Low blood pressure – or hypotension – occurs when the force at which the heart pumps blood through the arteries falls.

Hypotension can present with various symptoms: from nausea, dizziness to heart palpitations. Checking blood pressure is an important part of evaluating yourself or your patient.

Unfortunately, a problem doesn’t always announce itself with a fanfare of trumpets. Even the highest blood pressure can be entirely asymptomatic. Similarly, low blood pressure also known as hypotension can occur in your patient despite no symptoms seemingly being present. This is particularly true if the patient is lying still in an unmonitored bed.

What is Hypotension (Low Blood Pressure)?

In general, hypotension can be thought of as a rate, pump or volume problem. Examples of these include:

• Rate: bradycardia (abnormally slow heart action) or tachycardia (rapid, irregular heart rate) can cause a decrease in blood pressure.
• Pump (heart function): Myocardial infarction (heart attack) or cardiogenic shock causing low blood pressure. Other conditions such as hypothermia or cardiac depressant medications can also affect the pressure of the pump
• Volume: Hypovolaemic shock, severe dehydration, haemorrhage, septic shock, anaphylaxis, neurogenic shock from spinal cord injury.

Of course, the easiest way to know your patient has a blood pressure problem is by simply taking their pressure, but in some cases you may notice other symptoms that prompt you to check a pressure and find that it is low. Low blood pressure means poor perfusion, and it can be just as problematic as higher pressures.

Low blood pressure should be evaluated and treated urgently.

Assessment of a low blood pressure should include a recheck of the pressure and close monitoring. If a client has recently changed positions, they should be returned to a supine position and then rechecked in a few minutes.

Objective Signs of Low Blood Pressure / Hpyotension

The best objective symptom of a low blood pressure is taking an actual pressure and getting low numbers. It sounds obvious, but it may not occur to you to take a pressure when a patient complains of certain symptoms.

When a patient does complain, however, it is usually recommended that you get a complete set of vitals, and this will point to a problem with low blood pressure. How low is too low? What does low actually mean? It can mean different things for different patients.

The usual metric for measuring low blood pressure is that anything below 90/50 mm Hg (millimetres of mercury) is considered low enough to treat. However, you can have a symptomatic patient at 100/60 mm Hg. This is still a low blood pressure problem, and it needs to be treated.

You can also have symptoms of low blood pressure when someone with hypertension comes down from very high pressures. For instance, 120/80 mm Hg may be normal for everyone else, but if your patient lives at 190/100 mm Hg, they are going to feel the difference. For this reason, the objective sign of a pressure must be combined with the subjective symptoms the patient reports.

Subjective Signs of Low Blood Pressure / Hypotension

Subjective symptoms are those that the patient may report, though you may be able to see objective signs of these as well.

With low blood pressure, the patient may feel faint or lose consciousness. This is due to lack of blood flow to the brain, and usually laying the patient supine will help them come round. This is also known as a blackout, and it could be accompanied by a dizzy feeling and light-headedness. Generally, your patient will report trouble focusing, difficulty keeping upright and lack of coordination.

Your patient may also report nausea and could possibly vomit from the low blood pressure. In addition, heart palpitations are sometimes felt, and these can be easily seen with the use of telemetry or other monitoring. EKGs/ECGs may or may not show them, depending on the frequency and timing of the palpitations.

Some patients may also exhibit confusion, and this can make them seem like they are suffering from intoxication or some other neurological problem. Blurred vision is usually reported with extreme cases of low blood pressure. There are many other symptoms of low blood pressure to look out for.

Orthostatic Hypotension

Orthostasis literally means standing upright. Orthostatic hypotension, or postural hypotension, is defined as a decrease in systolic blood pressure of at least 20 mm Hg or at least 10mm Hg within 3 minutes of the patient standing. If orthostatic hypotension is present, the client may be at risk of falls and should be closely supervised with ambulation or advised to call for assistance with activity.

To test for orthostatic hypotension, take the blood pressure whilst the patient is supine and at rest. Then stand the patient – they must be able to stand for 3 minutes before taking the blood pressure again. If the measurements meet the criteria stated previously, then orthostatic hypotension is evident. If the result is equivocol, record it and request a formal assessment. (Note, the accuracy of orthostatic hypotension has been questioned in recent years.)

Treatment of Low Blood Pressure / Hypotension

One quick way to treat symptomatic low blood pressure is to lay the head of the bed down and put up the patient’s feet. This will encourage blood flow to the brain and aid perfusion.

You will also need to get a doctor’s order for fluids or electrolytes to help bring the blood pressure up to normal. Usually, 500 ml/cc of normal saline will be enough to raise the pressure above critical. Blood work should also be conducted to find out if there is an electrolyte imbalance that is leading to the loss of water.

For further learning, complete the Introduction to Common Electrolyte Abnormalities video course.

Treatment generally focuses on why the patient’s pressure dropped. If they’ve lost a great deal of blood, getting the bleeding under control and giving blood products may be the necessary course. If the patient is on a cocktail of blood pressure-lowering medications, these will need to be adjusted to prevent the low event from happening again.

As a nurse, you need to work with the doctor to find out the underlying cause of the low blood pressure to treat it beyond the normal emergency procedures of saline infusions and postural interventions.

---

For further learning on heart health and related conditions, see: Congestive Heart Failure – Common Reasons for CHF, Love Your Heart this Valentine’s Day, Lung, Chest and Bowel Sounds Assessment Guide, and What is Hypokalemia?

References

• Alterman, DM & Wake, D 2017, ‘Introduction to Common Electrolyte Abnormalities’, Ausmed Education, North Melbourne, VIC, viewed 4 August 2017, https://www.ausmed.com.au/learning-centre/introduction-to-common-electrolyte-abnormalities-description#content
• Better Health Channel 2017, ‘Blood pressure (low) – hypotension’, Better Health Channel, Victorian State Government, viewed 4 August 2017, https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/blood-pressure-low-hypotension
• Health Direct 2016, ‘Low Blood Pressure (Hypotension)’, Health Direct Australia, Sydney South, NSW, viewed 4 August 2017, https://www.healthdirect.gov.au/low-blood-pressure-hypotension
• Hewitt, D 2017, ‘What Are the Dangers of Low Blood Pressure?’, Livestrong, 14 August, Santa Monica, CA, USA, viewed 4 September 2017, http://www.livestrong.com/article/18491-dangers-low-blood-pressure/
• National Heart Foundation of Australia n. d., ‘Is my blood pressure normal?’, Heart Foundation, Phillip, ACT, viewed 4 August 2017, https://www.heartfoundation.org.au/your-heart/know-your-risks/blood-pressure/is-my-blood-pressure-normal
• NHS Inform 2017, ‘Low Blood Pressure (hypotension)’, NHS Inform, UK, viewed 4 August 2017 https://www.nhsinform.scot/illnesses-and-conditions/heart-and-blood-vessels/conditions/low-blood-pressure-hypotension
• Sathicq, L 2011, ‘Low Blood Pressure: What to Know’, My Body and Soul, 12 November, Surry Hills, NSW, viewed 4 August 2017, http://www.bodyandsoul.com.au/health/health-advice/low-blood-pressure-what-to-know/news-story/11de7c274deccb7289b105e6167d3b22