Quantitative Evaluation of the Regional Hemodynamic Changes after a Brachial Plexus Block

I hypothesized that pulsed wave Doppler ultrasound (PWD US) is a reliable method for measuring regional hemodynamic parameters in the upper extremity. It can be used to comprehensively quantify the regional hemodynamic changes after a brachial plexus block (BPB) and to determine the extent of these changes at different sites in the upper extremity and after different techniques for BPB. The following section outlines a series of studies that I undertook during this PhD project to corroborate my hypothesis.;Firstly, we sought to assess the intra-observer and inter-observer variability of measuring regional hemodynamic parameters, in the brachial and common palmar digital arteries of the upper extremity, using PWD US in 12 healthy young volunteers aged 21--34 yrs. The measurements were performed independently by two observers. Measured hemodynamic parameters included peak systolic velocity (PSV, cm/s), end diastolic velocity (EDV, cm/s), ratio of PSV and EDV (S/D), mean velocity (Vmean, cm/s), time-averaged mean velocity (TAVM, cm/s), resistance index (RI), pulsatility index (PI), the arterial diameter (d, cm), and blood flow (mL/min). The results showed that PWD US is a reliable and reproducible method of measuring regional hemodynamic parameters in the upper extremity (ICC>0.9).;Secondly, we comprehensively evaluated the regional hemodynamic changes in the ipsilateral brachial artery after an ultrasound guided (USG) axillary BPB in eight adult patients aged 24--70 yrs. Our results suggested that 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, and blood flow, 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 significantly greater than the increase in PSV (1.5-fold) and Vmean (2.8-fold).;Thirdly, the regional hemodynamic changes in the proximal (brachial artery) and distal (common palmar digital artery) artery of the upper extremity after an USG supraclavicular BPB was investigated in 15 adult patients aged 23--70 yrs. After the block, the common palmar digital artery showed more obvious vasodilatation on the power Doppler US scan. In the PWD spectral waveform, and in both arteries studied, the protodiastolic blood flow disappeared and there was an elevation of the diastolic curve. Also there was a significant increase in PSV, EDV, Vmean, TAVM, d, and blood flow, and a significant reduction in S/D ratio, PI and RI in both arteries. Relative changes of these parameters were greater in the common palmar digital artery than in the brachial artery. In this study, bilateral spread of local anesthetic was observed in 4 patients, as evidenced by an increase of skin temperature on the contralateral hand.;Fourthly, a prospective and randomized study was conducted to compare the regional hemodynamic changes in the upper extremity after an axillary and supraclavicular BPB. The two study groups were similar with respect to demographic data. Both axillary and supraclavicular BPB caused a significant increase in PSV, EDV, Vmean, TAVM, d, and blood flow, and a significant reduction in S/D ratio, PI and RI in both the brachial and common palmar digital arteries. Compared with the axillary approach, the supraclavicular approach produced significantly greater increases in TAVM and blood flow in the brachial artery. However, the onset of sensory blockade was faster after the axillary BPB than with the supraclavicular BPB. (Abstract shortened by UMI.).