The ASA Physical Status (PS) Classification System is a fundamental tool used worldwide in anesthesiology. Developed by the American Society of Anesthesiologists, its primary purpose is to provide a simple, standardized, and concise summary of a patient's overall pre-anesthesia health. It allows for rapid communication among anesthesiologists, surgeons, and other medical team members about a patient's co-existing medical conditions.
It is crucial to understand that the ASA PS score is not a surgical risk score. It does not account for the nature, complexity, or invasiveness of the planned surgery. A healthy patient (ASA 1) undergoing a high-risk procedure like a major vascular surgery may be at greater overall risk than a sicker patient (ASA 3) undergoing a low-risk procedure like a cataract removal. The score solely reflects the patient's physiological state.
The Six Classes and the "E" Modifier
The system consists of six main classes (I-VI) and an optional "E" modifier for emergency procedures.
ASA PS 1: Normal Healthy Patient
- Definition: A normal healthy patient.
- Explanation: This patient has no organic, physiologic, or psychiatric disturbances. They are not obese, do not smoke, and their lifestyle is generally healthy. Any surgical condition is localized and does not cause systemic disturbance.
- Examples:
- A 25-year-old marathon runner scheduled for an arthroscopic knee repair.
- A 30-year-old woman scheduled for an elective tubal ligation.
- A healthy 4-year-old undergoing a circumcision.
- A 22-year-old with an inguinal hernia and no other medical problems.
ASA PS 2: Patient with Mild Systemic Disease
- Definition: A patient with mild systemic disease.
- Explanation: This patient has a functional or physiological disturbance that is not life-threatening and is well-controlled. The disease does not cause significant functional limitations.
- Examples:
- A 45-year-old with well-controlled hypertension (HTN) on a single medication.
- A 60-year-old with diet-controlled Type 2 diabetes.
- A 35-year-old with intermittent, well-controlled asthma who uses an inhaler occasionally.
- A 50-year-old who is a smoker but has normal lung function.
- A patient with a mild anemia (Hgb 10 g/dL).
- A patient with a Body Mass Index (BMI) between 30-39.9 (Class I or II Obesity).
ASA PS 3: Patient with Severe Systemic Disease
- Definition: A patient with severe systemic disease that is not incapacitating.
- Explanation: This patient has a significant disease that creates a functional limitation and is a constant threat to their life. The disease is not optimally controlled or has already caused end-organ damage.
- Examples:
- A 65-year-old with poorly controlled hypertension (e.g., BP > 180/100) or on multiple medications.
- A 55-year-old with insulin-dependent diabetes who has complications like nephropathy or retinopathy.
- A 70-year-old with a history of a myocardial infarction (MI) more than 3 months ago.
- A patient with stable angina that limits their physical activity (e.g., can't walk a block without chest pain).
- A patient with severe COPD who is on home oxygen.
- A patient with a recent (less than 3 months ago) stroke.
- A patient with a BMI > 40 (Morbid Obesity).
ASA PS 4: Patient with Severe Systemic Disease that is a Constant Threat to Life
- Definition: A patient with severe systemic disease that is a constant threat to life.
- Explanation: This patient is critically ill with severe, poorly controlled disease that has already caused significant functional incapacity. They are at high risk of perioperative complications and death.
- Examples:
- A 70-year-old with unstable angina at rest.
- A patient with an acute myocardial infarction within the last 3 months.
- A patient with symptomatic, poorly controlled congestive heart failure (CHF), such as shortness of breath at rest or with minimal exertion.
- A patient in septic shock requiring vasopressors.
- A patient with severe respiratory compromise, such as a tension pneumothorax or severe ARDS.
- A patient with a ruptured abdominal aortic aneurysm who is in profound shock.
ASA PS 5: Moribund Patient Who is Not Expected to Survive Without the Operation
- Definition: A moribund patient who is not expected to survive without the operation.
- Explanation: This patient is critically ill and is not expected to survive beyond the next 24 hours, with or without the surgery. The operation is a last-ditch effort to save their life.
- Examples:
- A patient with a massive, devastating intracranial hemorrhage causing herniation.
- A patient with a massive trauma who is exsanguinating and has lost vital signs.
- A patient with a catastrophic intra-abdominal catastrophe (e.g., mesenteric ischemia with bowel infarction) who is in multi-organ failure.
ASA PS 6: Declared Brain-Dead Patient Whose Organs are Being Removed for Donor Purposes
- Definition: A declared brain-dead patient whose organs are being removed for donor purposes.
- Explanation: This is a unique category reserved for organ donors who have been legally declared brain-dead. The anesthesia provider's role is to manage the organ donor's physiology to preserve organ viability for transplantation.
- Example:
- A 35-year-old who suffered an irreversible, catastrophic brain injury and has been declared brain-dead. The patient is in the operating room for multi-organ procurement.
The "E" Modifier: Emergency
The "E" suffix is appended to the ASA PS classification (e.g., ASA 3E) to indicate that the surgical procedure is an emergency.
- Definition: An emergency is defined as existing when the delay in treatment would significantly alter the patient's outcome for the worse.
- Examples:
- A healthy ASA 1 patient who requires an emergency Caesarean section for fetal distress becomes ASA 1E.
- An ASA 3 patient with controlled diabetes and hypertension who presents with a ruptured appendix becomes ASA 3E.
- An ASA 4 patient with unstable angina who suffers a femur fracture and requires immediate surgery becomes ASA 4E.
ASA Physical Status Classification System Summary
|
ASA PS Class
|
Definition
|
Explanation
|
Examples
|
|---|---|---|---|
| ASA 1 | Normal healthy patient | No organic, physiological, or psychiatric disease; a healthy individual. | A 25-year-old for elective knee arthroscopy; a healthy child for circumcision. |
| ASA 2 | Patient with mild systemic disease | A well-controlled disease that does not cause major functional limitations. | Well-controlled hypertension on one medication; diet-controlled Type 2 diabetes; a smoker with normal lung function. |
| ASA 3 | Patient with severe systemic disease | A significant disease that causes functional limitation and is a constant threat to life. | Poorly controlled hypertension; insulin-dependent diabetes with complications; stable angina that limits activity; severe COPD. |
| ASA 4 | Patient with severe systemic disease that is a constant threat to life | A critically ill patient with severe, poorly controlled disease that is a constant, immediate threat to life. | Unstable angina at rest; recent myocardial infarction (< 3 months); symptomatic congestive heart failure (CHF); patient in septic shock. |
| ASA 5 | Moribund patient who is not expected to survive without the operation | A critically ill patient not expected to survive beyond 24 hours with or without the operation. | Massive intracranial hemorrhage with herniation; a patient exsanguinating from massive trauma. |
| ASA 6 | Declared brain-dead patient whose organs are being removed for donor purposes | A patient who is legally declared brain-dead and is undergoing organ procurement. | A brain-dead patient in the operating room for multi-organ donation. |
| "E" Modifier | Emergency | Suffix appended to any ASA class (e.g., ASA 3E) when the surgery is an emergency and delay would significantly worsen the patient's outcome. |