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Lower respiratory tract infection and pneumonia
- 1 Definition
- 2 Epidemiology
- 3 Pathophysiology
- 4 Risk Factors
- 5 Clinical Features
- 6 Investigations
- 7 Assessing severity
- 8 Management
- 9 Antibiotics
- 10 Oxygen and fluids
- 11 Prognosis
Lower respiratory tract infection - an infection of the lower respiratory tract without radiological change.
Pneumonia - an infection of the lower respiratory tract with radiological change.
Basically, viruses or bacteria gets into your lower respiratory tract and you get an infection. Go figure. Here are the different types which have different bacteria:
Lower respiratory tract infection (LRTI)
This one is acquired in the community, the most common pneumonia and the most common cause is Strep. pneumoniae. Other common pathogens are H. influenzae and M. pneumoniae. 15% are viral. Of the remaining bacteria, staph. aureus, legionella species, Moraxella catarrhalis, and Chlamydia are the most common. Everything else is rare.
Hospital-acquired (HAP or nosocomial)
Being old but besides that, not a lot else.
The main symptoms:
The key signs are
Other signs are pleural rub, reduced chest expansion on the affected side, bronchial breathing and increased vocal resonance/vocal and tactile fremitus. More general features of infection are: fever, rigors, malaise, tachycardia usually secondary to hypovolaemia, confusion (in elderly), and occasionally anorexia.
Don't forget to look for sepsis!
In the community, the important thing is to differentiate between viral and bacterial LRTI. Purulent sputum is usually the best way to do this.
You're basically trying to see how bad the pneumonia is.
- FBC - WCC↑
- U&Es - dehydration
- LFTs - baseline
- CRP - should be raised
- Blood cultures - rule out sepsis
CXR - this is really important. Technically, if there is no radiological abnormality, it's not a pneumonia.
You should also identify where the consolidation is. If the costophrenic angle is obscured the it's lower lobe. If the the heart border is obscure, then it's middle lobe. If it's at the top, it's upper lobe.
Use the CURB65 score. A positive criterion is +1:
- Urea > 7mmol/l
- Respiratory rate >/= 30/min
- Blood pressure < 90 systolic
- </=65 years old
0-1 can be managed at home; 2 indicates hospitalisation; >/=3 indicates severe pneumonia. Other things that make it worse are: comorbidity, multilobar/bilateral, PaO2<8kPa OR SaO2<92%.
Essentially, it's antibiotics, oxygen and fluids.
Use local guidlines and DON'T learn this off by heart. This is just to give you an idea of the sort of antibiotics you'll be using. They shouldn't ask you specific names in the exam but amoxicillin and co-amoxiclav are pretty common.
- LRTI - 1st: doxycycline, 2nd: amoxicillin
- Mild CAP (CURB65 0-1) - 1st: amoxicillin, 2nd/allergy: doxycycline, 3rd: clarithromycin/erythromycin
- Moderate CAP (CURB65 2) - 1st: co-amoxiclav + clarithromycin, 2nd/allergy: doxycycline
- Severe CAP (CURB 3-5) - 1st: IV co-amoxiclav + PO/IV clarithromycin, 2nd/allergy: cefuroxime + clarithromycin
- HAP (<5 days) - see mild CAP
- HAP (>5 days or severe) - 1st: piperacillin/tazobactam (Tazocin®), 2nd: meropenem
- Aspiration - IV co-amoxiclav/cefuroxime + metronidazole