Comparisons of normal saline and lactated Ringer's resuscitation on hemodynamics, metabolic responses, and coagulation in pigs after severe hemorrhagic shock

Abstract

Background: Ongoing improvements in trauma care now recommend earlier use of blood products as part of damage control resuscitation, but generally these products are not available at far forward battlefield locations. For the military, questions continue to arise regarding efficacy of normal saline (NS) vs. lactated Ringer's (LR). Thus, this study compared the effects of LR and NS after severe hemorrhage in pigs.

Methods: 20 anesthetized pigs were randomized into control (n = 6), LR (n = 7), and NS (n = 7) groups. Hemorrhage of 60% estimated total blood volume was induced in LR and NS groups by removing blood from the left femoral artery using a computer-controlled pump. Afterwards, the pigs were resuscitated with either LR at 3 times the bled volume or the volume of NS to reach the same mean arterial pressure (MAP) as in LR group. Hemodynamics were measured hourly and blood samples were taken at baseline (BL), 15 min, 3 h and 6 h after resuscitation to measure changes in coagulation using thrombelastograph®.

Results: MAP was decreased by hemorrhage but returned to BL within 1 h after resuscitation with LR (119 ± 7 ml/kg) or NS (183 ± 9 ml/kg, p < 0.05). Base excess (BE) was decreased by hemorrhage; resuscitation with LR recovered BE but not with NS. Total peripheral resistance was decreased with NS and LR, with a larger drop shown in NS. Serum potassium was increased with NS, but not affected with LR. Coagulation changes were similar between LR and NS.

Conclusions: NS may be inferior to LR in resuscitation due to its vasodilator effects and the risks of metabolic acidosis and hyperkalemia.

Figure 1

Experimental protocol.

Figure 2

Changes in mean arterial pressure (MAP), heart rate (HR), and urine output after hemorrhage and resuscitation with lactated Ringer’s solution (LR, 119 ± 7 ml/kg) or normal saline (NS, 183 ± 9 ml/kg) in pigs. *p < 0.05 compared to the corresponding baseline values. ^♣p < 0.05 compared to corresponding control values.

Figure 3

Changes in oxygen delivery (A), oxygen consumption (B), oxygen demand (C), and oxygen delivery/oxygen demand (D) after hemorrhage and resuscitation with lactated Ringer’s solution (LR, 119 ± 7 ml/kg) or normal saline (NS, 183 ± 9 ml/kg) in pigs. *p < 0.05 compared to the corresponding baseline values. ^§p < 0.05 LR group compared to NS group. ^♣p < 0.05 compared to corresponding control values.

Figure 4

Changes in acid-base status after hemorrhage and resuscitation with lactated Ringer’s solution (LR, 119 ± 7 ml/kg) or normal saline (NS, 183 ± 9 ml/kg) in pigs. *p < 0.05 compared to the corresponding baseline values. ^§p < 0.05 LR group compared to NS group. ^♣p < 0.05 compared to corresponding control values.

Figure 5

Changes in Thrombelastograph® (TEG) measurements after hemorrhage and resuscitation with lactated Ringer’s solution (LR, 119 ± 7 ml/kg) or normal saline (NS, 183 ± 9 ml/kg) in pigs. R time: latency time for initial fibrin formation. K time: a measure of speed to reach a certain level of clot strength. Angle a: the rapidity of fibrin build up and cross-linking. MA: maximum strength of the developed clot. *p < 0.05 compared to the corresponding baseline values.