What Is Ventilator-Associated Pneumonia?

VAP is one of the common and serious complications during mechanical ventilation. Once VAP occurs in patients, it is easy to cause offline difficulties, which prolongs the length of hospitalization, increases the cost of hospitalization, and even severely threatens the patient's life and leads to death. Cook and Morehead et al reported that the fatality rate of VAP was 20% to 71% ^[1-2] . Domestic literature reports that the prevalence of VAP is 43.1%, and the fatality rate is 51.6%. In view of the fact that the pathogenic bacteria, clinical diagnosis and treatment of VAP are different from general pneumonia, and the high mortality rate, researches on VAP have received extensive attention at home and abroad in recent years.

Kingship	(Attending physician)	Department of Respiratory and Critical Care Medicine, Nanjing General Hospital of Nanjing Military Region
Shi Yi	(Chief physician)	Department of Respiratory and Critical Care Medicine, Nanjing General Hospital of Nanjing Military Region

Ventilator associated pneumonia (VAP) refers to pneumonia that occurs within 48 hours after mechanical ventilation (MV) to 48 hours after extubation. It is an important type of hospital-acquired pneumonia (HAP). Among them, pneumonia that occurred within 4 days of MV was early-onset VAP, and those who were 5 days were late-onset VAP.

Western Medicine Name

Ventilator-associated pneumonia

English name

Ventilator associated pneumonia, VAP

Affiliated Department

Internal Medicine-Respiratory Medicine

Disease site

lung

Main cause

Hospital-acquired infection

Brief introduction to ventilator-associated pneumonia

VAP is one of the common and serious complications during mechanical ventilation. Once VAP occurs in patients, it is easy to cause offline difficulties, which prolongs the length of hospitalization, increases the cost of hospitalization, and even severely threatens the patient's life and causes death. Cook and Morehead et al reported that the fatality rate of VAP was 20% to 71% ^[1-2] . Domestic literature reports that the prevalence of VAP is 43.1%, and the fatality rate is 51.6%. In view of the fact that the pathogenic bacteria, clinical diagnosis and treatment of VAP are different from general pneumonia, and the high mortality rate, researches on VAP have received extensive attention at home and abroad in recent years.

Etiology of ventilator-associated pneumonia

VAP has certain characteristics of endemic and epidemic diseases, and its pathogenic spectrum varies from region to region, and is closely related to the underlying disease and previous antibiotic treatment, the route of transmission, the source of pathogenic bacteria and other factors. Bacteria are the most common pathogens, accounting for more than 90%, of which Gram-negative bacilli are 50% -70%, including Pseudomonas aeruginosa, Proteus, and Acinetobacter ^[3] . 15% -30% of Gram-positive cocci are mainly Staphylococcus aureus. Non-multidrug resistant bacteria are predominant in early-onset VAP. Such as Streptococcus pneumoniae, Haemophilus influenzae, MSSA and sensitive enteric gram-negative bacilli (such as E. coli, Klebsiella pneumoniae, Proteus and Serratia marcescens). Late-onset VAP is a multidrug-resistant bacterium. Such as ESBL-producing Klebsiella pneumoniae and Acinetobacter baumannii, drug-resistant enteric bacteria, Stenotrophomonas maltophilia, MRSA and so on. At present, the proportion of fungal infections has also gradually increased. The following reasons are considered: the increase of nosocomial infections caused by patient age, underlying disease status, low resistance, and long hospital stay; the application of immunosuppressants and hormones to make the body resistant The implementation of invasive operations such as tracheal intubation damages the local defense mechanism, making the upper respiratory tract pathogens easy to spread to the lower respiratory tract; the widespread use of broad-spectrum antibiotics makes the proliferation of drug-resistant condition-causing bacteria dominant, causing The flora is dysregulated and the infection rate of fungi rises.

Risk factors for ventilator-associated pneumonia

The main risk factors related to VAP are older and poorer condition those with chronic lung disease, long-term bedridden, loss of consciousness sputum difficult to cough long mechanical ventilation, antibiotics have been used before the machine, especially broad-spectrum Antibiotics cause dysbiosis. Bacterial translocation in the digestive tract. H-blockers and proton pump inhibitors have been used for a long time. Lack of gastric acid can easily colonize the digestive tract. Among them, long mechanical ventilation is the main risk factor for pneumonia in hospitals, and patients with continuous mechanical ventilation are 6-12 times more likely to have pneumonia in hospitals than those without mechanical ventilation. Recent studies have also identified hypotension as an independent risk factor for the prognosis of VAP.

Diagnostic criteria for ventilator-associated pneumonia

As the most common and important type of hospital-acquired pneumonia, VAP is more difficult to diagnose than any other hospital infection. Pulmonary histopathological findings and microbiological findings of pathogenic microorganisms are commonly identified as the gold standard for VAP diagnosis. The diagnostic criteria require traumatic examinations that are not easily accepted by patients and doctors, and have some difficulties in clinical application.

