What is the pathophysiology of stage I systemic inflammatory response syndrome (SIRS)?

Updated: May 07, 2018
  • Author: Lewis J Kaplan, MD, FACS, FCCM, FCCP; Chief Editor: Michael R Pinsky, MD, CM, Dr(HC), FCCP, FAPS, MCCM  more...
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Answer

Following an insult, cytokines are produced within immune effector cells de novo at the site. Local cytokine production incites a cellular inflammatory response, thereby promoting wound repair and recruitment of the reticular endothelial system. This process is essential for normal host defense homeostasis and if absent is not compatible with life. Local inflammation, such as in the skin and subcutaneous soft tissues, carries the classic description of rubor, tumor, dolor, calor and functio laesa.

Rubor or redness reflects local vasodilation caused by release of local vasodilating substances like nitric oxide (NO) and prostacyclin.

Tumor or swelling is due to vascular endothelial tight junction disruption and the local extravasation of protein-rich fluid into the interstitium, which also allows activated white blood cells to pass from the vascular space into the tissue space to help clear infection and promote repair.

Dolor is pain and represents the impact inflammatory mediators have on local somatosensory nerves. Presumably, this pain stops the host from trying to use this part of his or her body as it tries to repair itself.

Calor is the increased heat primarily due to increased blood flow but also increased local metabolism as white blood cells become activated and localize to the injured tissue.

Finally, functio laesa is loss of function, a hallmark of inflammation and a common clinical finding of organ dysfunction with the infection is isolated to a specific organ (eg, pneumonia—acute respiratory failure; kidney—acute kidney injury).

Importantly, on a local level, this cytokine and chemokine release by attracting activated leukocytes to the region may cause local tissue destruction (eg, abscess) or cellular injury (eg, pus), which appear to be the necessary byproducts of an effective local inflammatory response.


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