Aspiration pneumonia: what is it, causes, symptoms, treatment, prognosis

What is aspiration pneumonia?

Aspirationpneumonia - an infectious pulmonary process that occurs after fluid enters the lower respiratory tract. The aspirated fluid may be oropharyngeal secretions, solids, or may also be gastric contents. The term aspiration pneumonitis refers to acute inhalation injury to the lungs that occurs after aspiration of sterile gastric contents. In the course of an observational study, it was found that the risk of hospitalization of patients with community-acquired pneumonia about the development of aspiration pneumonia is about 13.8%. Mortality from aspiration pneumonia largely depends on the volume and content of aspirate (fluid) and can be up to 70%.

Symptoms and Signs

Aspiration pneumonia symptoms do not appear for at least one or two days. The most common symptom is:

• cough.

Coughing up phlegm (viscous or discolored mucus). Soon the phlegm begins to smell foul.

Other symptoms of aspiration pneumonia include:

• fever;
• shortness of breath (dyspnea);
• discomfort in the chest.

Causes and risk factors

Disruption of natural defense mechanisms such as closure of the glottis and cough reflex increases the risk of aspiration. Common risk factors for aspiration include changes in mental status, neurologic disorders, esophageal motility disorders, prolonged vomiting, and gastric outlet obstruction. Although the common microorganisms involved in the etiology of community-acquired pneumonia are streptococci, Pfeiffer's sticks and gram-negative sticks, the etiology of aspiration pneumonia depends on the content of the aspirate. A prospective study of 95 patients showed that gram-negative bacilli accounted for 49%, followed by anaerobes (16%). The main isolated anaerobes were fusobacteria, bacteroids and peptostreptococci. For nosocomial aspiration pneumonia, gram-negative organisms should be considered, especially Pseudomonas aeruginosa.

Conditions that increase the risk of aspiration pneumonia include:

• stroke;
• drug overdose;
• alcohol use disorder (alcoholism);
• epilepsy;
• general anesthesia;
• head trauma;
• intracranial formations;
• dementia;
• Parkinson's disease;
• strictures of the esophagus;
• gastroesophageal reflux disease;
• pseudobulbar paralysis;
• tracheostomy;
• nasogastric tube;
• bronchoscopy;
• lingering vomiting.

Epidemiology

Due to the lack of biomarkers, epidemiological studies to identify the incidence of aspiration pneumonia were difficult. Several studies have shown that aspiration pneumonia accounts for 5% to 15% of all community-acquired pneumonia. A retrospective study of 628 patients with aspiration pneumonia showed a 30-day mortality rate of 21%. The study also showed that the CURB-65 score, which is a predictor of mortality in community-acquired pneumonia, is not a reliable indicator of aspiration pneumonia. This pneumonia remains one of the most common complications after general anesthesia and occurs in every 2,000 to 30,000 cases.

A study conducted with the participation of persons over 65 years old who underwent cardiovascular surgery showed that the frequency aspiration pneumonia was 9.8%, while 12 out of 123 patients developed aspiration pneumonia after extubation. pneumonia. A case-control study (CSI) showed that the incidence of aspiration pneumonia was 18% in nursing home patients and 15% in community-acquired aspiration pneumonia. Since most cases of aspiration pneumonia go unnoticed or unnoticed, the true incidence is difficult to establish.

Pathophysiology

In normal healthy adults, the mucociliary mechanism and alveolar macrophages act as defense mechanisms in clearing oropharyngeal secretions from microexplosions. The pathological process of aspiration pneumonia occurs when the normal defense mechanisms do not work in a predisposed person. The ingress of fluid into the bronchi and alveolar space causes an anti-inflammatory reaction with the release of pro-inflammatory cytokines, tumor necrosis factor alpha and interleukins. Inoculation of organisms of the common flora from the oropharynx and esophagus leads to an infectious process.

Mendelssohn was the first to study the pathophysiology of aspiration pneumonitis by inducing gastric contents in the lungs of a rabbit and comparing it with 0.1 N. hydrochloric acid. More recent studies in rats using dilute hydrochloric acid have demonstrated a biphasic response with an initial corrosive phase to an acidic pH followed by an inflammatory response mediated neutrophils. Inoculation of normal oropharyngeal flora in the aspirate causes an infectious process and leads to aspiration pneumonia. If the bacterial load of the aspirate is low, the host's normal defenses will clear the secretions and prevent infection.

