This paper presents a statistical analysis of clinical data collected in surgeries under automatic closed-loop control of neuromuscular blockade. Four different control strategies have been applied in patients undergoing elective surgeries and clinical and technical evaluations of the control system were performed. Both transient and steady-state behaviour were analysed in detail and clearly suggest an automatic control approach relying on the information about the patient dynamics. The results can be a valuable start point to design personalized drug infusion control in anaesthesia.