Patients who suffer pulmonary embolism due to small or mid-sized emboli are usually asymptomatic. In general, there is no typical presentation of pulmonary embolism and the clinical picture depends of each separate case.

As a comprehensive guiding system, respiratory abnormalities are most often observed. Pleuritic chest pain occurs in almost all the patients and is often accompanied by pleural rub. These findings indicate that the embolus is located in the pulmonary periphery. Tachypnea, cough and dyspneic symptoms are also often observed, alongside hemoptysis, which is a rather uncommon finding. Hypotension, dilated neck veins and a second heart sound may indicate the presence of pulmonary hypertension secondary to embolism, and crackles may be heard during auscultation. If a patient presents with a cyanotic appearance, it is most likely due to a massive lung infarction.

In addition, patients who also suffer from sickle cell disease may manifest symptoms of pulmonary embolism, alongside symptoms that result from their existing condition, such as anemia, stroke and a sequestration crisis.

Symptoms from the cardiovascular system that may accompany pulmonary embolism include galloping rhythm, murmurs and peripheral edema.

Diagnosis of pulmonary embolism and infarction depend upon laboratory tests and imaging studies.

As far as the laboratory tests are concerned, the following procedures may be carried out:

• Arterial or capillary blood gas: may be normal, but the alveolar/arterial O2 ration can be increased.
• D-dimer levels
• Complete blood count: elevated white blood cells and diminished hematocrit in sickle cell disease patients.

Imaging studies can also be performed in patients suspected of pulmonary embolism and infarction. These include the following:

• Chest radiograph: an x-ray of the chest can be obtained, which will show defects in most of the patients. However, no pathognomonic finding can be established with the use of an x-ray; it is primarily conducted in order to eliminate other conditions.
• Ventilation/Perfusion scan (V/Q): it is a very useful test for the detection of pulmonary embolism. A positive result will illustrate a section of the lung that is ventilated and hypoperfused. The V/Q scan will detect cases of pulmonary embolism, except for the clinically unimportant cases.
• Computerized tomography (CT) and CT angiography: a CT angiography is used as the first step towards the evaluation of a possible pulmonary embolism.
• DVT radiologic confirmation, carried out to confirm a possible deep vein thrombosis case.
• Echocardiography: it can evaluate the pressure in the pulmonary artery and detect embolism-associated cardiac complications.

Pulmonary embolism should be treated as a medical emergency. Therapy should be directed towards preventing the formation of further clots with anticoagulants, supporting the cardiovascular and pulmonary system and, if the need arises, performing thrombolysis. Surgical treatment is also an option that can be considered.

Anticoagulation
The formation of clots should be prevented with the use of anticoagulants. Heparin is administered, usually unfractionated or low molecular weight heparin (LMWH), for up to 10 days. It is important to check the coagulation ability of the blood, in order to avoid potential hemorrhagic events due to the administration of anticoagulants. If a patient receives LMWH, their anti-factor Xa levels should be maintained within 0.5-1 U/mL; if unfractionated heparin is administered, the levels of activated partial thromboplastin time (aPTT) should amount to 2 times the control value.

Thrombolytic therapy
Thrombolysis is reserved for patients with massive embolism. The procedure should be performed by facilities with experience in thrombolysis, as the therapy is associated with an increased risk of hemorrhage.

Further support
The cardiovascular and pulmonary system should receive adequate functional support until the patient starts to recover. Dobutamine or dopamine are used, since their positive inotropic action helps the heart to maintain its functionality. Ventilation may be supported mechanically.

After a patient is discharged from the hospital, they frequently follow a therapeutic scheme with warfarin. Warfarin can interact with many other drugs and the patients should be adequately informed about this possibility upon discharge.

Surgical treatment
Surgical intervention is generally not viewed as a first-line treatment in cases of pulmonary embolism. Embolectomy, namely the surgical removal of the emboli, is an option in cases where thrombolytic or anticoagulation therapy cannot be performed due to a high risk of hemorrhagic events, or when the condition requires extremely immediate treatment. In patients who are expected to suffer from recurrent embolism, primarily due to DVT, vena cava filters are used, which collect the emboli that are transferred to the lungs from the feet before they reach the lung arterial network.

