Skeletal muscle oedema and muscle fibre necrosis during septic shock. Observations with a porcine septic shock model.

In domestic pigs, intermitted application of Escherichia coli-endotoxin was used to create an animal model for a prolonged hypo- and hyperdynamic septic shock-like state and to investigate mechanisms of multiple organ failure. Here, we describe the changes in skeletal muscle after 18 h (2 animals) and 48 h (6 animals) of septic shock. Two pigs for each observation period that received physiologic saline solutions instead of endotoxin served as controls. The earliest lesions were endothelial cell damage with endomysial oedema and swelling of mitochondria in muscle fibres. With increasing degree of endothelial cell damage, pericytes showed degenerative changes with cytoplasmic fragmentation and karyolysis. After 48 h of shock, endomysial oedema was increased with fibrinogen present. Muscle fibre diameters were increased and swollen mitochondria and segmental necrosis of muscle fibres were frequently observed. However, phagocytic reaction or regenerative changes were not detected. In this respect, skeletal muscle lesions in septic shock differ from ischemic damage, which is characterized by early phagocytosis. Tumour necrosis factor alpha (TNF alpha) was increased greatly and significantly in the serum of the pigs that received endotoxin. The lesions described may be the result of both direct damage to muscle fibres by the endotoxin and/or the increased levels of TNF alpha and indirect damage because of the increased diffusion distance, due to the endomysial oedema. The loss of blood proteins into the endomysium may also play a role in generating hypoproteinemia in patients with septic shock.