What is the clinical evidence from this study?

Study design: Observational. Population: Outpatient surgery (n=2089830). Intervention: ASA Physical Status IV vs. ASA Physical Status I (healthy patients). Primary outcome: 30-day mortality (OR 89, 95% CI 55-143, p=<0.001).

May 21, 2021Open Access

American Society of Anesthesiologists Physical Status Classification as a reliable predictor of postoperative medical complications and mortality following ambulatory surgery: an analysis of 2,089,830 ACS-NSQIP outpatient cases

Q: What are the key findings of this study?

Patients with an ASA Physical Status of IV had an 89-fold higher odds of 30-day mortality following outpatient surgery compared to healthy patients.

Key Result

Patients with an ASA Physical Status of IV had an 89-fold higher odds of 30-day mortality following outpatient surgery compared to healthy patients.

Study Design

Type

Observational (n=2,089,830)

Multicenter

Yes

Structured PICO

Does the ASA Physical Status Classification predict 30-day medical complications and mortality in patients undergoing outpatient surgery?

Population

2,089,830 adult patients undergoing outpatient surgery across multiple specialties in the US, evaluated for 30-day postoperative outcomes.

Exposure

Higher American Society of Anesthesiologists Physical Status (ASA PS) Classification

Comparator

Lower ASA PS Classification (ASA PS 1 used as reference)

Outcome

30-day medical complications (composite of deep vein thrombosis, pulmonary embolism, reintubation, failure to wean from ventilator, renal insufficiency, renal failure, stroke, cardiac arrest, myocardial infarction, pneumonia, urinary tract infection, systemic sepsis or septic shock)composite

The ASA Physical Status Classification is a reliable, independent predictor of 30-day medical complications, readmissions, and mortality following ambulatory surgery, suggesting high-risk patients may be better suited for inpatient settings.

Main Result

Odds Ratio: 89 (95% CI 55–143)

p-value: p=<0.001

Limitations

Certain procedures within a subspecialty could themselves be independent risk factors not fully accounted for by Relative Value Units (RVUs).
Excluded procedures not commonly performed on an outpatient basis (e.g., cardiac surgery and neurosurgery), limiting generalizability to those groups.
Unmeasured confounding factors such as health literacy and family support were not accounted for.

Abstract

BACKGROUND: Seventy percent of surgical procedures are currently performed in the outpatient setting. Although the American Society of Anesthesiologists (ASA) Physical Classification ability to predict risk has been evaluated for in-patient surgeries, an evaluation in outpatient surgeries has yet to be performed. The major goal of the current study is to determine if the ASA classification is an independent predictor for morbidity and mortality for outpatient surgeries. METHODS: The 2005 through 2016 NSQIP Participant Use Data Files were queried to extract all patients scheduled for outpatient surgery. ASA PS class was the primary independent variable of interest. The primary outcome was 30-day medical complications, defined as having one or more of the following postoperative outcomes: (1) deep vein thrombosis, (2) pulmonary embolism, (3) reintubation, (4) failure to wean from ventilator, (5) renal insufficiency, (6) renal failure, (7) stroke, (8) cardiac arrest, (9) myocardial infarction, (10) pneumonia, (11) urinary tract infection, (12) systemic sepsis or septic shock. Mortality was also evaluated as a separate outcome. RESULTS: A total of 2,089,830 cases were included in the study. 24,777 (1.19%) patients had medical complications and 1,701 (0.08%) died within 30 days. ASA PS IV patients had a much greater chance of dying when compared to healthy patients, OR (95%CI) of 89 (55 to 143), P < 0.001. Nonetheless, over 30,000 ASA PS IV patients had surgery in the outpatient setting. Multivariable analysis demonstrated a stepwise independent association between ASA PS class and medical complications (C statistic = 0.70), mortality (C statistic = 0.74) and readmissions (C statistic = 0.67). Risk stratifying ability was maintained across surgical procedures and anesthesia techniques. CONCLUSIONS: ASA PS class is a simple risk stratification tool for surgeries in the outpatient setting. Patients with higher ASA PS classes subsequently developed medical complications or mortality at a greater frequency than patients with lower ASA PS class after outpatient surgery. Our results suggest that the ambulatory setting may not be able to match the needs of high-risk patients.

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