Minimum Effective Volume of Lidocaine for Double-Injection Ultrasound-Guided Costoclavicular Block

With the approval of the ethics committee of McGill University Health Centre, a total of 60 patients undergoing upper extremity surgery (elbow or below elbow) will be recruited.

The costoclavicular block will be performed under direct US vision until the tip is between the medial cord and the axillary artery. Two thirds of the volume of LA will be injected in this first location. Subsequently, the needle will be advanced until its tip is positioned next to the lateral cord. The remaining third of the LA volume will be injected in this second location.

Dose assignation will be done using an up-and-down sequential method, where the dose of each subsequent patient depends on the response of the previous patient, called the Biased Coin Design. The first subject recruited will receive a total of 30 mL of lidocaine 1.5 % with epinephrine 1: 200 000. Injection will be carried out by slow increments (5 mL) with negative aspiration between each increment.

The assignment of each subsequent dose will be based on the response of the previous patient as follows: if the previous patient did not have a successful block, the patient will receive the next higher dose, which is the previous dose incremented by 3.0 ml (i.e., an increment of 2.0 mL between the medial cord and the axillary artery, and an increment of 1.0 mL next to the lateral cord). If the previous patient had a successful block, the patient will be randomized to either receive the next lower dose, which is the previous dose decremented by 3.0 ml (i.e., a decrement of 2.0 mL between the medial cord and the axillary artery, and a decrement of 1.0 mL next to the lateral cord), with a probability b = 0.11, or to receive the same previous dose, with a probability 1 - b = 0.89. These are the probabilities required for assigning doses under the BCD for estimating ED90. A maximal dose of 40 mL will not be exceeded to avoid LA toxicity. If the previous patient did not respond and had been given the maximal dose the patient will also get the maximal dose. As soon as we recruit 45 patients with random dose assignment, we will terminate the enrollment procedure.

A research assistant will prepare and administer the injectate using syringes connected to the block needle. The operator and the patient will be blinded to the volume injected.