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In order to obtain accurate data with the indirect blood pressure methods that are used in surveys, it is important to follow the prescribed procedures precisely. Otherwise, correlation with the true blood pressure no longer holds. Therefore, the instructions given in the following sections should be incorporated into Manuals of Operation in their entirety.
In daily life blood pressure changes from instant to instant and is influenced by many physiological and environmental factors. To obtain reproducible results, it is important to control these factors as much as possible and otherwise document them in the blood pressure data recording forms (see Appendix 3.1). The items that need to be recorded before beginning the measurement are: time of the day, room temperature, arm circumference and cuff width used. Also, if deviations from the measurement protocol are unavoidable, e.g. a person has lost his/her right arm and the measurement had to be taken from the left arm or if a person for some reason is not able to sit and measurement had to be taken in recumbent position, they have to be documented together with the blood pressure data.
For survey blood pressure measurements the following equipment is required (See Picture 3.1.):
Picture 3.1. Blood pressure measurement equipment
The simple mercury sphygmomanometer is recommended because there are no reliable automated devices on the market. This may change when the accuracy of future automated devices is found to be sufficient in validation against the simple mercury sphygmomanometer.
The bell of the stethoscope should be used because it gives clearer sounds than the diaphragm.
A set of 3-4 cuffs with different size should be available and special attention should be paid to the use of proper cuff width in relation to the size of the arm.
A measuring tape is used to measure arm circumference before selecting the proper cuff width.
Preparation for measurement
Before the blood pressure measurement begins the following conditions should be met:
Position of the subject
Measurements should be taken in sitting position so that the arm and back are supported. Subject's feet should be resting firmly on the floor, not dangling. If the subject's feet do not reach the floor, a platform should be used to support them.
Position of the arm
|The measurements should be made on
the right arm whenever possible.
The subject's arm should be resting on the desk so that the antecubital fossa (a triangular cavity of the elbow joint that contains a tendon of the biceps, the median nerve, and the brachial artery) is at the level of the heart and palm is facing up. To achieve this position, either the chair should be adjusted or the arm on the desk should be raised, e.g. by using a pillow (see Picture 3.2). The subject must always feel comfortable.
Picture 3.2. Position of the arm and placement of the cuff
Selection of the cuff
|The greatest circumference of the upper arm is measured, with the arm relaxed and in the normal blood pressure measurement position (antecubital fossa at the level of the heart), using a non-elastic tape (see Picture 3.3). The measurement should be read to the nearest centimeter. This reading should be recorded in the data form.||
Picture 3.3. Measurement of the arm circumference
Select the correct cuff for the arm circumference and record the size of the selected cuff in the blood pressure recording data form. The instructions for deriving rules to select the proper cuff size for each arm circumference are given in Appendix 3.2.
The cuff should be placed on the right arm so that its bottom edge is 2-3 cm above the antecubital fossa, allowing sufficient room for the bell of the stethoscope. The top edge of the cuff should not be restricted by clothing. (See Picture 3.2)
Number of measurements
Three measurements should be taken one minute apart. If three measurements are not feasible, two will suffice with a certain loss in data stability.
Procedure of the pulse rate and blood pressure measurement
When recruiting the measurers one should remember:
After persons have been recruited as candidates for blood pressure measurer, they have to pass a hearing test administered by an audiometrist, i.e. no loss of hearing in either ear.
Following the successful hearing test all candidates have to undergo thorough training covering theory and practice of indirect blood pressure measurements.
During the theoretical lectures the blood pressure measurement protocol is reviewed and discussed in detail. Possible problems during field operation are examined and solutions analyzed. Also, the quality control measures during the survey are presented, e.g. monitoring for terminal digit preference.
The practical training includes
Before being accepted as blood pressure measurers, the candidates have to pass a certification test that could be based on similar techniques as the training methods, but now a predefined minimal percentage of correct measurements has to be achieved for successful certification.
Quality control during the survey includes two parts, the checking of equipment and performance monitoring of the blood pressure measurers.
Measurers should check every day before the first blood pressure measurement are made that the mercury column of the sphygmomanometer is at zero, that the mercury column falls smoothly when the cuff is deflated, and that the column latches properly into vertical position. Any equipment failing these tests has to be replaced. The results of checking should be recorded in a log book.
It is important to continuously monitor the performance of blood pressure measurers to avoid an accumulation of data that will have to be discarded because of unreliability. Monitoring every blood pressure measurement onsite is not possible but there are several simple indicators that can be calculated regularly for monitoring purpose. For monitoring to be effective it is desirable that measurements from the field are reviewed regularly, preferably daily.
For each measurer the following information should be checked regularly during the survey:
If some problems are detected they need to be immediately discussed with the individual measurer and corrective action taken. Just letting the measurer know that he/she has problems with the measurement procedures may suffice. Otherwise, the measurer should be retrained and re-certificated or dismissed.
During extended surveys, a refresher session for all blood measurers every three months is a desirable practice.
The room temperature should be monitored during the survey on a regular basis and adjusted when needed.
External auditors should make surprise visits to the examining sites and observe measurers' performance by documenting step-by-step compliance with the protocol. Auditors should also act as guest subjects and participate actively in all steps of blood pressure measurement.
After the survey, it is important to assess and document the overall quality of blood pressure measurements. This information can be used to verify that results presented in publications are accurate and comparable with other studies. In addition, the information will also be useful for planning of future surveys and for designing the training of the future blood pressure measurers.
The retrospective quality assessment report for blood pressure measurements no longer focuses on the data of individual measurers, but instead concentrates on the pool of all measurements. The report should include the following information:
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