Advanced Chronic Kidney Disease Units in Spain: a national survey on standards of structure, resources, results and patient safety Mario Prieto-Velasco; María Dolores del Pino y Pino; Juan Manuel Buades Fuster; Lourdes Craver Hospital; Ramón Pons Prades; Juan Carlos Ruiz San Millán; Mercedes Salgueira Lazo; Patricia de Sequera Ortiz; Nicanor Vega Díaz;