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Accuracy of Blood Loss Measurement during Cesarean Delivery

Authors:

Abstract

Objective This study aims to compare the accuracy of visual, quantitative gravimetric, and colorimetric methods used to determine blood loss during cesarean delivery procedures employing a hemoglobin extraction assay as the reference standard. Study Design In 50 patients having cesarean deliveries blood loss determined by assays of hemoglobin content on surgical sponges and in suction canisters was compared with obstetricians' visual estimates, a quantitative gravimetric method, and the blood loss determined by a novel colorimetric system. Agreement between the reference assay and other measures was evaluated by the Bland–Altman method. Results Compared with the blood loss measured by the reference assay (470 ± 296 mL), the colorimetric system (572 ± 334 mL) was more accurate than either visual estimation (928 ± 261 mL) or gravimetric measurement (822 ± 489 mL). The correlation between the assay method and the colorimetric system was more predictive (standardized coefficient = 0.951, adjusted R² = 0.902) than either visual estimation (standardized coefficient = 0.700, adjusted R² = 00.479) or the gravimetric determination (standardized coefficient = 0.564, adjusted R² = 0.304). Conclusion During cesarean delivery, measuring blood loss using colorimetric image analysis is superior to visual estimation and a gravimetric method. Implementation of colorimetric analysis may enhance the ability of management protocols to improve clinical outcomes.
Accuracy of Blood Loss Measurement during
Cesarean Delivery
Sahar V. Doctorvaladan, MD1Andrea T. Jelks, MD1Eric W. Hsieh, BS2Robert L. Thurer, MD2
Mark I. Zakowski, MD3David C. Lagrew, MD4
1Department of Obstetrics and Gynaecology, Santa Clara Valley
Medical Center, San Jose, California
2Gauss Surgical, Inc., Los Altos, California
3OB Anesthesiology, Cedars-Sinai Medical Center, Los Angeles,
California
4Womens Health Institute, St. Joseph Hoag Health, Irvine, California
Am J Perinatol Rep 2017;7:e93e100.
Address for correspondence David C. Lagrew, MD, WomensHealth
Institute, St. Joseph Hoag Health, 3345 Michaelson, Irvine, CA 92612
(e-mail: drlagrew@drlagrew.net).
Obstetrical hemorrhage is a potentially preventable cause of
maternal morbidity and mortality, and its incidence is
steadily increasing.1,2 Standardized approaches are being
adopted to improve the care of these patients.3,4 Since
poor outcomes can result from both delayed recognition
and denial of the occurrence of signicant bleeding3and
changes in maternal vital signs or laboratory parameters
often provide late or misleading information,57effective
measurement of ongoing blood loss is critical to early
recognition.
Existing techniques for deter mining cumulative blood loss
during cesarean procedures include visual estimation and a
gravimetric method that involves weighing of soiled sponges
and measurement of uid in suction canisters. Since visual
estimation frequently either over or underestimates the
amount of bleeding8,9 and requires continual retraining
Keywords
cesarean delivery
blood loss
measurement
postpartum
hemorrhage
quality improvement
Abstract Objective This study aims to compare the accuracy of visual, quantitative gravi-
metric, and colorimetric methods used to determine blood loss during cesarean
delivery procedures employing a hemoglobin extraction assay as the reference
standard.
Study Design In 50 patients having cesarean deliveries blood loss determined by
assays of hemoglobin content on surgical sponges and in suction canisters was
compared with obstetriciansvisual estimates, a quantitative gravimetric method,
and the blood loss determined by a novel colorimetric system. Agreement between the
reference assay and other measures was evaluated by the BlandAltman method.
Results Compared with the blood loss measured by the reference assay (470 296
mL), the colorimetric system (572 334 mL) was more accurate than either visual
estimation (928 261 mL) or gravimetric measurement (822 489 mL). The
correlation between the assay method and the colorimetric system was more
predictive (standardized coefcient ¼0.951, adjusted R
2
¼0.902) than either visual
estimation (standardized coefcient ¼0.700, adjusted R
2
¼00.479) or the gravi-
metric determination (standardized coefcient ¼0.564, adjusted R
2
¼0.304).
Conclusion During cesarean delivery, measuring blood loss using colorimetric image
analysis is superior to visual estimation and a gravimetric method. Implementation of
colorimetric analysis may enhance the ability of management protocols to improve
clinical outcomes.
received
January 11, 2017
accepted after revision
February 20, 2017
DOI http://dx.doi.org/
10.1055/s-0037-1601382.
ISSN 2157-6998.
Copyright © 2017 by Thieme Medical
Publishers, Inc., 333 Seventh Avenue,
New York, NY 10001, USA
Tel: +1(212) 584-4662.
THIEME
Case Report e93
and constant vigilance during surgery,10 national organiza-
tions such as California Maternal Quality Care Collaborative
(CMQCC), the Association of Womens Health, Obstetric and
Neonatal Nurses (AWHONN), and the Council on Patient
Safety in Womens Healthcare recommend weighing sponges
to quantify blood loss. While this gravimetric method fo-
cuses providers on the importance of quantitatively asses-
sing blood loss, it is cumbersome and has mixed data to
validate its accuracy.11,12
The Triton system (Gauss Surgical, Inc., Los Altos, CA) is a
novel U.S. Food and Drug Administration-cleared mobile
application on a tablet computer (iPad) that uses the enabled
tablet camera to capture images of surgical sponges. It per-
forms colorimetric image correction and analysis and uses
cloud-based machine-learning models to quantify hemoglo-
bin (Hgb) mass on surgical sponges in real time. The tech-
nology can also be used to measure the Hgb content of uid
collected in suction canisters during surgery and is accurate
despite dilution with amniotic or other uids. The perfor-
mance of the device has been validated in bench-top and
clinical settings.1315
The objective of this study was to evaluate and compare
the accuracy of visual estimation, quantitative gravimetric
and colorimetric methods in determining cumulative blood
loss during cesarean delivery procedures using a validated
Hgb extraction assay method as the reference standard.
