Intravenous and Perineural Dexamethasone for Ultrasound-Guided Axillary Blocks

A Randomized Comparison Between Intravenous and Perineural Dexamethasone for Ultrasound-Guided Axillary Blocks

Dexamethasone prolong the duration of brachial plexus blocks, but the optimal route, intravenous (IV) or perineural (PN), remains controversial.

This Multi-centric trial compare IV and PN dexamethasone for ultrasound-guided axillary brachial plexus blocks (AXBs). Research hypothesis is that PN modality will outlast its IV counterpart. Since analgesic duration and sensory duration can be influenced by intake of pain medications and surgical trauma to small cutaneous nerves, the investigators will select motor block duration as the main outcome.

After Ethics Committee of the McGill University Health Centre, a total of 150 patients undergoing upper extremity surgery (below the elbow) will be recruited.

All AXBs will be supervised by one of the coauthors and conducted preoperatively in an induction room. This area will have full access to an oxygen source, resuscitative equipment and drugs.

All patients will have fasted for at least eight hours. An IV cannula will be placed prior the block and will be monitored and given oxygen at 2-4 L/min through nasal cannulas.

Light sedation will be provided for patient comfort if needed.Patients will be placed supine with the shoulder abducted and the elbow flexed. The AXB will have a puncture site superior to the axillary artery. After skin disinfection and draping, a skin wheal will be raised with 3 mL of lidocaine 1.5%.

In both groups, 30 mL of lidocaine 1.0%-bupivacaine 0.25% with epinephrine 5 µ/mL will be used. A 22-gauge, 5 cm block will be advanced under direct US vision toward the musculocutaneous nerve. Six mL of LA will be deposited in this location. The needle will then be directed posterior to the artery, at 6 o'clock position and twenty-four mL of LA will be deposited to obtain a spread around the artery.

Patients will be randomized to receive 8 mg of IV or PN dexamethasone. In the IV group, patients will receive 0.8 mL of dexamethasone (10 mg/mL) intravenously and 0.8 mL of normal saline will be added to the injectate through the block needle. In the PN group, patients will receive 0.8 mL of normal saline intravenously and 0.8 mL of dexamethasone (10 mg/mL) will be added to the injectate through the block needle.

A research assistant will prepare the IV and PN injectates. The operator, patient and investigator assessing the block will be blinded to group allocation.

If placement of the needle tip in the desired location is unsuccessful after 15 minutes, the procedure will be stopped and the patient excluded from the study. Brachial plexus blockade will be carried out using an alternative method. If the alternative method fails as well, the patient will be given general anesthesia and intravenous narcotics will be used for postoperative analgesia

Inclusion Criteria:

• Below Elbow surgery
• Age between 18 and 80 years
• American Society of Anesthesiologists classification 1-3
• Body mass index between 18 and 35 kg/m2

Exclusion Criteria:

• Adults who are unable to give their own consent
• Pre-existing neuropathy (assessed by history and physical examination)
• Coagulopathy (assessed by history and physical examination and, if deemed clinically necessary, by blood work up i.e. platelets ≤ 100, International Normalized Ratio ≥ 1.4 or partial prothrombin time ≥ 50)
• Renal failure (assessed by history and physical examination and, if deemed clinically necessary, by blood work up i.e. creatinine ≥ 100)
• Hepatic failure (assessed by history and physical examination and, if deemed clinically necessary, by blood work up i.e. transaminases ≥ 100)
• Allergy to local anesthetics (LAs)
• Pregnancy
• Prior surgery in the axillary region
• Chronic pain syndromes requiring opioid intake at home