Distributed health care systems require a pervasive design strategy to ensure security, stability and functionality of the system. Furthermore, distributed health care systems are potentially very complex, which makes it necessary to have appropriate abstraction strategies. In this paper we introduce the theory of communicating sequential processes to distributed health care system design. We use this theory to gain further insight into the communication between different system components. In particular this reasoning is applied to the problem of internal and external integration of distributed health care systems. We claim that a high level of internal and external integration can be achieved with the pervasive design strategy. With the pervasive concept of communicating sequential processes we have a formal method to create a model of the complete system. In the practical part of the paper we apply the formal system model to prove security, stability and functionality of a particular system.