This study examines the association between registered nurse (RN) staffing configurations and potentially nurse-sensitive patient outcomes in English Intensive Care Units (ICU) and to assess changes as the COVID-19 pandemic unfolded.

This was a longitudinal retrospective study analysing routinely collected patient and electronic roster data from 12 ICUs in NHS hospital trusts (January 2019–December 2022). The variables of interest were RN staffing levels and staff mix factors. The outcomes considered were unit-acquired infections, length of stay and readmissions. The relationships were analysed using covariate-adjusted generalised linear mixed models over the entire period and separately for pre-pandemic, pandemic and post-pandemic periods.

Data from 12 ICUs included 52,267 admissions, with RN staffing levels (mean) peaking during the later pandemic period (34.2 h per patient day [HPPD], Standard Deviation (SD) = 12.1) compared to pre-pandemic levels (27.0 HPPD, SD = 8.5). Higher RN HPPD were associated with reduced readmission risk overall, with the strongest protective effect during early pandemic periods. No statistically significant association was found between RN staffing and length of stay overall, though a 5 % reduction occurred during the late pandemic period (p = 0.035). The presence of low levels of nurse managers (band 7 + ) was associated with significantly reduced readmission risk (1.3 %-point decrease, p = 0.011), which arose from an association during the pandemic, but increased length of stay across all periods.

Higher RN staffing levels were consistently associated with reduced ICU readmissions, demonstrating the protective effect of adequate nursing resources. However, the impact of senior nursing staff on other patient outcomes was complex and context-dependent, varying across pandemic periods.

The findings emphasise the importance of evidence-based staffing policies that optimise skill mix and leadership deployment to improve ICU patient outcomes.

COVID-19

Critical care nursing

Unit-acquired Infections

Readmissions, Length of Stay

Nursing staff

© 2025 The Author(s). Published by Elsevier Ltd.