Pathophysiology:

The outer pericardium is made of fibrous tissue which does not easily stretch, and so once fluid begins to enter the pericardial space, pressure starts to increase.

If fluid continues to accumulate, then with each successive diastolic period, less and less blood enters the ventricles, as the increasing pressure presses on the heart and forces the septum to bend into the left ventricle, leading to decreased stroke volume. This causes obstructive shock to develop, and if left untreated then cardiac arrest may occur (in which case the presenting rhythm is likely to be pulseless electrical activity).

Diagnosis:

Initial diagnosis can be challenging, as there are a number of differential diagnoses, including tension pneumothorax, and acute heart failure.[citation needed] In a trauma patient presenting with PEA in the absence of hypovolemia and tension pneumothorax, the most likely diagnosis is cardiac tamponade.

Classical cardiac tamponade presents three signs, known as Beck's triad. Hypotension occurs because of decreased stroke volume, jugular-venous distension due to impaired venous return to the heart, and muffled heart sounds due to fluid inside the pericardium.

Other signs of tamponade include pulsus paradoxus (a drop of at least 10mmHg in arterial blood pressure on inspiration), and ST segment changes on the electrocardiogram, which may also show low voltage QRS complexes, as well as general signs & symptoms of shock (such as tachycardia, breathlessness and decreasing level of consciousness).
Tamponade can often be diagnosed radiographically, if time allows. Echocardiography often demonstrates an enlarged pericardium or collapsed ventricles, and a chest x-ray of a large cardiac tamponade will show a large, globular heart.

Treatment-Pre-hospital care:

Initial treatment given will usually be supportive in nature, for example administration of oxygen, and monitoring. There is little care that can be provided pre-hospital other than general treatment for shock. A number of the Helicopter Emergency Medical Services (HEMS) in the UK, which have doctor/paramedic teams, have performed an emergency thoracotomy to release clotting in the pericardium caused by a penetrating chest injury.
Prompt diagnosis and treatment is the key to survival with tamponade. Some pre-hospital providers will have facilities to provide pericardiocentesis, which can be life-saving. If the patient has already suffered a cardiac arrest, pericardiocentesis alone cannot ensure survival, and so rapid evacuation to a hospital is usually the more appropriate course of action.

Hospital management:

Initial management in hospital is by pericardiocentesis.[3] This involves the insertion of a needle through the skin and into the pericardium and through the fifth intercostal space, and aspirating fluid. Often, a cannula is left in place during resuscitation following initial drainage so that the procedure can be performed again if the need arises. If facilities are available, an emergency pericardial window may be performed instead,[3] during which the pericardium is cut open to allow fluid to drain. Following stabilization of the patient, surgery is provided to seal the source of the bleed and mend the pericardium.