Clinical diagnosis of ventilator-associated pneumonia

^[4] Guidelines for the diagnosis and treatment of hospital-acquired pneumonia formulated by the Respiratory Branch of the Chinese Medical Association ^[4] . Pulmonary diseases such as tuberculosis, lung tumors, and atelectasis are excluded: onset after 48 hours of using the ventilator; compared with the chest radiograph before mechanical ventilation, the lung infiltrates shadow or shows new inflammatory lesions; consolidation of the lung Wet rales can be heard on signs and / or lung auscultations, and one of the following conditions: a. Blood cells> 10.0 × 109 / L or <4 × 109 / L, with or without nuclear metastasis; b. Fever, body temperature> 37.5 ° C, a large number of purulent secretions in the respiratory tract; c. New pathogenic bacteria were isolated from bronchial secretions after the onset of disease. ^[5-6]

Etiological diagnosis of ventilator-associated pneumonia

The etiology diagnostic criteria are as follows: culture of aspirate in trachea. Quantitative bacterial culture was performed by suctioning secretions through a tracheal tube through a sterile pipette. If the bacterial concentration was 10 CFU / mL, it could be diagnosed with a sensitivity of 93% and a specificity of 80%. Protective hair brush via bronchoscope. Brushing secretions for quantitative culture, with 10 CFU / mL as the diagnostic standard, is the most reliable diagnostic method for VAP. When antibiotics are not used, the specificity is 90%, but the sensitivity is only 40% to 60%, which is related to the size of the material area. If antibiotics are used in advance, the sensitivity is lower. Bronchoalveolar lavage via bronchoscope. This method can overcome the shortcomings of the small sampling range of bronchoscopic protective brushes. It is positive to isolate bacteria 10 CFU / mL, and its sensitivity and specificity are 50% to 90%. The negative culture result is useful for confirming sterile lung tissue. The sensitivity is 63% and the specificity is 96%, so it plays an important role in excluding VAP. Positive pus or blood culture results. A number of studies have confirmed that bronchoscopic bronchoalveolar lavage and bronchoscopic protective brushes under bronchoscopy have the same effect as bronchoscopy, and are inexpensive and easy to operate. Any one of these 4 items can be satisfied ^[7-8] .

Histological diagnosis of ventilator-associated pneumonia

Percutaneous lung biopsy and open lung biopsy. The collected secretions and lung tissue can be used for histological examination, special pathogen examination and culture. The diagnosis rate is very high. It is the gold standard for the diagnosis of pneumonia, but both are trauma. Sexual examinations have relatively many complications and cannot be diagnosed early. Generally, it is only used for patients who are ineffective after initial treatment and have not been diagnosed by other methods.

Treatment and prevention of ventilator-associated pneumonia

The use of antibiotics is the most important treatment of VAP, but the treatment of primary disease, the prevention and treatment of risk factors leading to VAP, nutritional support, immunotherapy and intensive care can all improve the prognosis of VAP.

Anti-infective treatment of ventilator-associated pneumonia

Early correct antibiotic treatment can lead to significant mortality in VAP patients. Because the diagnosis of VAP is very difficult, when VAP is highly suspected clinically, the correct empirical antibiotic treatment should be started immediately. In recent years, with the changes of pathogenic bacteria and the emergence of multi-drug resistant strains, some new changes and trends have occurred in the selection of VAP antibiotics. The antibiotic spectrum of the initial empirical treatment should be selected to ensure that it covers all possible pathogens, including Gram-negative and positive bacteria (methicillin-resistant Staphylococcus aureus), in order to improve the success rate of first-time medication, some scholars have said For the first time antibiotic effect. Because critically ill patients with clinically suspected VAP have often been treated with antibiotics in advance, the possibility of bacterial resistance to previous antibiotics should be considered when selecting empirical treatment options before obtaining culture results. Combined treatment of gram-negative bacteria plus vancomycin to cover methicillin-resistant Staphylococcus aureus is the best combination antibiotic treatment plan. After the results of the pathogenic culture are returned, the targeted, sensitive and relatively narrow spectrum Generally speaking, the initial ultra-broad spectrum treatment may be switched to narrow-spectrum treatment after 24 to 72 hours ^[9] .

Ventilator-associated pneumonia actively treats primary disease

If the primary disease cannot be eliminated, everything in the intensive care unit will be futile. Any treatment should focus on eliminating the primary disease, and anti-infective treatment can only be effective if the primary disease is resolved.

Ventilator-associated pneumonia immunotherapy

Although antibiotic treatment of VAP is the most direct and effective method, due to the current non-standard application of antibiotics, more and more multi-drug resistant strains have appeared, prompting people to open up other ways to treat infections. Macrophage colony-stimulating factor and interferon have attracted widespread attention as auxiliary immunomodulators in the treatment of infections. In recent years, some scholars have proposed gene therapy to regulate the host's immunity. The advantage is that it directly affects infected cells or tissues and avoids possible side effects caused by systemic application of proteins.

Ventilator-associated pneumonia nutritional support

Enhancing nutrition is very important for patients with mechanical ventilation, especially those with VAP. Patients with malnutrition have weak respiratory muscles and are difficult to take offline, so patients with VAP are difficult to avoid ^[10] . Nutrition support treatment, including total parenteral nutrition, parenteral nutrition and parenteral nutrition at the same time or simple parenteral nutrition, correct hypoproteinemia, maintain water electrolyte and acid-base balance.

Ventilator-associated pneumonia strengthens nursing work

Nursing has played a considerable role in the prevention and treatment of VAP. Good nursing work can greatly reduce the incidence of VAP, including: clearing the secretions of the oropharynx; fully draining sputum; preventing cross-hospital Infection; Ventilator circuit pipes should be replaced after 48 hours of continuous use; Condensate bacteria on the circuit pipes are extremely high in concentration, avoid flowing back into the airways when cleaning; Maintain a good ventilation environment in the room can reduce exhaled airborne bacteria aerosols The temperature of the nebulizer fluid on the ventilator should not be lower than 45 to reduce bacterial contamination, and it must be thoroughly disinfected after use.

Expert opinion on ventilator-associated pneumonia

In short, the clinical diagnosis and treatment of VAP is a very difficult problem. Although some experience has been obtained in this area, further research is needed.