Blood Pressure Measurement

Blood Pressure Measurement Principles

• Blood pressure can be measured with an intraarterial catheter directly, or with a sphygmomanometer indirectly.
• A sphygmomanometer contains an inflatable rubber bladder in a cloth cover, a rubber bulb to inflate the bladder, and a manometer.
• The Korotkoff sounds are detected with auscultation to measure blood pressure indirectly over the compressed artery
• Korotkoff sounds are low-pitched sounds originating in the vessel related to turbulence from partially occluding an artery.
• As the occluding pressure drops, phases occur in sequence, with Phase 1 occurring when the occluding pressure falls to the systolic blood pressure.
• As the occluding pressure falls, tapping sounds become clearer and more intense during Phase 1.
• Tapping sounds are followed by murmurs in Phase 2, which occurs at a pressure approximately 10 to 15 mm Hg lower than Phase 1.
• Phase 3 occurs when occluding pressure drops sufficiently for a large amount of volume to pass through the partially occluded artery.
• As the pressure approaches the diastolic blood pressure, Phase 4 is the abrupt muffling and decreased intensity of sounds.
• Phase 5 is the complete disappearance of all sounds, as the vessel is no longer compressed, and turbulent flow is absent.
• Less than 120 mm Hg systolic and less than 80 mm Hg diastolic is considered normal blood pressure for adults
• A borderline prehypertensive blood pressure is 120 to 129 systolic and less than 80 diastolic.
• When systolic and diastolic readings are in different categories, the higher category determines blood pressure classification.
• Blood pressure ranges are applicable to most adults 18 and older without short-term serious illnesses.
• The Korotkoff sounds disappearance point is more precise than the point of muffling when measuring diastolic blood pressure.
• The muffling point is more accurate when the disappearance point is more than 10 mm Hg lower than it.
• Communicating effectively is aided by recording both the muffling and disappearance points.
• Systolic, muffling, and disappearance points are displayed as a blood pressure recording like 125/75 to 65.
• Accuracy for all sphygmomanometers is ±3 mm Hg, so blood pressure should only be recorded to the nearest 5 mm Hg.
• Normal blood pressure varies frequently; measuring to less than 5 mm Hg gives a false impression of accuracy.
• White coat hypertension, where blood pressure is higher in the doctor's office, affects around 15% to 20% of all stage 1 hypertensives.
• White coat hypertension patients are at low cardiovascular risk
• Masked hypertension is more serious, these individuals have normal medical facility blood pressures, but have higher blood pressures throughout the day.
• Masked hypertension affects about 10% of the general population and carries a high risk of CVD.
• The cuff should sit snugly on the arm, with its lowest edge 1 inch above the antecubital fossa.
• The cuff should be around 20% wider than the extremity's diameter for accurate blood pressure measurement.
• The bladder ought to be on top of the artery.
• Using a cuff that is too small for a large arm leads to blood pressure readings that are erroneously high.
• Lack of arm support or heart level cuff placement may also cause falsely elevated blood pressure readings; no skin indentations should occur if arm is held correctly.
• Raised pressure results the patient performing isometric exercise if the arm is not supported.
• A lower diastolic blood pressure reading without a substantial change in systolic pressure results from excessive stethoscope pressure on the diaphragm.
• Auscultatory gap is the silence between the Korotkoff sounds initial disappearance and reappearance at a lower pressure.
• Hypertension and aortic stenosis have the auscultatory gap when there is decreased blood flow to the extremities.
• It has clinical importance since the systolic blood pressure may be mistaken for the lower blood pressure, or the point of reappearance.

Determining Blood Pressure by Palpation

• Support the patient's right arm/elbow for blood pressure assessment.
• The cuff bladder should be centered over the right brachial artery.
• Use a large adult or thigh cuff if the arm is obese.
• Flex the arm slightly, and support it at about heart level; blood pressure should be assessed initially via palpation to determine systolic blood pressure.
• Inflate the cuff above the pressure to obliterate the pulse while palpating the right brachial or right radial artery; then slowly open the adjustable screw for deflation.
• Identify systolic pressure by the reappearance of the brachial pulse and rapidly open the adjustable screw.

Blood Pressure by Auscultation

• Place the diaphragm of the stethoscope as close as possible over the artery, ideally just under the edge and inflate to 20 mm Hg above the systolic.
• Deflate the cuff slowly as the Korotkoff sounds are evaluated.
• The point of muffling, point of disappearance, and systolic blood pressure are determined.
• Systolic blood pressure marks the point at which initial tapping sounds are heard and if the blood pressure is high, useful to do it again later when the patient is calmer.

Ruling Out Issues

• Baseline blood pressure and pulse rate are measured after the patient has been recumbent for at least 5 minutes.
• Patient should stand to repeat measurements quickly after this
• When the systolic BP drops by ≥20 mm Hg or diastolic BP drops by ≥10 mm Hg during standing vs sitting, orthostatic hypotension results.
• Symptoms like dizziness, and often an increase in heart rate, accompany the blood pressure drop.
• Once orthostatic hypotension is diagnosed, its cause must be determined, including medications, older age, heart problems, heat exposure, prolonged bed rest, pregnancy, and alcohol.
• Place the cuff on the patient's left arm to detect supraravalvular aortic stenosis when detecting hypertension in the right arm to determine the auscultatory pressure.
• It isn't necessary to reevaluate for othostatic changes and if there is a difference in the blood pressures in the arms, supraravalvular aortic stenosis may be present.
• Determination of the blood pressure in the lower extremities is important for ruling out coarctation of the aorta if blood pressure is elevated in the arms.
• Place the person on their abdomen and place the thigh cuff, 6 cm wider than the arm cuff, around the middle of the thigh. Place the stethoscope in the popliteal fossa over blood vessel. If unavailable, the regular cuff can be applied with the distal border at the malleoli
• If leg systolic blood pressure is lower than in the arm, coarctation of the aorta may be present, especially if the femoral pulse is delayed compared to the radial pulse.
• Rapid, feeble pulses with low arterial blood pressure necessitates the rule out of cardiac tamponade.
• A marked paradoxical pulse (pulsus paradoxus) suggests cardiac tamponade, characterized by exaggerated normal inspiratory fall in systolic pressure.
• The normal fall (approximately 5 mm Hg) in systolic arterial pressure during inspiration is called a normal paradoxical pulse.
• A magnitude exceeding 10 mm Hg indicates a marked abnormality, suggesting cardiac tamponade when measuring magnitude of paradoxical pulse

Arterial Pulse

• Palpation of the arterial pulse provides information like:
  • Rate and rhythm of the heart
  • Contour of the pulse
  • Amplitude of the pulse
• The radial pulse is commonly used to evaluate cardiac rate
• Stand in front of the patient when grasping radial arteries; second, third, and fourth fingers should overlie the artery, never the thumb.
• Multiply beats by 2 to get beats per minute after counting the pulse for 30 seconds.
• Pulse deficit may occur in atrial fibrillation, marked by an irregularly irregular rhythm

This lesson covers the principles of blood pressure measurement, including direct and indirect methods. It explains how a sphygmomanometer works and describes the Korotkoff sounds detected during auscultation. The different phases of Korotkoff sounds and their relation to systolic and diastolic blood pressure are also discussed.