Calibration Measuring to the Standard Blood Pressure Measurement Workshop Morehouse School of Medicine Presented by: Sandra Owen Georgia State University June 3, 2010

How would you define calibration? It is the process of comparing blood pressure measuring device against a validated standard. It can be done by a health care provider; by the company who made the device; or by an individual following instructions provided with the device.

Who determines and validates the standard? Association for Advancement of Medical Instrumentation (AAMI) Has statistical justification British Hypertension Society (BHS) Has no statistical justification yet similar to AAMI standard European Society of Hypertension (ESH) simplified test for automated devices yet not incorporated by the International Standards Organization Sphygmomanometer Committee

What is the validated standard and how likely are blood pressure devices maintained at the standard? ANSI-AAMI SP-9 and SP-10 + or – 3mmHg.; air leakage rate within 4mmHg./minute 1. leakage condition of cuff, tubing, and release valve 2. an air release rate greater than 60mmHg/minute constitutes device in poor condition Of a sample of 18 mercury, 62 aneroid, and 47 automated devices only 3% of the devices had an air leakage rate within 4mmHg./min and 25% of the devices failed to meet the calibration standard of + or – 3mmHg. (6% mercury; 31% aneroid; 26% automated. Greeff, Lorde, Wilton, Seed, Coleman, Shennen (April 2, 2009)

What is the Impact of poorly maintained and calibrated BP devices? 20% of the hypertensive patients would not be diagnosed and conversely, almost 33% of patients would be wrongly diagnosed with hypertension ( Greeff, Lorde, Wilton, Seed, Coleman, Shennen; April 2, 2009) According to Dr. Clarence Grim, an error of - 5mmHg. would miss the 21 million US hypertensives. Over the next 6 years, those 21 million would have a coronary artery disease death rate of 5/1,000 or 125,000 deaths. Whereas an error of + 5mmHg. would falsely classify 27 million people as hypertensive at a cost of $1,000 per year to treat an individual, adding $ 27 billion to the nation’s health care bill to treat a non-disease.

An Example of How a Hospital Can Regulate Blood Pressure Device Calibration At Mayo clinic, aneroid devices are calibrated every six months, at three sites, using a Digimano digital gauge from Netech Corporation and a mercury column. Two to three people are trained to test each device at 0mmHg and 10 points between 60 and 240 mmHg. It takes 5 to 20 minutes to test each unit and 6 months to cycle through each of the three sites. Cost per site is about $7,000 each year. Failure of a device occurs if zero is off; readings are + or – 3mmHg off standard; or the needle does not move smoothly. Dr. Morgenstern

Steps to Calibrating an Aneroid Gauge The following steps apply to a hand held, wall mounted, and/or floor stand aneroid device. Calibrate every 6 months. 1.Using the aneroid blood pressure gauge calibration tool,correct zero mark on gauge 2.Connect aneroid to a mercury manometer using a T tube (one arm to the gauge, one to the bulb, one to the mercury manometer) to check standard 3.Check leakage by wrapping the cuff around itself and secure the end. Inflate to 250mmHg and watch the pointer. If it slowly drops there is a leak. A pointed brush with soapy water on it will help find the leak

Troubleshooting and Maintenance for a Digital BP Device Interpreting Error Messages: 1. “ Air Leak” …check cuff and tubing 2. “Flow Error”…system cannot maintain a stable cuff pressure; check tubing Maintenance: 1. Check calibration at least once a year 2. Check valves and tubing for leakage every 6 months

Calibrating a Digital Device 1. Obtain a calibration kit for the device 2. Obtain a mercury manometer whose accuracy meets AAMI/ANSI SP9 3. Assemble calibration kit according to instructions 4. Place monitor in “Test Mode” by pressing and holding the start key while turning on the power, then release both keys 5. Inflate the system to 200mmHg. Hold the pressure at that point for 30 seconds. If doesn’t hold the pressure refer to technical assistance. 6. Inflate to 50mmHg, 100mmHg, 150 mmHg, 200mmHg 7. Inflate slowly to 290mmHg. Message center will stop updating, display “Overpress” and then turn off.

Blood pressure measurement screeners and health care providers must be aware that following the proper measurement technique and regularly calibrating blood pressure equipment using the ANSI-AAMI SP9 standard is necessary for the assurance of accuracy of readings.