Lower respiratory tract infection and pneumonia

Definition

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.

Epidemiology

Has incidence of 1-3/1000 and, of those admitted to hospital the mortality is 10%

Pathophysiology

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)

90% of these are caused by viral infections including rhinovirus, adenovirus and influenza and usually do not need antibiotics. Bacterial causes are similar to those for community-acquired pneumonia.

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 (HAP or 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).

In the community, the important thing is to differentiate between viral and bacterial LRTI. Purulent sputum is usually the best way to do this.

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, P_aO₂<8kPa OR S_aO₂<92%.

Management

Essentially, it's antibiotics, oxygen and fluids.

Antibiotics

Use local guidlines. 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

Oxygen and fluids

Basically keep the P_aO₂>8kPa and/or O₂>92%. If they have severe sepsis, see sepsis management for what to do next.