Materials and Methods
The protocol was approved by the Santa Clara Valley Medical
Center Institutional Review Board (San Jose, CA) reference
#12003; August 12, 2013. Canister and sponge samples
from 50 consecutive patients having cesarean deliveries on
weekdays between October and December 2015 were stu-
died, and relevant patient and procedural information were
collected and deidentied. Patients with known human
immunodeciency virus, hepatitis B virus or hepatitis C
virus, were excluded. Standard methods of care were used
throughout the procedures including uid administration
and the use and management of surgical sponges (RFDetect
L181804P01C-1 1818, RF Surgical Systems, Inc.) and
suction canisters (Medi-Vac Guardian65651230 3000 mL,
Cardinal Health, Inc.). Soiled laparotomy sponges were
individually stored in sponge counting bags, and suction
canisters were afxed with a label for recording amniotic
and irrigation uid volumes. Preprocedure and postopera-
tive day 1 Hgb values (g/dL) and all blood product transfu-
sions given in the operating room were documented.
Clinicians used only visually estimated blood loss (EBL) in
making patient management decisions; they were blinded
to results of the other assays.
For each patient, the cumulative blood loss was calculated
from direct extraction assays of Hgb content on surgical
sponges and in suction canisters. This result was compared
with the attending obstetricians visual estimate of blood
loss, the measured blood loss using a quantitative gravi-
metric method and the blood loss determined by the colori-
metric system.
Extraction assay: The Hgb recovery process draws from
previously published methodology.1620 Upon completion of
each procedure, all soiled laparotomy sponges, and suction
canisters were transferred to an on-site benchtop facility for
Hgb extraction. Sponges were individually soaked in 400 mL
of normal saline, compressed by hand for 60 seconds to a
mean weight of 50 g. This process was repeated four times.
Hemoglobin concentration of the nal extraction uid was
measured using the plasma/low spectrophotometer (Hemo-
Cue AB, Ängelholm, Sweden) and incorporated into the
following formula to determine the total Hgb content of
the sponge:
where m
uid
represents the mass of the extraction uid,
m
residual
the mass of the fully extracted sponge, m
dry
the
average dry weight of the sponge, ρthe density of the
extraction uid approximated as 1.0 g/mL, [Hgb]
uid
the
Hgb concentration of extraction uid, and %
yield
the yield
of the manual rinse extraction method. The yield was
independently characterized by depositing banked blood
on sponges in known quantities and performing the same
mechanical extraction. A linear regression analysis revealed
mean mHgb recovery rates of 89.5% (95% condence interval
[CI] ¼86.892.1%) for individual sponges (n¼116).
Canister Hgb was determined by gently remixing the
efuent, and transferring a 10 mL aliquot into a centrifuge
tube. Two samples were drawn from the tube and measured
using the plasma/low spectrophotometer for canisters ran-
ging from 0 to 2.00 g/dL, or Hb201þ(HemoCue AB) for
samples ranging from 2.0 to 25.6 g/dL, per instrument
guidelines.
The canister uid mass was measured using the digital
scale, with an approximated density conversion of 1.0 g/mL:
where m
efuent
represents the mass of the canister uid, ρits
density, and [Hgb]
efuent
the Hgb concentration averaged
over two samples.
The Hgb concentration in the canisters was separately
assayed by using either a whole blood or low-concentration
Hgb analyzer and converted to a canister blood volume rst
by converting the blood concentration (g/dL) of the canister
to Hgb mass (g) by multiplying by the known total uid
volume in the canister, and then by dividing this canister Hgb
mass (g) by the patients baseline Hgb concentration (g/dL).
All blood loss measurements (mL) were calculated by divid-
ing Hgb mass readings by the patients baseline (preopera-
tive) Hgb value (g/dL). The blood loss in the canisters was
then combined with the blood loss from the sponges to give a
total assayed blood loss.
Visually EBL: At the conclusion of the procedure, the
attending obstetrician visually estimated total blood loss
based on examination of the surgical sponges and suction
American Journal of Perinatology Reports Vol. 7 No. 2/2017
The accuracy of Blood Loss Measurement during Cesarean Delivery Doctorvaladan et al.e94
canisters, knowledge of the procedural specics, and his or
her estimate of the amount of amniotic uid. The results
were recorded independently, and the providers were
blinded to the results of gravimetric, colorimetric or refer-
ence assay measurements to prevent confounding.
Quantitati ve blood loss (QBL
Grav
): Quantitative gravimetric
measurement methods were adopted from published guide-
lines.3At the time of the uterine incision, the surgical
technician or nurse recorded the canister volume using the
graduated markings. After a spirating all of the amniotic uid,
a second measurement was made, and the difference was
recorded as the estimated amniotic uid volume. At the
conclusion of the procedure, the surgical technician re corded
the total amount of irrigation uid used. Immediately fol-
lowing the case, all sponges and suction canisters were
individually weighed using a calibrated digital scale (A&D
Co. Ltd., Tokyo, Japan). Dry sponge weights were determined
by weighing three packs of ve sponges each before the study
(mean ¼21 g, standard deviation [SD] ¼0.96 g) and pre-
measured canister weights were subtracted. To determine
the total QBL
Grav
estimate, all individual sponge and canister
QBL
Grav
measurements were tallied, and the amount of
amniotic and irrigation uid used was subtracted. The
sponge uid weight was expressed as a blood volume using
a 1.0 g/mL mean density conversion.
where m
wet
represents the mass of a soiled sponge, V
spongeQBL
the gravimetricblood volume estimate on a sponge, V
canisterQBL
the gravimetric blood volume estimate in a canister, V
amniotic
the amniotic uid volume estimate, and V
irrigation
the mea-
sured amount of irrigation uid.
Colorimetr ic: Following the case, all surgical sponges were
collected and scanned using the Triton sponge application
(Version 2.0.9). This resulted in a measured amount of Hgb
loss per sponge (g) that was converted to a volumetric
measure based on the patients preprocedure Hgb value
(g/dL). Also, the surgical canisters used to collect blood and
uid from the operative eld were scanned using the Triton
canister application (Version 1.0.3761), and the concentra-
tion of Hgb in the canisters was determined. This concentra-
tion was multiplied by the volume of uid in th e canister, and
the resultant total Hgb in the canister was converted to a
volumetric measurement of blood loss based on the patients
preprocedure Hgb value.
Statistical Analysis
Variables are expressed in mean SD, median/interquartile
range or count (%) as appropriate. KolmogorovSmirnov test
was used to evaluate whether the continuous variables
followed a normal distribution. For parameter estimates,
95% CIs are provided. Additional analyses were performed
using t-test, MannWhitney U test, Wilcoxon signed ranks
test, and Pearson or Spearman correlations as appropriate.
Volumetric blood loss measurement using the extraction
assay and the other measurements (EBL, QBL
Grav
, and colori-
metric) were compared using a two-sided paired t-test.
