**Abstract**

Sedation in the intensive care unit (ICU) is challenging, as both over- and under-sedation are detrimental. Optimal sedation and analgesic strategies, are a challenge in ICU and nurses play a major role in assessing a patient's agitation levels. Assessing the severity of agitation is a difficult clinical problem as variability related to drug metabolism for each patient. Multi-state models provide a framework for modelling complex event histories. Quantities of interest are mainly the transition probabilities e.g. between states, that can be estimated by the empirical transition matrix (ETM). Such multi-state models have had wide applications for modelling complex courses of a disease. In this chapter the ETM of multi-state and counting process (survival analytic) models which use the times for ICU patients to transition to varying states of violations (a violation being a carer's agitation rating outside socalled wavelet-probability bands (WPB)) confirm the utility of defining so-called trackers and non-trackers according to WPB-based control limits and rules. ETM and multi-state modelling demonstrate that these control-limit scoring approaches are suitable for developing more advanced optimal infusion controllers and coding of nurses A-S scores. These offer significant clinical potential of improved agitation management and reduced length of stay in critical care.

**Keywords:** agitation-sedation (A-S) control, nurses scores, empirical transition matrix (ETM), transition states, wavelet probability band (WPB)
