Abstract
Despite the considerable advances made in understanding the pathophysiology of systemic inflammation during critical illness, clinical progress has been elusive as it remains a very deadly condition. Cortisol and thyroid hormone levels can be as predictive of outcome as the commonly used severity parameters (i.e. APACHE). Indeed, levels of endocrine humoral substances such as arachidonic acids, nitric oxide, endothelin, calcitonin precursors, leptin and adenosine correlate with the severity and outcome of critical illness. Furthermore, calcitonin precursors represent a potentially new hormokine paradigm, being transcriptionally activated in all cells in response to infection. The cytokines are immune markers that often correlate with severity and outcome, but their release is transient. In contrast, the so-called acute phase proteins, such as C-reactive protein and serum amyloid A, are highly sensitive to inflammatory activity and can be important markers of severity and outcome. Leukocyte esterase, adhesion molecules, platelet activating factor and activated protein C are additional humoral immune markers; the replacement of the latter has been shown to be a promising therapeutic option. Natriuretic peptides are neurocrine humoral markers that have important cardiovascular implications. The level of macrophage migrating inhibitory factor, released by the pituitary, is elevated in sepsis and counteracts glucocorticoid action. Cellular markers to severe stress include the enhanced expression of protective substances in the form of heat shock proteins. High mobility group-1 is a DNA-binding protein and a late mediator of the inflammatory response. Apoptotic markers such as the soluble fas ligand are also elevated in inflammation. In summary, during critical illness, the endocrine, immune and nervous systems elaborate a multitude of humoral markers, the roles of which merit further scrutiny in order to improve therapeutic outcome.