Systemic Inflammatory Response Syndrome (SIRS) Clinical Presentation

Updated: Nov 12, 2020
  • Author: Kamran Boka, MD, MS; Chief Editor: Michael R Pinsky, MD, CM, Dr(HC), FCCP, FAPS, MCCM  more...
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Despite having a relatively common physiologic pathway, systemic inflammatory response syndrome (SIRS) has numerous triggers, and patients may present in various manners. The clinician's history should be focused around the chief symptom, with a pertinent review of systems being performed. Patients should be questioned regarding constitutional symptoms of fever, chills, and night sweats. This may help to differentiate infectious from noninfectious etiologies. The timing of symptom onset may also guide a differential diagnosis toward an infectious, traumatic, ischemic, or inflammatory etiology.

Pain, especially when it can be localized, may guide a physician in differential diagnosis and necessary evaluation. Although providing a differential for pain in the various body parts is beyond the scope of this article, a physician should carefully obtain information on the duration, location, radiation, quality, and exacerbating factors associated with the pain to help establish a thorough differential diagnosis.

In patients for whom a diagnosis cannot be made on the basis of the initial history, a complete review of systems is indicated to try to uncover a potential diagnosis.

The patient's medications should be reviewed. Medication side effects or pharmacologic properties may either induce or mask SIRS (eg, beta-blockers prevent tachycardia). Recent changes in medications should be addressed to rule out drug-drug interactions or a new side effect. Allergy information should be gathered and the specifics of the reaction should be obtained.


Physical Examination

A focused physical examination based on a patient's symptoms is adequate in most situations. Under certain circumstances, if no obvious etiology is obtained during the history or laboratory evaluation, a complete physical examination may be indicated. Patients who cannot provide any history should also undergo a complete physical examination, including a rectal examination, to rule out an abscess or gastrointestinal bleeding.

With the exception of white blood cell count abnormalities (>12,000/µL or < 4,000/µL or >10% immature [band] forms), the criteria for SIRS are based on vital signs, as follows:

  • Fever of more than 38°C (100.4°F) or less than 36°C (96.8°F)

  • Heart rate of more than 90 beats per minute

  • Respiratory rate of more than 20 breaths per minute or arterial carbon dioxide tension (PaCO2) of less than 32 mm Hg

Careful review of initial vital signs is an integral component of the diagnosis. Reassessing the vital signs periodically during the initial evaluation period is necessary, as multiple factors (eg, stress, anxiety, exertion of walking to the examination room) may lead to a false diagnosis of SIRS.

Key points associated with physical examination are as follows:

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

  • Patients receiving a beta-blocker or a calcium channel blocker are often unable to elevate their heart rate and, therefore, tachycardia may not be present

  • 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)

  • Respiratory rate is the most sensitive marker of the severity of illness



Complications vary based on underlying etiology. Potential complications include the following:

  • Respiratory failure, acute respiratory distress syndrome (ARDS), and nosocomial pneumonia

  • Renal failure

  • Stress ulcers

  • Superinfection

  • Gastrointestinal (GI) bleeding and stress gastritis

  • Anemia

  • DVT

  • Intravenous catheter–related bacteremia

  • Electrolyte abnormalities

  • Hyperglycemia