January 19, 2016

Did you know that the American Society of Anesthesiologists (ASA) has published a set of examples to guide the accurate use of the Physical Status (PS; P1-P6) modifiers?  The ASA House of Delegates approved the examples in October 2014.  They appear at http://www.asahq.org/resources/clinical-information/asa-physical-status-classification-system.

Key to abbreviations:  ARD, acid reflux disease; BMI, body mass index; CAD, coronary artery disease; COPD, chronic obstructive pulmonary disease; CVA, cerebral vascular accident; DIC, disseminated intravascular coagulation; DM, diabetes mellitus, ESRD, end-stage renal disease; HTN, hypertension; MI, myocardial infarction; PCA, postconceptual age; TIA, transient ischemic attack.

The original version of the anesthesia physical status classification system was published in 1941, by Meyer Saklad in Anesthesiology and then by ASA in a booklet for its members.  The pre-operative classification of physical state was, in Saklad's opinion, a useful statistical tool and he warned: ‘No attempt should be made to prognosticate the effect of a surgical procedure upon a patient of a given Physical State.’  Saklad gave several examples of systemic illnesses for the first four classes in order to standardize the classification.  (Fitz-Henry J. The ASA Classification and Peri-Operative Risk.  Ann R Coll Surg Engl. 2011 Apr; 93(3): 185–187.)

When the ASA adopted a revised version of the classification system in 1962, it did not include any examples.  The only subsequent revision was the addition of ASA PS class 6 to describe the brain-stem-dead organ donor.  Numerous studies have shown that clinicians’ assignment of the PS modifiers is subjective; inter-rater reliability and consistency is not impressive.  As Fitz-Henry explains,

A cohort of anaesthetists [sic] may ascribe different PS classes to the same patient; this is a well-known problem when the ASA PS is part of the standardisation [sic] data for a study. Some anaesthetists will class a patient with several ‘mild’ or well-controlled systemic illnesses as ASA PS2, whereas other anaesthetists will ‘add together’ the physical effect of those illnesses and classify that patient as ASA PS3.

Additionally, anaesthetists will also take into account factors that are not medical conditions in their own right but that adversely influence how a patient will tolerate a systemic medical condition or operative procedure. The most common of these are the extremes of age (neonates and age over 80) - many anaesthetists will grade a fit 80-year-old as ASA PS3. Other influencing factors are obesity and smoking history.

Today the ASA PS classification system is used for a variety of purposes beyond statistics and characterization of a patient’s preoperative medical conditions that might influence anesthetic management.   These purposes include allocating resources, paying for anesthesia services and predicting perioperative risk.  Amr E. Abouleish, MD, MBA; Marc L. Leib, MD, JD and Neal H. Cohen, MD, MPH, MS listed some of the non-anesthesia uses of the system in their article ASA Provides Examples to Each ASA Physical Status Class published in the ASA Newsletter in June, 2015 (footnotes omitted):

This use of the system by so many non-anesthesia clinicians, for so many different purposes, led the ASA to adopt the examples shown in the first table above “to aid clinicians and others in the determination of the ASA PS.”

An abstract (A1278) presented by Erin Hurwitz, MD at the October 2015 ASA Annual Meeting offered evidence that the examples improved the accuracy of ASA PS class assignment.  (Using Examples Best When Classifying ASA Physical Status.  Anesthesiology News, January 11, 2016.) 

Dr. Hurwitz and her colleagues recruited 779 anesthesia providers from 41 states and 110 nonanesthesia physicians (gastroenterologists, pulmonary critical care physicians, interventional radiologists, oral-maxillofacial surgeons) and nurses into the study. 

First the test subjects were asked to assign an ASA PS level to ten hypothetical cases using only the ASA PS class definitions.  Then they were given the examples along with the same ten hypothetical cases in a different order and again asked to assign an ASA PS level to each.  All the participants improved when they used the examples.  When they only had the definitions, they made the correct assignment in fewer than six of the ten cases.  Performance improved to almost eight out of ten with use of the examples.  The “correct” assignment meant only that the participants agreed with the ASA PS level selected in advance by the study team, since there is no “final authority … to determine physical status,” as Robert E. Johnstone, MD pointed out in the Anesthesiology News article.

As Dr. Johnstone also said, “The more consistency in physical status assignments the better, because work assignments, quality assessments and finances are affected.”  ASA’s adoption of the PS classification system examples can only help.

With best wishes,

Tony Mira
President and CEO