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Fast Five Quiz: How Much Do You Know About Systemic Inflammatory Response Syndrome?

Michael R. Pinksy, MD, CM, Dr(HC), FCCP, MCCM

February 12, 2018

In 1992, the American College of Chest Physicians and the Society of Critical Care Medicine introduced definitions for systemic inflammatory response syndrome (SIRS), sepsis, severe sepsis, septic shock, and multiple organ dysfunction syndrome. The idea behind defining SIRS was to define a clinical response to a nonspecific insult of either infectious or noninfectious origin. SIRS is defined as two or more of the following variables:

  • Fever of more than 100.4°F (38°C) or less than 96.8°F (36°C)
  • Heart rate of more than 90 beats/min
  • Respiratory rate of more than 20 breaths/min or arterial carbon dioxide tension of less than 32 mmHg
  • Abnormal white blood cell count (> 12,000/µL or < 4000/µL or > 10% immature [band] forms)

SIRS is nonspecific and can be caused by ischemia, inflammation, trauma, infection, or several insults combined. Thus, SIRS is not always related to infection. Although sepsis has diverged from SIRS criteria for diagnosis and management in recent years, focusing more on infectious etiologies, the pathophysiologic processes present in sepsis and noninfectious SIRS are remarkably similar, making a discussion of SIRS in critical illness appropriate.

Are you familiar with the background and presentation of SIRS, as well as key aspects of workup and treatment? Test yourself with this quick quiz.

Question 1: Which of the following is accurate about SIRS?

Answer 1: SIRS only develops when a localized aggressive injury process gains access to the whole body through the blood stream and lymphatics

Inflammation is an essential component of host defense and serves a very strongly positive survival function in suppressing and then eliminating local infection and tissue injury. It is only when a localized aggressive injury process gains access to the whole body through the blood stream and lymphatics that SIRS develops. Independent of the etiology, SIRS has the same pathophysiologic properties, with minor differences in inciting cascades. Many consider the syndrome a self-defense mechanism.

Women tend to have less inflammation from the same degree of proinflammatory stimuli due to the mitigating aspects of estrogen. The reasons for this are not completely known, but estrogen sustains adrenergic receptor activity in inflammation, when, in its absence, adrenergic receptor downregulation occurs. Thus, premenopausal women tend to have less vasoplegia and respond more vigorously to resuscitation efforts. This equates to women having a 10-year age benefit over men.

The true incidence of SIRS is unknown but probably very high, owing to the nonspecific nature of its definition. Not all patients with SIRS require hospitalization or have diseases that progress to serious illness. Indeed, patients with a seasonal head cold due to rhinovirus usually fulfill the criteria for SIRS. Because SIRS criteria are nonspecific and occur in patients who present with conditions ranging from influenza to cardiovascular collapse associated with severe pancreatitis, any incidence figures must be stratified based on SIRS severity.

For more on SIRS, read here.

Question 2: Which of the following is accurate about the presentation and physical examination findings associated with SIRS?

Answer 2: Respiratory rate is the most sensitive marker of severity in patients with SIRS

Respiratory rate is the most sensitive marker of the severity of illness. Although low blood pressure is not a criterion for SIRS, it is still an important marker. If the blood pressure is low, the establishment of intravenous access and fluid resuscitation is of utmost importance. Frank hypotension associated with SIRS is uncommon unless the patient is septic or severely dehydrated (hypotension may lead to the patient being admitted or transferred to a higher acuity unit).

Patients at the extremes of age (both young and old) may not manifest typical criteria for SIRS; therefore, clinical suspicion may be required to diagnose a serious illness (either infectious or noninfectious).

For more on the presentation of SIRS, read here.

Question 3: Which of the following is accurate about the workup of SIRS?

Answer 3: Bacteriologic cultures should be stressed in the diagnostic workup of patients with suspected SIRS

Because infectious SIRS etiologies have a high mortality if not effectively treated, and because effective treatment for infection often requires bacteriologic identification of the inciting organism, priority for bacteriologic cultures in the diagnostic workup needs to be stressed.

A white blood cell count of greater than 12,000/µL or less than 4000/µL or with greater than 10% immature (band) forms on the differential is a criterion for SIRS. An increased percentage of bands is associated with an increased incidence of infectious causes of SIRS.

Blood lactate levels are often measured in critically ill patients. These are thought to be indicators of anaerobic metabolism associated with tissue dysoxia. Although a reasonable presumption in patients presenting with circulatory shock and trauma, in septic patients they reflect more the inflammatory burden rather than level of tissue hypoperfusion and, as such, usually do not decrease, if elevated, in response to fluid resuscitation. Levels are commonly elevated from increased peripheral intraorgan production, reduced hepatic uptake, and reduced renal elimination. Numerous studies have found that lactate levels correlate strongly with mortality.

Leptin, a hormone generated by adipocytes that acts centrally on the hypothalamus to regulate body weight and energy expenditure, is an emerging marker that correlates well with serum interleukin (IL)-6 and tumor necrosis factor-alpha (TNF-alpha) levels. Using serum leptin levels with a cutoff of 38 µg/L, researchers have been able to differentiate sepsis from noninfectious SIRS with a sensitivity of 91.2% and a specificity of 85%. This test is not yet readily available for clinical practic

Which of the following is accurate about the treatment of SIRS?

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e in the United States.

For more on the workup of SIRS, read here.

Question 4: Which of the following is accurate about the treatment of SIRS?

Answer 4: Enteral feedings supplemented with arginine and omega-3 fatty acids are typically beneficial in patients with SIRS

Enteral feedings supplemented with arginine and omega-3 fatty acids have been shown to be beneficial (decreased infectious complications, hospital days, and duration of mechanical ventilation) in critically ill patients. The ability to feed a patient and the route of nutrition vary based on the etiology of SIRS.

Studies of TNF-alpha and IL-1 receptor antagonists, antibradykinin, platelet-activating factor receptor antagonists, and anticoagulants (antithrombin III) have not shown statistically significant benefits in SIRS. Variable results for sepsis and septic shock have been reported. These medications have no role in treating patients who meet criteria for SIRS only.

Steroids for sepsis and septic shock have been extensively studied, but no recommendations specific to SIRS are widely recognized. Low-dose steroids should be considered on an individual basis for patients with refractory hypotension (ie, septic shock) despite adequate fluid resuscitation and appropriate vasopressor administration.

For more on the treatment of SIRS, read here.

Which of the following is accurate about antibiotic, antiviral, and antifungal treatment in SIRS?

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