Capillary narrowing in hemorrhagic shock is rectified by hyperosmotic saline-dextran reinfusion

Previously, we showed that skeletal muscle capillaries narrow during hemorrhagic shock due to swelling of endothelial cells. The present study investigated if these narrowed capillaries affected reflow and compared the effects of fluid reinfusion with iso- and hyperosmotic solutions, in particular 7.5% NaCl/6% dextran 70 (HSD) and Ringer's lactate (RL). Intravital microscopy was used to visualize capillaries in the rabbit tenuissimus muscle during 1 h of shock (40% hemorrhage) and subsequent reinfusion period. Changes in capillary lumenal diameter were inferred by changes in the width of red blood cells traversing the capillary. At the end of the shock period, the capillary diameter was reduced by 20.4 +/- 8.0% (N = 24). With infusion of HSD (dose equal to one-seventh of the shed blood volume; N = 7), there was a sustained flow resurgence and complete return of the capillary diameter to control values after 30 min. The response appears to result from both the hypertonic saline and dextran components. Reinfusion with RL (dose equal to the shed blood volume; N = 7) caused only a transient increase in flow and no change in the lumenal narrowing. We conclude that HSD surpasses conventional RL treatment in reestablishing capillary hemodynamics owing to a decreased hydraulic resistance from osmotically induced endothelium shrinkage.