（1） Causes of sepsis
Whether the bacteria invading the human body will cause sepsis is closely related to the virulence, quantity and human defense immune function of the invading bacteria. The following may lead to the occurrence of septicemia: damage and inflammation of skin and mucous membrane, such as trauma and wound infection, large-area burn, open fracture, furuncle, carbuncle, infectious diarrhea, suppurative peritonitis, etc. bacteria are easy to enter lymph or blood circulation from the damage and inflammation; Chronic diseases such as malnutrition, hemopathy (especially with leukocyte deficiency), nephrotic syndrome, cirrhosis, diabetes, malignancy, innate immunoglobulin synthesis, and leukocyte phagocytosis are easy to induce bacterial infection. Squeeze skin sores and boils, especially in the face with rich blood supply, bacteria can enter the blood circulation in large quantities. The extensive wounds of large-area burn patients open the door for bacterial invasion. Skin necrosis, plasma exudation and eschar formation create a good environment for bacterial reproduction.
Various immunosuppressive drugs such as adrenocortical hormone, antimetabolic drugs, antitumor drugs and radiotherapy can weaken cellular or humoral immunity. Some can reduce leukocytes or inhibit inflammatory reaction, which is conducive to the spread and diffusion of bacteria. The long-term use of antibiotics is easy to lead to the reproduction of drug-resistant strains and increase the chance of infection. Various examination or treatment measures plus endoscopy, intubation, great saphenous vein intubation, indwelling catheter, intravenous hypernutrition therapy, various dialysis and organ transplantation can lead to bacteria entering the blood circulation or infectious thrombosis and septicemia.
Changes of pathogenic bacteria and common septicemia pathogenic bacteria: various bacteria with pathogenicity or conditional pathogenicity can become the pathogen of septicemia. Due to different age, different underlying diseases, different ways of introduction and different age groups, bacteria causing septicemia are also different. Before 1950, the pathogens of sepsis were mainly hemolytic streptococcus and pneumococcus, accounting for more than 50% of the total, Staphylococcus (Staphylococcus aureus + Staphylococcus epiphyte) accounted for 20%, and gram-negative bacilli accounted for about 12%. With the wide application of broad-spectrum antibiotics, corticosteroids and immunosuppressants, the pathogen spectrum of sepsis has also changed. Because hemolytic streptococcus and pneumococcus are highly sensitive to penicillin, they are rare as pathogens of sepsis.
In recent years, anaerobic bacteria account for 8% ~ 26% of septic pathogens (anaerobic bacteria cannot be detected in many hospitals), mainly fragile Bacteroides and digestive Streptococcus. Plural bacterial sepsis can also occur in patients with significantly lower body defense function, that is, 2 or more pathogenic bacteria are detected in the same sample, or a variety of pathogenic bacteria are cultured from several blood or bone marrow samples within 72 hours. Generally, plural bacterial sepsis accounts for about 10% of the total number of sepsis.
If the patient’s condition is poor (age, basic condition, current condition, immune function and other factors), the number of pathogenic bacteria is large and the virulence is strong, the pathogenic bacteria can invade the body through damaged skin and mucosa, or be released from its latent lesions, enter the blood circulation through lymphatic vessels or veins and reproduce in it. At this time, the body’s defense mechanism is activated. Under the regulation of antibody and complement, the pathogen is effectively eliminated by monocyte macrophage system, which becomes transient bacteremia. There are multiple organ dysfunction and failure in clinic. Whether bacteria can form an infection state after entering the human body and whether they can develop into sepsis after invading the blood circulation is closely related to many factors, such as the number and / or virulence of invading bacteria, the defense function of human body and the strength of immune response.
Newborns are prone to sepsis, which can occur before, during or after birth. This is caused by poor skin mucosal barrier function, less gastric acid, high intestinal permeability, weak monocyte phagocytosis, low antibody (IgM, serotype and secretory IgA) and low complement concentration. These contents have been described in detail in previous textbooks. Here we will introduce some research trends on pathogenesis in recent years.
Recent studies have shown that after entering the blood circulation, bacteria produce a large number of toxins while growing and proliferating. The endotoxin released by gram-negative bacteria or the complex formed by lipid cell wall acid contained in the cell membrane of Gram-positive bacteria and peptidoglycan first cause damage to the body tissue, and then activate TNF, il-l, IL-6, IL-8, infr and other cytokines, This triggers the body’s inhibitory response to invading bacteria, which is called systemic inflammatory response syndrome. These pathophysiological reactions include: the complement system, coagulation system and angiotensin kinin system are activated; Glucocorticoids and β- Endorphins are released; This kind of medium eventually increases the capillary permeability and leakage, and the blood volume is insufficient to the main organs such as heart, lung, liver and kidney, resulting in shock and DIC.
The pathological changes of sepsis may vary according to the type of pathogen, duration of disease and basic diseases. The changes of organs and tissues caused by pathogenic toxin in the early stage were mainly inflammatory reaction, with turbidity swelling, focal necrosis and steatosis. When the phagocytic system of monocytes increased, the liver and spleen were enlarged. The more persistent lesions such as edema, the longer the course of disease. Capillary damage causes skin mucosal ecchymosis and rash. Small edema, hydrops in joint cavity, suppurative meningitis, pleurisy, etc. can occur in heart, lung, liver, kidney and brain.