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We often hear about high blood pressure and how it can be dangerous to health, but low blood pressure isn’t talked about as much. For most people, a blood pressure reading lower than 90/60 mmHg may cause lightheadedness but otherwise is unlikely to cause long-term harm. However, in cases of severe disease or major injury, blood pressure may become so low that it causes circulatory failure.

Blood pressure is normally maintained at a high enough level to keep blood, oxygen and nutrients flowing to the organs, but not so high that it damages blood vessels. When blood pressure becomes too low, the cells become starved of the oxygen they need to function. This is called circulatory failure. If circulatory failure goes on long enough, the organs may not work as well as they should. For example, the kidneys may become damaged because they can’t filter blood to produce urine. This can lead to a more serious condition called circulatory shock. Symptoms of circulatory shock include confusion and unconsciousness—due to reduced oxygen delivery to the brain—and cold, pale and clammy skin caused by a lack of blood flow to the skin.

Circulatory failure happens for three main reasons:

• The heart may not pump enough or strong enough (heart failure). Heart attacks and valve problems are common causes of heart failure.
• The blood vessels may relax too much and blood redistributes from the heart to the rest of the body (called distributive shock). Severe allergic reactions, serious infections and shock that sometimes happens after a spinal cord injury can all lead to circulatory failure.
• There may not be enough blood to pump throughout the body. Severe bleeding and long-lasting bouts of vomiting or diarrhea may reduce blood volume so much that blood pressure cannot be maintained. Inflammation after severe burn injuries can also cause blood volume to drop drastically.

Treatment for circulatory failure is generally aimed at addressing the underlying cause of low blood pressure, such as stopping bleeding or repairing a blocked coronary artery. People with circulatory failure often need additional basic treatment—like getting extra blood or fluids through an IV or receiving medication—before medical professionals can treat the primary cause.

Low blood pressure can happen to anyone and is often no more than an annoyance, such as seeing stars when standing up. However, people who show signs of circulatory shock—confusion, unconsciousness, rapid and shallow breathing, pale clammy skin—need immediate medical attention.

Michael Hultström, MD, PhD, is a critical care anesthesiologist and associate professor of physiology at Uppsala University in Sweden. His research group works with circulatory function and the development of acute and chronic kidney damage both in experimental models and in patients undergoing major surgery.