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PNEUMONIA

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					Definition:
 Pneumonia is an infection of the pulmonary parenchyma.
  Despite being the cause of significant morbidity and
  mortality, pneumonia is often misdiagnosed, mistreated,
  and underestimated.
 It is usually caused by bacteria.
 Clinically it presents as an acute illness characterized in the
  majority of cases by the presence of cough, purulent
  sputum and fever together with physical signs or
  radiological changes compatible with consolidation of the
  lung.
Classification :
Pneumonia can be classified both anatomically and on the
  basis of the aetiology.
Anatomical classification :
 Pneumonias are either localized, with the whole of one or
  more lobes affected (lober pneumonia) , or diffuse, when
  they primarily affect the lobules of the lung, often in
  association with the bronchi and bronchioles - a condition
  referred to as 'bronchopneumonia'.
Aetiological classification :
 An aetiological factor can be discovered in
  approximately 75% of patients.
 The term 'atypical pneumonia' has been used to
  describe pneumonia caused by agents such as
  Mycoplasma, Legionella, Chlamydia and Coxiella
  burnetii.
 While these pneumonias can differ from
  pneumococcal disease, there is a considerable
  overlap in clinical presentation and as these agents
  account for almost one-fifth of the cases of
  pneumonia , the term 'atypical' has been dropped.
 Pneumonias may also result from:
I. chemical causes, such as in the aspiration of vomitus
II. radiotherapy
III. allergic mechanisms.
Precipitating factors :
 Strep. pneumoniae - often follows viral infection with
  influenza or para-influenza.
 Hospitalized 'ill' patients - often infected with Gram-
  negative organisms.
 Cigarette smoking (the strongest independent risk
  factor for invasive pneumococcal disease).
 Alcohol excess.
 Bronchiectasis (e.g. in cystic fibrosis).
 Bronchial obstruction (e.g. carcinoma) -
  occasionally associated with infection with 'non-
  pathogenic' organisms.
 Immunosuppression (e.g. AIDS or treatment with
  cytotoxic agents) - organisms include
  Pneumocystis carinii, Mycobacterium avium,
  cytomegalovirus.
 Intravenous drug abuse - frequently associated
  with Staph. aureus infection.
 Inhalation from oesophageal obstruction - often
  associated with infection with anaerobes.
 Pathology:
Classic pneumonia evolves through a series of pathologic
  changes.
 The initial phase is one of edema, with the presence of a
  proteinaceous exudate—and often of bacteria—in the
  alveoli. This phase so rapidly followed by
 Red hepatization phase. The presence of
  erythrocytes in the cellular intra-alveolar exudate gives
  this second stage its name, but neutrophils are also present
  and are important from the standpoint of host defense.
  Bacteria are occasionally seen in cultures of alveolar
  specimens collected during this phase.
 Gray hepatization, no new erythrocytes are
  extravasating, and those already present have been lysed
  and degraded. The neutrophil is the predominant cell,
  fibrin deposition is abundant, and bacteria have
  disappeared.
 This phase corresponds with successful elimination of
  the infection and improvement in gas exchange.
 Resolution, the macrophage is the dominant cell type
  in the alveolar space, and the debris of neutrophils,
  bacteria, and fibrin has been cleared, as has the
  inflammatory response.
 This pattern has been described best for pneumococcal
 pneumonia and may not apply to pneumonias of all
 etiologies.
Clinical features:
 The clinical presentation varies according to the
  immune state of the patient and the infecting agent.
  In the most common type of pneumonia - caused
  by Strep. pneumoniae - there is often a preceding
  history of a viral infection.
Symptoms:
 The patient rapidly becomes ill with a high fever
 pleuritic pain
 Dry cough. A day or two later, rusty-coloured
  sputum is produced and at about the same time the
  patient may develop labial herpes simplex.
Signs:
 high temperature (up to 39.5°C)
 Rapid and shallow breathing
 the affected side of the chest moves less, and signs of
  consolidation may be present together with a pleural
  rub.
Investigations :
 Chest radiography
- Plain, X-ray
confirms the area of consolidation but radiological
  changes lag behind the clinical course so that X-ray
 changes may be minimal at the start of the illness.
 Conversely, consolidation may remain on the chest
 X-ray for several weeks after the patient is clinically
 cured.
The chest X-ray usually returns to normal by 6
  weeks, except in patients with severe airflow
  limitation.
- Persistent changes on the chest X-ray after this
  time suggest a bronchial abnormality, usually a
  carcinoma, with persisting secondary pneumonia.
  Chest X-rays should rarely be repeated more
  frequently than at weekly intervals during the
  acute illness and then at 6 weeks after discharge
  from hospital.
- CT chest may be needed .
