Infection S3 - Innate Immunity & Acute Sepsis Flashcards
What are the clinical features of SIRS?
Two or more of:
- Temperature >36 or >38
- Heart rate >90 bpm
- Respiratory rate >20/min
- WBC count >4x10^9/L or >12x10^9/L
What is a purpuric rash?
A dark purple rash that does not fade upon application of pressure (glass tumbler test)
What is sepsis?
A generalised response to a documented or presumed infection with the presence of SIRS
What is SIRS?
Systemic Inflammatory Response Syndrome
It’s a response to a non specific insult eg ischaemia, trauma, infection
Define bacteraemia
The presence of bacteria in the blood (+/-) clinical features
Define septicaemia
Clinical term meaning generalised sepsis
Define severe sepsis
SIRS + organ dysfunction/hypoperfusion (due to infection)
Characterised by reduced urine output and hypotension
Define septic shock
Severe sepsis + persistent hypotension despite administration of IV fluids
How does sepsis interfere with coagulation?
Cytokines initiate production of thrombin and thus promote coagulation
Cytokines also inhibit fibrinolysis
Coagulation cascade leads to micro vascular thrombosis
This causes organ ischaemia, dysfunction and failure
Micro vascular thrombosis is the leading cause of shock and multi organ failure
What urgent investigations should be undertaken if sepsis is suspected?
Full blood count (FBC) Urea Electrolytes EDTA bottle for PCR Blood sugar Liver function tests C-reactive protein (CRP) Clotting studies Blood gases
What are the ‘Sepsis Six’?
Six actions to be completed within an hour of seeing a suspected septic patient:
1- Deliver high flow O2
2- Take blood and other cultures, consider source control
3- Administer empirical IV antibiotics
4- Measure serum lactate
5- Start IV fluid resuscitation
6- Commence accurate urine output measurement
What is an “empirical antibiotic”?
A broad spectrum antibiotic treatment that’s decided upon based on the doctor’s best guess at the pathogen responsible for the infection
Define the immune system
Cells and organs which contribute to immune defences agains infectious and non-infectious conditions
Define infectious disease
When a pathogen succeeds in evading and/or overwhelming the hosts’ immune defences
What factors determine the outcome of the host-pathogen relationship?
Number of organisms present
Virulence of the pathogen
The host’s immune response
What are the roles of the immune system?
Pathogen recognition
Containing/eliminating the infection
Regulating itself
Remembering pathogens
How does the immune system identify pathogens?
By cell surface and soluble receptors
How does the immune system contain/eliminate the infection?
By clearance and killing mechanisms
Why does the immune system regulate itself?
To ensure minimum damage to the host (in other words, to allow complete resolution)
Why does the immune system recognise pathogens?
To prevent a recurrence of the disease
What protection does innate immunity confer?
Immediate:
- Fast (within seconds)
- Recognises groups of pathogens
- Lacks memory
- No change in intensity
What protection does adaptive immunity confer?
Long-lasting:
- Slow (3-4 days)
- Specific to one pathogen
- Immunologic memory
- Increases in intensity
How does innate immunity work?
- First line of defence is factors that limit entry and growth of pathogens
- Second line of defence is factors that will contain and clear the infection
What are the types of first line defence?
Physical barriers
Physiological barriers
Chemical barriers
Chemical barriers