Diagnostics

- History and physical signs.

Common clinical signs that should raise suspicion of aspiration include sudden onset shortness of breath, fever, hypoxemia, radiographic signs of bilateral infiltrates and wheezing on auscultation in the lungs of a hospitalized patient. The typical lesion depends on the position during aspiration, usually the lower lobes are involved in an upright position and the upper lobes can be involved in the supine position. X-ray findings will appear within 2 hours of aspiration, and bronchoscopy may reveal erythematous bronchi.

- Analysis and visualization.

There should be a high degree of suspicion in the diagnosis of aspiration pneumonia, especially in critically ill hospitalized patients. Antibiotic treatment should be started immediately and imaging should not delay treatment. The most commonly used imaging tests are chest x-rays, chest computed tomography (CT) scans to help locate the site of the aspiration. However, in most cases, the fluid goes unnoticed, so it is very difficult to distinguish aspiration pneumonitis from aspiration pneumonia. Clinical features can help distinguish between the two. In aspiration pneumonitis, a large volume of gastric contents must be aspirated to cause chemical pneumonitis, and it can progress rapidly to acute lung injury followed by acute respiratory distress syndrome (ARDS). Whereas in aspiration pneumonia, aspiration may have smaller volumes and may be imperceptible, which, when bacteria are inoculated, progresses to signs of pneumonia and subsequent development acute respiratory distress syndrome (ARDS).

Arterial blood gas can be used to assess pH and oxygenation status. Sputum analysis is useless because it usually detects many organisms, while blood cultures are poor and not used often.

On a chest x-ray, the lower right lobe is most commonly affected. Patients who have performed vertical aspiration may have bilateral lower lobe involvement. In patients lying on the left side, the infiltrates are usually left-sided. Lesion of the right upper lobe is more common in patients who perform supine aspiration and in patients with alcohol use disorder.

Bronchoscopy is indicated for aspirating food particles. This method also allows the extraction of organisms for cultivation.

- Differential diagnosis.

The differential diagnosis of aspiration pneumonia is as follows:

• acute respiratory distress syndrome;
• bronchitis;
• mycoplasma pneumonia;
• chronic obstructive pulmonary disease;
• viral pneumonia;
• septic shock.

Treatment

There is a difference between the treatment of aspiration pneumonia and aspiration pneumonitis.

The position of the patient should be adjusted, followed by aspiration of the contents of the oropharynx with the placement of a nasogastric tube. Patients who are not intubated are given humidified oxygen and the head of the bed should be raised 45 degrees.

Close monitoring of patient oxygen saturation is essential, and if hypoxia is noted, immediate ventilated intubation should be provided. Flexible bronchoscopy is usually indicated for high volume aspiration to clear secretions and to obtain a bronchoalveolar lavage sample for quantitative bacteriological testing.

In general practice, antibiotics are given immediately, even if they are not required for aspiration pneumonitis, to prevent disease progression. As antibiotics for community-acquired aspiration pneumonia, you can choose ampicillin-sulbactam or a combination of metronidazole and amoxicillin. Patients allergic to penicillin prefer clindamycin. However, for nosocomial aspiration pneumonia, antibiotics are needed to cover resistant gram-negative bacteria and S. aureus, therefore the most widely used combination of vancomycin and piperacillin-tazobactam. After culture results are obtained, the antibiotic regimen should be narrowed down to organism-specific.

Oxygenation is often required, and some patients may even require mechanical ventilation.

Aspiration pneumonia carries enormous morbidity and mortality. Delays in diagnosis and treatment lead to long hospital stays and additional complications.

Forecast

The prognosis depends on the patient's age and other comorbidities. However, despite optimal treatment, mortality rates of 11 to 30% have been reported. Even those who survived show long-term recovery and repeated hospitalizations.

Complications

Complications include:

• acute respiratory distress syndrome;
• empyema;
• lung abscess;
• parapneumonic effusion;
• breathing disorder.

Postoperative and Rehabilitation Care

After aspiration treatment, steps should be taken to prevent further episodes. Patients should be advised to sleep with the head of the bed raised.

Those who have difficulty swallowing should eat thick foods in small portions.