Blood Pressure Crash Course for nurses
Published: March 3, 2022
Last Updated: March 23, 2023
Blood pressure is one of the 5 vital signs, and it is so important to understand what normal and abnormal blood pressures are, and how we manage them (don’t get me started on the “6th” vital sign…).
Within the hospital, vital signs are typically checked every 4 hours, and you will frequently run into both high and low blood pressures.
Low blood pressure is often much more worrisome, and you may want to call an RRT if the BP is significantly low, especially when the patient is altered or has significant symptoms.
High blood pressure is common, but often is not considered a big deal unless VERY high. In these cases, we want to slowly decrease the blood pressure instead of too quickly.
What is Blood Pressure?
As you probably know, blood pressure is not the pressure of your blood, but rather the pressure within your vascular system.
The vascular system refers to your arteries and veins. When speaking of systemic blood pressure, we are specifically talking about the pressure in the arteries.
This pressure temporarily increases with each heartbeat, and decreases in-between each heartbeat.
The pressure in your arteries when your heart beats or contracts is called the systolic blood pressure. Systolic just means during the heartbeat. Systolic blood pressure can never be below the diastolic pressure.
When the heart is not beating, the pressure “rests” back to its normal baseline pressure. This is called the diastolic blood pressure. The diastolic blood pressure should never be 0.
This pressure is measured in millimeters of mercury (mmHg).
“Normal” Blood Pressure
As we said above, systolic is the pressure during contraction of the heart, and diastolic is the pressure in-between beats. When looking at a blood pressure reading, there are two numbers: a numerator and a denominator. The numerator or top number is the systolic blood pressure. The denominator or the bottom number is the diastolic blood pressure.
Normal systolic blood pressures are between 100 – 120 mmHG. Normal diastolic pressures are between 60-80 mm Hg. Traditionally 120/80 mmHg was considered the “gold standard” for blood pressure, but now its recommended to be at most 120/80 mmHg.
A "Good" Pressure
A “good pressure” is relative. In the ER, a pressure below 160/90 tends to be considered pretty good and usually won’t require any medications. However, a pressure of 160/90 is considered very high if that is the normal daily blood pressure at home, and should be started on medications.
How to Measure Blood Pressure
We check people’s blood pressures in the hospital, in the outpatient office setting, and pretty much every area of patient care. Nowadays, we have machines that do most of it for us. But machines aren’t perfect, and its an essential nursing skill to know how to check blood pressure.
In general, there are 3 main ways to check someone’s blood pressure:
Manual Blood Pressure
A manual blood pressure is checked using a sphygmomanometer and a stethoscope. The stethoscope if placed over the brachial artery, and the cuff is placed on the patient’s bicep.
The cuff is pumped up to about 160 or 180 (in most people unless BP is very high). Slowly release the cuff pressure while you auscultate the brachial artery.
Systolic blood pressure is identified by the first Korotkoff clicking sound. The diastolic is noted when you can’t hear anything left.
You can palpate the patient’s radial artery when a machine or cuff is pumping up or down. When the radial artery disappears, this is your systolic pressure. There is no way to check diastolic with palpation
Automated Blood Pressure
An automated blood pressure is checked by a machine, often a portable Dinamap or a bedside monitor. These machines essentially perform a manual BP on their own.
They have a sensor which detects tiny oscillations from your pulse. So when the pulse goes away – this is your systolic pressure. When the pulse reappears, this is your diastolic pressure.
A-Line Blood Pressure
Arterial lines are commonly placed in the ICU for strict BP monitoring. This is the most accurate way to check a blood pressure because it is directly measured by a sensor within the arteries, instead of indirectly like with the methods above. This gives you real-time changes in blood pressure.
What’s the deal with the “MAP”?
If you’ve been working for a bit, or in clinicals, you may hear about the term “MAP”. While systolic blood pressure is often considered the most important part of the blood pressure, the actual important number is the MAP.
