Treatment of Diffuse Alveolar Hemorrhage: Controlling Inflammation and Obtaining Rapid and Effective Hemostasis

Diffuse alveolar hemorrhage (DAH) is a life-threatening pulmonary complication in patients with hematologic malignancies or systemic autoimmune disorders. Pathologic findings show pulmonary capillaritis, bland hemorrhage, diffuse alveolar damage, and hemosiderin-laden macrophages, but in the majority of cases, pathogenesis remains unclear. Despite the severity and high mortality, the current treatment options for DAH remain empirical. Systemic treatment to control inflammatory activity including high-dose corticosteroids, cyclophosphamide, and rituximab and supportive care have been applied, but largely unsuccessful in critical cases. Activated recombinant factor VII (FVIIa) can achieve rapid local hemostasis and has been administered either systemically or intrapulmonary for the treatment of DAH. However, there is no randomized controlled study to evaluate the efficacy and safety, and the use of FVIIa for DAH remains open to debate. This review discusses the pathogenesis, diverse etiologies causing DAH, diagnosis, and treatments focusing on hemostasis using FVIIa. In addition, the risks and benefits of the off-label use of FVIIa in pediatric patients will be discussed in detail.


Introduction
Diffuse alveolar hemorrhage (DAH) is a clinical syndrome characterized by acute onset of alveolar infiltrates and hypoxemia which result in progressive diffuse alveolar bleeding, requiring immediate treatment [1]. Many systemic diseases can cause DAH, but the pathogenesis is not well understood in the majority of cases, and the standard treatment for DAH has not been established even for the systemic autoimmune disorders. The treatment includes supportive cares such as correction of hemodynamic instability or coagulopathy and ventilatory support, high-dose corticosteroids, immunosuppressants, and plasmapheresis. Though, the overall mortality still remains high. To control systemic inflammation, subsequent cytokine storm, and life-threatening bleeding, multidisciplinary treatment is required. Although the role of systemic immunosuppressive treatment has been emphasized, systemic immunosuppressive treatment alone is not enough to stop the life-threatening bleeding, and it takes times to work: these single-disciplinary approaches often lead to treatment failure.
Recombinant factor VIIa (FVIIa) was developed for the management of bleeding in hemophilic patients with inhibitors or in FVII-deficient patients. Despite this narrow indication, the off-label use of FVIIa has been increasing in non-hemophiliac patients to prevent or to treat uncontrolled bleeding in adults, children, neonates, and even preterm neonates [2,3]. The FVIIa has been reported to have a significant hemostatic effect in DAH as well [4][5][6][7]. However, there is no randomized controlled study to evaluate the efficacy in various conditions but also no consensus on the formulations, routes of administration, doses, and dosing regimens of FVIIa for the treatment of DAH. In addition, few studies have been reported in children. This review discusses the pathogenesis, pathologic findings, infections have been implicated as the initial injury to the lung leading to post-transplant DAH [27]. Animal models suggest that alveolitis develops during the acute phase of graft-versus-host disease (GVHD), and it is characterized by alveolar hemorrhage, increase in the alveolar leukocytes, platelet microthrombi, damage of alveolar endothelial and epithelial cells, increased turnover rate of alveolar cells, and increased cell counts and protein concentration of the bronchoalveolar lavage (BAL) fluid [28,29]. Irrespective of post-transplant leukopenia, neutrophils and neutrophil products are detected in the lower respiratory tract of HCT recipient at the time of DAH [30]. Besides, vasculitis of small muscular arteries and thrombotic microangiopathy in the form of endothelial swelling and thrombi are frequently observed in acute hemorrhagic pulmonary edema after transplantation [9,31]. The vasculopathy manifests as concentric intimal or medial hyperplasia with luminal narrowing, prominent myxoid changes, extravasated RBCs, and the presence of foamy histiocytes apart from thrombotic microangiopathy [31][32][33]. Add on, hematopoietic growth factors (G-CSF) and cytokine storms make worse the alveolar damage and capillary leakage by increasing neutrophil infiltration into the lungs [30]. Dysregulated cytokine release including both TH1 (IL-2, IL-6, IFN-γ, and TNF-α) and TH2 (IL-9 and IL-15) cytokines further potentiates the inflammatory response [34].

