To see if ET50 is dependent on the dosage of medication given, we will determine the ET50 for 2 doses of hyperbaric bupivicaine. Both of the doses we will study are used routinely in clinical practice. Using a computerized randomization schedule, we will randomly assign patients to receive either 2 ml or 1.5 ml of 0.75% hyperbaric bupivacaine, for a total of 15 mg or 12.5 mg of bupivacaine respectively.