Regional hemodynamic changes after an axillary brachial plexus block: a pulsed-wave Doppler ultrasound study.

Background: Brachial plexus block (BPB) causes vasodilatation and an increase in blood flow to the ipsilateral upper limb. However, no reports have comprehensively evaluated the regional hemodynamic changes after a BPB.
Methods: Eight healthy adult patients who were scheduled for elective hand surgery had an ultrasound-guided axillary BPB for anesthesia. Regional hemodynamic parameters were measured in the ipsilateral brachial artery, using pulsed-wave Doppler (PWD) ultrasound before the block (0 minute) and at regular intervals for 30 minutes after the block. Skin temperature on the dorsum of the ipsilateral hand was also recorded at the same time intervals. Regional hemodynamic parameters that were measured in the brachial artery included peak systolic velocity (PSV, cm/s), end-diastolic velocity (EDV, cm/s), mean velocity (Vmean) and time-averaged mean velocity (TAVM, cm/s), ratio of PSV and EDV (S/D), diameter (d, cm), resistance index (RI), and pulsatility index (PI). Brachial artery blood flow (Q) was calculated as the product of TAVM and cross-sectional area.
Results: The ultrasound-guided axillary BPB was successful in all the patients studied. The earliest change after the BPB was a change in the morphology of the PWD spectral waveform from a triphasic to a monophasic waveform and an elevation in the diastolic blood flow velocity. Over time, there was also a significant increase in PSV, EDV, Vmean, TAVM, d, brachial artery blood flow, and skin temperature and a decrease in S/D ratio, RI, and PI. Most of these changes were seen as early as 5 minutes after the block. The increase in EDV (3.7-fold) was the most notable change, and it was greater (P < 0.05) than the increase in PSV (1.5-fold) and Vmean (2.8-fold).
Conclusions: Regional hemodynamic changes that occur after an axillary BPB include a change in the morphology of the PWD spectral waveform, arterial vasodilatation, an increase in blood flow velocity, and an increase in blood flow through the ipsilateral brachial artery.