Inhalatory analgesia with nitrous oxide vs paracervical infiltration vs control group in hysteroscopic polypectomy: randomised controlled clinical trial - Cristina del Valle Rubido; J.A. Solano Calvo; Antonio Rodríguez Miguel; Juan José Delgado Espeja; Jerónimo González Hinojosa; Álvaro Zapico Goñi (Gynecological Surgery, 2015)