Measuring Blood Pressure: Hospital Techniques And Tools

Blood pressure is a measure of the force with which blood passes through the body's arteries. It is measured in millimetres of mercury (mm Hg) and is given as two numbers: systolic blood pressure (the first and higher number) and diastolic blood pressure (the second and lower number). In a hospital, a healthcare provider will measure blood pressure manually or with an automated device. For manual measurements, a stethoscope is placed over the brachial artery in the upper arm and elbow joint, while an automated device involves a blood pressure cuff that automatically inflates, deflates, and measures pressure.

Manual vs. automated measurement

Blood pressure is a measure of how forcefully blood moves through the arteries. It is measured in two ways: systolic blood pressure, which measures the force of blood inside the arteries when the heart beats, and diastolic blood pressure, which measures the force when the heart rests between beats.

There are two main methods for measuring blood pressure in a hospital: manual and automated. For manual measurement, a healthcare provider wraps a blood pressure cuff, a strap-like device, around the patient's upper arm. They inflate the cuff using a small hand pump or a button on an automated device. If done manually, the provider places a stethoscope over the brachial artery in the upper arm and elbow joint to listen to the blood flow and pulse as the cuff inflates and deflates. The provider then opens a valve on the cuff to slowly release air, taking a measurement when the sound of blood pulsing is first heard (systolic pressure) and when it completely stops (diastolic pressure).

Automated measurement involves a machine automatically inflating and deflating the blood pressure cuff and measuring the pressure. This method does not require a stethoscope. Automated office blood pressure (AOBP) machines provide a third option for accurate measurement, eliminating factors influencing imprecise BP. However, manual recording is widely accepted to be more accurate than automated devices, which may fail to record blood pressure in persistent hypotension or give inaccurate readings in people with arteriosclerotic or atherosclerotic changes. A study found that manual readings were 13.4 to 14.5 mm Hg (systolic) higher than automated readings in patients with hypertension. Another study found that manual measurements showed higher BP, affecting up to 15 mmHg higher, especially in critical situations.

Despite the accuracy of manual measurements, many western healthcare systems have shifted towards automated recording. This shift raises concerns about the potential loss of manual blood pressure recording skills among nurses.

Systolic and diastolic pressure

Blood pressure is the amount of force exerted by blood as it moves through the arteries. It is measured in millimetres of mercury (mm Hg). A blood pressure reading consists of two numbers: the systolic pressure (the first or top number) and the diastolic pressure (the second or bottom number).

Systolic blood pressure measures the force or pressure of blood inside the arteries when the heart beats. This is the highest pressure point and is considered normal when the reading is below 120 mmHg while a person is sitting quietly at rest. A systolic reading of 180 or higher may indicate a hypertensive crisis, requiring immediate medical attention.

Diastolic blood pressure, on the other hand, measures the pressure inside the artery when the heart rests between beats. Diastolic blood pressure is considered Stage 1 hypertension when it falls between 80 and 89, which can often be reversed with temporary medications and lifestyle changes. A diastolic reading of 90 or above is considered Stage 2 hypertension, which significantly increases the risk of stroke or heart attack and may require prolonged medication. If your diastolic reading is 120 or higher, you are experiencing a hypertensive crisis and should seek immediate medical attention.

Both systolic and diastolic blood pressure readings are important indicators of cardiovascular health. However, healthcare providers may place more emphasis on systolic pressure when determining an individual's risk of heart disease, especially for those over 50 years of age.

Preparing for accurate measurement

To prepare for an accurate blood pressure reading, there are several steps you can take. Firstly, ensure you are relaxed and comfortable. Your blood pressure can be influenced by your emotional state, so try to remain calm and still during the procedure. Avoid heavy exercise, caffeine, and smoking for at least 30 minutes before the test. It is also important to go to the bathroom beforehand, as a full bladder can affect the reading.

If you are taking the reading yourself, at home, ensure you are familiar with the correct procedure. You can refer to online resources or ask your healthcare provider to check you are using the monitor correctly. Make sure the cuff fits your arm properly and take the reading while seated with your arm supported on a flat surface. Take multiple readings, at different times of the day, to ensure accuracy. Keep a record of your results and share them with your healthcare provider.

For 24-hour ambulatory blood pressure monitoring, you will need to wear a cuff on your arm, along with a small recording device. You should try to maintain your normal daily routine, but it is important to avoid bathing, swimming, and heavy exercise while wearing the monitor. Keep a journal of your activities, including sleep patterns, medication, and meals. This will help your healthcare provider interpret the data.

If you are concerned about your blood pressure, or if your readings are consistently high (above 180/120 mm Hg), contact your healthcare provider immediately. They may advise you to make lifestyle changes or prescribe medication to manage your blood pressure.

24-hour ambulatory monitoring

Ambulatory blood pressure monitoring (ABPM) is a method of evaluating blood pressure in which patients wear a small monitor connected by tubing to a cuff on their arm for 24 hours. The monitor takes readings at regular intervals throughout the day and night, usually every 10 to 30 minutes. Patients are advised to go about their usual activities during this time, only removing the device for bathing or vigorous exercise. The lightweight monitor, weighing less than 1 kg, is small enough to be worn on the body during daily activities. It can be programmed to take readings when the patient is awake and asleep, providing valuable data for risk assessment.

After 24 hours, the patient returns to the hospital or clinic, and the data from the monitor is downloaded. This includes the 24-hour average blood pressure, the average daytime blood pressure, the average nighttime blood pressure, and the percentage drop in blood pressure at night. This information is useful for diagnosing and managing hypertension, as it provides a more comprehensive view of a patient's blood pressure than in-office readings.

ABPM is particularly recommended for patients with suspected masked hypertension, white-coat hypertension, or suspected episodic hypertension. It can also be used to assess nocturnal decreases in blood pressure and to follow up on hypertensive therapies, including pregnant women with elevated office blood pressure and individuals with orthostatic hypotension or supine hypertension.

The start-up costs of ABPM can be a barrier for some hospitals or clinics, but it can be cost-effective for those with a significant number of commercially insured patients. The American Heart Association and the European Society of Hypertension have both published guidelines for 24-hour ambulatory blood pressure monitoring.

Interpreting blood pressure readings

Blood pressure readings are measured with two key metrics: the top number, known as systolic blood pressure, and the bottom number, known as diastolic blood pressure. The systolic number represents the pressure that the blood exerts against the artery walls as the heart contracts, while the diastolic number represents the pressure that the blood exerts against the artery walls as the heart relaxes. Both numbers are important indicators of heart health, with systolic pressure being considered a major risk factor for cardiovascular disease.

A normal blood pressure reading is generally considered to be below 120/80. In other words, the systolic pressure is below 120, and the diastolic pressure is below 80. If your reading falls between 120-139/80-89, this is considered prehypertension, and you may be at risk of developing hypertension.

High blood pressure, or hypertension, is typically classified into two stages of severity. Stage 1 hypertension is indicated by a systolic reading between 130-139 and a diastolic reading between 80-89. At this stage, a doctor may advise lifestyle changes and prescribe blood pressure medication to reduce the risk of cardiovascular events such as heart attacks or strokes. Stage 2 hypertension is characterised by a systolic reading of 140 or above and a diastolic reading of 90 or above. This stage often requires medication and lifestyle changes to manage blood pressure.

A hypertensive crisis, a medical emergency, occurs when an individual's systolic pressure exceeds 180 and their diastolic pressure exceeds 110-120. This can lead to a hemorrhagic stroke if left untreated. If you experience a hypertensive crisis, seek immediate medical attention.

Frequently asked questions