Marga Hoogendoorn

12 those factors determines how much is asked from the nurse and is commonly translated in the term nursing workload. The definition of nursing workload is however complex 20,21 . Morris and his colleagues defines nursing workload as the amount of direct and indirect patient care activities carried out by nurses during their shift 21 . In this definition the nursing workload has different aspects, which can roughly divided into two dimensions; the amount of work for patient care and the impact of this work for the nurse 21,22 . The first dimension, the amount of work, is the time the nurse needed to perform the nursing activities, an objective and measurable parameter. In this thesis we therefore use the term ‘objective workload’ for this dimension of workload. The second dimension of the nursing workload could be described as the cognitive or the mental demand 22-24 . Taking care for a critical ill dying young patient and his or her family can weigh much more in terms of nursing workload than taking care for a planned postoperative cardiac surgery patient. The workload can also be different for a graduated ICU nurse with a lot of experience than for a student ICU nurse. This dimension of nursing workload represents the experienced, subjective workload for the nurse. In this thesis we use the term ‘perceived workload’ for this dimension of nursing workload. Over the last decades there has been a wide interest in the substantiation and weighing of nursing workload. A high workload in combination with a shortage of certified ICU nurses increases the risk of burn-out in ICU nurses 25,26 . Nursing workload has therefore been shown to be associated with the nurse’s well-being and satisfaction, and equally important associated with patient outcome, ICU costs, hospital costs and ICU bed availability 27-29 . Giving the importance of nursing workload it is clear that one needs a reliable validated tool to quantify this workload. 1.2.1 Quantif ication of the objective nursing workload Over the years, many systems have been developed to measure the objective nursing workload 30 . The way inwhich thosemodels classify the need for nursing staff varies widely. The first model used for measuring nursing workload was the Therapeutic Intervention Scoring System (TISS) 31 . Although originally developed as early as in 1974 to classify the severity of illness, this system is still used to measure the nursing workload 23,32-34 . Because the TISS focusses on medical interventions and not on nursing activities it is not representing the actual nursing time. Therefore, Reis Miranda and his colleagues developed the Nursing Activity Score 35 . This system represents a total of 23 nursing activities in direct and indirect patient care with a score representing a mean time per activity. The sum score of the activities can be translated to the need for nursing staff. The developers validated the NAS and concluded that 81% of the total nursing time can be