PY Van MD SD Cho MD SJ Underwood MS GJ Hamilton BS LB Ham MD MA Schreiber MD Background Hemorrhage leading cause of preventable death in trauma victims Decreased peripheral hematocrit pHct used as marker for blood loss ID: 321704
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Slide1
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, MDSlide2
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)Slide3
BackgroundSlide4
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 2004Slide5
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 tracerSlide6
Concentration of tracer injected
Volume of sample withdrawn
Conc. tracer in sample withdrawn
Unknown volume (plasma volume)
Indicator Dilution Principle
C
1
V
1
C
2
V
2
=Slide7
Blood Volume Analysis
Single injection
radiolabeled
131
I-albumin.
Serial blood samples drawn over 40 minutesAnalysis yields actual and ideal TBV, RBCV, PVSlide8
Blood Volume Analysis
pHct
RBCV
RBCV
=
+
PV
TBV = RBCV + PVSlide9
Blood Volume Analysis
Normalized hematocrit (nHct)
pHct is adjusted for volume derangement:
nHct =
pHct
x
Measured TB
V
Ideal TBVSlide10
Blood Volume Analysis
Ideal volumes determination
Based on math model from Metropolitan Life height and weight tables ( > 100,000 data points)
Blood volume dependent on body composition
Weight and body surface areas alone not adequate
Lean
vs fat tissue proportions
Feldschuh J et al. Circulation. 1977Slide11
Hypothesis
Use of pHct alone in critically ill trauma patients will result in over-diagnosis of anemiaSlide12
Methods
Trauma ICU pts recruited 24hrs post admission
Baseline blood sample
Injection of 1mL 25 µ
Ci
of
131I-albumin12 minute equilibration periodThen 5 serial blood draws, 6 minutes apartSamples processed on BVA-100 Blood Volume Analyzer (Daxor Corporation, NY, NY)Slide13
Methods
Measured volumes compared to ideal -- percent deviation from ideal calculatedSlide14
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 Slide15
Characteristics
Patients (n =
27)
Male / Female
13 / 14
Age
49.6 ± 3.8
Body
Mass Index29.3 ± 6.2APACHE II17.9 ± 1.5
Injury Severity Score29.8 ± 2.5
All values are mean ± standard deviationSlide16
ResultsSlide17
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 statusSlide18
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 (R
2
= 0.3)Slide19
Results
No differences in ISS when compared across the volume status groups
No correlation between ISS and rate of albumin transudationSlide20
pHct versus nHct
pHct
nHct
Difference
pHct
< 30
nHct < 30
Overdiagnosis
of anemiaHypovolemic(n=12)
26.120.9*
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
< 0.05Slide21
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 ptsSlide22
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 Slide23
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
hemodilutionSlide24
Acknowledgements
Martin Schreiber, MD
S David Cho, MD
Samantha Underwood, MS
Richard Loftus, Daxor Corporation
OHSU Nuclear MedicineSlide25Slide26
Blood Volume Analysis