Quantification of the vasodilatory effect of axillary plexus block. A prospective controlled study

Axillary plexus block is a common method for regional anesthesia, especially in hand and wrist surgery. Local anesthetics (e.g., mepivacaine) are injected around the peripheral nerves in the axilla. A vasodilatory effect due to sympathicolysis has been described, but not quantified.

In a prospective controlled study between October 2012 and July 2013, we analyzed 20 patients with saddle joint arthritis undergoing trapeziectomy under axillary plexus block. Patients received a mixture of mepivacaine 1% and ropivacaine 0.75% in a 3:1 ratio. The measurements were carried out on the plexus side and the contralateral hand, which acted as the control. Laser-Doppler spectrophotometry (oxygen to see [O2C] device) was used to measure various perfusion factors before and after the plexus block, after surgery and in 2-h intervals until 6 h postoperatively.

Compared with the contralateral side, the plexus block produced an enhancement of tissue oxygen saturation of 117.35 ± 34.99% (cf. control SO₂: 92.92 ± 22.30%, P < 0.010) of the baseline value. Furthermore, blood filling of microvessels (rHb: 131.36 ± 48.64% versus 109.12 ± 33.25%, P < 0.0062), peripheral blood flow (219.85 ± 165.59% versus 129.55 ± 77.12%, P < 0.018), and velocity (163.86 ± 58.18% versus 117.16 ± 45.05%, P < 0.006) showed an increase of values.

Axillary plexus block produces an improvement of peripheral tissue oxygen saturation of the upper extremity over the first 4 h after the inception of anesthesia.