title: Relationship between volume and survival in closed intensive care units is weak and apparent only in mechanically ventilated patients.
abstract: BACKGROUND
  Recent studies have found an association between increased volume and increased intensive care unit (ICU) survival; however, this association might not hold true in ICUs with permanent intensivist coverage. Our objective was to determine whether ICU volume correlates with survival in the Spanish healthcare system.
  
  
  METHODS
  Post hoc analysis of a prospective study of all patients admitted to 29 ICUs during 3 months. At ICU discharge, the authors recorded demographic variables, severity score, and specific ICU treatments. Follow-up variables included ICU readmission and hospital mortality. Statistics include logistic multivariate analyses for hospital mortality according to quartiles of volume of patients.
  
  
  RESULTS
  The authors studied 4,001 patients with a mean predicted risk of death of 23% (range at hospital level: 14-46%). Observed hospital mortality was 19% (range at hospital level: 11-35%), resulting in a standardized mortality ratio of 0.81 (range: 0.5-1.3). Among the 1,923 patients needing mechanical ventilation, the predicted risk of death was 32% (14-60%) and observed hospital mortality was 30% (12-61%), resulting in a standardized mortality ratio of 0.96 (0.5-1.7). The authors found no correlation between standardized mortality ratio and ICU volume in the entire population or in mechanically ventilated patients. Only mechanically ventilated patients in very low-volume ICUs had slightly worse outcome.
  
  
  CONCLUSIONS
  In the currently studied healthcare system characterized by 24/7 intensivist coverage, the authors found wide variability in outcome among ICUs even after adjusting for severity of illness but no relationship between ICU volume and outcome. Only mechanically ventilated patients in very low-volume centers had slightly worse outcomes.
authors.affiliation: * Director, Intensive Care Unit, Fundació Althaia, Manresa, CIBERES, Universitat Internacional de Catalunya, Barcelona, Spain. † Intensive Care Unit, Hospital G.U., Castello, Castello, Spain. ‡ Intensive Care Unit, Hospital de Barcelona SCIAS, Barcelona, Spain. § Intensive Care Unit, Hospital de Sagunt, Sagunt, Spain. ‖ Intensive Care Unit, C.Hosp.U. de Santiago de Compostela, Santiago de Compostela, Spain. # Intensive Care Unit, Hospital del Mar, Barcelona, Spain. ** Intensive Care Unit, Hospital Virgen de la Luz, Cuenca, Spain. †† Intensive Care Unit, C. Hosp. de Vic, Vic, Spain. ‡‡ Intensive Care Unit, Hospital San Agustin, Aviles, Spain. §§ Intensive Care Unit, Hospital Mateu Orfila, Menorca, Spain. ‖‖ Intensive Care Unit, Hospital Moncloa, Madrid, Spain. ## Intensive Care Unit, Hospital U. Carlos Haya (Hospital Civil), Malaga, Spain. *** Intensive Care Unit, Hospital Virgen de las Nieves, Granada, Spain. ††† Statistical Department, Fundació Parc Taulí, Corporació Sanitaria Universitaria Parc Taulí, Universidad Autònoma de Barcelona, Sabadell, Spain. ‡‡‡ Members of the Sabadell Score Group are listed in the appendix. Hospital Xeral Cies, Vigo, Spain Hospital de Salamanca, Salamanca, Spain Clinica Universitaria de Navarra, Navarra, Spain Hospital Virgen Macarena, Sevilla, Spain Hospital Virgen de la Victoria, Malaga, Spain Hospital Son Llatzer, Mallorca, Spain Hospital Universitario de Getafe, Getafe, Spain, CIBER Enfermedades Respiratorias Hospital Severo Ochoa, Leganes, Spain Hospital Reina Sofia, Murcia, Spain Hospital Virgen de la Concha, Zamora, Spain Hospital Sant Joan de Reus, Reus, Spain Hospital Reina Sofia, Cordoba, Spain Hospital de Cruces, Baracaldo, Spain Hospital Morales Messeguer, Murcia, Spain Hospital General Yague, Burgos, Spain Hospital Universitario de A Coruña, A Coruña, Spain Hospital La Fe, Valencia, Spain Hospital Marques de Valdecilla, Santander, Spain Hospital Infanta Sofia, San Sebastian de los R
authors.forename: Rafael
authors.initials: R
authors.lastname: Fernández
authors.forename: Susana
authors.initials: S
authors.lastname: Altaba
authors.forename: Lluis
authors.initials: L
authors.lastname: Cabre
authors.forename: Victoria
authors.initials: V
authors.lastname: Lacueva
authors.forename: Antonio
authors.initials: A
authors.lastname: Santos
authors.forename: Jose-Felipe
authors.initials: JF
authors.lastname: Solsona
authors.forename: Jose-Manuel
authors.initials: JM
authors.lastname: Añon
authors.forename: Rosa-Maria
authors.initials: RM
authors.lastname: Catalan
authors.forename: Maria-Jose
authors.initials: MJ
authors.lastname: Gutierrez
authors.forename: Ramon
authors.initials: R
authors.lastname: Fernandez-Cid
authors.forename: Vicente
authors.initials: V
authors.lastname: Gomez-Tello
authors.forename: Emilio
authors.initials: E
authors.lastname: Curiel
authors.forename: Enrique
authors.initials: E
authors.lastname: Fernandez-Mondejar
authors.forename: Joan-Carles
authors.initials: JC
authors.lastname: Oliva
authors.forename: Ana Isabel
authors.initials: AI
authors.lastname: Tizon
authors.forename: Javier
authors.initials: J
authors.lastname: Gonzalez
authors.forename: Pablo
authors.initials: P
authors.lastname: Monedero
authors.forename: Manuela Garcia
authors.initials: MG
authors.lastname: Sanchez
authors.forename: M Victoria
authors.initials: MV
authors.lastname: de la Torre
authors.forename: Pedro
authors.initials: P
authors.lastname: Ibañez
authors.forename: Fernando
authors.initials: F
authors.lastname: Frutos
authors.forename: Frutos
authors.initials: F
authors.lastname: Del Nogal
authors.forename: M Jesus
authors.initials: MJ
authors.lastname: Gomez
authors.forename: Alfredo
authors.initials: A
authors.lastname: Marcos
authors.forename: Paula
authors.initials: P
authors.lastname: Vera
authors.forename: Jose Manuel
authors.initials: JM
authors.lastname: Serrano
authors.forename: Isabel
authors.initials: I
authors.lastname: Umaran
authors.forename: Andres
authors.initials: A
authors.lastname: Carrillo
authors.forename: M-Jose
authors.initials: MJ
authors.lastname: Lopez-Pueyo
authors.forename: Pedro
authors.initials: P
authors.lastname: Rascado
authors.forename: Begoña
authors.initials: B
authors.lastname: Balerdi
authors.forename: Borja
authors.initials: B
authors.lastname: Suberviola
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Hernandez
mesh_terms: D000368:Aged; D015331:Cohort Studies; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D007362:Intensive Care Units / Q000706:statistics & numerical data*; D007902:Length of Stay / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D063868:Patient Outcome Assessment; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000401:mortality*; D013030:Spain; D016019:Survival Analysis