PY Van, MD ∙ SD Cho, MD ∙ SJ Underwood, MS GJ Hamilton, BS ∙ LB Ham, MD ∙ MA Schreiber, MD

1. Blood Volume Analysis Can Distinguish True Anemia from Hemodilution in Critically Ill Trauma Patients PY Van, MD ∙ SD Cho, MD ∙ SJ Underwood, MS GJ Hamilton, BS ∙ LB Ham, MD ∙ MA Schreiber, MD

2. Background • Hemorrhage leading cause of preventable death in trauma victims • Decreased peripheral hematocrit (pHct) used as marker for blood loss • pHct may not represent true red blood cell volume (RBCV)

3. Background

4. Background • Surrogate measures to deduce volume status • Vital signs and physical exam • Laboratory tests • Invasive monitoring • Experienced clinicians frequently wrong • 51% concordance with blood volume analysis Androne, AS et al. Am J Cardiol 2004

5. Blood Volume Analysis • Indicator dilution principle • Known quantity of tracer injected into unknown volume (intravascular space) • After equilibration of tracer, plasma sampled • Concentration of tracer in sample is measured • Unknown volume is inversely proportional to concentration of tracer in the sample volume • Larger the unknown volume, more dilute the tracer

6. Indicator Dilution Principle C2 C1 = V2 V1 Concentration of tracer injected Unknown volume (plasma volume) Conc. tracer in sample withdrawn Volume of sample withdrawn

7. Blood Volume Analysis • Single injection radiolabeled131I-albumin. • Serial blood samples drawn over 40 minutes • Analysis yields actual and ideal TBV, RBCV, PV

8. Blood Volume Analysis RBCV = pHct + PV RBCV TBV = RBCV + PV

9. Blood Volume Analysis • Normalized hematocrit (nHct) • pHct is adjusted for volume derangement: Measured TBV nHct = pHct x Ideal TBV

10. Hypothesis Use of pHct alone in critically ill trauma patients will result in over-diagnosis of anemia

11. Methods • Trauma ICU pts recruited 24hrs post admission • Baseline blood sample • Injection of 1mL 25 µCi of 131I-albumin • 12 minute equilibration period • Then 5 serial blood draws, 6 minutes apart • Samples processed on BVA-100 Blood Volume Analyzer (Daxor Corporation, NY, NY)

12. Methods Measured volumes compared to ideal -- percent deviation from ideal calculated

13. Methods • Pts stratified into 3 groups based on deviation from ideal total blood volume • Hypovolemic: > 8% deficit relative to ideal • Normovolemic: < 8% variation relative to ideal • Hypervolemic: > 8% excess relative to ideal

14. Characteristics All values are mean ± standard deviation

15. Results

16. Volume Status and Fluids All values are medians (interquartile range) All p = NS, Mann-Whitney U test No significant difference in volume of fluids given or net fluid balance between each volume status

17. Results • No linear correlation between net fluid balance and changes in TBV, RBCV, and PV between each analysis • Moderate linear correlation between pHct and RBCV (R2 = 0.3)

18. Results • No differences in ISS when compared across the volume status groups • No correlation between ISS and rate of albumin transudation

19. pHct versus nHct Paired t-test * p < 0.05 Chi-squared † p < 0.05

20. Conclusions • Assessing volume status is challenging • No differences in amount of fluids administered to volume status groups • pHct compared to nHct • Overestimates anemia in hypervolemic pts • Underestimates anemia in hypovolemic pts

21. Limitations • Preliminary study -- small number of patients • BVA not a dynamic test – snapshot in time • Assume RBCV constant during testing • Not reasonable if bleeding > 100mL/hr • Availability of tracer and personnel

22. Future Directions • Further characterize effects of fluid and blood product administration on volume status • Blood volume analysis upon ICU admission • Establish baseline • Initiate therapies based on blood volumes • Avoid unnecessary CT scans and transfusion when BVA shows low pHct due to hemodilution

24. Blood Volume Analysis