Pneumonia
How microbes overcome the lung’s defences, why inflammation fills alveoli with exudate, why consolidated lung causes hypoxaemia with a normal or low PaCO2, and how lobar and bronchopneumonia differ.
By the end, you can
- Describe how the airways and alveoli normally keep microbes out.
- Explain how a virulent organism, a large inoculum or weakened defences lead to infection.
- Explain how acute inflammation fills alveoli with exudate and produces consolidation.
- Relate shunt in consolidated lung to hypoxaemia with a normal or low PaCO2.
- Distinguish lobar pneumonia, bronchopneumonia and an interstitial pattern.
- Recognise the classic stages, severity score and tests of pneumonia, and explain how antibiotics and other treatments act on its mechanism.
What it is
Pneumonia is acute infection of the alveoli and distal airways, in which inflammation fills alveoli with exudate. It is classified by where it is acquired (community, hospital, ventilator-associated), by the host (aspiration, immunocompromise) and by its anatomical pattern (lobar, bronchopneumonia, interstitial).
3 types to tell apart
- Community-acquired
- Arises outside hospital; Streptococcus pneumoniae is the commonest bacterial cause, with Haemophilus influenzae, respiratory viruses and atypical organisms such as Mycoplasma.
- Hospital-acquired and ventilator-associated
- Arises 48 hours or more after admission or intubation; Gram-negative bacteria and Staphylococcus aureus are more common.
- Aspiration pneumonia
- Follows inhalation of a large volume of mouth or stomach contents, usually when cough and swallowing are impaired; it favours dependent segments.
US spelling: litres → liters.
Normal function
Keeping the alveoli clean, dry and full of air
An adult breathes in about 10,000 litres of air a day, with the particles and microbes it carries, yet the alveoli normally hold very few microbes. Defence works in layers: in the airways, mucus traps particles and cilia carry them up to be swallowed; cough expels larger loads; secretions contain IgA and lysozyme.
The alveoli have no cilia. There, engulf whatever arrives, and surfactant from lowers surface tension and contains proteins that coat microbes for phagocytosis.
Gas exchange needs each to be both filled with air and wrapped in perfused capillaries. Anything that fills alveoli with fluid or cells breaks this match.
Underlying change · Step 1 of 4
Microbes reach the alveoli and overcome the defences
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Underlying change · Step 2 of 4
Inflammation fills the alveoli with exudate
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 4
Perfused but not ventilated: shunt and hypoxaemia
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 4 of 4
Lobar pneumonia and bronchopneumonia
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .