SIRS criteria
| Criteria | Condition |
|---|---|
| Temperature | >38.3°C or <36.0°C |
| Heart Rate | >90 beats/minute |
| Respiratory Rate | >20 breaths/minute or PaCO₂ <32 mm Hg |
| White Blood Cell (WBC) Count | >12,000 cells/mL, <4,000 cells/mL, or >10% immature (band) forms |
Note: Two or more of the above conditions must be met to fulfill the SIRS criteria (Systemic Inflammatory Response Syndrome) .
Explanation:
SIRS Criteria Table with Detailed Explanation
| Criteria | Condition | Detailed Explanation |
|---|---|---|
| Temperature | >38.3°C or <36.0°C | – Fever (>38.3°C): Often caused by infection, inflammation, or tissue injury. Fever is a systemic response to pyrogens (fever-inducing substances). – Hypothermia (<36.0°C): May indicate severe infection (e.g., sepsis) or a dysregulated immune response. |
| Heart Rate (Tachycardia) | >90 beats/minute | – Elevated heart rate is a sign of stress on the body, often due to infection, inflammation, or hypoxia. – Tachycardia helps maintain cardiac output and oxygen delivery in response to systemic demands. |
| Respiratory Rate (Tachypnea) | >20 breaths/minute or PaCO₂ <32 mm Hg | – Tachypnea (>20 breaths/minute): Increased breathing rate to compensate for metabolic demands or hypoxia. – Low PaCO₂ (<32 mm Hg): Indicates hyperventilation, often due to respiratory alkalosis from stress. |
| White Blood Cell (WBC) Count | >12,000 cells/mL, <4,000 cells/mL, or >10% immature (band) forms | – Leukocytosis (>12,000 cells/mL): Elevated WBCs indicate infection or inflammation. – Leukopenia (<4,000 cells/mL): Low WBCs may suggest severe infection or bone marrow suppression. – Bands (>10%): Immature WBCs (bands) indicate an acute infection, as the body releases immature cells to fight the infection. |
Key Points About SIRS
- Definition of SIRS:
- SIRS is a clinical syndrome characterized by a systemic inflammatory response to a wide range of insults. It is not specific to infection and can occur due to non-infectious causes like trauma, burns, or pancreatitis.
- Diagnosis of SIRS:
- Two or more of the above criteria must be present to diagnose SIRS.
- SIRS is a nonspecific response and does not indicate the cause of the inflammation.
- Progression to Sepsis:
- If SIRS is caused by an infection, it is termed sepsis.
- Sepsis is a life-threatening condition that can progress to septic shock (sepsis with hypotension unresponsive to fluid resuscitation) and multi-organ dysfunction syndrome (MODS).
- Non-Infectious Causes of SIRS:
- Trauma, burns, surgery, pancreatitis, ischemia, hemorrhage, or autoimmune diseases can trigger SIRS without an infection.
- Pathophysiology of SIRS:
- The body releases pro-inflammatory cytokines (e.g., TNF-α, IL-1, IL-6) in response to injury or infection.
- This leads to systemic effects like vasodilation, increased vascular permeability, and activation of the coagulation cascade.
- If unchecked, it can cause tissue damage, organ failure, and death.
Clinical Significance of SIRS
- Early Recognition: Identifying SIRS early is critical to prevent progression to sepsis or septic shock.
- Monitoring: Patients with SIRS should be closely monitored for signs of organ dysfunction (e.g., altered mental status, low urine output, hypotension).
- Treatment: Management focuses on treating the underlying cause (e.g., antibiotics for infection, surgery for trauma) and providing supportive care (e.g., fluids, oxygen, vasopressors).
Example of SIRS in Practice
A patient presents with:
- Temperature: 39.0°C (fever)
- Heart rate: 110 beats/minute (tachycardia)
- Respiratory rate: 24 breaths/minute (tachypnea)
- WBC count: 15,000 cells/mL (leukocytosis)
This patient meets three out of four SIRS criteria, indicating a systemic inflammatory response. If an infection is confirmed (e.g., pneumonia or urinary tract infection), the diagnosis would be sepsis.
