There are probably 3 main different ‘types’ of pneumonia that are of particular relevance to anaesthetists and critical care physicians:
Community acquired pneumonia
Ventilator associated pneumonia
Community acquired and nosocomial pneumonia are similar to each other, differing in the pathogens that cause them. Ventilator associated pneumonia is quite a different clinical entity though and will be discussed separately.
Pneumonia represents an acute inflammation of the lungs caused by infection. There is intense neutrophil infiltration of the tissue around the alveoli and terminal bronchioles. The alveoli become filled with pathogen, inflammatory cells and fluid, impairing function.
The respiratory tract is normally constantly exposed to microorganisms which reside as flora, kept in check by the innate defensive systems of humans. These defences include:
Proteases (in saliva)
IgA in saliva
Angulation of airways
Immunoglobulins in the alveoli
These defence systems usually prevent the progression of organisms to causing disease. Certain conditions (e.g. smoking, malnutrition) may impact on these defensive factors however and increase the susceptibility to pneumonia.
Community Acquired Pneumonia
The definition is important to distinguish from other respiratory tract infections, which are common.
CAP is defined as the following. In the community:
Symptoms of a lower respiratory tract infections (cough plus one other feature)
New focal chest signs on examination
At least one systemic feature
No other explanation for symptoms
In hospital (where x-ray is available):
Symptoms and signs consistent with a lower respiratory tract infection
Radiological features without another cause
The illness is the primary reason for admission to hospital
A number of organisms have been identified as causing pneumonia. This includes a number of bacteria, viruses, fungi and parasites.
The most common pathogens will vary depending on a number of host factors, including:
Location (hence differentiation into CAP and nosocomial)
The most common pathogens are:
Other less common pathogens include:
Common viral pathogens include: respiratory syncytial virus, influenza, parainfluenza. Common fungal pathogens (though rare overall) include: histoplasma capsulatum and coccidioides immitis.
The atypical pathogens are probably less common now. Strep pneumoniae is also decreasing in incidence compared to historically (now about 30%). A significant number of cases simply do not have a pathogen identified.
As noted above, these could be considered as factors which impair the normal innate defences of the respiratory tract to pathogens
Air space opacification is the hallmark radiological sign. It is the radiological equivalent of consolidation, which is the pathological feature of pneumonia (alveoli filled with debris and fluid). Characteristically the larger airways remain patent, creating air bronchograms.
CT imaging may be useful in cases of diagnostic uncertainty but is generally unlikely to add additional useful information.
Blood tests U&Es should be performed to guide severity assessment. An FBC can aid diagnosis (elevated WBC) and other diagnoses. A CRP can aid diagnosis and act as a baseline measure. Procalcitonin is developing some role in bacterial disease, perhaps to aid antibiotic stewardship, but this is not fully clear yet.
Microbiological Testing Microbiological testing should be performed in patients with moderate or severe pneumonia to help with pathogen diagnosis. This will be guided clinically but NICE recommends:
Sputum cultures/gram stain
Pneumococcal urinary antigen test
Legionella urinary antigen test
Other focused microbiological tests include:
Respiratory virus PCR (throat swab)
Mycoplasma PCR (sputum or throat swab)
Chlamydophila antigen or PCR
Sputum culture for legionella - should be attempted if urinary antigen is positive.
A BAL sample should be considered in patients that are severely unwell to get a good sample. Ideally, samples for culturing should be obtained prior to commencing antimicrobials.
An assessment of severity of the pneumonia should be undertaken to guide management local (inpatient vs outpatient) and antibiotic choice. Clinical judgement is important to take into account both the acute disease, and the impact of existing comorbidity.
The CURB65 score is an important severity assessment tool which should be applied to all patients (recommended by NICE) alongside clinical judgement.
The components are: C - Confusion - New onset confusion U - Urea - serum urea over 7 mmol/l R - Respiratory rate - rate over 30 per minute B - Blood pressure - systolic blood pressure below 90mmHg 65 - Age over 65
1 point is allocated to each domain that is positive. The score can provide a risk stratification:
Low risk - 0 to 1 - (mortality risk <3%)
Intermediate risk - 2 - (mortality risk 3-15%)
High risk - 3 or more - (risk of mortality >15%)
Patients in the low risk group can be considered for management in the community. Patients in the high risk group should be considered for critical care review. In the community, the score will not include the serum urea (which is unavailable).
General management principles will include:
Targeted oxygen therapy - titrated to SpO2 94-98%
Mobilisation to some degree is recommended (at least 20 mins out of bed on first day and increased as able)
VTE prophylaxis as indicated
Consideration of fluid status - encouragement of oral intake or intravenous fluids as indicated.
Advice on sputum expectoration should be given to patients.
