Nursing Team Composition and Mortality Following Acute Hospital Admission.

Importance: Many studies show the adverse consequences of insufficient nurse staffing in hospitals, but safe and effective staffing is unlikely to be just about staff numbers. There are considerable areas of uncertainty, including whether temporary staff can safely make up shortfalls in permanent staff and whether using experienced staff can mitigate the effect of staff shortages. Objective: To explore the association of the composition of the nursing team with the risk of patient deaths. Design, Setting, and Participants: This patient-level longitudinal observational study was conducted in 185 wards in 4 acute hospital trusts in England between April 2015 and March 2020. Eligible participants were patients with an overnight stay and nursing staff on adult inpatient wards. Data analysis was conducted from month April 2022 to June 2023. Exposure: Naturally occurring variation during the first 5 days of hospital admission in exposure to days of low staffing from registered nurses (RNs) and nursing support (NS) staff, the proportion of RNs, proportion of senior staff, and proportion of hospital-employed (bank) and agency temporary staff. Main Outcomes and Measures: The primary outcome was death within 30 days of admission. Mixed-effect Cox proportional hazards survival models were used. Results: Data from 626 313 admissions (319 518 aged ≥65 years [51.0%]; 348 464 female [55.6%]) were included. Risk of death was increased when patients were exposed to low staffing from RNs (adjusted hazard ratio [aHR], 1.08; 95% CI 1.07-1.09) and NS staff (aHR, 1.07; 95% CI, 1.06-1.08). A 10% increase in the proportion of temporary RNs was associated with a 2.3% increase in the risk of death, with no difference between agency (aHR, 1.023; 95% CI, 1.01-1.04) and bank staff (aHR, 1.02; 95% CI, 1.01-1.04). A 10% increase in the proportion of agency NS was associated with a 4% increase in risk of death (aHR, 1.04; 95% CI, 1.02-1.06). Evidence on the seniority of staff was mixed. Model coefficients were used to estimate the association of using temporary staff to avoid low staffing and found that risk was reduced but remained elevated compared with baseline. Conclusions and Relevance: This cohort study found that having senior nurses in the nursing team did not mitigate the adverse outcomes associated with low nurse staffing. These findings indicate that while the benefits of avoiding low staffing may be greater than the harms associated with using temporary staff, particularly for RNs, risk remains elevated if temporary staff are used to fill staffing shortages, which challenges the assumption that temporary staff are a cost-effective long-term solution to maintaining patient safety.