Shock (circulatory)

Shock happens when the body’s tissues don’t get enough blood flow because something goes wrong with the circulatory system. It’s a medical emergency that needs immediate attention. Early signs can include weakness, a fast heart rate, rapid breathing, sweating, anxiety, and unusual thirst. As things get worse, confusion, unconsciousness, or cardiac arrest may follow. The condition has four main types, each with a different cause: hypovolemic, cardiogenic, obstructive, and distributive.

Hypovolemic shock, or low-volume shock, comes from not enough blood or fluid in the circulation. Bleeding is the most common cause, but in children, vomiting and diarrhea are more frequent triggers. Burns and excessive urine loss from conditions like diabetic ketoacidosis or diabetes insipidus can also cause it. Signs include a weak, thready pulse, cool skin, rapid shallow breathing, hypothermia, thirst, dry mouth, and cold, mottled skin, especially on the limbs. A tool called the shock index—heart rate divided by systolic blood pressure—can better predict blood loss severity than heart rate or blood pressure alone, though this isn’t well-studied in pregnancy-related bleeding.

Cardiogenic shock happens when the heart fails to pump effectively, often due to a large heart attack. Other causes include abnormal heart rhythms, cardiomyopathy, myocarditis, congestive heart failure, a bruised heart muscle, or valve problems. Symptoms can include distended neck veins from high jugular pressure, a weak or absent pulse, abnormal heart rhythms (usually fast), pulsus paradoxus in tamponade cases, low blood pressure, and shortness of breath from lung congestion.

Obstructive shock results from a physical blockage in the major blood vessels of the systemic or pulmonary circulation. Conditions that cause it include cardiac tamponade (fluid in the sac around the heart), constrictive pericarditis, tension pneumothorax, pulmonary embolism, aortic stenosis, hypertrophic sub-aortic stenosis, and abdominal compartment syndrome (intra-abdominal pressure over 20 mmHg with organ failure). Many signs look like cardiogenic shock, but treatment differs. Symptoms include abnormal heart rhythms (often fast), low blood pressure, cool clammy mottled skin, and decreased urine output.

Distributive shock involves low blood pressure from blood vessel dilation. The most common cause is septic shock from a severe systemic infection, often due to Gram-negative bacteria like *Escherichia coli* or *Proteus* species. Other causes include anaphylaxis (a severe allergic reaction), spinal cord injury (neurogenic shock), or certain overdoses.

Diagnosis is usually based on symptoms, a physical exam, and lab tests. A fast heart rate or a narrowed pulse pressure (the difference between systolic and diastolic blood pressure) can raise concern. While low blood pressure, decreased urine output, and confusion are general signs, they aren’t always present. A fast heart rate is common, but it can be normal or slow in people on beta-blockers, in athletes, or in about 30% of cases with internal abdominal bleeding. Early signs can also include dry mucous membranes, reduced skin elasticity, slow capillary refill, weak peripheral pulses, and cold extremities.

If shock is suspected, emergency help should be called right away. While waiting, if it’s safe and there’s no head or back injury, lay the person down, raise their legs if possible, and keep them warm. If they become unresponsive, monitor their breathing and be ready to perform CPR.