• Gram's Stain and Culture of Sputum :
 The main purpose of the sputum Gram's stain is to ensure
  that a sample is suitable for culture. However, Gram's
  staining may also help to identify certain pathogens (e.g., S.
  pneumoniae, S. aureus, and gram-negative bacteria) by
  their characteristic appearance.
 The sensitivity and specificity of the sputum Gram's stain
  and culture are highly variable; even in cases of proven
  bacteremic pneumococcal pneumonia, the yield of positive
  cultures from sputum samples is 50%.
 Blood Culture in the presence of bacteramia .
Antigen Tests
Two commercially available tests detect pneumococcal and
  certain Legionella antigens in urine.
 Polymerase Chain Reaction
   Polymerase chain reaction (PCR) tests are available for a
     number of pathogens. However, the use of these PCR
     assays is generally limited to research studies.
Serology:
 A fourfold rise in specific IgM antibody titer between acute-
  and convalescent-phase serum samples is generally
  considered diagnostic of infection with the pathogen in
  question, such as Coxiella burnetii.
 Recently, however, they have fallen out of favor because of
  the time required to obtain a final result for the convalescent-
  phase sample.
TYPES OF PNEUMONIA
Mycoplasma pneumonia:
• Mycoplasma pneumonia is relatively common and often
  occurs in patients in their teens and twenties.
• Generalized features such as headaches and malaise often
  precede the chest symptoms by 1-5 days.
• Cough may not be obvious initially and physical signs in
  the chest may be scanty.
• On chest X-ray, usually only one lobe is involved but
  sometimes there may be dramatic shadowing in both
  lungs. There is frequently no correlation between the X-ray
  appearances and the clinical state of the patient.
• The white blood cell count is not raised.
• Cold agglutinins occur in 50% of the cases.
• The diagnosis is confirmed by a rising antibody
  titre.
• Treatment is with macrolides, e.g. erythromycin
  500 mg four times daily for 7-10 days. Tetracycline
  is also effective. Although most patients recover in
  10-14 days, the disease can be protracted for weeks
  and relapses occurring.
• Lung abscesses and pleural effusions are rare.
Viral pneumonia:
Primary viral pneumonia is uncommon in adults,
  influenza A virus or adenovirus infection being the
  commonest causes.
 It predisposes patients to bacterial pneumonia by
  damaging the respiratory epithelium and
  facilitating bacterial infection. Influenza A (HSNI)
  normally does not affect humans but recently has
  been transmitted from fowls (Avian flu), crossing
  the species barrier. Patients present with fever,
  breathlessness, cough and diarrhoea.
 Lymphopenia and thrombocytopenia are present
  and pulmonary infiltrates are seen on chest X-ray.
 The mortality rate is high.
 Severe acute respiratory syndrome (SARS) is due to
  a novel coronavirus. The incubation period is
  approximately 5 days with spread between humans
  mainly by droplet infection.
 The outbreak in 2003 affected many healthcare
  workers. Fever, malaise, headache and rigors were
  followed in the second week by cough,
  breathlessness and diarrhoea.
 Lymphopenia, thrombocytopenia and pulmonary
  infiltrates (mainly in the lower zones) occur.
 At the end of the second week 20% of patients
  deteriorate, developing ARDS, and the mortality is
  high.
 Haemophilus influenzae
 H. influenzae is a frequent cause of exacerbation of chronic
  bronchitis and can cause pneumonia in COPD patients.
 The pneumonia can be diffuse or confined to one lobe.
 There are no special features to separate it from other
  bacterial pneumonias.
 It responds well to treatment with oral amoxicillin 500 mg
  × 4 daily.
 Staphylococcus aureus
Staph. aureus rarely cause pneumonia except after a
  preceding influenzal viral illness.
The infection starts in the bronchi, leading to patchy areas of
  consolidation in one or more lobes, which break down to
  form abscesses. These may appear as cysts on the chest X-
  ray.
 Pneumothorax, effusion and empyemas are
  frequent.
 Septicaemia develops with metastatic abscesses in
  other organs.
 Fulminating staphylococcal pneumonia can lead
  to death in hours.
 Areas of pneumonia (septic infarcts) are also seen
  in staphylococcal septicaemia. This is frequently
  seen in intravenous drug abusers.
 Pulmonary symptoms are often few but
  breathlessness and cough occur and the chest X-
  ray reveals areas of consolidation.
 Abscess formation is frequent.
    Gram-negative Pneumonia:
These are the cause of many hospital-acquired pneumonias but
 they are occasionally responsible for cases in the community.
Klebsiella pneumoniae:
• Pneumonia due to Klebsiella usually occurs in elderly people
    with a history of heart or lung disease, diabetes, alcohol excess
    or malignancy.
•    The onset is often sudden, with severe systemic upset.
•   The sputum is purulent, gelatinous or blood-stained.
•    The upper lobes are more commonly affected and the
    consolidation is often extensive.
•   The organism can be found in the sputum or in the blood.
