Diagnostic Performance of Serial bedside Capillary Lactate, Hemoglobin, and Shock Index for Severe Postpartum

Objective: To assess the diagnostic capacity of bedside capillary lactate (CLact), capillary Haemoglobin (CHb), and shock index (SI) for severe postpartum haemorrhage (SPPH > 2000 ml) at diagnosis, 15 minutes and 30 minutes later. Method: A cohort study was carried out in a reference hospital in San Luis Potosi, Mexico from February 2020 to March 2021, and included sixty women in vaginal labor or c-section who presented PPH (≥500 ml in labor or ≥1000 ml in c-section) measured by the gravimetric method. CLact, SI, and CHb concentrations were analyzed at diagnosis of PPH, 15 minutes, and 30 minutes. Patients who presented total blood loss of >2000 ml were considered SPPH. A T-test or Wilcox test was performed to compare the groups of non-severe and severe. Sensitivity, specificity, and performance were calculated by A Receiver Operating Curve. Results: A CLact measure-ment at 30 minutes was significantly different between the non-severe and severe groups (4.0 + 1.9 vs 4.8 + 1.15 P-value 0.001, with an optimal cut point of 4.3 mmol/dl at AUC 0.75, sensitivity 0.85, and specificity of 0.62. With a cut-point of 1.17, an AUC of 0.76, sensitivity of 0.43, and specificity of 0.98, SI at diagnosis was significantly different between the non-severe and severe groups (0.70 + 0.20 vs. 0.90 + 0.38 P-value 0.0228). Conclusion: SI is an early sign of SPPH; CLact can significantly identify SPPH after 30 minutes.

DOI: 10.4236/arsci.2021. 94018 190 Advances in Reproductive Sciences bidity in the world accounting for approximately 10% of all births and the most common form of obstetric haemorrhage, which traditionally has been defined as a blood loss greater than 500 ml after vaginal delivery or 1000 ml after caesarean section [1]. In 2017 the American College of Gynecology and Obstetrics (ACOG) published a recent definition as a cumulative blood loss greater than or equal to 1000 ml or a blood loss accompanied by signs or symptoms of hypovolemia within 24 hours of the delivery regardless of the route of birth [1]. Some institution still considers the traditional definition as appropriate [2]. In most developing countries, maternal mortality, and morbidity due to obstetric haemorrhage are caused by difficulties in early identification of the causes and lack of timely and adequate treatment. During the medical management of these cases, it is of great importance the early recognition of patients with severe cases o may develop severe haemorrhage [3] [4]. For this reason, Obstetricians need to have reliable bedside clinical and biochemical tools to identify patients at risk of a critical condition if they are not provided immediate resuscitation. The schemes studied for this purpose include non-capillary schemes such as the shock index, venous serum lactate and Haemoglobin levels. Some studies reported the combination of these schemes to be useful but not studied at the capillary level for bedside use [5]. It is well established that SI correlates with SPPH and is a good predictor for transfusion and complications in patients with hypovolemic shock.
[5] [6] [7] [8] [9] but it is also known that the vital signs are dynamic states, which means they can rapidly change over a short time, and the physiological changes during pregnancy may make vital signs not reliable for the early identification of severe haemorrhage as they are lately modified [10], the calculation of SI involves the use of vital signs (heart rate divided by systolic blood pressure), for this reason, we investigate whether the SI is consistently useful over time as an indicator for SPPH.
On other hand, venous serum lactate has been used as a biochemical marker to guide fluid recusation in patients with postpartum haemorrhage and it has also been established as an indicator of severe postpartum haemorrhage [5] [11].  [13], It is reported that women without PPH, the mean Hb decrease is approximately 1 g/dl, while a 2 g/dl to 3 g/dl decreases are commonly observed in women with occult PPH or overt PPH, respectively [14]. But this drop of Haemoglobin is neither described in terms of time nor in capillary level.  We included Pregnant patients in labor or cesarean section with postpartum haemorrhage, without conditions that might elevate lactate concentration such as eclampsia, leukemia, lymphoma, and solid tumors, poorly controlled diabetes, liver failure, and 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 the consent or to leave the study were eliminated. Bleeding volume was calculated by the gravimetric method as described here, blood-Stained Surgical Gauzes from delivery or c-section were weighed, and its dry weight was subtracted from the total blood-stained weight.

Method
Blood weight (g) was converted into blood volume (ml) using the accepted approximation of blood density of 1 g = 1 mL. At the diagnosis of postpartum haemorrhage (≥500 ml in labor or ≥1000 ml in c-section, Institutional definition of postpartum haemorrhage), Capillary lactate and Haemoglobin were determined by bedside equipment Acuttrend plus©, and Shock index was calculated as the heart rate (HR) divided by systolic blood pressure (SBP). These parame-Advances in Reproductive Sciences ters were also measured at 15 and 30 minutes after the diagnosis. At the end of the obstetric event the patients with total blood loss of >2000 were considered SPPH.

