Blood Pressure

Aka: Blood Pressure, BP Examination, Korotkoff Sound, Blood Pressure Measurement, Blood Pressure Monitoring, Blood Pressure Determination

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II. Precautions

  1. Blood Pressures are frequently inaccurate due to improper cuff size, technique, or inadequate rest before measurement
  2. Recent Nicotine in last 30-60 minutes can raise systolic Blood Pressure as much as 25 mmHg
    1. Unlike Nicotine, typical Caffeine doses are not associated with significant Blood Pressure increase in regular users
  3. Avoid finger Blood Pressure monitors (and aside from morbidly obese patients, avoid wrist monitors)

III. Physiology

  1. See Blood Pressure Physiology
  2. Automated Blood Pressure mechanism (Oscillometric BP cuffs)
    1. Automated BP cuffs measure the mean arterial pressure during cuff deflation
    2. Automated cuffs often cycle repeatedly to obtain a single Blood Pressure reading
    3. Automated machine use the measured MAP to calculate the systolic (SBP) and diastolic Blood Pressure (DBP)

IV. Efficacy: Automated Blood Pressure

  1. U.S. Blood Pressure Validated Devices
    1. https://www.validatebp.org/
  2. Automated Blood Pressure is now recommended over manual Blood Pressures
    1. Mercury sphygmomanometers have largely been replaced due to toxicity risk
      1. Both manual and automatic non-mercury Blood Pressure cuffs require ongoing calibration
    2. Manual Blood Pressures have significant inter-operator variation
      1. Blood Pressure Measurement should be performed by slowly lowering pressure in 2-3 mmHg increments
  3. Some studies find automated Blood Pressures inaccurate, overestimating both systolic and diastolic Blood Pressure
    1. When accurate systolic or diastolic readings are needed emergently (e.g. Aortic Dissection), Arterial Lines are preferred
    2. Confirm elevated automated Blood Pressure with 2 manual, auscultated Blood Pressures
    3. Inaccurate readings are more common at the extremes of BMI (morbidly obese, very thin patients)
    4. Arrhythmias also result in inaccurate Blood Pressure readings (obtain multiple serial values)
    5. Flynn (2012) J Pediatr 160(3): 434-40 [PubMed]
    6. Mansoor (2016) Open Access Maced J Med Sci 4(3): 404–9 [PubMed]
      1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5042623/
  4. Other studies find automated Blood Pressures to be lower than manual when patient is at home or alone in clinic
    1. Roerecke (2019) JAMA Intern Med 179(3): 351-62 [PubMed]

V. Technique: Blood Pressure cuff size

  1. Poor cuff fit results in inaccurate Blood Pressure
    1. Undersized cuff artificially raises Blood Pressure
    2. Oversized cuff artificially lowers Blood Pressure
  2. Pediatric Cuff size
    1. Based on arm circumference measured at point midway between acromion and olecranon
    2. Minimum Cuff Width
      1. Width >2/3 length of upper arm
      2. Width >40% of arm circumference
    3. Minimum Cuff length
      1. Bladder nearly encircles arm
      2. Bladder length 80-100% of circumference
  3. Adult Cuff size
    1. Cuff Width: 40% of limb's circumference
    2. Cuff Length: Bladder at 80% of limb's circumference
    3. Indications for large cuff or thigh cuff
      1. Upper arm circumference >34 cm
    4. Indications for Forearm cuff (with radial palpation)
      1. Upper arm circumference >50 cm

VI. Technique: Positioning of Blood Pressure Cuff

  1. Cuff applied directly over skin (not through clothes)
    1. Clothes artificially raises Blood Pressure
  2. Center inflatable Bladder over brachial artery
  3. Position lower cuff border 2.5 cm above antecubital
  4. Patient's arm slightly flexed at elbow
  5. Position stethoscope bell over brachial artery

VII. Technique: Blood Pressure Measurement

  1. Patient should be comfortable, seated with back supported and with empty Bladder
  2. Legs uncrossed and feet flat on the floor
  3. Patient should not speaking during measurement
  4. Wait 5 minutes of rest before checking Blood Pressure, and avoid Nicotine within prior 30 minutes
  5. Check Blood Pressure while seated, in right arm (Aortic Coarctation may falsely lower BP measurement)
  6. Take Blood Pressure with arm supported at heart level
  7. Inflate cuff rapidly to level above suspected SBP
  8. Deflate cuff slowly at a rate of 2-3 mmHg per second
  9. Listen for auditory vibrations from artery (Korotkoff)
    1. Systolic Blood Pressure: Onset of consecutive sounds
    2. Diastolic Blood Pressure: Disappearance of sounds

VIII. Technique: Obtain Multiple Blood Pressure Measurements

  1. Validation of abnormal readings
    1. Recheck Blood Pressure at least once or twice more at same visit
    2. Blood Pressure improves to <160/89 after 30 minutes rest in >30% with Severe Hypertension
      1. Grassi (2008) J Clin Hypertens 10(9): 662-7 [PubMed]
  2. Aortic Coarctation
    1. Left and right arm, and one lower extremity
  3. Orthostatic Hypotension
    1. Most common chronically in the elderly (Fall Risk)
    2. Check Blood Pressure and Pulse, Supine and Standing (Postural Blood Pressure)
  4. Hypertension
    1. See Hypertension Criteria
    2. Confirm office Blood Pressures on Home Blood Pressure Monitor (or Ambulatory Blood Pressure Monitoring)

IX. Interpretation

  1. See Hypertension Criteria
  2. See Hypotension

X. Interpretation: Children

  1. See Pediatric Vital Signs
  2. Formulas for Systolic Blood Pressure estimate (for over age 1 year)
    1. Median SBP = 90 mmHg + (2 x Age in years)
    2. Minimum SBP = 70 mmHg + (2 x Age in years)
  3. Rough estimate for Systolic Blood Pressure (SBP)
    1. Typical systolic Blood Pressure
      1. Infant: 80
      2. Preschool: 90
      3. Adolescent: 100
    2. Minimal systolic Blood Pressure
      1. Infant: >60
      2. Toddler >70
      3. Preschool >75
      4. School-age: >80
      5. Teen >90
  4. Term Newborn (3 kg)
    1. Age 12 hours: 50-70 / 25-45
    2. Age 96 hours: 60-90 / 20-60
    3. Age 7 days: 74 +/- 22 mmHg (Systolic BP)
    4. Age 42 days: 96 +/- 20 mmHg (Systolic BP)
  5. Infant (6 months old)
    1. Blood Pressure: 87-105 / 53-66
  6. Toddler (2 years old)
    1. Blood Pressure: 95-105/53-66
  7. School age (7 years old)
    1. Blood Pressure: 97-112 / 57-71
  8. Adolescent (15 years old)
    1. Blood Pressure: 112-128 / 66-80

XI. References

  1. Handler (2009) Perm J 13(3): 51–54 [PubMed]
    1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2911816/
  2. Kallioinen (2017) J Hypertens 35(3): 421–441 [PubMed]
    1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5278896/

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