The Volume-Outcome Relationship in Critical Care: A Systematic Review and Meta-analysis.
OBJECTIVE
The purpose of this study was to systematically review the research on volume and outcome relationships in critical care.


METHODS
From January 1, 2001, to April 30, 2014, MEDLINE and EMBASE were searched for studies assessing the relationship between admission volume and clinical outcomes in critical illness. Bibliographies were reviewed to identify other articles of interest, and experts were contacted about missing or unpublished studies. Of 127 studies reviewed, 46 met inclusion criteria, covering seven clinical conditions. Two investigators independently reviewed each article using a standardized form to abstract information on key study characteristics and results.


RESULTS
Overall, 29 of the studies (63%) reported a statistically significant association between higher admission volume and improved outcomes. The magnitude of the association (mortality OR between the lowest vs highest stratum of volume centers), as well as the thresholds used to characterize high volume, varied across clinical conditions. Critically ill patients with cardiovascular (n = 7, OR = 1.49 [1.11-2.00]), respiratory (n = 12, OR = 1.20 [1.04-1.38]), severe sepsis (n = 4, OR = 1.17 [1.03-1.33]), hepato-GI (n = 3, OR = 1.30 [1.08-1.78]), neurologic (n = 3, OR = 1.38 [1.22-1.57]), and postoperative admission diagnoses (n = 3, OR = 2.95 [1.05-8.30]) were more likely to benefit from admission to higher-volume centers compared with lower-volume centers. Studies that controlled for ICU or hospital organizational factors were less likely to find a significant volume-outcome relationship than studies that did not control for these factors.


CONCLUSIONS
Critically ill patients generally benefit from care in high-volume centers, with more substantial benefits in selected high-risk conditions. This relationship may in part be mediated by specific ICU and hospital organizational factors.
Anesthesiology and Surgical Critical Care Department, Cochin Hospital, Assistance Publique - Hôpitaux de Paris (APHP), Paris Descartes University, Paris, France; Clinical Epidemiology Center, Institut National de la Santé et de la Recherche Médicale (INSERM) U1153, Hôtel-Dieu Hospital, APHP, Paris, France; Institut Pierre Louis d'Epidémiologie et de Santé Publique INSERM U1136, UPMC Université Paris 06, Sorbonne Universités, Paris, France. Electronic address: yenlanc.nguyen@gmail.com.
Yên-Lan
YL
Nguyen
CRISMA Center, Department of Critical Care Medicine, University of Pittsburgh Medical Center, Pittsburgh, PA.
David J
DJ
Wallace
Clinical Epidemiology Center, Institut National de la Santé et de la Recherche Médicale (INSERM) U1153, Hôtel-Dieu Hospital, APHP, Paris, France; Emergency Department, Saint Antoine Hospital, APHP, Paris, France.
Youri
Y
Yordanov
Clinical Epidemiology Center, Institut National de la Santé et de la Recherche Médicale (INSERM) U1153, Hôtel-Dieu Hospital, APHP, Paris, France; French Cochrane Centre, The Cochrane Collaboration, Paris, France.
Ludovic
L
Trinquart
Clinical Epidemiology Center, Institut National de la Santé et de la Recherche Médicale (INSERM) U1153, Hôtel-Dieu Hospital, APHP, Paris, France; French Cochrane Centre, The Cochrane Collaboration, Paris, France.
Josefin
J
Blomkvist
CRISMA Center, Department of Critical Care Medicine, University of Pittsburgh Medical Center, Pittsburgh, PA.
Derek C
DC
Angus
CRISMA Center, Department of Critical Care Medicine, University of Pittsburgh Medical Center, Pittsburgh, PA.
Jeremy M
JM
Kahn
Clinical Epidemiology Center, Institut National de la Santé et de la Recherche Médicale (INSERM) U1153, Hôtel-Dieu Hospital, APHP, Paris, France; French Cochrane Centre, The Cochrane Collaboration, Paris, France.
Philippe
P
Ravaud
Institut Pierre Louis d'Epidémiologie et de Santé Publique INSERM U1136, UPMC Université Paris 06, Sorbonne Universités, Paris, France; Medical Intensive Care Unit, Saint Antoine Hospital, APHP, Paris, France.
Bertrand
B
Guidet
D000328:Adult; D003422:Critical Care / Q000458:organization & administration* / Q000706:statistics & numerical data*; D017052:Hospital Mortality; D006801:Humans; D017063:Outcome Assessment, Health Care; D010343:Patient Admission / Q000706:statistics & numerical data*