Blood Pressure Measurement

Blood Pressure Measurement Principles

• Blood pressure is measurable directly via intraarterial catheter or indirectly via sphygmomanometer.
• A sphygmomanometer includes an inflatable bladder, cloth cover, rubber bulb, and a manometer.
• Indirect blood pressure measurement involves listening for Korotkoff sounds caused by artery compression.
• Korotkoff sounds are low-pitched, originating from turbulence caused by partial artery occlusion.
• Multiple phases occur in sequence as occluding pressure reduces.
• Phase 1: Tapping sounds appear and intensify as occluding pressure lowers to systolic blood pressure.
• Phase 2: Tapping sounds followed by murmurs, occurring 10-15 mm Hg below phase 1.
• Phase 3: More blood flows through partially occluded artery; tapping sounds similar to phase 2.
• Phase 4: Sounds abruptly muffle as pressure nears diastolic level.
• Phase 5: Sounds disappear completely, vessel no longer compressed, and turbulent flow stops.
• Normal adult blood pressure is below 120 mm Hg systolic and 80 mm Hg diastolic.
• Prehypertension is 120-129 systolic and less than 80 diastolic.
• Classify blood pressure using the higher category when systolic and diastolic readings differ in category.
• Blood pressure ranges apply to adults 18+ without short-term serious illnesses.
• Diastolic blood pressure is more accurately determined by the disappearance of Korotkoff sounds.
• Muffling is more accurate if the disappearance point is more than 10 mm Hg below the muffling point.
• Recording both muffling and disappearance helps communication; Example: 125/75 to 65.

AHA Blood Pressure Categories (2018)

• Normal: Systolic less than 120 and diastolic less than 80.
• Prehypertension: Systolic 120-129 and diastolic less than 80.
• Stage 1 Hypertension: Systolic 130-139 or diastolic 80-89.
• Stage 2 Hypertension: Systolic 140 or higher or diastolic 90 or higher.
• Hypertensive Crisis: Systolic higher than 180 and/or diastolic higher than 120, requiring emergency care.

Additional Considerations for Accurate Blood Pressure Measurement

• Record blood pressure to the nearest 5 mm Hg due to sphygmomanometer accuracy limits (±3 mm Hg).
• Normal blood pressure fluctuates, measuring to less than 5 mm Hg can give a false impression of accuracy.
• White coat hypertension is when blood pressure is higher in the doctor's office (15-20% of stage 1 hypertensives) and indicates low cardiovascular risk.
• Masked hypertension is when normal pressures are recorded in the medical facility but elevated pressures occur regularly, this indicates higher cardiovascular risk and affects 10% of the general population.
• The cuff should be snug, 1 inch above the antecubital fossa, and 20% wider than the arm's diameter.
• The bladder should overlie the artery.
• An undersized cuff can cause high readings.
• Lack of arm support and incorrect arm positioning lead to false readings, the cuff should be at heart level.
• Isometric exercise raises recorded pressure if arm is unsupported.
• Excessive stethoscope pressure lowers diastolic pressure without altering systolic pressure.
• Auscultatory gap is silence between Korotkoff sounds' disappearance and reappearance; linked to decreased blood flow, hypertension and aortic stenosis.

Blood Pressure Assessment by Palpation

• Support the patient's right arm under the examiner's arm/elbow.
• Center the cuff bladder over the right brachial artery.
• Use a large or thigh cuff for obese arms.
• Keep the arm slightly flexed and supported at heart level.
• Palpation first assesses blood pressure to rule out errors from an auscultatory gap.
• Inflate the cuff above the pressure needed to stop the pulse while palpating brachial or radial artery.
• Open the adjustable screw slowly to deflate the cuff.
• Systolic pressure is identified by the reappearance of the brachial pulse.

Blood Pressure Assessment by Auscultation

• Inflate the cuff ~20 mm Hg above the systolic pressure that was determined by palpation.
• Support arm as previously described.
• Place the stethoscope's diaphragm over the artery, close to the cuff's edge.
• Deflate the cuff slowly while listening for Korotkoff sounds.
• Determine systolic blood pressure (initial tapping sounds), muffling point, and disappearance point.
• If blood pressure is high, re-measure at the end of the examination.

Orthostatic Hypotension (Postural Hypotension) Assessment

• Measure baseline blood pressure and pulse after patient lies down for at least 5 minutes.
• Have the patient stand and immediately repeat measurements.
• Diagnose orthostatic hypotension if systolic BP drops ≥20 mm Hg or diastolic BP drops ≥10 mm Hg within 3 minutes of standing.
• Symptoms like dizziness and increased heart rate may occur.
• Risk factors for orthostatic hypotension: older age, medications, cardiac conditions, heat, prolonged bed rest, pregnancy, alcohol.

Supravalvular Aortic Stenosis Assessment

• If hypertension is detected in the right arm: measure auscultatory pressure in the left arm.
• Do not recheck palpatory pressure or orthostatic changes.
• Supravalvular aortic stenosis consideration: a difference in arm blood pressures is an indicator.

Coarctation of the Aorta

• Coarctation of the aorta is a congenital defect affecting 5-8% of congenital heart defects.
• May occur alone or with other issues like bicuspid aortic valve and ventricular septal defect (VSD).
• Always check BP in lower extremities for new hypertension patients.
• If arm BP is high, check lower extremities to rule out aortic coarctation.
• Use a thigh cuff (6 cm wider than arm) around the midthigh with patient in abdomen-lying position
• The stethoscope is placed over the artery in the popliteal fossa to determine Korotkoff sounds.
• A regular cuff, if thigh cuff is unavailable, can be applied to the lower leg.
• Lower leg systolic pressure compared to the arm suggests coarctation, mainly if the femoral pulse is delayed compared to the radial.

Cardiac Tamponade Assessment

• With low arterial blood pressure and a rapid, feeble pulse, rule out cardiac tamponade
• Presence of marked paradoxical pulse suggests cardiac tamponade, also known as a pulsus paradoxus.
• Normal paradoxical pulse relates to fall (approx. 5 mm Hg) in systolic arterial pressure during inspiration.
• The magnitude of the phenomenon is what determines whether the pulsus paradoxus is normal or abnormal.
• Assess magnitude of paradoxical pulse by inflating the cuff until no sounds are heard deflate until sounds heard only during expiration (note pressure); continue deflating until sounds are heard during inspiration (note pressure).
• If the pressure difference between the two pressures exceeds 10 mm Hg, a marked paradoxical pulse exists.
• Results from increased intrapericardial pressure, interfering with diastolic filling.
• A marked paradoxical pulse can be evident in conditions associated with increased ventilatory effort.

Arterial Pulse Assessment

• Arterial pulse palpation provides info about:
  • Heart Rate Rhythm
  • Pulse Contour
  • Pulse Amplitude

Cardiac Rate Determination

• Cardiac rate is routinely assessed by the radial pulse.
• Palpate both radial arteries with the second, third, and fourth fingers overlying the artery.
• Don't use your thumb as its own pulse may be stronger than the patient's.
• For regular rhythms count the pulse for 30 seconds and multiply by 2 to get beats per minute.
• If the patient has an irregularly irregular rhythm, a pulse deficit may be present.