Differences in degree, differences in kind: characterizing lung injury in trauma.
BACKGROUND
Acute lung injury following trauma remains a significant source of morbidity and mortality. Although multiple trauma studies have used hypoxemia without radiographic adjudication as a surrogate for identifying adult respiratory distress syndrome (ARDS) cases, the differences between patients with hypoxemia alone and those with radiographically confirmed ARDS are not well described in the literature. We hypothesized that nonhypoxemic, hypoxemic, and ARDS patients represent distinct groups with unique characteristics and predictors.


METHODS
Laboratory, demographic, clinical, and outcomes data were prospectively collected from 621 intubated, critically injured patients at an urban Level 1 trauma center from 2005 to 2013. Hypoxemia was defined as PaO2/FIO2 ratio of 300 or lower. ARDS was adjudicated using Berlin criteria, with blinded two-physician consensus review of chest radiographs. Group comparisons were performed by hypoxemia and ARDS status. Logistic regression analyses were performed to separately assess predictors of hypoxemia and ARDS.


RESULTS
Of the 621 intubated patients, 64% developed hypoxemia; 46% of these hypoxemic patients developed ARDS by chest radiograph. Across the three groups (no hypoxemia, hypoxemia, ARDS), there were no significant differences in age, sex, or comorbidities. However, there was an increase in severity of shock, injury, and chest injury by group, with corresponding trends in transfusion requirements and volume of early fluid administration. Outcomes followed a similar stepwise pattern, with pneumonia, multiorgan failure, length of intensive care unit stay, number of ventilator days, and overall mortality highest in ARDS patients. In multiple logistic regression, early plasma transfusion, delayed crystalloid administration, body mass index, and head and chest injury were independent predictors of hypoxemia, while head and chest injury, early crystalloid infusion, and delayed platelet transfusion were independent predictors of ARDS.


CONCLUSIONS
Hypoxemia and ARDS exist on a spectrum of respiratory dysfunction following trauma, with increasing injury severity profiles and resuscitation requirements. However, they also represent distinct clinical states with unique predictors, which require directed research approaches and targeted therapeutic strategies.


METHODS
Prognostic and epidemiologic study, level III.
From the Department of Surgery (B.M.H., L.Z.K., B.J.R., A.S.C., M.F.N., R.A.C., M.J.C.), and Division of Pulmonary and Critical Care Medicine, Departments of Medicine and Anesthesia (C.M.H., C.S.C.), University of California San Francisco and San Francisco General Hospital, San Francisco, California.
Benjamin M
BM
Howard
Lucy Z
LZ
Kornblith
Carolyn M
CM
Hendrickson
Brittney J
BJ
Redick
Amanda S
AS
Conroy
Mary F
MF
Nelson
Rachael A
RA
Callcut
Carolyn S
CS
Calfee
Mitchell Jay
MJ
Cohen
D015998:Abbreviated Injury Scale; D000328:Adult; D001803:Blood Transfusion / Q000706:statistics & numerical data; D002140:California / Q000453:epidemiology; D016638:Critical Illness; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D000860:Hypoxia / Q000401:mortality / Q000628:therapy; D015601:Injury Severity Score; D007442:Intubation, Intratracheal; D055370:Lung Injury / Q000145:classification* / Q000000981:diagnostic imaging / Q000401:mortality* / Q000628:therapy; D008297:Male; D008875:Middle Aged; D009102:Multiple Organ Failure / Q000401:mortality; D011446:Prospective Studies; D011859:Radiography; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging / Q000401:mortality / Q000628:therapy; D014193:Trauma Centers; D016896:Treatment Outcome