Minimum Effective Dose of Ropivacaine for Peripheral Nerve Block on Posture-evoked Pain for Spinal Anesthesia in Patients With Hip Fracture

Patients with hip fractures are anticipated to endure sever pain caused by positional changes required for spinal anesthesia. Providing analgesia before positioning not only increases patient comfort but also improves positioning and successful spinal block. Peripheral nerve block is an effective strategy for relieving pain during postures change for spinal anesthesia in patients with hip fractures. Three types of peripheral nerve block, including fascia iliaca block, femoral nerve block and Pericapsular nerve group block (PENG block), has been successfully used for analgesia for spinal anesthesia positioning in patients with hip fractures. However, the minimum effective dose of local anesthetics for these three types of peripheral nerve block is not known. This study aims to determine the minimum effective dose of ropovacaine in the three types of peripheral nerve block using a biased coin design up-and-down sequential method. Successful block is defined as NRS score ≤3 by positional changes for spinal anesthesia, achieved at 20min after the block. MED90 of ropivacaine for fascia iliaca block, femoral nerve block and PENG block be assessed respectively. Patients will receive ultrasound guided peripheral nerve block. The initial dose is chosen as 80 mg on the basis of clinical experience. Subsequently, if a patient has an inadequate block, the ropivacaine dose is increased by 8 mg in the next subject. If a patient has a successful block, the next subject is randomized to receive either a lower dose (with a decrement of 8 mg), with a probability of b = 0.11, or the same dose, with a probability of 1 - b = 0.89. Forty five successful blocks for each type of nerve block will be accomplished. MED90 of each type of nerve block will be calculated by isotonic regression.