Nosocomial pneumonia

According to currently accepted criteria, nosocomial pneumonia (synonyms: hospital pneumonia, ventilator-associated pneumonia) includes only cases of infectious lung damage that developed no earlier than 48 hours after the patient's admission to a medical facility. Nosocomial pneumonia (NP) associated with mechanical ventilation (NPIVL) is an inflammatory lung damage that developed no earlier than 48 hours after intubation and the start of mechanical ventilation, in the absence of signs of pulmonary infection at the time of intubation. However, in many cases, in surgical patients, the manifestation of nosocomial pneumonia is possible at an earlier time.

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Epidemiology of nosocomial pneumonia

Nosocomial pneumonia ranks second in the structure of all hospital infectious complications and accounts for 15-18%. The incidence of NP in surgical patients after elective surgeries is 6%, after emergency abdominal surgeries (inflammatory and destructive diseases) - 15%. NP is the most frequent infectious complication in the ICU. NPVL accounts for 36% of all cases of postoperative pneumonia. The incidence of NPVL is 22-55% in elective surgery with mechanical ventilation for more than 2 days, in emergency abdominal surgery - 34.5%, with ARDS - 55%. The incidence of nosocomial pneumonia in patients of surgical ICUs who do not undergo mechanical ventilation does not exceed 15%. Mortality with NPV is 19-45% (depending on the severity of the underlying disease and the scope of the operation). Mortality with NPILV in purulent-septic abdominal surgery reaches 50-70% depending on the underlying disease, pathogen and adequacy of treatment tactics. Attributable mortality with NPILV is 23% or more. The prevalence of NPILV in a specific intensive care unit for a certain period of time is calculated using the formula:

Frequency of development of NPVL x 1000 / Total number of days of mechanical ventilation

Mortality in NPVL also depends on the pathogen detected in the department.

Mortality in nosocomial pneumonia associated with artificial ventilation of the lungs, depending on the causative agent

Pathogens	Mortality, %
Ps. aeruginosa	70-80
Gram-positive bacteria	5-20
Aerobic gram-negative bacteria	20-50

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Etiological structure of nosocomial pneumonia

The spectrum of pathogens of nosocomial pneumonia depends on the "microbiological landscape" of a particular medical institution and intensive care unit. In addition, the etiological structure of nosocomial pneumonia is influenced by concomitant diseases (especially COPD) and the nature of the underlying pathological process that required the use of mechanical ventilation (traumatic shock with aspiration, severe sepsis, surgical interventions in high-risk patients). In general, with NPV in surgical patients, gram-negative microorganisms predominate: Pseudomonas aeruginosa, Acinetobacter, representatives of the Enterobactriaceae family, H. Influenzae is detected much less often. Among gram-positive cocci, Staphylococcus aureus occupies a special place in the development of nosocomial pneumonia, significantly surpassing S. pneumoniae in its etiological role. In some cases (4-6%), fungi of the genus Candida play a certain role in maintaining pneumonia.

Pathogenesis of nosocomial pneumonia associated with artificial ventilation of the lungs

There are two sources of infection for patients in intensive care:

• exogenous,
• endogenous.

Exogenous sources of lung infection include objects in the external environment that directly or indirectly come into contact with the patient's respiratory tract: air, inhaled medical gases, equipment for mechanical ventilation (endotracheal and tracheostomy tubes, respirators, breathing circuits, catheters for sanitation of the tracheobronchial tree, bronchoscopes), as well as the microflora of other patients and medical personnel.

The endogenous source of lung infection is the microflora of the oropharynx, gastrointestinal tract, skin, urinary tract, paranasal sinuses, nasopharynx, as well as pathogens from alternative foci of infection.

Highly contaminated oropharyngeal secretions enter the tracheobronchial tree by microaspiration. The risk of aspiration of oropharyngeal secretions increases in patients undergoing mechanical ventilation due to the presence of an endotracheal tube, which damages the mucous membrane of the oropharynx and trachea, disrupts the function of the ciliated epithelium and prevents both spontaneous expectoration of sputum and the act of swallowing. Bacterial colonization of the oropharynx increases the risk of developing NPVL due to the possibility of bacterial migration near the cuff of the endotracheal tube.

