Most patients report pain during their stay in the intensive care unit (ICU). Pain is multifactorial and can be caused by critical illness, invasive treatment, and standard care procedures [1, 2]. Moreover, pain can induce stress responses that may play an important role in critical illness (e.g., tachycardia, polypnea, increased oxygen consumption), as well as long term psychological stress [1]. Therefore, it is paramount that nurses and physicians be able to monitor and detect pain using valid tools, to titrate analgesic doses, minimise their overuse and serious side-effects, as well as to detect medical complications during ICU stay. Monitoring pain is associated with improved patients’ outcomes in ICU (e.g., decrease in sedative use, reduction of mechanical ventilation duration and length of stay) [3, 4] and should be adjusted to the patient’s condition (Fig. 1) [1]. The same tool should be used in a given patient with a given condition to monitor change.