•   Treatment is dependent on the sensitivity of the organism, but
    a cephalosporin is usually required.
•    The mortality is high, partly owing to the presence of the
    predisposing condition.
Pseudomonas aeruginosa
• Pneumonia due to Pseudomonas is of considerable
  significance in patients with cystic fibrosis, since it
  correlates with a worsening clinical condition and
  mortality.
• It is also seen in patients with neutropenia following
  cytotoxic chemotherapy.
• The isolation of P. aeruginosa from sputum must be
  interpreted with care because may simply represent
  contamination from the upper airways.
• Treatment with the 4-quinolone antibiotic ciprofloxacin
  (200-400 mg i.v. over 30-60 minutes twice daily) or
  ceftazidime (2 g bolus i.v. 8-hourly). Ticarcillin (15-20 g
  daily i.v. infusion) and piperacillin are active against these
  bacilli. These penicillins are usually given in combination
  with an aminoglycoside, e.g. gentamicin, for maximum
  benefit.
GENERAL MANAGEMENT OF PNEUMONIA:

 Sputum and blood should always be sent for culture but
  antibiotic treatment should not be delayed.
 Severe cases need to be admitted to hospital and a chest X-ray
  performed. Other investigations, e.g. blood gases, are useful to
  detect respiratory failure and provide a baseline for
  comparison if the patient deteriorates.
 The choice of antibiotics is inevitably empirical, and is
  largely directed at Strep. pneumoniae infections.
 For treatment of mild community-acquired pneumonia, oral
  amoxicillin at a dose of at least 500 mg 8-hourly. Oral
  erythromycin (or clarithromycin, which is better tolerated) is
  an alternative choice for those sensitive to penicillin.
 For more severe cases treated in hospital, combined
    therapy with amoxicillin and a macrolide (erythromycin or
    clarithromycin) is recommended. When oral therapy is
    contraindicated, parenteral ampicillin or benzylpenicillin
    should be combined with clarithromycin.
   ForStaph. aureus infection intravenous flucloxacillin ±
    sodium fusidate should be added. Fluoroquinolones are
    recommended for those intolerant of penicillins or
    macrolides.
    For severe cases, parenteral antibiotics should be given
    with the combination of a broad-spectrum lactamase-
    stable beta-lactam antibiotic (co-amoxiclav or cefuroxime)
    and clarithromycin.
   Parenteral antibiotics should be switched to oral once the
    temperature has settled for a period of 24 hours and
    provided there is no contraindication to oral therapy.
    The choice of antibiotics may be narrowed once
    microbiological results are available but it should be
    remembered that up to 10% of pneumonias may have
    mixed infections.
Criteria for the diagnosis of severe community-
  acquired pneumonia:
Clinical features
 Respiratory rate ≥ 30/min
 Diastolic blood pressure ≤ 60 mmHg
 Confusion
 Old age particularly in those > 65 years old
 Co-morbidity
Investigations
 Chest X-ray - more than one lobe involved
 Pao2 < 60 mmHg
 Low albumin (< 35 g/L)
 White cell count (low <4 × 109/L or high > 20 ×
  109/L)
 Raised serum urea (> 7 mmol/L)
 Blood culture - positive
 For more severe cases treated in hospital in addition to
    antibiotic therapy fluids should be given to avoid dehydration,
    care of the mouth and skin.
    Cough should normally be encouraged, but if it is
    unproductive and distressing, cough suppressants can be
    given.
    Physiotherapy is needed to help and encourage the patient to
    cough.
   Pleuritic pain may require analgesia, but powerful analgesia
    (e.g. opiates) should be used with care because they cause
    respiratory depression.
   severe hypoxia, oxygen therapy should be given.
    COMPLICATIONS OF PNEUMONIA
Lung abscess
 This term is used to describe severe localized suppuration in the
    lung associated with cavity formation on the chest X-ray, often
    with the presence of a fluid level.
   Abscesses may develop during the course of specific pneumonias,
    particularly when the infecting agent is Staph. aureus or Klebsiella
    pneumoniae. Septic emboli, usually staphylococci, result in
    multiple lung abscesses.
    Infarcted areas of lung occasionally cavitate and rarely become
    infected.
   Amoebic abscesses may occasionally develop in the right lower
    lobe following transdiaphragmatic spread from an amoebic liver
    abscess.
   The patient is often anaemic with a high ESR.
Empyema:
 Empyema means the presence of pus within the pleural
  cavity.
 This usually arises from bacterial spread from a severe
  pneumonia or after the rupture of a lung abscess into the
  pleural space.
 Typically an empyema cavity becomes infected with
  anaerobic organisms and the patient is severely ill with a
  high fever and a neutrophil granulocytosis.
 Empyemas should be treated by prompt tube drainage or
  by rib resection and drainage of the empyema cavity under
  ultrasound control.

				
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