Which of the following is a cause of cardiogenic shock in a trauma patient?A. Hemothorax
In trauma patients the differential diagnosis of cardiogenic shock consists of a short list: (1) tension pneumothorax, (2) pericardia! tamponade, (3) myocardial contusion or infarction, and ( 4) air embolism. Tension pneumothorax is the most frequent cause of cardiac failure. Traumatic pericardia! tamponade is most often associated with penetrating injury to the heart. As blood leaks out of the injured heart, it accumulates in the pericardia! sac. Because the pericardium is not acutely distensible, the pressure in the pericardia! sac rises to match that of the injured chamber. Since this pressure is usually greater than that of the right atrium, right atrial filling is impaired and right ventricular preload is reduced. This leads to decreased right ventricular output and increased central venous pressure (CVP). Increased intrapericardial pressure also impedes myocardial blood flow, which leads to subendocardial ischemia and a further reduction in cardiac output. This vicious cycle may progress insidiously with injury of the vena cava or atria, or precipitously with injury of either ventricle. With acute tamponade, as little as 100 mL of blood within the pericardia! sac can produce life-threatening hemodynamic compromise. Patients usually present with a penetrating injury in proximity to the heart, and they are hypotensive and have distended neck veins or an elevated CVP. The classic findings of Beck's triad (hypotension, distended neck, and muffled heart sounds) and pulsus paradoxus are not reliable indicators of acute tamponade. Ultrasonography (US) in the emergency department (ED) using a subxiphoid or parasternal view is extremely helpful if the findings are clearly positive (Fig. below); however, equivocal findings are common. Early in the course of tamponade, blood pressure (BP) and cardiac output will transiently improve with fluid administration. This may lead the surgeon to question the diagnosis or be lulled into a false sense of security.
A. Ad mission chest fi lm may not show the fu ll extent of the patient's pulmonary parenchymal i njury. B. Th is patient's left pulmonary contusion blossomed 12 hours later, and its associated opacity is noted on repeat chest radiograph.