Download - PY Van, MD ∙ SD Cho, MD ∙ SJ Underwood, MS GJ Hamilton, BS ∙ LB Ham, MD ∙ MA Schreiber, MD
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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∙ ∙
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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)
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Background
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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
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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
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Concentration of tracer injected
Volume of sample withdrawnConc. tracer in sample withdrawnUnknown volume (plasma volume)
Indicator Dilution Principle
C1
V1
C2
V2
=
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Blood Volume Analysis
• Single injection radiolabeled 131I-albumin.• Serial blood samples drawn over 40 minutes• Analysis yields actual and ideal TBV, RBCV, PV
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Blood Volume Analysis
pHct
RBCV
RBCV=
+ PV
TBV = RBCV + PV
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Blood Volume Analysis
• Normalized hematocrit (nHct)– pHct is adjusted for volume derangement:
nHct = pHct xMeasured TBV
Ideal TBV
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Hypothesis
Use of pHct alone in critically ill trauma patients will result in over-diagnosis of anemia
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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)
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Methods
Measured volumes compared to ideal -- percent deviation from ideal calculated
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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
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CharacteristicsPatients (n = 27)
Male / Female 13 / 14
Age 49.6 ± 3.8
Body Mass Index 29.3 ± 6.2
APACHE II 17.9 ± 1.5
Injury Severity Score 29.8 ± 2.5
All values are mean ± standard deviation
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Results
Hyper-volemic50.8%
Normo-volemic30.8%
Hypo-volemi
c18.4%
Volume status (n = 65)
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Volume Status and Fluids
Hypovolemic(n = 12)
Normovolemic(n =19)
Hypervolemic(n = 33)
Fluid In (mL) 17,881(10065, 41396)
30,306(14752, 52026)
22,016(18100, 33397)
Net Fluid (mL) 13,579(4702, 18708)
2,799(1969, 15861)
11,807(6924, 17373)
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
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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)
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Results
• No differences in ISS when compared across the volume status groups
• No correlation between ISS and rate of albumin transudation
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pHct versus nHctpHct nHct Difference pHct < 30 nHct < 30 Overdiagnosi
s of anemiaHypovolemic
(n=12) 26.1 20.9* 5.2 ± 3.3 91.7% (11) 91.7% (11) --
Normovolemic(n=20) 27.1 27.1 0.0 ± 1.2 80.0% (16) 80.0% (16) --
Hypervolemic(n=33) 26.5 32.9* -6.4 ± 4.4 81.8% (27) †27.3% (9) 54.5% (18)
All(n=65) 26.6 28.9 -2.3 ± 5.7 83.1% (54) 55.4% (36) 27.7% (18)
Paired t-test* p < 0.05
Chi-squared† p < 0.05
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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
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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
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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
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Blood Volume Analysis