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Systemic inflammatory response syndrome
Systemic inflammatory response syndrome (SIRS) is a condition where there is widespread unregulated inflammation in the body.
Definition:
SIRS is defined as having two or more of the following parameters:
- Body temperature < 36℃ or >38℃
- Heart rate > 90 bpm
- Respiratory rate > 20/min
- White blood cell count < 4000/µL or > 12000/µL
Etiology:
- Infectious causes
- Non-infectious causes
- Severe burns
- Severe trauma
- Circulatory shock
- Pancreatitis
- Vasculitis
- Severe ischaemia
- Severe tissue injury
Pathomechanism:
See the pathomechanism of sepsis below; they’re similar.
Sepsis and septic shock
Sepsis is an acute life-threatening condition characterised by organ dysfunction caused by a dysregulated host response to infection. It’s related to SIRS in pathomechanism. It has a very high mortality rate and can lead to multiple organ dysfunction syndrome (MODS) and death.
Definition:
Sepsis is accurately defined as “A life-threatening organ dysfunction caused by a dysregulated host response to infection.” The definition of “organ dysfunction” can itself be difficult to accurately establish. To help with this, a set of assessment criteria called “sequential organ failure assessment score” or SOFA score can help. These criteria assess the function of important organ systems like lungs, liver, CNS, kidneys, circulation and the coagulation and gives scores from 0 (normal function) to 4 (worst function). The score for each organ system is then summed up. Acute organ dysfunction is defined as an acute change in total SOFA score of 2 points or more.
Septic shock is defined as “A subset of sepsis in which underlying circulatory and cellular or metabolic abnormalities lead to substantially increased mortality risk.” As the name implies it implies the state where a person has sepsis and circulatory shock, often of the distributive type. A person is said to be in septic shock if:
- The patient has sepsis, and:
- Vasopressors are required to maintain a mean blood pressure of above 65 mmHg, and:
- The serum level of lactate is > 2.0 mM
Sepsis used to be evaluated by the criteria of “systemic inflammatory response syndrome” (SIRS), but that is not recommended anymore. Sepsis now has its own criteria (SOFA).
Etiology:
- Primary infection
- Pneumonia
- Genitourinary infections
- Gastrointestinal infections
- Skin infections
- Soft tissue infections
- Pathogens
- Gram positive bacteria
- Gram negative bacteria
- Risk factors
- Age < 1 year
- Age > 65 year
- Comorbidities
- Diabetes mellitus
- Cancer
- Obesity
- Cirrhosis
- Alcoholism
- Immunosuppression
- Being in an intensive care unit
- Invasive medical treatment
- Endotracheal tube
- Intravenous lines
- Urinary catheters
The most common primary infection that leads to sepsis is pneumonia, especially community-acquired pneumonia. The pathogen is more frequently gram positive than gram negative; fungal, viral or parasitic etiology is rare.
Bacteraemia is found in 50% of cases of sepsis.
Pathomechanism:
The underlying mechanism of sepsis is a hyperinflammatory systemic reaction. A normal, physiological immune response requires a balance of proinflammatory and anti-inflammatory signals. In sepsis, this balance is lost. The exact mechanism that leads to the loss of this balance is not well known. Hyperactivation of the innate immune system occurs, which leads to decreased oxygen delivery to tissues.
In gram negative bacteria the LPS molecule of their cell envelope is recognized by TLR4 receptors on macrophages and other immune cells. In gram positive bacteria the cell wall is recognized by TLR2 receptors on the same cells. The immune cells will then produce inflammatory cytokines like TNF-α, IL-1, IL-6 and IL-8. This has multiple consequences:
- The endothelium will become dysfunctional, allowing fluid and other molecules to cross in the interstitium. Fluid is lost to the interstitium, decreasing the oxygenation of tissues
- Cells will be damaged, releasing damage-associated molecular patterns (DAMP) that are recognized by immune cells and cause further inflammation
As fluid is lost to the interstitium, intravascular hypovolaemia occurs. DIC occurs due to endothelial dysfunction and intravascular hypovolaemia. Widespread tissue ischaemia and decreased tissue oxygenation causes widespread cell injury and thereby multisystem organ dysfunction.