Translocation of opportunistic bacteria from the gastrointestinal tract plays a major role in the pathogenesis of nosocomial pneumonia. The gastrointestinal tract of a healthy person is inhabited by a great many microbes - both anaerobes and aerobes. They maintain adequate motor, secretory and metabolic functions of the gastrointestinal tract. It is the anaerobic part of the intestinal microflora that provides colonization resistance and suppresses the growth of potentially pathogenic aerobic bacterial microflora. However, under the influence of injuries, hemodynamic and metabolic disorders or other pathological conditions, intestinal wall ischemia develops and the motor, secretory and barrier functions of the intestine are impaired. Retrograde colonization of the upper gastrointestinal tract by intestinal microflora occurs, as well as, due to impaired barrier function of enterocytes, translocation of bacteria and their toxins into the portal and systemic bloodstream. A multisystemic multifactorial bacteriological analysis in intensive care unit patients confirmed that the dynamics of contamination of the abdominal cavity, gastrointestinal tract, bloodstream, and lung tissue depend on the morphofunctional insufficiency of the intestine.

The development of an infectious process in the lungs can be considered as a result of an imbalance between aggressive factors that facilitate the entry of a large number of highly virulent microorganisms into the respiratory tract and factors of anti-infective protection. Only under conditions of a critical weakening of protective factors are pathogens able to demonstrate their pathogenicity and cause the development of an infectious process.

Features of nosocomial pneumonia in surgery

• Early development (in the first 3-5 days of the postoperative period - 60-70% of all nosocomial pneumonia)
• Multifactorial infection.
• Difficulties in nosological and differential diagnosis.
• The complexity of prescribing empirical therapy.
• The incidence of NPI development in patients with purulent-inflammatory foci in the abdominal cavity is 64%.

Reasons for the high incidence of NP in patients with abdominal sepsis:

• long-term mechanical ventilation,
• repeat surgeries and anesthesia,
• the use of "invasive" medical and diagnostic procedures,
• severe intestinal insufficiency syndrome, predisposing to the translocation of pathogenic microorganisms and their toxins from the gastrointestinal tract,
• the possibility of hematogenous and lymphogenous infection from septic foci in the abdominal cavity,
• Acute lung injury syndrome associated with abdominal sepsis is a “fertile” ground for the development of nosocomial pneumonia.

Factors contributing to the early development of nosocomial pneumonia:

• severity of the condition (high APACHE II score),
• abdominal sepsis,
• massive aspiration,
• age over 60 years,
• concomitant COPD,
• disturbance of consciousness,
• emergency intubation,
• conducting long-term (more than 72 hours) mechanical ventilation,
• the use of invasive treatment and diagnostic methods, which increases the risk of exogenous infection,
• development of acute respiratory distress syndrome as a non-specific reaction of the lungs,
• inadequacy of previous antibacterial therapy,
• re-hospitalization within 6 months,
• thoracic or abdominal surgeries,
• nasotracheal and nasogastric intubation,
• position on the back with the head end of the bed lowered (angle less than 30°).

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Diagnosis of nosocomial pneumonia

Recommendations health. A. Science policy committee of the American college of chest physians, 2000.

Suspicion of nosocomial pneumonia during mechanical ventilation should arise in the presence of two or more of the following signs:

• purulent nature of sputum,
• fever >38 °C or hypothermia <36 °C,
• leukocytosis >11x10 ⁹ /ml or leukopenia <4x10 ⁹ /ml, shift in the leukocyte formula to the left (>20% band neutrophils or any number of juvenile forms),
• paO ₂ /FiO ₂ (respiratory index) <300.

In the absence of the above symptoms, there is no need for further examination, but observation is advisable (level II evidence).

If two or more of the above symptoms are present, an X-ray examination is necessary. If the X-ray is normal, it is necessary to look for alternative causes of the symptoms (level III evidence).

If there are infiltrates on the radiograph, two tactical options are possible (level III evidence).

If infiltrates are present on the radiograph, microbiological examination should be performed (quantitative methods endobronchial aspirate, BAL, protected brushes, bronchoscopic methods) and empirical antibiotic therapy (ABT) should be prescribed. Adequate empirical ABT in patients with suspected pneumonia increases survival (level II evidence). In the absence of bacteriological confirmation in a stable patient, ABT can be stopped.

