PENUMONIA (Nosocomial)

DEFINITION
Hospital acquired.

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INCIDENCE

Risk Factors
Individual factors: Extremes of age - very young and very old.
Environmental factors: Low socio-economic conditions.
Predisposing conditions: Concurrent disease increases the risk of pneumonia and the mortality.

- Compromised immune status
- Conditions that lead to accumulated secretions:
- Bronchial obstruction - eg bronchial carcinoma.
- Impaired mucociliary clearance - eg amotile cilia syndrome, cystic fibrosis, squamous metaplasia, COPD.
- Pulmonary oedema - heart failure.
- Loss or suppression of the cough reflex - coma, anaesthesia, neuromuscular disorders, drugs, previous viral infection.

Risk factors
Proton pump inhibitors (5% risk vs 2% risk)

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AETIOLOGY

Hospital Acquired
(Nosocomial) - developing 2 or more days after admission to hospital for another reason.
- and not incubating prior to admission.
May follow antibiotic use, result from impaired host defences or aspiration of nasopharyngeal secretions.
Facilitated by intubation in ICU, impaired cough reflex in anaesthesia, or failure to cough because it is too painful.
Commonly Pseudomonas, Klebsiella.
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BIOLOGICAL BEHAVIOUR

May be either lobular or bronchopneumonia.

Pathophysiology
Acute congestion
Organism enters the lungs and initiates an acute inflammatory reaction.
Blood flow to the area increases.
capillaries are engorged with erythrocytes and changes in vessel permeability result in an outpouring of protein rich oedematous fluid into the alveolar spaces.
This is acute congestion - affected lobe is heavy, dark red and firm.

Red hepatisation
Neutrophils and erythrocytes enter the alveoli.
Fibrin networks form amongst the exudate - consolidation.
Neutrophils attack and digest organisms releasing free radicals and lysosomal enzymes resulting in tissue damage.

Grey hepatisation
Vasodilation is reduced, macrophages are recruited.
Alveolar spaces are consolidated by a dense fibrin network.

Resolution
By 8-10 days ( in untreated cases) the exudate is liquefied by fibrinolytic enzymes and macrophages, and coughed up.
Permanent fibrinous adhesions may remain between the pleura.

Complications
Pleural effusion.
Pleurisy - fibrinosuppurative pleural effusion.
Empyema - spread of infection to the pleural cavity.
Septicaemia, meningitis.
Abscesses - especially Klebsiella pneumoniae infections.
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MANIFESTATIONS

Not all patients will have fever and leucocytosis.

Symptoms
Local
Productive cough.
Difficulty breathing - often sudden in onset.
Pleuritic chest pain - worst when breathing deeply or coughing due to (fibrinosuppurative exudate in the pleural space).
May be haemoptysis.

Systemic
Fever, sweating, rigors.
Confusion - may be the only sign in elderly.
Malaise.
Anorexia.

Metastatic
Features of complications above.

Signs
Observe
Dyspnoea.
If rapid, shallow breathing, & RR>30/min = severe.
(Caused by a part of lung being non-functional - high PCO2, low PO2 increases respiratory drive. Can restore PO2 to normal but not PCO2).

Rusty coloured sputum (haemosiderin due to RBC breakdown)
Cyanosis (unable to restore PO2 to normal by increasing ventilation)
BP <60mmHg if severe.
Tachycardia if severe.
Febrile.

Palpate
Decreased movement over affected area.
Increased vocal fremitus.

Percussion
Dullness.
Note distribution.

Auscultate
Bronchial breath sounds over affected area.
Increased vocal resonance.
Pleural rub.
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INVESTIGATIONS
As above, for severe.

Bloods
FBC, ABG, U & Es, LFTs.

Imaging
CXR - opacification of the affected area.

Microbiology
Diagnosis may not be found in ~75% of cases as prior use of antibiotics confounds microbiologic diagnosis.
Blood - culture, serology (mycoplasma and chlamydia) Sputum - microscopy, culture and pneumococcal antigen testing.
LRT secretions - Gram stain, culture and direct fluorescent antibody stain.

NB - sputum sample must be adequate :
Not saliva:  >25 WBC, < 5-10 epithelial cells per CPF is a satisfactory sample.
Non-specific - oropharyngeal contamination.
Single/ predominant organism or heavy growth from purulent sputum is likely pathogen - correlates well with LRT samples.

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MANAGEMENT

Risk Factors for Poor Outcome
Late onset after hospitalization (5+d)
Old (>60yrs).
Chronic illness.
Confusion.
High RR (>30/min).
Diastolic BP <60mmHg.
>1 lobe involved.

Early
Hypoxaemia (PaO2 <8kPa).
Leucopaenia (<4x109).
Leucocytosis (>20x109).
Blood urea (>7.0mmol/L).
>1 lobe involved.

Late
Bacteraemia.
Staph infection.
Hypoalbuminaemia.

Medical
Supportive care:
IV fluids (maintain urine output of >1.5L/24 hours).
Oxygen to maintain oxygen saturations - 90%.
Bronchodilators.
Pain relief.
Physiotherapy (to assist removal of secretions).
Intensive care management - recommended if two or more of:
1) RR >30/min 2) Diastolic BP < 60mmHg 3) Serum urea > 7mmol/L.

Treatment depends on suspected agent.
Hence depends on epidemiological/aetiological classification.
Empiric antibiotics without delay.

Antibiotic Regimens

Hospital acquired pneuomnia
Common pathogens: enterobacter, klebsiella, acinetobacter, pseudomonas, legionella
Common regimen: Ticarcillen / clavulanic acid: 3.1g q6hr + gentamycin
Other regimens:
- piperacillin 3-4g IV q6h + tobramycin
- ceftazidime 1-2g IV q8h + tobramycin
- imipenem 500mg IV q6h

Aspiration
Common pathogens: klebsiella, e.coli, serratia, staph, bacteroides, pepto-streptococci
- clindamycin 600 mg iv q6-8h
- augmentin 625 qid

CAP (comm. acquired), no comorbidity, <60 yrs.
Macrolide (preferred) or doxycycline.
1/3-1/2 no organism identified.
Benzyl penicillin suitable for pneumococcal disease, narrow spectrum precludes use as a first line agent (eg won't work against mycoplasma or chlamydia).

CAP, no comorbidity, <60 yrs.
Second generation cephalosporin.
Eg cefuroxime or ceftriaxone.
Or beta-lactam + beta-lactamase inhibitor.
Or a macrolide (to cover Chlamydia, Mycoplasma, Legionella).
Mortality up to 25% in first week.
If severe an aminoglycoside should be used + an antipseudomonal agent eg beta-lactam or quinolone + macrolide.
(To cover Chlamydia, Mycoplasma and Legionella) + rifampicin if Legionella likely.

CAP, requiring hospitalisation.
Second or third generation cephalosporin.
(-lactam + (-lactamase inhibitor.
Macrolide.

Follow-up
Chest x-ray at 6 weeks.

Failure to Respond
Consider following:
Failure to respond clinically within 48-72 hours.
Inappropriate choice or dose of antibiotics.
Resistant or alternate organism.
Development of complication.
Presence of underlying disease eg endobronchial obstruction.
Alternate diagnosis - interstitial lung disease, atypical heart failure.
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