American Society of Anesthesiologists Physical Status Classification System

Function

Perioperative staff may find the ASA classification system useful for managing perioperative outcomes. However, this must be considered in the larger context of the variability and inconsistency with classification between different entities. Meta-analyses have shown that the ASA physical status classification has a sensitivity of approximately 0.74 (95% CI, 0.73 to 0.74), a specificity of approximately 0.67 (95% CI, 0.67 to 0.67), and a receiver operating curve area under the summary of around 0.736 (95% CI, 0.725 to 0.747) in predicting mortality postoperatively.[4][7] For a robust and reliable preoperative risk assessment, it is essential to consider a range of additional factors discretely in addition to the information provided by a composite index classification, including:

• Age
• Comorbidities, relative severity, and level of optimization
• Intended surgical procedure and invasiveness
• Potential additional surgical procedures that may be needed intraoperatively
• Location, extent, and adjacent structures of the intended lesion for surgical intervention
• Intended surgical equipment to be used
• Intended implants
• Intended duration versus possible duration of surgical procedure and anesthesia administration
• Composition, experience, ability, and skill of the surgical team
• Need for blood products, including volume, type, and rapidity at which they may be required intraoperatively
• Intended medications that may be required along with the possibility of precise timing requirements depending on surgery type
• Intended anesthetic technique, along with the availability and  likelihood of needing additional rescue equipment or interventions
• Composition, experience, ability, and skill of the anesthesia team
• Intended anesthetics and additional adjunct medication, including reversal agents as indicated
• Surgical facility equipment, personnel, and resources
• Composition, experience, ability, and skill of preoperative and postoperative teams
• Intended postoperative plan, location, and course, along with the likelihood of alternative postoperative plans, locations, and complications
• Timing of the surgical procedure, such as morning versus night, weekday versus weekend, or time of year (especially in teaching hospitals)
• The surgical operating room location logistics related to the likelihood of needing transport of the patient under anesthesia intraoperatively
• The classification of the surgery as elective, urgent, or emergent [8]

Issues of Concern

Although the simplicity of the ASA Physical Status Classification System is arguably its greatest strength, it provides the basis for its biggest issue of concern. There is growing concern that its use has been broadened to include numerous applications, purposes, healthcare providers, and guidelines for which it is not valid, leading to a range of unintended and potentially negative consequences. This is further complicated by interrater variability when classifying an individual patient, even when used in the ideal setting. For example, anesthesiologists can significantly differ in the ASA physical status classification, especially when considering age, anemia, obesity, or a history of myocardial infarction. Interrater inconsistencies may be even worse when the classification system is used as it wasn't intended, a concern that has been substantiated by notable differences between classifications made by anesthesiologists and non-anesthesiologists.[8][9][5] Not only can inconsistencies arise when different clinicians classify the same patient at the same time, but these inconsistencies may be magnified when classifications are made at different times due to the clinical lability of the disease.[5][8] 

Clinical Significance

The ASA Physical Status Classification System is a numeric score assigned to a particular patient based on the extent of systemic disease as assessed through the patient's medical history and the extent of the patient's function limitation. When used as intended, the scoring system provides a general conceptual approach to perioperative risk assessment and may be useful to individualize management of surgical patients.[9] However, it does not necessarily correlate with overall risk because other factors (as mentioned above) also contribute to perioperative risk. For example, the operative risk for a patient with ASA Class IV undergoing cataract surgery under topical anesthesia is different than that for the same patient undergoing an esophagectomy. Likewise, a patient with ASA Class IV due to severe underlying disease burden who walks 500 meters daily is different than the same underlying disease burden who is wheelchair-bound. Finally, a healthy patient (ASA Class I) without any physical or external contraints is different than a healthy patient with a known difficult airway or orthodox Jehovah's Witnesses who refuses blood and blood products. In these examples, the ASA physical status classification system score may be the same, but the patient's overall operative risk is not.[9][3][10] 

Other Issues

The table below is the latest version of the ASA physical status classification system, as approved by the ASA House of Delegates on October 15, 2014, and last amended on December 13, 2020. Although no specific classification is assigned to patients with moderate systemic disease, the system provides classifications for patients with mild systemic disease (ASA 2) and those with severe systemic disease (ASA 3).[5][9]

Table 1. American Society of Anesthesiologists Physical Status Classification System

Abbreviations: ASA, American Society of Anesthesiologists; BMI, body mass index; CHF, congestive heart failure; COPD, chronic obstructive pulmonary disease.