Prognosis depends upon early and correct diagnosis of pulmonary infarction, proper treatment in the hospital, comorbidities and the patient's adherence to the therapeutic scheme upon their discharge. The patients who have overcome the initial phase immediately after the embolism has occurred run a smaller risk of complications or recurrence.

Pulmonary infarction requires the presence of emboli or thrombi is order to arise. Patients who have an underlying condition predisposing them to the formation of blood clots, primarily deep vein thrombosis (DVT), can also develop lung infarction.

The general categories which illustrate the pathologies leading to pulmonary necrosis are described by Virchow's triad and include:

• Diminished blood flow (stasis), due to lack of mobility
• Hypercoagulability
• Massive traumatization of vascular walls

Keeping these general rules in mind, we can outline the following conditions as possible etiologic factors for the occurrence of pulmonary infarction:

Cardiac causes: Dilated cardiomyopathy has been associated with the formation of thrombi, which are transferred to the lungs via circulation, causing arterial occlusion.

Surgical causes: Mostly major surgical procedures (orthopedic, heart surgery) involve a considerable risk of developing DVT, pulmonary embolism and, ultimately, lung infarction, if the patient is prophylactically not treated with anticoagulation drugs.

Venous catheters (central): Studies have shown that as many as 21% of pediatric patients and 35% of adult patients presenting with emboli in the lungs or deep vein thrombosis had central venous catheters for other causes [1] [2]. Thrombi are usually formed at the region where the catheter adheres to the vascular wall, due to the catheters being used for long periods of time.

Traumatization: May be associated with surgical procedures performed on trauma patients or prolonged immobility.

Sickle cell disease: Frequent chest infections in sickle cell disease patients often present with low O2 in the blood, dehydration and fever. Blood is sludged in the pulmonary arteries and the patient runs a high risk of thrombus formation. Other than that, bone marrow infarction, which can be observed in this condition, can lead to the release of fat emboli, which function exactly like a thrombus, causing lung infarction [3].

Malignancy: Pulmonary embolism and subsequent infarction has been observed in patients with leukemia, lymphoma and various other types of tumors, irrespective of the use of a central venous catheter [4].

Dehydration: Particularly hyperosmolar dehydration has been incriminated for the formation of thrombi in children during infancy.

Hyperalimentation: Hyperalimentation is the process of receiving an excessive amount of nutritional elements through parenteral feeding. It has been incriminated for the production of clots in pediatric patients who are treated with parenteral nutrition for a long time.

Coagulation disorders: Conditions such as deficiency of protein S or C and antithrombin III deficiency [1].

In the light of the aforementioned causes, it must be stressed that the most important risk factors for the development of pulmonary embolism include pregnancy, smoking and contraceptive pills.

Pulmonary embolism is generally seldom observed in pediatric patients; its slightly increased frequency in developed countries during the recent years is attributable to the wider use of central venous catheters for various causes, in comparison to the past [5]. It has been estimated that approximately 1/3 of pediatric patients admitted with pulmonary embolism will eventually succumb to the infarction of the lung [6], although it is not generally accepted worldwide, as other studies calculate the percentage as amounting to a mere 5% of children [7]. It is generally accepted that cases of massive embolism are the most severe occurrences and children run a higher risk of dying when they suffer from a massive embolism [8].

Adults who present with pulmonary embolism run the highest risk of death in the first stages after the occurrence; should they recover from the initial period, they are expected to fully recover. Treatment complications may include pulmonary hypertension, ventricular failure (right) and medication side-effects [9] [10]. Complications that arise as a direct result of the pulmonary embolism include immediate death, hemorrhagic occurrences and thrombocytopenia.

In healthy individuals, the lungs are not particularly susceptible to infarction, due to the fact that their perfusion is derived from two separate systems, the pulmonary and bronchial vascular system; in this way, thrombi can access the pulmonary parenchyma via two different routes, thus making it more likely for them to be transferred to the arteries responsible for providing lung blood flow.

The bronchial vascular system provides most of the oxygen required for normal pulmonary function and are anastomosed with the pulmonary vascular system at multiple locations. The latter receive blood from the right ventricle and direct it to the alveolar system.

