Shock (circulatory)

Shock is a life-threatening medical emergency caused by insufficient blood flow to the body's tissues. This condition is fundamentally a failure of the circulatory system to meet the body's needs. When blood flow drops, the body cannot deliver enough oxygen to its cells. This creates a dangerous imbalance where oxygen demand exceeds the available supply.

If not treated immediately, shock can progress through a runaway cycle. Poor blood supply causes cellular damage, which triggers an inflammatory response to increase flow. This response can inadvertently deprive other areas of oxygen, creating an escalating cascade of homeostatic failure.

Medical professionals categorize shock into four primary types based on their underlying causes. The first is hypovolemic shock, which results from a lack of circulating blood volume. The second is cardiogenic shock, caused by the heart's inability to pump effectively. The third is obstructive shock, which involves a physical blockage in the blood vessels. Finally, distributive shock occurs when blood vessels dilate or widen excessively. Each type requires a different medical approach to stabilize the patient.

Hypovolemic shock is the most common form of shock. It is often caused by hemorrhage, which is significant bleeding either inside or outside the body. In children, vomiting and diarrhea are more frequent causes of low volume. Other causes include severe burns or excessive urine loss from conditions like diabetes insipidus. Doctors grade the severity of hemorrhagic shock on a scale from 1 to 4. A Class I hemorrhage involves losing less than 15% of blood volume, or about 0.75 liters. Class IV is the most critical, involving a loss of more than 40%, or over 2 liters, of blood.

Cardiogenic shock happens when the heart muscle fails to function as a pump. This is most often caused by a large myocardial infarction, commonly known as a heart attack. Other causes include arrhythmias, which are abnormal heart rhythms, or cardiomyopathy. Patients may also experience this due to congestive heart failure or valvular heart disease. Signs of this type of shock include distended jugular veins and shortness of breath. These symptoms occur because the heart cannot move blood forward, leading to pulmonary congestion.

Obstructive shock occurs when a physical obstruction prevents blood from moving through the systemic or pulmonary circulation. One example is cardiac tamponade, where fluid builds up in the pericardium and prevents blood from entering the heart. Another cause is a tension pneumothorax, which increases pressure in the chest and impedes blood return. A pulmonary embolism, or a blood clot in the lungs, can also block circulation. Additionally, abdominal compartment syndrome can occur if pressure in the abdomen rises above 20 mmHg. This pressure reduces the blood's ability to return to the heart.

Distributive shock is characterized by a massive dilation of the blood vessels. Septic shock is the most frequent cause, triggered by an overwhelming systemic infection. This infection causes the release of histamine, which makes blood vessels widen and lowers blood pressure. Anaphylactic shock is another form, caused by a severe allergic reaction to an allergen or drug.

This reaction also involves histamine release and increased capillary permeability. Finally, neurogenic shock can result from high spinal cord injuries, which affects the nervous system's control over blood vessels.

Symptoms of shock vary depending on the type and severity. Common signs include low blood pressure, confusion, and a fast heart rate, known as tachycardia. However, some people, such as athletes or those taking beta-blockers, might have a normal or even slow heart rate. Other early signs include cold, mottled skin, or a prolonged capillary refill time.

If shock is suspected, emergency medical services must be called immediately. While waiting, the person should be laid down and kept warm, unless they have a suspected head or back injury.

Understanding these complex systems helps doctors intervene before a fatal outcome occurs. By identifying whether the problem is volume, pumping, blockage, or vessel dilation, they can provide targeted care. For example, anaphylaxis might require an epinephrine auto-injector.

Septic shock requires early administration of broad-spectrum antibiotics. Each specific cause must be addressed to break the cycle of declining oxygenation and restore stability to the body's metabolism.