EHS Manual

· An error in measurement of only few millimeters of mercury may cause a patient to be misdiagnosed and wrongly classified as either a normotensive or hypertensive.

· Decisions by doctors to start treatment or change treatment plans are based on accurate blood pressure readings.

· Giving approximate or round figures (terminal digit measurement 0 or 5) is not accepted. Blood pressure should be reported to the closest 2 mmHg. Accurate blood pressure measurement depends upon 3 elements:

1. Trained observer or doctor.

2. Calibrated and good functioning instrument (sphygmomanometer).

3. Well-prepared patient.

Measurement of Blood Pressure

FACTORS AFFECTING THE ACCURACY OF BLOOD

PRESSURE MEASUREMENT

Observer

This is the individual measuring blood pressure who can be a nurse, a doctor, a medical student, family member or the patient himself. Specialized training is essential which includes:

· Instructions about standardized techniques (see next section).

· Videotape or filmed blood pressure readings.

· Double stethoscope to verify accurate readings.

· Identify and correct observer’s errors.

Potential errors in BP measurement secondary to the observer:

1. Lack of mental concentration, hurry, interruption and lack of time.

2. Deteriorating visual or auditory acuity.

3. Wrong viewing distance and angle from the sphygmomanometer.

4. Unconscious bias towards raising or lowering the patient’s BP, e.g. to classify patient as normotensive or hypertensive depending upon the circumstances and observer’s impression.

5. Preference for certain terminal digits usually 0 or 5.

6. Incorrect application of stethoscope: Heavy pressure will distort the artery and produce a sound heard below the diastolic pressure.

7. Fast deflation rate of the cuff can cause an inaccurate reading.

Equipment

Mercury Sphygmomanometer

· Simplest, most accurate and most economic.

· Regular maintenance is necessary.

Manometer

· Column of the manometer should be vertical.

· Mercury level should be at zero when the cuff is detached. Measurement of Blood Pressure

· Airvent at the top of the manometer column should be clean with no blockage.

· Vent cap should be secured to prevent mercury leakage.

The Cuff and Bladder

· Appropriate cuff size (in relation to patient’s mid-arm circumference) must be used. If the cuff bladder is too wide, the pressure will be underestimated. If it is too narrow, the pressure will be overestimated.

· Most cuffs are approximately 1 cm wider than the enclosed bladder.

· Most bladders are 12-13 cm wide, for obese arm 15-16 cm. The recommended bladder length is 23-35 cm depending upon the mid-arm circumference.

· For children, the recommended bladder dimensions are 4-8 cm in width and 13-18 cm in length.

Rubber Tubing

· In good condition, free from leaks.

· Minimum length of tubing between the cuff and manometer should be 70 cm and between the inflation source and the cuff should be at least 30 cm.

· Connection should be air tight and easily disconnected.

Control Valve

· When defective may cause leakage.

· Filter may become blocked with dirt when demands excessive effort.

· When closed it should hold the mercury at constant level.

· When released it should allow controlled fall in the level of mercury.

Measurement of Blood Pressure

Patient Factors

Blood Pressure Variability

· Blood pressure varies continuously throughout the day.

· Blood pressure is affected by many biological, emotional and environmental factors.

· Clinician should be aware of all the circumstances, which may produce variations in blood pressure and attempt to control or avoid them before taking the measurement.

SOURCES OF BLOOD PRESSURE VARIABILITY

I. Changes Related to Sympatho-Adrenal Activation

A. Instantaneous (seconds):

1. Sleep: Can produce drop in BP within seconds.

2. Arousal: Is associated with immediate elevations in blood pressure.

3. Pain.

4. Dynamic Exercise: Raises systolic pressure and heart rate with little effect on diastolic pressure.

5. Static (Isometric) Exercise: e.g., weight lifting produces a marked increase in both systolic and diastolic pressure.

6. Sexual Intercourse: Produces a dramatic transient rise in blood pressure.

7. Posture: Changes from the supine to the upright position, cause an increase in diastolic pressure with little or no changes in systolic pressure.

8. Talking: A potent pressor stimulus with both physical and psychological components.

9. Mental activity and emotions produce rise in blood pressure.

10. Distended bladder or bowel increases blood pressure.

11. Respiration: Pressure falls during inspiration.

12. White Coat Effect: Very significant elevations of blood pressure in response to the physician measuring the pressure. It can be explained as part of the defense reflex.

Measurement of Blood Pressure

B. Rapid (minutes):

1. Postprandial alterations (following meals): A decrease in diastolic pressure and little change in systolic pressure 3 hours after meal. In older subjects there may be a pronounced fall in both systolic and diastolic pressure after food intake.

2. Cigarette smoking: Raises systolic and diastolic pressures. The increases are more marked in subjects with family history of hypertension.

3. Temperature changes: Cold weather can produce elevations in blood pressure.

4. Hypoglycemia: May raise blood pressure due to sympathetic stimulation.

C. Intermediate (hours):

1. Diurnal Variations: Blood pressure tends to be highest in the morning with gradual decrease over the course of the day, and lowest during the night.

