py van, md ∙ sd cho, md ∙ sj underwood, ms gj hamilton, bs ∙ lb ham, md ∙ ma schreiber,...

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∙ ∙

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)

Background

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

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

Concentration of tracer injected

Volume of sample withdrawnConc. tracer in sample withdrawnUnknown volume (plasma volume)

Indicator Dilution Principle

C1

V1

C2

V2

=

Blood Volume Analysis

• Single injection radiolabeled 131I-albumin.• Serial blood samples drawn over 40 minutes• Analysis yields actual and ideal TBV, RBCV, PV

Blood Volume Analysis

pHct

RBCV

RBCV=

+ PV

TBV = RBCV + PV

Blood Volume Analysis

• Normalized hematocrit (nHct)– pHct is adjusted for volume derangement:

nHct = pHct xMeasured TBV

Ideal TBV

Hypothesis

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

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)

Methods

Measured volumes compared to ideal -- percent deviation from ideal calculated

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

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

Results

Hyper-volemic50.8%

Normo-volemic30.8%

Hypo-volemi

c18.4%

Volume status (n = 65)

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

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)

Results

• No differences in ISS when compared across the volume status groups

• No correlation between ISS and rate of albumin transudation

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

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

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

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

Blood Volume Analysis