"improving intensive care in Scotland"




In 1991 the American College of Chest Physicians and the Society of Critical Care Medicine produced a consensus document defining sepsis and the systemic inflammatory response syndrome, differentiating between infectious and non-infectious aetiologies (see table 1 below). These definitions are now 20 years old though are still widely used.


Systemic Inflammatory

Response Syndrome


2 or more of:

  • Temperature < 36°C or > 38°C
  • Heart rate > 90 beats/min
  • Respiratory rate > 20 or PaCO2 less than 4.5 kPa or mechanically ventilated
  • White Cell Count < 4 or > 11 or > 10% immature forms


SIRS plus documented or suspected infection

Severe Sepsis

Sepsis plus organ dysfunction or hypoperfusion (e.g.

hyperlactataemia, oliguria or hypotension)

Septic Shock

Sepsis with hypotension (Systolic blood pressure <

90mmHg or need for vasopressor infusion) despite

adequate fluid resuscitation

Table 1: ACCP/SCCM Consensus Definition of SIRS and Sepsis


Although they encompass the vast majority of patients with sepsis they do not adequately stratify what is a very heterogeneous group of patients. Indeed the SIRS definition would apply to a great proportion of all critical care patients. In an attempt to address this, the PIRO system was proposed by a further consensus conference held in 2001 and this is outlined in Table 2 below.



Past Medical History

Genetic predisposition


Insult or Infection

Known pathogens

Amenable to surgery/source control

Non infectious precipitants

Gene profile 



Shock and hypoperfusion


• Impaired host response (e.g. HLA-DR)

• Activated inflammatory process (e.g. CRP, PCT)

• Therapy Targets (e.g. protein C)

Organ Dysfunction

Number of organ systems failing 

Table 2: The PIRO Classification

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