Affectionately known by its acronym PE in medical circles, pulmonary embolus is when a blood clot, usually (but not exclusively) from a deep venous thrombosis in the legs breaks off and courses through the bloodstream to the right side of the heart and then on to the lungs, eventually getting wedged in one of the branches of the pulmonary arteries and blocking off perfusion to part of the lung.

Thrombus forms in veins due to several factors, as stated in Virchow's triad. Stasis of blood flow caused by immobility would probably be the most common cause of DVTs. Long periods of post-operative bed rest, lying in bed because of some disability or even sitting still in a aeroplane economy class seat for many hours can lead to DVTs forming. The other major risk factor for a DVT is having blood that is more coagulopathic than others. This can result from being genetically predisposed to it or from the effect of some drugs or from having some sorts of cancers.

Large PEs can result in nearly instantaneous death, if the dislodged embolus is large enough to obstruct the entire outflow of the right side of the heart. This results, of course, in blood not flowing anywhere else in the body because one end of the double circulatory system is completely blocked.

Features of smaller PEs include: chest pain which is usually of sudden onset and pleuritic (worse on inspiration) in nature, shortness of breath, haemoptysis (coughing up blood) and tachycardia in sinus rhythm (a quickened pulse which is of regular rhythm). Associated features would include pain and/or swelling in the calves or thighs where the deep venous thrombosis may have developed.

Tests that should be performed include ECGs (electrocardiograms), ABGs (arterial blood gases) and a CXR (chest X-ray). There may be evidence of right heart strain on the ECG. The ABGs should show a lowered pO2 (partial pressure of oxygen in the arterial blood), indicating that the lungs are not providing as much oxygen as they should to the body.

In the management of someone with suspected PE, the firstline treatment is to administer supplemental oxygen. If the index of suspicion is relatively high and there are no contraindications to it, the patient should be heparinised to reduce the risk of further clots forming, dislodging and getting stuck in pulmonary vessels. A V/Q scan (ventilation/perfusion) should be done to identify if there is a defect in perfusion in the lungs resulting in a ventilation perfusion mismatch. Venous doppler ultrasound studies of the legs can be carried out to look for existing DVTs.


More to come later.

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