Mesenteric microcirculatory changes in nonlethal hemorrhagic shock: the role of resuscitation with balanced electrolyte or hypertonic saline/dextran.

Class I and II hemorrhage has been routinely treated clinically with 2-2.5 times the volume of shed blood as balanced electrolyte solution. Although this regimen has been shown to adequately restore arterial pressure in trauma patients, it is not clear that it uniformly restores regional perfusion. Since it is becoming apparent that the gut plays a major role in the development of the posttraumatic septic state, we studied the effects of graded doses of balanced electrolyte resuscitation on the mesenteric microcirculation. Regimens consisting of one (1 x LR), two (2 x LR), or three (3 x LR) times the volume of shed blood as lactated Ringer's (LR) solution or 7.5% hypertonic saline and 6% dextran (HSD) equal to one seventh the volume of shed blood were given to groups of anesthetized (urethane-chloralose) male Sprague-Dawley rats after 30 minutes of hemorrhage to 50% of baseline mean arterial blood pressure. The microcirculation of the distal ileum was observed using an in vivo video microscope. Mean arterial pressure and ileal A1 diameters returned to baseline values with HSD within 20 minutes following this moderate hemorrhage. Additionally, A1 diameters returned to baseline in the 2 x LR and 3 x LR groups. A1 vessels remained significantly constricted in the 1 x LR group. Mean arterial pressure remained significantly lower than the baseline value in all of the LR groups. We conclude that in this model, HSD is superior to LR for restoration of blood pressure. In restoring A1 diameters, LR is equivalent to HSD only when volumes of balanced electrolyte two and three times shed blood volume are given.