Diagnosis of DAH
The differential diagnosis of DAH is broad, and the etiologies of DAH can be broadly divided into immune-and non-immune-mediated causes (Table 1) [35]. A careful history, physical examination, and laboratory tests can often help to establish the risk factors and most likely etiology of the alveolar hemorrhage. Bronchoscopy is the key investigation needed to diagnose DAH by lavage and to exclude other associated infections. Bronchoscopy has higher yield if performed within the first 48 h. Persistent or increasing blood on three sequential lavage aliquots from one affected area of lung supports the diagnosis of DAH [36]. The number of hemosiderin-laden macrophages should be counted in cases of subacute or recurrent DAH [8,16]. The finding of ≥20% hemosiderin-laden macrophages in BAL fluid is commonly regarded as diagnostic of DAH and closely associated with severity [36][37][38]. BAL specimens should be sent for routine bacterial, mycobacterial, fungal, and viral cultures, and Pneumocystis stains to exclude infections. The role of transbronchial lung biopsy is not established in the diagnosis of DAH as the area of involvement is often patchy [8], but in any patients presenting with DAH of unclear causes a lung biopsy is strongly recommended to determine the underlying etiologies [10,39,40]. Imaging studies including chest radiographies and high-resolution chest computed tomography (CT) scans provide additional information to support a diagnosis of DAH. Typical pattern of DAH includes focal or diffuse areas of ground glass opacities or consolidations as a consequence of alveolar filling. Laboratory tests include a complete blood count with differential; coagulation studies; serum BUN and creatinine analysis; ANCA testing (c-ANCA and p-ANCA); antigen-specific ELISA [proteinase 3(PR3) and myeloperoxidase (MPO)], analysis of anti-phospholipid antibodies (APL), lupus anticoagulant, anti-cardiolipin (CL) antibodies, anti-β-2 glycoprotein1 (β2GP) antibodies, anti-glomerular basement membrane (GBM) antibodies, anti-nuclear antibodies (ANA), and rheumatoid factor (RF); urinalysis with urine sediment assessment; and a urine drug screen [9,41].

Treatment of DAH
DAH, especially acute macroscopic hemorrhage, has a high mortality rate, requiring prompt and aggressive multidisciplinary management. Treatment for DAH involves three major disciplines: (1) supportive care including hemodynamic correction, transfusion, and ventilator support, ranging from oxygen supplementation to mechanical ventilation with high positive end-expiratory pressure (PEEP) producing a tamponade effect to limit capillary bleeding; (2) treatment of underlying disease including intensive immunosuppressive treatments to control disease activity, plasmapheresis to remove autoantibodies, and antivirals or antibiotics for infection-associated pulmonary hemorrhages; and (3) rapid and effective local hemostasis [7].
The most immediate life-threatening complication of DAH is acute hypoxemic respiratory failure. When severe DAH results in ARDS, high levels of FiO 2 and PEEP are often needed to achieve acceptable oxygenation. Although there is no consensus on ideal PEEP levels for DAH and it should be adjusted by the severity of respiratory failure and lung recruitability, DAH has been managed with high PEEP and permissive hypercapnia to reduce the active bleeding and prevent lung collapse [42]. The PEEP used in severe ARDS lies around 8.5 cm H 2 O [43], but the PEEP level should be selected by carefully considering oxygenation advantage and the putative benefits on lung protection [44].
