Pneumonia means infection of the alveoli. This occurs when protective processes fail to prevent inhaled or blood- borne microbes reaching and colonising the lungs.
PREDISPOSING FACTORS.
- IMPAIRED COUGHING: Coughing is an effective cleaning mechanism,but if it is impaired by,eg, unconsciousness,damage to respiratory muscles or the nerves supplying them,or painful coughing,then respiratory secretions may accumulate and become infected.
- DAMAGE TO THE EPITHELIAL LINING OF THE TRACT. Ciliary action may be impaired or the epithelium destroyed by,eg, tobacco smoking, inhaling noxious gases,infection.
- IMPAIRED ALVEOLAR PHAGOCYTOSIS. Depressed macrophage activity may be caused by tobacco smoking,alcohol,anoxia,oxygen toxicity.
- Other factors. The risk of pneumonia is increased in :
A)extremes of age.
B)leukopenia.
C)chronic disease,eg.cardiac failure,cancer,chronic renal failure,alcoholism.
D)suppression of immunity caused by,eg.ionising radiation,corticosteroid drugs.
E)hypothermia.
F)mechanically assisted ventilation.
CAUSATIVE ORGANISM.
A wide variety of organisms,including bacteria,viruses,mycoplasma,protozoa and fungi,can cause pneumonia under appropriate conditions. The commonest pathogen especially in lobar pneumonia,is the bacterium streptococcus pneumoniae. Others include staphylococcus aureus and Haemophilus influenza.
