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Systemic Inflammatory Response Syndrome (SIRS)

Systemic Inflammatory Response Syndrome (SIRS) is a clinical syndrome caused by an exaggerated systemic inflammatory response to an infectious or non-infectious insult. It may occur with infections, but it can also develop after trauma, burns, pancreatitis, major surgery, or other severe inflammatory conditions

Also called

Systemic inflammatory syndrome

ICD-10

N/A

Specialty

Infectious

Onset

Acute

Reviewed

August 2026

On This Page

Overview

–Traditionally, Systemic Inflammatory Response Syndrome (SIRS) is present when at least two of the following criteria are met:

  • Temperature >38°C or <36°C
  • Heart rate >90 beats/minute
  • Respiratory rate >20 breaths/minute or PaCO₂ <32 mmHg
  • White blood cell count >12,000/mm³, <4,000/mm³, or >10% immature bands

SIRS may occur with or without infection. Therefore, it should be used as a warning of systemic inflammation rather than as a synonym for sepsis.

Etiology & Risk Factors

-Etiology

–Common triggers include:

  • Severe infection
  • Major trauma
  • Extensive burns
  • Acute pancreatitis
  • Major surgery
  • Severe tissue ischemia
  • Other significant inflammatory insults

 

-Risk Factors

  • Severe infection
  • Major trauma
  • Extensive burns
  • Recent major surgery
  • Severe inflammatory disease

Pathophysiology

Systemic insult → activation of innate immunity → release of inflammatory mediators → endothelial activation and vasodilation → altered vascular permeability → impaired tissue perfusion → systemic inflammatory response → possible organ dysfunction

Clinical Presentation

-Symptoms:

  • Patients with Systemic Inflammatory Response Syndrome (SIRS) may develop:

    • Fever or chills
    • Weakness
    • Malaise
    • Shortness of breath
    • Confusion
    • Reduced urine output

    Symptoms are largely determined by the underlying cause.

 

-Signs

  • Fever or hypothermia
  • Tachycardia
  • Tachypnea
  • Abnormal white blood cell count
  • Altered mental status
  • Reduced peripheral perfusion

 

-Severe Disease

Severe Systemic Inflammatory Response Syndrome (SIRS) may progress to:

  • Hypotension
  • Acute Kidney Injury (AKI)
  • Acute respiratory failure
  • Coagulopathy
  • Metabolic acidosis
  • Multiple organ dysfunction
  • Shock

History Taking

-Ask about:

  • Fever or chills
  • Recent infection
  • Trauma
  • Burns
  • Recent surgery
  • Abdominal pain
  • Respiratory symptoms
  • Urinary symptoms
  • Medication and procedure history

Physical Examination

-General Examination

  • Temperature
  • Heart rate
  • Blood pressure
  • Respiratory rate
  • Oxygen saturation
  • Mental status
  • Peripheral perfusion

Look for:

  • Fever
  • Hepatosplenomegaly
  • Lymphadenopathy

 

-System-Specific Examination:

  • Search for the underlying cause, including:

    • Respiratory infection
    • Abdominal pathology
    • Urinary infection
    • Skin or soft-tissue infection
    • Surgical complications
    • Traumatic injury

Investigations

-Complete Blood Count

CBC is one of the traditional SIRS criteria and may demonstrate:

  • Leukocytosis

  • Leukopenia

  • Neutrophilia

  • Other inflammatory abnormalities

 

It may be performed when a hematological abnormality is suspected.

 

-Biochemistry / Specific Tests

Depending on the clinical setting:

  • Serum lactate when tissue hypoperfusion is suspected

  • Serum electrolytes

  • Urea and creatinine

  • Liver function tests

  • Blood cultures when infection is suspected

  • Cultures from the suspected source

 

-Imaging

Imaging is directed toward the suspected underlying cause:

  • Chest X-ray for suspected pneumonia

  • Ultrasound for selected abdominal or urinary pathology

  • Computed Tomography (CT) for suspected deep infection, trauma, or other structural pathology

 

Special / Confirmatory Tests

There is no single confirmatory test for Systemic Inflammatory Response Syndrome (SIRS).

Diagnosis depends on the clinical criteria while simultaneously investigating the underlying cause.

Diagnosis

-Systemic Inflammatory Response Syndrome (SIRS) is identified when at least two traditional SIRS criteria are present.

 

-The diagnostic approach is:

Recognize systemic inflammation → Confirm SIRS criteria → Determine infectious versus non-infectious cause → Assess for organ dysfunction → Treat the underlying condition

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Management

1. First-Line / Emergency Management

There is no specific emergency treatment for Systemic Inflammatory Response Syndrome (SIRS) itself.

Immediate priorities include:

  • Airway and breathing assessment
  • Circulatory assessment
  • Oxygen when indicated
  • Intravenous fluids when clinically appropriate
  • Rapid identification of the underlying cause

 

2. Definitive Treatment

Treatment targets the underlying trigger.

-For infection:

  • Appropriate antimicrobial therapy
  • Source control

 

-For non-infectious causes:

  • Treatment of trauma
  • Burn management
  • Treatment of pancreatitis
  • Management of ischemia or other inflammatory conditions

 

3. Medical Treatment

  • Intravenous crystalloids when indicated
  • Antimicrobials when infection is suspected
  • Vasopressors if persistent hypotension develops
  • Organ-supportive treatment when required

 

4. Supportive Management

  • Continuous vital-sign monitoring
  • Serial assessment of perfusion
  • Lactate monitoring when indicated
  • Urine-output monitoring
  • Electrolyte correction

Complications

  • Hypotension
  • Acute Kidney Injury (AKI)
  • Acute respiratory failure
  • Coagulopathy
  • Metabolic acidosis
  • Multiple organ dysfunction
  • Shock
  • Death

Prognosis

The prognosis of Systemic Inflammatory Response Syndrome (SIRS) depends mainly on its underlying cause, severity, development of organ dysfunction, and response to treatment. SIRS caused by a reversible non-infectious insult may resolve completely, whereas severe infection or major tissue injury can progress to shock and multiorgan failure.

Key Points / Clinical Pearls

  • Systemic Inflammatory Response Syndrome (SIRS) describes a systemic inflammatory response.
  • It can occur with infection or without infection.
  • Traditionally, at least two SIRS criteria are required.
  • Criteria involve temperature, heart rate, respiratory rate/PaCO₂, and white blood cell count.
  • SIRS is not synonymous with sepsis.
  • Infection should always be considered but is not required.
  • Trauma, burns, pancreatitis, and surgery can trigger SIRS.
  • Lactate can help assess tissue hypoperfusion when clinically indicated.
  • Blood cultures are appropriate when infection is suspected.
  • There is no specific treatment for SIRS itself.
  • Treatment should target the underlying cause.
  • Severe cases may develop Acute Kidney Injury (AKI) or respiratory failure.
  • Persistent inflammation can progress to shock and multiple organ dysfunction.
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