What is hypotension?

Hypotension is a medical term used to describe the condition of abnormally low blood pressure — lower than 90/60.

Blood pressure is represented by two numbers, the first being systolic pressure — the pressure in the arteries as the heart fills them with blood.

The second number is diastolic pressure — the pressure in the arteries between beats, as the heart rests. Optimal is blood pressure less than 120/80.

Low blood pressure in healthy people, without any symptoms, is not usually a concern. But low blood pressure, especially in elderly people, can indicate an underlying problem and lead to insufficient blood to the heart, brain, and other vital organs.

Hypotension can cause dizziness, weakness and blurred vision. More severe cases lead to loss of consciousness and can be life-threatening.

What can cause cause hypotension?


Hypotension is often linked to the symptoms of allergic reaction. When a person goes into anaphylactic shock, weakness, dizziness, blurred vision and loss of consciousness can swiftly follow.

Anaphylaxis is a severe type of allergic reaction, or more accurately, an overreaction to a ‘trigger.’ This trigger causes the immune system to respond by creating antibodies, but the process escalates into a series of immune system reactions.

The reaction between the antibody and the allergen causes the sudden release of chemical substances stored in the cells of the blood and tissues of the body, such as histamine.

The histamine released during an anaphylactic reaction causes blood vessels to widen, which leads to a sudden and severe drop in blood pressure — hypotension.

The immune systems of people with anaphylaxis react to such an extent that it becomes dangerous to them. If anaphylaxis is not treated as a medical emergency, death can result.

Other causes of hypotension


Low blood pressure can be caused by a variety of factors, including:

  • Standing up quickly
  • Emotional stress
  • Dehydration (can reduce blood volume)
  • Heat (the 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 (can hinder the pumping action of the heart)
  • Some nervous system disorders

What are the symptoms of hypotension?


Symptoms of Hypotension include:

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

How to treat Anaphylactic shock


Given that hypotension often follows on from anaphylaxis, you should take the following steps if the signs and symptoms suggest a person is suffering anaphylaxis:

  • Lay the person down, do not allow them to stand or walk. If breathing is difficult, allow them 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.
  • Administer more adrenaline if no response after 5 minutes.
  • If breathing stops, follow resuscitation and life support procedures.

Further information about anaphylactic shock can be found in our What Is Anaphylaxis article.

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