Impact of the Non-pneumatic Antishock Garment on pelvicblood flow in healthy postpartum womenFelicia Lester, MD, MPH, MS; Amy Stenson, MD, MPH; Carinne Meyer, MPH;Jessica Morris, MA; Juan Vargas, MD; Suellen Miller, PhD, CNM
OBJECTIVE: The Non-pneumatic Antishock Garment (NASG) is a com-pression device that has shown significantly decreased blood loss incases of obstetric hemorrhage. However, there are no physiologic stud-ies of the NASG in postpartum women. This study used Doppler ultra-sound to measure the resistive index (RI) in the internal iliac artery, thusapproximating blood flow to the pelvis with and without the garmentapplied.
STUDY DESIGN: In this study, RI of the internal iliac artery was mea-
sured in a sample of 10 postpartum volunteers with and without the
NASG applied. Median RI was calculated and compared between base-line and full application.
RESULTS: Internal iliac artery median RI was 0.83 (SD 0.11) at baselineand increased to 1.05 (SD 0.15) with full NASG application (P � .02).
CONCLUSION: This study suggests a significant increase in internal il-iac artery RI with NASG application and provides a physiological expla-nation of how the NASG might reduce postpartum hemorrhage.
Antishock Garment, postpartum hemorrhage, resistive index
Cite this article as: Lester F, Stenson A, Meyer C, et al. Impact of the Non-pneumatic Antishock Garment on pelvic blood flow in healthy postpartum women. Am J
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Postpartum hemorrhage remains theleading cause of maternal death
worldwide, particularly in developingcountries where access to definitivetreatment is often delayed and difficultto access. Thousands of women die ofthis preventable complication of child-birth each year. The Non-pneumatic An-tishock Garment (NASG; ZOEX Corpo-ration, Ashland, OR) is a neoprene andvelcro device designed to reverse the ef-fects of shock by shunting blood fromthe lower extremities and pelvis to thevital organs.1 The NASG is composed of
From the Department of Obstetrics and GyneBoston, MA (Dr Lester); and the DepartmentCalifornia, Los Angeles, David Geffen SchoolDepartment of Obstetrics, Gynecology, and RRadiology (Dr Vargas), University of CalifornObstetrics, Gynecology, and Reproductive ScHealth and Policy, San Francisco, School of Mand Dr Miller), CA.
Presented, in part, at the XIX World Congress ofFederation of Gynecology and Obstetrics, Cape
The study was funded by the Program for ApproClinical and Translational Science Institute, Univ
lower extremity segments, a pelvic seg-ment, and an abdominal segment, whichincludes an abdominal compression ballto provide increased pressure specificallyto the lower abdomen and pelvis. Thisdevice has been shown in preliminarytrials in Egypt and Nigeria to not onlyreverse shock and improve maternaloutcomes, but also to significantly de-crease blood loss by 33-78%.2,3 This find-ng suggests that in addition to shuntinglood from the lower extremities and pro-iding autotransfusion, the NASG mayave a direct effect on the pelvic vascula-
ogy, Brigham and Women’s Hospital,bstetrics and Gynecology, University ofedicine, Los Angeles (Dr Stenson), and the
oductive Sciences, and Department ofSan Francisco, CA; and the Department ofe, Bixby Center for Global Reproductivecine, San Francisco (Ms Meyer, Ms Morris,
necology and Obstetrics of the Internationalwn, South Africa, Oct. 4-9, 2009.
epted Dec. 27, 2010.
omen’s Health, Department of Obstetrics andTremont Ave., Third Floor–OBC, Boston, MA
te Technology in Health and a grant from thety of California, San Francisco, CA.
/j.ajog.2010.12.054
MAY 2011 Americ
ure, inhibiting blood flow to the pelvic or-ans and decreasing blood loss.