To objectify the assessment of clinical, laboratory and radiological data in patients with suspected NPI, it is advisable to use the CPIS (Clinical Pulmonary Infection Score) scale.

• Temperature, °C
  • 36.5-38.4 - 0 points,
  • >38.5 or <38.9 - 1 point,
  • >39 or <36 - 2 points
• Leukocytes, x10 ⁹
  • 4-11 - 0 points,
  • <4 or >11 - 1 point + 1 point if there are young forms
• Bronchial secretion
  • need for TBD sanitation <14 times per day - 0 points,
  • need for sanitation of the TBD >14 = 1 point + 1 point if the secretions are purulent
• pаO2/FiO2 mmHg
  • >240 or OPL/ARDS - 0 points,
  • <240 in the absence of ALI/ARDS - 1 point
• X-ray of the lungs
  • absence of infiltrates - 0 points,
  • diffuse infiltrates - 1 point,
  • localized infiltrate - 2 points.
• Microbiological analysis of tracheal aspirate (semi-quantitative method 0, +, ++ or +++)
  • no growth or 0-+ - 0 points.
  • ++-+++ - 1 point + 1 point, when the same microorganism is isolated (Gram staining).

The diagnosis of NPVL is considered confirmed with a score of 7 or more on the CPIS scale.

Considering that CPIS is inconvenient in routine practice, its modified version, the DOP scale (diagnostic and assessment scale for the severity of pneumonia), which is presented in the table, has become more acceptable.

The sensitivity of the scale is 92%, specificity - 88%. A score of 6-7 points corresponds to moderate pneumonia, 8-9 - severe, 10 and more - extremely severe pneumonia. The diagnostic value of the DOP scale has been proven. Its use is advisable for dynamic monitoring of patients, as well as for assessing the effectiveness of the therapy.

Pneumonia diagnostic and severity rating scale

Indicator	Meaning	Points
Body temperature, C	36.0-37.9 38.0-39.0 <36 0 or >39.0	0 1 2
Number of leukocytes, x10 9	4.9-10.9 11 0-17 0 or >20 rod-shaped forms >17.0 or presence of any number of juvenile forms	0 1 2
Respiratory index paO2/FiO2	>300 300-226 225-151 <150	0 1 2 3
Bronchial secretion	+/-	0
	+++	2
Infiltrates in the lungs (based on X-ray results)	Absence	0
	Local	1
	Confluent, bilateral, with abscess formation	2

Among patients with suspected NPVL, three diagnostic groups can be distinguished

• Group I - the diagnosis of pneumonia is reliable in the presence of clinical, radiological and microbiological criteria. As clinical experience shows, a full range of diagnostic signs can be identified in 31% of patients.
• Group II - probable diagnosis of pneumonia, in the presence of only clinical and laboratory, or clinical and radiological, or laboratory and radiological criteria. Such a "diagnostic set" can be identified in 47% of patients.
• Group III - doubtful diagnosis of pneumonia - there are only clinical, or only laboratory, or only radiological signs of pneumonia. This diagnostic group makes up 22% of all patients with suspected NPVL.

Antimicrobial therapy is mandatory for patients of diagnostic groups I and II. In case of doubtful diagnosis of nosocomial pneumonia, further dynamic observation is advisable.

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Features of microbiological diagnostics of nosocomial pneumonia

Collection of material for microbiological examination must be performed before the start (or change) of antibacterial therapy.

The following methods are most often used to collect and perform microbiological examination of material from the tracheobronchial tree.

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Diagnostic bronchoscopy and bronchoalveolar lavage

The study is preceded by preoxygenation with FiO2 ₌ 1.0 for 10-15 min. The procedure is carried out under total intravenous anesthesia, since the use of local anesthetics is limited, given their possible bactericidal effect. The sample is taken from the area of greatest damage, determined by X-ray data and visually. In case of diffuse infiltrative lung damage, samples of material are taken from the middle lobe of the right lung or from the lingual segment of the left lung. The discharge (lavage fluid) of the lower respiratory tract from the internal catheter is placed in a sterile test tube and immediately delivered to the microbiology laboratory.

