PURPOSE: It is a top priority health policy to guarantee medical safety and to regain public reliance on medical care. The purpose of this study is to clarify the relation between human resources and patient safety, and to review rational safety measures from the patient's viewpoint.

METHODS: Work duration of nurses, incidents and accidents were collected retrospectively in four acute care hospitals for six months. Self-reported daily information of 580 staff nurses concerning work hours, errors, near misses and perception of fatigue were recorded prospectively for seven days in six acute care hospitals. We estimate the relation between human resources and patient safety using the data in both methods.

RESULTS: 4.54 incidents or accidents per 1000 patient-days were reported. Those often occurred when work loads were heavy, that is, when inpatients per nurse were too many or when some patients required special attention. Looking at the items, 1.61 patient falls per 1000patient-days happened. Those occurred mostly when direct-care hours per patient was short. 1.15 incidents or accidents related with drugs happened in connection with the number of patients in and out of the unit. It became clear that the factors which an incident or accident generates were number of inpatients per nurse, critical patients and admission or discharge per day.

On the other hand, 41.2 errors and near misses per 1000 patient-days were reported. Those mostly occurred on the day when the number of admission, discharge, operation, examinations, patient transportation and nurse calls were large. A nurse has a role of the monitoring function of patient safety. However, there is a threat that this does not function well when hours of care per patient is limited, or when sudden business such as nurse calls is requested.

CONCLUSIONS: It became clear that work performance, fatigue and stress of staff nurses influenced patient safety considerably. A risk of the medical accident hides behind in insufficient staff placement. It may be said that the utmost staff placement is important prior investment to secure patient safety.