forearm BP measurements: are they accurate?

16 Oct

SOME DIFFERING OPINIONS:

 

(scroll to the bottom for the 30-second recap)

 

study from Spain, 54 patients, 108 arms (n=108).  BMI >26 kg/m2

  • Mean differences between arm and forearm measurements
    • SBP: 5.5 mmHg (95% CI, -14.5 to 25.5) 
    • DBP: 1.53 mmHg [95% CI, -13.5 to 16.5] 
  • their conclusion: not that accurate
  • my 2 cents: could the difference is due to crappy upper arm measurements in obese folks?

 

SUNY study, 151 patients

  • mean forearm SBP 129.8+/-20.7 mm Hg
  • upper arm SBP 126.2+/-17.6 mm Hg (p = 0.002).
  • mean forearm DBP 80.7+/-14.5 mm Hg
  • upper arm DBPs 76.8+/-13.4 mm Hg (p<0.001).
  • differences between forearm and upper arm systolic and diastolic BPs were within 20 mm Hg in 86% and 94% of patients, respectively.
  • their conclusion: Forearm BP is a fairly good predictor of standard upper arm BP in most patients
  • my 2 cents: 20mmHg is a big difference, but if you can’t get an upper arm BP due to BMI/size, its better than nothing

 

study from Canada, 51 patients, 1285 forearm, & intra-arterial pressures; 352 later got upper arm BPs in post-op

  • compared upper arm & forearm pressure to OR intra-arterial pressures (seems most relevant)
    • Correlation between the intra-arterial and the forearm measures was 0.90 (P < 0.001)
    • Compared to intra-arterial, the forearm method overestimated systolic (6 ± 16 mm Hg, P < 0.001) and underestimated diastolic blood pressure (2 ± 11 mm Hg, P = 0.03).
    • Compared to intra-arterial, upper-arm underestimated systolic (8 ± 16 mm Hg, P < 0.01) and overestimated diastolic blood pressure (9 ± 7 mm Hg, P < 0.001).
  • their conclusion: magnitude of differences between the intra-arterial and forearm method was less than differences between the intra-arterial and upper-arm method.  
  • my two cents: sounds like forearm pressures are as crappy as upper arm BPs in large BMI folks, so somewhat useable, though forearm tends to overestimate the SBP

 

BOTTOM LINE:

some variable differences in upper arm and forearm BPs in large BMI patients

most promising is that intra-arterial BPs matched up ok with forearm BPs compared to upper arm BPs (i.e. just as [in]accurate)

in a pinch, if you can’t use the upper arm (size/fistula), try the forearm — beats nothing

however, this may be a time where mentation/peripheral pulses/perfusion may be as useful a clinical indicator as the BP number

OR, if your patient’s sick, throw in an arterial line.

 

References: spain study; canadian study; SUNY study; picture

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