The definition of PPH, which means massive bleeding at birth, is defined as the bleeding volume within 24 hours after delivery is 500 ml or more for vaginal delivery and 1,000 ml or more for cesarean section . According to the 2019 report of the Perinatal Committee of the Japan Society of Obstetrics and Gynecology, analysis of a datebase of 236,475 Japanese pregnant women revealed that 52.4% of all cases had bleeding volume less than 500 g and 47.6% of all had bleeding 500 g or more. Bleeding of 1,000 g or more accounted for 16.4% of the total, and bleeding of 1,500 g or more accounted for 6.1% of the total. 90%tile of total bleeding is 800 ml for single vaginal delivery, 1,500 ml for cesarean delivery, 1,600 ml for multiple vaginal delivery, and 2,300 ml for cesarean delivery. In our study, the median total bleeding volume was 481 ml (77-2474 ml), close to the standard 500 ml for massive bleeding, and the 90% tile was 1,536 ml. It is considered that our center mainly handles high-risk delivery and that HDP itself is a high risk of abnormal postpartum bleeding. In this study, the amount of bleeding was assumed to be the weight of blood (assumed to be 1 ml/g) collected in a clean drape or gauze laid on the buttocks of pregnant women, but it was difficult to measure the actual amount of bleeding. Although the visual estimation of bleeding has been conventionally performed for postpartum management, it has been reported that the amount of bleeding may be underestimated by 33–50%, especially in cases of heavy bleeding . It is necessary to recognize that the estimated value of the amount of hemorrhage at delivery may be inaccurate. The amount of amniotic fluid excreted with blood at the time of delivery is subtracted from the drape weight is subjective to the doctor or midwife, and may not reflect the actual amount of bleeding. Due to this background and the fact that the cause of obstetric shock is not only due to external bleeding, only measuring external blood loss as a indicator of PPH may not reduce the maternal mortality. An obstetrical early warning system that emphasizes vital signs is now being introduced around the world, including Japan . One of these is MEOWS (modified early obstetric warning system), which has been introduced at many facilities in the United Kingdom (UK). In the UK, maternal deaths have been registered for more than 50 years, and based on this, CEMACH (Confidential Inquiry into Maternal and Child Health) reported that there ware some cases in which the prognosis was thought to have improved if treatment or transportation to a advanced medical facility was taken after noticing an early abnormality. Based on this report, MEOWS has been widely used and its validity has been verified . MEOWS defines red and yellow trigger criteria for eight vital signs and clinical findings: body temperature, systolic blood pressure, diastolic blood pressure, Heart rate, respiratory rate, oxygen saturation, pain score, and neurological response. These items do not include the amount of external bleeding, nor do blood tests that take time to determine the results. It was reported that the sensitivity was 89%, specificity was 79%, the positive predictive value was 39%, and the negative predictive value was 98% in the prediction of obstetric complications including bleeding of 1,500 ml or more . ACOG (American College of Obstetricians and Gynecologists) recommends that continuous bleeding, heart rate of 110 / min or higher, blood pressure of less than 85/45 mmHg, and blood oxygen saturation of less than 95% as triggers for suspected PPH  . In Japan, the '' Guideline for Obstetric Critical Bleeding 2017 '' prepared and revised by a committee composed of five organizations, such as the Japanese Society of Perinatal and Neonatal Medicine and the Japanese Society of Obstetrics and Gynecology provide guidelines for dealing with PPH. In this guideline, a visual estimate of the amount of bleeding is one of the judgment indexes, but SI, vital sign abnormalities (oliguria, peripheral circulatory insufficiency), and obstetrical DIC score are also listed as indicators. It is characteristic that SI is a important indicator . One of the reasons is considered to be the large number of deliveries at primary facilities in Japan. When PPH is observed at the primary facilities, transportation of a patient to a advanced medical facilities should be considered. Using SI as the indicator of PPH, the decision to transport a patient is simplified and clinical usefulness can be expected.
