Shock en Obstetricia

1. CLINICAL ARTICLE
Use of the “obstetric shock index” as an adjunct in identifying significant
blood loss in patients with massive postpartum hemorrhage
Abigail Le Bas a,
⁎, Edwin Chandraharan a
, Anthony Addei b
, Sabaratnam Arulkumaran c
a
Department of Obstetrics and Gynaecology, St George’s Healthcare NHS Trust, London, UK
b
Department of Anesthetics, St George’s Healthcare NHS Trust, London, UK
c
St George’s University of London, London, UK
a b s t r a c ta r t i c l e i n f o
Article history:
Received 14 June 2013
Received in revised form 18 August 2013
Accepted 25 November 2013
Keywords:
Blood transfusion
Estimated blood loss
Massive postpartum hemorrhage
Obstetric shock index
Visual estimation of blood loss
Objective: To establish the normal range for the “obstetric shock index” (OSI) after birth and to determine its use-
fulness as an aid to estimate blood loss in postpartum hemorrhage (PPH). Methods: A retrospective case–control
analysis was conducted involving pregnant women admitted to St Georges Hospital for delivery: 50 with no PPH
(control group) and 50 with massive PPH (N30% loss of blood volume; case group). The OSI was calculated at 10
and 30 minutes from PPH onset. Results: Mean OSI in the control group at 10 and 30 minutes was 0.74 (range,
0.4–1.1) and 0.76 (range, 0.5–1.1), respectively. In the case group, mean OSI at 10 and 30 minutes was 0.91
(range, 0.4–1.5) and 0.90 (range, 0.5–1.4), respectively, with 64% requiring blood products. In the case group,
89% of women with an OSI of 1.1 or more at 10 minutes required transfusion; 75% with an OSI of 1.1 or more
at 30 minutes required transfusion. Conclusion: We recommend that the normal OSI range should be 0.7–0.9.
An OSI of more than 1 seems to be a useful adjunct in estimating blood loss in cases of massive PPH and in
predicting the need for blood and blood products.
© 2013 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved.
1. Introduction
Postpartum hemorrhage (PPH) is a continued cause for concern in
modern obstetrics, accounting for 8% of direct maternal deaths in the
UK in the past 3 years [1]. Visual estimation of blood loss is very inaccu-
rate and contributes to delays in recognition and treatment of massive
PPH. Confounding factors such as maternal anemia prior to delivery
and low body mass index may mean that, even in cases involving
lower volumes of blood loss, hemodynamic instability may result.
Hence, a more reliable measure is required to predict the need for
blood product transfusion. The shock index is defined as heart rate
divided by systolic blood pressure and was first introduced in 1967 by
Allgöwer and Burri [2]. It has been studied in trauma and non-trauma
patients and is used in clinical practice to assess hypovolemic shock or
the severity of non-hypovolemic shock and to aid acute management
in this setting [3–6]. In the normal non-pregnant population, the normal
shock index range is 0.5–0.7.
Massive PPH results in a reduction in venous return and a compensa-
tory increase in maternal heart rate. However, the systolic blood pres-
sure remains stable until no further increase in heart rate is possible,
after which it begins to fall. Therefore, a young, fit woman could lose
up to 30% of her blood volume before a change in her systolic blood pres-
sure became apparent, which could result in a false sense of security;
“too little being done too late” has been highlighted as a contributing fac-
tor in Confidential Enquiries into Maternal Deaths [1].
Although the shock index has been reported to be a useful adjunct
in non-pregnant populations, it has not, to the best of our knowledge,
been assessed so far in a pregnant population. Therefore, an “obstetric
shock index” (OSI)—which reflects the physiological changes in the
cardiovascular system (in both pulse rate and systolic blood pressure)
during pregnancy—may be useful in identifying significant blood loss
earlier, prior to any change in systolic blood pressure, and hence im-
prove outcomes [7].
The first aim of the present study was to determine the normal OSI
range for a pregnant population. The second aim was to investigate
the usefulness of the OSI as an adjunct in the early identification of
significant blood loss. The third aim of the study was to investigate the
usefulness of the OSI in predicting the need for blood transfusion.