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Technique of using a blind protected catheter

After 5 minutes of preoxygenation with FiO2 ₌ 1.0, the catheter is inserted as distally as possible through the endotracheal or tracheostomy tube. The inner catheter is then withdrawn (this destroys the film protecting the inner catheter from tract contamination). Aspiration is performed using a 20 ml sterile syringe attached to the proximal end of the inner catheter. The device is then removed from the endotracheal tube, and the lower respiratory tract secretions from the inner catheter are placed in a sterile tube and immediately delivered to the microbiology laboratory.

The diagnostic value of quantitative cultures of endotracheal aspirates depends on the degree of bacterial contamination and previous antibiotic use.

Sensitivity and specificity of quantitative diagnostic methods for nosocomial pneumonia associated with artificial ventilation of the lungs

Methodology	Diagnostic value, CFU/ml	Sensitivity, %	Specificity, %
Quantitative endotracheal aspiration	10 5 -10 6	67-91	59-92
"Protected" brush biopsy	>10 3	64-100	60-95
BALL	>10 4	72-100	69-100
"Protected" BAL	>10 4	82-92	VZ-97
"Protected blind" catheter	>10 4	100	82.2

Bronchoscopic (invasive) methods require the use of special equipment, additional personnel, and have low reproducibility. "Invasive" diagnostics of NPI does not lead to a reliable improvement in the long-term treatment results.

Criteria for severe nosocomial pneumonia

• Severe respiratory failure (RR>30 per minute).
• Development of cardiovascular failure (SBP <100 mm Hg, DBP <60 mm Hg).
• Body temperature >39 °C or <36 °C.
• Impaired consciousness.
• Multilobar or bilateral lesion.
• Clinical signs of organ dysfunction.
• Hyperleukocytosis (>30x10 ⁹ /l) or leukopenia (<4x10 ⁹ /l).
• Hypoxemia (paO2 _< 60 mmHg)

Antibacterial therapy of nosocomial pneumonia in surgical patients

To prescribe adequate empirical therapy, the following fundamental factors should be taken into account:

• the impact of the duration of the patient's stay in the intensive care unit and the duration of mechanical ventilation on the presumed etiology of the disease,
• features of the species composition of pathogens of NPILV and their sensitivity to antimicrobial drugs in a specific medical institution,
• the influence of previous antibacterial therapy on the etiological spectrum of NPI and on the sensitivity of pathogens to antimicrobial drugs.

Schemes of empirical antibacterial therapy for nosocomial pneumonia in surgical patients

Clinical situation	Antibacterial therapy regimen
Nosocomial pneumonia in patients of the surgical department	Second-generation cephalosporins (cefuroxime), Third-generation cephalosporins without antipseudomonal activity (ceftriaxone, cefotaxime), Fluoroquinolones (ciprofloxacin, pefloxacin, levofloxacin), Amoxicillin/clavulanate
Nosocomial pneumonia in patients in intensive care without mechanical ventilation	Cephalosporins of the third generation with antipseudomonas activity (ceftazidime cefoperazone), Cephalosporins of the fourth generation, Fluoroquinolones Cefoperazone + sulbactam
Nosocomial pneumonia without MVD (APACHE II less than 15)	Third-generation cephalosporins with antipseudomonal activity (ceftazidime, cefoperazone) + amikacin Fourth-generation cephalosporins (cefepime) Cefoperazone + sulbactam Fluoroquinolones (ciprofloxacin)
NP ivl + MODS (APACHE II more than 15)	Imipenem + cilastatin Meropenem IV generation cephalosporins (cefepime) ± amikacin Cefoperazone + sulbactam

Notes

• If there is a reasonable suspicion of MRSA, any of the regimens can be supplemented with vancomycin or linezolid.
• In case of a high risk of aspiration or its verification by clinical diagnostic methods, it is advisable to combine antibacterial drugs that are not active against anaerobic pathogens with metronidazole or clindamycin.