Statistical Analysis
Statistical analysis was performed using Statistical program R 3.6 version and R

Discussion
Results of this study have shown the capacity of shock index, capillary lactate in identifying severe postpartum haemorrhage defined as blood loss of more than 2000 ml. Additionally, reports an optimal moment for analysis of these parameters. Shock index is defined as the heart rate divided by systolic blood pressure, has been studied in patients e at risk of or experiencing shock from a variety of causes such as trauma, myocardial infarction, haemorrhage, pulmonary embolism, sepsis, and obstetric haemorrhage. Schroll R. Et al reported Shock Index ≥ 1 had a sensitivity of 67.7% (95% CI 49.5% -82.6%) and specificity of 81.3% (95% CI 78.0% -84.3%) for predicting massive transfusion in trauma patients. In obstetrics, Nathan et al reported that SI ≥ 1.7 had 25.0% sensitivity (95% CI 5.5 -57.2) and 97.7% specificity (CI 94.8 -99.3), for predicting ICU admission in postpartum haemorrhage [13]. Welsh et al reported SI de 0.9 as a good predictor of necessity for transfusion in postpartum haemorrhage [14]. Most of these studies which investigated the clinical application of SI have not determined an optimal moment for its determination. This study determined that the value of the shock index, dynamically evaluated, at the time of diagnosis, and 30 minutes after diagnosis, allows early identification of those patients who present massive bleeding with the sensitivity of 0.43 and specificity of 0.98 and 0.64 sensitivity and specificity 0.7 respectively. Our study's cut point did not differ much from other studies. Generally, we recommend considering SI > 1 as the predictor of adverse effects in most of the clinical scenarios independent of the moment of its determination. At initial phases of shock, the compensatory mechanism of the cardiovascular system responds by increasing the heart rate, increasing myocardial contractility, and constricting peripheral blood vessels as a result of the direct stimulation via the sympathetic system this compensatory mechanism maintains the stable blood pressure and elevated heart rate, these mechanisms make the shock index an early indicator of severe haemorrhage. Serum lactate has been studied as a strong biochemical marker of tissue hypoperfusion in obstetric haemorrhage; increased lactate concentration may indicate hypovolemic shock before traditional markers such as hemoglobin concentrations, and vital signs in pregnant women. Previously it was reported that venous lactate of 2.6 mmol/dl at the diagnosis of postpartum haemorrhage may be a good predictor for severe haemorrhage (sensitivity of 0.85 and specificity was 0.76) [10]. We found that at the capillary level the cut point of 4.3 mmol/dl at 30 min had good performance (AUC 0.75), with sensitivity 0.85, specificity 0.62 AUC 0.75. At the diagnosis and 15 min we obtained higher cut points but with low performance. High cut points for capillary lactate compared to venous lactate may be due to multifactorial effects including lactate detection methods and compensatory mechanisms of peripheric blood constriction to guarantee blood flow to vital organs. There are portable lactate analyzers that require 15 -50 μL of blood and take approximately 60 seconds to process which makes it easier for the bedside monitoring by capillary lactate. Putting into practice our results, the bedside serum capillary lactate as a point-of-care test can differentiate the severe group from non-severe to allow quick during lactate-guided recusation and probably reduce risk of thrombophlebitis that may result from venous sampling capillary hemoglobin was not statistically significant in differentiating between patients with severe bleeding. Had unstable changes (i.e., with negative and positive values) may explain that the capillary hemodynamics y phenomena de redistributions of hemoglobin affect the hemoglobin concentration at this level. we found that a capillary hemoglobin value of 8.4 at 15 minutes has a sensitivity of 90% and specificity of 42% for identification of patients who are at risk of reaching a critical condition if immediate resuscitation is not provided, and thus assist in the rapid and objective recognition of patients with severe postpartum haemorrhage (those who require massive transfusion during the immediate phase of resuscitation, including fluids and blood products) since patients with haemorrhage obstetrics requiring blood transfusion are a significant cause of maternal morbidity in our setting.
The limitation of this study is that it was carried out in a tertiary level hospital where there is the availability of human resources and materials to combat severe haemorrhage for this reason very few patients may present complications such as coagulopathy and needs for intensive care unit admission, for this reason, we cannot tell the exact risk those complications using our capillary scheme.
On another side, one of its advantages is that the materials needed to obtain these results are portable devices that can be easily obtained in the market, and thus low resourced facilities can obtain them for their patient monitoring.

Conclusion
Although the vital signs changes delay in identifying severe cases, SI is still an early sign of SPPH; CLact can significantly identify SPPH after 30 minutes probably due to different capillary hemodynamics compared to venous. Finally, capillary hemoglobin is not an early detector of SPPH probably due to the mechanism of hemoglobin redistribution. These three bedside markers may be combinedly used to optimize the diagnosis and management of SPPH. More studies are required in different populations to increase the external validity of these results.