In recent years, many reports have been made on the normal range of SI in the delivery of so-called "low risk" pregnant women without complications. Borovac-Pinheiro A, et al. reported SI of uncomplicated pregnant women with less than 500 ml of bleeding two hours after delivery. According to their report, SI was highest within 20 minutes after delivery and tended to decrease with time. And the average SI values was 0.82 ± 0.14 and 0.79 ± 0.13 in the preterm birth range from 33 to 36 weeks and after 37 weeks, respectively . Similarly, HL. Nathan, et al. reported blood pressure and SI of 316 pregnant women with less than 500 ml of bleeding up to one hour after delivery. The median SI was 0.66 (0.52–0.89), indicating that the normal SI value up to one hour after delivery was less than 0.9 (the risk of serious consequences increases with SI value of 0.9 or higher) . HL.Nathan, et al. also conducted a retrospective study of 233 patients with postpartum bleeding of 1,500 ml or more. They evaluated vital signs up to one hour after diagnosing PPH. Among the various vital signs, SI was the most sensitive vital sign for predicting serious consequences (ICU; Intensive Care Unit admission, blood transfusion of 4 units or more, surgical intervention, Hb < 7 g / dl), and SI less than 0.9 was a reassuring state. They concluded that SI 0.9 or higer required caution, and 1.7 or higer was urgent state . Thus, evidence has been accumulated on the management of PPH in normal pregnancy, but there are few reports on the management of PPH in cases of complications or abnormal pregnancy, and this is the research task from now on .
We retrospectively examined whether SI and delta SI (ΔSI) were useful for estimating the amount of bleeding in HDP cases (50 cases with PPH). In this study, we used the conventional measurement of blood loss up to two hours after delivery. Borovac-Pinheiro A, et al. reported the amount of postpartum bleeding and vital signs in normal pregnancy over twenty-four hours. 73% of the amount of twenty-four hours bleeding was lost in the first 40 minutes after delivery, and 91% of participants had 90% of the amount of twenty-four hours bleeding within two hours after delivery . It is considered that the evaluation of the amount of bleeding up to two hours after delivery is a valid evaluation method in a study examining the management of PPH.
The concept of the delta shock index (ΔSI) has been reported for its usefulness in the field of emergency department. The SI at the trauma site where the ambulance arrives is the baseline SI, and the change from the SI when the patient arrives at the Emergency room (ΔSI) is more sensitive than the conventional SI, resulting in an increase in mortality due to trauma, necessity of blood transfusion, and staying at the ICU . In recent years, in the obstetrics field, Kohn JR et al. had been retrospectively examining vital signs in 41 cases of PPH in normal pregnancy and 41 cases in the control group. SI and ΔSI (peak SI-baseline SI) was a useful indicator, and ΔSI was reported to be the most sensitive indicator for predicting the necessity of treatment intervention .
In our study, SI and ΔSI are considered to be both useful and related to the amount of bleeding in the management of PPH in HDP, and ΔSI is more useful as an early warning system for obstetrics.
Consider the actual clinical response based on the results of this study. In HDP cases, at the time of SI is greater than 0.77, it is necessary to recognize that the bleeding volume is 500 ml, which is the definition of massive bleeding at delivery. When the SI reaches 0.99, a bleeding volume of 1,500 ml is expected. As with non-HDP pregnancies, it is required to treat PPH at the SI reaches 1.0 according to the flowchart of ''Guideline for Critical Bleeding in Obstetrics 2017 ''.
As an actual clinical response using ΔSI, at the time of ΔSI is 0.25, it is necessary to recognize that the volume of bleeding is 500 ml, which is the first definition of massive bleeding at delivery. Bleeding volume of 1,500 ml is expected at SI reaches 0.43, and it is necessary to respond as PPH. Management using ΔSI can be more sensitive to recognition of massive bleeding and abnormal bleeding than SI evaluation in the results of ROC analysis, ΔSI was excellent in sensitivity, specificity, and AUC at any of the 500 ml, 1,000 ml, and 1,500 ml bleeding volumes.
The limitation of this study is that it is a short-term retrospective case-control study in a singleton perinatal maternal and child medical center.
Also, as shown at the beginning of this discussion, the bleeding volume may be inaccurate. This is always a problem in the study of bleeding disorders such as bleeding due to trauma as well as postpartum hemorrhage. Especially with regard to postpartum hemorrhage the amount of amniotic fluid contained in the clean drape laid in the delivery field is determined by the medical staff.