Association of Intensive Care Unit Patient-to-Intensivist Ratios With Hospital Mortality | Critical Care Medicine | JAMA Internal Medicine | JAMA Network
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Original Investigation
March 2017

Association of Intensive Care Unit Patient-to-Intensivist Ratios With Hospital Mortality

Author Affiliations
  • 1Division of Critical Care Medicine, Albert Einstein College of Medicine, Montefiore Medical Center, Bronx, New York
  • 2Intensive Care National Audit & Research Centre, Napier House, London, United Kingdom
  • 3Departments of Medicine and Community Health Sciences, University of Manitoba, Winnipeg, Canada
  • 4Interdepartmental Division of Critical Care Medicine, University of Toronto, University Health Network, Toronto, Ontario, Canada
  • 5Interdepartmental Division of Critical Care Medicine, University of Toronto, Sunnybrook Health Sciences Center, Toronto, Ontario, Canada
  • 6Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, New York
  • 7Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, New York
JAMA Intern Med. 2017;177(3):388-396. doi:10.1001/jamainternmed.2016.8457
Key Points

Question  What is the association of patient-to-intensivist ratio with hospital mortality for intensive care unit patients?

Findings  In this retrospective cohort analysis including 49 686 adults in 94 United Kingdom intensive care units, a patient-to-intensivist ratio of 7.5 was associated with the lowest risk adjusted hospital mortality, with higher mortality at both higher and lower patient-to-intensivist ratios.

Meaning  Intensivist staffing should ensure that patient volume is sufficient for proficiency in care, but allows for sufficient time and care to be taken with each patient to minimize harm.


Importance  The patient-to-intensivist ratio (PIR) across intensive care units (ICUs) is not standardized and the association of PIR with patient outcome is not well established. Understanding the impact of PIR on outcomes is necessary to optimize senior medical staffing and deliver high-quality care.

Objective  To test the hypotheses that: (1) there is significant variation in the PIR across ICUs and (2) higher PIRs are associated with higher hospital mortality for ICU patients.

Design, Setting, and Participants  Retrospective cohort analysis of patients (≥16 years) admitted to ICUs staffed by a single intensivist during daytime hours in the United Kingdom from 2010 to 2013.

Exposures  Patient-to-intensivist ratios, which we defined for each patient as the number of patients cared for by the intensivist each day averaged over the patient’s stay.

Main Outcomes and Measures  Using standard summary statistics, we evaluated PIR variation across ICUs. We used multivariable, mixed-effect, logistic regression analysis to evaluate the association between PIR and hospital mortality at ultimate discharge from acute hospital (primary outcome) and at ICU discharge.

Finding  Among 49 686 adults in 94 ICUs, median age was 66 (interquartile range [IQR], 52-76) years, and 45.1% were women. The ultimate hospital mortality was 25.7%. The median PIR for patients was 8.5 (IQR, 6.9-10.8; full range, 1.0-23.5), and varied substantially among individual ICUs. The association between PIR and ultimate hospital mortality was U-shaped; there was a reduction in the odds of mortality associated with an increasing PIR up to 7.5 after which the odds of mortality increased again significantly (average patient mortality for lowest PIR, 22%; PIR of 7.5, 15%; highest PIR, 19%; P = .003). A similar U-shaped association was seen for PIR and mortality in the ICU (nadir of mortality at a PIR of 7.8, P < .001).

Conclusions and Relevance  PIR varied across UK ICUs. The optimal PIR in this cohort of UK ICU patients was 7.5, with significantly increased ICU and hospital mortality above and below this ratio. The number of patients cared for by 1 intensivist may impact patient outcomes.