Agreement between the extraction assay and other mea-
surements (EBL, QBL
Grav
, and colorimetric) was evaluated
using the BlandAltman method, an analysis framework that
has been widely established as the standard for the compar-
ison of the clinical differences between two different mea-
surement methods.21 The BlandAltman bias (mean the
difference between the two measures) and upper and lower
limits of agreement (mean 1.96 SD) with their respective
95% CIs were computed.
As in previous studies, an acceptance criterion of 30 g of
Hgb per case was set a priori as the clinically acceptable
maximum bias.22 This difference represents approximately
5% of the total blood volume of an average adult (Hgb content
of ~250 mL [approximately 1/2 unit] of whole blood). Prior
studies with Triton1315 indicated that the SD of the Hgb
mass bias was relatively low (10 g or less) compared with
the acceptance criterion (30 g), and therefore a sample size
of 50 cases was deemed adequate as it provided a 95% CI of
0.5 SD (approximately 5 g) around the limits of agree-
ment.23 This sample size would allow 90% certainty that the
limits of a two-sided 95% CI will exclude a bias of 7.25 SD if
there were truly no difference between the two measure-
ment methods. Statistical analyses were performed using
SPSS (version 13.0, SPSS, Inc.).
Results
Data were successfully collected from all 50 cases. Mean pre-
and postoperative Hgb levels were 12.2 1.0 and 10.8 1.2
g/dL, respectively (p<0.001 for the paired comparison of
pre- and postoperative Hgb levels). One patient received a
single unit packed red cell transfusion intraoperatively.
The mean patient age was 31.9 years (range ¼1944
years). Overall, 44 mothers were multiparas. All babies were
singleton. A total of 41 procedures were elective. The indica-
tions for delivery included 32 elective repeat deliveries, eight
breech presentations, and the remainder for a variety of other
reasons. Six mothers labored before delivery although all had
intact membranes. Gestational ages ranged from 31 to
41 weeks and one day with 38 being 39 weeks or greater.
The mean amniotic uid volume as recorded intraopera-
tively by marking the suction canister for volumetric assess-
ment was 632 507 mL (median ¼500 mL, Fig. 1)andthe
mean measured irrigation uid volume was 759 437 mL.
As measured by the assay the mean amount of blood con-
tained in a laparotomy sponge was 24.5 20.3 mL, and the
average canister contained 236 137 mL of blood (Fig. 2).
An average of 15 sponges and one canister were used for each
procedure. The mean blood loss per procedure as measured
by the assay was 470 296 mL (range ¼1131,614 mL). In
four cases, the total blood loss exceeded 1,000 mL (Fig. 3).
American Journal of Perinatology Reports Vol. 7 No. 2/2017
The accuracy of Blood Loss Measurement during Cesarean Delivery Doctorvaladan et al. e95
The visual, gravimetric, and colorimetric methods of
estimating blood loss all demonstrated positive bias (mean
difference between t wo methods of measurement) about the
extraction assay, at 458, 352, and 102 mL, respectively. Both
the visual and gravimetric methods systematically overesti-
mated blood loss more than the clinical tolerance of 1/2 a
unit of whole blood, or 250 mL (Table 1).
The gravimetric method was evaluated to understand the
source of its inaccuracy better. Of the 757 sponges measured,
QBL
Grav
exceeded the blood content determined by the assay
method in all but 8. The QBL
Grav
measurements exhibited
poor correlation (r
2
¼0.2682) with the assay and system-
atically overestimated sponge blood content (Fig. 4)most
likely due to the addition of absorbed amniotic and irrigation
uid to the blood collected on the sponges. This inaccuracy
persisted despite the corrections for amniotic and irrigation
uid that were made to the total blood loss measures.
The relationship between blood losses measured by the
various methods versus the extraction assay method is de-
scribed in Table 2 and illustrated by scatter plots in Fig. 5.
Assessment of agreement between the various measurements
and the extraction assay method according to BlandAltman
method is provided in Table 3 and Figs. 68.
Comment
This study demonstrates that when using an extraction assay
method as a reference standard, cumulative blood loss is
Fig. 2 (A) Distribution of sponge blood content as measured by the assay method. (B) Distribution of canister blood content as measured by the
assay method.
Fig. 1 Distribution of amniotic uidvolumerecordedbymarkingthe
suction canister for volumetric assessment.
Fig. 3 Distribution of blood loss as determined by the assay method.
American Journal of Perinatology Reports Vol. 7 No. 2/2017
The accuracy of Blood Loss Measurement during Cesarean Delivery Doctorvaladan et al.e96
more accurately assessed by the colorimetric method than by
either visual estimation or the widely recommended quan-
titative gravimetric method. Vis ual estimation demonstrated
a slightly better correlation to the assay than gravimetric
estimation because, despite adjustments, the quantitative
gravimetric method tended to overestimate blood loss con-
sistently. This was presumably due to the effects of amniotic
uid and irrigants that inevitably mix with the blood col-
lected on surgical sponges and within suction canisters
confounding the results of weighing the sponges and mea-
suring the volume in the canisters.
The regression curve for visual estimation demonstrates a
slope well below 1.0 suggesting that the providersestimates
of the amount of blood loss were virtually unrelated to the
reference values (Fig. 5A). In fact, if a few of the high
estimates were removed the slope would have approached
zero. Clinicians never estimated a blood loss of less than
500 mL, and yet the reference data demonstrates that 66% of
patients had such values. These data conrm that surgeons
and other medical personnel are inaccurate in visually
estimating blood loss.9
Historical data supporting the quantitative gravimetric
method of measuring blood loss is mixed. For example, Lilley
et al,12 concluded that in a mixed group of vaginal and
cesarean deliveries gravimetric assessment of blood loss
during postpartum hemorrhage (PPH) was effective, while
Johar et al,11 determined that in surgical procedures the
technique was frequently inaccurate due to issues such as
recording bias, amniotic uid/saline corruption, and human
error. Data from this study illustrate the persistent chal-
lenges posed by this methodology in cesarean deliveries
where blood and nonsanguineous uids frequently mix.
