Lower respiratory tract infection and pneumonia
Definition
An lower respiratory tract infection of the chest that can be detected radiologically
Epidemiology
Has incidence of 1-3/1000 and, of those admitted to hospital the mortality is 10%
Pathophysiology
Basically, bacteria gets into your lower respiratory tract and you get an infection. Go figure. Here are the different types which have different bacteria:
Community-acquired (CAP)
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 (nosocomial)
The most common are enterobacteriaceae or Staph. aureus. Pseudomonas, Klebsiella, Bacteriodes and Clostridia can be the culpirts too.
Aspiration
Likely in those with stroke, myasthenia, bulbar palsies, reduced consciousness, oesophageal disease (achalasia, GORD), or poor dental hygeine (aspirate anaerobic bacteria).
Immunocompromise
All those bacteria in CAP are common. Others are gram negative bacteria and Pneumocystis jiroveci. Fungi, viruses (CMV, HSV) and mycobacteria are also far more common.
Risk Factors
Being old but besides that, not a lot else.
Clinical Features
- General features are fever, rigors, malaise, tachycardia, confusion (in elderly), and anorexia.
- Chest symptoms are: shortness of breath, cough, purulent sputum, pleuritic pain and haemoptysis.
- Chest signs include: tachypnoea, dyspnoea, pleural rub, consolidation (reduced chest expansion, dull on percussion, bronchial breathing and increased vocal resonance/vocal and tactile fremitus).
Investigations
You're basically trying to see how bad the pneumonia is.
Bloods
- FBC - WCC↑
- U&Es - dehydration
- LFTs - baseline
- CRP - should be raised
- Blood cultures - rule out sepsis
Imaging
- Chest X-Ray - this is really important. Technically, if there is no radiological abnormality, it's not a pneumonia.
Others
- Pulse oximetry
- Sputum culture
You may consider pleural fluid and bronchoscopy if the patient is really ill. To that end....
Assessing severity
Use the CURB65 score. A positive criterion is +1:
- Confusion
- 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%.
Management
Essentially, it's antibiotics, oxygen and fluids.
Antibiotics
The treatments vary on where you got the infection. These lists are all alternatives:
Community
If it's mild and had NO previous treatment use ONE of:
If it's mild but has been previously treated use ONE of:
- Amoxicillin + Erythromycin (see above for doses)
- Fluoroquinolone
- If IV required use ampicillin 500mg/6h + erythromycin 500mg/6h IVI
If it's severe:
- Erythromycin 1g/6h IV
WITH one of:
- Co-amoxiclav IV
- Cefuroxime 1.5g/8h IV
If it's atypical use ONE of:
- Clarithromycin 500mg/12h po/IVI +/- rimfampicin - Legionella pneumophilia
- Tetracycline - Chlamydia species
- Co-trimoxazole - Pneumocystis jiroveci
Hospital
Use:
- Aminoglycoside IV (gentamicin)
WITH one of:
- Antipseudomonal penicillin
- 3rd generation cephalosporin IV
Aspiration
Use cefuroxime 1.5g/8h IV + Metronidazole 500mg/8h IV
Neutropenic
Use: Aminoglycoside IV WITH one of
- Antipseudomonal penicillin IV
- 3rd generation cephalosporin IV
Consider using antifungals after 48h of infection.
Oxygen and fluids
Basically keep the PaO2>8kPa and/or O2>92%. With regards to IV fluids, give if there is anorexia, dehydration or shock