Routine surgical procedure monitoring with an electrocardiogram, sphygmomanometer, and pulse oximeter was performed. One experienced anesthesiologist performed an ultrasound guided axillary brachial plexus block (S Series, FUJIFILM Sonosite, Seattle, USA) with the patient in the supine position. Local anesthetic injection was performed on each nerve identified in this pathway (i.e., the radial nerve, the ulnar nerve, the median nerve, and the musculocutaneous nerve) In the group bupicavaine 0.25%, 10 ml of 0.25% bupivacaine was injected into each nerve, for a total of 40 ml per patient.

Routine surgical procedure monitoring with an electrocardiogram, sphygmomanometer, and pulse oximeter was performed. One experienced anesthesiologist performed an ultrasound guided axillary brachial plexus block (S Series, FUJIFILM Sonosite, Seattle, USA) with the patient in the supine position. Local anesthetic injection was performed on each nerve identified in this pathway (i.e., the radial nerve, the ulnar nerve, the median nerve, and the musculocutaneous nerve). In the group bupivacaine 0.5% , 5 ml of 0.5% bupivacaine was injected into each nerve, for a total of 20 ml per patient.

Venous blood samples were collected prior to blocking , every 15 min during the first hour after completion of the blocking and every 30 min during the second hour after completion using an exclusive cannula. Then, 5 ml was drawn off and was stored in two EDTA tubes (BD, Franklin Lakes, NJ, USA). The EDTA tubes were centrifuged at 3,500xg for 10 min to obtain the blood plasma. This plasma was then stored in cryogenic tubes in a freezer at -80 °C until the time of the analysis. A high-performance liquid chromatography apparatus (Shimadzu, Kyoto, Japan) coupled to a Bruker mass spectrometer (MS), model Amazon (USA), with electrospray source ionization and a sequential mass spectrometry system (MS/MS) were used for the analysis. After obtaining the precursor ion, a fragment was obtained via a collision-induced dissociation process. The following molecular ions were selected: 289.0 m/z==>140.1 m/z. The methodology was validated according to the international FDA recommendations.

The aim of this study was to evaluate the difference in peak plasma levels obtained after ultrasound guided axillary brachial plexus block using two different bupivacaine concentrations to maintain the infused mass. Venous blood samples were collected prior to blocking , every 15 min during the first hour after completion of the blocking and every 30 min during the second hour after completion using an exclusive cannula. Then, 5 ml was drawn off and was stored in two EDTA tubes (BD, Franklin Lakes, NJ, USA). The EDTA tubes were centrifuged at 3,500xg for 10 min to obtain the blood plasma. This plasma was then stored in cryogenic tubes in a freezer at -80 °C until the time of the analysis. A high-performance liquid chromatography apparatus (Shimadzu, Kyoto, Japan) coupled to a Bruker mass spectrometer (MS), model Amazon (USA), with electrospray source ionization and a sequential mass spectrometry system (MS/MS) were used for the analysis.

This evaluation occurred every 5 min until the 30th min after blocking. During this period, if surgical anesthesia was not obtained, then a complementary bupivacaine injection was administered distal to the axilla and the patient was excluded from the protocol. Surgical anesthesia was defined as a motor scale of 2 or lower; an absence of cold and pinprick sensation.