Effect of dose of hypertonic saline on its potential to prevent lung tissue damage in a mouse model of hemorrhagic shock

Recent studies have shown that hypertonic saline (HS) resuscitation can reduce hemorrhage-induced lung damage by preventing neutrophil activation. In this study, we examined whether this protective effect can be improved by increasing the HS dose used for resuscitation. The protective effect of two HS doses was tested in a mouse model of hemorrhagic shock. BALB/c mice were bled to a mean arterial blood pressure of 35 +/- 5 mmHg for 1 h. Then the animals were resuscitated with lactated Ringer's (LR) or with HS (7.5% NaCl) at doses of 4 mL/kg or 6 mL/kg body weight, sacrificed after 24 h, and lung tissue samples were collected. Evidence of lung injury was evaluated morphologically by scoring histology specimens in a blinded fashion. In a separate set of mice, plasma Na+ and osmolarity were determined 15 min after resuscitation. Resuscitation of hemorrhaged mice with 4 and 6 mL/kg HS increased plasma Na+ concentrations by 5 and 11 mM, respectively. LR treatment reduced plasma Na+ concentrations by 6 mM and resulted in a lung injury score of 6.1 +/- 0.8, accompanied by focal thickening of alveolar membranes, congestion, pulmonary edema, and interstitial and intra-alveolar neutrophil infiltration. HS at 4 mL/kg decreased focal thickening, congestion, pulmonary edema, and neutrophil infiltration, and the injury score to 3.8 +/- 0.9, which was not significantly different from controls (3.6 +/- 0.8), and lung damage was lowest in animals that received 6 mL/kg HS (2.5 +/- 0.2, P < 0.005 vs. LR). Lung damage scores inversely correlated with plasma Na+ concentrations (r > 0.9999). Our data suggest that the protective effect of HS may be a function of the plasma Na+ concentration and that HS at 6 mL/kg is at least equally effective in reducing hemorrhage-induced lung damage compared to the more commonly used HS dose of 4 mL/kg.