A comprehensive cohort study revealed that low nurse staffing levels and higher proportions of temporary staff were associated with increased risk of patient mortality in acute care settings. The research, conducted by a team of UK-based investigators, provided detailed insights into how nursing team composition affected patient outcomes.

Key Findings

• Each day of low registered nurse (RN) staffing was associated with a 7.9% increase in risk of death (adjusted hazard ratio [aHR] = 1.08; 95% confidence interval [CI] = 1.07-1.09; P < .001).
• Each day of low nursing support (NS) staffing was associated with a 7.2% increase in risk of death (aHR = 1.07; 95% CI = 1.06-1.08; P < .001).
• Every 10% increase in temporary RNs (both bank and agency) was associated with a 2.3% increase in mortality risk.
• Every 10% increase in agency NS staff was associated with a 4% increase in mortality risk.

Study Methods and Patient Characteristics

The study, published in JAMA Network Open, analyzed data from 626,313 admissions across 185 wards in four acute hospital trusts in England between April 2015 and March 2020. Researchers used mixed-effect Cox proportional hazards survival models to examine the association between nursing team composition and 30-day mortality.

The study included 319,518 patients who were aged 65 years or older (51.0%) and 348,464 female patients (55.6%). Of all admissions, 502,717 (80.3%) were emergencies, and 412,403 (65.8%) were to medical specialties. The median hospital stay was 3.63 days (interquartile range = 1.77-8.28 days).

Patient case-mix adjustment was performed using the Summary Hospital Mortality Indicator risk score. The majority of admissions had at least one comorbidity, with 279,415 (44.6%) having a Charlson Comorbidity Index score greater than 5.

Detailed Results

Staffing Levels

• Mean staffing over the first 5 days was 5.29 (standard deviation [SD] = 4.22) RN hours per patient-day (HPPD) and 2.93 (SD = 1.37) NS HPPD.
• Low staffing occurred on 1,116,749 of 2,468,860 patient days (45.2%).

Staff Composition

• Mean RN proportion was 61.50% (SD = 0.12%).
• RN hours included 25.44% (SD = 0.18%) from senior staff (band 6 and above).
• 5.20% (SD = 0.10%) of RN hours were from temporary bank staff and 4.84% (SD = 0.10%) were from agency staff.
• 1.97% (SD = 0.06%) of NS hours were provided by senior staff (band 4).
• 14% of NS hours were from temporary staff, mostly bank (SD = 12.28% [0.19%]).

Mortality Risk

• Of 514,899 patients exposed to days of low RN staffing, 27,397 (5.3%) died, compared to 4,488 of 111,414 (4.0%) who were not exposed. Similar results were observed for low NS staffing exposure.

Staff Mix Effects

• Small reductions in mortality risk were observed with increased proportions of senior RN and NS staff, but these were not statistically significant.
• Bank NS staff had a similar association with mortality as temporary RNs (aHR = 1.02; 95% CI = 1.01-1.03; P < .001).

Nonlinear Associations

• The marginal effect of understaffing increased with more days of exposure.
• The marginal effect of higher proportions of bank assistants and senior NS staff reduced as levels approached 20%.

Trade-offs

• Using temporary staff to avoid low staffing resulted in an estimated net reduction in mortality risk of 4.1% for RNs and bank NS, compared to a 7.7% decrease with permanent RNs.
• When agency NS staff were used, the reduction in mortality risk was only 1.2%.

Sensitivity Analyses

• Results were similar when low staffing was defined at different thresholds below the mean.
• Models using the first 3 and 10 days of staffing gave similar results to those using 5 days.
• Models with ward as a fixed effect and those including weekend admission as a factor yielded similar estimates for staffing effects.

The study's strengths included its large sample size, diverse hospital settings, and longitudinal design. Limitations included its observational nature, preventing causal inferences, and the use of mean staffing as a reference point for expected staffing levels.

Conclusions

The study found that using temporary staff to avoid low staffing showed some benefits in reducing mortality risk but did not fully mitigate the increased risk associated with staffing shortages. The research revealed statistical associations between nursing team composition, including the use of temporary staff, and patient mortality rates in acute care settings.

The authors declared having no competing interests.