Hospital-acquired pneumonia

Intrahospital pneumonia develops at least 48 hours after hospitalization. The most frequent pathogens are gram-negative bacilli and Staphylococcus aureus; drug resistant microorganisms are a significant problem. The causes are the same as for community-acquired pneumonia, but pneumonia in ventilated patients may also be associated with worsening oxygenation and an increase in tracheal secretion. The diagnosis is suspected on the basis of clinical manifestations and chest X-ray and is confirmed by bacteriological examination of blood or samples taken from the lower respiratory tract with bronchoscopy. Treatment is done with antibiotics. Hospital nosocomial pneumonia has an unfavorable prognosis, in part this is due to concomitant pathology.

[1], [2], [3], [4]

Causes

The most common cause of nosocomial pneumonia is the microaspiration of bacteria that colonized the oropharynx and upper respiratory tract in critically ill patients.

Pathogens and the range of their resistance to antibiotics vary in different institutions and can vary within the same institution in a short period (for example, monthly). In general, the most important pathogen is the Pseudomonas aeruginosa (Pseudomonas aeruginosa), which occurs most frequently with pneumonia acquired under intensive care, and in patients with cystic fibrosis, neutropenia, early AIDS, and bronchiectasis. Other important microorganisms are the intestinal Gram-negative flora (Enterobacter, Klebsiella pneumoniae, Escherichia coli, Serratia marcescens, Proteus Acinetobacter ) and the sensitive and methicillin-resistant Staphylococcus aureus.

Staphylococcus aureus, pneumococcus and Haemophilus influenzae are more common when pneumonia develops within 4-7 days after hospitalization, and intestinal Gram-negative microorganisms with an increase in the duration of intubation.

Preceding antibiotic therapy greatly increases the likelihood of polymicrobial infection, infection with resistant organisms, especially methicillin-resistant Staphylococcus aureus, and Pseudomonas infections. Infection with resistant organisms significantly increases lethality and complicates the course of the disease.

Glucocorticoids in high doses increase the risk of Legionella and Pseudomonas infection.

[5], [6], [7], [8], [9]

Risk factors

Endotracheal intubation with artificial ventilation is the greatest common risk; the pneumonia associated with pneumonia is more than 85% of all cases, pneumonia occurs in 17-23% of patients on ventilator. Endotracheal intubation disrupts the protection of the respiratory tract, worsens the cough and clearance of the ciliated epithelium, and facilitates the microaspiration of the bacteria-infected secret that accumulates above the inflated cuff of the intubation tube. In addition, bacteria form a biofilm on and in the endotracheal tube, which protects them from antibiotics and host immunity.

In non-intubated patients, risk factors include previous antibiotic therapy, high pH of gastric juice (due to prophylactic treatment of stress ulcers) and concomitant cardiac, pulmonary, hepatic and renal insufficiency. The main risk factors for postoperative pneumonia are age over 70 years, surgical intervention on the abdominal or thoracic cavity and dependent functional status.

[10], [11], [12], [13], [14], [15]

Symptoms

In general, the symptoms of nosocomial pneumonia in non-intubated patients are the same as for community-acquired pneumonia. Nosocomial pneumonia in critically severe, mechanically ventilated patients more often causes fever and an increase in the frequency of respiratory movements and / or cardiac contractions or changes in respiratory rate such as an increase in purulent discharge or worsening of hypoxemia. Non-infectious causes of worsening pulmonary function, for example acute respiratory distress syndrome (ARDS), pneumothorax and pulmonary edema should be excluded.

Forms

Hospital-acquired pneumonia includes pneumonia associated with ventila- tion, postoperative pneumonia and pneumonia, which develops in patients without mechanical ventilation, but hospitalized in hospitals in a medium or severe state.

[16], [17], [18], [19], [20], [21]

Complications and consequences

The mortality associated with hospital pneumonia due to gram-negative infection is approximately 25-50%, despite the availability of effective antibiotics. It is unclear whether death is the result of a major illness or pneumonia itself. The risk of death in women is higher. The mortality from pneumonia caused by Staphylococcus aureus is 10 to 40%, in part because of the severity of comorbid conditions (eg, the need for mechanical ventilation, elderly age, chemotherapy for malignant neoplasm, chronic pulmonary diseases).

