PNEUMONIA

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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.

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• 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'.

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• 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.

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• Pneumonias may also result from
• chemical causes, such as in the aspiration of
  vomitus
• radiotherapy
• allergic mechanisms.
• Precipitating factors
• Strep. pneumoniae - often follows viral infection
  with influenza or parainfluenza.

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• 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).

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• 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-intracellulare, cytomegalovirus.
• Intravenous drug abuse - frequently associated
  with Staph. aureus infection.
• Inhalation from oesophageal obstruction - often
  associated with infection with anaerobes.

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• Pathology
• Classic pneumonia evolves through a series of
  pathologic changes.
• The initial phase is one of edema, with the
  presence of a proteinaceous exudateand often of
  bacteriain the alveoli. This phase so rapidly
  followed by
• Red hepatization phase. The presence of
  erythrocytes in the cellular intraalveolar
  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.

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• 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.

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• 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.

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• 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.

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• Signs
• high temperature (up to 39.5C)
• 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.

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• 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 .

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• 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.

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• 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.

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• 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.

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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.

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• The white blood cell count is not raised.
• Cold agglutinins occur in half 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.

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• 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.

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• 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.

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• 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.

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• 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.

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• Gram-negative bacteria 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.

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• 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.

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• 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.
• There is no convincing evidence that newer
  antibiotics provide any significant therapeutic
  advantage over established therapies.
• 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.

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• 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.

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• 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. .

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• Criteria for the diagnosis of severe
  community-acquired pneumonia
• Clinical features
• Respiratory rate 30/min
• Diastolic blood pressure 60 mmHg
• Confusion
• High mortality particularly in those gt 65 years
  old
• Co-morbidity

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• Investigations
• Chest X-ray - more than one lobe involved
• Pao2 lt 8 kPa
• Low albumin (lt 35 g/L)
• White cell count (low lt 109/L or high gt 20
  109/L)
• Raised serum urea (gt 7 mmol/L)
• Blood culture - positive

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• 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.

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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.

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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.