to the international normalized ratio, a test that determines the dose. in terms of injectable treatments, lmwh may reduce bleeding among people with pulmonary embolism as compared to ufh. according to the same review, lmwh reduced the incidence of recurrent thrombotic complications and reduced thrombus size when compared to heparin. there was no difference in overall mortality between participants treated with lmwh and those treated with unfractionated heparin. vitamin k antagonists require frequent dose adjustment and monitoring of the international normalized ratio (inr). in pe, inrs between 2.0 and 3.0 are generally considered ideal. if another episode of pe occurs under warfarin treatment, the inr window may be increased to e.g. 2.5–3.5 (unless there are contraindications) or anticoagulation may be changed to a different anticoagulant e.g. lmwh. in recent years, many anticoagulants have been introduced that offer similar to warfarin but without a need for titration to the inr. known as the directly acting oral anticoagulants, these treatments are now preferred over vitamin k antagonists by american professional guidelines. two of these (rivaroxaban and apixaban) do not require initial heparin or fondaparinux treatment, whereas dabigatran and edoxaban do. a cochrane review found that there is no evidence of a difference between oral dtis (dabigatran, rivaroxaban, edoxaban, apixaban) and standard anticoagulation in the prevention of recurrent pulmonary embolism. in people with cancer who develop pulmonary embolism, therapy with a course of lmwh is favored over warfarin or other oral anticoagulants. similarly, pregnant women are treated with low molecular weight heparin until after delivery to avoid the known teratogenic effects of warfarin, especially in the early stages of pregnancy, but it can be used while breastfeeding. anticoagulation therapy is usually continued for 3–6 months, or "lifelong" if there have been previous dvts or pes, or none of the usual transient risk factors is present. in those without a known cause that can be reversed 2 years of treatment may be better than 6 months. for those with small pes (known as subsegmental pes) the effects of anticoagulation is unknown as it has not been properly studied as of 2020. thrombolysis massive pe causing hemodynamic instability (shock and/or low blood pressure, defined as a systolic blood pressure <90 mmhg or a pressure drop of 40 mmhg for >15 min if not caused by new-onset arrhythmia, hypovolemia or sepsis) is an indication for thrombolysis, the enzymatic destruction of the clot with medication. in this situation, it is the best available treatment in those without contraindications and is supported by clinical guidelines. it is also recommended in those in cardiac arrest with a known pe. catheter-directed thrombolysis (cdt) is a new technique found to be relatively safe and effective for massive pes. this involves accessing the venous system by placing a catheter into a vein in the groin and guiding it through the veins by using fluoroscopic imaging until it is located next to the pe in the lung circulation. medication that breaks up blood clots is released through the catheter so that its highest concentration is directly next to the pulmonary embolus. cdt is performed by interventional radiologists or vascular surgeons, and in medical centers that offer cdt, it may be offered as a first-line treatment. catheter-based ultrasound-assisted thrombolysis is being investigated. the use of thrombolysis in non-massive pes is still debated. some have found that the treatment decreases the risk of death and increases the risk of bleeding including intracranial hemorrhage. others have found no decrease in the risk of death. inferior vena cava filter used inferior vena cava filter. there are two situations when an inferior vena cava filter is considered advantageous, and those are if anticoagulant therapy is contraindicated (e.g. shortly after a major operation), or a person has a pulmonary embolus in spite of being anticoagulated. in these instances, it may be implanted to prevent new or existing dvts from entering the pulmonary artery and combining with an existing blockage. in spite of the device's theoretical advantage of preventing pulmonary emboli, there is a lack of evidence supporting its effectiveness. inferior vena cava filters should be removed as soon as it becomes safe to start using anticoagulation. although modern filters are meant to be retrievable, complications may prevent some from being removed. the long-term safety profile of permanently leaving a filter inside the body is not known. surgery surgical management of acute pulmonary embolism (pulmonary thrombectomy) is uncommon and has largely been abandoned because of