Antimicrobial agents are an essential component of complex therapy for sepsis. In recent years, convincing evidence has been obtained that early, adequate empirical antibacterial therapy for sepsis leads to a reduction in mortality and complication rates (category of evidence C). A series of retrospective studies also suggests that adequate antibiotic therapy reduces mortality in sepsis caused by gram-negative microorganisms (evidence category C), gram-positive microorganisms (evidence category D) and fungi (evidence category C). Given the data on improved disease outcomes with early adequate antibacterial therapy, antibiotics for sepsis should be prescribed urgently after clarification of the nosological diagnosis and before obtaining the results of bacteriological testing (empirical therapy). After receiving the results bacteriological research The antibacterial therapy regimen can be changed taking into account the isolated microflora and its antibiotic sensitivity.
Etiological diagnosis of sepsis
Microbiological diagnosis of sepsis is decisive in the selection of adequate antibacterial therapy regimens. Antibacterial therapy aimed at a known pathogen provides a significantly better clinical effect than empirical therapy aimed at a wide range of likely pathogens. That is why the microbiological diagnosis of sepsis should be given no less attention than the choice of treatment regimen.
Microbiological diagnosis of sepsis involves examination of the probable source(s) of infection and peripheral blood. If the same microorganism is isolated from the suspected focus of infection and from the peripheral blood, its etiological role in the development of sepsis should be considered proven.
When isolating various pathogens from the source of infection and peripheral blood, it is necessary to evaluate the etiological significance of each of them. For example, in the case of sepsis, having developed
occurring against the background of late nosocomial pneumonia, when isolated from respiratory tract P. aeruginosa in a high titer, and from the peripheral blood - coagulase-negative staphylococcus, the latter, most likely, should be regarded as a contaminating microorganism.
The effectiveness of microbiological diagnostics depends entirely on the correct collection and transportation of pathological material. The main requirements are: maximum proximity to the source of infection, prevention of contamination of the material with foreign microflora and proliferation of microorganisms during transportation and storage before the start of microbiological research. The listed requirements can be met to the greatest extent when using specially designed industrial devices (special needles or blood collection systems compatible with transport media, containers, etc.).
The use of nutrient media for blood culture prepared in the laboratory, cotton swabs for collecting material, as well as various kinds of improvised means (food containers) should be excluded. Specific protocols for the collection and transportation of pathological material must be agreed upon with the microbiological service of the institution and strictly followed.
Of particular importance in the diagnosis of sepsis is the study of peripheral blood. The best results are obtained when using industrial production media (vias) in combination with automatic bacterial growth analyzers. However, it must be borne in mind that bacteremia - the presence of a microorganism in the systemic circulation is not a pathognomonic sign of sepsis. Detection of microorganisms even in the presence of risk factors, but without clinical and laboratory confirmation of systemic inflammatory response syndrome, should be regarded not as sepsis, but as transient bacteremia. Its occurrence is described after therapeutic and diagnostic procedures, such as broncho- and fibrogastroscopy, colonoscopy.
Subject to strict requirements for the correct collection of material and the use of modern microbiological techniques, a positive blood culture in sepsis is observed in more than 50% of cases. When isolating typical pathogens such as Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, mushrooms, one positive result is usually enough to make a diagnosis. However, when isolating microorganisms that are skin saprophytes and capable of contaminating the sample ( Staphylococcus epidermidis, other coagulase-negative staphylococci, diphtheroids), two positive blood cultures are required to confirm true bacteremia. Modern automatic methods for studying blood culture make it possible to record the growth of microorganisms during 6-8 hours of incubation (up to 24 hours), which allows for an accurate identification of the pathogen after another 24-48 hours.
To conduct an adequate microbiological blood test, the following rules should be strictly observed.
1. Blood for testing must be collected before antibiotics are prescribed. If the patient is already receiving antibacterial therapy, then blood should be collected immediately before the next administration of the drug. A number of commercial media for blood testing contain sorbents of antibacterial drugs, which increases their sensitivity.
2. The standard for testing blood for sterility is to take material from two peripheral veins with an interval of up to 30 minutes, and from each vein blood must be taken into two bottles (with media for isolating aerobes and anaerobes). However, recently the feasibility of testing for anaerobes has been questioned due to the unsatisfactory cost-effectiveness ratio. Given the high cost of consumables for research, the frequency of isolation of anaerobes is extremely low. In practice, with limited financial resources, it is enough to limit blood sampling to one bottle for the study of aerobes. If a fungal etiology is suspected, special media must be used to isolate fungi.
It has been shown that a larger number of samples does not have an advantage in terms of pathogen detection rates. Taking blood at high fever does not increase the sensitivity of the method ( category of evidence C). There are recommendations for taking blood two hours before the peak of fever, but this is only feasible in those patients in whom the rise in temperature has a stable periodicity.
3. Blood for research must be taken from a peripheral vein. No benefit has been shown from taking blood from an artery ( category of evidence C).
Drawing blood from a catheter is not allowed! The exception is cases of suspected catheter-associated sepsis. In this case, the purpose of the study is to assess the degree of microbial contamination of the inner surface of the catheter and blood sampling from the catheter is adequate for the purpose of the study. To do this, a simultaneous quantitative bacteriological study of blood obtained from an intact peripheral vein and from a suspicious catheter should be carried out. If the same microorganism is isolated from both samples, and the quantitative ratio of contamination of the catheter and vein samples is equal to or more than 5, then the catheter is most likely the source of sepsis. The sensitivity of this diagnostic method is more than 80%, and the specificity reaches 100%.
4. Blood sampling from a peripheral vein should be carried out with careful asepsis. The skin at the venipuncture site is treated twice with iodine or povidone-iodine solution in concentric movements from the center to the periphery for at least 1 minute. Immediately before collection, the skin is treated with 70% alcohol. When performing venipuncture, the operator uses sterile gloves and a sterile dry syringe. Each sample (about 10 ml of blood or in the volume recommended by the bottle manufacturer’s instructions) is taken into a separate syringe. The cap of each bottle with the medium is treated with alcohol before being pierced with a needle to inoculate blood from a syringe. In some systems for inoculating blood, special lines are used that allow blood to be taken from a vein without the help of a syringe - by gravity, under the suction action of a vacuum in a bottle with nutrient medium. These systems have the advantage because eliminates one of the stages of manipulation that potentially increases the likelihood of contamination - the use of a syringe.
Careful treatment of the skin, vial cap and the use of commercial blood collection systems with an adapter can reduce the degree of sample contamination to 3% or less)
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