Accepted Article
Article type
: Clinical Article
CLINICAL ARTICLE
Early prognostic capacity of serum lactate for severe postpartum hemorrhage
Venance Basil-Kway1, Roberto Castillo-Reyther2,3, L. Andrés Domínguez-Salgado1, Ricardo
Espinoza-Tanguma4, Úrsula Medina1,5,*, Antonio Gordillo-Moscoso1
1Department of Clinical Epidemiology, School of Medicine, Universidad Autonoma de San
Luis Potosi, Mexico
2Department of
Obstetrics and Gynecology, Hospital Central Dr. Ignacio Morones Prieto,
San Luis Potosi, Mexico
3School of Medicine, Universidad Autonoma de San Luis Potosi, Mexico
4Department of Physiology, School of Medicine, Universidad Autonoma de San Luis Potosi,
Mexico
5Department
of Pharmacology, School of Medicine, Universidad Autonoma de San Luis
Potosi, Mexico
*Correspondence
Ursula Medina, Avenida Venustiano Carranza 2405, Los Filtros, 78210, San Luis Potosi,
México.
Email: ursula.medina@uaslp.mx
Keywords
Critical medicine; Gynecology; Intensive care unit; Obstetrics; Prognosis; Serum lactate;
Severe postpartum hemorrhage
Synopsis
A serum lactate concentration of ≥2.6 mmol/L measured at the time of diagnosis of
postpartum hemorrhage could predict severe hemorrhage in the following 24 hours.
This article has been accepted for publication and undergone full peer review but has not been
through the copyediting, typesetting, pagination and proofreading process, which may lead to
differences between this version and the Version of Record. Please cite this article as doi:
10.1002/IJGO.13446
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ABSTRACT
Objective: To evaluate whether the concentration of serum lactate during the diagnosis of
postpartum hemorrhage (bleeding ≥500 mL during labor or ≥1000 mL during cesarean
delivery) predicts severe hemorrhage (SPPH; blood loss ≥1500 mL at end of labor or in the
following 24 hours).
Methods: A prospective cohort pilot study was conducted of women with a vaginal or
cesarean delivery from February 2018 to March 2019 who presented with bleeding ≥500 mL
measured by the gravimetric method in a reference hospital in San Luis Potosi, Mexico.
Venous blood samples were taken for analysis of serum lactate. A receiver operating
characteristic curve determined the serum lactate threshold value for SPPH and χ2 test
assessed the difference in serum lactate elevation between SPPH and non-SPPH groups.
Lastly, the prognostic capacity between the thresholds was compared.
Results: SPPH developed in 43.33% of the 30 women in the study group. The best
prognostic threshold was 2.68 mmol/L of serum lactate (odds ratio [OR] 17.88, 95%
confidence interval [CI] 2.7–16.8, P<0.001); sensitivity was 0.85 (95% CI 0.55–0.98);
specificity was 0.76 (95% CI 0.50–0.93).
Conclusion: Serum lactate may be a useful prognostic marker for SPPH, more studies are
needed to validate these findings.
1 INTRODUCTION
Of maternal deaths worldwide, 25% are due to postpartum hemorrhage (PPH). In Mexico, it
is the first cause of death followed by pre-eclampsia [1–4]. A universally accepted definition
of PPH is blood loss of 500 mL or more after a vaginal delivery or 1000 mL or more during a
cesarean delivery. Some authors consider significant (severe) hemorrhage (SPPH) to be
blood loss of 1500 mL or more in cases of twin pregnancies [5]. In daily clinical practice,
SPPH can also be any hemorrhage that can alter the hemodynamic state of the patient and
may lead to complications such as hypovolemic shock, intravascular coagulation, multiorgan
failure, and even death [4, 6, 7].
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Early diagnosis of PPH is vital to improve the patient’s condition and prevent complications.
The major problems facing the diagnosis and management of PPH are the lack of an
excellent and accurate method of estimating blood loss [8–10]. Hemodynamic changes in
pregnancy make it difficult to follow vital signs to evaluate the risk of PPH and 50% of
patients with bleeding do not have any risk factors. The search for a simpler and faster
method, capable of predicting severe bleeding in patients with a diagnosis of PPH, is of
great importance [11, 12].
Serum lactate has shown to be a good predictor of severity and mortality in different clinical
conditions such as polytrauma and sepsis. Its measure is currently included in protocols for
patient management such as the Survival Campaign of Sepsis 2016 and Advanced Trauma
Life Support (ATLS) guidelines [13]. Evidence shows that during the first 24 hours after
admission to the intensive care unit (ICU), the dynamic indices of hyperlactatemia have
significant independent predictive value and can improve the performance of outcome
predictions based on illness severity scores [13].