Specically, the quantitative gravimetric technique showed
a lower correlation with actual blood loss than the colori-
metric method as evidenced by the lower R-value. This
variation includes several cases where th ere was a signicant
deviation, both above and below the actual blood loss. In 34%
of the cases the quantitative gravimetric method overesti-
mated the blood loss by greater than 500 mL when compared
with the reference standard ( mean ¼761 370 mL for those
cases) and in two cases the quantitative gravimetric method
underestimated the blood loss by more than 500 mL. How-
ever, unlike visual estimation, gravimetric methods did
effectively quantify blood losses of less than 500 mL in
many patients. The cases where the gravimetric estimate
Table 1 Blood loss determinations
Method Extraction Assay Visual EBL QBL
Grav
(adjusted)
a
Colorimetric
Sponge (mL) Mean SD 280 222 759 317 332 255
Median (IQR) 203 (138) 695 (426) 251 (181)
Bias (95% CI) 480 (428531) 52 (3271)
pValue <0.001 <0.001
Canister (mL) Mean SD 190 133 63 335 240 137
Median (IQR) 142 (173) 13 (285) 199 (202)
Bias (95% CI) 127
(228 to 26)
50 (2674)
pValue 0.014 <0.001
Tot a l b lood lo s s
per procedure
(mL)
Mean SD 470 296 928 261 822 489 572 334
Median (IQR) 384 (296) 800 (200) 651 (475) 481 (332)
Bias (95% CI) 458 (396520) 352 (237467) 102 (72132)
pValue <0.001 <0.001 <0.001
Abbreviations: CI, condence interval; EBL, estimated blood loss; IQR, interquartile range; QBL
Grav
, quantitative blood loss; SD, standard deviation.
a
Adjusted by subtracting the measured amniotic uid volume and irrigation volume.
Note: pValues reect the statistical signicance level of paired t-tests comparing each method with the extraction assay (reference standard).
Fig. 4 Scatter plot of the blood content of each sponge comparing
the assay and gravimetric methods.
American Journal of Perinatology Reports Vol. 7 No. 2/2017
The accuracy of Blood Loss Measurement during Cesarean Delivery Doctorvaladan et al. e97
of blood loss was greater than the blood loss calculated from
the Hgb loss determined by the extraction assay method can
be plausibly explained by visual underestimation of the
amount of irrigation and amniotic uid in the canister, lower
preoperative Hgb concentration (since the weight of addi-
tional plasma is i ncluded) or signicant amounts of irrigation
and/or amniotic uid on the sponges. Underestimation by
the quantitative gravimetric method likely resulted from the
reverse of these conditions.
Accurate blood loss estimation is clinically valuable and
may substantially alter the timing of inter ventions to control
hemorrhage. Overestimation during cesarean delivery may
lead patients, particularly those who have minimal post-
partum blood loss following the procedure, to have unne-
cessary laboratory evaluation and exposure to unneeded
medications and/or transfusions. Conversely, underestima-
tion may lead to a delay in evaluation and treatment,
particularly if further blood loss occurs postpartum. This
risk may be exacerbated by the fact that patients with
presumed low blood loss may be placed in care environ-
ments with the lower nurse to patient ratios and less
intensive monitoring. Furthermore, patients with
Table 2 Linear correlation of blood loss measurements versus extraction assay (reference standard)
Method Correlation coefficient (95% CI) Standardized coefficient pValue Adjusted R
2
Visual EBL 0.700 (0.5230.819) 0.700 <0.001 0.479
QBL
Grav
(adjusted) 0.564 (0.3390.728) 0.564 <0.001 0.304
Colorimetric 0.951 (0.9150.972) 0.951 <0.001 0.902
Abbreviations: CI, condence interval; EBL, estimated blood loss; QBL
Grav
, quantitative blood loss.
Fig. 5 Scatter plots of blood loss measured by (A) visual estimation, (B) gravimetric method, and (C) colorimetric method compared with the
assay method. A line of unity representing per fect correlation is shown for comparison.
Table 3 Assessment of agreement between methods of measuring blood loss and the extraction assay (reference standard)
Visual EBL (mL) QBL
Grav
(adjusted) (mL) Colorimetric (mL)
Bias (95% CI) (mL) 458 352 102
SD (error) (mL) 218 405 106
Upper limit of agreement (95% CI) (mL) 886 1,145 309
Lower limit of agreement (95% CI) (mL) 31 441 105
RMSE (mL) 507 533 146
CI (bias) 62 115 30
CI (LOAs)calculated as 105 194 51
Abbreviations: CI, condence interval; EBL, estimated blood loss ; LOA, limits of agreement; QBL
Grav
, quantitative blood loss; RMSE, root mean square
error; SD, standard deviation.
American Journal of Perinatology Reports Vol. 7 No. 2/2017
The accuracy of Blood Loss Measurement during Cesarean Delivery Doctorvaladan et al.e98
underestimated blood loss may not receive appropriate
blood, or blood component therapy is potentially leading
to excessive hemorrhage from dilutional anemia and/or
coagulopathy.
A limitation of this study is that it investigated a patient
population having surgical blood losses mostly within the
normal range. The population studied did not have a sub-
stantial number of patients with excessive blood loss, and
therefore comparisons between the various methods could
not be made for that situation. Nonetheless, the colorimetric
method is likely to be accurate in patients experiencing
massive hemorrhage since the study validates the compara-
tive accuracy of colorimetry in measuring blood loss on
individual sponges and in each canister. In cases with in-
creased hemorrhage, one would expect that there would
simply be more sponges and larger volumes in the canisters.
In contrast, both visual estimation and the quantitative
gravimetric method would be prone to greater variation
with increased blood loss. A strength of this study is that a
rigorous and detailed evaluation of all three methods was
conducted and compared the results to a validated reference
standard. Although all sponge/canister image capture and
analysis in this study was done at the conclusion of surgery,
the use of this tool has previously been effectively imple-
mented real-timeduring surgical procedures, thus provid-
ing continuous and ongoing monitoring of blood loss.15
The blood losses measured in this study were typically
less than that commonly estimated for cesarean delivery.
This may be due to the failure of the extraction assay,
colorimetric and gravimetric methods to account for blood
loss on surgical drapes. Alternatively, the data could be
interpreted as demonstrating that those traditional esti-
mates are often incorrect. Further studies are needed to
determine whether data using the colorimetric method is
sufciently accurate to predict postoperative Hgb levels and
guide therapy.
This study demonst rates that both visual and quantitative
gravimetric methods of measuring blood loss during cesar-
ean deliveries are unreliable and colorimetric image analysis
using a computer-based algorithmic system provides more
accurate results. Accurate, real-time measurement of blood
loss has the potential to facilitate proper implementation of
obstetric hemorrhage protocols to improve patient care.