poor long-term outcomes. however, recently, it has gone through a resurgence with the revision of the surgical technique and is thought to benefit certain people. chronic pulmonary embolism leading to pulmonary hypertension (known as chronic thromboembolic hypertension) is treated with a surgical procedure known as a pulmonary thromboendarterectomy. epidemiology there are roughly 10 million cases of pulmonary embolisms per year. in the united states, pulmonary embolisms are the primary cause of at least 10,000 to 12,000 deaths per year and a contributing cause in at least 30,000 to 40,000 deaths per year. true incidence involving pulmonary embolisms is unknown because they often go undiagnosed or unnoticed until autopsy. from 1993 to 2012, there have been an increased number of admissions in hospitals due to pulmonary embolisms, jumping from 23 cases per 100,000 people to 65 cases per 100,000 people. despite this increase, there has been a decrease in mortality during that same time period due to medical advances that have occurred. venous thromboembolism (vte), a common risk factor, is present at much higher rates in those over the age of 70 (three times higher compared to those aged 45 to 69). this is likely due to there being a generally lower level of activity among the elderly, resulting in higher rates of immobility and obesity. vte has a large, and continuously rising, case fatality rate. this rate is roughly 10% after 30 days, 15% after three months and up to 20% after one year. pulmonary embolisms alone (when resulting in hospitalizations) have a case fatality rate of about 5% to 10% so vte can play a large factor in the severity of the embolisms. when looking at all cases, the rate of fatal pulmonary emboli has declined from 6% to 2% over the last 25 years in the united states. in europe, an average of approximately 40,000 deaths per year with pulmonary embolism as the primary cause were reported between 2013 and 2015, a conservative estimate because of potential underdiagnosis. prognosis large saddle embolus seen in the pulmonary artery (white arrows). fewer than 5 to 10% of symptomatic pes are fatal within the first hour of symptoms. there are several markers used for risk stratification and these are also independent predictors of adverse outcomes. these include hypotension, cardiogenic shock, syncope, evidence of right heart dysfunction, and elevated cardiac enzymes. some ecg changes including s1q3t3 also correlate with a worse short-term prognosis. there have been other patient-related factors such as copd and chronic heart failure thought to also play a role in prognosis. prognosis depends on the amount of lung that is affected and on the co-existence of other medical conditions; chronic embolisation to the lung can lead to pulmonary hypertension. after a massive pe, the embolus must be resolved somehow if the patient is to survive. in thrombotic pe, the blood clot may be broken down by fibrinolysis, or it may be organized and recanalized so that a new channel forms through the clot. blood flow is restored most rapidly in the first day or two after a pe. improvement slows thereafter and some deficits may be permanent. there is controversy over whether small subsegmental pes need treatment at all and some evidence exists that patients with subsegmental pes may do well without treatment. once anticoagulation is stopped, the risk of a fatal pulmonary embolism is 0.5% per year. mortality from untreated pes was said to be 26%. this figure comes from a trial published in 1960 by barrit and jordan, which compared anticoagulation against placebo for the management of pe. barritt and jordan performed their study in the bristol royal infirmary in 1957. this study is the only placebo-controlled trial ever to examine the place of anticoagulants in the treatment of pe, the results of which were so convincing that the trial has never been repeated as to do so would be considered unethical. that said, the reported mortality rate of 26% in the placebo group is probably an overstatement, given that the technology of the day may have detected only severe pes. predicting mortality the pesi and spesi (= simplified pulmonary embolism severity index) scoring tools can estimate mortality of patients. the geneva prediction rules and wells criteria are used to calculate a pre-test probability of patients to predict who has a pulmonary embolism. these scores are tools to be used with clinical judgment in deciding diagnostic testing and types of therapy. the pesi algorithm comprises 11 routinely available clinical variables. it puts the subjects into one of five classes (i–v), with 30-day mortality ranging from 1.1% to 24.5%. those in classes i and ii are low-risk and those in classes iii–v are high-risk.