Emboli formed at any of the locations adjacent to the vasculature supplying the lung with blood can be carried to the organ and cause an arterial occlusion, which can result to a pulmonary infarction.

Prevention simply relies upon the treatment of the conditions that can cause pulmonary embolism and the proper patient information on risk factors.

Anticoagulation therapy should be administered to patients prior and after a major surgical procedure, patients with DVT or coagulation disorders should be appropriately treated and monitored and pregnant women should be informed of the risk to develop pulmonary embolism. Patients who smoke and women who use contraceptive pills should also be informed about a higher-than-normal risk of developing pulmonary embolism.

Pulmonary infarction is the necrosis of a part of the lung, arising as a result of diminished perfusion of the part in question. The necrotic pulmonary part is termed an infarct. Lung infarction is a direct result of embolism, namely blood clots or air bubbles that have traveled to the pulmonary arteries from a distant location such as the heart, or of thrombus formation, a process which involves the formation of blood clots in the location where has occurred the occlusion itself. Under normal circumstances, collateral circulation is formed when an arterial occlusion is present, in order to redirect the blood to the lung and avoid tissue necrosis. In cases of diseased lungs, an infarction results from a blockage in one of its arteries and a failure to re-route the blood volume through new channels.

Pulmonary infarction is the death of a part of the lung, which is caused when the blood that reaches the part concerned is not enough to keep it functional.
A pulmonary infarction is caused when a substance is blocking the arteries that supply blood to the lung: emboli are blood clots that were produced in another location and were transferred to the lung via circulation, and thrombi are blood clots that were formed in some part of a pulmonary artery. Both emboli and thrombi can block the blood flow to the lung and cause infarction.

Signs and Symptoms

• Difficulty to breathe
• Rapid breathing
• Chest pain
• Cough, possibly with blood
• Fever
• Sweating

Pulmonary infarction is usually due to embolism and requires emergency treatment. The medical team initially administers anticoagulants, to stop another thrombus or embolus from forming. Since these medications can cause excessive bleeding, they will need to monitor various values to make sure that this will not happen. Thrombolytic medications are very aggressive drugs used to dissolve the clots that have formed. They are used less than anticoagulants. A patient may receive further drugs to help their lungs and heart function adequately, until pulmonary embolism has been treated. Patients who cannot receive drugs because of another condition which prohibits their use may undergo surgery to excise the thrombi from the arteries.

1. David M, Andrew M. Venous thromboembolic complications in children. J Pediatr. 1993 Sep; 123(3):337-46.
2. Biss TT, Brandao LR, Kahr WH, Chan AK, Williams S. Clinical features and outcome of pulmonary embolism in children. Br J Haematol. 2008 Sep;142(5):808-18.
3. Vichinsky EP, Neumayr LD, Earles AN, et al. Causes and outcomes of the acute chest syndrome in sickle cell disease. National Acute Chest Syndrome Study Group. N Engl J Med. 2000 Jun 22; 342(25):1855-65.
4. van den Heuvel-Eibrink MM, Lankhorst B, Egeler RM, Corel LJ, Kollen WJ. Sudden death due to pulmonary embolism as presenting symptom of renal tumors. Pediatr Blood Cancer. 2008 May; 50(5):1062-4.
5. Van Ommen CH, Peters M. Acute pulmonary embolism in childhood. Thromb Res. 2006; 118(1):13-25.
6. Evans DA, Wilmott RW. Pulmonary embolism in children. Pediatr Clin North Am. 1994 Jun; 41(3):569-84.
7. Rajpurkar M, Warrier I, Chitlur M, et al. Pulmonary embolism-experience at a single children's hospital.Thromb Res. 2007; 119(6):699-703.
8. Baird JS, Killinger JS, Kalkbrenner KJ, Bye MR, Schleien CL. Massive pulmonary embolism in children. J Pediatr. 2010 Jan; 156(1):148-51. 
9. Babyn PS, Gahunia HK, Massicotte P. Pulmonary thromboembolism in children. Pediatr Radiol. 2005 Mar; 35(3):258-74. 
10. Cook A, Shackford S, Osler T, et al. Use of vena cava filters in pediatric trauma patients: data from the National Trauma Data Bank. J Trauma. 2005 Nov; 59(5):1114-20.