The Pneumatic Antishock GarmentPASG) predated the NASG and al-hough it initially showed promise forse in general trauma, several studies in-luding a Cochrane Database Reviewaised concerns about the safety and ef-cacy of the PASG in these patients.4 De-pite these findings in general trauma,he PASG gained recognition as a possi-le first-aid device for obstetric hemor-hage based on several case reports thatocumented favorable outcomes inases of severe hemorrhage and shock.5
These findings are consistent with thethinking that the PASG has differentialeffectiveness depending on whetherblood loss is from injuries below thewaist vs above the waist.5 The favorablease reports in obstetrics were furtherupported by studies of the hemody-amic impact of the PASG showing a sig-ificant decrease in aortic blood flowelow the level of the renal arteries, sug-esting that the device would be usefulor stemming blood loss from the uterushat is supplied by a branch of the inter-al iliac artery, a branch of the distalorta below the renal arteries.6,7
Poiseuille law states that the flow ratethrough a vessel is exponentially relatedto the radius of the vessel. Laplace lawdescribes how tension is related to trans-mural pressure and the radius of a vessel.Bernoulli principle describes how the
FIGURE 1Doppler images of internal iliac art
A, NASG not applied, resistive index (RI) � 0.80.13 indicating absent or reverse flow.
NASG, Non-pneumatic Antishock Garment (ZOEX Corporation, Po
Lester. Impact of the NASG on postpartum pelvic blood flow.
rate of bleeding depends on the size of
409.e2 American Journal of Obstetrics & Gynecolo
the opening of the vessel and the trans-mural pressure. The circumferentialpressure provided by the antishock gar-ment compresses the radius of bloodvessels and decreases the transmuralpressure, which, according to these laws,should have important physiologic ef-
with and without NASG applied
cating forward flow. B, NASG fully applied, RI �
d, OR).
J Obstet Gynecol 2011.
fects. First, the compression of the ves-
gy MAY 2011
sels should cause increased systemic vas-cular resistance, which decreases bloodflow peripherally. Thus, if the blood can-not flow forward, it will back up and in-crease the blood flow through the non-compressed vessels, which should lead toincreased preload and cardiac output, ef-fectively providing autotransfusion. Sec-ond, it should lessen blood flow throughthe compressed vessels and if blood is be-ing lost through these open vessels, thisshould result in a decrease or cessation ofbleeding due to tamponade.
Like the PASG, the NASG applies cir-cumferential counterpressure, but usesneoprene, a foam compression ball, andvelcro rather than inflatable segments todo so.1 It is thought that the NASG isparticularly well designed for treatmentof obstetric hemorrhage because it canbe rapidly applied, has a compressionball over the abdomen, and avoids therisk of overinflation that can lead to sideeffects.5 Although there is evidence fromnonrandomized clinical trials that theNASG can decrease blood loss and re-verse shock associated with obstetrichemorrhage, and a recent study hasdemonstrated decreased blood flow inthe distal aorta with application of theNASG, there are no published studies ofthe impact of the NASG on pelvic bloodflow in postpartum patients.9
The objective of this study was to use anoninvasive method to estimate bloodflow to the pelvis in nonhemorrhagingpostpartum patients with the NASG ap-plied. Delineating the physiologic mech-anism of action of the NASG on pelvicblood flow is important for understand-ing how the NASG can impact blood lossdue to obstetric hemorrhage.
MATERIALS AND METHODSApproval for this study was obtainedfrom the University of California, SanFrancisco, Institutional Review Boardand from the Program for AppropriateTechnology in Health Institutional Re-view Board. Participation was voluntaryand all study subjects gave written in-formed consent.
This study was conducted at San Fran-cisco General Hospital on the labor and
ery
indi
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delivery ward from June 2008 through
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plSep
www.AJOG.org Obstetrics Research
January 2009. Healthy female postpar-tum volunteers were recruited within 24hours of a vaginal delivery. They were ex-cluded if they had any underlying healthproblems, a cesarean section, an opera-tive delivery, blood loss �500 mL post-partum, delivered �24 hours ago, anonsingleton pregnancy, preeclampsia,an unstable hematocrit, pulmonary orcardiac problems, an unhealthy new-born, did not speak English or Spanish,or were �18 years of age. Demographicdata were collected including patientage, gravidity, parity, and body mass in-dex. The type of delivery, time since de-livery, and uterotonic administrationwere noted. The objective of this studywas to estimate the change in blood flowto the pelvis with application of theNASG. To use the least invasive form of
FIGURE 2Photographs of Non-pneumaticAntishock Garment at differentphases of application
A, Not applied. B, Leg segments applied. C, Fullapplication.NASG; ZOEX Corporation, Portland, OR.