To control the inflammatory activity, high-dose corticosteroids are recommended to start promptly, along with treatment for underlying disease. Corticosteroids have been accepted as a mainstay of treatment aimed at reducing acute inflammatory responses such as lung alveolar epithelial swelling, thrombotic microangiopathy, and increased inflammatory cells and cytokines [10,40,45]. Based on anecdotal reports and retrospective studies, systemic high-dose corticosteroids (500 mg to 2 g/day or 30 mg/kg/day of intravenous (iv) methylprednisolone for 3-5 days followed by gradual tapering over 4 weeks) are recommended to treat DAH [4,40,46,47]. However, steroid treatment alone is not sufficient to stop acute macroscopic pulmonary bleeding and is often fatal if the etiology is infectious or if the patient is in an immunocompromised status; the benefit of high-dose corticosteroids in critically ill patients remains undefined. Despite the widespread use of high-dose corticosteroids for DAH, the mortality exceeds 50%, especially in patients requiring intensive care unit (ICU) admission or in patients received HCT [48]. For the treatment of AAV, reduced-dose glucocorticoids had comparable efficacy to standard-dose corticosteroids with respect to mortality or incidence of end-stage renal disease (ESRD) but also reduced the incidence of serious infections at 1 year [49]. A study investigating the dose effect of corticosteroids for DAH suggested that patients treated with low-dose methylprednisolone (<250 mg/day) had a significantly lower ICU mortality rate compared to the patients treated with medium-dose (250-1000 mg/day) or high-dose (>1000 mg/day) methylprednisolone, and overall mortality did not differ by the doses of corticosteroids, raising questions about the validity of high-dose corticosteroids for DAH [48].
To eliminate autoreactive antibodies or triggering factors rapidly, plasmapheresis has been used as an adjunctive therapy particularly in autoimmune connective disorders, such as anti-GBM disease, AAV or SLE-associated pulmonary capillaritis. Plasmapheresis is performed daily or on alternating days for 14 days. Each exchange involves 1-1.5 times the total plasma volume and is replaced with albumin or FFP. Although retrospective studies reported excellent patient outcome and safety [50], long-term follow-up data or matched analyses to compare the efficacy of plasmapheresis to methylprednisolone have failed to show significant benefit [51][52][53]. The evidence-based guidelines of the American Society for Apheresis recommend using plasmapheresis in AAV patients with DAH presenting with hypoxemic respiratory failure requiring either high-flow supplemental oxygen or mechanical ventilation [54]. Recently released data of randomized controlled trial of plasma exchange and glucocorticoids for treatment of AAV (NCT00987389) suggested that the use of plasmapheresis did not reduce the mortality or the incidence of ESRD [49].
Rituximab, a chimeric monoclonal antibody targeting CD20, has been used as another viable alternative. Antibody-mediated modification and/or depletion of ANCA producing CD20(+) plasma cells is a proposed mechanism for rituximab to decrease autoantibody production and to control disease activity [55,56]. Although most of the studies have been limited, they suggest that rituximab is an effective therapeutic option for DAH in connective tissue disease or autoimmune disorders. Rituximab on a compassionate use basis for patients with refractory AAV reported successful treatment outcomes [57][58][59][60]. These encouraging results led to randomized controlled trials evaluating the effect of rituximab as a remission induction therapy in patients with severe AAV (NCT00104299, NCT01731561). Comparison between rituximab and cyclophosphamide pulse therapy for AAV showed a similar efficacy [61]. A randomized trial comparing the effect of combination therapies of glucocorticoids plus rituximab (375 mg/m 2 once weekly for 4 weeks) and glucocorticoids plus cyclophosphamide (2 mg/kg/day) also demonstrated comparable efficacy of rituximab for the remission induction in severe AAV, and rituximab showed a better effectiveness for recurrent disease, major renal disease, or alveolar hemorrhage [58]. For long-term remission, rituximab was compared to azathioprine maintenance (NCT00748644), and rituximab treatment showed significantly longer remission duration and improved overall survival [61].
