Left-sided tension pneumothorax. Note the area without lung markings which is air in the pleural space. Also note the tracheal and mediastinal shift from the patient's left to right. Causes include any obstruction of blood flow to and from the heart. There are multiple, including pulmonary embolism, cardiac tamponade, and tension pneumothorax. Other causes include abdominal compartment syndrome, severe aortic valve stenosis, and disorders of the aorta. Constrictive pericarditis is a rare cause. Masses can grow to press on major blood vessels causing shock. Tension pneumothorax A pneumothorax occurs when air collects in the pleural space around the lungs. Normally, this space has negative pressure to allow the lung to fill. Pressure increases as more air enters this space. The lung collapses, impairing normal breathing. Surrounding structures may also shift. When severe enough to cause these shifts and hypotension, it is called a tension pneumothorax. This is life-threatening. The veins supplying the heart are compressed. Thus, venous return is decreased. With the heart unable to fill, cardiac output drops. Hypotension and shock ensue. If not rapidly treated, it can lead to cardiac arrest and death. Pulmonary embolism "Saddle" embolism on CT. The filling defect in the pulmonary artery is the clot. A pulmonary embolism (PE) is an obstruction of the pulmonary arteries. Deaths from PE have been estimated at ~100,000 per year in the United States. However, this may be higher in recent years. Most often, the obstruction is a blood clot that traveled from elsewhere in the body. Most commonly, this is from a deep vein thrombosis (DVT) in the legs or pelvis. Risk factors are conditions that increase the risk of clotting. This includes genetic (factor V Leiden) and acquired conditions (cancer). Trauma, surgery, and prolonged bed-rest are common risks. Covid-19 is a recent risk factor. This obstruction increases the pulmonary vascular resistance. If large enough, the clot increases the load on the right side of the heart. The right ventricle must work harder to pump blood to the lungs. With back-up of blood, the right ventricle can begin to dilate. Right heart failure can ensue, leading to shock and death. A PE is considered "massive" when it causes hypotension or shock. A submassive PE causes right heart dysfunction without hypotension. Cardiac tamponade Echocardiogram of cardiac tamponade. Fluid surrounding the heart impairs proper filling. This swinging of the heart causes electrical alternans seen on EKG. A pericardial effusion is fluid in the pericardial sac. When large enough, the pressure compresses the heart. This causes shock by preventing the heart from filling with blood. This is called cardiac tamponade. The chambers of the heart can collapse from this pressure. The right heart has thinner walls and collapses more easily. With less venous return, cardiac output decreases. The lack of blood flow to vital organs can cause death. Various conditions can cause a pericardial effusion. Inflammation of the pericardium is called pericarditis. This is caused by infection, renal failure or autoimmune disease. Trauma can cause blood to fill the pericardium. Cancer can also cause effusions. Whether an effusion causes tamponade depends on the amount of fluid and how long it took to accumulate. When fluid collects slowly, the pericardium can stretch. Thus, a chronic effusion can be as large as 1 liter. Acute effusions can cause tamponade when small because the tissue does not have time to stretch.
Obstructive shock
Distributive shock
Hypovolemic shock
Cryptic shock
Neurogenic shock
Vasodilatory shock
Septic shock
Cardiogenic shock