Community-acquired pneumonia

This form of pneumonia is responsible for over 1 000 000 admissions per year in the UK. Infection is usually spread by droplet inhalation and, while most patients affected are previously well, cigarette smoke, alcohol and corticosteroid therapy all impair ciliary and immune function. Other risk factors include old age, recent influenza infection, pre-existing lung disease and, for certain forms of pneumonia, contact with sick birds (Chlamydia psittaci) or farm environments (Coxiella burnetii). Knowledge of the patient's recent travel history and local epidemics is also valuable. Appropriate investigation allows a microbiological diagnosis to be made in approximately 60% of patients with pneumonia. 'Lobar pneumonia' is a radiological and pathological term referring to homogeneous consolidation (red hepatisation) of one or more lung lobes, often with associated pleural inflammation; bronchopneumonia refers to more patchy alveolar consolidation associated with bronchial and bronchiolar inflammation often affecting both lower lobes. It is particularly common in winter in countries with temperate climates.

Eighty percent of community acquired pneumonia is pneumococcal pneumonia.

Other causes of community acquired pneumonias include haemophilus influenzae, staphylococcal aureus, atypical pneumonias (e.g. due to mycoplasma pneumoniae), mycobacterium tuberculosis, and viruses.

Clinical features

Patients present with a short illness of cough, fever and malaise, often associated with pleuritic chest pain which is occasionally referred to the shoulder or anterior abdominal wall. The cough is characteristically short, painful and at first dry, but later becomes productive and may become rust-coloured or even frankly blood-stained. The sudden onset of a high fever can result in rigors or, in children, vomiting or a febrile convulsion. Appetite is usually lost and headache is a frequent accompanying symptom. In patients with severe pneumonia confusion can be an early and dominant problem.

Physical signs include a significant pyrexia, tachycardia, tachypnoea, evidence of hypoxaemia and, not infrequently, hypotension and confusion. Pleurisy often results in diminution of respiratory movement and a pleural rub on the affected side. At a variable time after onset, generally within 2 days, signs of consolidation appear, with impairment of the percussion note and high-pitched bronchial breath sounds. When resolution begins, numerous coarse crepitations are heard, indicating liquefaction of the alveolar exudate. If a para-pneumonic pleural effusion develops, physical signs of fluid in the pleural space are usually found, but bronchial breath sounds can persist and the presence of an empyema may be suspected only from the recurrence or persistence of pyrexia. Upper abdominal tenderness is sometimes apparent in patients with lower lobe pneumonia or if there is associated hepatitis.

Investigations

The main objectives of investigating patients with a clinically based diagnosis of pneumonia are:

· to obtain a radiological confirmation of the diagnosis

· to exclude other conditions that may mimic pneumonia

· to obtain a microbiological diagnosis

· to assess the severity of the pneumonia

· to identify the development of complications.

Radiological examination

In lobar pneumonia, the chest radiograph shows a homogeneous opacity localised to the affected lobe or segment; this usually appears within 12-18 hours of the onset of the illness. Radiological examination is also particularly helpful if a complication such as pleural effusion, intrapulmonary abscess formation or empyema is suspected. Hilar lymphadenopathy is occasionally seen in mycoplasma pneumonia, and lung cavities are more frequently observed in patients with staphylococcal or pneumococcal serotype 3 pneumonia. Follow-up radiological examination is essential as failure of a pneumonia to resolve may indicate underlying bronchial obstruction (e.g. a foreign body or carcinoma)

Microbiological investigations

Every effort should be made to establish a microbiological diagnosis, as such information is invaluable in tailoring antibiotic therapy and in managing any complications. The identification of organisms such as Legionella pneumophila also has important public health implications. Rapid results can sometimes be obtained with 'bedside' complement fixation tests for antigen levels (for example, of H. influenzae and Pneumocystis carinii) in urine and other body fluids. In patients who are severely ill a microbiological diagnosis becomes essential and, if sputum cannot be obtained, an attempt should be made to aspirate secretions or washings from the trachea or lower respiratory tract either by bronchoscopy or by inserting a needle through the cricothyroid membrane. Some patients can be induced to produce sputum by the administration of nebulised hypertonic saline.

Arterial blood gas measurements

These should be measured in all patients admitted to hospital with a diagnosis of pneumonia.

General blood tests

A high neutrophil leucocytosis favours a diagnosis of bacterial (particularly pneumococcal) pneumonia; patients with pneumonia caused by atypical agents tend to have a marginally raised or normal white cell count. A marked leucopenia indicates either a viral aetiology or an overwhelming bacterial infection.

Дата добавления: 2015-11-14