Then , four sites randomly received injections of equal volumes ( 0.1 mL ) of either normal saline ( NS ) , lidocaine 0.5 % ( L ) , sufentanil 0.75 microg ( S ) , lidocaine 0.5 % plus sufentanil 0.75 microg ( L+S ) , and one site was not injected and served as reference ( REF ) .