Reasons for the ineffectiveness of antibacterial therapy for nosocomial pneumonia:

• unsanitized focus of surgical infection,
• severity of the patient's condition (APACHE II >25),
• high antibiotic resistance of NPI pathogens,
• persistence of problematic pathogens (MRSA, P. aeruginosa, Acinetobacter spp, S. maltophilia),
• microorganisms "outside the spectrum" of action of empirical therapy (Candida spp., Aspergillus spp, Legionella spp., P. carinnii),
• development of superinfection (Enterobacter spp., Pseudomonas spp., fungi, Clostridium difficile),
• inadequate choice of drugs,
• late initiation of adequate antibacterial therapy,
• failure to comply with the drug dosage regimen (method of administration, single dose, interval between administrations),
• low doses and concentrations of antibiotic in plasma and tissues.

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Prevention of nosocomial pneumonia

Prevention of nosocomial pneumonia can be effective only if it is carried out within the framework of a general infection control system covering all elements of the treatment and diagnostic process and aimed at preventing various types of hospital-acquired infections. Here are only some of the measures most directly aimed at preventing nosocomial pneumonia. Such measures as, for example, isolation of patients with infectious complications, implementation of the principle of "one nurse - one patient", reduction of the preoperative period, timely detection and adequate surgical sanitation of alternative foci of infection, certainly play an important role in preventing nosocomial pneumonia, as well as other forms of hospital-acquired infections, but are more universal in nature and are not considered in this document.

All requirements set out in this subsection are based on the results of scientific research and practical experience, take into account the requirements of the legislation of the Russian Federation and international practice. The following system of ranking events according to their degree of justification is applied here.

Requirements that are mandatory and convincingly justified by data from methodologically sound experimental, clinical or epidemiological studies (meta-analyses, systematic reviews of randomized controlled trials (RCTs), individual well-organized RCTs). In the text they are designated - 1A.

Requirements that are mandatory and justified by data from a number of noteworthy experimental, clinical, or epidemiological studies with a low probability of systematic error and a high probability of causal relationship (cohort studies without randomization, case-control studies, etc.) and that have a convincing theoretical justification. In the text, they are designated as 1B.

Requirements, the mandatory fulfillment of which is dictated by the current federal or local legislation. In the text they are designated - 1B.

Requirements recommended for implementation, which are based on hypothetical data from clinical or epidemiological studies and have a certain theoretical justification (based on the opinion of a number of authoritative experts). In the text, they are designated by the number 2.

Requirements that are traditionally recommended for implementation, but there is no convincing evidence either for or against their implementation, and expert opinions differ. In the text, they are designated by the number 3.

The ranking system provided does not imply an assessment of the effectiveness of the measures and reflects only the quality and quantity of the studies whose data formed the basis for the development of the proposed measures.

Combating endogenous infection

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Prevention of aspiration

• Invasive devices such as endotracheal, tracheostomy, and/or enteral (naso-, orogastric, -intestinal) tubes should be removed immediately when the clinical indication for their use no longer exists (1B).
• In septic acute lung injury (ALI) or acute respiratory distress syndrome (ARDS), noninvasive mechanical ventilation is ineffective and life-threatening.
• Repeated endotracheal intubation should be avoided whenever possible in patients who have been mechanically ventilated (1B).
• The risk of developing NPVL with nasotracheal intubation is higher than with orotracheal intubation (1B).
• Continuous aspiration of secretions from the supracuff space is advisable (1B).
• Before extubating the trachea (deflating the cuff), make sure that the secretion has been removed from the supracuff space (1B).
• In patients with a high risk of aspiration pneumonia (those on mechanical ventilation, with a nasogastric or nasointestinal tube), the head of the bed should be elevated by 30-45° (1B).
• To prevent oropharyngeal colonization, adequate toilet of the oropharynx should be performed - aspiration of mucus with a special catheter, as well as treatment with antiseptic solutions (for example, 0.12% chlorhexidine bigluconate solution) in patients after cardiac surgery (2) and other patients with a high risk of developing pneumonia (3).

Combating exogenous infection

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Hand hygiene of medical personnel

• Hand hygiene of medical workers is a general concept that refers to a range of activities including hand washing, hand antisepsis and cosmetic care of the skin of the hands of medical personnel.
• If contaminated, wash your hands with water and soap. In other cases, perform hygienic hand antisepsis using an alcohol antiseptic (1A). Hygienic hand antisepsis is the antisepsis of the hands of medical personnel, the purpose of which is considered to be the removal or destruction of transient microflora.
• Hand hygiene should be performed even if hands are not visibly dirty (1A)

Hygienic hand antisepsis should be carried out:

• before direct contact with the patient,
• before putting on sterile gloves when inserting a central intravascular catheter,
• before inserting urinary catheters, peripheral vascular catheters or other invasive devices, unless these procedures require surgical intervention,
• after contact with the patient's intact skin (for example, when measuring pulse or blood pressure, moving the patient, etc.),
• after removing gloves (1B).

