Systemic inflammatory response syndrome

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at November 4, 2016
StartDiseasesSystemic inflammatory response syndrome

Systemic inflammatory response syndrome (SIRS) occurs when inflammation becomes widespread, affecting the whole body. It is an immune system response to either infection or non-infectious causes. Inflammatory response is a somewhat misleading name for the condition, which actually includes both inflammatory and anti-inflammatory reactions in the body.


Definition & Facts

SIRS is a serious and life-threatening condition affecting the entire body and can result in organ dysfunction, damage, and failure. This syndrome was defined in 1991 at the Conference for the American College of Chest Physicians/Society of Critical Care Medicine Consensus. It was defined to provide additional criteria to aid in detection of sepsis. SIRS is not a disease; it is a syndrome. Therefore, it is a non-specific condition.

While systemic inflammatory response syndrome can result in multiple organ dysfunction syndrome (MODS) or death, not all cases of SIRS will progress to serious illness. Because such a vast range of illnesses, from a common cold or the flu to end-stage cancer, can cause SIRS, a wide variety of outcomes are likely.

Symptoms & Complaints

Possible symptoms resulting from systemic inflammatory response syndrome include a wide range of complaints. Symptoms range from respiratory, cardiac, cognitive, and renal irregularities and dysfunctions to whole-body complaints.

Respiratory effects may include difficulty breathing, shortness of breath, and fast breathing. Cardiac issues can include elevated heart rate (tachycardia) and reduced blood pressure (hypotension).

Cognition can be affected by confusion, delirium, sleepiness, or otherwise altered consciousness. The renal system may be affected by insufficient production of urine.

Whole body and central nervous system symptoms can include a range of complaints, including both fever and lowered body temperature, chills, shivering, night sweats, fatigue, dizziness, flushing, and skin discoloration.

Raised or lowered white blood cell counts, elevated blood sugar (hyperglycemia) in non-diabetic patients, reduced blood plasma volume (hypovolemia), gastrointestinal bleeding, organ failure, and shock are also possible symptoms. 


SIRS is caused by a cytokine storm subset, where various cytokines are abnormally regulated. This response can be triggered by infection and by trauma or other non-infectious causes. Infections and conditions likely to trigger SIRS include, but are not limited to: pneumonia, cellulitis, urinary tract infections and respiratory infections, influenza, bacteremia, cholecystitis, diabetic foot infection, erysipelas, diverticulitis, appendicitis, meningitis, pyelonephritis (kidney infection), toxic shock syndrome, and gastroenteritis.

Traumatic triggers may include burns, hemorrhage, surgical complications, ischemia, anaphylaxis, aortic aneurysm, pulmonary embolism, adrenal insufficiency, pericardial tamponade, pancreatitis, vasculitis, transfusion reactions, upper gastrointestinal bleeding, immunosuppression, drug overdose, and seizures. Polypropylene surgical mesh can also lead to SIRS. Multi drug-resistant infection may also contribute to the development of this condition. 

Diagnosis & Tests

SIRS is diagnosed when at least two of the following are present:

  • Fever greater than 38 degrees Celsius (100 degrees Fahrenheit), or body temperature lower than 36 degrees Celsius (96.8 degrees Fahrenheit)
  • Heart rate greater than 90 beats per minute
  • Respiratory rate greater than 20 breaths per minute
  • Abnormal white blood cell count that is either extremely high or low

The respiratory rate is the most sensitive indicator of the severity of SIRS. Proper diagnosis depends on a full medical history, an evaluation of any localized pain, and careful and repeated testing of vital signs. It is important to know what medications a patient is currently using, as medications can both induce and mask SIRS symptoms.

For example, beta blockers can prevent tachycardia, so elevated heart rate will not be present in patients using these drugs. When a patient's full medical history is not available, a full physical examination, including rectal examination to rule out abscess or gastrointestinal bleeding, is performed.

Physicians will also obtain a complete blood count to evaluate white blood cell levels. A basic metabolic profile may also be performed. Doctors may order a check of procalcitonin levels, to differentiate between infectious and non-infectious causes. A test of lactic acid levels may indicate septic shock. Clinical urine tests and sputum gram cultures, tests of cardiac markers, liver profiles, cerebrospinal fluid analysis, and tests for amylase and lipase levels are also possible. Doctors may order additional laboratory tests or medical imaging (computed tomography (CT) scans, magnetic resonance imaging (MRI) scans, X-rays for example) as well. 

Treatment & Therapy

Treatment varies with cause and symptoms. Antibiotics are administered in SIRS cases brought about by bacterial infections. Specific antibiotic treatment varies with the infection and patient history. Gram-positive, gram-negative, and broad-spectrum antibiotics are all possibilities. Patients presenting with pancreatitis or hypovolemia will receive IV fluids.

Anaphylaxis is treated with corticosteroids or antihypotensive agents (vasopressors) such as epinephrine, or diphenhydramine. While viral causes for SIRS are less common, they do occur and are treated with antiviral drugs. A course of low-dose steroids is sometimes preferred, though patients receiving steroid therapy will need more careful blood glucose monitoring.

Polypropylene surgical mesh may be surgically removed. More general therapies for all types of SIRS include oxygen supplementation, selenium, glutamine, eicosapentaenoic acid, high doses of vitamin E, and nonsteroidal anti-inflammatory drugs such as acetaminophen or ibuprofen. Insulin therapy is a consideration, as careful control of blood glucose levels significantly improves outcomes and decreases duration of SIRS in most patients, including those with multiple organ failure. 

Prevention & Prophylaxis

Washing hands frequently prevents the spread of infection. Proper cleaning of all wounds with a povidone-iodine solution and covering with sterile gauze also prevents against infection. In hospital and health care settings, careful monitoring of patients and aggressive treatment of infection can prevent the onset of systemic inflammatory response syndrome and sepsis.

Inflammatory pathways should be interrupted as early as possible. In addition, staff should maintain sterile conditions and use proper aseptic technique. Medically, the prescription NSAID indometacin works as a cyclooxygenase inhibitor and is helpful in prevention. Damage control orthopaedics (DCO) reduce incidences of SIRS related to surgical repair of bone fractures.