Risk Factors for In-Hospital Mortality in Smoke Inhalation-Associated Acute Lung Injury: Data From 68 United States Hospitals

Abstract

Background: Mortality after smoke inhalation-associated acute lung injury (SI-ALI) remains substantial. Age and burn surface area are risk factors of mortality, whereas the impact of patient- and center-level variables and treatments on survival are unknown.

Methods: We performed a retrospective cohort study of burn and non-burn centers at 68 US academic medical centers between 2011 and 2014. Adult inpatients with SI-ALI were identified using an algorithm based on a billing code for respiratory conditions from smoke inhalation who were mechanically ventilated by hospital day 4, with either a length-of-stay ≥ 5 days or death within 4 days of hospitalization. Predictors of in-hospital mortality were identified using logistic regression. The primary outcome was the odds ratio for in-hospital mortality.

Results: A total of 769 patients (52.9 ± 18.1 years) with SI-ALI were analyzed. In-hospital mortality was 26% in the SI-ALI cohort and 50% in patients with ≥ 20% surface burns. In addition to age > 60 years (OR 5.1, 95% CI 2.53-10.26) and ≥ 20% burns (OR 8.7, 95% CI 4.55-16.75), additional risk factors of in-hospital mortality included initial vasopressor use (OR 5.0, 95% CI 3.16-7.91), higher diagnostic-related group-based risk-of-mortality assignment and lower hospital bed capacity (OR 2.3, 95% CI 1.23-4.15). Initial empiric antibiotics (OR 0.93, 95% CI 0.58-1.49) did not impact survival. These new risk factors improved mortality prediction by 9.9% (P < .001).

Conclusions: In addition to older age and major surface burns, mortality in SI-ALI is predicted by initial vasopressor use, higher diagnostic-related group-based risk-of-mortality assignment, and care at centers with < 500 beds, but not by initial antibiotic therapy.

Keywords: adult respiratory distress syndrome; burns; epidemiology; risk factors; smoke inhalation.

Figure 1

Trends in four respiratory system burn injury diagnosis codes among discharges from 154 academic medical centers and affiliates between October 2008 and October 2014. A trend analysis of the most common International Classification of Diseases, version 9, diagnosis codes representing respiratory system burn injury in discharge abstracts at 154 centers in the University System Health Consortium was performed for the period between October 2008 and October 2014. The diagnosis code diagnosis (dx) 508.2 (respiratory conditions from smoke inhalation), which was introduced in October 2011, nearly replaced dx 987.8 (toxic effect of unspecified gas, fume, or vapor) as being the most frequently assigned. Diagnosis 947.0 (burn of mouth and pharynx) and dx 947.1 (burn of larynx, trachea and lung) remained relatively unchanged over time.

Figure 2

Flowchart describing the selection of patients with smoke inhalation-associated acute lung injury based on a prespecified algorithm. ^aDischarged between October 2011 and March 2014. ^bContains encounter-level date-stamped charges on medications administered and services rendered. CDB/RM = clinical database/resource manager of the University Health System Consortium; ICD-9 = International Classification of Diseases, version 9.

Figure 3

Receiver-operator characteristic (ROC) curves showing improved discrimination using a ^afive-risk factor model compared with a ^btwo-risk factor model. A, Primary analysis of all patients with SI-ALI (n = 769): ΔAUC = 9.9% (P < .001). B, Secondary analysis of patients transferred from other facilities otherwise meeting SI-ALI criteria (n = 542): ΔAUC = 12.0% (P < .001). ^aAge, TBSA, 3M; all patients refined DRG admission ROM assignment, hospital size, and initial vasopressor use (IV norepinephrine, epinephrine, dopamine, vasopressin, and phenylephrine). ^bAge and TBSA. 3M = 3M All Patient Refined Diagnosis-Related Group Classification System; AUC = area under receiver-operator characteristic curve; ΔAUC = mortality risk-prediction increment; ROM = risk of mortality; SI-ALI = smoke inhalation-associated acute lung injury; TBSA = total burn surface area.