Pneumonia is an inflammation of the lung parenchyma caused by various microorganisms, including bacteria, mycobacteria, fungi, and viruses. Pneumonitis is a more general term that describes an inflammatory process in the lung tissue that may predispose or place the patient at risk for microbial invasion.

Pathophysiology

Normally, the upper airway prevents potentially infectious particles from reaching the sterile lower respiratory tract. Pneumonia arises from normal flora present in patients whose resistance has been altered or from aspiration of flora present in the oropharynx; patients often have an acute or chronic underlying disease that impairs host defenses. Pneumonia may also result from bloodborne organisms that enter the pulmonary circulation and are trapped in the pulmonary capillary bed.

Pneumonia affects both ventilation and diffusion. An inflammatory reaction can occur in the alveoli, producing an exudate that interferes with the diffusion of oxygen and carbon dioxide. White blood cells, mostly neutrophils, also migrate into the alveoli and fill the normally air-filled spaces. Areas of the lung are not adequately ventilated because of secretions and mucosal edema that cause partial occlusion of the bronchi or alveoli, with a resultant decrease in alveolar oxygen tension. Bronchospasm may also occur in patients with reactive airway disease. Because of hypoventilation, a ventilation–perfusion mismatch occurs in the affected area of the lung. Venous blood entering the pulmonary circulation passes through the underventilated area and travels to the left side of the heart poorly oxygenated. The mixing of oxygenated and unoxygenated or poorly oxygenated blood eventually results in arterial hypoxemia.

If a substantial portion of one or more lobes is involved, the disease is referred to as lobar pneumonia. The term bronchopneumonia is used to describe pneumonia that is distributed in a patchy fashion, having originated in one or more localized areas within the bronchi and extending to the adjacent surrounding lung parenchyma. Bronchopneumonia is more common than lobar pneumonia.

Summary of Pathophysiology: Pneumonia is an infection of the lungs involving an acute inflammatory response that impairs the work of the alveoli and interferes with ventilation.

Classification
Pneumonia can be classified as:
• community-acquired pneumonia;
• hospital-acquired pneumonia;
• aspiration pneumonia;
• pneumonia in immunocompromised patients.
Clinical manifestations
The clinical manifestations of pneumonia are:

• Shortness of breath due to inflammation within the lungs, impairing gas exchange
• Difficulty breathing (dyspnea) due to inflammation and mucus within the lungs
• Fever due to infectious process
• Chills due to increased temperature
• Cough due to mucous production and irritation of the airways
• Crackles due to fluid within the alveolar space and smaller airways
• Rhonchi due to mucus in airways; wheezing due to inflammation within the larger airways
• Discolored, possibly blood-tinged, sputum due to irritation in the airways or microorganisms causing infection
• Tachycardia and tachypnea as the body attempts to meet the demand for oxygen
• Pain on respiration due to pleuritic inflammation, pleural effusion, or atelectasis development
• Headache, muscle aches (myalgia), joint pains, or nausea may be present depending on the infecting organism

Diagnosis
The following investigations are used in diagnosis (Woodhead 2010):

• Chest X-ray: Shadows on chest x-ray, indicating infiltration, may be in a lobar or segmental
  pattern or more scattered.
• Blood analysis: Elevated WBC (leukocytosis) showing sign of infection.
• Blood pressure monitoring;
• Blood urea measurement;
• Low oxygen saturation on pulse oximetry.
• ABGs: Arterial blood gas may show low oxygen and elevated carbon dioxide levels.
• Blood culture; Culture and sensitivity of the sputum to identify the infective agent and the
  appropriate antibiotics.
• Sputum samples for C & S.

Assessment and management
Assessment of severity is important to determine the management of the patient with pneumonia, and the CURB65 score can be used for this. This scores 1 point for each of:

• C (confusion);
• U (blood urea >7 mmol/L);
• R (respiratory rate >30/min);
• B (blood pressure: systolic <90 mmHg, diastolic <60 mmHg);
• 65 (>65 years of age).

Medical management includes the prompt and appropriate administration of intravenous antibiotic therapy, oxygen and intravenous fluids to correct the fluid balance. If an oxygen saturation of more than 92% is not achieved using oxygen, NIV may be considered.

• Administer oxygen as needed.
• For bacterial infections, administer antibiotics such as macrolides (azithromycin, clarithromycin), fluoroquinolones (levofloxacin, moxifloxacin), beta-lactams (amoxicillin/clavulanate, cefotaxime, ceftriaxone, cefuroxime axetil, cefpodoxime, ampicillin/sulbactam), or ketolide (telithromycin).
• Administer antipyretics when fever >101 for patient comfort:
• acetaminophen, ibuprofen
• Administer brochodilators to keep airways open, enhance airflow if needed:
• albuterol, metaproterenol, levalbuterol via nebulizer or metered dose inhaler
• Increase fluid intake to help loosen secretions and prevent dehydration.
• Instruct the patient on how to use the incentive spirometer to encourage deep breathing; monitor progress.

NURSING DIAGNOSES

• Risk for aspiration
• Impaired ventilation
• Ineffective airway clearance

NURSING INTERVENTION

• Monitor respiration for rate, effort, use of accessory muscles, skin color, and breath sounds.
• Record fluid intake and output for differences, signs of dehydration.
• Record sputum characteristics for changes in color, amount, and consistency.
• Properly dispose of sputum.
• Explain to the patient:
• Take adequate fluids—3 liters per day—to prevent excess fluid loss through the respiratory system with exhalation.
• Use of incentive spirometer.