Respiratory - Pneumonia and lung abscesses Flashcards
What is pneumonia? What are the clinical features?
An acute LOWER respiratory tract infection causing consolidation of the lung tissue by the presence of an intra-alveolar inflammatory exudate.
Signs: - pyrexia, cyanosis, confusion, tachypnoea, tachycardia, hypotension, signs of consolidation and a pleural rub
Symptoms: - dyspnoea, fever, rigors, malaise, productive cough, haemoptysis, pleural chest pain (worse on inspiration)
What are the typical examination findings in pneumonia?
Pnuemonia causes consildation, so examination findings include:
- coarse crepitations/ crackles
- reduced chest expansion
- bronchial breathing
- dull percussion note
- increased vocal fremitus/ vocal resonance
What is the most common cause of community acquired pneumonia?
CAP may be primary or secondary to underlying disease. Agents that cause CAP can be divided into typical and atypical.
Typical:
- Strep pneumoniae
- Haemophilus
- Mycoplasma pneumoniae
Atypical:
- Legionella
- Pneumocystis
- Chlamydial spp
What are the most common causes of hospital acquired pneumonia?
HAP is defined as pneumonia contracted > 48 hours following hospital in patient admission. It is also called a nosocomial infection.
Gram negative bacilli (e.g. enterobacteraciae), staph aureus and anaerobes (e.g. bacteroides, clostridia) are common. Pseudomonas and Klebsiella should also be considered.
What patients are at risk of aspiration pnuemonia? What agents cause these?
Patients with:
- Stroke
- Myasthenia
- Bulbar palsies
- Decreased GCS (e.g. head injury, drunk)
- Oesophageal disease (e.g. achalasia, reflux)
- Poor dental hygeine
…risk aspirating oropharyngeal anaerobes.
The main agents responsible for aspiration pneumonia are Strep pneumoniae and anaerobic bacteria (e.g. bacteroides, clostridia, enterobacteraciae)
What are the possible outcomes of aspiration pneumonia?
1) Sterile aspiration: often complicated by a secondary pneumonia
2) Infected aspiration: often results in extensive necrotizing bronchopneumonia with abscess formation
3) Other effects include:
- asphyxia –> death due to massive aspiration
- diffuse alveolar damage/ ARDS
- bronchiolitis obliterans from recurrent gastric acid aspiration
- bronchiectasis
- localised pneumonia
- lipid pnuemonia
What factors predispose to pneumonia?
1) Suppression of cough reflex - e.g. coma, anaesthesia (esp. opioids)
2) Impaired mucociliary apparatus - smoking, genetics (Kartageners syndrome), viral disease (e.g. influenza)
3) Impaired alveolar macrophages - smoking, oxygen toxicity
4) Impaired immune response - drugs, AIDS, leukaemias, congenital immunodeficiencies
5) Pulmonary oedema
6) Retention of secretions
7) Indwelling devices - ET tube, mechanical ventilation
8) Drugs - previous broad spectrum antibiotics
9) Prior viral respiratory tract infection - e.g. post influenza
How can pathogens reach the lung parenchyma and cause infection?
1) Inhalation from the environment - e.g. nebuliser circuit
2) Aspiration of oropharyngeal flora
3) Colonisation of a diseased lower respiratory tract - e.g. bronchiectasis
4) Direct spread from adjacent focus of infection
5) Blood spread - bacteraemia and sepsis
What investigations should be performed in a case of suspected pneumonia?
- CXr: lobar or multilobar infiltrates, air bronchogram, pleural effusion
- Assess oxygenation: oxygen saturation (ABG if sats below 92%)
- Bloods: FBC, U+E, LFT, CRP, Blood cultures
- Sputum: MC&S - in some cases check for Legionella (sputum culture AND urinary antigen)
- Pleural fluid aspiration: MC&S
- Bronchoscopy or bronchoalveolar lavage: if patient immunocompromised or ITU
How is the severity of pneumonia stratified?