For obtaining rapid hemostasis, coagulopathy should be closely monitored and quickly corrected. Commonly accepted targets are platelet counts more than 50,000/µL and a prothrombin time-international normalized ratio (PT-INR) less than 1.5. Depending on the causes, platelet transfusions, vitamin K supplementation, cryoprecipitates, and fresh frozen plasma should be supplemented. Besides, in order to stop the bleeding, various prothrombotic treatments including antifibrinolytics, particularly lysine analogues tranexamic acid (TXA) and epsilon aminocaproic acid (EACA), thrombin, and FVIIa have been used for DAH and reported with a variety of success rates. Mechanisms of the hemostatic agents are described in Figure 1.
Society for Apheresis recommend using plasmapheresis in AAV patients with DAH presenting with hypoxemic respiratory failure requiring either high-flow supplemental oxygen or mechanical ventilation [54]. Recently released data of randomized controlled trial of plasma exchange and glucocorticoids for treatment of AAV (NCT00987389) suggested that the use of plasmapheresis did not reduce the mortality or the incidence of ESRD [49].
Rituximab, a chimeric monoclonal antibody targeting CD20, has been used as another viable alternative. Antibody-mediated modification and/or depletion of ANCA producing CD20(+) plasma cells is a proposed mechanism for rituximab to decrease autoantibody production and to control disease activity [55,56]. Although most of the studies have been limited, they suggest that rituximab is an effective therapeutic option for DAH in connective tissue disease or autoimmune disorders. Rituximab on a compassionate use basis for patients with refractory AAV reported successful treatment outcomes [57][58][59][60]. These encouraging results led to randomized controlled trials evaluating the effect of rituximab as a remission induction therapy in patients with severe AAV (NCT00104299, NCT01731561). Comparison between rituximab and cyclophosphamide pulse therapy for AAV showed a similar efficacy [61]. A randomized trial comparing the effect of combination therapies of glucocorticoids plus rituximab (375 mg/m 2 once weekly for 4 weeks) and glucocorticoids plus cyclophosphamide (2 mg/kg/day) also demonstrated comparable efficacy of rituximab for the remission induction in severe AAV, and rituximab showed a better effectiveness for recurrent disease, major renal disease, or alveolar hemorrhage [58]. For long-term remission, rituximab was compared to azathioprine maintenance (NCT00748644), and rituximab treatment showed significantly longer remission duration and improved overall survival [61].
For obtaining rapid hemostasis, coagulopathy should be closely monitored and quickly corrected. Commonly accepted targets are platelet counts more than 50,000/μL and a prothrombin time-international normalized ratio (PT-INR) less than 1.5. Depending on the causes, platelet transfusions, vitamin K supplementation, cryoprecipitates, and fresh frozen plasma should be supplemented. Besides, in order to stop the bleeding, various prothrombotic treatments including antifibrinolytics, particularly lysine analogues tranexamic acid (TXA) and epsilon aminocaproic acid (EACA), thrombin, and FVIIa have been used for DAH and reported with a variety of success rates. Mechanisms of the hemostatic agents are described in Figure 1.  TXA prohibits conversion of plasminogen into plasmin inhibiting fibrinolysis and stabilizes blood clots [62]. In addition to intravenous use, intrapulmonary or aerosolized TXA has been used for DAH [63][64][65]. Nebulized TXA led to complete or near cessation of bleeding in 10/18 pediatric patients with DAH [65], and recently, Neil et al. published a successful treatment outcome in 19 pediatric patients with DAH: 18 out of 19 patients had stopped bleeding after TXA inhalation [64]. However, TXA therapy failed to show significant effect on reducing bleeding-associated mortality in patients with hematologic malignancies [66] but also increased risk of post-operative seizures [67] and showed limited efficacy on profound and recurrent bleedings [65]. EACA, another option for hemostatic treatment, is a lysine analog that binds competitively to plasminogen, blocking plasminogen from binding to fibrin and the subsequent conversion to plasmin, resulting in the inhibition of fibrin degradation (fibrinolysis) [68]. EACA has been used in addition to corticosteroids in patients with post-transplant DAH and reported to reduce 100-day mortality rate from 83% to 44% in patients treated with corticosteroids [69]. Though, a recent follow-up study reported that adjuvant treatment with EACA did not yield a significant difference in the outcomes of patients with DAH after HCT. The overall mortality on day 100 was still high at 85% [48].
