The Association of Registered Nurse Staffing Levels and
Systematic Review and Meta-Analysis
Robert L. Kane, MD,* Tatyana A. Shamliyan, MD, MS,* Christine Mueller, PhD, RN,†
Sue Duval, PhD,* and Timothy J. Wilt, MD, MPH‡
To examine the association between registered nurse
(RN) stafFng and patient outcomes in acute care hospitals.
Twenty-eight studies reported adjusted odds ratios
of patient outcomes in categories of RN-to-patient ratio, and met
inclusion criteria. Information was abstracted using a standardized
Random effects models assessed heterogeneity and
pooled data from individual studies. Increased RN stafFng was
associated with lower hospital related mortality in intensive care
odds ratios (OR), 0.91; 95% conFdence interval (CI),
, in surgical (OR, 0.84; 95% CI, 0.80–0.89), and in
medical patients (OR, 0.94; 95% CI, 0.94–0.95) per additional full
time equivalent per patient day. An increase by 1 RN per patient day
was associated with a decreased odds ratio of hospital acquired
pneumonia (OR, 0.70; 95% CI, 0.56–0.88), unplanned extubation
(OR, 0.49; 95% CI, 0.36–0.67), respiratory failure (OR, 0.40; 95%
CI, 0.27–0.59), and cardiac arrest (OR, 0.72; 95% CI, 0.62–0.84) in
ICUs, with a lower risk of failure to rescue (OR, 0.84; 95% CI,
0.79–0.90) in surgical patients. Length of stay was shorter by 24%
in ICUs (OR, 0.76; 95% CI, 0.62–0.94) and by 31% in surgical
patients (OR, 0.69; 95% CI, 0.55–0.86).
Studies with different design show associations be-
tween increased RN stafFng and lower odds of hospital related
mortality and adverse patient events. Patient and hospital character-
istics, including hospitals’ commitment to quality of medical care,
likely contribute to the actual causal pathway.
nursing staff, hospital, quality, length of stay,
mortality, safety, failure to rescue
urses are crucial to providing high-quality care.
pital restructuring in the last 2 decades, in response to
the advent of managed care and diagnosis-related groups,
shortened hospitalizations of acutely ill patients and placed
new stresses on nurses to provide safe patient care.
creasing the nurse-to-patient ratios has been recommended as
a means to improve patient safety.
California is the only
state that has mandatory nurse-to-patient ratios, although man-
datory nurse stafFng legislation has been proposed in several
as well as all Medicare participating hospitals.
However, these mandatory stafFng regulations are not supported
by evidence-based optimal nurse-to-patient ratios.
We undertook a systematic review of the extant literature
on the association between registered nurse (RN)-to-patient
ratios, and outcomes. These ratios have been expressed in 2
One method uses a ratio of full time equiva-
lents (±TEs) of RNs per patient day, whereas the second uses the
number of patients assigned to 1 RN per shift in the unit (see
Appendix A which can be found on the Medical Care website,
www.lww-medicalcare.com). This study is part of a larger