How ASA scores help make anesthesia safer for your pet patients

And how it’ll make conversations about complicated procedures with pet owners easier to explain

Picture three patients:

  • The first is a 6-month-old, happy, healthy female intact kitten.
  • The second is a 6-year-old, overall healthy but very pregnant bulldog that needs a C-section.
  • The third is a 12-year-old, diabetic, cushingoid female intact poodle who is depressed, dehydrated, hypotensive and has a closed pyometra.

All three patients need to be spayed, yet each patient’s anesthesia risk is vastly different. Each will require different drugs and monitoring. Their recovery should be handled differently. Their prognosis is greatly different. Therefore, your conversation with each owner should be completely different.

Scoring System

This is where ASA classification can help. An ASA risk is a 1-to-5 score adapted for animals from human medicine’s American Society of Anesthesiologists. The system is based on the patient’s overall health, not the procedure being performed.

ASA Classifications

CLASS 1: Minimal risk of a normal healthy patient with no underlying disease.

CLASS 2: Slight risk of a slight to mild systemic disease. Neonates, geriatrics, obesity.

CLASS 3: Moderate risk, obvious systemic disease. Anemia, moderate dehydration, fever, low-grade heart murmur or cardiac disease.

CLASS 4: High risk with severe, systemic, life-threatening disease. Severe dehydration, shock, uremia, toxemia, high fever, uncompensated heart disease, uncompensated diabetes, pulmonary disease, emaciation.

CLASS 5: Extreme risk, moribund; patient will probably die with or without surgery. Advance cases of heart, kidney, liver or endocrine disease; profound shock, severe trauma, pulmonary embolus, terminal malignancy.

CLASS E: Emergency. Can be attached to each class in case of emergency surgery.

Attributing an ASA score is somewhat subjective, but it should help to label certain patients as needing more preop testing, preop stabilization, a more experienced anesthesia technician or more advanced intraop monitoring.

Even though patients may be having the same surgery, such as a spay, their ASA risk may be completely different.

A Spanish study1 evaluated over 2,000 dogs that underwent anesthesia. A death rate of just over 1 percent (26 patients) was recorded. A direct correlation was found between the patients’ ASA score and the death rate:

  • 0.3 percent of fatalities involved ASA 1 and 2 scores.
  • 1.7 percent of fatalities had ASA 3 scores.
  • 13 percent of fatalities were ASA 4 or 5 patients.

Keep Closer Watch

About one-fourth of the deaths happened during surgery, while the others occurred in the postop period. This serves as a good reminder that patients should be monitored closely after extubation. Walking away from patients as soon as they’re extubated is so last century.

Although differences of opinion exist about the usefulness of ASA scores, the authors of the Spanish study wrote:

“The state of health of the patient (as demonstrated by the ASA grade allocated) and the potential risk of the surgery has been described as the main prognostic factor of likelihood of death. This relation is logical, as the patient’s health status directly indicates the anesthetic risk. Animals with physiological alterations before the anesthesia cannot adequately compensate all the imbalances in physiological systems, and death is more likely to occur.”

A French study2 that evaluated the anesthetic death risk for dogs and cats in a referral private practice reached similar conclusions: “Patients of ASA status 3 and over appear to be considerably more at risk than patients of ASA status 1 and 2. These animals should be thoroughly prepared for anesthesia and closely monitored by well-trained staff.”

Embracing these conclusions will allow you to:

  • Better communicate anesthetic risks with pet owners.
  • Recommend more thorough workups, including full blood work, urinalysis, chest X-rays, abdominal ultrasound, ECG and clotting profile.
  • Choose an anesthesia technician with enough experience to recognize potential complications, such as hypotension, heart blocks and VPCs.

It is important to understand that the ASA score is like a snapshot of a patient’s health status just before anesthesia. It does not change during the procedure.

Just because a patient has a low ASA status doesn’t guarantee that anesthesia will be smooth sailing. A dropped pedicle during a “routine” spay on a “healthy” patient with a “boring” class 1 ASA score can turn into a stressful disaster.


  • If you are faced with a complicated case, be humble and consider enrolling the help of an anesthesiologist who can act as a remote or onsite consultant. Another option is to refer a high-risk patient to a trusted referral practice.
  • Like any tool, the ASA score is only as good as how well you use it. Score every single patient for a month and it will be become the norm.
  • Implementing the ASA score in your clinic is easy. Doctors and technicians should discuss it before every anesthesia. It will improve patient care and even team member satisfaction.


  1. L. Gil et al. “Canine Anaesthetic Death in Spain: A Multicentre Prospective Cohort Study of 2012 Cases” Vet. Anaesthesia & Analgesia, 2013, Vol 40, N 6, p. 57-67.
  2. C. Bille et al. “Risk of Anaesthetic Mortality in Dogs and Cats: An Observational Cohort Study of 3,546 Cases” Vet. Anaesthesia & Analgesia, 2012, Vol 39, 59–6.

Dr. Phil Zeltzman is a board-certified veterinary surgeon and author. His traveling practice takes him all over eastern Pennsylvania and western New Jersey. You may visit his website at  and follow him at Columnists’ opinions do not necessarily reflect those of Veterinary Practice News. 

Kelly Serfas, CVT, of Bethlehem, Pa., contributed to this article. 

Originally published in the November 2016 issue of Veterinary Practice News. Did you enjoy this article? Then subscribe today! 

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