In addition, the effects of thrombin or fibrinogen-thrombin for treatment of severe hemoptysis have also been reported [70,71]. Recently, Lee et al. published the efficacy of intrapulmonary thrombin treatment for DAH in patients with hematologic malignancies. Intrapulmonary thrombin stopped bleedings rapidly in 13 of 15 patients' refractory to corticosteroids with TXA treatment and significantly improved oxygenation status without thromboembolic complications [72]. Thrombin production is the final coagulation step required to convert fibrinogen to fibrin which produces a hemostatic lattice for platelet aggregation and thrombus formation at the site of injury [73]. Besides the coagulation cascade, thrombin causes vasoconstriction at the smooth muscle cell level and promotes platelet aggregation at the site of the thrombus [74].

Recombinant FVIIa Treatment for DAH
Recombinant FVIIa (FVIIa) is also used as an alternative 'broad spectrum hemostatic agent' to enhance hemostasis in patients with life-threatening intractable bleeding. Given that tissue factor (TF) pathway inhibitors (TFPI) increased in inflamed alveoli and these TFPIs prevent FVIIa-TF formation and FX activation, the inflamed lungs are more susceptible to bleeding [75]. FVIIa can overcome the effect of TFPI and restore thrombin generation. It promotes hemostasis via both a TF-dependent pathway at the sites of endothelial injury and a TF-independent pathway which directly activate factors IX and X on the surface of activated platelets in the absence of TF (Figure 1). Factor X converts prothrombin to thrombin, which in turn converts fibrinogen to fibrin. Alveolar TF remains high in inflammatory pulmonary conditions, including DAH, acute respiratory distress syndrome (ARDS), and pneumonia, as well as after lipopolysaccharide local challenge in the alveoli [5,[76][77][78]. Alveolar TF-FVIIa complex activates coagulation factors IX and X, which in turn initiates a cascade of reactions, leading to thrombin burst and fibrin formation at the site of injury [5]. However, due to the separation between the alveolar and systemic compartments of the lung, FVIIa, similarly to most biologics, requires a high systemic concentration to affect specific receptors in the alveolar compartment. This requires higher and repeated doses of intravenous FVIIa, associated with a higher risk of thromboembolic complications [7,79,80]. On the other hand, intrapulmonary locally administered FVIIa has been reported to have successful outcomes with a relatively small dose (50 µg/kg) and less frequent administration [5,81,82]. Intrapulmonary (ip) administration can ensure that FVIIa reaches its alveolar receptor, TF, and it decreases systemic adverse effects because the alveolocapillary membrane does not allow the transmembranous passage of FVIIa. Pulmonary-administered FVIIa combines with TF and forms TF-FVIIa complex which activates coagulation factor IX and X, inducing balanced hemostasis. With relatively small doses, FVIIa results in both durable hemostasis and a significant improvement in oxygen transport capacity [7]. Moreover, TFPIs produced by alveolar macrophages are highly expressed in the airspace in inflammatory conditions secondary to acute lung injury and contribute to the balanced hemostasis without the theoretical risk of intra-alveolar thrombotic complications with intrapulmonary FVIIa [7,83,84]. Accordingly, treatment with FVIIa has a potentially high benefit-to-risk ratio in DAH when administered via the local intrapulmonary route.
Case reports and clinical studies have reported the effectiveness of FVIIa in various conditions, including thrombocytopenia, functional platelet defects, hemorrhagic complications after HCT (e.g., DAH and hemorrhagic cystitis), gunshot wounds, and coagulopathy of liver failure [85][86][87][88][89][90][91][92]. However, the efficacy and side effects of FVIIa in non-hemophiliac settings are largely anecdotal, and many questions still remain regarding the appropriate indications and guidelines for use, risks of thrombotic complications, monitoring, dosing, and integration with transfusion therapy. A Cochrane review of the off-label use of FVIIa reported that FVIIa did not have a significant mortality benefit over placebo but showed a trend toward control of bleeding, a lower number of transfusions, and arterial thromboembolic events [93].