Different studies have reported that higher concentrations of serum lactate correlate with the
risk of death in critical patients. The inability to normalize serum lactate within 24 hours of
admission to an ICU was related to a mortality of 100% and a decrease in mortality of 11%
for every 10% of serum lactate cleared [14–17].
Serum lactate could be a general indicator of severity or physiological response before
aggression or deficiency. There is much evidence investigating the production of serum
lactate apart from the anaerobic reaction [18,19]. Furthermore, the measurement of serum
lactate is a routine procedure in many healthcare facilities, which could provide immediate
results for fast decision making. With all that in mind, the aim of the present study was to
evaluate whether the concentration of serum lactate measured at the time of diagnosis of
PPH (≥500 mL in labor or ≥1000 mL during cesarean delivery) predicts SPPH.
2 MATERIALS AND METHODS
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A prospective cohort pilot study was carried out from February 2018 to March 2019 on
pregnant women with PPH (the institutional definition of PPH is ≥500 mL in labor or ≥1000
mL during cesarean delivery) in a reference hospital in San Luis Potosi Mexico (Hospital
Central Dr. Ignacio Morones Prieto). The study was approved by the Institutional Ethical
Committee (CONBIOETICA-24CEI-001-20160427) No.15-18.
Pregnant women with vaginal or cesarean deliveries with PPH were included. Exclusion
criteria were conditions that might cause type ß-lactic acidoses not associated with
anaerobioses such as eclampsia, leukemia, lymphoma, and solid tumors, poorly controlled
diabetes, liver failure, ingestion of antiretroviral drugs and biguanides, confirmed sepsis or
diagnosed with severe shock, or documented anemia at the beginning of the study. Patients
who decided to withdraw their consent or to leave the study were also excluded.
On admission to the labor ward, a full clinical history and physical examination were
performed as a normal routine where demographic and laboratory test data were obtained.
After fetal delivery, the volume of bleeding was measured by the gravimetric method as
described elsewhere, in short: blood-stained surgical gauze from the delivery were weighed
and its dry weight subtracted from the total blood-stained weight (Fig. 1). The weight of the
blood (g) was converted into volume (mL) using the accepted approximation of blood density
of 1 g = 1 mL [20, 21]. When the quantified bleeding was ≥500 mL in labor or ≥1000 mL
during a cesarean delivery, a venous blood sample was taken to measure the concentration
of serum lactate (Fig. 1). In accordance with the service protocol, if patients needed an
urgent transfusion, it was performed after taking the blood sample.
Measurements of serum lactate were performed by a spectrophotometric method using
RAPIDLab1265 SIEMENS® (Siemens Healthcare Diagnostics S. de R.L. de C.V., Mexico
City, Mexico). This equipment is maintained and recalibrated every 3 months to ensure its
quality and performance. Blood samples were taken from a free vein, avoiding the use of a
tourniquet, although when necessary it was applied in less than 30 seconds to avoid
significant ischemia. Samples were immediately sent to the laboratory. Before moving the
patient to the recovery room, those who had a total loss of 1500 mL or more at the end of
labor or cesarean delivery were classified as SPPH.
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The statistical analysis was performed using Statistical Program R 3.6 version and R Studio
1.2.1335. As proposed by Browne et al [22], 30 patients were included as an adequate
sample size for pilot studies since there are no previous publications about elevation of
serum lactate and severe obstetric hemorrhage [23].
The distribution of continuous data was assessed by Shapiro-Wilk test, a comparison
between severe and non-severe hemorrhage groups was done by Student t-test for data in
the case of normal distribution and Wilcox test for non-normal distribution data. Proportions
were expressed as percentages and compared by χ2 test.
A receiver operating curve (ROC) analysis was carried out to determine the best serum
lactate threshold for SPPH. Finally, the diagnosis capacity between two different serum
lactate concentration thresholds (the one obtained by ROC analysis vs 2.2 mmol/L used in
other clinical scenarios such as polytrauma and sepsis) was compared to predict SPPH by
relative risk ratio (RR), odds ratio (OR), and sensibility and specificity analyses. In all cases,
P≤0.05 were considered statistically significant.
3 RESULTS
A total of 209 obstetric hemorrhage cases were observed during the study period. Of the
patients, 41 were postpartum, 30 met the inclusion criteria, 13/30 (43%) had SPPH (>1500
mL), and 23/30 (76%) had cesarean deliveries (Fig. 2). The mean maternal age was
22.5±8.2 years. Significant differences were observed between the SPPH group versus the
non-SPPH group as follows: serum lactate concentration at diagnosis (3.24±2.08 vs
2.28±1.76, P=0.012), bleeding volumes (1700±690 mL vs 1100±224 mL, P<0.001); volume
of crystalloid for resuscitation (3400±2000 mL vs 2000±1500 mL, P=0.028); blood
transfusion (69% vs 17.64%, P=0.013); and birth weight (3470±83.2 g vs 3200±93.4,
P=0.044). No statistically significant differences between the two groups were observed in
maternal age, gestational age, hematocrit, surgical management, cesarean delivery, and
use of a Bakri balloon (Table 1).
