The effect of nurse-to-patient ratios on nurse-sensitive patient outcomes in acute specialist units: a systematic review and meta-analysis

Background: Nurses are pivotal in the provision of high quality care in acute hospitals. However, the optimal dosing of the number of nurses caring for patients remains elusive. In light of this, an updated review of the evidence on the effect of nurse staffing levels on patient outcomes is required. Aim: To undertake a systematic review and meta-analysis examining the association between nurse staffing levels and nurse-sensitive patient outcomes in acute specialist units. Methods: Nine electronic databases were searched for English articles published between 2006 and 2017. The primary outcomes were nurse-sensitive patient outcomes. Results: Of 3429 unique articles identified, 35 met the inclusion criteria. All were cross-sectional and the majority utilised large administrative databases. Higher staffing levels were associated with reduced mortality, medication errors, ulcers, restraint use, infections, pneumonia, higher aspirin use and a greater number of patients receiving percutaneous coronary intervention within 90 minutes. A meta-analysis involving 175,755 patients, from six studies, admitted to the intensive care unit and/or cardiac/cardiothoracic units showed that a higher nurse staffing level decreased the risk of inhospital mortality by 14% (0.86, 95% confidence interval 0.79-0.94). However, the meta-analysis also showed high heterogeneity (I-2=86%). Conclusion: Nurse-to-patient ratios influence many patient outcomes, most markedly inhospital mortality. More studies need to be conducted on the association of nurse-to-patient ratios with nurse-sensitive patient outcomes to offset the paucity and weaknesses of research in this area. This would provide further evidence for recommendations of optimal nurse-to-patient ratios in acute specialist units.