This work proposes a system complexity metric and its application to Intensive Care Unit (ICU) system. The methodology for applying said complexity metric comprises: (i) parameters sensitivity indices calculation, (ii) mapping connections dynamics between system components, and (iii) system’s complexity calculation. After simulating the ICU computer model and using the proposed methodology, we obtained results regarding: number of admissions, number of patients in queue, length of stay, beds in use, ICU performance, and system complexity values (in regular or overloaded operation). As the number of patients in queue increased, the ICU system complexity also increased, indicating a need for policies to promote system robustness.