Does hemodilution exist? Effects of saline infusion on hematologic parameters in euvolemic subjects

The effects of intravenous fluids on hematocrit are debated. We sought to determine whether maintenance or bolus fluid therapy causes a significant change in the hematocrit and other hematologic parameters included in the complete blood count. Nine subjects completed a randomized three-period crossover designed trial in which they were given no fluid, maintenance fluid, or a bolus of fluid followed by maintenance fluid. We measured complete blood counts at baseline, 1 hour, 4 hours, and 8 hours. In the bolus fluid trial, the hemoglobin and hematocrit values (mean ± SEM) decreased by a maximum of 1.5 ± 0.1 g/dL and 4.1 ± 0.3% at 1 hour. There was no difference in hemoglobin or hematocrit during the no fluid or maintenance fluid treatments. No significant changes occurred in white blood cell or platelet counts. We demonstrated that maintenance fluid infusions do not significantly alter the complete blood count. Saline bolus is associated with a significant decrease in hemoglobin and hematocrit, but these parameters trend toward baseline over time.