Systemic inflammatory response syndrome

Systemic inflammatory response syndrome

Systemic inflammatory response syndrome

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SIRS Criteria - The Body's Red Alert

SIRS is diagnosed when ≥2 of the following criteria are met, indicating a widespread inflammatory state.

  • Temperature: <36°C (96.8°F) or >38°C (100.4°F)
  • Heart Rate: >90 bpm
  • Respiratory Rate: >20 breaths/min or PaCO₂ <32 mmHg
  • White Blood Cell Count: <4,000/mm³ or >12,000/mm³ or >10% immature bands

📌 Mnemonic: Remember the 4 T's: Temperature, Tachycardia, Tachypnea, Terrific (or Terrible) white count.

⭐ SIRS is a non-specific inflammatory response. It can be triggered by non-infectious conditions like pancreatitis, burns, or trauma. Sepsis is defined as SIRS with a presumed or confirmed source of infection.

Pathophysiology - The Cytokine Storm

  • Trigger: An insult (e.g., surgery, trauma, infection) activates the innate immune system, primarily macrophages and endothelial cells.
  • Key Mediators: A massive, uncontrolled release of pro-inflammatory cytokines creates the "storm."
    • TNF-α & IL-1: Early, primary mediators causing fever and inflammation.
    • IL-6: Drives the acute-phase response; correlates with morbidity.

⭐ IL-6 is a key driver of the hepatic acute-phase response, stimulating the liver to produce C-reactive protein (CRP), a major inflammatory marker.

SIRS Pathophysiology: From Infection/Trauma to MODS

Progression - SIRS to Sepsis Spiral

  • SIRS → Sepsis: SIRS criteria met due to a suspected or confirmed infection.
  • Sepsis → Septic Shock: Sepsis with persistent hypotension requiring vasopressors to maintain MAP ≥ 65 mmHg AND serum lactate > 2 mmol/L despite adequate volume resuscitation.
  • Septic Shock → MODS: Development of progressive dysfunction in two or more organ systems.

⭐ The concept of "Severe Sepsis" (sepsis + signs of end-organ damage) is largely replaced by the Sepsis-3 definition, which frames sepsis itself as life-threatening organ dysfunction caused by a dysregulated host response to infection.

Management - Taming the Inferno

  • Initial Resuscitation (The "Sepsis Six" within 1 hour):
    • High-flow oxygen to maintain SpO₂ >94%.
    • IV fluid challenge: 30 mL/kg crystalloid for hypotension.
    • IV broad-spectrum antibiotics after blood cultures.
    • Measure serum lactate.
    • Monitor urine output.
  • Source Control: The definitive treatment. Drain abscesses, debride tissue, or remove infected hardware.
  • Hemodynamic Support:
    • Vasopressors (Norepinephrine first-line) if MAP remains <65 mmHg after fluids.

Refractory Septic Shock: For patients unresponsive to fluids and vasopressors, consider IV corticosteroids (e.g., hydrocortisone 200 mg/day).

Sepsis Management Algorithm

  • SIRS is a widespread inflammatory response triggered by infectious (sepsis) and non-infectious causes like trauma, burns, or pancreatitis.
  • Diagnosis requires ≥2 criteria: abnormal temperature (<36°C or >38°C), heart rate (>90/min), respiratory rate (>20/min), or WBC count (<4k, >12k, or >10% bands).
  • Sepsis is distinguished from SIRS by the presence of a documented or suspected infection.
  • Unchecked, it can progress to septic shock and Multiple Organ Dysfunction Syndrome (MODS).

Practice Questions: Systemic inflammatory response syndrome

Test your understanding with these related questions

A 25-year-old man presents to the emergency department after a motor vehicle accident. He was the unrestrained front seat driver in a head on collision. The patient is unresponsive and his medical history is unknown. His temperature is 99.5°F (37.5°C), blood pressure is 67/38 mmHg, pulse is 190/min, respirations are 33/min, and oxygen saturation is 98% on room air. The patient is started on IV fluids, blood products, and norepinephrine. A FAST exam is performed and a pelvic binder is placed. One hour later, his temperature is 98.3°F (36.8°C), blood pressure is 119/66 mmHg, pulse is 110/min, respirations are 15/min, and oxygen saturation is 97% on room air. The patient is currently responsive. Management of the patient's pelvic fracture is scheduled by the orthopedic service. While the patient is waiting in the emergency department he suddenly complains of feeling hot, aches, and a headache. The patient's temperature is currently 101°F (38.3°C). He has not been given any pain medications and his past medical history is still unknown. Which of the following is the most likely diagnosis?

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Flashcards: Systemic inflammatory response syndrome

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Increased pressure within a fascial compartment of a limb experiencing Compartment Syndrome is defined by a fascial compartment pressure to diastolic pressure gradient of _____

TAP TO REVEAL ANSWER

Increased pressure within a fascial compartment of a limb experiencing Compartment Syndrome is defined by a fascial compartment pressure to diastolic pressure gradient of _____

< 30 mmHg

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