Simple analgesia may be needed for chest pain
Patients should be advised against smoking
Antibiotic therapy Antibiotic policy is often determined at a local level based on local pathogens, and there is usually clear guidance on choice in these patients. The selection of antibiotic is usually based on severity, as ascertained by the CURB65 score.
Low risk (0-1) A 5 day antibiotic course is generally advised. The first choice antibiotic is usually amoxicillin 500mg TDS orally A macrolide (clarithromycin) or tetracycline (doxycycline) are appropriate second line agents or in patients with penicillin allergy.
Moderate risk (2) A 7-10 day course is generally indicated. Dual antibiotic therapy (Amoxicillin plus a macrolide) is usually indicated. Oral doxycycline is the main alternative agent in penicillin allergy.
High risk (3+) As per moderate risk, a beta-lactamase stable beta-lactam (e.g. co-amoxiclav) is used instead of amoxicillin. The parenteral route is generally used.
Community acquired infections generally don’t involve severly resistant organisms. Therefore very broad spectrum antibiotics e.g. tazocin, not usually needed.
Glucocorticoids Steroid treatment is not recommended.
Respiratory support In general, there isn’t a role for non-invasive ventilatory support (including CPAP) in patients with pneumonia and respiratory failure. However, in experienced hands and appropriate clinical scenarios there is sometimes scope for a trial of non-invasive respiratory support, if conducted in a well monitored clinical environment with rapid recourse for initiation of mechanical ventilation.
Complications of pneumonia include:
All patients who develop an effusion should have it tapped to assess for an empyema. Pleural drainage is indicated in those patients with an empyema or pleural fluid with a pH of less than 7.2.
Hospital Acquired Pneumonia
This is differentiated from CAP due to the different causative pathogens and therefore different management approach. Much of the other aspects are the same.
The definition of hospital acquired pneumonia (HAP) is that it develops at least 48 hours after hospital admission. There is often differentiation between an early (within 4 days of admission) and late HAP, with some difference in organisms. ICU admission and ventilation are a notable risk factor for HAP, but ventilator associated pneumonia is considered elsewhere.
Common pathogens of early HAP:
Common pathogens of late HAP:
Gram negative enterobacteria
There are often multiple organisms involved. The flora and resistance pattern can vary notably between hospitals. As such, antimicrobial choice should be based on local hospital policy, which will take this local information into account.
Some pathogens are described as having a more characteristic clinical picture.
Strep. Pneumoniae Is a gram positive, encapsulated, diplococcus, found as normal nasopharyngeal flora in 5-10% of the population. Risk factors for infection include: immunocompromised, elderly, hypo/asplenic. Usually has an acute onset with dramatic symptoms: cough, high temperature, pleuritic chest pain. Usually penicillin sensitive.
H Influenza A common pathogen in the older patient, particularly those with underlying respiratory disease. The clinical picture is generally indistinguishable from other pneumonia pathogens.
Legionella pneumophila An aerobic, motile, beta-lactamase producing gram negative bacillus. Usually lives in a water rich environment in nature (ponds, lakes) and within the human environment (air conditioning systems, cooling towers). A facultative intracellular parasite which replicates within amoeba in nature and within human macrophages in the disease state. More commonly seen in younger patients and smokers, but with severe disease in the immunocompromised and elderly. Multisystem involvement at presentation is common. Multilobar involvement can be seen on CXR. It is sensitive to macrolides, rifampicin, and fluoroquinolones.
Staph Aureus Is an aerobic, coagulase positive, gram positive diplococci which is a very common skin and mucosal commensal. Can be a complication of influenza and often produces a very severe pneumonia. There may be cavitating lesions on CXR, or pneumothoraces. Beta-lactamase production is common. Panton-valentine Leukocidin (PVL) is a toxin produced by certain strains of staph aureus. It is commonly associated with cutaneous lesions and can result in a severe necrotising pneumonia.
C. Pneumoniae Is a common cause of pneumonia in the younger population. It is often responsible for outbreaks of pneumonia within close communities e.g. families, college dormitories.
Chlamydia psittaci (psittacosis) Occurs in patients who own birds (20% of cases will have some history of contact). Uncommon
Kott, L. Pneumonia. Patient.info. 2015. Available at: https://patient.info/doctor/pneumonia-pro
British Thoracic Society. Guidelines for the management of community acquired pneumonia in adults. Update 2009. Available at: https://www.brit-thoracic.org.uk/standards-of-care/guidelines/bts-guidelines-for-the-management-of-community-acquired-pneumonia-in-adults-update-2009/
NICE. Pneumonia in adults:diagnosis and management [CG191]. NICE. 2014. Available at: https://www.nice.org.uk/guidance/cg191