Further study of these methods and workows, particularly
in patients with larger amounts of perioperative bleeding, is
warranted.
Conict of Interest
Mr. Hsieh and Dr. Thurer are employees of Gauss Surgical,
Inc. The remaining authors have no conicts to report.
Acknowledgments
Financial Support: Gauss Surgical, Inc. provided statistical
support services and the colorimetric device used in the
study. Gauss personnel also participated in study design,
data collection, and analysis, and article preparation.
The authors would like to recognize and thankKeng-Tsai
Lin, BS, Xuan Dang, BS, and John-Allen Smith, BA, Research
Associates, Gauss Surgical, Inc. and Mazyar Javidroozi, MD,
PhD, Director, Clinical Research, Department of
Fig. 6 BlandAltman plot: Visual method.
Fig. 7 BlandAltman plot: Gravimetric method.
Fig. 8 BlandAltman plot: Colorimetric method.
American Journal of Perinatology Reports Vol. 7 No. 2/2017
The accuracy of Blood Loss Measurement during Cesarean Delivery Doctorvaladan et al. e99
Anesthesiology, Englewood Medical Center, Englewood, NJ
for their contributions to this study.
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American Journal of Perinatology Reports Vol. 7 No. 2/2017
The accuracy of Blood Loss Measurement during Cesarean Delivery Doctorvaladan et al.e100
... In a previous publication that compared visually estimated blood loss, gravimetric QBL, and a colorimetric method of estimating blood loss to a reference hemoglobin assay measurement of the amount of blood on surgical sponges and in suction canisters during scheduled cesarean delivery, we found that gravimetric QBL measurements were poorly correlated to the more accurate reference hemoglobin assay results. 7 The aim of this secondary analysis was to determine the sources of error and limitations of the gravimetric QBL method in greater detail, using both correlations and Bland-Altman measures of agreement. ...
... The details of the study methodology have been previously described. 7 Briefly, all sponges and calibrated surgical canisters from 50 patients having scheduled cesarean deliveries were evaluated, and relevant patient and procedural information was collected. The original study compared visually estimated blood loss, gravimetric QBL, and a colorimetric blood loss estimation to a reference hemoglobin extraction assay during scheduled cesarean delivery. ...
... For the reference hemoglobin extraction assay method, all soiled laparotomy sponges and calibrated suction canisters were transferred to an on-site benchtop facility for hemoglobin measurement at the completion of each procedure. 7 Sponges were individually soaked in 400 mL of normal saline, compressed by hand for 60 seconds to a mean weight of 50 g. This process was repeated four times and the hemoglobin concentration of the final extraction fluid was measured using the plasma/low spectrophotometer (Hemo-Cue AB, Ängelholm, Sweden). ...
Article
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Objective This study examined the accuracy, sources of error, and limitations of gravimetric quantification of blood loss (QBL) during cesarean delivery. Study Design Blood loss determined by assays of the hemoglobin content on surgical sponges and in suction canisters was compared with QBL in 50 parturients. Results QBL was moderately correlated to the actual blood loss (r = 0.564; p < 0.001). Compared with the reference assay, QBL overestimated blood loss for 44 patients (88%). QBL deviated from the assayed blood loss by more than 250 mL in 34 patients (68%) and by more than 500 mL in 16 cases (32%). Assayed blood loss was more than 1,000 mL in four patients. For three of these patients, QBL was more than 1,000 mL (sensitivity = 75%). QBL was more than 1,000 mL in 12 patients. While three of these had an assayed blood loss of more than 1,000 mL, 9 of the 46 patients with blood losses of less than 1,000 mL by the assay (20%) were incorrectly identified as having postpartum hemorrhage by QBL (false positives). The specificity of quantitative QBL for detection of blood loss more than or equal to 1,000 mL was 80.4%. Conclusion QBL was only moderately correlated with the reference assay. While overestimation was more common than underestimation, both occurred. Moreover, QBL was particularly inaccurate when substantial bleeding occurred. Key Points
... The efficacy of the treatment (loss of blood) was assessed by differences in the hemoglobin and hematocrit count (before and 24 hours after the end of the caesarean section), as well as from differences in intraoperative blood loss (calculated by weighing the gauzes and compresses before and after the operation), from the amount of blood collected in the suction bag and from any blood in the environment of the surgical bed area [15]. ...
... For example, visual estimation has been found to estimate a value 30% lower than gravimetric estimations and visual estimation and gravimetric estimation both overestimate compared with colorimetric methods. 62,63 Indeed, the domain that provided the predominant source of bias for our EBL network was "measurement of the outcome," with 7 and 11, respectively, out of the 22 included studies judged to be at "high risk" of bias or "some concerns" for bias. This highlights the need for researchers to employ a core set of outcomes and establish a consensus on the optimal measurement tool for this important outcome. ...
Article
Background Postpartum hemorrhage causes a quarter of global maternal deaths. WHO recommends oxytocin as the first line agent to prevent hemorrhage at cesarean delivery. However, some randomized controlled trials suggest other uterotonics are superior. Objective We conducted a network meta-analysis comparing pharmacological agents in reducing blood loss and minimizing need for additional uterotonics at cesarean delivery. Study design We searched the CENTRAL, Embase, and Medline databases, from inception to May 2020, for randomized controlled trials that compared oxytocin, carbetocin, misoprostol, ergometrine, carboprost or combinations of these. Quality of evidence was assessed with the “Confidence in Network Meta-Analysis” approach and GRADE tool within the summary of findings table. Our primary outcomes were estimated blood loss and need for additional uterotonics. Secondary outcomes included nausea and postpartum hemorrhage of > 1000 ml. We performed sensitivity analyses to explore the influence of surgical context and oxytocin administration strategy. Results 46 studies with 7368 participants were included. 21 trials (6 agents and 3665 participants) formed the “estimated blood loss” network, and considering treatment effects, certainty in the evidence and SUCRA scores, carbetocin was assessed to be probably superior to oxytocin but only to reduce estimated blood loss by a clinically insignificant volume (54.83 [95% CI: 26.48 more to 143.78 less] ml). Misoprostol, ergometrine and the combination of oxytocin + ergometrine were assessed as probably inferior whilst the combination of oxytocin + misoprostol was assessed as definitely inferior to oxytocin. 37 trials (8 agents and 6193 participants) formed the “additional uterotonic” network and, again, carbetocin was assessed as probably superior to oxytocin, requiring additional uterotonics 185 (95% CI: 130 to 218) fewer times per 1000. Oxytocin + misoprostol, oxytocin + ergometrine and misoprostol were assessed to be probably inferior whilst carboprost, ergometrine and placebo were definitely inferior to oxytocin. For both primary outcomes, oxytocin administration strategies had a higher probability of being the best uterotonic if they were initiated with a bolus. Conclusions Carbetocin is probably the most effective agent in reducing blood loss and the need for additional uterotonics. Oxytocin appears to be more effective when initiated with a bolus.
