Minimum Effective Concentration of Ropivacaine for Brachial Plexus Block Via the Supraclavicular and Infraclavicular Approach, Femoral Nerve Block, Sciatic Nerve Block Via the Popliteal and Parasacral Approach

Inclusion Criteria: * American Society of Anesthesiologists physical status I to III (patients may be healthy or have systemic disease, but any disease does not pose a constant threat to life, and patients are neither moribund, nor not expected to survive without the operation). * Age 18 or above * Undergoing elective ambulatory surgery of the upper limb (excluding the shoulder), lower limb (excluding the hip), or lower abdomen with sensory blockade as part of the pain management plan. Exclusion Criteria: * Body mass index of \>35 kg/m2 (higher chance of failure) * Deformities of the leg (for patients in the parasacral, femoral, and popliteal groups), or the chest or shoulder (for patients in the supraclavicular, infraclavicular, and TAP groups) * Preexisting infection at the injection site * Existing neurologic disease * Allergy to local anesthetic agents * Severe respiratory disease * Coagulopathy * Any other contraindication to the block being considered * Patients requiring total motor blockade as well as sensory blockade