Published: 18 Jun 2025

ICD9: 995.91      ICD10: A41.9      ICD11: MG46

The terms "Sepsis," "Systemic Inflammatory Response Syndrome (SIRS)," and "Septicemia" are related and often used in clinical settings to describe conditions involving infection and inflammation.
However, their precise meanings and usage have evolved over time. Here's a breakdown:

1. Septicemia (Outdated Term):

Traditional Definition: Historically, septicemia referred to the presence of bacteria or other microorganisms in the bloodstream. It was often used broadly to describe bloodstream infections.
Current Usage: This term is largely outdated and discouraged in modern medical practice. The presence of microorganisms in the blood is now more accurately described as "bacteremia" (bacteria in the blood), "fungemia" (fungi in the blood), or "viremia" (viruses in the blood). The presence of these microorganisms doesn't automatically mean sepsis is present.

2. Systemic Inflammatory Response Syndrome (SIRS):

Definition: SIRS is *not* necessarily caused by infection. It's a systemic (body-wide) inflammatory response triggered by a variety of insults.
Criteria: SIRS is defined by meeting two or more of the following criteria:
Temperature: >38°C (100.4°F) or <36°C (96.8°F)
Heart Rate: >90 beats per minute
Respiratory Rate: >20 breaths per minute or PaCO2 < 32 mmHg (4.3 kPa)
White Blood Cell Count: >12,000/mm3 or <4,000/mm3 or >10% immature band forms (a type of white blood cell)

Causes: SIRS can be caused by:
Infection
Trauma
Burns
Pancreatitis
Surgery
Other inflammatory conditions

Significance: SIRS is a sign that the body is mounting a significant inflammatory response. It's a warning sign that needs investigation to determine the underlying cause. Importantly, SIRS does not necessarily mean sepsis is present.

3. Sepsis:

Definition (Sepsis-3): Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection.
Key Concepts:
Infection: Sepsis *always* involves an infection (bacterial, viral, fungal, or parasitic).
Dysregulated Host Response: The body's immune system overreacts to the infection, causing damage to its own tissues and organs. It's *not* just the infection itself causing the damage; it's the body's exaggerated response.
Organ Dysfunction: This is the crucial element. Sepsis is diagnosed when the dysregulated response leads to failure or impairment of one or more organ systems (e.g., lungs, kidneys, heart, brain).
SOFA Score: The Sequential Organ Failure Assessment (SOFA) score is often used to assess organ dysfunction. An increase in the SOFA score of 2 points or more is suggestive of sepsis.

Clinical Manifestations:
Fever or hypothermia
Tachycardia (rapid heart rate)
Tachypnea (rapid breathing)
Altered mental status (confusion, disorientation)
Hypotension (low blood pressure)
Decreased urine output
Elevated lactate levels
Signs of organ dysfunction (e.g., difficulty breathing, kidney failure)

Severe Sepsis (Outdated Term): The term "severe sepsis" is no longer used. The severity of sepsis is now classified based on the degree of organ dysfunction, rather than being a separate entity.

Septic Shock: Septic shock is a subset of sepsis where there is profound circulatory, cellular, and metabolic abnormalities that are associated with a greater risk of mortality than sepsis alone. It is usually defined by:
Sepsis
Persistent hypotension requiring vasopressors to maintain a mean arterial pressure (MAP) ≥65 mmHg
Serum lactate level >2 mmol/L (18 mg/dL)

Simplified Relationship:

Infection can lead to...
SIRS (Systemic Inflammatory Response Syndrome). However, SIRS can also be caused by non-infectious conditions.
Sepsis is SIRS *specifically* caused by infection *with* organ dysfunction.
Septic Shock is a severe form of sepsis with circulatory failure.

In Summary:

Think of it like this: You have a fire (infection). SIRS is like the smoke alarm going off. Sepsis is when the fire is spreading and damaging the building (organs). Septic shock is when the fire has engulfed the building, and it's on the verge of collapse.

Why the Changing Definitions?

The definitions have been refined over the years to improve:

Accuracy: To better reflect the underlying pathophysiology of these conditions.
Specificity: To distinguish sepsis from other inflammatory conditions.
Clinical Management: To guide appropriate and timely interventions.

Important Note: These are complex medical conditions. If you suspect sepsis, seek immediate medical attention. Early recognition and treatment are crucial for improving outcomes.