This paper presents a free Critical Care Information System (CCIS) that shows an essential infrastructure for critical care medical and nursing practice. Specifically, a Patient Integral Analysis Aid System (SAIP) in Intensive Care Units (ICU) has been developed to cover the needs discovered in these scenarios. An importart part of this system is related to medical equipment that offers important information to help in medical diagnosis. ICU patients are usually connected to several of these devices which register their physiological parameters. The integration of these devices, in order to exchange the generated information, is difficult because they are developed by different manufacturers and with different communication protocols and information representations. To reach this objective, the developed drivers have a common interface for the access and collection of medical device data. The main goal of the present paper is to show the work done to obtain a real interoperability among medical devices from different manufacturers and with different communication protocols in ICU services for automatic data collection, storage and retrieval.