Anaphylaxis and Hypotension

Hypotension, or low blood pressure, can be caused by a wide range of factors. One of these factors is allergic reactions.

When someone goes into anaphylactic shock, hypotension is associated with symptoms such as weakness, dizziness, blurred vision and loss of consciousness.

What is hypotension?

Hypotension is low blood pressure. It means that the blood circulating through a person’s body is abnormally low.

Your body will usually adjust blood pressure so that your brain, kidneys and other vital organs receive enough blood and oxygen. When blood pressure is too low it can have negative effects on the body. The most extreme symptom of sudden hypotension is loss of consciousness.

How does anaphylaxis cause hypotension?

Anaphylaxis is the most severe type of allergic reaction. Allergic reactions occur when someone’s immune system overreacts to an allergen that is generally harmless to other people.

This substance is called a ‘trigger’. When someone comes into contact with a trigger, their immune systems responds by creating an antibody to attack the allergen. This then sets off a series of immune system reactions. The immune system of people with anaphylaxis reacts to such an extent that it becomes dangerous to them and can result in death if it is not treated as a medical emergency.

In an anaphylactic reaction the body suddenly releases chemical substances, such as histamine, that are stored in the cells of blood and tissue. This sudden release is caused by the reaction between the antibody and the allergen. The chemicals released from the cells cause swelling by acting on blood vessels. These chemicals also cause other problems such as a fall in blood pressure, also known as hypotension. The histamine released by your body during an anaphylactic reaction causes blood vessels to widen which leads to a sudden and severe drop in blood pressure.

What are the symptoms of hypotension?

Hypotension can cause the following symptoms:

  • Lightheadedness
  • Unsteadiness
  • Weakness
  • Dizziness
  • Blurred vision
  • Fatigue
  • Loss of consciousness

Other causes of hypotension

Low blood pressure can be caused by a variety of factors. These include:

  • Standing up quickly
  • Emotional stress
  • Dehydration: reduces your blood volume
  • Heat: your body responds to heat by pushing blood into the vessels of the skin which leads to dehydration
  • Donating blood
  • Blood loss from trauma
  • Pregnancy
  • Some medications: e.g. for high blood pressure, some heart conditions, depression
  • Heart disease: this condition can hinder the pumping action of the heart
  • Some nervous system disorders

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What do you do if someone is showing signs of Anaphylactic shock?

If someone’s symptoms and signs suggest anaphylaxis you should take the following steps:

  • Lay victim flat, do not stand or walk, if breathing is difficult, allow to sit
  • Prevent further exposure to the triggering agent if possible
  • Administer adrenaline through auto-injector:
    • Child less than 5 years - 0.15 mg intramuscular injection.
    • Older than 5 years - 0.3mg intramuscular injection
  • Call an ambulance
  • Administer oxygen and / or asthma medication for respiratory symptoms.
  • Further adrenaline should be given if no response after five minutes.
  • If breathing stops follow resuscitation and life support procedures.

For more information about anaphylactic shock read our ‘What is Anaphylaxis’ article.

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