After the ROC curve analysis, the best threshold of serum lactate was 2.6 mmol/L, with a
sensitivity of 85.6% and specificity of 76.5%. The area under the curve (AUC) was 0.774
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(Fig. 3). This threshold was validated with another 30 patients from an independent group
with the same clinical characteristics and it reported the same predictive capacity. A
comparison was made between 2.2 mmol/L (ATLS guidelines for The Management of
Critical Patients) and 2.6 mmol/L (from the present study) as a good threshold. Regarding
performance in the context of SPPH, the 2.6 mmol/L threshold had a sensitivity of 0.85 (95%
confidence interval [CI] 0.55–0.98), specificity of 0.76 (95% CI 0.50–0.93), and positive
predictive value of 3.60 (95% CI 1.48–8.74) (Table 2).
4 DISCUSSION
The present study shows that 2.6 mmol/L of serum lactate measured at the time of diagnosis
of PPH could be a good predictor of SPPH and a possible biomarker to identify patients at
risk and prevent complications. The sample in the present study has shown to be
homogenous in most of the studied variables. Nevertheless, a significant difference in serum
lactate was observed between the SPPH and non-SPPH groups, explaining the capacity of
serum lactate to discriminate against these groups from earlier stages.
SPPH is a condition with a higher risk of maternal and fetal complications. The prevention of
these complications considerably reduces the number of maternal deaths related to
childbearing. Although serum lactate has been frequently used in obstetrics, it is believed
that the present study is among the first to explore the early prognostic capacity for SPPH.
Most studies have aimed to identify new methods of controlling bleeding and its
complications but not methods of prevention.
Regarding the analysis of the prognostic capacity of serum lactate to predict SPPH, most of
those studies, such as the one by Garcia-Velasquez et al [24], included patients who were
already experiencing severe hemorrhage and even shock. Hypoperfusion that occurs during
bleeding leads to anaerobic respiration and the production of lactic acid. This phenomenon
seems to occur with a blood loss as low as 500 mL, including patients without the clinical
manifestation of hypoperfusion.
A systematic review and meta-analysis of observational studies by Bauer et al.[25] reported
that the maternal concentration of serum lactate outside of labor was less than 2 mmol/L,
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and that during labor periods, the range was higher than 2 mmol/L. While the pooled ranges
were less than 4 mmol/L, few individual studies reported ranges higher than 4 mmol/L during
labor. However, that systematic review did not report the values of serum lactate concerning
blood volume and most of the elevated concentrations of serum lactate were reported in
studies that included patients with sepsis [26].
The concentration of serum lactate of 2.6 mmol/L at early diagnosis of PPH was observed to
have a good sensitivity and specificity in the prediction of evolution to SPPH in the present
study. The use of 2.2 mmol/L of serum lactate as the threshold has been adapted from
ATLS into different obstetric guidelines to guide resuscitation, without validation [27]. But in
the present study, this threshold has shown good sensitivity but low specificity, implying that
the use of 2.6 mmol/L as a threshold could be an early surveillance point at which to identify
patients who may need initiation of resuscitation, even before evident clinical manifestations.
Considering that obstetric patients have unique characteristics, and that an excessive
resuscitation can be harmful as it can cause severe hemorrhage due to hemodilution and/or
a poor resuscitation can cause the persistence of acidosis, hypothermia, and coagulopathy
(a lethal triad), there is a need to establish and validate these thresholds.
The study by Garcia-Velasquez et al [24] showed that the threshold of 3.75 mmol/L at the
diagnosis of SPPH or shock discriminated patients with a higher probability of complications
such as acute renal failure, coagulopathy, and death (sensitivity 70%, specificity 70%, AUC
0.772). In the present study, the cut-off point obtained was 1.15 mmol/L less than the one
proposed by those authors. This may be because the inclusion criteria in the present study
were women in the immediate postpartum period who presented bleeding of 500 mL or more
compared to 1000 mL in their study.
More blood transfusions were observed in the SPPH group compared to the non-SPPH
group, indicating that most of the patients with blood loss higher than 1500 mL may need a
transfusion. Studies such as the one carried out by Lee et al [27], Sohn et al [28], and
Hoskins and Berg [29] reported that a level of lactate higher than 4.0 mmol/L was associated
with good specificity, sensitivity, and positive predictive value for massive transfusions in
obstetric patients. Lactate from different samples such as the fetal scalp, amniotic fluid, and
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vaginal fluids has been used to detect fetal and maternal outcomes; however, none of them
is applicable in cases of PPH due to the possible mixture of blood and other fluids during
childbirth [30, 31].
