Hospital and patient characteristics associated with variation in 28-day mortality rates for very low birth weight infants. Vermont Oxford Network.

BACKGROUND The outcomes for very low birth weight infants vary among neonatal intensive care units (NICUs), but the reasons for this variation are not well understood. We used the database of a large neonatology research network to determine whether either admission characteristics of the infants or specific characteristics of the units such as annual patient volume and the presence of a pediatric residency program could account for observed differences in neonatal mortality rates among units. METHODS We studied 7672 infants with birth weights from 501 to 1500 g treated during 1991 and 1992 at 62 NICUs participating in the Vermont Oxford Network Database. RESULTS Overall, 14.7% of the study infants died within 28 days of birth (interquartile range 9.9% to 18.1%). The ratio of the number of observed deaths at an NICU to the number of deaths predicted based on the characteristics of infants treated at the NICU (standardized neonatal mortality ratio, [SNMR]) varied significantly among units (range 0 to 1.69, z = 4.24). There was no association between annual patient volume and either mortality rate (r = .17) or SNMR (r = .22). Observed mortality rates (17% vs 13%) and SNMR (1.04 vs .87) were both higher at the 24 hospitals with pediatric residency training programs than at the 38 hospitals without such programs. Hospitals with residency programs had higher average annual patient volumes (104 vs 66). In an analysis simultaneously adjusting for patient characteristics, volume, and presence of a residency program, neither volume (odds ratio [OR] per 10 additional cases treated 1.01, 95% confidence interval [CI], .98 to 1.04) nor presence of a pediatric residency program (OR 1.18, 95% CI, .94 to 1.47) was significantly associated with neonatal mortality risk. CONCLUSION There are differences in neonatal mortality rates among NICUs that cannot be explained by differences in the measured admission characteristics of the infants, suggesting that the effectiveness of medical care varies among units. Neither the annual volume of very low birth weight infants treated in a unit nor the presence of a pediatric residency training program was independently associated with neonatal mortality rates for very low birth weight infants.

[1]  J D Horbar,et al.  The Vermont-Oxford Neonatal Network: integrating research and clinical practice to improve the quality of medical care. , 1995, Seminars in perinatology.

[2]  J D Horbar,et al.  An assessment of data quality in the Vermont-Oxford Trials Network database. , 1995, Controlled clinical trials.

[3]  S. Hurd,et al.  Is chronic lung disease in low birth weight infants preventable? A survey of eight centers. , 1987, Pediatrics.

[4]  S. Wallenstein,et al.  The choice of place of delivery. Effect of hospital level on mortality in all singleton births in New York City. , 1987, American journal of diseases of children.

[5]  J. Hanley,et al.  The meaning and use of the area under a receiver operating characteristic (ROC) curve. , 1982, Radiology.

[6]  D. Richardson,et al.  Access to neonatal intensive care. , 1995, The Future of children.

[7]  J. Horbar.  Antenatal corticosteroid treatment and neonatal outcomes for infants 501 to 1500 gm in the Vermont-Oxford Trials Network. , 1995, American journal of obstetrics and gynecology.

[8]  A Donner,et al.  Methods for comparing event rates in intervention studies when the unit of allocation is a cluster. , 1994, American journal of epidemiology.

[9]  L. Wright,et al.  Evidence from multicenter neworks on the current use and effectiveness of antenatal corticosteroids in low birth weight infants , 1995 .

[10]  J. Scanlon,et al.  Effect of surfactant on morbidity, mortality, and resource use in newborn infants weighing 500 to 1500 g. , 1994, The New England journal of medicine.

[11]  D. Richardson,et al.  Birth weight and illness severity: independent predictors of neonatal mortality. , 1993, Pediatrics.

[12]  C. Bose,et al.  Chronic lung disease in infants with very low birth weight. A population-based study. , 1987, American journal of diseases of children.

[13]  W. Knaus,et al.  An evaluation of outcome from intensive care in major medical centers. , 1986, Annals of internal medicine.

[14]  D. Richardson,et al.  Score for Neonatal Acute Physiology: a physiologic severity index for neonatal intensive care. , 1993, Pediatrics.

[15]  S. Zeger,et al.  Longitudinal data analysis using generalized linear models , 1986 .

[16]  J. Horbar,et al.  Predicting mortality risk for infants weighing 501 to 1500 grams at birth: A National Institutes of Health Neonatal Research Network report , 1993, Critical care medicine.

[17]  L. Iezzoni,et al.  Severity measurement methods and judging hospital death rates for pneumonia. , 1996, Medical care.

[18]  D. Blumenthal.  The variation phenomenon in 1994. , 1994, The New England journal of medicine.

[19]  Predicting hospital-associated mortality for Medicare patients. A method for patients with stroke, pneumonia, acute myocardial infarction, and congestive heart failure. , 1988 .

[20]  C R Bauer,et al.  Very-low-birth-weight outcomes of the National Institute of Child Health and Human Development Neonatal Network, November 1989 to October 1990. , 1995, American journal of obstetrics and gynecology.

[21]  G. Cassady,et al.  Variability in 28-day outcomes for very low birth weight infants: an analysis of 11 neonatal intensive care units. , 1988, Pediatrics.

[22]  J. Bronstein,et al.  The effects of patient volume and level of care at the hospital of birth on neonatal mortality. , 1996, JAMA.

[23]  H S Luft,et al.  Chance, continuity, and change in hospital mortality rates. Coronary artery bypass graft patients in California hospitals, 1983 to 1989. , 1993, JAMA.

[24]  R H Brook,et al.  Explaining variations in hospital death rates. Randomness, severity of illness, quality of care. , 1990, JAMA.

[25]  T. Arbuckle,et al.  An analysis of birth weight by gestational age in Canada. , 1989, CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne.

[26]  A A Rimm,et al.  Hospital characteristics and mortality rates. , 1989, The New England journal of medicine.

[27]  Urs E. Ruttimann,et al.  Impact of quality-of-care factors on pediatric intensive care unit mortality , 1994 .

[28]  G. Coffman,et al.  In-hospital mortality for surgical repair of congenital heart defects: preliminary observations of variation by hospital caseload. , 1995, Pediatrics.

[29]  Model Estimation when Observations are not Independent: , 1989 .

[30]  E L Hannan,et al.  Coronary Artery Bypass Surgery: The Relationship Between Inhospital Mortality Rate and Surgical Volume After Controlling For Clinical Risk Factors , 1991, Medical care.

[31]  R. Williams.  Measuring the Effectiveness of Perinatal Medical Care , 1979, Medical care.

[32]  J. Horbar,et al.  Decreasing mortality associated with the introduction of surfactant therapy: an observational study of neonates weighing 601 to 1300 grams at birth. The Members of the National Institute of Child Health and Human Development Neonatal Research Network. , 1993, Pediatrics.

[33]  E. Draper,et al.  Value and cost of teaching hospitals: A prospective, multicenter, inception cohort study , 1993, Critical care medicine.

[34]  J D Horbar,et al.  Very low birth weight outcomes of the National Institute of Child Health and Human Development Neonatal Network. , 1991, Pediatrics.