2. Blood volume changes.

D. Slow (days or weeks):

1. Menstrual cycle.

2. Seasonal changes: Blood pressure tends to be higher in winter than in summer.

II. Blood Pressure Variability Secondary To Drug Intake

Drugs known to cause acute or chronic increases in blood pressure

1. Alcohol in excessive amounts increase BP within one hour specially in hypertensive patients.

2. Non–steroidal anti-inflammatory drugs, e.g., Indomethacin, Ibuprofen. Measurement of Blood Pressure

3. Caffeine: Increase in blood pressure begins within 15 minutes of drinking coffee, maximum in 1 hour, and may last for as long as 3 hours. Changes are dependent on the level of habitual caffeine intake, less in regular coffee drinkers. Increased caffeine intake is not associated with sustained hypertension.

4. Corticosteroids, e.g., Prednisone.

5. Oral contraceptives.

6. Appetite suppressants, e.g., Amphitamines.

7. Nasal decongestants, e.g., Phenylephrine.

8. Oral nasal decongestants, e.g., Pseudoephedrine.

9. Mineralocorticoids.

10. Tricyclic antidepressants.

11. Monoamine oxidase inhibitors taken with tyramine rich foods or sympathomimetics.

12. Cocaine.

13. Cyclosporins.

14. Erythropoeitin.

15. Licorice.

16. Thyroxin.

17. Ergot preparations.

RECOMMENDED STEPS FOR BLOOD PRESSURE

MEASUREMENT

Measurement of Blood Pressure

Blood Pressure Measurement Procedure

Before Taking Blood Pressure

1. Explain the procedure to the patient.

2. The patient should not talk during the procedure.

3. The observer should be in a comfortable, relaxed position.

4. The urinary bladder should be emptied at least 30 minutes prior to the measurement of blood pressure.

5. Wait for at least 30 minutes after eating, 2 hours in the elderly.

6. Smoking and caffeine should be avoided at least 2 hours before blood pressure measurements.

7. Patient should rest at least 5 minutes in quiet, comfortable environment prior to blood pressure measurement.

8. Temperature of examining room should be comfortable.

Technique of Blood Pressure Measurement

1. Support the patient’s arm so that it is at heart level.

2. Remove any restrictive clothing from the arm and expose the area of the brachial artery.

3. Choose an appropriate cuff size.

4. Ensure that the sphygmomanometer is at eye level.

5. Palpate the brachial artery and center the bladder over the artery.

6. Wrap cuff tightly around the arm, so that the edge of the cuff is 3 cm above the crease of the elbow.

7. Determine the level of maximum inflation by palpating the radial or brachial artery and rapidly inflating the cuff until the pulse is no longer palpable. Note this pressure on the sphygmomanometer and add 30 mmHg (maximal inflation pressure).

8. Rapidly deflate the cuff, wait 30-60 seconds before re-inflating.

9. Place the stethoscope gently over the brachial artery.

10. Rapidly inflate the cuff to the maximal inflation level.

11. Release the air in the cuff so that the pressure falls at a steady rate of 2 mmHg per beat or 2-3 mmHg/sec.

12. Do not reinflate the cuff once the air is being released to recheck either systolic or diastolic pressure.

13. Note the systolic pressure at the onset of two consecutive beats and diastolic pressure at the point, at which the sounds disappear (Phase V).

14. Read the pressure to the closest 2 mmHg and mark at the manometer. Measurement of Blood Pressure

15. Listen for at least 10-20 mmHg below the last sound to confirm disappearance, then deflate rapidly.

16. If sounds persist to zero, or close to zero, use the muffling of sounds (Phase IV) to indicate diastolic pressure.

17. Use Phase IV when reporting pressures in children, pregnant women or hyperkinetic circulation.

18. Note any auscultatory gap or irregular pulse. If sounds are heard close to the zero, record both Phases IV and V.

19. Record patient’s position, cuff size and areas used for measurement.

20. If sounds are difficult to hear, ask the patient to elevate his arm, reposition the arm and relocate the brachial artery by palpation.

21. Wait for 30-60 seconds and repeat the measurement again and take the average.

22. If the first two readings differ by more than 5 mmHg, additional readings should be obtained (JNC V Guidelines).

23. Ask the patient to stand for 1 minute and repeat blood pressure measurements while standing.

24. At an initial examination blood pressure should be measured in both arms, if there is a persistent difference, use the arm with higher pressure.

Problems with Blood Pressure Measurements

1. Obesity: Use the proper cuff size – large adult size or even the thigh cuff.

2. Absent Phase V Korotkoff Sounds (arterial pulsations continue to be heard till zero): Use Phase IV, which is sudden muffling of sounds. If there is a big difference between Phases IV and V, report both phases. This is indicated in children, pregnant women, hyperkinetic circulation, arterial vasodilatation or aortic valve insufficiency.

3. Cardiac Arrhythmias: Report pressure at the start (systolic) and end (diastolic) of continued frequent beats. Take a large number of readings and compute the average. Measurement of Blood Pressure

4. Faint Sounds: To identify Korotkoff’s Sounds, ask the patients to raise his arm. This will empty his arm veins; diminish effect of tissue edema on sounds. Inflate the bladder rapidly when checking pressure.

6. Auscultatory Gap: In elderly subjects, sometimes sounds disappear while deflating the cuff to reappear again then disappear. Determine the level for maximal inflation pressure by palpating the radial or brachial artery and rapidly inflate the cuff until the pulse is no longer palpable.

* Modified after Canadian Guidelines.

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