The MAP stands for Mean Arterial Pressure. This is the average pressure in the arteries from one cardiac cycle (systolic + diastolic). This is measured by a calculation:
But don’t go busting out your calculators. The bedside monitors should automatically calculate this for you, or possibly your EMR. If you need to calculate it, there are plenty of good online calculators to quickly do it.
MAP is a great indicator of tissue perfusion. If the MAP stays above 65 mmHg, then this should be enough pressure to provide essential tissue perfusion and prevent anoxic injury (injury from a lack of oxygen to the cells!).
Nurses and Providers in the ICU will care much more about MAP than systolic blood pressure, especially when looking at low blood pressures.
Hypertension, also known as high blood pressure, comes in many different forms. While often thought of as “not a big deal”, it really is the silent killer, and can put a lot of strain on the heart, vasculature, and kidneys.
Overtime, this organ damage becomes more pronounced, placing the patient at risk for heart disease, strokes, kidney failure, and more!
Another reason why it’s termed the silent killer is because it often is asymptomatic – meaning there are no symptoms. But just because there aren’t any symptoms doesn’t mean it isn’t dangerous, especially in the long run.
In medicine, we use JNC8 guidelines to classify and manage hypertension.
Blood pressure levels include:
Normal: < 120 / 80 mmHg
Stage 1 HTN: 130 – 140 / 80-89 mmHg
Stage 2 HTN: > 140 / 90 mmHg
Hypertension can be chronic or acute. Its also important to know if the patient is having any symptoms such as chest pain, SOB, headache, etc.
3 main types of hypertension that we’ll talk about include:
Primary hypertension, previously referred to as essential hypertension, is a chronic hypertension that has no clear cause, but is thought to involve genetic, dietary, and lifestyle factors. This is what most people are diagnosed with when they have high blood pressure. Risk factors include:
- Increased age
- Family History of HTN
- Black race
- High sodium diet
- Excessive ETOH
- Sedentary lifestyle
Hypertensive urgency is a very high blood pressure > 180/110 mmHg. While there is no evidence of organ damage (i.e. lack of symptoms or lab abnormalities), the patient is at risk for organ damage or strokes to occur.
Hypertensive emergency is a very high blood pressure > 180/110 mmHg when there IS evidence of organ damage. The patient should have at least one of the following signs or symptoms:
- Chest Pain or SOB
- Pulmonary Edema
- Severe headache, Seizures, or confusion
- Elevated Troponin
- Acute Kidney Injury (elevation in creatinine levels)
Treatment of Hypertension:
Treatment of hypertension is often not aggressive, and is often made by slow gradual changes to outpatient medication regimens.
However, if the patient is symptomatic, blood pressure medications should be given.
At home blood pressures should be checked, as patients BPs are often higher in emergency and urgent care settings, and “White coat hypertension” is common.
Some oral medications used to lower BP include:
- ACE Inhibitors like Lisinopril
- ARBs like Losartan
- Calcium channel blockers like Amlodipine
- Beta-blockers like Labetalol
- Diuretics like Hydrochlorothiazide
- Alpha blockers like Clonidine
In hypertensive urgency and when in the hospital, sometimes IV medications may be required including:
- IV Hydralazine
- IV Cardizem or Nicardipine
- IV Labetalol
- IV Lopressor (metoprolol)
In general, blood pressure should never be lowered too fast. In severe cases, the goal should be to lower the MAP by 10-20% within the first hour, then another 5-15% over the next day. In many cases, this is less than 180/120 in the first hour, and less than 160/110 after 24 hours.
Lowering the blood pressure too quickly can actually cause ischemic damage in patients who have had elevated blood pressure for a long time. Basically the body becomes used to that high pressure, and while it is dangerous to have high blood pressure in general, lowering it too quickly can cause damage as well.
BP & Symptoms
When it comes to blood pressure (and even heart rates while we’re at it), its always important to ask the patient if they have any symptoms. Ask about any CP, SOB, dizziness, palpitations, headache, numbness/tingling/ etc.
Hypotension is when the blood pressure is too low. Low blood pressure is defined as any pressure less than 100/60 mmHg. However, this is often not considered true hypotension until below 90/50 mmHg.
