 To find the optimal dose and combination of small dose of Levobupivacaine LB coadministered intrathecally with Fentanyl F or Sufentanil S with the highest probability for not developing hypotension and the lowest opioid side effect that would be sufficient to achieve and maintain a sensory block to the tenth thoracic dermatoma T10 in elderly patients for surgery lasting 45 minutes as compared with large dose of Levobupivacaine alone. 