Erector Spinae Plane Block in Breast Surgery: A dose finding trial

Erector Spinae Plane block is performed for post operative pain control in Breast Surgery.This block has been used in different volumes by different investigators. Specific volume for a particular concentration of local anesthetic is yet to be found.We are conducting a dose finding study with .375% ropivacaine in erector spinae plane block.A unilateral ESPB will be performed before the induction of general anaesthesia at the level of T4 vertebra under USG guidance. Patient giving consent for the study will be taken to procedure room. Iv line will be secured and routine ASA monitors will be attached.  ESP block will be given  before giving general anesthesia to the patient. After the needle tip will be correctly placed in the ESP using an ‘in-plane’ technique, a widespread application of 15 to 30 ml of a predefined dose of ropivacaine 0.375% will be injected. Two experienced investigators will administer ESPB to avoid the bias of having only one physician performing all of the blocks. Investigators performing the ESPB will neither be involved in the management of the general anaesthesia nor in the postoperative care and the pain assessment of the patients. Patients will be blinded to the volume of ropivacaine injected. To assess the ropivacaine MEV90, we will use up-and down sequential allocation method. The dose of ropivacaine received by the subsequent patients will be determined by the response of the previous patient. For successful responses, the volume will be reduced by 3mL, and for unsuccessful responses, the next patient will receive a dose increased by 3mL. General anaesthesia will be induced with fentanyl 2mcg/kg, propofol 2mg/kg and atracurium 0.5mg/kg.Anaesthesia will be maintained with isoflurane (MAC 1). During the surgical procedure, fentanyl (1mcg/kg) will be given if the heart rate or arterial pressure increased by 20% relative to the baseline measurement. All the patients will receive 1gm paracetamol after induction intraoperatively. The success or failure of the study dose of ropivacaine will be assessed using the NPS at rest 30min after arrival to the recovery room. Two outcomes will be considered; effective: NPS of 3 or lower out of 10 (directing a decrement for the next patient); and ineffective: NPS greater than 3 out of 10 (directing an increment for the next patient). In case of NPS greater than 3 out of 10 within the 6 h of the study, the dose will be considered ineffective, and the patient will be given rescue analgesia. Injection Fentanyl 0.5 mcg/kg will be used as rescue analgesic if NPS > 3 at any time postoperatively.

Study end point will be 6 hours after performance of the block. After shifting to post anesthesia care unit pain score and patient satisfaction score will be noted every 30 minutes till study end end point is reached.