Immune system function. Implications for critical care nursing practice.

The purpose of the immune system is to protect the body from invasion from microorganisms. Natural defenses encompassing epithelial surfaces and secretions, nonspecific phagocytosis and inflammatory process, and the acquired defenses of humoral and cell-mediated immunity work together to defend the internal environment of the body. If microorganisms penetrate the external surfaces and enter the body, the inflammatory process is triggered. During phagocytosis by monocytes/macrophages, the invading antigen is identified as nonself. The antigen is presented to the T4-lymphocyte. This cell line orchestrates the activation of B-lymphocytes and a humoral response of antibody or Ig production and initiates the cytotoxic cell-mediated T cell response. Following an appropriate level of response, T8 cells suppress immune system response to the antigen, but not before memory B and T cells have formed. These memory cells protect the body against future exposure to the antigen, thus creating immunity. As concepts of immunology are identified and validated by future research, the knowledge base of immune system function and dysfunction will continue to grow. Critical care nurses must incorporate new knowledge related to immune system function into their practice, as patients in the ICU are at risk for immunocompromise from their underlying disease state and the therapeutic interventions used in their treatment. Nurses must expand their physiologic data base to include a nursing assessment of the immune system. A framework for organizing the data collection process would include: (1) a survey of factors affecting immune system function in each patient, (2) assessment of the cells and structures of the immune system, (3) monitoring of the status of first line defenses, (4) observing for activity of nonspecific defenses, and (5) evidence of specific acquired immune responses. After complete immune system assessment has identified areas of risk for compromise or the presence of immunocompromise, specific individualized nursing care plans can be developed to provide nursing support to maintain and enhance the patient's defenses.