Patients who are small in stature and thin may have borderline low blood pressures at baseline.
Worried about the patient’s BP? Trend what their BP has been this hospital visit, as well as previous hospital visits. If their BP is 92/48 but they always run around there and are asymptomatic otherwise – this is reassuring.
Remember if the MAP is less than 65 mmHg, this places the patient at risk for tissue ischemia and organ damage.
Low blood pressure is often a serious sign, especially in the hospital setting. Common causes of hypotension include:
Septic shock is when there is a severe systemic response to infection. These patients will have persistent hypotension despite adequate fluid resuscitation (30ml/kg bolus). They usually require IV vasopressors, a central line, IV antibiotics, and ICU admission.
Anaphylactic shock is a type of distributive shock that occurs with a severe allergy. Release of inflammatory mediators causes massive systemic vasodilation, swelling, and hypotension. This is treated with IV steroids and antihistamines, +/- epinephrine.
When the patient loses enough blood, they will become hypotensive. These patients need STAT blood, usually O negative blood that hasn’t been crossmatched.
Cardiogenic shock occurs when the heart can’t keep up with the body’s demand. This can occur in severe CHF or bradyarrhythmias.
Drugs / Medications
Maintenance medications given for blood pressure can cause low BP, especially if taken in wrong doses or if they become toxic. Some other medications have hypotension as a possible side effect such as amiodarone.
Patients with a history of adrenal insufficiency will often require stress-dosed steroids to maintain their blood pressure.
Dehydration needs to be severe before the patient becomes hypotensive. This can occur in those with DKA or diabetes insipidus, or really anything that causes dehydration.
Treatment of Hypotension:
Treatment of hypotension will involve treating the underlying cause, but generally involves 2 steps:
- IV Fluid boluses: to increase the volume of the blood
- Vasopressors: To cause constriction of the blood vessels
If fluid boluses do not improve blood pressure, or if the BP drops back again once its done, then the patient may need vasopressors in the ICU.
Depending on the cause, the underlying cause should be addressed, including:
- Blood for blood loss
- Antibiotics and fluids for sepsis
- Steroids for adrenal crisis
- Steroids & Antihistamines for Anaphylaxis
You are going to run into TONS of patients who either have high blood pressure, or low blood pressure. Managing vital signs is a huge part of our jobs as nurses and doctors, and its so important to understand how to manage blood pressure!
Remember these important concepts when it comes to blood pressure:
Double Check the Pressure
Double check your blood pressures. If it doesn’t seem right – check a manual BP. The provider may ask you to do this anyway.
Always ask about Symptoms
If your patients BP is high or low, ask them if they have any symptoms. Focus on any headache, chest pain, shortness of breath, dizziness, lightheadedness, palpitations, syncope, etc.
Trend the Pressures
Remember high blood pressure shouldn’t be corrected too quickly. Look at previous trends. Don’t freak out about blood pressures that are high unless the patient has symptoms. Worry more about low blood pressures!
Basil, J., & Bloch, M. J. (2022). Overview of hypertension in adults. In T. W. Post (Ed.), Uptodate. https://www.uptodate.com/contents/evaluation-of-and-initial-approach-to-the-adult-patient-with-undifferentiated-hypotension-and-shock
Calder, S. A. (2012). Shock. In B. B. Hammond & P. G. Zimmerman (Eds.), Sheey’s manual of emergency care (7th ed., pp. 213-221). Elsevier.
Gaieski, D. F., & Mikkelsen, M. E. (2022). Evaluation of and initial approach to the adult patient with undifferentiated hypotension and shock. In T. W. Post (Ed.), Uptodate. https://www.uptodate.com/contents/overview-of-hypertension-in-adults
Roe, D. M. (2015). Cardiac emergencies. In B. A. Tscheschlog & A. Jauch (Eds.), Emergency nursing made incredibly easy! (2nd ed., pp. 97-197). Lippincott Williams & Wilkins.
Very informative and easy to understand
I’m glad you found it helpful!
Very informative. Thank you so much. I will be forever in debt for this information. This has actually helped my family.