Why Paramedics May Measure Blood Pressure on the Forearm
Forearm blood pressure measurement is an acceptable alternative when upper arm measurement is not feasible, though it systematically overestimates both systolic and diastolic pressures by approximately 3-4 mmHg and should be interpreted with this limitation in mind. 1
When Forearm Measurement is Appropriate
The American Heart Association explicitly recognizes forearm blood pressure measurement as a legitimate alternative in specific clinical circumstances: 1
- Morbid obesity where arm circumference is too large even for thigh cuffs and upper arm geometry prevents proper cuff placement 1
- Trauma or injury to the upper arm preventing cuff placement
- Bilateral upper extremity access restrictions (burns, IV lines, dialysis access) 2
- Emergency situations where rapid assessment is needed and upper arm access is impaired 3
Understanding the Accuracy Trade-off
Systematic Measurement Differences
Forearm measurements produce predictable deviations from standard upper arm readings: 3
- Systolic pressure: Averages 3.6 mmHg higher on forearm (129.8 vs 126.2 mmHg) 3
- Diastolic pressure: Averages 3.9 mmHg higher on forearm (80.7 vs 76.8 mmHg) 3
- Correlation: Strong correlation exists (r=0.75 for systolic, r=0.72 for diastolic) 3
- Clinical acceptability: 86% of systolic and 94% of diastolic readings fall within 20 mmHg and 10 mmHg respectively 3
Critical Positioning Requirements
When measuring on the forearm, the cuff must be placed over the radial artery with the same rigorous positioning standards as upper arm measurement: 1
- Position the forearm at exact heart level (mid-sternum/fourth intercostal space) 1, 2
- Support the forearm—never have the patient hold it up 1, 2
- Hydrostatic errors of 2 mmHg per inch deviation from heart level still apply 1, 2
Why Upper Arm Remains the Gold Standard
Upper arm (brachial artery) measurement continues to be the most reliable and is the preferred location for the majority of patients. 1
The American Heart Association and American College of Cardiology prioritize upper arm measurement because: 1
- All epidemiological studies linking blood pressure to cardiovascular outcomes used brachial artery measurements 1
- Brachial measurements have the most extensive validation data 1
- Systolic and diastolic pressures vary substantially in different parts of the arterial tree, with systolic pressure increasing and diastolic pressure decreasing in more distal arteries 1
Common Pitfalls to Avoid
Wrist vs. Forearm Confusion
Do not confuse forearm measurement (over radial artery) with wrist monitors: 1
- Wrist monitors are not generally recommended for routine clinical use due to poor validation and high failure rates 1
- Most wrist monitors tested have failed validation studies 1
- Wrist monitors require the device to be held precisely at heart level, increasing error potential 1
Finger Monitors
Finger monitors are very inaccurate and should never be used. 1
Interchangeability Error
Forearm and upper arm measurements are not interchangeable in acutely ill patients. 4
- Research in ICU patients shows statistically significant differences that make the measurements non-interchangeable 4
- The systematic overestimation by forearm measurement must be considered when making clinical decisions 3, 4
Practical Guidance for Paramedics
When forearm measurement is necessary: 1, 3
- Document the measurement site clearly in the patient record
- Apply proper technique: Place cuff over radial artery, support forearm at heart level 1
- Interpret with caution: Expect readings 3-4 mmHg higher than true brachial pressure 3
- Transition to upper arm measurement as soon as clinically feasible for ongoing management 1
The paramedic's decision to use forearm measurement was likely driven by practical necessity rather than preference, and represents an acceptable compromise when standard upper arm measurement cannot be performed safely or accurately. 1, 3