Extremity trauma impairs renal tolerance to hemorrhage

Abstract

BACKGROUDHemorrhage is often accompanied and/or caused by extremity trauma (ET) in both battlefield or civilian trauma scenarios. However, the impacts of ET on tolerance to hemorrhage and resultant renal injury remain unclear. We hypothesize that ET impairs tolerance to hemorrhage and renal ischemia, resulting in increased acute kidney injury (AKI) and mortality.METHODSSprague Dawley rats (11–13 wks) underwent pressure‐controlled hemorrhage (at MAP of 70 or 55 mmHg) with or without ET. Animals were randomly divided into groups: (time) control, ET (without hemorrhage), 70mmHg, 55mmHg, ET+70mmHg, and ET+55mmHg (n ≥ 7 for each group). Rats were anesthetized (inactin), and the femoral and carotid arteries were catheterized to measure MAP and to induce hemorrhage. Renal blood flow (RBF) was measured using a perivascular ultrasonic flow probe. After baselines were recorded, ET was induced via clamping the retrofemoral tissue groups for 30 sec using an L‐shaped hemostat, followed by closed fibula fracture using a 15‐gauge needle. Hemorrhage was induced 5 minutes after ET with target MAP maintained for up to 3 hours by withdrawal or reinfusion of shed blood with a dual direction pump (0.5 ml/min). Blood and urine samples were collected from arterial and bladder catheters before, and 1, 2, and 3 hours after hemorrhage.RESULTSET alone without hemorrhage caused a transient increase in heart rate without significantly affecting other measurements. Less blood withdrawal was required to maintain the target MAP during pressure‐controlled hemorrhage in groups with ET compared to groups without ET, and infusion back of shed blood was required 1 hour after hemorrhage in the 55mmHg+ET group (Figure A). Hemorrhage to 70mmHg caused significant decreases in RBF (Figure B), urine flow, and renal oxygen delivery (RDO2), but increased filtration fraction (FF) with no effect on creatinine clearance (Ccr), potassium, lactate, or urine albumin levels. In ET+70mmHg group, decreases in RBF and RDO2 were exacerbated, and impaired Ccr and FF with significant increases in circulating creatinine, potassium, lactate, and urine albumin levels were observed. All animals in groups 70mmHg and ET+70mmHg survived. Hemorrhage to 55mmHg caused significant decreases in RBF, urine flow, and RDO2 which were greater than observed the 70mmHg group. Hemorrhage to 55mmHg also caused decreases in Ccr and FF and increases in circulating creatinine, potassium, lactate, and urine albumin levels. When ET was combined with hemorrhage to 55mmHg, no further decreases in RBF and RDO2 were observed. However, ET+55mmHg animals showed exacerbated decreases in urine flow and exacerbated increases in circulating creatinine, potassium, and lactate levels. All animals survived for 3 hours following hemorrhage to 55mmHg, but only 50% animals survived in ET+55mmHg group.CONCLUSIONSOur data suggest that ET impairs tolerance to hemorrhage, exacerbates renal hypoperfusion, and increases risks for AKI and mortality. Although underlying mechanisms are unclear, the study provides important evidence that traumatic tissue injury should be considered as a critical component if using animal models to conduct translational studies on hemorrhage.Figures A and B represent the volume loss to maintain target MAP and related renal blood flow following different levels of hemorrhage with or without ET. ET is extremity trauma, Bas is baseline, Pre is Pre‐hemorrhage (5 minutes after ET). * P< 0.05 70mmHg vs ET+70mmHg, + P< 0.01 55 mmHg vs ET+55mmHg, n = 7 for 70mmHg and ET+70mmHg; n = 8 for 55mmHg and ET+55mmHg.Figure 1