Hygienic hand antisepsis when performing patient care procedures should be performed when moving from contaminated areas of the patient's body to clean ones, as well as after contact with environmental objects (including medical equipment) located in close proximity to the patient (2).

Do not use antiseptic-impregnated wipes/balls for hand antisepsis (1B).

Hand hygiene improvement activities should be an integral part of the infection control program in a healthcare facility and should be given priority funding (1B).

Caring for patients with a tracheostomy

Tracheostomy should be performed under sterile conditions (1B).

Tracheostomy tube changes should be performed under sterile conditions and tracheostomy tubes should be sterilized or subjected to high-level disinfection (1B).

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Respiratory tract sanitation

When performing tracheobronchial tree (TBT) sanitation, sterile or clean disposable gloves should be worn (3).

When using open systems for aspiration of respiratory secretions, sterile, single-use catheters should be used (2).

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Care of respiratory equipment

The breathing circuit should not be changed for use in the same patient based solely on the duration of use without specific indications (obvious contamination, malfunction, etc.) (1A).

Reusable breathing circuits must be sterilized or subjected to high-level disinfection (IB-C) before use.

Any condensate in the circuit (1A) must be removed promptly.

It is recommended to use bacterial filters when performing artificial ventilation (2).

Sterile or pasteurized distilled water should be used to fill humidifier reservoirs (1B).

It is recommended to use heat and moisture exchange filters (HME) (2).

Closed aspiration systems (CAS) are designed to perform sanitation, lavage of the tracheobronchial tree and collection of tracheobronchial tree (TBT) secretions for microbiological analysis in a closed mode, i.e. in conditions completely separated from the environment. The purpose of creating such systems was to exclude contamination of the lower respiratory tract through the lumen of the endotracheal tube during "traditional" sanitation of the TBT and to reduce the negative impact of the tracheal sanitation procedure on ventilation parameters during "aggressive" modes of mechanical ventilation. The closed aspiration system is built into the "patient-ventilator" circuit between the breathing filter and the endotracheal tube. If active humidification using a stationary humidifier is used during mechanical ventilation, the system is installed between the endotracheal tube and the Y-shaped connector of the breathing circuit.

In this way, a single closed hermetic space is created: "artificial ventilation apparatus - respiratory filter - closed aspiration system - endotracheal tube - patient". In the distal part of the system there is a vacuum control button and a connector to which the vacuum aspirator tube is connected and, if necessary, a device for taking tracheobronchial aspirate for laboratory and microbiological studies. Since the closed aspiration system involves protecting the aspiration catheter from contact with the external environment, it is covered with a special protective sleeve, the presence of which excludes contact of the personnel's hands with the catheter surface. At the same time, the air in the protective sleeve (potentially contaminated with the patient's flora) is removed into the external environment when the catheter is inserted into the endotracheal tube, and the air entering from the external environment into the protective sleeve when the catheter is removed from the trachea may, in turn, be contaminated with flora foreign to the patient. Repeated unimpeded air movement in both directions during repeated episodes of tracheal sanitation becomes a source of mutual infection of the patient and the environment of the department. Obviously, ideally, the air moving from the protective sleeve and back should undergo microbiological "cleaning". From this point of view, in the ICU, it is preferable to use truly closed aspiration systems that are equipped with their own built-in antibacterial filter, eliminating the possibility of mutual contamination of the ICU environment and the patient with pathogenic microflora. The currently accumulated data on the use of ZAS with a built-in filter indicate a significant decrease in the incidence of nosocomial tracheobronchitis and pneumonia associated with mechanical ventilation, a significant increase in the average time from the onset of mechanical ventilation to the onset of pneumonia, which can be an effective means of preventing respiratory tract infections in patients with long-term mechanical ventilation.

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