Marga Hoogendoorn

65 activities (left atrial monitoring, cardiopulmonary resuscitation after arrest, and specific interventions in the ICU, respectively) and six subcategories 1b, 1c, 4b, 4c, 7b, and 8c (the nursing activities that required more than 2, 3 or 4 hours of the nurses’ time) did not happen often enough (so, ten times or more) during the measurements, which makes the validation of the NAS incomplete. Given the fact that the median time of nursing care per patient is 2.4 hours (144.3 minutes), nursing activities taking more than 2, 3 or 4 hours rarely occur in daily ICU practice, so it is not likely that our results have been affected by this situation. Nurses took care of two or three patients in 60% of our measurements; we assume that nurses taking care of only one patient can perform nursing activities in a shorter amount of time. We did not specifically study this, but further research could eventually point out what is the optimum time per nursing activity. Furthermore, the observed patients seem to have been more severely ill and consequently had a longer length of stay compared with all Dutch patients in the same time period, which is likely caused by our selection mechanism. In order to measure as many nursing activities as possible we probably more often choose nurses who took care of patients that were expected to stay the whole shift and these patients were probably more severely ill. This may have biased our results since our aim was to validate the NAS and check for underestimations or overestimations compared with time-and- motion measurements and it is possible that observed times in where the NAS gives an underestimation of the observed time. This study showed that 35% of nursing time is explained by the NAS model (R 2 = 0.35). The converted NAS time per patient (202.6 minutes per shift) in our study was comparable with the converted NAS times per patient in other studies. Bernet et al 17 . found 150 to 156 minutes per shift and Deberg et al 18 . found 180 to 228 minutes per shift. The different articles on the NAS give variable NAS times per shift. A full shift of work equals 480 minutes of nursing time. The low correlation of Pearson’s R and R 2 (0.59 and 0.35) implicates that the NAS is not accurate enough to estimate the nursing time at patient level. However, it is currently still the best nursing workload model for quantifying nursing workload in ICUs 5 . There is no clear cut-off point from which the model can be identified as ‘good enough’ based on the R 2 . However, since the NAS is used for capacity planning, an R 2 closer to 1 would be more desirable. Since ICU nurses also spend time on non-nursing duties in almost every shift, such as coaching a student or participating in an emergency team within the hospital, we performed a sensitivity analysis to determine whether these non-nursing duties were affecting the correlation. According to several studies nurses spend approximately 3 to 6% of their shift on non- nursing duties 19,23 . We therefore took the average of 4.5% and