) 5:281–4.

2. Sankar A, Johnson SR, Beattie WS, Tait G, Wijeysundera DN. Reliability of the American Society of Anesthesiologists physical status scale in clinical practice. Br J Anaesth. 2014 Sep;113(3):424-32.

3. McMillan M, Brearley J. Assessment of the variation in American Society of Anaesthesiologists Physical Status Classification assignment in small animal anaesthesia. Vet Anaesth Analg. (2013) 40:229–36.

4. Portier K & Ida KK. The ASA Physical Status Classification: What Is the Evidence for Recommending Its Use in Veterinary Anesthesia?-A Systematic Review. Front Vet Sci. 2018 Aug 31;5:204.

5. Smith MD, Barletta M, Young CN, Hofmeister EH. Retrospective study of intra-anesthetic predictors of prolonged hospitalization, increased cost of care and mortality for canine patients at a veterinary teaching hospital. Vet Anaesth Analg. 2017 Nov;44(6):1321-1331.

2,125 views0 comments

Recent Posts

See All


bottom of page