Lester. Impact of the NASG on postpartum pelvic bloodflow. Am J Obstet Gynecol 2011.
evaluation possible, the blood flow was
measured using transabdominal ultra-sonography of the internal iliac artery.The internal iliac artery provides theblood supply to the pelvis and was able tobe visualized using transabdominal ul-trasound even with the NASG in place.
The resistive index (RI) of the inter-nal iliac artery was measured as an ap-proximation of pelvic blood flow. RImeasurement is noninvasive and canbe easily obtained using standard equip-ment available in the obstetrics depart-ment and provides information on thedistal vessels of interest.10 The RI is de-
ned as the peak of systole divided by theum of systole and diastole [RI � S/(S �
D)]. A higher RI is correlated with de-creased blood flow to a given vessel. Avalue �1.0 indicates forward flow;whereas a value of �1.0 indicates absentor reverse flow (Figure 1).
An ultrasonographer used portableDoppler ultrasound to measure the RI inthe internal iliac artery with incrementalapplication of the NASG. Figure 2 showsthe NASG at 3 different stages of appli-cation. We sequentially measured the vi-tal signs and internal iliac artery RI at thefollowing 9 time points:1. Baseline.2. Immediately after application of the
leg segments.3. Ten minutes after application of the
leg segments.4. Immediately after full application of
the NASG.5. Ten minutes after full application.6. Immediately after removal of the ab-
dominal segment.7. Ten minutes after removal of the ab-
dominal segment.8. Immediately after removal of all
segments.9. Ten minutes after removal of all
segments.Patients were asked to report any side
effects they experienced during the mon-itoring period and this information wasrecorded.
Data were entered into Microsoft Ex-cel for Mac 2008 (Microsoft Corp, Red-mond, WA) and analyzed using JMP,version 8, SAS software package (SAS In-stitute, Cary, NC). Comparative statis-tics were reported using Wilcoxon
matched-pairs signed-rank tests.
MAY 2011 Americ
RESULTSAll 10 patients in this study delivered bynormal spontaneous vaginal delivery. Themajority (9/10) had received prophylacticintravenous oxytocin after delivery, while1 had not received any uterotonics. Themean time from delivery to study inclu-sion was 12 hours (range, 2-18 hours).Mean age, gravidity, parity, and gestationalage at time of delivery are described in Ta-ble 1. The majority of patients were normalweight, none were underweight, and 4were overweight.
The median internal iliac RI at the 9time points is shown in Table 2 and de-
icted graphically in Figure 3. There wasittle change in RI from baseline (0.83,D 0.11) with application of the leg pan-ls (0.84, SD 0.12). When the abdominalanel was applied, the median value in-
TABLE 1Participant demographics
Participantdemographics
Mean (range)n � 10
Age, y 25 (18–37)...........................................................................................................
creased significantly (1.05, SD 0.15) andstayed high after full application for 10minutes (1.00, SD 0.15). The RI rapidlyreturned to baseline with removal of theabdominal segment (0.82, SD 0.04), andremained low and near baseline after theremoval of the entire garment (0.81, SD0.11). There was a significant change inRI from baseline to full application (Wil-coxon matched-pairs signed-rank test;P � .02), as depicted in Figure 4. Vitalsigns remained stable throughout theapplication with little change noted inany of the parameters.
COMMENTThis study demonstrates a significant in-crease in the RI of the internal iliac arterywith application of the NASG in healthypostpartum women. The internal iliacartery supplies the majority of bloodflow to the uterus via the uterine arteriesand thus this finding is consistent withthe decrease in blood loss from postpar-tum hemorrhage that has been reportedin published studies of the NASG.2,3,11
The observed increase in the RI of theinternal iliac artery with NASG applica-tion provides a physiologically plausiblemechanism to explain how hemorrhageis reduced by NASG application.
