SIRS Criteria Overview

Systemic Inflammatory Response Syndrome (SIRS) is a widespread inflammatory condition. Diagnosis requires at least two of the following four criteria:

• Temperature: Core body temperature > $38^\circ C$ (hyperthermia) OR < $36^\circ C$ (hypothermia).
• Heart Rate: Rate > 90 beats per minute (tachycardia).
• Respiratory Rate: Rate > 20 breaths per minute OR partial pressure of carbon dioxide ($P_aCO_2$) < 32 mmHg.
• White Blood Cell (WBC) Count: WBC count > 12,000 cells/mm$^3$ OR < 4,000 cells/mm$^3$ OR > 10% immature forms (bands).

Analyzing SIRS Features

Let's evaluate the given options based on the SIRS criteria:

• Hyperthermia (more than $38^\circ C$): This meets the temperature criterion for SIRS.
• Hypothermia (less than $36^\circ C$): This also meets the temperature criterion for SIRS.
• Leucocytosis: This signifies an elevated WBC count, which is a direct criterion for SIRS.
• Bradycardia: This refers to a heart rate that is too slow (typically less than 60 beats per minute).

Identifying the NON-SIRS Feature

The SIRS criterion related to heart rate is tachycardia (a rate > 90 beats per minute). Bradycardia, a slow heart rate, is the opposite and is therefore NOT a feature or diagnostic criterion of SIRS.

Thus, Bradycardia is the correct answer as it is not a feature of SIRS.