[22], [23], [24], [25]

Diagnostics

Diagnosis is imperfect. Practically hospital pneumonia is often suspected on the basis of the appearance of a new infiltrate on the roentgenogram of the chest or leukocytosis. However, no symptoms of nosocomial pneumonia, signs or radiographic findings are sensitive or specific for the diagnosis, since all symptoms can be caused by atelectasis, pulmonary embolism or pulmonary edema and may be part of the ARDS clinical picture. The feasibility of Gram staining, sputum analysis and bacteriological examination of endotracheal aspirates remains in question, because samples are often contaminated with bacteria that are either colonizing or pathogenic, so that a positive culture does not always indicate the etiologic role of the isolated microorganism. Bronchoscopic fecal secretion from the lower respiratory tract is likely to yield more reliable specimens, but the effectiveness of this approach is controversial. The study of mediators of inflammation in bronchoalveolar lavage fluid can play a role in diagnosis in the future; for example, the concentration of a soluble trigger receptor expressed by myeloid cells (this protein is expressed by immune cells during infection) of more than 5 pg / ml can help distinguish bacterial and fungal pneumonia from non-infectious causes of clinical and radiologic changes in ventilated patients. However, this approach requires further investigation, and the only finding that reliably identifies both pneumonia and the microorganism that caused it is the culture of the respiratory pathogen isolated from the blood or from the pleural fluid.

[26], [27]

Treatment

Some patients may have a pneumonia risk index so low that it is necessary to seek an alternative diagnosis. Nevertheless, the treatment of nosocomial pneumonia is carried out with antibiotics that are chosen empirically, based on the nature of the perception of certain risk factors in the patient and conditions.

Uncontrolled use of antibiotics is the main reason for the development of antimicrobial resistance. Therefore, treatment can begin with the appointment of a wide range of drugs that are replaced by the most specific drug effective against microorganisms identified in culture. Alternative strategies for limiting resistance that have not proven effective include stopping antibiotics after 72 hours in patients whose pulmonary infection rates have decreased to less than 6 and regular alternation of empirically prescribed antibiotics (eg, 3-6 months).

Inocial antibiotics

There are many regimens, but all should include antibiotics that encompass resistant gram-negative and Gram-positive microorganisms. The choice includes carbapenems (imipenem-cilastatin 500 mg intravenously every 6 hours or meropenem 1-2 g intravenously every 8 hours), monobactams (aztreonam 1-2 g intravenously every 8 h), or antipseudomonasal beta-lactams (ticarcillin 3 g intravenously with or without clavulanic acid every 4 hours, piperacillin 3 g intravenously with or without tazobactam every 4-6 h, ceftazidime 2 g intravenously every 8 hours, or cefepime 1-2 g every 12 h), administered alone or in combination with an aminoglycoside (gentamicin or tobramycin 1.7 mg / kg intravenously every 8 hours or 5-6 mg / kg once a day and and amikacin 15 mg / kg every 24 h) and / or vancomycin 1 g every 12 h. Linezolid can be used for certain lung infections, including methicillin-resistant staphylococcus aureus (MRSA), especially in patients who may not be assigned to vancomycin. Daptomycin should not be used to treat pulmonary infections.

Prevention

Non-invasive ventilation using continuous positive airway pressure (CPAP) or bi-level positive airway pressure (BiPAP) prevents a violation in the protection of the airways that occurs with endotracheal intubation and eliminates the need for intubation in some patients. A semi-vertical or vertical position reduces the risk of aspiration and pneumonia compared to the prone position.

Continuous aspiration of the sublingual secretion through a special intubation tube attached to the aspirator probably reduces the risk of aspiration.

Selective decontamination of the oropharynx (using local forms of gentamycin, colistin and vancomycin cream) or the entire gastrointestinal tract (using polymyxin, aminoglycosides or quinolone and / or nystatin, or amphotericin) appears to be also effective, although it may increase the risk of colonization by resistant organisms.

Hospital-acquired pneumonia is prevented by monitoring culture and routinely replaceable ventilation loops or endotracheal tubes.

[28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39]