The Impact of a Preoperative Nerve Block on the Consumption of Sevoflurane

Arthroscopic rotator cuff surgery of the shoulder is performed under general anesthesia. Pain control for after the surgery can be achieved purely with intravenous and oral pain medication or in combination with freezing of the nerves. Nerve freezing (nerve block) placed before surgery has the potential to substantially reduce the amount of inhaled anesthetic given to the patient during surgery. This can benefit the patient by minimizing the opioid usage after surgery and also reduce cost to the system in terms of duration of hospital stay. The purpose of the study is to investigate whether the inclusion of a nerve block to the general anesthetic for rotator cuff repair surgery will also reduce the amount of inhaled anesthetic and thereby lowering the environmental footprint from the anesthetic. The investigators of the proposed study plan to quantify the amount of inhaled anesthetic used for each case and will compare how the consumption is affected by whether the nerve block is applied before or after surgery. Patients will have a nerve block catheter (interscalene catheter) placed under ultrasound-guidance prior to the induction of general anesthetic by an experienced regional anesthesiologist. The nerve block catheter will be bolused with a solution to which the anesthesiologist is blinded which will either be local anesthetic or normal saline (sham). The general anesthetic will be conducted according to a the protocol with the aim of maintaining a standard anesthetic depth monitored by patient state index (PSI). Measurements of the MAC-Value (minimum alveolar concentration) of inhaled anesthetic will be recorded every five minutes and the total amount of volatile anesthetic (in ml and ml/kg) will be noted down by a blinded observer. At the end of the case the anesthesiologist blinded to the solution will inject another solution (now a saline (sham) or local anesthetic before the patient is woken up.