5 The Predictive Capacity of ASA PS in Burn Patients

Abstract Introduction The four main prognostic models used to determine risk of burn mortality are the revised Baux (rBaux), Belgian Outcome in Burn Injury (BOBI), Abbreviated Burn Severity Index (ABSI), and quick Sequential Organ Failure Assessment (qSOFA). These models fail to factor in medical comorbidities. The ASA PS (American Society of Anesthesiologists Physical Status) is a simple scale incorporating severity of traumatic injury with comorbidities, which strongly predicts mortality in surgical patients. The purpose of this study is to determine whether the ASA PS is an adequate adjunct to measure burn severity. Methods All adults admitted to an ABA verified burn center from January 2016 to April 2019 with TBSA ≥10% who underwent surgery were reviewed. Demographics (age, gender, TBSA, race, ASA PS), vital signs (GCS, blood pressure, respiratory rate), and outcome variables (length of stay [LOS], mechanical ventilation [MV] days, and complications) were evaluated. rBaux, BOBI, ABSI, and qSOFA scores were calculated. The primary outcome was in-hospital mortality. After descriptive statistical analysis, mortality associations of the models were assessed by determining odds ratios. Firth’s logistic regression and area under the receiver operator curves determined the predictive utility of the prognostic scores. Results Of the 183 patients who fit inclusion criteria, median age was 44 years (30–57), and the majority (70%) were male. Median TBSA was 20%, 65% (n=118) had full thickness burns, 14% (n=25) had inhalation injury, and mortality was 9% (n=17). rBaux score was the best predictor of mortality (AUC=.84), ICU LOS (R2=.04), and MV days (R2=.06). For every 10-point increase in rBaux score, there was a 1.7 times increase in mortality (OR=1.7, CI 1.4–2.3, p< .00). The predicted ICU LOS increases from 2.8 to 31.4 days for the lowest and highest rBaux score quartiles. Compared to rBaux scores of 30–53, patients with scores of 54–70 had 4 times more MV days (CI 1.5–11, p< .00). The ASA PS was slightly inferior to rBaux in predicting mortality (AUC=.72), although not statistically significant (p=0.1). As ASA PS score went from I/II to III, III to IV, and IV to V/VI; mortality increased by 2.8 (OR=2.8, CI 1.5–5.5, p< .00). Conclusions rBaux is the best predictor of mortality, ICU LOS, and MV days although ASA PS also predicts mortality. Future studies should determine the combined predictive ability of ASA PS and rBaux. Applicability of Research to Practice rBaux and ASA PS scores can be used to determine risk of mortality in burn patients.