Risk assessment can be made using CURB-65. The patient receives 1 point for each of the following:
- Confusion (abbreviated mental test <8)
- Urea > 7mmol/L
- Respiratory rate >30/min
- BP <90 systolic
- age >65
0-1: home treatment possible
2: hospital therapy
>3: severe pneumonia indicates mortality 15-40% - consider ITU
What is one of the problems with CURB-65 risk stratification tool?
It “underscores” the young - i.e. these patients compensate in severe infection so may seem more stable than they actually are. Treat the patient not the score.
What is the antibiotic treatment of choice for CAP?
Typical CAP is caused by either Strep pneumoniae, Haemophilus or Mycoplasma pneumoniae.
Treatment of choice is oral amoxicillin or clarithromycin (in penicillin allergic patients) or doxycycline provided the patient is not vomiting and only has mild or moderate pneumonia (CURB-65). If the patient has moderate pneumonia a loading dose of 200mg of the antibiotic of choice is given followed by maintenance dose over a longer period of time.
How is severe CAP treated?
Severe typical CAP is caused by the same agents as mild to moderate disease. Severe patients should be admitted to hospital and started on IV antibiotics.
Co-amoxiclav or 2nd generation cephalosporin (e.g. cefuroxime) AND clarithromycin should be used.
How is Legionella pneumonia treated?
Legionella pneumonia is an atypical cause of CAP.
Fluoroquinolone combined with clarithromycin is the treatment of choice.
How is chlamydia pneumonia treated?
Tetracycline - e.g. doxycycline
How is Pneumocystis pneumonia treated?
Remember that pneumocystis pneumonia is highly suggestive of immunocompromise and should be treated with high doses of co-trimoxazole.
How are hospital acquired pneumonias treated?
HAP can be caused by gram negative bacilli, gram positive cocci and anaerobes (e.g. bacteroides, clostridia, legionella etc) so broad antibiotic coverage is needed.
An aminoglycoside (e.g. gentamicin) + antipseudomonal penicillin (e.g. Tazoscin)
How are aspiration pneumonias treated?
Cephalosporin IV (e.g. cefuroxime) + metronidazole (for anaerobes)
What is lobar pneumonia?
Pneumonia can be classified by either anatomical location (e.g. broncho or lobar pneumonia) or clinically (e.g. HAP, CAP, recurrent pneumonia, aspiration, immunocompromised etc)
Lobar pneumonia is characterised by large areas of uniform consolidation of a part of a lobe or entire lobe of the lung.
What agents most commonly cause lobar pneumonia?
Lobar pneumonia is the commonest cause of CAP. It usually affects healthy adults and rarely the very young or old.
90% are due to pneumococcus (e.g. strep pneumoniae). The pathogenicity of subtypes depends on virulence factors - e.g. pneumolysin, resistance to phagocytosis - capsular polysaccharide etc
Other gram negative organisms - e.g. Klebsiella, Haemophilus and Legionella - account for other cases but are in the minority.
What is the macroscopic appearance of lobar pneumonia?
The classic appearance is for pneumococcal infection: consolidation that is sharply defined to the lobes which are diffusely affected.
Describe the stages of lobar pneumonia?
The progession of lobar pneumonia is as follows:
Stage 1 - congestion: lungs are heavy, red and boggy. There is alveolar wall congestions and early acute inflammatory changes (e.g. polymorphs)
Stage 2 - red hepatization: lung are firm, deep red and airless. A fibrinous pleurisy is often seen. Increased alveolar exudate of fibrin, polymorphs and phagocytosed organisms with some red cell extravasation
Stage 3 - grey hepatization: lungs are firm, grey//brown and airless. The intra-alveolar exudate is still present but red cells have lysed and alveolar walls are no longer congested
Stage 4 - resolution: exudate is digested and absorbed rapidly so that the lungs return to normal without parenchymal destruction. Pleural inflammation often organises with fibrosis and adhesions.
