In case of an acute pulmonary embolism, the clot must first be dissolved. In order not to aggravate the symptoms, patients are positioned in a sitting position and supplied with oxygen via a nasal probe. In addition, the patients are sedated and the pain is treated by morphine administration.
To dissolve the embolus, 5,000 to 10,000 units of heparin are administered intravenously. Injections into the muscle must be avoided at all costs. In case of circulatory arrest due to a grade 4 pulmonary embolism, cardiopulmonary resuscitation with cardiac massage and intubation must be initiated immediately.
The specific therapy of clot dissolution offers various possibilities. In stages 1 and 2 of embolism, the embolus is treated with heparin. Heparin activates the inhibiting factors of clot formation present in the body and potentiates their effect.
Heparin is therefore the prophylactic agent of choice, provided that there are no contraindications. In addition, the lung itself has spontaneous fibrinolytic activity, and can therefore dissolve the embolus itself within days to weeks. In stage 3 and 4 of pulmonary embolism, fibrinolytic therapy is used.
In this therapy, streptokinase is used to activate the body’s own plasmin. This serves to dissolve clots and can thus dissolve both the embolus and the original thrombus, for example in the leg veins. In addition to these drug-based methods of clot dissolution, surgical or mechanical interventions can also be used.
Indications for invasive clot dissolution are mainly contraindications for fibrinolysis. These include in particular In stage 3 or 4 of an embolism, when there is a contraindication to fibrinolysis, the embolus can be removed using a catheter via the right heart. Pulmonary embolectomy is the last option to resolve an embolism.
In this procedure, patients are connected to a heart–lung machine and the affected arteries are opened under visual control. This allows the embolus to be sucked out of the artery. However, since this procedure is associated with a lethality rate of 25%, this measure is only taken if the other therapy attempts have failed.
- Previous major surgery in the past 3 weeks,
- A previous stroke of unknown cause,
- Known bleeding tendencies and
- Bleeding of the gastrointestinal tract in recent months.
Heparin is the lead substance of non-oral anticoagulants, which means that this substance must be injected for administration. There are a number of different heparins that differ in their chemical structure and can therefore have different lengths of action, application routes and side effects. The main mechanism of action is the same for all heparins, namely the inhibition of various stages of the body’s own blood coagulation.
A rare but important side effect, especially of unfractionated heparins, is heparin-induced thrombocytopenia (HIT). This can lead to antibody formation, which can result in a massive drop in platelets. It is therefore important to regularly monitor blood levels when administering heparins in order to be able to detect and prevent further, sometimes serious, complications at an early stage.
In the context of a pulmonary embolism, high doses of unfractionated heparin are usually used at first, which must be administered intravenously via an infusion. Subsequently, the therapy can be switched to low-molecular-weight heparin. This is injected subcutaneously, i.e. under the skin, and is dosed differently depending on body weight and kidney function.
Depending on the extent to which pulmonary vessels are displaced by the thrombus in pulmonary embolism, the clinical picture may vary. If it is a comparatively large thrombus (blood clot) that blocks large parts of the pulmonary circulation, pulmonary embolism can under certain circumstances lead to the need for resuscitation. In such a case, acute right heart strain usually occurs, since the blood accumulates in front of the thrombus and the cardiac output can no longer compensate sufficiently.
This is known as hemodynamic instability, which in addition to the need for resuscitation is an indication for lysis therapy. A substance called alteplase is usually used for this purpose, which acts as a tissue plasminogen activator. The tissue plasminogen is a molecule produced naturally in the body that helps to dissolve thrombi.
This process is called fibrinolysis.In the context of lysis therapy, this is therefore imitated pharmaceutically in order to expose the blocked vessel to the blood stream again as far as possible. At the same time, anticoagulation (inhibition of blood clotting) with heparin should be carried out to prevent the formation of a new thrombus. Lysis therapy is always associated with an increased risk of bleeding, which is why it should only be carried out under inpatient conditions.
Furthermore, there are a number of contraindications for lysis therapy. However, as soon as resuscitation is required, these are no longer valid, as the patient is in acute danger of death in such a case. A surgical intervention in the context of a pulmonary embolism is rarely performed and is usually the last therapeutic option.
Only when other therapeutic measures such as lysis, anticoagulation and resuscitation fail can surgery be considered. This in turn is associated with a high risk of further complications and usually requires a good previous general condition of the patient. In order to be able to remove the thrombus surgically, the cardiopulmonary circulation must be temporarily removed from the body and taken over by a heart-lung machine. During this time, the surgeon can then attempt to remove the thrombus either mechanically using a catheter or by local lysis.