Up down sequential analysis is a method developed by Dixon to determine the point where 50% of people will have a positive response and 50% will have a negative response to an intervention. It is a very powerful technique that has been used to determine the median effective dose (referred to as ED50) of many medications. Using this method, patient number 1 is given a certain amount of the intervention being studied. If patient 1 has the desired response, patient 2 in the series is given less of the intervention, and if patient 1 does not have the desired response, patient 2 is given more of the intervention. This is repeated through a series of patients until the dose where there is a 50% response rate is determined. In this study, we wish to use up down sequential analysis to determine the time period a patient should remain seated after intrathecal injection of hyperbaric medication that result in a 50% rate of hypotension, what we will call the ET50 (Estimated Time for 50% of patients to have hypotension). We would like to explore this relationship with 2 clinically used doses of hyperbaric bupivicaine.