... Our de nition of postpartum hemorrhage followed the current clinical guidelines [22][23][24][25] , however, we did not evaluate other relevant clinical indicators of acute blood loss, including a deep perineal hematoma from a laceration of the birth canal, blood ow velocity and properties, the bleeding was uid or turbulent or exudative, and whether it clotted or contained clots [46] . The blood loss in predictive models needs to be measured by means of the quantitative blood loss (QBL) methods, such as basic methemoglobin colorimetric method [47] or image spectral analysis [45] , Shock Index (SI) [48] and so on. ...
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Objective The morbidity and mortality caused by postpartum hemorrhage has been increased since 2016 in China, in addition, promoting vaginal delivery is an important task in China currently. This study aimed to develop a clinical decision support system (CDSS) to predict postpartum hemorrhage among vaginal delivery women. Design A retrospective cohort study. Methods We performed a retrospective analysis of medical records among 1587 vaginal delivery women, who had visited the obstetrics clinic at the Third Affiliated Hospital of Zhengzhou University from 2018 to 2020, these women then were randomly divided into a training set (70%), a validation set (15%) and a test set (15%). We adopted a univariate logistic regression model to select the significant features (P < 0.01). Afterward, we trained several artificial neural networks and binary logistic regression to predict the postpartum hemorrhage, the neural networks included multi-layer perceptron (MLP), back propagation (BP) and radial basis function (RBF). In order to compare and identify the most accurate network, we used the confusion matrix and the receiver operating characteristic (ROC) curve. We finally developed a clinical decision support system based on the most accurate network. All statistical analyses were performed by IBM SPSS (version 20), and MATLAB 2013b software was applied to develop the clinical decision support system. Results Initially, 45 potential variables were addressed by the univariate logistic regression, 16 significant predictors were then selected to enter the binary logistic regression and neural networks (P-value < 0.01). After validation, the best performing model was the multi-layer perceptron network with the highest discriminative ability (AUC 0.862, 95% CI 0.838–0.887). Followed by the back propagation model (AUC 0.866; 95% CI 0.842–0.890), the logistic regression model (AUC 0.856; 95% CI 0.832–0.880). The radial basis function model (AUC 0.845; 95% CI 0.820–0.870) had lower discriminative ability. Conclusion In summary, in terms of predicting postpartum hemorrhage, the multi-layer perceptron network performed better than the back propagation network, logistic regression model, and radial basis function network. The developed clinical decision support system based on the multi-layer perceptron network is expected to promote early identification of postpartum hemorrhage in vaginal delivery women, thereby improve the quality of obstetric care and the maternal outcome.
Article
Objective: To evaluate if the implementation of a colorimetric quantitative blood loss (QBL) system during cesarean delivery improves clinical outcomes. Methods: We conducted a retrospective cohort analysis after cesarean section before and after implementation of the Triton based colorimetric QBL system. Prevalence of postpartum hemorrhage, amount of blood products transfused, length of hospitalization, and rates of intensive care unit (ICU) admission were compared. Results: A total of 2221 patients were included. There were 1192 patients in the pre-intervention group and 1029 patients in the post-intervention group. There was no significant difference between groups in the prevalence of postpartum hemorrhage (8.6% vs 9.3%, P = 0.57), amount of packed red blood cells (pRBCs) transfused (45 vs 30, P = 0.41) or average length of hospital stay in days (3.0 vs 3.0, P = 0.37). There was a statistically significant decrease in ICU admissions between the pre- and post-intervention groups (2.2% vs 1.0%, P = 0.02). Conclusion: There was no effect of implementation of the colorimetric QBL application system on diagnosis of postpartum hemorrhage, amount of blood products transfused, or length of hospital stay. Although a significant decrease in ICU admissions was observed, we could not determine if these transfers were hemorrhage related.
Article
Carbetocin or oxytocin are given routinely as first‐line uterotonic drugs following delivery of the neonate during caesarean delivery to prevent postpartum haemorrhage. Low doses may be as effective as high doses with a potential reduction in adverse effects. In this double‐blind, randomised, controlled, non‐inferiority trial, we assigned low‐risk patients undergoing elective caesarean delivery under spinal anaesthesia to one of four groups: carbetocin 20 μg; carbetocin 100 μg; oxytocin 0.5 IU bolus + infusion; and oxytocin 5 IU bolus + infusion. The study drug was given intravenously after delivery of the neonate. Uterine tone was assessed by the obstetrician 2, 5 and 10 minutes after study drug administration according to an 11‐point verbal numerical rating scale (0 = atonic, 10 = excellent tone). The primary outcome measure was uterine tone 2 min after study drug administration. The pre‐specified non‐inferiority margin was 1.2 points on the 11‐point scale. Secondary outcomes included uterine tone after 5 and 10 minutes, use of additional uterotonics, blood loss and adverse effects. Data were available for 277 patients. Carbetocin 20 μg resulting in uterine tone of (median (IQR [range])) 8 (7–8 [1–10]) was non‐inferior to carbetocin 100 μg with tone 8 (7–9 [3–10]), median (95%CI) difference 0 (−0.44–0.44). Similarly, oxytocin 0.5 IU with tone 7 (6–8 [3–10]) was non‐inferior to oxytocin 5 IU with tone 8 (6–8 [2–10]), median (95%CI) difference 1 (0.11–1.89). Carbetocin 20 μg was also non‐inferior to oxytocin 5 IU, and oxytocin 0.5 IU was non‐inferior to carbetocin 100 μg. Uterine tone after 5 and 10 minutes, use of additional uterotonics, blood loss and adverse effects were similar in all groups.
