Objectives: To assess whether Massachusetts legislation directed at ICU nurse staffing was associated with improvements in patient outcomes.
Design: Retrospective cohort study; difference-in-difference design to compare outcomes in Massachusetts with outcomes of other states (before and after the March 31, 2016, compliance deadline).
Setting: Administrative claims data collected from medical centers across the United States (Vizient).
Patients: Adults between 18 and 99 years old who were admitted to ICUs for greater than or equal to 1 day.
Interventions: Massachusetts General Law c. 111, § 231, which established 1) maximum patient-to-nurse assignments of 2:1 in the ICU and 2) that this determination should be based on a patient acuity tool and by the staff nurses in the unit.
Measurements and main results: Nurse staffing increased similarly in Massachusetts (n = 11 ICUs, Baseline patient-to-nurse ratio 1.38 ± 0.16 to Post-mandate 1.28 ± 0.15; p = 0.006) and other states (n = 88 ICUs, Baseline 1.35 ± 0.19 to Post-mandate 1.31 ± 0.17; p = 0.002; difference-in-difference p = 0.20). Massachusetts ICU nurse staffing regulations were not associated with changes in hospital mortality within Massachusetts (Baseline n = 29,754, standardized mortality ratio 1.20 ± 0.04 to Post-mandate n = 30,058, 1.15 ± 0.04; p = 0.11) or when compared with changes in hospital mortality in other states (Baseline n = 572,952, 1.15 ± 0.01 to Post-mandate n = 567,608, 1.09 ± 0.01; difference-in-difference p = 0.69). Complications (Massachusetts: Baseline 0.68% to Post-mandate 0.67%; other states: Baseline 0.72% to Post-mandate 0.72%; difference-in-difference p = 0.92) and do-not-resuscitate orders (Massachusetts: Baseline 13.5% to Post-mandate 15.4%; other states: Baseline 12.3% to Post-mandate 14.5%; difference-in-difference p = 0.07) also remained unchanged relative to secular trends. Results were similar in interrupted time series analysis, as well as in subgroups of community hospitals and workload intensive patients receiving mechanical ventilation.
Conclusions: State regulation of patient-to-nurse staffing with the aid of patient complexity scores in intensive care was not associated with either increased nurse staffing or changes in patient outcomes.