The ischial spines can be palpated at approximately a finger's length into the vagina at 4 and 8 o'clock. The pudendal nerve runs behind the sacrospinous ligament and is located about 1 cm antero–medial and posterio–medial to the ischial spine. The needle needs to be inserted to about 1 cm depth.
If you are going to perform a pudendal block, it is wise to do this first as it usually takes about 10 minutes for optimal effect.
After cleaning the vulva, perform the pudendal block. You can then prepare the rest of the instrumental trolley, assemble the instrument and catheterise.