Extravascular lung water following resuscitation of hemorrhagic shock in swine: comparison between Ringers' lactate and normal saline

Introduction

Pulmonary edema is a common consequence of hemorrhagic shock resuscitation. The type and amount of fluid used in resuscitation may be important determinants of the amount of edema formed. Ringers' lactate (RL) and normal saline (NS) remain common resuscitative fluids. These experiments were designed to measure the extravascular lung water (EVLW) after resuscitation from hemorrhagic shock with RL vs NS, to determine whether the fluid type results in differences in the amount of EVLW, and to determine whether there exists a threshold amount of fluid that results in the development of edema.

Methods

This was a randomized controlled trial using 20 female Yorkshire crossbred pigs. Animals were mechanically ventilated. Anesthesia was maintained using 2% isofluorane in 100% oxygen. Continuous hemodynamic monitoring, blood sampling, and determination of EVLW by single indicator transpulmonary dilution was done using a PiCCO plus monitor (Pulsion Medical System, Munich, Germany). The animals underwent a midline celiotomy, suprapubic Foley catheter placement, and splenectomy. The spleen was weighed and, based on randomization, either LR or NS solution was infused to replace three times the spleen weight in grams. Following a 15-minute stabilization period, a standardized Grade V liver injury (injury to a central hepatic vein) was then created using a specialized clamp. Following 30 minutes of uncontrolled hemorrhage, we blindly randomized the swine to receive either NS or RL resuscitation at 165 ml/min. Resuscitation fluid was administered to achieve and maintain the baseline mean arterial pressure (MAP) for 90 minutes post injury.

Results

All animals spontaneously stopped bleeding within 12 minutes of injury after losing approximately 25% of their blood volume. There were no differences in initial blood loss between the two groups – estimated blood loss (mean ± standard error) RL group 22 ± 1.7 ml/kg vs NS group 19.0 ± 1.7 ml/kg, P = 0.15. During the resuscitative phase the NS group required more fluid to maintain the goal MAP than the RL group: 330.8 ± 38.1 ml/kg vs 148.4 ± 20.2 ml/kg, P = 0.001. There was nearly a fourfold increase in mean EVLW between the groups: 5.24 ± 1.26 ml/kg NS vs 1.46 ± 0.57 ml/kg RL, P = 0.013. The difference in EVLW was accounted for entirely by the difference in the volume infused (P = 0.008), with no difference seen with fluid type (P = 0.7). The EVLW began to increase immediately with fluid administration without exhibiting a threshold effect. An increase of 1 ml/kg EVLW occurred at a resuscitative volume of 63 ± 25 ml/kg.

Conclusion

In this swine model of traumatic hemorrhagic shock, resuscitation with RL as compared with NS required less fluid to maintain goal MAP and resulted in less EVLW formation. The near fourfold difference in EVLW increase was accounted for entirely by the differences in volumes needed to maintain goal MAP with no differences seen with fluid type. This study suggests that, in order to limit increases in EVLW during early resuscitation of hemorrhagic shock prior to the arrival of blood products, RL should be used preferentially instead of NS and the volume infused limited to approximately 60 ml/kg.