Sepsis, septicemia, septic shock and SIRS

Sepsis is an acute condition which threatens death and disability to patients of all ages. But what actually is sepsis? What are SIRS, septicaemia, and septic shock?

Sepsis is a pathological state which arises when the bloodstream contains a high concentration of infectious components which active the immune system. This is usually caused by bacteria but can also occur in response to viruses, fungi or protozoa.

 

Physiology

1. The immune system includes many cells around the body which recognise signatures (called antigens) of pathogens. 
2. An activated cell can trigger local inflammation. 
3. Inflamed blood vessels dilate to allow immune cells to reach the tissues at a greater rate (local vasodilation). 
4. Leukocytes (white blood cells) and tissue cells release signals to attract more leukocytes (chemotaxis). 
5. Leukocytes can respond to signals by detaching from their tissues, migrating towards the signal source, and extravasating through the walls of blood vessels (diapedesis). 
6. This allows immune cells to reach high numbers at a point of infection. 

Sepsis pathology

1. In sepsis, an infection has spread to such an extent, that the entire bloodstream contains a high concentration of antigen. Immune stimulation and inflammatory responses occur throughout the entire vascular system simultaneously. 
2. The blood vessels throughout the entire body dilate (systemic vasodilation). Since the intravascular volume has expanded, the blood pressure falls. 
3. To maintain the blood pressure, the heart must contract harder (increased stroke volume) and more rapidly (increased heart rate). Tachycardia is seen. This refers to a heart rate above the normal range for an individual. In an average adult, this would be above 100bpm. 
4. In young patients, the heart is very good at compensating and the blood pressure may appear stable despite massive vasodilation. Eventually the heart cannot compensate further and the blood pressure collapses. This can be a very sudden decline. In elderly patients, this is likely to be a gradual decline. At some point in sepsis, hypotension develops. This refers to blood pressure below the normal range for an individual. In an average adult, this would be below 90mmHg systolic blood pressure, and/or below 60mmHg diastolic blood pressure. 
5. Since there is little force acting on the blood, the contents of the blood cannot reach tissues at a sufficient rate. Tissue perfusion falls. 
6. Once the blood pressure becomes too low to maintain tissue perfusion, the condition can be described as septic shock. 
7. Disseminated intravascular coagulation may occur. 
8. Ultimately, tissue hypoxia and necrosis occur leading to irreversible damage, organ failure and death. 

 

Systemic inflammatory response syndrome (SIRS)

This term refers to essentially the same process as above, where systemic inflammation is triggered in a patient and circulatory shock develops.
However, if there is a suspected or proven infection, then the condition can be called sepsis. If a patient without any evidence of infection begins to appear septic, it would be appropriately called SIRS. Non-infectious causes of SIRS include:

• Trauma
• Burns
• Haemorrhage
• Ischaemia
• Pancreatitis

 

Terminology

• What does the word sepsis come from?

In ancient Greece this condition was referred to as "σήψις" (sêpsis), meaning decay, decomposition.

• What is septic shock?

There will be further articles on the types of circulatory shock. Septic shock is explained in detail above.

• So what is septicaemia? What is blood poisoning? 

These are old terms which are currently discouraged in healthcare and science, because they have ambiguous meanings. This renders them relatively useless because they convey little information.

Septicaemia literally means septic blood. This usually describes a bacterial contamination of the blood. However bacteria in the blood may not necessarily cause sepsis, and may not even cause harm.

Blood poisoning is highly ambiguous because the "poison" could refer to contamination by any harmful substance. An overdose of a medication could be called blood poisoning.

 

Management

A campaign known as SEPSIS SIX has been widely promoted and accepted in the United Kingdom for managing patients with suspected sepsis. This is composed of  "3 in" and "3 out". 

1. In: High-flow oxygen to raise oxygenation to a target of 94%.
2. Out: Take blood cultures to identify bacterial concentration in the blood. 
3. In: Empiric intravenous antibiotics.
4. Out: Measure serial serum lactates.
5. In: Intravenous fluid resuscitation.
6. Out: Urine output measurement.

Critically ill patients who will benefit from intensive care should be transferred to the ICU as soon as possible. There are limits to the capabilities of ICU and the treatment options themselves can cause harm. Sometimes a patient is too ill to be supported even by ICU. 

 

The future

With the rise of antibiotic resistance, sepsis is becoming more and more of a cause for concern. Without antibiotics, the treatment of sepsis will become entirely supportive and the prognosis will become even more dire. Hopefully advances in immunology will facilitate modulation of the systemic inflammation.