Original contribution
Effect of crystalloid infusion on hematocrit and intravascular volume in healthy, nonbleeding subjects

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We evaluated the effect of IV crystalloid administration on hematocrit in 28 healthy, nonbleeding volunteers. Normal saline boluses of 10, 20, and 30 mL/kg were delivered at a mean rate of 115 ± 4 mL/min, followed by a continuous infusion of either 1 or 5 mL/kg/hr. Hematocrit values determined immediately after bolus infusion declined from baseline a mean ± SEM of 4.5 ± 0.6 (P < .001), 6.1 ± 0.4 (P < .001), and 6.3 ± 0.6 points (P < .001) in the 10, 20, and 30 mL/kg groups, respectively. Twenty minutes into the maintenance infusion, hematocrits had risen 1.5 ± 0.8 (P = .03), 2.4 ± 0.4 (P = .004), and 2.3 ± 0.7 points (P = .005) when compared with postbolus hematocrits in the 10, 20, and 30 mL/kg groups, respectively. These data show that in healthy, nonbleeding subjects, crystalloid infusion may cause significant changes in hematocrit. Calculations reveal that approximately 60% of infused saline, when delivered as a bolus, will diffuse from the intravascular space within 20 minutes of administration.

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Presented at the American College of Emergency Physicians Scientific Assembly in San Francisco 1987.

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