Obstructive shock

Obstructive shock is one of the four types of shock, caused by a physical obstruction in the flow of blood. Obstruction can occur at the level of the great vessels or the heart itself. Causes include pulmonary embolism, cardiac tamponade, and tension pneumothorax. These are all life-threatening. Symptoms may include shortness of breath, weakness, or altered mental status. Low blood pressure and tachycardia are often seen in shock. Other symptoms depend on the underlying cause.

The physiology of obstructive shock is similar to cardiogenic shock. In both types, the heart's output of blood (cardiac output) is decreased. This causes a back-up of blood into the veins entering the right atrium. Jugular venous distension can be observed in the neck. This finding can be seen in obstructive and cardiogenic shock. With the decrease cardiac output, blood flow to vital tissues is decreased. Poor perfusion to organs leads to shock. Due to these similarities, some sources place obstructive shock under the category of cardiogenic shock.

However, it is important to distinguish between the two types, because treatment is different. In cardiogenic shock, the problem is in the function of the heart itself. In obstructive shock, the underlying problem is not the pump. Rather, the input into the heart (venous return) is decreased or the pressure against which the heart is pumping (afterload) is higher than normal. Treating the underlying cause can reverse the shock. For example, tension pneumothorax needs rapid needle decompression. This decreases the pressure in the chest. Blood flow to and from the heart is restored, and shock resolves.

As in all types of shock, low blood pressure is a key finding in patients with obstructive shock. In response to low blood pressure, heart rate increases. Shortness of breath, tachypnea, and hypoxia may be present. Because of poor blood flow to the tissues, patients may have cold extremities. Less blood to the kidneys and brain can cause decreased urine output and altered mental status, respectively.

Other signs may be seen depending on the underlying cause. For example, jugular venous distension is a significant finding in evaluating shock. This occurs in cardiogenic and obstructive shock. This is not observed in the other two types of shock, hypovolemic and distributive. Some particular clinical findings are described below.

A classic finding of cardiac tamponade is Beck's triad. The triad includes hypotension, jugular vein distension, and muffled heart sounds. Kussmaul's sign and pulsus paradoxus may also be seen. Low-voltage QRS complexes and electrical alternans are signs on EKG. However, EKG may not show these findings and most often shows tachycardia.

Tension pneumothorax would have decreased breath sounds on the affected side. Tracheal deviation may also be present, shifted away from the affected side. Thus, a lung exam is important. Other findings may include decreased chest mobility and air underneath the skin (subcutaneous emphysema).

Pulmonary embolism similarly presents with shortness of breath and hypoxia. Chest pain worse with inspiration is frequently seen. Chest pain can also be similar to a heart attack. This is due to the right ventricular stress and ischemia that can occur in PE. Other symptoms are syncope and hemoptysis. DVT is a common cause. Thus, symptoms including leg pain, redness, and swelling can be present. The likelihood of pulmonary embolism can be evaluated through various criteria. The Wells score is often calculated. It gives points based on these symptoms and patient risk factors.