Pneumonia

Top tip for clinical exams but not for real clinical life- If a patient has any respiratory symptoms, and you can’t think of anything, say pneumonia. If the symptoms don’t quite add up, say atypical presentation of pneumonia. Well, that’s my game plan anyway.


Pneumonia

Definition: an inflammation of the substance of the lungs, usually caused by bacteria, associated with fever, symptoms and signs in the chest and abnormalities on the chest x-ray.  Can be classified anatomically (e.g. lobar or bronchopneumonia) or by aetiology.

Clinically, we think of Community Acquired Pneumonia (CAP) and Hospital Acquired Pneumonia (HAP).

Aetiology/ risk factors:

-CAP: may be primary or secondary due to underlying disease.

1 ⇒Streptococcus pneumoniae– CAP, usually previously healthy patients (most common in UK- 60-75%)

2 ⇒Haemophilus influenzae in pre-existing lung disease e.g. COPD

3 ⇒Mycoplasma pneumoniae CAP, usually previously healthy patients

Staphylococcus aureus– children, IV drug abusers, associated with influenza virus infections (found more commonly in ICU patients)

⇒Legionella pneumophilia- institutional outbreaks (hospitals, hotels), sporadic, endemic

Moraxella catarrhalis

⇒Chlamydia pneumonia

Chlamydia psittaci-contact with birds

Coxiella burnetti- abattoir and animal-hide workers (rarer)

⇒ Viruses account for up to 15% (Influenza A). Flu may be complicated by community acquired MRSA pneumonia.

-HAP (>48h after hospital admission):

⇒Gram negative enterobacteria or Staphylococcus aureus- most commonly

Pseudomonas (P. aeruginosa especially in Cystic Fibrosis, bronchiectasis, COPD), Klebsiella, Bacteroides, Clostridia

-Aspiration (e.g of vomit): risk of aspirating oropharyngeal anaerobes in those with stroke, myasthenia, bulbar palsies (CN9/10/11/12), reduced consciousness, oesophageal disease (reflux, achalasia) or poor dental hygiene

Immunocompromised patient (AIDs, lymphoma, leukaemia, chemotherapy, corticosteroids):

Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Moraxella catarrhalis, Mycoplasma pneumoniae

⇒Gram negative bacilli

Pneumocystis jiroveci (fungus, especially in HIV), Aspergillus fumigates (fungus)

Cytomegalovirus, Herpes Simplex Virus

⇒Mycobacteria

Risk factors: underlying lung disease, smoking, alcohol abuse, immunosuppression, contact with other individuals with pneumonia

-Contact with birds (possible psittacosis)

-Farm animals (Coxiella burnetti)

-Recent stays in large hotels (Legionella pneumophilia- from air conditioning)

-Chronic alcohol abuse (M. tuberculosis)

Epidemiology: incidence is 5-11/1000, increased in the very young and old

Symptoms and signs vary according to the infecting agent and the immune state of the patient. Elderly patients often have fewer symptoms than younger patients.

Symptoms:

-Fevers, rigors, malaise, anorexia

-Respiratory symptoms: dyspnoea, cough, sputum production (purulent- yellow or green, ‘rusty‘ with pneumococcus), haemoptysis, pleurisy (pleuritic chest pain, pain from diaphragmatic irritation referred to shoulder)

Signs:

-pyrexia, cyanosis, tachypnoea, tachycardia, hypotension

-herpes labialis (pneumococcus)

-ConfusionImage result for vesicular bronchial breath soundsal state (elderly-may be only sign, may also be hypothermic)

consolidation: diminished expansion, dull percussion note, increased vocal fremitus/vocal resonance, bronchial breathing (higher pitch, louder, inspiration and expiration are equal and there is a pause between inspiration and expiration)

pleural rub

-there may be a pleural effusion: stony dull percussion note, decreased vocal fremitus/ vocal resonance

Investigations:

-Most fit patients with mild CAP are treated as outpatients and only need a CXR. Patients admitted to hospital require investigations to identify cause and severity of the pneumonia.

Chest X-ray: confirms the area of consolidation (when the alveoli fill with yucky pus, inflammatory cells, fluid and that area of lung becomes hard). These changes may lag behind the clinical course.

May see:

  -Lobar or multilobar infiltrates (consolidation)

Consolidation = alveoli & small airways fill with dense material (white- pacification on CXR). Not always infection- pus (pneumonia), fluid (pulmonary oedema), blood (pulmonary haemorrhage), or cells (cancer).

Air bronchogram = If an area of lung is consolidated it becomes dense and white. If the larger airways are spared, they are of relatively low density (blacker). This phenomenon is known as air bronchogram and it is a characteristic sign of consolidation.

