Marga Hoogendoorn

58 during a shift and hence 1 NAS point corresponds to 1% of care time provided by one nurse. As stated by the author of the NAS, a nurse is productive in 80% of the 8-hour shift; this means that one NAS point corresponds to 3.84 minutes of nursing care during an 8-hour shift ((8 hours * 60 mins)/100)*0.8) 7, 15 . With this information, we were able to convert the NAS scores into an estimated nursing time per patient and per nursing activity (from now on referred to as ‘converted NAS time’. Next we compared the time per NAS item and the total nursing time per patient, based on NAS scores according to the model, with observed times from the time-and-motion measurements. For the observed time, we took the sum of the times of all performed nursing activities per patient per shift in minutes (from now on referred to as ‘observed time’. The median and interquartile ranges (IQR) of the converted NAS times and the observed times were calculated. First, the difference between the total converted NAS times and the total observed times per patient were visualized by scatterplots. Second, the correlation between the total converted NAS times and the total observed times per patient were assessed with the Pearson’s correlation test. In addition, we also assessed the R2, a measure for the proportion of the variance. For each nursing activity separately, medians and interquartile ranges (IQR) of the converted NAS times and observed times were calculated and differences were tested with the Wilcoxon signed-rank test. All statistical analyses were performed using R statistical software, version 3.3.2 16 . RESULTS Baseline results Table 1 shows the ICU characteristics of the seven included ICUs compared with all Dutch ICUs; no significant differences were found between the included ICUs and all Dutch ICUs. During our study, a total of 287 unique patients were observed during 371 different shifts with time-and-motion measurements. In these patients, 46,319 nursing activities were measured. In 45% of the measurements, nurses took care of two patients per shift. In 15% nurses took care of three patients per shift. For the remaining 40%, nurses cared for one patient per shift. The patients in our study had a significantly higher in-hospital mortality rate (22.3% versus 13.0%) and length of ICU stay (3.2 days versus 1.0 day) compared with all Dutch patients in the same period (table 2). Furthermore, acute renal failure, chronic respiratory insufficiency, and cirrhosis differed between the groups, with a higher percentage in the patients in our study. For the other patient characteristics, the included patients and all Dutch ICU patients in this period were comparable.