Resuscitation With Normal Saline (Ns) Results in Increased Volume Requirement, Increased Cardiac Output and Decreased Systemic Vascular Resistance Compared to Lactated Ringers (Lr) in an Uncontrolled Hemorrhagic Shock Model in Anesthetized Swine

Objective: LR and NS solutions are used interchangeably for resuscitation of hemorrhagic shock. We hypothesized that physiologic response to resuscitation differs between these solutions. Methods: Twenty swine were randomized to blinded resuscitation with LR or NS. Animals underwent anesthesia, invasive line placement, celiotomy, splenectomy, and grade V liver injury followed by 30 minutes of uncontrolled hemorrhage. Blood loss was measured. Resuscitation was administered to achieve and maintain baseline mean arterial pressure (MAP). Blood pressure (BP), MAP, cardiac output (CO), systemic vascular resistance (SVR), stroke volume (SV) and tissue oxygenation (STO2) were monitored. Results: Blood loss was 763 ± 206 ml in the NS and 649 ± 158 in the LR group, p = 0.183. Animals required 10,901 ± 3820 ml of NS vs. 5,175 ± 1965ml of LR, p = 0.001. The NS group had a lower MAP at T = 67-99, p <0.05. During resuscitation, NS pigs had a higher HR, 128 vs. 100 beats/min (p = 0.026), and CO, 5.76 vs. 4.62 L/min (p = 0.017), while stroke volume (SV) remained comparable to LR pigs. SVR was lower in NS pigs, 748 vs. 1018 (dyne*sec)/cm5 (p < 0.001). STO2 did not differ between groups. Hematocrit was lower in the NS pigs, 12.7% ± 3.3, than LR pigs, 16.6% ± 3.6, p = 0.029, at the end of the study. Urine output was greater in pigs receiving NS (1459 ± 886 vs. 651 ± 392 ml, p = 0.021). Conclusions: In an anesthetized swine model of uncontrolled hemorrhagic shock, utilizing MAP as the resuscitation endpoint, use of NS results in greater required volume, decreased SVR and increased cardiac output compared to LR, suggesting significantly different hemodynamic effects.