What are the Systemic Inflammatory Response Syndrome (SIRS) criteria?

From the Guidelines

The SIRS criteria are defined by the presence of two or more of the following: body temperature above 38°C or below 36°C, heart rate greater than 90 beats per minute, respiratory rate over 20 breaths per minute or PaCO2 less than 32 mmHg, and white blood cell count greater than 12,000/mm³, less than 4,000/mm³, or with more than 10% immature neutrophils (band forms) 1.

Key Criteria

The key criteria for SIRS include:

• Temperature of >38 °C or <36 °C
• Heart rate of >90 beats per minute
• Respiratory rate of >20 breaths per minute or partial pressure of CO2 of <32 mmHg
• White blood cell count of >12,000 per ml or <4,000 per ml, or >10% immature (band) forms These criteria are used to identify patients with potential systemic inflammation that may indicate infection or other serious conditions 1.

Clinical Application

Understanding SIRS remains important as it forms the foundation for recognizing the inflammatory response that characterizes many critical illnesses and helps guide initial assessment and management decisions 1.

Limitations

While SIRS criteria are sensitive for detecting systemic inflammation, they lack specificity and have been largely replaced in clinical practice by newer scoring systems like qSOFA and SOFA for sepsis identification 1.

Additional Context

The definition of SIRS has been consistent across different studies and guidelines, including the 2012 Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections 1.

From the Research

SIRS Criteria

• The Systemic Inflammatory Response Syndrome (SIRS) criteria are used to define severe sepsis, which requires suspected or proven infection, organ failure, and signs that meet two or more criteria for SIRS 2.
• The SIRS criteria include:
  • Body temperature greater than 38°C or less than 36°C
  • Heart rate greater than 90 beats per minute
  • Tachypnea, with more than 20 breaths per minute, or hyperventilation, as evidenced by a PaCO2 less than 32 mmHg
  • White blood cell count greater than 12,000 cells/mm^3, less than 4,000 cells/mm^3, or the presence of more than 10% immature neutrophils (bands)
• The use of SIRS criteria in defining severe sepsis has been debated, with some studies suggesting that it may not be the best approach 3, 4.
• Other scoring systems, such as the quick sequential organ failure score (qSOFA) and the Shapiro criteria, have been compared to SIRS in terms of their performance in identifying patients with sepsis 5.

Clinical Application

• The SIRS criteria have been used to identify patients with sepsis and to guide treatment decisions, including the use of antibiotics and other supportive therapies 2, 6.
• However, the criteria have been criticized for being too broad and for not accurately capturing the complexity of sepsis 3, 4.
• The use of SIRS criteria in clinical practice has been influenced by the availability of other scoring systems and the need for early identification and treatment of sepsis 5.