[Problems in intensive care posed by imbalance in the protease--protease inhibitor system]

Proteases have a wide range of functions: digestion (pancreatic proteases), protein catabolism (lysosomal proteases), blood coagulation, immune defences (complement), cellular division and proliferation, generation of biologically active oligopeptides (kinins, hormones) from inactive polypeptide precursors, inactivation of these oligopeptides, etc. The body protects itself against its own proteases, either by confining them to a given compartment (lysosome), by synthesising them in the form of inactive precursors (trypsinogen, prothrombin, etc.), or by synthesising proteins with an antiprotease activity. Any disturbance in one of the elements of this protective system may lead to severe pathological consequences: acute hemorrhagic pancreatitis with shock, coagulation disturbances (deficient hepatic synthesis of coagulation factors, congenital antithrombin III deficiency), angioneurotic oedema (congenital deficiency of C'l esterase inhibitor) pulmonary emphysema (local secretion of leukocyte elastase, congenital deficiency of alpha a-antitrypsin).