Within a 4 mmHg range – That’s how accurate aneroid sphygmomanometers are. Maybe you were expecting a big build up until the answer to the question, but there it is.
Now, read on if you’d like a quick explanation of what that number means. We’ll also hit a short review of aneroid sphygmomanometers, cover how they work, and tell you why they’re accurate.
What Does That mmHg Number Mean?
Every nurse is familiar with numbers measured in mmHg because that’s how you take a blood pressure reading. Millimeters of mercury is what mmHg stands for. The first sphygmomanometers used columns of mercury to get the reading, hence the name.
It’s the standard of measurement for reading the pressure of any fluid – in healthcare’s case, that’s blood pressure. A range within 4 mmHg is considered very accurate and sensitive enough for use in hospital and clinical settings.
How Accurate Are Aneroid Sphygmomanometers?
Even though mercury sphygmomanometers are considered the gold standard and the most accurate, aneroid models still provide highly accurate readings. Even aneroid sphygmomanometers that can be purchased for home use are as accurate.
A study done in 2001 found that with the proper care and calibration, standard aneroid sphygmomanometers used in hospitals worldwide were accurate within the 4 mmHg range recommended by the Association for the Advancement of Medical Instrumentation.
Why Nurses And Doctors Use Aneroid Sphygmomanometers
Next to the stethoscope, the aneroid sphygmomanometer is probably the most widely recognized piece of medical equipment. Nurses use them every day, with lots of high-quality, accurate, and easy to use aneroid sphygmomanometers to choose from – So which is the best sphygmomanometer for nurses? Find out here.
So remember when we said that mercury sphygmomanometers were considered the gold standard? Which is better mercury or aneroid sphygmomanometer? Find out. And if mercury models are so accurate, why aren’t all nurses and doctors using them? Well, in fact, nurses and doctors do use mercury sphygmomanometers, but aneroid models have some features mercury ones don’t:
Most mercury sphygmomanometers are mounted on the wall or a rolling stand because of the mercury column they used to take the measurement. Aneroid sphygmomanometers are light and easily carried.
Aneroid sphygmomanometers are much more budget-friendly than mercury ones.
Many hospitals are phasing out mercury sphygmomanometers because the mercury in them is an environmental hazard. For the most part, nurses and doctors use aneroid sphygmomanometers because they’re light, portable, and easy to use, while still providing measurements that are sensitive enough to meet medical standards.
How Does An Aneroid Sphygmomanometer Work?
An aneroid sphygmomanometer is a fairly simple device and so cleverly designed that the design has hardly changed since the first modern model was invented in the late 1800s.
An Aneroid Sphygmomanometer Has 4 Main Parts:
It houses the air bladder and secures the sphygmomanometer to the upper arm. It’s usually made out of tough synthetic fabrics like nylon and includes a velcro strap.
The air bladder inflates to restrict the blood flow to the arm. Usually made from rubber or PVC.
Air Tube, Pump Bulb, And Pressure Release Valve
This three-piece part is how you inflate the air bladder and release the air pressure to get the diastolic reading. Made from rubber or PVC.
This is the round dial with the numbers and indicator arrow to measure the pressure. Usually made from stainless steel. When the bladder is inflated, the patient’s blood pressure can be measured indirectly by the pressure the pumping of the veins in the arm puts on the air bladder. This is registered on the dial gauge by moving the needle.
How An Aneroid Sphygmomanometer Is Calibrated
For an aneroid sphygmomanometer to be accurate, it has to be properly calibrated. A good indicator of an aneroid sphygmomanometer out of calibration is the needle not pointing directly down through the oval at the bottom of the gauge.
An aneroid sphygmomanometer should be calibrated at least once a year either by:
- Taking it to an accredited testing lab
- Testing it against a reference standard- a manometer of known accuracy, most likely a mercury sphygmomanometer
Generally, it’s not recommended that anyone, be they a nurse, doctor, clinician, or other healthcare professional to do the calibration themselves. As always, you should check with your facility’s protocols regarding equipment use and maintenance.
So to recap, just how sensitive is an aneroid sphygmomanometer? Sensitive to measure blood pressure within a 4 mmHg range close to 100% of the time providing that the sphygmomanometer is in good working order and has been properly calibrated.
That’s more than sensitive enough to accurately read a patient’s blood pressure and make an accurate diagnosis of hypertension or hypotension in a hospital or clinical setting.