2. Materials and methods
A retrospective case–control study was undertaken involving preg-
nant women admitted to St Georges Hospital, London, UK, for delivery
between January 1, 2011, and January 1, 2013. There were 50 randomly
selected cases (i.e. women who experienced massive PPH) and 50 ran-
domly selected controls (i.e. women who experienced normal blood
loss). Normal blood loss was defined as less than 500 mL at vaginal
International Journal of Gynecology and Obstetrics 124 (2014) 253–255
⁎ Corresponding author at: Department of Obstetrics and Gynaecology, St George’s
Healthcare NHS Trust, London SW17 0RE, UK. Tel.: +44 7841829251; fax: +44
2087251975.
E-mail address: abigail.lebas@gmail.com (A. Le Bas).
0020-7292/$ – see front matter © 2013 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.ijgo.2013.08.020
Contents lists available at ScienceDirect
International Journal of Gynecology and Obstetrics
journal homepage: www.elsevier.com/locate/ijgo

2. delivery and less than 1000 mL at cesarean delivery. Massive PPH was
defined as a minimum of 30% loss of blood volume at delivery. The infor-
mation was collected from the Maternity Electronic Information System
at St Georges Hospital, as approved by the hospital ethics committee.
Informed consent was not required because all patients received the
same care.
Baseline circulating blood volume was estimated to be 100 mL per
kilogram of body weight for all patients, using body weight measured
at the booking appointment prior to 12 weeks of pregnancy. The
OSI (pulse rate divided by systolic blood pressure) was calculated—
retrospectively—at 10 minutes and 30 minutes after the onset of post-
partum bleeding. Data were analyzed via Excel (Microsoft, Redmond,
WA, USA).
3. Results
Mean parity was 0.86 ± 2.64 in the case group and 0.64 ± 2.08 in
the control group. Mean booking weight was 64.02 ± 23.44 kg in the
case group and 69.06 ± 35.10 kg in the control group.
Mean blood loss in the control group was 417 mL (range,
200–1000 mL), compared with 2483 mL (range, 1500–5500 mL) in
the case group. Mean percentage loss of blood volume (i.e. estimated
blood loss divided by body weight in kilograms at prenatal booking
visit) was 39% (range, 30%–94%) in the case group.
Risk factors for PPH were more prevalent in the case group than in
the control group (Fig. 1). The cumulative total number of risk factors
present in the case group was 101, compared with 48 in the control
group. Cesarean delivery in the index pregnancy and assisted vaginal
delivery were associated with increased risk of massive PPH in the
study population. There was no significant difference in parity between
the 2 groups (Fig. 2); the majority of massive PPH cases involved
primiparous women.
In the control group, the mean OSI was 0.74 ± 0.30 (range, 0.4–1.1)
at 10 minutes and 0.76 ± 0.27 (range, 0.5–1.1) at 30 minutes (Fig. 3).
In the case group, the mean OSI was 0.91 ± 0.42 (range, 0.4–1.5) at
10 minutes and 0.90 ± 0.33 (range, 0.5–1.4) at 30 minutes (Fig. 4).
In total, 32 patients (64%) who experienced massive PPH required
blood transfusion (Fig. 5), of whom 4 required platelets and 14 also
required fresh frozen plasma. None of the patients in the control
group required blood or blood products.
In the case group, 89% (n = 8) of women with an OSI of 1.1 or
higher at 10 minutes required a blood transfusion; 75% (n = 6) of
women with an OSI of 1.1 or higher at 30 minutes required a blood
transfusion (Fig. 6). If the OSI was less than 1.1 at 10 minutes, the
chance of requiring a blood transfusion was 59% (n = 24); if the OSI
was less than 1.1 at 30 minutes, the chance of requiring a blood trans-
fusion was 62% (n = 26).
4. Discussion
Visual estimation of blood loss is fraught with the danger of un-
derestimation (or, rarely, overestimation), which can lead to delays
in diagnosing and treating ongoing massive PPH. This scenario of
“too little being done too late” can lead to serious maternal morbidity
and mortality, as highlighted by Confidential Enquiries into Maternal
Deaths [1].
In patients with normal blood loss at delivery, the mean OSI was
0.74 at 10 minutes. No individual value in this group was above 1.1.
Therefore, we propose that the normal OSI range should be 0.7–0.9,
compared with the reported range of 0.5–0.7 for the shock index in
non-pregnant populations. The increased observed value is probably
due to the normal physiological changes in the cardiovascular system
during pregnancy. At term, the pulse rate remains higher than in the
Fig. 1. Risk factors for postpartum hemorrhage (PPH). Abbreviations: IUD, intrauterine device; MROP, manual removal of placenta; PET, pre-eclamptic toxemia.
Fig. 2. Parity in the case and control groups. Abbreviation: PPH, postpartum hemorrhage.
Fig. 3. Obstetric shock index (OSI) for patients with no postpartum hemorrhage (control
group).
254 A. Le Bas et al. / International Journal of Gynecology and Obstetrics 124 (2014) 253–255

3. non-pregnant state, while the systolic blood pressure may have normal-
ized in the third trimester.
The mean OSI at 10 and 30 minutes was higher in the group with
massive PPH than in the control group. This was expected because the
shock index reflects hemodynamic stability and indicates that the OSI
might be a valuable marker of hemodynamic instability in cases of mas-
sive PPH. When the OSI was higher than the normal range (i.e. ≥1.1),
the use of blood products also increased, with an 89% chance of blood
transfusion when the OSI was higher than 1.1 at 10 minutes. This evi-
dence seems to support the usefulness of the OSI in not only identifying
significant blood loss in cases of massive PPH but also predicting
the need for blood and blood products. In order to simplify the use
of the OSI in an acute obstetric emergency, we propose that an OSI
higher than 1 (i.e. pulse rate N systolic blood pressure) is a marker for
clinical severity.
A limitation of the OSI is its use in cases of pre-eclampsia because
resting systolic blood pressure would be elevated and, therefore,
might produce a falsely reassuring OSI. The use of the OSI in clinical
practice is based on a normal physiological response to hypovolemia,
and thus should always be considered in clinical context. A limitation
of the present study was that blood transfusion or fluid resuscitation oc-
curred within 30 minutes for some patients in the dataset. Therefore,
the OSI values could have been lower in these cases owing to correction
of hemodynamic parameters, which may have influenced the results.
Indeed, some patients may compensate well for large blood loss without
significant changes in their heart rate or systolic blood pressure. There-
fore, clinicians need to interpret OSI values with caution after intensive
resuscitation because they may not reflect the actual blood loss. We
attempted to reduce the potential for error by calculating the OSI at
both 10 and 30 minutes after massive PPH.
It is routine practice in the UK to assess patient weight at booking
but not thereafter unless specifically indicated. Therefore, the original
booking weight was used in the calculation of blood volume. Although
changes in weight occur throughout pregnancy, which could have
affected the calculations, similar changes should have occurred in the
case and the control groups, so the effect should have been balanced.
The effectiveness of the OSI based on booking weight means that it
can easily be applied in current practice.
Prompt recognition of hemodynamic instability in cases of massive
PPH enables timely and appropriate treatment to improve outcomes
and save lives [8,9]. The OSI is of value in raising suspicion when it is
outside the normal range, even when heart rate and blood pressure
are not. The decision to carry out blood transfusion should be based
on clinical parameters and, based on the present pilot study, we recom-
mend the use of an OSI value higher than 1 as an additional assessment
tool for significant blood loss, as well as a simple marker (i.e. pulse
rate N systolic blood pressure) to predict the need for blood and blood
products. Although further research is required to validate this, based
on experience from management of major trauma, an OSI value higher
than 1 seems to be clinically useful in the obstetric population.
Conflict of interest
The authors have no conflicts of interest.
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Fig. 5. Blood product usage in cases of massive postpartum hemorrhage. Abbreviation:
FFP, fresh frozen plasma.
Fig. 6. Percentage of patients with massive postpartum hemorrhage who underwent
transfusion in relation to obstetric shock index (OSI).
Fig. 4. Obstetric shock index (OSI) for patients with massive postpartum hemorrhage
(case group).
255A. Le Bas et al. / International Journal of Gynecology and Obstetrics 124 (2014) 253–255