Sepsis is a condition where the body launches a large immune response to an infection that causes systemic inflammation and affects the functioning of the organs of the body.
The bacteria or other pathogens are recognised by macrophages, lymphocytes and mast cells. These cells release vast amounts of cytokines like interleukins and tumor necrosis factor to alert the immune system of an invader. These cytokines activate other parts of the immune system. This immune activation leads to further release of chemicals such as nitrous oxide that causes vasodilation. This full immune response causes inflammation throughout the body.
Many of these cytokines cause the endothelial lining of blood vessels to become more permeable. This causes fluid to leak out of the blood and in to the extracellular space leading to oedema and a reduction in intravascular volume. The oedema around blood vessels creates a space between the blood and the tissues reducing the amount of oxygen that reaches the tissues.
Activation of the coagulation system leads to deposition of fibrin throughout the circulation further compromising organ and tissue perfusion. It also leads to consumption of platelets and clotting factors as they are being used up to form the clots within the circulatory system. This leads to thrombocytopenia, haemorrhages and an inability to form clots and stop bleeding. This is called disseminated intravascular coagulopathy (DIC).
Blood lactate rises due to hypoperfusion of tissues that starves the tissues of oxygen causing them to switch to anaerobic respiration. A waste product of anaerobic respiration is lactate.
Septic shock is defined when arterial blood pressure drops and results in organ hypo-perfusion. This leads to a rise in blood lactate as the organs begin anaerobic respiration. This can be measured as either:
This should be treated aggressively with IV fluids to improve the blood pressure and the tissue perfusion. If IV fluid boluses don’t improve the blood pressure and lactate level then they should be escalated to high dependency or intensive care where they can use medication called inotropes(such as noradrenalin) that help stimulate the cardiovascular system and improve blood pressure and tissue perfusion.
Severe sepsis is defined when sepsis is present and results in organ dysfunction, for example: