Postpartum pulmonary embolism (PPE) is a rare disorder, occurring in 1 in 80,000 pregnancies [1]. PPE encompasses amniotic fluid embolism (AFE), venous thromboembolism (VTE), and others; it is characterized by a variety of symptoms ranging from relatively minor, such as sudden chest pain or difficulty breathing after delivery, to serious symptoms such as coagulopathy, renal failure, and cardiac arrest. However, it is associated with fatal complications in pregnancy and childbirth. PPE manifests in a variety of ways immediately after delivery, making diagnosis more difficult and challenging, unless it is suspected clinically. Moreover, clinical outcomes vary, ranging from recovery and discharge to death, depending on circumstances and prompt treatment. Advance preparation is critical, as there is no time to prepare when it occurs.

Postpartum pulmonary embolism (PPE) is a rare disorder in the puerperium, and it is the most common cause of maternal mortality, accounting for about 10% of all maternal deaths in the United States [2]. In this series, two of five PPE patients died.

The early signs of PPE may progress to potentially fatal conditions including low blood pressure, cardiac arrest, coagulopathy, and multi-organ failure, sometimes leading to death. At even a slight suspicion, aggressive diagnosis and treatment should be performed concomitantly. Given that management and prognosis vary by condition, as seen in the discussion below, differential diagnosis in an emergency department is very important. However, accurate diagnosis is difficult based on medical examinations and inquiries in an emergent situation. Clinical experience and medical facilities for differential diagnosis, an expert medical team, and senior doctors to offer appropriate recommendations are thought necessary. When patients with suspected symptoms of PPE visit the hospital, adequate supplies of oxygen can be attempted preferentially. Then, more accurate diagnosis and treatment can be achieved by screening cardiac output, systemic vascular resistance (SVR), pulmonary vascular resistance (PVR), and other predictors via hemodynamic monitoring after the insertion of a pulmonary catheter. However, this procedure may be challenging in emergent circumstances. And treatment should be initiated after contrast-enhanced chest CT and echocardiography for differential diagnosis, to identify the exact cause of the condition (Table 1).

PPE is known to be influenced by coagulopathy of cardiovascular origin, such as hypertension, toxemia of pregnancy, preeclampsia, or hemolysis, elevated liver enzymes, and low platelets (HELLP syndrome) in pregnancy [3]. In the current study, three of five patients had medical histories of cardiovascular disorders associated with toxemia of pregnancy. Previous studies have examined the postnatal effects of respiratory diseases during pregnancy [4], but none of the patients in our study had a history of lung disorder. Because hypoxia, hypotension, and shock immediately after delivery are predominantly of pulmonary or cardiovascular origin, differential diagnosis between PPE and other diseases is crucial.

Contrast-enhanced chest CT is the first-line imaging approach for diagnosing PPE; by contrast, simple chest PA is not useful in making a diagnosis of PPE. In cases of pulmonary embolism (PE), several considerations are crucial. First, the increased risk of PE is recognized to result from the hypercoagulable state associated with pregnancy and puerperium [2], and pregnancy-induced venous stasis and damage in vein endothelial cells are known to increase the risk of complications such as deep vein thrombosis (DVT) [5]. For these reasons, PE should be primarily considered in pregnant women with symptoms such as hypoxia, tachycardia, hemoptysis, and so forth. Second, PE should be differentiated from pneumonia because they present with similar symptoms. Third, immune system changes during pregnancy and intrapartum aspiration may also increase the risk for infection, and acute respiratory distress syndrome (ARDS) is one of the known complications during pregnancy [6].

Amniotic fluid embolism (AFE) is a rare but fatal obstetric condition characterized by cardiorespiratory collapse. The causes of AFE are considered to include pregnancy in women aged $\ge$ 35 years, Cesarean section, forceps delivery, placenta previa, abruptio placentae, and pre-eclampsia-eclampsia, among others [7]. Many studies have reported that AFE is associated with cardiovascular and hemodynamic changes [8, 9, 10, 11]. Women who are pregnant and have severe pre-eclampsia-eclampsia require especially close attention. In this study, three of five patients had histories of conservative treatment after being diagnosed with gestational hypertension and toxemia of pregnancy on prenatal examination; furthermore, these conditions occurred in those three women after cesarean delivery. The process of labor and delivery itself causes significant hematological changes, and mothers can be exposed to multiple problems during postpartum recovery. Pregnant women with gestational hypertension appear to be particularly prone to PPE due to severe hematological changes related to blood pressure regulation after delivery or postpartum hemorrhage. This seems to be attributable to the fact that, unless uterine atony occurs, C-section delivery is more likely to result in greater blood loss and transfusion and less stable hematological parameters than is NSVD.

Because PPE may be associated with disseminated intravascular coagulation (DIC) and systemic inflammatory responses and early manifestations include septic shock, an immediate supply of oxygen and fluid is needed in cases where PPE is suspected. However, excessive fluid supply should be avoided because PPE is often associated with right ventricular failure. Treatment for both PPE and DIC should be started simultaneously. When starting treatment, DIC should be simultaneously managed to improve patient outcomes. ECMO can be considered but, generally, the use of ECMO is not recommended. Coagulation therapy is initially started for the management of pulmonary thromboembolism (PTE), thereby reducing the risk of heart failure associated with PTE. Aggressive treatment can be initiated, including ECMO and other approaches, in severe cases.

PPE must also be discriminated from postpartum cardiomyopathy (PPCM), as it can mimic PPCM. PPE may be suspected in patients with congestive heart failure and left ventricular dysfunction without other heart diseases. In such cases, the cardiac ejection fraction (EF) is reduced below 45%, and clinical signs mostly manifest within the first week postpartum. Echocardiography seems to be essential to discriminate embolism from other heart problems.

Given that management and prognosis vary by condition, as seen in the discussion above, differential diagnosis in an emergency department is very important. However, accurate diagnosis is difficult based on medical examinations and inquiries in an emergent situation.

When PPE is suspected, after various causes are considered, early and adequate management and accurate diagnosis via contrast-enhanced chest CT and echocardiography can prevent conditions that could cause death in pregnant women with high blood pressure during the antepartum or intrapartum period, those at risk for intrapartum or postpartum hemorrhage, and those with symptoms of heart problems such as dyspnea and hypotension during or after delivery.

The article does not contain any studies with human participant or animal performed by any of the authors.

All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript.

This work was supported by the Soonchunhyang University Research Fund.

The authors declare no competing interests.