The addition of "E" to the ASA physical status classification system, for example, ASA 2E, denotes an emergency surgical procedure. According to the ASA, an emergency is defined as a situation in which a delay in treating the patient significantly increases the threat to life or body parts.

Examples of the American Society of Anesthesiologists Physical Status Classification System

Patient 1: A 20-year-old, healthy college athlete is scheduled to undergo an elective anterior cruciate ligament repair. The patient is a nonsmoker and nondrinker who takes no medications and has a BMI of 23. This patient is classified as ASA class 1. 

Patient 2: A 19-year-old college student is scheduled to undergo emergency surgery following a motor vehicle collision. He has a BMI of 29 and reports a history of recreational substance use only (mainly alcohol and cannabis) and well-controlled gastroesophageal reflux disease. This patient is classified as ASA class 2E for overweight BMI, recreational substance use, well-controlled reflux, and emergency nature of the surgery. Notably, the patient's full stomach does not impact his ASA classification but still increases his overall anesthetic risk.

Patient 3: A 30-year-old woman is scheduled to undergo elective surgery to remove a large ovarian cyst. Comorbidities include anemia from menorrhagia and type II diabetes treated with metformin. She is a nonsmoker, an occasional social drinker, and has a BMI of 42. This patient is classified as ASA class 3 due to the severity of obesity.

Patient 4: A 70-year-old woman is scheduled to undergo an emergency laparoscopic appendectomy. Comorbidities include 100 pack-year smoking history and poorly controlled chronic obstructive pulmonary disease, morbid obesity (BMI 46), and insulin-dependent type II diabetes mellitus. She experiences shortness of breath after walking more than a few meters. This patient is classified as ASA class 4E.

Patient 5: A 55-year-old man is scheduled for emergency repair of a large laceration to his abdominal aorta after being thrown from a horse and impaled on a fence post. He additionally sustained has 8 rib fractures and a pelvic fracture during the fall. He had circulatory arrest in the emergency department from a massive hemorrhage and required 2 rounds of CPR before return of spontaneous circulation. He is currently requiring massive blood and blood product transfusion due to ongoing blood loss from his laceration and pelvic fracture. This patient is classified as ASA class 5E, as he is not expected to survive beyond the next 24 hours with or without surgery.

Patient 6: A 25-year-old man sustained a severe head and cervical spine injury in a motorcycle accident while not wearing a helmet. Despite surgical decompression and aggressive management of his intracranial process, he remains unresponsive to all noxious stimulation during his intensive care unit stay. Testing for brain death is carried out according to the American Academy of Neurology guidelines for Brain Death Determination, which reveals a complete absence of central nervous system function. His family agrees to make his organs available for transplantation. This patient is classified as ASA class 6.[9][11]

Enhancing Healthcare Team Outcomes

The ASA physical status classification system is a crucial tool that enhances communication and patient safety across the entire healthcare team. Accurate understanding and application of this classification system require a collaborative effort among anesthesiologists, surgeons, nurses, advanced practitioners, and other healthcare providers involved in perioperative care.

Each team member brings valuable perspective in assessing a patient's physiological status and potential operative risks. Nurses identify trends in vital signs during preoperative assessment, pharmacists can provide insight into medication-related risks, and primary care clinicians often possess detailed knowledge of the patient's baseline health status. By working together to accurately classify and communicate a patient's ASA status, the healthcare team creates a shared understanding that guides clinical decision-making and improves patient outcomes.