To evaluate variation in nurse staffing ratios in intensive care unit (ICU) and medical-surgical units in Chilean public hospitals and the extent to which nurse staffing is associated with patient mortality and length of stay.

Cross-sectional.

Out of a population of 45 general high-complexity Chilean public hospitals, 43 participated in the study.

514 ICU and 1850 medical-surgical bedside nurses answered an online survey to provide data on their working conditions, including staffing. Patient outcomes were measured using the 2023 national discharge database from the Ministry of Health containing data from 344 567 adult patients admitted to an ICU or a medical-surgical unit.

Primary patient outcomes were mortality within 30 days after admission and length of stay. The association between nurse staffing and the primary outcomes was tested using mixed logistic regression models for mortality and mixed zero-truncated negative binomial regression for length of stay.

The analytical sample represented 95.6% of public Chilean hospitals. In the average hospital, ICU nurses cared for 3.0 patients at a time (range: 1.1–4.5); nurses on medical-surgical units cared for 10.1 patients (range: 6.9–13.6). Each additional patient in a nurse’s workload was associated with a statistically significant higher odds of death and longer length of stay in medical-surgical units (OR 1.043, 95% CI 1.042 to 1.043; incidence rate ratio 1.032, 95% CI 1.007 to 1.058, respectively) and higher odds of death in ICU (OR 1.12, 95% CI 1.112 to 1.128).

There is considerable variation in nurse staffing among Chilean public hospitals with negative consequences for patient outcomes. Regardless of the unit type, patients in hospitals where nurses care for more patients at a time are more likely to die; in medical or surgical units, they are more likely to have longer lengths of stay. Systematically reducing the numbers of patients in a nurses’ workload has the potential to decrease inequalities across the public healthcare system by decreasing preventable deaths and decreasing the length of patient stays to thereby improve access for patients on waitlists.