Maintenance of glucose levels in intensive care unit (ICU) patients via control of insulin inputs is currently an active research field. Different published models that address this problem are analysed from control theory point of view. This paper analyzes the three most used ICU metabolic system models in the literature, two of which have been validated in clinical trials or alternate clinical use. Global control theoretical characteristics are determined using nonlinear analysis. Quasi affine linear parameter varying (qALPV) modeling methodology is then investigated for further robust nonlinear model based control.