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98 Chapter 3: Respiratory system

of the illness or presence of bronchopneumonia suggest Table 3.7 Impaired mechanisms predisposing to pneumonia
secondary bacterial infection.
Conditions impairing
Defence mechanism defence mechanism
Pneumonia Cough Coma/anaesthesia
Respiratory depression
Definition
Neuromuscular weakness
Pneumonia is an infective, inflammatory disease of the Ciliary function Smoking, influenza, colds
lung parenchyma. Bronchiectasis (including
cystic fibrosis and
Kartagener’s syndrome)
Aetiology
Ciliary function can also be
It is useful to classify pneumonia according to the impaired mechanically by
causative organism or the clinical setting, e.g. commu- obstruction, e.g. foreign
nity-acquired or nosocomial (hospital-acquired), im- body, bronchial
munosuppressed. This helps to determine the choice of carcinoma
Phagocytosis Smoking
antibiotics for treatment.
Alcohol
Pneumonia most often occurs in children and the el- Hypoxia
derly, but may also affect young, fit adults. The following T-cell response HIV and AIDS
risk factors increase the likelihood of pneumonia and Lymphoma
also influence the likely organism: Cytotoxic therapy
Immunosuppressive therapy
Cigarette smoking and underlying lung disease.

including steroids
Stroke or other neuromuscular disorder (aspiration

pneumonia often by anaerobes).
Immunosuppression and AIDS in particular P. grants and alcoholics. Organisms spread rapidly

jirovecii. through the alveolar spaces to involve the whole seg-
Intravenous drug abusers. ment, lobe or lung. Ninety per cent of cases in healthy

Alcoholics and vagrants. adultsarecausedbyStrep.pneumoniae,manyofthere-

Hospital patients (more often Gram-negative organ- maining cases are due to Klebsiella.Males are affected

isms). more often than females.
Viralpneumonia is less common, but bacterial pneumo- Atypical pneumonias cause predominantly interstitial
nia may be a secondary complication. inflammation in the lung, clinically are less abrupt in
onset and slower to resolve. Causes include the atypi-
Pathophysiology cal bacteria Chlamydia, Coxiella, Mycoplasma and Le-
The infection may be as a result of impairment of one or gionella.
more normal defence mechanisms (see Table 3.7)
Pulmonary oedema also predisposes to infection by Clinical features
acting as a growth medium. Pathologically pneumonia Symptoms may include fever, dyspnoea, pleuritic pain
can be divided into broncho-, lobar or atypical pneumo- and cough often productive of green sputum; however,
nia depending on the pattern of inflammation. at extremes of age the presentation may be non-specific.
Bronchopneumonia is most commonly seen at ex- On examination, classically there are signs of consoli-

tremes of age. It is predisposed to by immobility and dation (such as dullness to percussion, increased vocal
viral infections which lead to retention of secretions resonance, bronchial breathing) but even if frank con-
especially in the lower lobes. The infection is centred solidation is not present, most patients have tachypnoea
on the bronchi and bronchioles and spreads to involve (>20 breaths/minute) and crackles. In atypical pneu-
adjacent alveoli, which become consolidated with an monia the signs of consolidation in the lung are often
acute inflammatory exudate. Common causes include minor or absent, despite severe symptoms. Specific fea-
Strep. pneumoniae, M. catarrhalis or H. influenzae. tures, investigations and management of different types
Lobar pneumonia is seen most commonly in adults of pneumonia are summarised in Table 3.8 (see pp. 100–

whomay otherwise be healthy, but particularly va- 101).