(See also Overview of Thoracic Trauma.)
Fluid in the pericardial sac can impair cardiac filling, leading to low cardiac output and sometimes shock and death. If fluid accumulates slowly (eg, due to chronic inflammation), the pericardium can stretch to accommodate up to 1 to 1.5 L of fluid before cardiac output is compromised. However, with rapid fluid accumulation, as occurs with traumatic hemorrhage, as little as 150 mL may cause tamponade.
In trauma, the cause is more often a penetrating rather than blunt mechanism. The wound is often medial to the nipples (for anterior wounds) or the scapulae (for posterior wounds). Tamponade due to blunt trauma involves cardiac chamber rupture, which is typically fatal before patients can be brought for treatment.
Classically, patients have Beck's triad, which consists of the following:
However, hypotension has multiple potential causes in trauma patients, muffled heart tones can be difficult to assess during a noisy trauma resuscitation, and neck vein distention can be absent due to hypovolemia. Pulsus paradoxus, a decrease in systolic blood pressure during inspiration of > 10 mm Hg, is also suggestive, but again not easy to assess in a noisy setting.
Diagnosis can be difficult. Beck's triad is considered diagnostic but may not be present or easy to recognize. In addition, tension pneumothorax also should be considered in patients with hypotension and neck vein distention, although this disorder typically causes markedly decreased breath sounds and hyperresonance on the affected hemithorax. Bedside transthoracic echocardiography can be diagnostic and can be done during the initial evaluation and resuscitation but may be falsely negative. The diagnosis sometimes is suggested by unexplained failure to respond to volume resuscitation.
Subxiphoid pericardiocentesis is done in unstable patients when cardiac tamponade is suspected. Electrocardiographic monitoring during the insertion needle for ST segment elevation (indicating contact with the epicardium and the need to withdraw the needle) is done if possible. Pericardiocentesis is a temporizing measure. Removal of as little as 10 mL of blood may normalize blood pressure. However, failure to aspirate blood does not exclude the diagnosis; fresh blood in the pericardium is often clotted.
Thoracotomy with pericardiotomy or establishment of a subxiphoid pericardial window are more definitive treatments, which are indicated in patients in whom the diagnosis is confirmed or strongly suspected. If adequately trained personnel are available and the patient is unstable and fails to respond to other resuscitative measures, one of these procedures can be done at the bedside in the emergency setting. Otherwise, the procedure is done in the operating room as soon as feasible.
Cardiac tamponade is most often caused by a penetrating wound medial to the nipples (for anterior wounds) or the scapulae (for posterior wounds).
The triad of muffled heart tones, hypotension, and neck vein distention is diagnostic but not always present; in their absence, bedside echocardiography should be done if the diagnosis is suspected.
Subxiphoid pericardiocentesis is a temporizing measure and may be falsely negative; a pericardial window or pericardiotomy is more definitive.