Clinical features:
- Fever
- Tachycardia
- Tachypnoea
- Features of organ dysfunction, depending on which organs are affected
- ARDS
- Hypotension
- Acute renal failure, oliguria
- Altered mental status
- DIC
Diagnosis:
Diagnosis of sepsis can be difficult. A series of criteria called qSOFA (quick SOFA) can be used to quickly create suspicion about whether the patient has sepsis. qSOFA is said to be positive of 2 or more of the following criteria are present:
- Altered mental status (GCS < 15)
- Respiratory rate > 22 breaths per minute
- Systolic blood pressure < 100 mmHg
If qSOFA is positive, blood cultures should be performed to look for the pathogen. The function of important organ systems should be evaluated according to the SOFA system. Blood tests should be performed to measure the following:
- CBC (complete blood count)
- Procalcitonin – a serum protein that increases significantly in sepsis
- CRP – which signals inflammation
- Lactate – which is proportional to the degree of tissue hypoxia
Treatment:
Empiric antibiotic treatment should begin immediately after blood cultures has been drawn; mortality increases the longer the patient goes without antibiotic therapy. The goal should be to administer antibiotics before 1 hour has passed after recognition.
Any source of infection, like foreign bodies, abscesses or infected wounds should be assessed and treated appropriately.
Depending on the patient’s condition, fluid therapy, intubation and/or vasopressors might be necessary to maintain ventilation and circulation.
Multiple organ dysfunction syndrome
Multiple organ dysfunction syndrome (MODS), also called multiple organ failure (MOF), is a clinical syndrome characterised by the development of progressive and potentially reversible dysfunction in 2 or more organs or organ systems. It’s often the result of acute insults like sepsis.
Like in sepsis, organ dysfunction can be diagnosed by the use of the SOFA criteria, or by the use of the MODS criteria.
Etiology:
- Sepsis
- Severe trauma
- Severe burns
- Pancreatitis
- Eclampsia
MODS is considered primary if it occurs early after the insult and can be directly attributable to the insult itself. An example is if renal failure develops due to rhabdomyolysis.
MODS is considered secondary if it occurs as a consequence of the host’s response to the insult. An example is if ARDS develops due to pancreatitis.
Trauma
Trauma is a sudden insult which can have severe impact on health. Trauma is a major cause of death in all age groups; especially road traffic accidents are responsible. They can range from simple bone fractures to poles sticking through your skull. We distinguish blunt and penetrating trauma.
We distinguish multiple trauma and polytrauma. Multiple trauma refers to the presence of multiple independent traumas, like if one simultaneously fractures multiple bones. Polytrauma refers to the presence of multiple severe, life-threatening traumas which worsen each other, for example in a severe car crash.
In this discussion we will discuss mostly polytraumatic patients.
Mortality of traumas:
Mortality of trauma can occur in one of three possible periods:
| Period | Time after trauma | Cause of death |
| Acute death | 1 – 4 hours | Exsanguination, pneumothorax, acute heart failure |
| Early death | 4 hours – 2 weeks | Single organ failure |
| Late death | > 2 weeks | MODS, sepsis |
Pathophysiology:
Acute death occurs if there is significant damage to an artery or vital organ like the heart or lungs. Pneumothorax, acute heart failure and exsanguination are common causes of death.
If no acute death occurs there can still be widespread tissue injury. SIRS can develop and cause distributive shock. Reperfusion injury can occur. These factors may be enough to kill the patient in the early phase, or they can lead to MODS and sepsis, which can kill the patient later.
Symptoms of a trauma patient:
- Hypotension
- Tachycardia
- Cool, moist skin with cyanosis
- Oliguria
- Apathy
Treatment:
Treatment involves trying to maintain vital parameters. Fluid balance, electrolyte balance, oxygen supply, blood glucose and acid-base status should all be monitored and treated as necessary.