The Inflammatory Response

SIRS, MODS, and Related Phenomena Infection and inflammation are not the same thing, and failure to recognize this can lead to errors in management [Chest 101: 1644, 1992]

SIRS requires two or more of the following symptoms [Chest 101: 1644, 1992] and can be caused by infection, trauma, shock, ischemia, pancreatitis, intestinal endotoxin, noxious substances, or thermal injury. One study showed that 93% of SICU patients have SIRS [Intensive Care Med 21: 302, 1995] and another that infection only occurs in 25 – 50% of these [JAMA 273: 117, 1995]

Diagnostic Criteria of SIRS

Requires two or more of the following:

  • T > 38 (or < 36)
  • HR > 90
  • RR > 20 (or pCO2 < 32)
  • WBC > 12,000 (or < 4000) or > 10% bands

Chest 101: 1644, 1992

These criteria are, however, very non-specific, and one study of 170 SICU patients (followed for 28 days) showed that 93% had two or more of the above criteria – infection, on the other hand, was only found in 49% of these patients [Intensive Care Med 21: 302, 1995]. A larger study of 3708 patients in both medical wards and the ICU showed that 68% met the criteria for SIRS over 28 days (86, 81, and 54% in the surgical, medical, and cardiovascular ICUs). Among patients with SIRS, 26% developed sepsis [JAMA 273: 117, 1995]. Mortality rates in the hierarchy from SIRS, sepsis, severe sepsis, and septic shock: 7%, 16%, 20%, and 46%, respectively [JAMA 273: 117, 1995]

Multiple Organ Dysfunction Syndrome (MODS) is a functional abnormality in one or more organ system – most common are the lungs, kidneys, CV system, and CNS. This is an inflammation-mediated process but is not dependent on infection. Mortality is related to the MODS score, which is dependent on PAO2/FiO2, Cr, bilirubin, adjusted heart rate (HR x RAP/MAP), platelet count, and GCS [Crit Care Med 23: 1638, 1995]. The mortality rate of MOF increases linearly (approximately 20% per organ [Crit Care Med 26: 1793, 1998; Crit Care Med 29: 1303, 2001])

Severe sepsis and septic shock are identical except for blood pressure – both involve organ failure and known infection. They occur in about 20% of patients with SIRS [5,6]. The most likely agents are gram negative enterics (38%), coagulase-negative staphylococcus (18%), S.aureus (11%), enterococci (10%), streptococci (7%), anaerobes (5%), and fungi (5%) [JAMA 271: 1598, 1994]. The initial phases of septic shock are characterized by hypovolemia due to either venodilation or transudation. Oxygen extraction is reduced as well (may be due to inhibition of pyruvate metabolism and not tissue dysoxia [Am Rev Respir Dis 145: 348, 1992]), resulting in hyperlactatemia [Crit Care Med 18S: 70, 1990]. For these reasons, volume infusion is the ideal first-line therapy (goal RAP 8–10 and PCWP 18–20) [Marino]. Empiric antibiotic therapy can begin with vanc/aztreonam or vanc/aminoglycoside pending culture results [Marino]. Steroids may be harmful and are advised against by the Infectious Disease Society of America [J Infect Dis 165: 1, 1992].