Flat or fat? Inferior vena cava ratio is a marker for occult shock in trauma patients

Identification of occult shock (OS) or hypoperfusion is critical in the initial management of trauma patients. Analysis of inferior vena cava (IVC) ratio on computed tomography (CT) scan has shown promise in predicting intravascular volume. We hypothesized that a flat IVC is a predictor of OS and associated with worse outcomes in major trauma patients.

We performed a 1-y retrospective analysis of our level 1 trauma center database to identify all major trauma activations that underwent evaluation with a CT scan of the torso, arterial blood gas, and serum lactate. A flat IVC was defined as a transverse-to-anteroposterior ratio ≥2.5 at the level of the suprarenal IVC. OS was defined as a base deficit ≥4.0 in the absence of hypotension (systolic blood pressure ≤90 mm Hg).

Two hundred sixty-four patients were included, of which 52 had a flat IVC. Patients with a flat IVC were found to have a higher injury severity score, lactate, and base deficit compared with patients with a fat IVC. Flat IVC patients also required greater amounts of fluids (P < 0.04) and blood (P < 0.01). On multivariate analysis, a flat IVC was independently associated with an increased risk for OS (odds ratio = 2.87, P < 0.007) and overall complications (odds ratio = 2.26, P = 0.05). The area under the receiver operating characteristic curve for a flat IVC to predict OS was 0.74.

A flat IVC on CT is an accurate marker for OS in major trauma victims and may help stratify patients who require more aggressive resuscitation, monitoring, and support.