Silhouette sign = Normal adjacent anatomical structures of differing densities form a crisp contour or ‘silhouette’. Loss of a specific contour can help determine the position of a disease process. This phenomenon is known as the silhouette sign. e.g. Loss of clarity of the right heart contour (formed by the right atrium) implies disease of the right middle lobe which lies next to the right atrium.

Image result for CONSOLIDATION WITH AIR BRONCHOGRAM

  -Cavitation

  -Pleural effusion

Oxygenation assessment:

-If SaO2 <92% or severe pneumonia, perform and ABG

ABG- PaO2 < 8kPa or rising PaCO2 indicates severe pneumonia

Blood pressure

Sputum: microscopy (gram stain), culture and sensitivity tests

Bloods: white cell count  > 15 x 109/L suggest bacterial infection, high CRP

                   May have lymphopenia with Legionella pneumonia

                  LFTs may be non-specifically abnormal

                  U&Es may show raised urea and hyponatraemia

                  Red cell agglutination- Mycoplasma pneumonia (raised cold agglutinins in 50%)

Blood cultures if pyrexial

Serology- for atypicals

Mycoplasma pneumonia- raised IgM antibody or 4x rise in antibody titre from blood taken early in clinical course and 10-14 days later. (Cold agglutinins)

Urine- legionella and pneumococcal antigen testing in patients with indicators of severe pneumonia

-Pleural fluid aspiration may be performed for culture

Viral throat swabs if appropriate

Bronchoscopy and bronchoalveolar lavage if patient on ICU or immunocompromised

Image result for curb 65CURB-65 Severity Score (Estimates mortality of CAP to help determine inpatient vs. outpatient treatment.)


1 point each:

Confusion (AMT score ≤ 8)

Urea (Blood Urea Nitrogen) > 19 mg/dL (> 7 mmol/L)

Respiratory Rate ≥ 30

Blood pressure- SBP < 90 mmHg or DBP ≤ 60 mmHg

≥65 years old

Score Risk Disposition
0 or 1 1.5% mortality outpatient care
2 9.2% mortality inpatient vs observation admission
≥ 3 (severe pneumonia) 22% mortality inpatient admission with consideration for ICU admission (4 or 5)

Markers of severe pneumonia: CURB-65 score ≥ 3, CXR showing multi-lobar involvement, PaO2 < 8kPa, low albumin, white cell count (< 4 x 109/L or > 20 x 109/L), positive blood cultures.

Management:

(Prevention- Pneumococcal vaccine for at risk groups)

Antibiotics, orally if not severe and not vomiting. If severe, give IV.

→ Mild CAP with Strep pneumo or H.influenzae = amoxicillin (penicillin) or clarithromycin (macrolide)

  Moderate CAP = amoxicillin + clarithromycin

  Severe CAP = co-amoxiclav (amoxicillin + clavulanic acid) + clarithromycin (IV)

Oxygen– keep PaO2 > 8kPa and/ or saturation ≥94%

IV fluids (because of dehydration, anorexia, shock)

Venous Thromboembolism prophylaxis (e.g. stockings or pharmacological)

Analgesia- if pleurisy, e.g. paracetamol 1g/6h.

-Consider ICU if shock, hypercapnia, or uncorrected hypoxia. If failure to improve or CRP remains high, repeat CXR and look for progression/ complications.

-Follow up at 6weeks (+/- CXR)

Complications:

-lung abscesses- results from localised suppuration (pus formation) of the lung associated with cavity formation (i.e. holes full of pus).  Swinging fever; cough; purulent, foul smelling sputum; pleuritic chest pain; haemoptysis; malaise; weight loss; finger clubbing;  crepitations; anaemia; neutrophilia; CXR- walled cavity often with fluid level. ABx, postural drainage, repeated aspiration, ABx instillation, surgical excision.

-pleural effusion- may need drainage if large and symptomatic or infected (empyema)

-empyema- pus in the pleural space, usually from rupture of a lung abscess or bacterial spread in severe pneumonia. Should be suspected if patient with a resolving pneumonia develops a recurrent fever. Aspirated pleural fluid = yellow and turbid, pH < 7.2, ↓ glucose, ↑LDH

-respiratory failure- Type 1 relatively common (PaO2 < 8kPa)

-septicaemia- may cause metastatic infection e.g. infective endocarditis, meningitis

-hypotension- combination of dehydration and vasodilation due to sepsis

-brain abscess

-pericarditis

-myocarditis

-cholestatic jaundice (the right lower lung lobe is close to the liver, I guess stuff happens. On further reading- may be due to sepsis or secondary to ABx therapy.)

-Acute Kidney Injury

-Atrial fibrillation- quite common, particularly in elderly. Usually resolves with pneumonia treatment. (β-blocker or digoxin may be required short-term).

Prognosis: Mortality is ~21% in hospital, most resolve with treatment (1-3 wks)

References: Kumar and Clark’s, Cheese & Onion, Radiologymasterclass.co.uk, MDCalc
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