Introduction

Aspiration pneumonia results from the micro- or macroaspiration of stomach contents or secretions of the oropharynx.  In many healthy adults, microaspiration is a routine event, but the normal defence mechanisms (cough, lung cilia) remove the material with no ill effects.  However, in certain patients or circumstances, the inoculum is large and/or is not removed, resulting in one or more possible complications including infection.

The main risk factors for aspiration pneumonia are impaired consciousness or impaired swallowing reflex. 

The middle lobe of the right lung is more frequently involved in aspiration pneumonia because it is the anatomical continuation of the trachea.

Aetiology of aspiration pneumonia

The organisms involved in aspiration pneumonia are generally those colonising the upper oropharynx and gut. The rapid transformation of the flora of the oropharynx during sickness or injury, with a dramatic increase in Gram-negative bacilli, is reflected in the pathogens responsible for aspiration pneumonia if the aspiration event occurs after an extended hospital stay. Therefore, the pathogens involved in aspiration pneumonia differ, depending on where and when the aspiration event occurred.

• Community-acquired aspiration pneumonia.
• Nosocomial aspiration pneumonia.

Diagnosis of aspiration pneumonia

The key issue in management of aspiration pneumonia is the differentiation between chemical pneumonitis and infection.  Infection is indicated by signs of superinfection such as sepsis, or foul-smelling sputum in the late stages (the patient may report foul-tasting sputum).

The diagnostic techniques for aspiration pneumonia are the same as for other forms of pneumonia:

• Patients admitted from the community
• Hospitalised patients:
  • Non-ventilated
  • Ventilated.

Management of established aspiration pneumonia

It is important to initiate treatment promptly without waiting for investigation results or until a scheduled drug round.

Antibiotic rationale

The choice of antibiotic therapy will be influenced by whether the original aspiration occurred in the community or in hospital.  However, if the infection was caused by microaspiration, the original event may not be recalled by the patient or their carers.

• If community-acquired aspiration pneumonia is suspected, then the regimens should cover oral anaerobes (which are often penicillin-resistant) and organisms of Streptococcus ‘milleri’ group.
• If nosocomial aspiration pneumonia is suspected, aerobic Gram-negative bacilli should also be covered. 

Because of the wide range of possible pathogens, the antibiotics chosen should be broad-spectrum and be capable of penetrating into lung parenchyma in high concentrations. 

If the patient is severely ill, unconscious or vomiting, intravenous therapy will be required. Treatment should be continued for at least five days, or longer if the patient is slow to respond (see Assessment of response).

Empirical therapy

Suitable empirical regimens for severe aspiration pneumonia include:

Community-acquired aspiration pneumonia

• Clindamycin.
• Amoxicillin plus metronidazole.

Nosocomial aspiration pneumonia

The choice of antibiotics will influenced by:

• Any recent previous antibiotic treatment
• Any available microbiology results
• The patient’s condition.

A suitable combination in patients who have not already recently been treated with these antibiotics is:

• Cefuroxime plus metronidazole

Consult expert opinion.

If MRSA is suspected, consult your local microbiologist.