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Forth stage
Medicine
Lec-6
.د
رامي
1/1/2014
Pneumonia
Pneumonia is an acute respiratory illness caused by an infection of the lung parenchyma,
associated with recently developed radiological shadowing. This may take the form of
"lobar pneumonia" referring to homogenous consolidation of one or more lung lobes, often
with associated pleural effusion, or "bronchopneumonia", a more patchy alveolar
consolidation associated with bronchial inflammation, often affecting lower lobes.
Pneumonia is best classified clinically according to the context in which it has developed;
therefore, pneumonia is community-acquired (CAP), hospital-acquired (HAP) or pneumonia
in immuno-compromised patient.
Community acquired pneumonia
Epidemiology
Around 5-12/1000 adults suffer CAP each year in developed countries. The incidence
almost doubles after 60 years of age, and those old patients have higher mortality rate.
Most cases are spread by droplet infection, and occur in previously healthy individuals but
certain factors increase the risk of CAP. These include:
1. Smoking
2. Upper respiratory tract infections
3. Alcohol drinking
4. Pre-existing lung disease
5. Corticosteroid therapy
Aetiology
Although there is an extensive list of potential aetiological agents in CAP, most cases are
caused by relatively few pathogens. Streptococcus pneumoniae is the most common
infecting agent. Common pathogens also include Mycoplasma pneumoniae, Chlamydophila
pneumoniae, Haemophilus influenzae and respiratory viruses. Legionella pneumophila is
also important (especially in inpatients). Staphylococcus aureus (including methicillin
resistant Staphylococcus aureus (MRSA)) and Gram negative bacilli (Klebsiella pneumoniae
and pseudomonas aeroginosa) should be considered in selected cases.
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Clinical features
Pneumonia usually presents acutely with fever, shivering and/or rigor and vomiting.
Anorexia and headache are also common. Respiratory symptoms include cough, which is
initially dry and painful, but later accompanied by mucoid, purulent or even bloody sputum.
Rust coloured sputum is characteristic of Streptococcus pneumoniae infection. Pleuritic
chest pain may be present, which may refer to the shoulder or upper abdomen (mimicking
surgical acute abdomen). The presence and degree of breathlessness depends on the
severity of the disease.
On clinical examination, the patient is usually febrile with tachycardia, sweating or
shivering. Tachypnoea and use of accessory muscle of respiration are markers of respiratory
distress. The patient may be cyanosed is severe cases. Findings on chest examination
depend on the degree of consolidation and the presence or absence of significant pleural
effusion. Accordingly, vocal fremitus may be increased or decreased, and the percussion
notes vary from impairment to stony dullness. Crackles, bronchial breath sounds and
friction rub may be heard on auscultation. Elderly patients may present with confusion with
few other respiratory manifestations. Severely ill patients may have evidence of septic
shock of organ failure.
Clinical characteristics of various aetiological gents of pneumonia
1. Streptococcus pneumoniae is the most common cause, characteristically has rapid
onset, with high fever, pleuritic pain, rusty sputum, herpes labialis and lobar
consolidation on chest X-ray.
2. Mycoplasma pneumoniae is the second most common pathogen, especially affecting
children and young adults. It tends to occur in epidemics. Unique complications
include haemolytic anaemia, erythema multiforme, erythema nodosum, Guillain
Barre syndrome as well as myocarditis, pericarditis and encephalitis.
3. Chlamydophila pneumoniae also affects young people with epidemic potential. It is
often mild and self limiting disease. Long duration of symptoms before presentation
is characteristic.
4. H. influenzae is more common in old age and those with COPD or bronchiectasis. It
tends to cause bronchopneumonia
5. Respiratory viruses: Viruses are responsible for about 18% of adult pneumonia. It can
be caused by influenza and parainfluenza (commonly complicated by secondary
bacterial infections), respiratory syncytial virus and adenoviruses. Recently two
coronaviruses were responsible for epidemic acute respiratory syndromes with viral
pneumonia (SARS and MERS CoV).
6. Legionella pneumophila tends to affect middle and old aged, usually as local
epidemics around contaminated source (like cooling systems). Common associated
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symptoms include mental confusion and diarrhoea, with special lab abnormalities
(hyponatraemia, elevated liver enzymes and hypoalbuminaemia)
7. Staphylococcus aureus occur in association with debilitating illness, or complicating
influenza. Multiple lobe involvement, cavitation, pneumatocoele and abscess
formation are characteristic. The infection may disseminate to other organs (as
osteomyelitis)
8. Klebsiella pneumoniae is more common in alcoholic, diabetics and old men. It usually
affects upper lobes with tendency to suppuration and abscess formation
9. Pseudomonas aeroginosa most commonly causes pneumonia in patients with
bronchiectasis, cystic fibrosis and severe COPD
10. Chlamydia psittaci is considered in those who are in contact with birds causing severe
headache and hepatosplenomegaly.
