The relationship between nursing skill mix and severity of illness of patients admitted in Australian and New Zealand intensive care units

Background: Critically ill patients in the intensive care environment require an appropriate nursing workforce to improve quality of care and patient outcomes. However, limited information exists as to the relationship between severity of illness and nursing skill mix in the intensive care. Objective: The aim of this study was to describe the variation in nursing skill mix across different hospital types and to determine if this was associated with severity of illness of critically ill patients admitted to adult intensive care units (ICUs) in Australia and New Zealand. Design & Setting: A retrospective cohort study using the Australia and New Zealand Intensive Care Society Adult Patient Database (to provide information on patient demographics, severity of illness, and outcome) and the Critical Care Resources Registry (to provide information on annual nursing staffing levels and hospital type) from July 2014 to June 2020. Four hospital types (metropolitan, private, rural/regional, and tertiary) and three patient groups (elective surgical, emergency surgical, and medical) were examined. Main outcome measure: The main outcome measure was the proportion of critical care specialist registered nurses (RNs) expressed as a percentage of the full-time equivalent (FTE) of total RNs working within each ICU each year, as reported annually to the Critical Care Resources Registry. Results: Data were examined for 184 ICUs in Australia and New Zealand. During the 6-year study period, 770 747 patients were admitted to these ICUs. Across Australia and New Zealand, the median percentage of registered nursing FTE with a critical care qualification for each ICU (n = 184) was 59.1% (interquartile range [IQR] = 48.9–71.6). The percentage FTE of critical care specialist RNs was highest in private [63.7% (IQR = 52.6–78.2)] and tertiary ICUs [58.1% (IQR = 51.2–70.2)], followed by metropolitan ICUs [56.0% (IQR = 44.5–68.9)] with the lowest in rural/regional hospitals [55.9% (IQR = 44.9–70.0)]. In ICUs with higher percentage FTE of critical care specialist RNs, patients had higher severity of illness, most notably in tertiary and private ICUs. This relationship was persistent across all hospital types when examining subgroups of emergency surgical and medical patients and in multivariable analysis after adjusting for the type of hospital and relative percentage of each diagnostic group. Conclusions: In Australian and New Zealand ICUs, the highest acuity patients are cared for by nursing teams with the highest percentage FTE of critical care specialist RNs. The Australian and New Zealand healthcare system has a critical care nursing workforce which scales to meet the acuity of ICU patients across Australia and New Zealand.