Effectiveness and safety of ultra-low-dose spinal anesthesia versus perineal blocks in hemorroidectomy and anal fistula surgery: a randomized controlled trial.
Peterson Soares Santos R, Dias de Oliveira-Filho A, de Freitas Lins Neto MÁ, Correia Lins L, Timbó Barbosa F, Felizardo Neves SJ.