The long term goal of this research is to improve patient outcomes after hypovolemic shock by increasing our understanding of how patient and treatment variables affect outcome. In severely diarrheic calves (one cause of hypovolemic shock) the addition of the synthetic colloid 6% dextran 70 to the intravenous fluid resuscitation of affected calves was investigated. In this clinical, prospective study (10 control calves and 12 calves that received 10 ml/kg 6% dextran 70), no decrease in hospitalization or mortality (0 for both groups) was noted, suggesting 6% dextran 70 use in this setting would not be cost effective. In a rat hemorrhagic shock and resuscitation model, the association between gastrointestinal intraluminal CO2 partial pressure (PiCO2) and outcome was investigated. An infrared air-flow based PiCO2 monitoring system consisting of CO2 permeable (silicone) and impermeable (Teflon) tubing, and an end-tidal CO2 monitor was used. Male Wistar-Furth rats (23 without and 74 with an 18 hour pre-hemorrhage fast) were anesthetized, hemorrhaged (MAP = 35-40mmHg) for 90 minutes, and volume resuscitated (MAP > 80mmHg) for 3 hours. Survivors were euthanized at 48 hours. In non-fasted rats, the start of resuscitation colon PiCO2 was 90 ± 7 mmHg in non-survivors and 66 ± 3 mmHg in survivors (p < 0.01, two-way ANOVA for repeated values). The start of resuscitation base excess was -16.8 ± 2.0 mEq/l in non-survivors and -10.4 ± 1.1 mEq/l in survivors (p < 0.01, two-way ANOVA for repeated measures). The incidence of organ pathology was 0% lung, 26% liver, and 45% small intestine. Mortality was 35%. In the fasted rats, neither PiCO2 nor base excess predicted mortality. (Start of resuscitation PiCO2: non-survivors, 59 ± 2 mmHg; survivors, 62 ± 2 mmHg. Start of resuscitation base excess: non-survivors, -14.4 ± 0.6 mEq/l; survivors -13.6 ± 0.5 mEq/l.) The incidence of organ pathology was 26% lung, 45% liver, and 85% small intestine (p < 0.05 for each compared to non-fasted, [chi]2). Mortality was 66% (p < 0.05 compared to non-fasted, [chi]2). Also, hypertonic saline dextran administration was 100% fatal in fasted rats.