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. Diagnosis
Rapid evaluation of shock is essential given its life-threatening nature. Diagnosis requires a thorough history, physical exam, and additional tests. One must also consider the possibility of multiple types of shock being present. For example, a trauma patient may be hypovolemic from blood loss. This patient could also have tension pneumothorax due to trauma to the chest.Vital signs in obstructive shock may show hypotension, tachycardia, and/or hypoxia. A physical exam include be thorough, including jugular vein exam, cardiac and lung exams, and assessing skin tone and temperature. Response to fluids may aid in diagnosis. Labs including a metabolic panel can assess electrolytes and kidney and liver function. Lactic acid rises due to poor tissue perfusion. This may even be an initial sign of shock and rise before blood pressure decreases. Lactic acid should lower with appropriate treatment of shock. EKG should also be performed. Tachycardia is often present, but other specific findings may be present based on the underlying cause.At the bedside, point-of-care echocardiography should be used. This is non-invasive and can help diagnose the four types of shock. Echocardiography can look for ventricular dysfunction, effusions, or valve dysfunction. Measurement of the vena cava during the breathing cycle can help assess volume status.
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 hearts 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.