Midazolam in Supraclavicular Brachial Plexus Block

Overview

An effective brachial plexus block (BPB) provides a useful alternative to general anesthesia for upper arm surgery producing complete muscular relaxation. It provides surgical anesthesia in upper extremity surgery, post-operative analgesia and chronic pain management. In addition to surgical procedure on conscious patients and early eating after the procedure make regional anesthesia more attractive. Brachial plexus block also maintains stable intraoperative hemodynamic and associated sympathetic block. The sympathetic block decreases postoperative pain, vasospasm and edema. The nerve of brachial plexus may be blocked anywhere along its course. The approach for blocking brachial plexus nerve is interscalene, supraclavicular, infraclavicular and axillary approach. Supraclavicular approach for blockade of the brachial plexus is the most commonly used approach in providing surgical anesthesia. In recent years, the technique has gained importance as regional anesthetic technique for surgical, diagnostic and therapeutic purposes in interventional pain management. It includes blocking of the brachial plexus where it is most compactly arranged, with fewer requirements of the anesthetic solution and rapid onset of action. Supraclavicular nerve block is technically easy to perform because of reliable and fixed landmark but association of pneumothorax is a profound complication. The extent of blockade following injection into the sheath surrounding the brachial plexus may depend on the volume and concentration of local anesthetic (LA) used. Because of bupivacaine long duration of action, it is used most frequently among local anesthetics for BPB. Inevitably, the effects of single-injection BPB dissipate after several hours unmasking the moderate-to-severe pain of the surgical insult. Efforts to prolong BPB duration by increasing LA dose are limited by their narrow therapeutic window and indeed may not be effective as recent studies have demonstrated equivalent analgesic duration with volumes as low as 5 ml. Midazolam is known to produce antinociception and potentiate the effect of LA when given in neuraxial block. It produces this effect by its action on Gamma Aminobutyric Acid-A (GABA-A) receptors and also on the peripheral nerves which contain these receptors. Several studies showed midazolam to be effective when used in intrathecal, epidural and caudal blocks and now recently midazolam with bupivacaine has been found to improve analgesic characteristics in peripheral blocks compared to bupivacaine alone. Due to the high blood concentration of benzodiazepine through conventional routes and profound sedation, proper assessment of analgesic effect was difficult to obtain. With the advent of the less toxic water soluble benzodiazepine (midazolam), it became possible to use it directly over the nerve tissues.

The day prior to surgery, all patients will undergo pre-anesthetic checkup including detailed history, thorough general, physical, systemic examination and weight of the patient. All patients will be kept nil by mouth for at least 6 hours. * Written consent, coagulation profile, intravenous line, emergency resuscitation equipments including airway devices, advanced cardiac life support drugs for LA toxicity will be available. * Patients will be monitored using standard monitoring (ECG, non-invasive blood pressure and pulsoximetry) * All patients will be lightly sedated with 1 mg midazolam I.V. SonoAce 6 ultrasound machine with high frequency linear probe will be used in our study. Palpation of the subclavian artery in the supraclvicular fossa, just lateral to the sternocledomastoid and above the clavicle (landmark located one finger or 1 cm above the clavicle at the junction of inner 2/3 and outer 1/3 of clavicle). Position to perform supraclavicular BPB; the anesthetist will stand behind the patient's head, with the ultrasound machine on the side being blocked. The head of the bed is slightly raised to allow the shoulder to drop somewhat the patient's head will be turned to the opposite side, resting directly on the table without a pillow, the hand holding the probe will rest against the patient's jaw, the probe is placed in the supraclavicular fossa in a coronal oblique plane, the needle will be inserted from the lateral side, The pulsating hypoechoic supraclavicular artery is identified, lying above the hyperechoic first rib, the probe is then angled until both the first rib and the pleura are also seen simultaneously, The nerve structures (trunks or divisions) are usually visualized as a collection of hypoechoic round structures (a bunch of grapes) lying superior and postero-lateral to the subclavian artery. A 3 cm long 22 G needle with 10 cc syringe filled with respective LA agent will be inserted directing downward, forward and medially at the angle of 20° to the skin till the parasthesia elicited in the hand or the 1st rib hit, then the needle will be fixed at that point. After the negative aspiration respective agents will be given. A gentle massage over the area will be done with an idea of uniform spread. All brachial plexus injections will be administered slowly with repeated aspiration to prevent or detect early intravascular injection. The end of the injection will be considered time 0.