Hemorrhage is the leading cause of maternal mortality worldwide. A maternal health priority is improving how health care providers prevent and manage postpartum hemorrhage (PPH). Because anesthesiologists can help facilitate how hospitals develop approaches for PPH prevention and anticipatory planning, we review the potential utility of PPH risk assessment tools, bundles, and protocols. Anesthesiologists rely on clinical and diagnostic information for initiating and evaluating medical management. Therefore, we review modalities for measuring blood loss after delivery, which include visual, volumetric, gravimetric, and colorimetric approaches. Point-of-care technologies for assessing changes in central hemodynamics (ultrasonography) and coagulation profiles (rotational thromboelastometry and thromboelastography) are also discussed. Anesthesiologists play a critical role in the medical and transfusion management of PPH. Therefore, we review blood ordering and massive transfusion protocols, fixed-ratio versus goal-directed transfusion approaches, coagulation changes during PPH, and the potential clinical utility of the pharmacological adjuncts, tranexamic acid and fibrinogen concentrate.
Article
Objective: To validate the use of placenta accreta risk-antepartum (PAR-A) score as a predictive tool of clinical outcomes of placenta accreta spectrum (PAS). Methods: This is a prospective study, conducted in six PAS specialized centers in six different countries. The study was conducted between October 1, 2020 and March 31, 2021. Women who were provisionally diagnosed with PAS during pregnancy were considered eligible. A machine-learning-based PAR-A score was calculated. Diagnostic performance of the PAR-A score was evaluated using a receiver operating characteristic curve, for perioperative massive blood loss and admission to intensive care unit (ClinicalTrials.gov identifier NCT04525001). Results: Of 97 eligible women, 86 were included. PAS-associated massive blood loss occurred in 10 patients (11.63%). Median PAR-A scores of massive blood loss in the current cohort were 8.9 (interquartile range 6.9-14.1). In predicting massive blood loss, the area under the curve of PAR-A scores was 0.85 (95% confidence interval [CI] 0.74-0.95), which was not significantly different from the original cohort (P = 0.2). PAR-A score prediction of intensive care unit admission was slightly higher compared with the original cohort (0.88, 95% CI 0.81-0.95; P = 0.06). Conclusion: PAR-A score is a novel scoring system of PAS outcomes, which showed external validity based on current data.
Article
Full-text available
Introduction: Real-time monitoring of blood loss is critical in fluid management. Visual estimation remains the standard of care in estimating blood loss, yet is demonstrably inaccurate. Photometric analysis, which is the referenced "gold-standard" for measuring blood loss, is both time-consuming and costly. The purpose of this study was to evaluate the efficacy of a novel tablet-monitoring device for measurement of Hb loss during orthopaedic procedures. Methods: This is a prospective study of 50 patients in a consecutive series of joint arthroplasty cases. The novel System with Feature Extraction Technology was used to measure the amount of Hb contained within surgical sponges intra-operatively. The system's measures were then compared with those obtained via gravimetric method and photometric analysis. Accuracy was evaluated using linear regression and Bland-Altman analysis. Results: Our results showed a significant positive correlation between Triton tablet system and photometric analysis with respect to intra-operative hemoglobin and blood loss at 0.92 and 0.91, respectively. Discussion: This novel system can accurately determine Hb loss contained within surgical sponges. We believe that this user-friendly software can be used for measurement of total intraoperative blood loss and thus aid in a more accurate fluid management protocols during orthopaedic surgical procedures.
Article
Background We set out to validate the accuracy of gravimetric quantification of blood loss during simulated major postpartum haemorrhage and to evaluate the technique in a consecutive cohort of women experiencing major postpartum haemorrhage. The study took part in a large UK delivery suite over a one year period. All women who experienced major postpartum haemorrhage were eligible for inclusion. Methods For the validation exercise, in a simulated postpartum haemorrhage scenario using known volumes of artificial blood, the accuracy of gravimetric measurement was compared with visual estimation made by delivery suite staff. In the clinical observation study, the blood volume lost during postpartum haemorrhage was measured gravimetrically according to our routine institutional protocol and was correlated with fall in haemoglobin. The main outcome measure was the accuracy of gravimetric measurement of blood loss. Results Validation exercise: The mean percentage error of gravimetrically measured blood volume was 4.0 ± 2.7% compared to visually estimated blood volume with a mean percentage error of 34.7 ± 32.1%. Clinical observation study: 356 out of 6187 deliveries were identified as having major postpartum haemorrhage. The correlation coefficient between measured blood loss and corrected fall in haemoglobin for all patients was 0.77; correlation was stronger (0.80) for postpartum haemorrhage >1500 mL, and similar during routine and out-of-hours working. Conclusion The accuracy of the gravimetric method was confirmed in simulated postpartum haemorrhage. The clinical study shows that gravimetric measurement of blood loss is correlated with the fall in haemoglobin in postpartum haemorrhage where blood loss exceeds 1500 mL. The method is simple to perform, requires only basic equipment, and can be taught and used by all maternity services during major postpartum haemorrhage.
Article
Accurate measurement of intraoperative blood loss is an important clinical variable in managing fluid resuscitation and avoiding unnecessary transfusion of blood products. In this study, we measured surgical blood loss using a tablet computer programmed with a unique algorithm modeled after facial recognition technology. The aim of the study was to assess the accuracy and performance of the system on surgical laparotomy sponges in vitro. Whole blood samples of premeasured hemoglobin (Hb) and volume were reconstituted from units of human packed red blood cells and plasma and distributed across surgical laparotomy sponges. Normal saline was added to simulate the presence of varying levels of hemodilution and/or irrigation use. Soaked sponges from 4 different manufacturers were scanned using the Triton System with Feature Extraction Technology (Gauss Surgical, Inc., Palo Alto, CA) under 3 different ambient light conditions in an operating room. Accuracy of Hb loss measurement was evaluated relative to the premeasured values using linear regression and Bland-Altman analysis. Correlations between studied variables and measurement bias were analyzed using nonparametric tests. The overall mean percent error for measure of Hb loss for the Triton System was 12.3% (95% confidence interval [CI], 8.2%-16.4%). A strong positive linear correlation between the premeasured and actual Hb masses was noted across the full range of intraoperative lighting conditions, including (A) high (r = 0.95 [95% CI, 0.93-0.96]), (B) medium (r = 0.94 [95% CI, 0.93-0.96]), and (C) low (r = 0.90 [95% CI, 0.87-0.93]) mean ambient light intensity. Bland-Altman analysis revealed a bias of 0.01 g [95% CI, -0.03 to 0.06 g] of Hb per sponge between the 2 measures. The corresponding lower and upper limits of agreement were -1.16 g (95% CI, -1.21 to -1.12 g) per sponge and 1.19 g (95% CI, 1.15-1.24 g) per sponge, respectively. Measurement bias of estimated blood loss and Hb mass using the new system were not associated with the volume of saline used to reconstitute the samples (P = 0.506 and P = 0.469, respectively), suggesting that the system is robust under a wide range of sponge saturation conditions. Mobile blood loss monitoring using the Triton system is accurate in assessing Hb mass on surgical sponges across a range of ambient light conditions, sponge saturation, saline contamination, and initial blood Hb. Utilization of this tool could significantly improve the accuracy of blood loss estimates.
