Many of my friends have had epidurals and still been in horrible pain. I want the maximum pain relief available by epidural. In a fashion magazine I read that ropivicaine is the best local anesthetic to use in the pump. A sensory block refers to the effect of a local anesthetic drug to block sensation - in other words, the feeling of someone touching you or the sensation of pain. Motor block refers to the ability of these same local anesthetics to block the function of your muscles - this leads to weakness or inability to move, walk, etc. until the anesthesia wears off.
Motor block requires a higher concentration of medication than sensory block.
Ideally, for labor and delivery anesthesiologists strive to achieve complete or maximal sensory block while minimizing the amount of motor block. This allows the mother to more in control of her position and surroundings and helps to maintain the force of contractions at the time of delivery. The way this is achieved it by varying the concentration of the drug delivered. There are many reasons that an epidural may not work initially. Many of these are correctable and the efforts of an attentive anesthesiologist can assure success in most situations.