Not all patients meet the 1 day per percent burn rule: A simple method for predicting hospital length of stay in patients with burn

Introduction Hospital length of stay (LOS) is utilized to estimate resource utilization and quality of care. In burns the LOS estimation is 1 day per percent total body surface area burn (1 day/%TBSA). Our purpose was to evaluate the 1 day/%TBSA burn rule and develop simple accurate formulas to predict LOS. Methods The American Burn Association National Burn Repository (NBR) from 2000 to 2013 was utilized to collate data on patients >18 years. We divided 106,543 records in half, utilizing one set to develop a model (training set) and the other to test the model (test set). We calculated the difference between observed and predicted LOS for all patients, and then examined the effect of inhalation injury and age using a linear regression model containing TBSA, age, inhalation injury and all two-way interactions. We compared predictive performance of the linear regression model to the 1 day/%TBSA rule. Finally, we developed and validated three simple formulas to more accurately predict LOS than the 1 day/% TBSA rule. Results LOS was significantly associated with patient age, TBSA, inhalation injury, and all two-way interactions. For patients <40 years without inhalation injury the main effect of TBSA was 0.71. For each decade increase in age, LOS increased by 0.74 days/TBSA burn; inhalation injury added 1.70 days. LOS was highly variable among patients with similar burn size, age and inhalation injury due to concomitant trauma, complications, and comorbidities. We developed 3 formulas to estimate patient LOS: (1) inhalation injury present, regardless of age (2) no inhalation injury and ≥40 years old (3) no inhalation injury and <40 years old. Conclusions Traditional LOS estimates of 1 day/%TBSA burn rule is biased, underestimating LOS, particularly for patients?>40 years with inhalation injury. The following formulas applied at admission can accurately estimate hospital LOS, improve prediction over 1 day/%TBSA, and provide results comparable to complicated models: I. Patients with inhalation injury: LOS=(age10)+(1.5×TBSA).II. Patients without inhalation injury <40 years of age, LOS = 1 day/%TBSA.III. Patients without inhalation injury ≥40 years, LOS = ((age/10) − 2) + TBSA.