Lower respiratory tract infection and pneumonia

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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

Common.jpgHas 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

The main symptoms are being short of breath, having a cough and a change in sputum colour (usually, it goes green in infection). Other chest symptoms are: pleuritic pain and haemoptysis.

The key signs are tachypnoea and dyspnoea, crackles and dullness to percussion. Other signs are pleural rub, other signs of consolidation (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.

Investigations

You're basically trying to see how bad the pneumonia is.

Bloods

Imaging

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.

Others

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

Use local guidlines and DON'T learn this of 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

Oxygen and fluids

Basically keep the PaO2>8kPa and/or O2>92%. If they have severe sepsis, see sepsis management for what to do next.

Prognosis

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