Differential diagnosis
Pneumonia should be differentiated from:
1. Pulmonary infarction (due to pulmonary embolism)
2. Pulmonary and pleural tuberculosis
3. Radiation pneumonitis
4. Pulmonary oedema (can be unilateral)
5. Rare cases (as pulmonary oesinophilia and bronchoalveolar carcinoma)
Investigations
A chest X-ray is usually sufficient to confirm the clinical diagnosis of pneumonia. In lobar
pneumonia, a homogenous opacity localized to the affected lobe or segment usually
appears within 12 – 18 hours of the onset of illness. Chest X-ray helps in differentiating CAP
from other diagnosis and can provide information about severity (cavitation and multilobar
involvement) and about complications (pleural effusion or abscess formation). It can
occasionally suggest an aetiological agent (pneumatocoele in Staphylococcus aureus
pneumonia). CT scan is rarely required, except for suspected underlying bronchial
obstruction caused by tumour or foreign body.
Pulse oximeter non-invasively assesses the arterial oxygen saturation (SpO
2
). Arterial blood
gas analysis is required when the SpO
2
<93% to assess the need for ventilator therapy.
WBC is normal or only marginally raised in pneumonia caused by atypical pathogens
(mycoplasma, chlamydia, legionella and viruses), whereas a neutrophilic leukocytosis of
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more than 15
10
9
/L suggests a bacterial aetiology. Urea, electrolytes and liver function
tests should be checked.
Etiologic diagnosis is not necessary in most cases. However microbiological tests are
required in cases of severe pneumonia which include:
Sputum Gram and Zeihl Neelsen stains and sputum culture and sensitivity
Serology: antibody titres (mycoplasma, chlamydia and viruses), antigen detection in
serum or urine (pneumococcus and legionella) and PCR (mycoplasma)
Assessment of disease severity
CURB-65 scoring system helps guiding antibiotic and admission policies and predicts
prognosis. It encodes for:
Confusion
Urea>7mmol/L
Respiratory rate>30/min
Blood pressure (systolic<90 mmHg or diastolic<60 mmHg)
Age>65.
Scoring 1 point for each point, 0-1: home treatment, 2: short stay in hospital or hospital
supervised treatment, 3: hospital management, 4-5: consider intensive care unit (ICU)
admission. ICU admission is also indicated in patients with hypoxaemia, hypercapnoea,
acidosis, septic shock and reduced conscious level regardless to the score.
Management
Oxygen therapy is indicated in patients with tachypnoea, hypoxaemia, hypotension or
acidosis. PaO
2
should be maintained around 60 mmHg (or SpO
2
at 92%) giving high flow
oxygen (>35%). Mechanical ventilation should be considered in those who remain
hypoxaemic despite oxygen therapy. Non-invasive ventilation has limited role in
pneumonia.
Fluid balance: Oral fluid intake should be encouraged. IV fluids are required in severely
ill, old patients and those with vomiting. Vasopressors may be required in patients with
severe sepsis and septic shock.
Antibiotic therapy: prompt institution of antibiotics improves outcome. The initial
choice of antibiotics is primarily guided by the severity of illness. Oral antibiotics are
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adequate in mild cases. The duration of treatment of uncomplicated pneumonia is 7-10
days. The following protocol is usually followed:
1. Outpatients:
Previously healthy patients, who have not received antibiotics during the
preceding 3 months are treated with an oral macrolide (clarithromycin 500mg
twice daily, or azithromycin 500mg once daily)
Patients with co-morbidities (and those who had received antibiotics within 3
months) are better treated with an oral respiratory quinolone (moxifloxacin
400 mg once or levofloxacin 750mg once)
2. Inpatients:
A respiratory quinolone (oral or IV) (OR)
A β-lactam (co-amoxiclav 1-2 gm three time daily IV or cefotaxime 1-2gm IV
three time daily or ceftriaxone 1-2 gm IV daily)
PLUS, a macrolide (oral or IV)
(If Staphylococcus aureus is suspected, add vancomycin or linezolid).
Pleuritic pain is treated with paracetamol or NSAID. If not sufficient, opiates may be
required (taking caution of possible respiratory depression)
Physiotherapy may be required to assist expectoration.
Complications
1. Para-pneumonic effusion and empyema
2. Suppurative pneumonia and lung abscess
3. Lobar collapse due retained secretions
4. Pneumothorax (particularly in Staphylococcus aureus pnemonia)
5. Multi-organ failure (including ARDS and ATN)
6. DVT and pulmonary embolism
Prognosis
Most patients respond to antibiotic therapy. Fever may persist for many days. Chest X-ray
takes several weeks or months to resolve especially in elderly.
Delayed clinical recovery may suggest:
1. Complications
2. Incorrect diagnosis
3. The pneumonia is secondary to proximal obstruction or recurrent aspiration
The mortality rate ranges from 1% in mild cases treated as outpatients to 50% in critically
ill patients treated in the ICU.