There is growing literature supporting the use of FVIIa to stop acute pulmonary hemorrhage following various diseases and injuries, including pneumonia, HCT, metastatic cancer, idiopathic pulmonary hemosiderosis (IPH), and immune-associated vasculitis. Due to lack of randomized controlled studies, FVIIa has been used as a final effort to stop the bleeding, and many studies have reported the successful use of FVIIa for lifethreatening DAH [5,81,82,94,95]. Although the optimal dose and dosing intervals remain to be determined, systemic administration usually entails the intravenous administration of 35-200 µg/kg as either a single dose or repeated doses every 2-4 h [4,6,95,96], and intrapulmonary therapy typically involves bronchoscopy with a total dose of 50-90 µg/kg of FVIIa diluted in normal saline as either a single dose or, if bleeding continues, as repeated doses over 24 h [7,81,97,98]. The FVIIa treatment for pulmonary hemorrhage in adults is listed in Table 2. Twenty-nine in 111 cases were related to immune disorders, and the remaining 82 cases were non-immune-related DAH where hematopoietic stem cell transplant (HCT)-related DAH showed a majority (75%, 62 cases). While the mortality of immune-mediated DAH was 25% (7 in 28 patients), that of non-immune-mediated DAH showed a higher mortality rate, 47% (27 in 58 patients: the outcome for the other 24 patients was not specified). Although the mean dose of FVIIa for iv injection was 427 µg/kg/episode for immune-related DAH and 167 µg/kg/episode for non-immunerelated DAH, most of the fatality cases were not directly related to DAH, and the complete response rate was similar in both groups; 19 in 21 patients and 23 in 23 patients. For iv use, approximately 250 µg/kg/episode of FVIIa was administered, while, 50µg/kg/episode of FVIIa was used for ip administration. The response rate did not differ by the administration route or administered dose: 42 in 44 patients with iv FVIIa and 19 in 21 patients with ip FVIIa showed complete response.

Recombinant FVIIa Treatment for DAH in Children
The off-label use of FVIIa in pediatric patients has also been expanding despite the absence of adequate studies addressing safety and efficacy. According to a multi-center cohort study, 83% of FVIIa use was off-label, and the off-label use of FVIIa increased 10-fold between 2000 and 2007 [114]. The Haemostasis Registry reported the results of the off-label use of FVIIa in 388 children [115]. The median age was 12 months, and the medians of the first dose and total dose were 114 µg/kg and 1.2 mg, respectively. They observed a reduction in the number of transfusions after the use of FVIIa (p < 0.01) and a subjective response rate of 82%; thromboembolic complications were reported in 5.4% to 10.9% of the patients, which were similar to the published incidence in adults [79,116,117]. These results suggest that FVIIa is an effective hemostatic agent in severely ill pediatric patients experiencing life-threatening hemorrhage, and FVIIa can reduce blood product requirements [2,115,118]. However, its benefit for neonates and infants less than 1 year of age remains unclear. Young et al reported that neonates had a lower response rate of 47% and a higher risk of thrombosis (17.6%) than older aged groups (more than 1 month) [118]. The SeveNBleeP registry, a web-based registry of FVIIa use in non-hemophiliac pediatric patients including 42 infants less than 1 year reported that there was no significant reduction in requirements for blood products after FVIIa treatment and no significant increase in thromboembolic complication (2.4%) [2]. The FVIIa has a shorter half-life and more rapid clearance in children compared with adults; therefore, higher and more frequent doses of FVIIa are often required to control significant bleeding in children, especially in neonates and infants [2,115,118]. Considering the relatively poor results of FVIIa and the low levels of natural anticoagulants (proteins C and S and antithrombin-III), the risk of thromboembolic complication can increase in neonates and infants, and the risk-to-benefit ratio can be higher, requiring careful decision.