Article
Accurate measurement of intraoperative blood loss is an important clinical variable in managing fluid resuscitation and avoiding unnecessary transfusion of blood products. In this study, blood lost onto laparotomy sponges during surgical cases was measured using a tablet computer programmed with a unique algorithm modeled after facial recognition technology. In this study, we assessed the accuracy and performance of the system in surgical cases. In this prospective, multicenter study, 46 patients undergoing surgery with anticipated significant blood loss contributed laparotomy sponges for hemoglobin (Hb) loss measurement using the Triton System with Feature Extraction Technology (Gauss Surgical, Inc., Los Altos, CA). The Hb loss measured by the new system was compared with that measured by manual rinsing of the sponges. Accuracy was evaluated using linear regression and Bland-Altman analysis. In addition, the new system's calculation of blood volume loss was compared with the gravimetric method of estimating blood loss from intraoperative sponge weights. A significant positive linear correlation was noted between the new system's measurements and the rinsed Hb mass (r = 0.93, P < 0.0001). Bland-Altman analysis revealed a bias of 9.0 g and narrow limits of agreement (-7.5 to 25.5 g) between the new system's measures and the rinsed Hb mass. These limits were within the clinically relevant difference of ±30 g, which is approximately half of the Hb content of a unit of allogeneic whole blood. Bland-Altman analysis of the estimated blood loss on sponges using the gravimetric method demonstrated a bias of 466 mL (overestimation) with limits of agreement of -171 and 1103 mL, due to the presence of contaminants other than blood on the laparotomy sponges. The novel mobile monitoring system provides an accurate measurement of Hb mass on surgical sponges as compared with that of manual rinsing measurements and is significantly more accurate than the gravimetric method. Further study is warranted to assess the clinical use of the technology.
Article
A rapid method for the determination of menstrual blood loss has been evaluated. The procedure is based upon the formation of alkaline haematin after the blood has been extracted from vaginal tampons and sanitary towels by an automatic Stomacher Lab-Blender.Fifteen minutes of extraction in 2 litres of 5% sodium hydroxide is sufficient to produce a good and constant recovery. Thirteen types of tampons and towels have been tested under optimal conditions and 11 were found to produce acceptable blank values. The recovery of blood (from 5–200ml) was >82% and the coefficient of variation on replicate analysis was < 11%.
Article
Background Estimates of blood loss in the operating room are typically performed as a visual assessment by providers, despite multiple studies showing this to be inaccurate. Use of a less subjective measurement of blood loss such as direct measurement of the hemoglobin (Hb) mass lost from the surgical field may better quantify surgical bleeding. The objective of this investigation was to compare anesthesiologist estimates of intraoperative blood loss with measured Hb loss. Study Design and Methods Sixty patients undergoing posterior spine surgery were enrolled in a prospective, randomized trial comparing intraoperative blood loss using unipolar cautery alone or with use of a bipolar tissue sealant device. Hb concentration and fluid volume were measured from all surgical sponges, suction canisters, and the cell salvage device. Using the volume and concentration of Hb from each solution allowed calculation of Hb mass, which was converted into volume of blood lost and compared with estimates of blood loss documented by the anesthesia team. A single-sample t test of no difference was used to compare estimated with measured blood loss. ResultsMean estimated blood loss exceeded measured blood loss by 246mL (860mL vs. 614mL, p<0.0001). Conclusion Estimated blood loss exceeded measured blood loss by 40% on average. The likely etiology of this discrepancy relates to the inability to visually determine Hb concentration of sanguineous solutions in suction canisters and surgical sponges. Ramifications of excessive bleeding estimates include unnecessary transfusion and overadministration of intravenous fluids, both of which may have deleterious effects.
Article
It is important to recognize excessive blood loss during childbirth, which is a significant cause of morbidity and mortality. This article reviews methods to measure blood loss that could be used during childbirth. PubMed, CINAHL, and MEDLINE databases were searched using the phrases “blood loss” and “measurement.” The bibliographies of publications were scanned for applicable references. A total of 46 publications are included in this review. The methods used to measure blood loss are categorized into visual estimation, direct measurement, gravimetric, photometry, and miscellaneous. Methods are described and compared. A combination of direct measurement and gravimetric methods are the most practical. Photometry is the most precise, but also the most expensive and complex to use. A variety of miscellaneous methods are presented, but none is a practical or reliable method. Visual estimation of blood loss is so inaccurate that its continued use in practice is questionable and it should not be used in research to evaluate treatment.
Article
BACKGROUND: Traditional techniques for obtaining hemostasis during orthopedic surgery, such as conventional electrocautery and sealants, have limited clinical effectiveness in reducing hemoglobin (Hb) loss and requirement for transfusion. The bipolar tissue sealant device studied in this trial combines radiofrequency energy with saline irrigation to hemostatically seal both cut bone and soft tissue, potentially aiding hemostasis. STUDY DESIGN AND METHODS: Sixty patients undergoing multilevel posterior lumbar instrumentation and fusion were randomly assigned to unipolar cautery alone (control group) or unipolar cautery plus use of the bipolar tissue sealant device (treatment group). Hb loss from the surgical field was measured (rather than estimated) and compared between the two groups. The primary hypothesis was that the treatment group would lose significantly less Hb than the control group. RESULTS: The control group experienced a mean Hb loss of 102.4 g while the treatment group showed a significantly lower mean Hb loss of 66.2 g (p = 0.0004). No significant difference was found between groups with respect to secondary endpoints including length of surgery, number of red blood cell units transfused, number of total blood component units transfused, transfusion avoidance, length of stay, or serious adverse events. CONCLUSION: Use of a bipolar tissue sealant device in addition to unipolar cautery significantly decreased Hb loss during multilevel, posterior lumbar spinal instrumentation and fusion when compared with unipolar cautery alone.