The acute effects of acetate-balanced colloid and crystalloid resuscitation on renal oxygenation in a rat model of hemorrhagic shock.

Introduction: Fluid resuscitation therapy is the initial step of treatment for hemorrhagic shock. In the present study we aimed to investigate the acute effects of acetate-balanced colloid and crystalloid resuscitation on renal oxygenation in a rat model of hemorrhagic shock. We hypothesized that acetate-balanced solutions would be superior in correcting impaired renal perfusion and oxygenation after severe hemorrhage compared to unbalanced solutions.

Methods: In anesthetized, mechanically ventilated rats, hemorrhagic shock was induced by withdrawing blood from the femoral artery until mean arterial pressure (MAP) was reduced to 30 mmHg. One hour later, animals were resuscitated with either hydroxyethyl starch (HES, 130/0.42 kDa) dissolved in saline (HES-NaCl; n=6) or a acetate-balanced Ringer's solution (HES-RA; n=6), as well as with acetated Ringer's solution (RA; n=6) or 0.9% NaCl alone (NaCl; n=6) until a target MAP of 80 mmHg was reached. Oxygen tension in the renal cortex (CμPO2), outer medulla (MμPO2), and renal vein were measured using phosphorimetry.

Results: Hemorrhagic shock (MAP=30 mmHg) significantly decreased renal oxygenation and oxygen consumption. Restoring the MAP to 80 mmHg required 24.8±1.7 ml of NaCl, 21.7±1.4 ml of RA, 5.9±0.5 ml of HES-NaCl (p<0.05 vs. NaCl and RA), and 6.0±0.4 ml of HES-RA (p<0.05 vs. NaCl and RA). NaCl, RA, and HES-NaCl resuscitation led to hyperchloremic acidosis, while HES-RA resuscitation did not. Only HES-RA resuscitation could restore renal blood flow back to ∼85% of baseline level (from 1.9±0.1 ml/min during shock to 5.1 ml±0.2 ml/min 60 min after HES-RA resuscitation) which was associated with an improved renal oxygenation (CμPO2 increased from 24±2 mmHg during shock to 50±2 mmHg 60 min after HES-RA resuscitation) albeit not to baseline level. At the end of the protocol, creatinine clearance was decreased in all groups with no differences between the different resuscitation groups.

Conclusion: While resuscitation with the NaCl and RA (crystalloid solutions) and the HES-NaCl (unbalanced colloid solution) led to hyperchloremic acidosis, resuscitation with the HES-RA (acetate-balanced colloid solution) did not. The HES-RA was furthermore the only fluid restoring renal blood flow back to ∼85% of baseline level and most prominently improved renal microvascular oxygenation.