There are several methods for analyz-ing Doppler blood flow including flowvolume or velocity measurement, resis-tance indices, and waveform analysis.10
Flow volume analysis most closely ap-proximates true blood flow; however, itis difficult to perform and prone to error,as accurate measurement is dependent
FIGURE 3Median resistive index withapplication of Non-pneumaticAntishock Garment at 9time points (n � 10)
0.830.82
0.82
1.05
1
0.86
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
1 2 3 4 5 6 7 8 9
Timepoint
Res
istiv
e In
dex
NASG; ZOEX Corporation, Portland, OR.
Lester. Impact of the NASG on postpartum pelvic bloodflow. Am J Obstet Gynecol 2011.
on the angle of insonation, vessel diam- t
409.e4 American Journal of Obstetrics & Gynecolo
eter measurement, and the tortuosity ofthe vessels. Most ultrasounds used inroutine obstetrics are not able to calcu-late flow volume due to the high analyticrequirements of these calculations. Re-sistance indices are indirect measures offlow volume; however, they are angle in-dependent and are considered to be use-ful for estimating blood flow in vesselsdistal to the point of the examination.One drawback of RI calculation is that itmay not be as accurate in cases whenblood flow is not continuous throughoutthe cardiac cycle. Waveform analysis ismore complicated; however, it may pro-vide a more accurate estimate of bloodflow in conditions of noncontinuousblood flow during the cardiac cycle.10
In this study, the blood flow to the pel-vis was measured transabdominally us-ing Doppler ultrasound. Due to the loca-tion of the NASG’s abdominal/pelvicsegment and uterine compression ball inrelationship to where the transabdomi-nal ultrasound probe should be placed toimage the uterine artery, an accuratemeasurement of the RI in these vesselswas not possible. However, we were ableto measure the RI in the internal iliac ar-teries with a transabdominal approach,which approximates blood flow to thepelvis and is an indirect measure ofblood flow to the uterus. Future studiesmight consider transvaginal imaging toattempt to directly capture blood flowthrough the uterine arteries.
This study was conducted in euv-olemic volunteers who were not suffer-ing from hemorrhage or shock. Vitalsigns remained stable in the volunteersin this study; however, we know fromNASG studies conducted with patientssuffering from hypovolemic shock thatthere is a rapid and significant improve-ment in vital sign parameters (bloodpressure, pulse, and shock index) withNASG placement.11 It is likely that theardiovascular profile would differ sig-ificantly between euvolemic volunteersnd women with hemorrhagic shock.oreover, the mean time from deliveryas 12 hours in this study thus the find-
ngs do not represent the immediateostpartum physiology when most hem-rrhagic shock occurs. Investigation of
he hemodynamics and cardiovascular c
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hysiology in patients with active hem-rrhage and shock would better charac-erize the true effect of the NASG on ob-tetric hemorrhage in the immediateostpartum period.This study was limited by a small sample
ize, the use of an indirect measure (RI) oflood flow, the use of the internal iliac ar-ery instead of the uterine artery, the use ofransabdominal rather than transvaginalltrasound, and by the use of healthy non-emorrhaging volunteers who were stud-
ed a mean of 12 hours after delivery.uture studies should focus on under-tanding how the NASG works in patientsho are in hypovolemic shock immedi-
tely following delivery, should use moreirect measures of uterine blood flow withransvaginal ultrasound and potentiallyhe use of flow volume measurements, andhould endeavor to more fully characterizehe cardiovascular effects of the NASG, in-
FIGURE 4Comparison of median resistiveindex (RI) at baseline andfull application
Lester. Impact of the NASG on postpartum pelvic bloodflow. Am J Obstet Gynecol 2011.
luding measurement of venous return,
www.AJOG.org Obstetrics Research
cardiac output, central venous pressure,and systemic vascular resistance.
Despite these limitations, applicationof the NASG appears to significantly in-crease the RI of the internal iliac artery,providing a plausible physiologic expla-nation for decreased blood flow to thepelvis and the finding of decreased bloodloss in patients with obstetric hemor-rhage who are treated with the NASG.This study is an initial step toward ex-plaining one of the NASG’s mechanismsof action. Further investigation is mer-ited to more fully understand the physi-ologic impact of the NASG in obstetricpatients with hemorrhagic shock. f
ACKNOWLEDGMENTSThe following individuals contributed to thestudy professionally: Jennifer Clark, Hilarie Mar-
tin, Elizabeth Butrick, Sheri Lippman.
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