Many causes such as perinatal asphyxia, very low birth weight (VLBW), mechanical ventilation, respiratory distress syndrome (RDS), exogenous surfactant therapy, sepsis, hypothermia, patent ductus arteriosus, and coagulopathies can trigger pulmonary hemorrhage in pediatric patients including neonates [3,119]. The FVIIa treatment for pulmonary hemorrhage in pediatric patients is listed in Table 3. Data on 45 children are available, the majority were classified as non-immune related DAH, and only 3 cases were immune related DAH. Among 33 pediatric cases with past history information, 16 cases were associated with hematologic malignancies, 5 cases were associated with HCT, 4 cases were preterm, and 5 cases were related to cardiovascular disease. The overall mortality was 30% (10 of 33 cases with detailed information), and the pediatric patients with hematologic malignancies showed a high mortality (9 in 16 patients, 56%). Complete response after treatment of FVIIa was observed in 64.4%, and a partial response (bleeding improved but not ceased) was in 24.4%, with 11.1% having no response to treatment. Two thromboembolic complications were reported (4.4%) [118,120]. Among 45 cases, 29 patients received iv rFVIIa and 16 patients received ip rFVIIa treatment. The mean dose of rFVIIa was 400 µg/kg per episode (range, 60-3150 µg/kg) for iv treatment and 46 µg/kg per episode for ip treatment, respectively. However, the outcome for ip rFVIIa was not inferred to iv rFVIIa: among 29 patients who received iv rFVIIa, 15 achieved complete response, 9 showed partial response, and 5 had no response (82% of response rate); among patients who received ip rFVIIa, 14 had complete response and 2 had partial response (100% of response rate). The patients who received iv FVIIa required multiple doses to achieve satisfactory hemostasis. Although these data cannot represent the effect of FVIIa for DAH in pediatrics, iv FVIIa appears to be less effective for DAH than other life-threatening bleedings [95,118]. Due to pharmacokinetic characteristics of children, higher and multiple doses of FVIIa may be needed. On the other hand, the patients treated with ip FVIIa showed a significant improvement in their oxygenation capacities (PaO2/FiO2 ratio) on subsequent days after FVIIa treatment [89,99], and one child experienced thrombotic obstruction in his endotracheal tube (ETT); there was no evidence of intra-alveolar thrombotic deposition (hyaline membrane formation) [120]. We experienced successful immediate hemostasis after treatment of ip FVIIa in pediatric patients with refractory severe DAH which did not respond to other treatments including TXA, high-dose corticosteroids, rituximab, and multiple transfusions [89]. These data showed that pulmonary hemostasis can be induced more easily from the alveolar side than from the endothelial side with reduced systemic risk of complication, suggesting intrapulmonary administration of FVIIa as an effective strategy for DAH in children as well as in adults.

Conclusions
DAH should be suspected in any patient with alveolar infiltrates on chest radiographs, hypoxemia, anemia, and hemoptysis. DAH is a clinical syndrome that can be a manifestation of multiple different etiologies, and identifying the underlying etiology is important to determine treatment strategy. In life-threatening DAH, rapid and effective hemostasis along with the appropriate treatment for the underlying disease contributes to patient survival. Considering the substantial risk of thromboembolic complications with the use of a large amount of FVIIa, intrapulmonary administration of relatively small-dosed FVIIa could be an effective and reasonable treatment option for DAH in pediatric patients as well as in adults, requiring a prospective or randomized trial to verify the effect and standardize the FVIIa treatment. However, most importantly, many studies including our case series have suggested that instant hemostasis alone cannot ensure successful treatment outcome without successful treatment of primary disease or inflammation. We have experienced a refractory hemophagocytic lymphohistiocytosis (HLH) pediatric case presented with severe DAH (unpublished data). Although immediate and near complete hemostasis was achieved after intrapulmonary FVIIa instillations, the patients experienced multiple episodes of profound DAH and expired with sepsis and multiorgan failure, strongly implicating the importance of a multidisciplinary treatment approach for a successful outcome.