External validation of a substratification of the American Association for the Surgery of Trauma renal injury scale for grade 4 injuries.

BACKGROUND: The traditional American Association for the Surgery of Trauma (AAST) grading of renal injury does not adequately identify the subset of patients who are most likely to require intervention for bleeding. Recently, several high-risk criteria (HRC) for bleeding after renal injury were identified, and we sought to externally validate these criteria among patients with grade 4 renal injury.

STUDY DESIGN: All patients presenting to a level I trauma center with blunt grade 4 renal injuries from 2003 to 2010 were reviewed, and stage was determined by the 1989 AAST staging criteria. Dependent variables included the presence of a hilar injury or any of the HRC (perirenal hematoma size, intravascular contrast extravasation, and medial or complex laceration). The primary outcome was the need for intervention (renorrhaphy, nephrectomy, or angiography) for hemodynamic instability.

RESULTS: A total of 84 patients with grade 4 renal lacerations were identified. Two or more HRC were present in 18 patients (21%), and intervention for hemodynamic instability was performed in 14 patients (17%). Compared with patients with 0 or 1 HRC, those with ≥ 2 HRC were approximately 25 times more likely to require intervention for hemodynamic instability (odds ratio [OR]24.9, 95% CI 5.5 to 112.9, p < 0.001). Patients with no HRC were unlikely to require intervention for hemodynamic instability.

CONCLUSIONS: Among patients with blunt grade 4 renal injury, the presence of ≥ 2 HRC effectively predicts the need for intervention for hemodynamic instability and can be used to identify patients who require intensive monitoring. The AAST grading system for renal injury should be modified to better reflect injury severity.