Post-Operative Pneumonia

Pneumonia is defined as a lower respiratory tract infection with accompanying consolidation visible on chest x-ray. There are four main types of pneumonia:

  • Community-acquired pneumonia (CAP)
  • Hospital-acquired pneumonia (HAP)
  • Aspiration pneumonia
  • Immunocompromised pneumonia

In the post-operative setting, hospital-acquired pneumonia is the predominating type. HAP is a pneumonia that has onset >48hrs since hospital admission and was not present on admission. Whilst incidence varies across countries, they remain a major burden on healthcare services.


Surgical patients are predisposed to developing lower respiratory tract infections due to a combination of:

  • Reduced chest ventilation – reduced mobility in bedridden patients results in an inability to fully ventilate their lungs, leading to accumulation of fluid secretions which subsequently become infected.
  • Change in commensals – the hospital environment microflora will vary compared to what the patient may normally be exposed to, nor have immunity to.
    • Common pathogens for HAP include E. Coli, S. Aureus (including MRSA), S. Pneumoniae, and Pseudomonas.
  • Debilitation – many patients undergoing surgery are likely to be sick or have several co-morbidities, compromising their immune systems and predisposing to pulmonary infections.
  • Intubation – patients undergoing major surgery may need a stay in ICU and require intubation and ventilation, a major risk factor for a HAP.
Fig 1 - Common causes of HAP under Gram Stain (A) E. Coli (B) MRSA (C) S. Pneumonia (D) P. Aeuroginosa

Fig 1 – Common causes of HAP under Gram Stain (A) E. Coli (B) MRSA (C) S. Pneumonia (D) P. Aeuroginosa

Risk Factors

Numerous risk factors have been identified for developing hospital-acquired pneumonia, many of which overlap with CAP risk factors. They include:

  • Age
  • Smoking
  • Known respiratory disease or recent viral illness
  • Poor mobility (either baseline or post-operatively)
  • Mechanical ventilation
  • Immunosuppression
  • Underlying co-morbidities, such as DM or cardiac disease

Clinical Features

Patients with hospital-acquired pneumonia classically present with a combination of cough (productive or non-productive), dyspnoea, or chest pain.

However, many post-operative patients may not present as ‘clear-cut’ as this, due to factors such as intubation, reduced consciousness, or other co-morbidities. Indeed, the only clinical features may be a general malaise, impaired cognition, or changes in physiological parameters.

On examination, patients may have a reduced oxygen saturation, increased RR or HR, or with features of a septic response, such as pyrexia. Bronchial breath sounds (localised or diffuse) and inspiratory crackles may be heard on auscultation, associated with a dull percussion note.

Differential Diagnosis

The differential diagnoses for pneumonia include acute heart failure or acute coronary syndrome, PE, asthma or COPD exacerbation, pleural effusion or empyema, thyroid disease, and psychological (e.g. anxiety disorder).


Laboratory Investigations

Any suspected pneumonia should have routine bloods (FBC, CRP, and U&Es) taken, which may show evidence of an inflammatory response (raised WCC and CRP). An arterial blood gas may be required in severe cases of oxygen desaturation; this may show a type 1 respiratory failure, or a type 2 failure (if exacerbating pre-existing COPD).

If the cough is productive, a sputum sample should be taken for culture. Any signs of a severe infection or sepsis should warrant blood cultures being taken during times of pyrexia.


Patients with a suspected HAP will require a chest x-ray to confirm the infection, presenting as consolidation, either lobar or bronchopneumonia. Consolidation can be differentiated from other shadowing on a CXR by the presence of air bronchograms.

If a sputum sample is unobtainable, severe or non-responding infections may require a bronchoalveolar lavage, yet you should gain specialist advice before requesting this.

Fig 2 - A CXR showing left lower zone consolidation

Fig 2 – A CXR showing left lower zone consolidation

CURB-65 Score

The severity of pneumonia can be graded based on the CURB-65 score:

Clinical Criteria Points
Confusion 1
Urea >7.0mmol 1
Respiratory rate >30 1
Systolic <90 or diastolic <60 1
Age >65 1

A score 0-1 is mild, 2 is moderate, and ≥3 is severe. The CURB-65 score not only indicates the severity of the pneumonia but will also inform the management plan.


All patients should receive appropriate O2 therapy as indicated, targeting ≥94% saturation. Any signs of sepsis or septic shock should be treated aggressively.

Confirmed pneumonia should be treated with empirical antibiotics, pending sensitivities. In the UK, the antibiotic decision should be based upon the CURB-65 score and guided by local policy. An example regimen:

  • Mild: Co-amoxiclav 625mg oral TDS
  • Moderate: Co-amoxiclav 625mg oral TDS
  • Severe: Tazocin 4.5g TDS IV


Any post-operative patients with prolonged bedrest or reduced mobility are at risk of developing HAP (secondary to fluid stasis in the pulmonary tissue). The best practice is for post-operative patients to have chest physiotherapy to increase lung ventilation and reduce fluid stasis.


The major complications of pneumonia are:

  • Pleural effusion
  • Empyema
  • Respiratory failure
  • Sepsis

Aspiration Pneumonia

Aspiration of the gastric contents into the pulmonary tissue will result in a chemical pneumonitis. However, this is not necessarily an infection, as only if any oropharyngeal bacteria are aspirated into the lung tissue as well will a lung infection result. Classically, any aspirated content will affect the right middle or lower lung lobes, due to the anatomy of the bronchi.

Fig 3 - Anatomy of the trachea and bronchi

Fig 3 – Anatomy of the trachea and bronchi

In surgical patients, the main risk factors for an aspiration are:

  • Reduced GCS (e.g. secondary to anaesthesia).
  • Iatrogenic interventions (e.g. misplaced NG tube).
  • Prolonged vomiting without NG tube insertion.
  • Underlying neurological disease.
  • Oesophageal strictures or fistula.
  • Post-abdominal surgery.

Much of the clinical features and investigations for an aspiration pneumonia will be the same as for HAP. Importantly, aspiration pneumonia should be suspected over a pneumonitis if there is a persistent fever or purulent sputum.

Management is mainly preventative, identifying the patients who are at an increased risk of aspirating and placing suitable precautions (e.g. NG tube feeding) in place until suitable. This will require involvement from both the nursing staff and the Speech and Language Therapists (SALT).

Any pneumonitis only needs supportive measures, yet an aspiration pneumonia will need antibiotic therapy, similar to that of HAP. Suction of any aspirated contents is rarely performed as has no real benefit to overall outcomes.


Question 1 / 6
Which of these pathogens is most associated with hospital-acquired pneumonia?


Question 2 / 6
Which of these is NOT a risk factor for HAP (hospital-acquired pneumonia)?


Question 3 / 6
Which of the following blood gas results are typically seen in Type 1 respiratory failure?


Question 4 / 6
Which of these features differentiates consolidation from other shadowing on X-ray?


Question 5 / 6
A 60 year old woman has no new mental confusion, a urea of 8.1mmol/L, respiratory rate of 22 and a blood pressure of 95/65. What is her CURB 65 score?


Question 6 / 6
Which of the following is a common complication of pneumonia?


Further Reading

Preoperative intensive inspiratory muscle training to prevent postoperative pulmonary complications in high-risk patients undergoing CABG surgery: a randomized clinical trial
Hulzebos EH et al., JAMA

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