Effect of sphygmomanometer cuff pressure on the differentiation of veins from arteries on ultrasound imaging: an observational cross-sectional study.

Background: Ultrasound guidance is commonly used for accessing difficult peripheral veins. For successful access, a tourniquet is required for venodilation. Tourniquets decrease the compressibility and increase the diameter of veins; they also obfuscate artery-vein differentiation on ultrasound. We aimed to establish the upper limit of sphygmomanometer cuff pressure that facilitates artery-vein differentiation during ultrasound-guided peripheral intravenous access.

Methods: We employed the sphygmomanometer cuff as a tourniquet for venodilation and tested it on seven participants at six different levels as follows: 0 mmHg, DBP/2, DBP, (DBP+SBP)/2, SBP, and SBP+20 mmHg. We used an ultrasound probe attached to a pressure-measuring instrument to record cross-sectional images of the cubital artery and vein. During ultrasonography, compression was applied to the blood vessels through the skin. The following day, we measured the wrist pulse pressure and observed the oximeter pulse wave at six different tourniquet pressure levels. Repeated-measures analysis of variance (ANOVA) on ranks and Tukey's post-hoc analysis were used for multiple comparisons.

Results: Arterial pulsation was maintained at tourniquet pressures between 0 mmHg and (DBP+SBP)/2. However, arterial pulsation decreased or disappeared when the tourniquet pressure reached or exceeded the SBP. Moreover, at this pressure level, the superior compressibility of veins compared to that of arteries was no longer observed. Compression of the artery to 75% and 50% of its original diameter increased arterial pulsation.

Conclusion: Arterial pulsation and the superior compressibility are useful indicators for differentiating veins from arteries until the tourniquet pressure reaches (DBP+SBP)/2. However, these indicators are not reliable once the tourniquet pressure exceeds the SBP.