ED90 of 0.75% Bupivacaine for Bilateral Tubal Ligation (BTL)

"The dose for the first subject (A#X) will be 12 mg 0.75% hyperbaric bupivacaine. Two possible outcomes will be recorded: satisfactory or unsatisfactory anesthesia which is determined by occurrence of intraoperative pain and the need for intraoperative analgesia supplementation. Satisfactory analgesia will be defined as a sensory block to the T8 dermatome and the patient shall require no further supplementation for discomfort during her procedure. Unsatisfactory analgesia will be defined as a block not achieving a T8 dermatomal level or when a patient requests additional medication for discomfort at any time during her procedure.~The dose for the next (A#X+1) will be adjusted based on the outcome from previous subjects respectively using up-down sequential allocation method with a biased-coin design. This process will continue in similar fashion with dose adjustments for next subjects to be based on outcome from subjects immediately prior."