The present study has some limitations, such as a lack of previous studies during the study
period which led to the present pilot study with a sample size of 30 patients. For this reason,
the study group is working on validating the results with a larger sample size in a Mexican
population to improve its external validity. Serum lactate as an indicator of SPPH needs
more research in a larger study of patients with different characteristics to validate the
optimal threshold obtained as well as for possible complications.
Author contributions
AGM, ÚM, RET, and VBK were responsible for the design of the study. Patients LADS and
RCR were responsible for recruitment and data collection. AGM and VBK conducted the
statistical analysis. ÚM, RET, and VBK edited the final manuscript. ÚM submitted the
manuscript. All the authors approved the final manuscript.
Acknowledgments
The authors acknowledge the participation of the resident physicians at the Department of
Obstetrics and Gynecology from the Central Hospital Dr. Ignacio Morones Prieto, San Luis
Potosi, Mexico. They also acknowledge the financial support and funding provided by The
National Council of Science and Technology (Consejo Nacional de Ciencia y TecnologíaCONACYT).
Conflicts of interest
The authors have no conflicts of interest.
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FIGURE LEGENDS
Figure 1. Measuring blood loss using the gravimetric method.
Figure 2. Flow chart of patients.
Figure 3. Determination of the best cut-off point using the receiver operating characteristic
curve (ROC curve).
Table 1. General characteristics of the study groupa
Variable
Total group
SPPH (n=13)
(n=30)
Non-SPPH
P value
(n=17)
Maternal age (years)
22.5±8.2
22.0±7.0
24.0±8.0
NS
Gestational age (weeks)
39.2±3.2
39.2±4.0
39.2±3.28
NS
Serum lactate at diagnosis
2.7±1.8
3.2±3.0
2.3±0.54
0.01 b
Hematocrit at diagnosis
37.6±4.4
37.8±5.5
37.5±3.50
NS
Hematocrit 24 h postpartum
29.4±4.81
28.5±4.16
30.1±5.26
NS
Crystalloids reposition (mL)
2500±1475
3400±2000
2000±1500
0.03 b
Blood volume (mL)
1260±691
1700±690.1
1100±224
0.004 b
Birth weight (g)
3245±595
3470±810
3200±470
0.04 b
Serum lactate >2.2
23 (76.7)
12 (92.30)
11 (64.7)
NS
Cesarean delivery
17 (56.7)
8 (61.5)
9 (52.9)
NS c
Use of Bakri
8 (26.7)
5 (38.5)
3 (17.6)
NS d
Surgical management
12 (40)
7 (53.8)
5 (29.4)
NS d
Transfusion
12 (40)
9 (69.2)
3 (17.6)
0.0131 d
(mmol/L)
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Abbreviation: NS, no statistical significance; SPPH, severe postpartum hemorrhage.
a Values are given as number (percentage) or mean ± standard deviation.
b Wilcoxon test.
c χ2 test.
d χ2 test with Yates´ continuity correction.
Table 2. Comparison of cut-off points 2.2 mmol/L vs 2.6 mmol/L in the prediction of severe
postpartum hemorrhage.a
Cut-off points
2.2 mmol/L
2.6 mmol/L
RR
3.6 (0.6–23.3)
5.50 (1.5–20.71)
OR
6.6 (0.7–63.3)
17.88 (2.7–16.8)
P value
0.077
<0.001***
Sensitivity
0.92 (0.6–1.0)
0.85 (0.55–0.98)
Specificity
0.35 (0.3–0.7)
0.76 (0.50–0.93)
PPV
0.52 (0.31–0.73)
0.73 (0.45–0.92)
NPV
0.86 (0.42–1.00)
0.87 (0.60–0.98)
PLR
1.42 (0.97–2.10)
3.60 (1.48–8.74)
NLR
0.22 (0.03–1.59)
0.20 (0.05–0.74)
Abbreviations: NLR, negative likelihood ratio; NPV, negative predictive value; OR, odds
ratio; PLR, positive likelihood ratio; PPV, positive predictive value; RR, relative risk.
a Values in parentheses are 95% confidence intervals.
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Figure 1. Measuring blood loss using the gravimetric method.
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Figure 2. Flowchart of patients.
Cases of obstetric
hemorrhage
n=209
Postpartum
hemorrhage
Other
(n=41)
Cesarean delivery
Vaginal delivery
(n=23)
(n=18)
Did not meet selection
criteria (n=6)
Did not meet
selection criteria
(n=5)
Met selection criteria
Met selection
criteria
(n=17)
(n=13)
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Figure 3. Determination of the best cut-off point using the receiver operating
characteristic curve (ROC).
Abbreviation: AUC, area under the ROC curve.
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