Abstract
Nurse staffing in hospital inpatient units varies by country and region, highlighting the need for more equitable, evidence-based planning to measure workload based on complexity, thus enabling appropriate staffing in these units. The objective of this study is to determine the relationship between the nurse-to-patient ratio and the incidence of adverse events in adult conventional inpatient units. A descriptive, cross-sectional observational study with an analytical approach was conducted to calculate the relationship between the nurse-to-patient ratio and adverse events in conventional inpatient units at a tertiary care hospital, the Albacete University Hospital Complex (CHUA), from 2018 to 2023, analyzing a total of 113,117 patients. The 24-h median nurse-to-patient ratio was slightly higher in surgical units (11.35) than in medical units (10.79). Spearman's correlation analysis identified significant relationships (rho > 0.4) between the 24-h nurse-to-patient ratio and events such as hospital-acquired pressure injuries (HAPIs), community-acquired pressure injuries, and mortality. However, the multiple linear regression analysis focused on HAPI as the dependent variable, excluding mortality due to its multifactorial nature and community-acquired injuries as they predated admission. The linear regression results showed that for every one-point increase in the 24-h nurse-to-patient ratio, the probability of HAPI increased by 1.94%. Additionally, the probability of HAPI decreased by 2.63% in surgical units compared with medical units. When analyzing the units separately, the relationship was more pronounced in medical units: a one-point increase in the 24-h ratio was associated with a 2.81% increase in the likelihood of HAPI. In surgical units, the 24-h ratio did not show a significant relationship with HAPI, with the patient turnover index being the relevant predictor. The findings confirm that the operational nurse-patient ratios in Spain position the system in a state of room for improvement regarding safety and economic efficiency. The differences observed between medical and surgical units underscore the necessity for staffing policies not to be uniform but rather to become dynamic and contextualized to optimize clinical outcomes and resource management.