🩺 Non-invasive Blood Pressure (NIBP) Monitoring

♦️ Introduction

When you hear the term circulatory monitoring, the first things that probably come to mind are the following two:

• Blood pressure (non-invasive and invasive)
• Electrocardiogram (ECG)

☝️ These days, blood pressure devices can be found almost everywhere in Japan.

☝️ A standard 13-cm cuff (author’s photo).

Hypertension, together with diabetes, is considered one of the major risk factors for many diseases. Blood pressure measurement is less invasive and easier to perform than glucose monitoring, and nowadays you can see BP monitors not only at home, in outpatient clinics, on hospital wards, and in operating rooms, but also in rest areas of many shops.

In this article, I will briefly explain the basics of non-invasive blood pressure measurement (NIBP). Invasive arterial pressure monitoring—so-called “A-line”—will be covered in another article.

In examinations such as the Perioperative Management Team exam or the Anesthesiology Board exam, questions usually focus on factors that influence measurement accuracy.

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♦️ Blood Pressure Measurement: Then and Now

Back in the day (perhaps when today’s 50- to 60-year-old anesthesiologists were still trainees), automatic BP monitors hardly existed. Anesthesiologists had to place a stethoscope under the cuff and inflate/deflate it manually every few minutes. Hard to imagine nowadays… 😱

Of course, at that time there were no digital automated anesthesia record systems. (There were mechanical recorders with a pencil moving automatically… have you ever seen one? 😅) Everything was handwritten. Life was tough for anesthesiologists back then!😅 (I belong to the generation who heard those stories from my seniors 🤗. In my early years, I also wrote anesthesia records by hand ✏️).

Telling these anecdotes is fine, but if you emphasize them too much, people may jokingly call you “old-timer” or “nostalgic boomer.” I sometimes catch myself drifting into such stories, so I try to be careful 😅.

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♦️ Measurement Methods

🔷 Auscultatory method (Korotkoff method)

As mentioned above, the traditional method where anesthesiologists or nurses inflate the cuff and listen with a stethoscope is called the auscultatory method or Korotkoff method.

The cuff is inflated to occlude blood flow, then slowly deflated. The reappearance of flow is detected by the Korotkoff sounds.

However, accuracy depends on the examiner. Inexperienced users or those who deflate too quickly tend to record falsely low systolic values (because they miss the sound). Environmental noise also interferes.

Nowadays, mercury sphygmomanometers are no longer used (production/import/export banned since 2021 in Japan). Aneroid or electronic devices are the standard.

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🔷 Oscillometric method

This is the method used in most automatic BP monitors. The steps are similar to the auscultatory method—inflate the cuff to stop flow, then gradually deflate.

The device detects oscillations in the arterial wall (pressure pulse waves) and calculates BP:

Thus, mean arterial pressure (MAP) is quite reliable, while systolic/diastolic values are calculated using algorithms that differ by manufacturer. In the past, sensor performance was poor and results less reliable, but with current technology, differences compared with the auscultatory method are minimal.

Another advantage is that measurement is possible at any site where a cuff can be applied and arterial pulsation can be detected.

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♦️ Proper Cuff Size and Application

The width of the cuff should be about 1.2–1.5 times the diameter of the limb (or roughly 40% of the arm circumference).

Tightness: insert 1–2 fingers between cuff and arm (a practical but somewhat vague rule).

☝️ Remember these numbers! If inappropriate, measurement errors occur:

🔷 Cuff width

For adults with average body habitus, a 13-cm cuff is standard. For small adults or children, 10 cm, 7 cm, or 5 cm cuffs are used.

🔷 Cuff tightness

If loose, the inflatable bladder expands outward instead of compressing the artery effectively, requiring more inflation pressure and yielding an artificially high value.

Obese patients with “wine-glass-shaped” arms can be particularly challenging 😅.

🔷 Arm position relative to the heart

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♦️ Other Important Points

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📝 Take Home Messages

🔗 Related articles

📚 References & Links