If you ever try to take a manual blood pressure with an aneroid sphygmomanometer, you may notice that sometimes the needle starts to fall normally, but suddenly, it will stall and bounce in place. Why is that happening? The answer is usually because you aren’t releasing the air from the valve at a proper rate (see video example below):
Let me explain…
When you take a manual blood pressure, you must first tighten the valve so that you can inflate the cuff. Once you have inflated the cuff with enough air, you slowly release the air by turning the valve counterclockwise.
As you do this slowly, the cuff will begin to deflate, and the needle on the gauge will begin to fall. You must watch the rate the needle is falling carefully. If you let too much air out, the needle will fall too fast, making it difficult (or even impossible) to obtain an accurate blood pressure reading.
On the other hand, if you release air out of the valve too slowly, the needle may begin to bounce in place, and you risk causing venous congestion, which also leads to an inaccurate reading.
The solution to both problems is to release the right amount of air so that the needle falls at a proper rate.
How Fast Should the Needle Fall When Taking a Blood Pressure?
Ideally, the needle should fall approximately 2-3 mmHg per second. This will allow you to get an accurate blood pressure reading. If it is much faster or slower than that, the reading may be inaccurate.
That may sound easy, but in truth, it can be quite difficult to find the right rate of air release. Not only do you have to carefully listen for the “tapping” sounds (Korotkoff sounds) that you use to determine the systolic and diastolic pressures, but you also have to hold the stethoscope over the brachial artery while simultaneously releasing air from the valve at a proper rate to maintain that 2-3 mmHg needle drop.
It can be difficult, and it definitely takes a lot of practice!
You Often Have to Keep Letting Air Out of the Valve!
Just because the needle starts to drop at the proper rate, it doesn’t mean it will keep doing so as you are listening and watching the gauge! Many times, you will need to continue to adjust the valve very slowly as the needle is dropping to maintain that ideal rate of air release.
That’s where most people go wrong. They get the right rate of drop initially, but as the pressure falls, they forget to keep adjusting the valve on the bulb, which is why it can begin to stall and bounce in place.
Learn How to Take a Manual Blood Pressure
Taking a manual blood pressure can be difficult and require a lot of practice, but once you get it down, it is a great nursing skill to master.
Below is a video tutorial on how to take a manual blood pressure: