Objective: To study the relation between blood and saline administration, postresuscitation hematocrit (Hct) level, and metabolic recovery after hemorrhagic shock. Summary Background Data: It is generally believed that crystalloid can be substituted, in whole or in part, for blood during resuscitation of hemorrhagic shock. This is based on the belief that Hct can be safely reduced but should not fall below a critical level. Methods: Male rats weighing 200 g were subjected to an isobaric hemorrhagic shock at a mean arterial pressure of 30 mmHg for 14 minutes, after which they were randomized to one of three resuscitation regimens. Control group (n = 36) were resuscitated by return of all shed blood. Mid-Hct (n = 39) and low- Hct (n = 60) groups were depleted of one third and one half of their circulating blood volumes, respectively, and were resuscitated with three times that volume of normal saline. Skeletal muscle intracellular energetics and pH were measured serially using 31P magnetic resonance spectroscopy at baseline, during shock, and after resuscitation. Arterial blood was sampled at the same time points. The number of surviving animals in each group at 24 hours was recorded. Results: After resuscitation, surviving rats in the low- Hct group demonstrated a greater consumption of high-energy phosphocreatine stores than did the other groups (control = 0.479 ± 0.003, mid-Hct = 0.465 ± 0.004, low-Hct = 0.457 ± 0.007, mean ± standard error of the mean; p < 0.01 low-Hct vs. other groups by analysis of variance). The rats that received saline resuscitation developed a relative intracellular acidosis (control = 7.29 ± 0.02, mid-Hct = 7.25 ± 0.02, low-Hct = 7.23 ± 0.02; p < 0.05 controls vs. other groups by analysis of variance). At 24 hours, the death rates were significantly different among the groups: control = 1 of 36 rats (2.8%), mid-Hct = 6 of 39 (15.4%), and low-Hct = 14 of 60 (23.3%) (p < 0.05 by chi square analysis). Conclusion: The oxygen-carrying capacity of resuscitation fluid has an important impact on intracellular metabolism and outcome.
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