Patient Outcomes After the Introduction of Statewide ICU Nurse Staffing Regulations

Abstract

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.

Figure 1. Monthly risk-standardized mortality of patients receiving intensive care in the 24 months before and 12 months after Massachusetts legislation regulating intensive care unit nurse staffing

Dates of legislation milestones (signing of MA General Law c.111, § 231, approval of 958 CMR 8.00 governing implementation, and the official compliance deadline) are shown against the x-axis timeline. The 36-month period was divided into three time periods for the purposes of study analysis and are shown above the plot. All difference-in-difference (DD) analyses compared two 12-month time periods: a “Baseline” period from April 1, 2014 – March 31, 2015 and a “Post-mandate” period from April 1, 2016 –March 31, 2017. Primary analyses excluded the year immediately preceding the compliance date from April 1, 2015 – March 31, 2016, which was a “Preparation” preparation period during which MA ICUs may have begun implementing changes to staffing. Interrupted time series (ITS) analyses included all time periods.

Figure 2. Mortality in the Baseline period vs. Post-mandate periods, comparing intensive care units within Massachusetts and intensive care units outside of Massachusetts

Panel A. The unadjusted mortality rate remained stable in Massachusetts (10.9% to 10.7%, p = 0.32) and rose outside of Massachusetts (9.2% to 9.4%, p =0.003). The difference-in-difference in unadjusted mortality for patients in intensive care units in Massachusetts as compared to outside of Massachusetts was not significantly different (p = 0.09). Panel B. The expected mortality remained stable in Massachusetts (9.1% to 9.2%, p = 0.53) and increased outside of Massachusetts (8.0% to 8.6%, p<.001). The difference-in-difference in expected mortality for Massachusetts compared with non-Massachusetts hospitals was not significantly different (p=.06). Panel C. The risk-standardized mortality ratio in Massachusetts was 1.20 (95% CI 1.16-1.24) in the Baseline period and 1.15 (1.11-1.19) (p = 0.11) in the Post-mandate period, while the mortality index outside of Massachusetts was 1.15 (1.14-1.16) in the Baseline period and 1.09 (1.08-1.10) in the Post-mandate control period (p <.001). The difference-in-difference estimate for risk-standardized mortality associated with implementation of the Massachusetts nursing staffing mandate was not significant (OR = 1.01, 95% CI 0.96-1.06, p = 0.69). Error bars represent 95% confidence intervals.