Low blood pressure (hypotension): causes and symptoms

A low BP may be normal for you, especially if close family members have the same, or if you’re young and fit. It can be a normal part of pregnancy as blood vessels adapt to changing hormones, then it returns to normal after delivery.

Dehydration is a common cause, so ensure you stay hydrated, especially after exercise or in hot climates. Certain medications can cause BP to become low, especially medication to treat high BP (hypertension). In more extreme situations, it may occur if you’re very unwell with an infection or sepsis, or in an accident or injury where you have severe blood loss.

Postural hypotension

If you feel lightheaded, dizzy or faint when you stand up, you may have postural hypotension (also called orthostatic hypotension). This is where your blood pressure drops considerably on changing position, and it takes a good while for it to climb back up. Your nurse or doctor can check this. A diagnosis is made if your BP drops by 20 mmHg or more on the top number (the systolic pressure), or by 15 mmHg or more on the bottom number (the diastolic pressure), and this remains so for a minute or more. It can be more common in the elderly or those who have had a prolonged period of bed rest.

Neurally Mediated Hypotension (NMH)**

NMH is characterised by a sudden drop in blood pressure, often triggered by certain events or stimuli, such as stress or pain. Dysfunction in the autonomic nervous system, emotional stress, and prolonged standing may contribute to neurally mediated hypotension. This combination results in a sudden drop in blood pressure, leading to symptoms like fainting. This is one of the most common causes of fainting.

Severe Hypotension (Shock)

This is an extreme and potentially life-threatening form of hypotension where blood pressure drops significantly, leading to inadequate blood flow to vital organs. Conditions such as sepsis, major bleeding, or severe allergic reactions can cause shock.

Postprandial hypotension

Postprandial hypotension, or a drop in blood pressure after eating, occurs due to changes in blood flow and circulation that happen in response to the digestive process. After a meal, there is an increased blood flow to the digestive system to support the process of breaking down and absorbing nutrients from food. This leads to a temporary redistribution of blood away from other parts of the body, including the brain and muscles. However, ordinarily, the blood flow to the brain does not fluctuate from the normal - 13% of all blood flow.

Primary hypotension

Primary hypotension is a chronic form of low blood pressure that isn't related to any other medical condition. It is often a benign condition. Normally found in athletes, but, the cause is not often clear and can be caused by genetic factors as well.

Secondary hypotension

This type of low blood pressure results from an underlying medical condition or medication. Conditions such as endocrine disorders (e.g., Addison's disease), heart problems, severe infections, or certain medications can lead to secondary hypotension.

Hypotension due to medications

Some medications, such as antihypertensives, can cause a drop in blood pressure as a side effect. Use of medications that relax blood vessels or reduce cardiac output.

Dizziness or lightheadedness

Especially when standing up quickly from a sitting or lying position. This is known as postural hypotension.

Fainting (Syncope)

In severe cases of low blood pressure, particularly when there's a sudden drop in blood pressure, such as in neurally mediated hypotension or postural hypotension.

Blurred or narrowed vision

Particularly during changes in posture or after standing for a prolonged period, seen in postural hypotension.

Nausea & vomiting

Especially when standing up quickly, during prolonged standing, or in response to certain triggers, common in postural hypotension can cause nausea and vomiting.

Fatigue

Throughout the day, and may be more pronounced after physical exertion. It can be associated with chronic low blood pressure.

Shortness of Breath

In severe cases, such as shock, where low blood pressure compromises oxygen delivery to vital organs, including the lungs, which can lead to breathlessness.

Cold, clammy skin

In severe cases, such as shock, where the body redirects blood flow to essential organs, reducing blood supply to the skin. In shock, symptoms differ from normal: low blood pressure, rapid breathing, weak and rapid pulse, confusion, and unconsciousness.

Thirst

Dehydration, which can contribute to low blood pressure, may lead to increased thirst.

How to manage hypotension

There are simple measures you can take to make sure things don’t get worse. Make sure you stay well-hydrated, especially if it’s hot or you are unwell with a fever. If moving from lying or sitting to standing is a trigger, make sure you take a few minutes to hold onto something and get your balance, before walking off. It can be more common in the elderly or those who have had a prolonged period of bed rest.

Fludrocortisone

Fludrocortisone is a synthetic cortico-steroid that works by increasing the reabsorption of sodium and water in the kidneys, leading to an expansion of blood volume. This expansion of blood volume helps raise blood pressure. It is often prescribed for individuals with orthostatic hypotension or hypotension related to low blood volume. Monitoring blood pressure, electrolytes, and fluid balance is essential while on fludrocortisone. Potential side effects and risks, including fluid retention and electrolyte imbalances, should be discussed with the healthcare provider.

Midodrine

Midodrine is an alpha-adrenergic agonist that causes blood vessels to constrict, leading to an increase in blood pressure. It primarily acts on the arterioles, raising both systolic and diastolic blood pressure. It is commonly prescribed for postural hypotension. The dosage is typically adjusted to find the minimum effective dose. Monitoring for supine hypertension (elevated blood pressure when lying down) is important.

Erythropoietin

Not commonly prescribed for most hypotensions, erythropoietin is a hormone that stimulates the production of red blood cells in the bone marrow. Increasing red blood cell production contributes to an increase in blood volume and, consequently, blood pressure. Erythropoietin may be considered for individuals with hypotension related to anaemia. Its use requires closely monitoring haemoglobin levels, blood pressure, and overall response. Potential risks, including thrombotic events, should be discussed with the healthcare provider.

When should I see my doctor?

If you suffer these symptoms on a regular basis, you should get your BP checked with either your doctor's practice nurse or at a pharmacy. Alternatively, you can book a routine appointment with your doctor to discuss symptoms and review any medications you’re taking. They may suggest further investigations such as a blood test or electrocardiogram (ECG) that traces the electric system of your heart.

When to Seek Emergency Medical Intervention

If low blood pressure is severe and leads to symptoms such as confusion, rapid or weak pulse, or unconsciousness, emergency medical attention is crucial. In cases of shock, where blood pressure is critically low, prompt emergency intervention is necessary to stabilise the individual and restore blood flow to vital organs.