Acute exacerbation of chronic obstructive pulmonary disease
Investigations
1st investigations to order
arterial blood gas (in hospital)
Test
Perform in patients with a moderate to severe acute exacerbation of COPD, when there is any evidence of hypercapnia, in all hypoxic patients, in all patients requiring oxygen, and in all patients who seem unwell.
Use to detect chronic hypercapnia and assess for acute respiratory acidosis.
Ensure you compare results with prior baseline ABG (when available).
Document the fraction of inspired oxygen (FiO2) or O2 flow rate of any supplemental oxygen given (controlled oxygen given via a Venturi mask).
Performing the ABG while the patient is on controlled oxygen allows the A-a gradient to be established.
PaO2 <8.0 kPa (approximately 60 mmHg) indicates respiratory failure.
pH <7.35 and PaCO2 >6.5 kPa define acute respiratory acidosis.[102]
Acidaemia implies a severe exacerbation and predicts in-hospital and 30-day mortality.[103]
Repeat the ABG after 30-60 minutes of treatment with controlled oxygen and bronchodilators to check for a rise in PaCO2 or a fall in pH.[98]
If possible, perform a blood gas analysis within 30-60 minutes of starting acute NIV.
Although the British Thoracic Society (BTS) recommends performing a blood gas analysis within 2 hours of starting acute NIV, in practice specialists recommend ideally waiting only 30-60 minutes to check for changes in PaCO2 and pH.[104]
Arrange review by a specialist healthcare professional with expertise in managing patients on NIV within 30 minutes if blood gas measurements fail to improve.[104]
Venous blood gas sampling is not considered a reliable alternative measure.[105]
Practical tip
Some patients with known hypoxaemia (e.g., those on long-term oxygen therapy) may have low oxygen saturations usually. However, deteriorating oxygen saturation is concerning and should warrant an urgent assessment.
How to obtain an arterial blood sample from the radial artery.
Result
PaO2 <8.0 kPa (approximately 60 mmHg) indicates respiratory failure
pH <7.35 and PaCO2 >6.5 kPa define acute respiratory acidosis[102]
pulse oximetry (in hospital and in the community)
Test
In hospital, use pulse oximetry at presentation to measure oxygen saturations as part of vital signs.[1][98]
In the community, use pulse oximetry if there are clinical features of a severe exacerbation.[90]
Ensure a good pulse wave is picked up by the device.
During an exacerbation, oxygen saturation is frequently depressed below the patient's baseline level.
Document the fraction of inspired oxygen (FiO₂) or O₂ flow rate if supplemental oxygen is given.
Result
low oxygen saturation, depressed below the patient’s baseline level
ECG (in hospital and in the community if available)
Test
Perform an ECG as cardiovascular disease is common in people with COPD.[106]
Consider a myocardial infarction or pneumothorax if chest tightness or other chest discomfort is present. However, note that chest tightness is also a symptom of COPD due to airflow limitation and chest hyperinflation.
Patients with COPD are at higher risk of developing cardiac ischaemia and/or arrhythmias, such as new-onset atrial fibrillation, that can also lead to dyspnoea.
How to record an ECG. Demonstrates placement of chest and limb electrodes.
Result
may be right heart enlargement, arrhythmia, ischaemia
FBC with platelets (in hospital)
Test
Perform in patients with moderate to severe exacerbations.
Screens for abnormalities that may suggest additional medical disorders, such as infection or anaemia.
Result
may show elevated haematocrit, elevated WBC count, or anaemia
urea, electrolytes, and creatinine (in hospital)
Test
Perform in patients with moderate to severe exacerbations.
An abnormal result may suggest additional medical disorders.
Patients with COPD exacerbations may have decreased oral intake and may become volume depleted.
Result
usually normal
CRP (in hospital)
Test
Perform in patients with moderate to severe exacerbations.
An abnormal result may suggest presence of infection.
Result
elevated CRP suggests presence of infection
CXR (in hospital)
Test
Request for patients with moderate to severe disease and/or suspected pneumonia.
Can be used to exclude differential or comorbid diagnoses, including pneumothorax, congestive heart failure, and pleural effusion.
Radiological changes seen in COPD include (but be aware these are not diagnostic of an exacerbation):
Flattened diaphragm and increased retrosternal air space volume, indicating lung hyperinflation
Hyperlucency of the lungs
Rapid tapering of vascular markings.[1]
Result
hyperinflation, flattened diaphragm, increased retrosternal air space (seen on lateral x-ray, if performed), bullae, and a small vertical heart suggest COPD, but are not diagnostic for an exacerbation
sputum microscopy, culture, and Gram stain (in hospital)
Test
Obtain for potential bacterial pathogens that may have triggered the episode. Use in severe disease and if hospitalisation is being considered.
Result
may suggest bacterial infection
vitamin D (in hospital or in the community)
Test
Once they are stable, investigate all patients who have required hospitalisation for an exacerbation of COPD for vitamin D deficiency. Vitamin D levels are lower in patients with COPD. Supplementation of patients with severe deficiency results in a reduction in exacerbations and hospitalisation. Assess for severe vitamin D deficiency (<10 ng/mL or <25 nM) and supplement if required.[1]
Result
<10 ng/mL or <25 nM indicates severe deficiency
Investigations to consider
blood cultures
Test
Request if the patient has pyrexia.
Result
may indicate sepsis
respiratory virus diagnostics
Test
Consider in severe disease.
Use to identify any treatable agent.
Use to identify the need for expanded infection control precautions in hospital.
Result
may confirm viral infection
cardiac troponin
Test
Assess for an elevation, which would indicate myocardial injury.
COPD exacerbations can lead to myocardial injury.
Elevations in troponin may be associated with increased mortality.[107]
Result
normal if no myocardial injury
serum theophylline level
Test
Measure on admission for patients who are taking theophylline (or aminophylline).[90]
Result
therapeutic range: 10-20 mg/L (55–110 micromols/litre)
pro-brain natriuretic peptide (BNP)
Test
Use to exclude heart failure, a possible differential of COPD exacerbation.
Result
normal BNP <100 picograms/mL but some variability according to gender and age
CT scan of chest
Test
Only request a chest CT to exclude alternative diagnoses if the diagnosis and basis of respiratory decompensation remains uncertain after routine CXR, or when considering surgery.[1][90]
May identify a pulmonary embolus, pneumonia, pleural effusion, or a malignancy.
Result
may still show presence of emphysema, even if no pneumonia, pleural effusion, malignancy, or pulmonary embolus present
spirometry
Test
Arrange for all patients admitted to hospital with an acute exacerbation if previous spirometry results are not available to confirm the diagnosis of COPD.[93]
During periods of high prevalence of COVID-19 in the community, spirometry should be restricted to patients requiring urgent or essential tests for the diagnosis of COPD and/or to assess lung function status for interventional procedures or surgery.[1][99]
Practical tip
Do not assess the patient using peak flow as an acute investigation. This is not recommended for assessment of an exacerbation due to the results being of lower quality or unreliable.[108] In practice, patients are often unable to perform a good-quality forced expiratory manoeuvre during an acute exacerbation.
Result
confirms diagnosis of COPD
Emerging tests
procalcitonin
Test
Procalcitonin is being investigated as a biomarker for the diagnosis of bacterial infections.[109][110]
Higher levels of procalcitonin have been detected in severe bacterial infections.[109]
It may have a function in guiding when to use antibiotics for the treatment of lower respiratory tract infection; however, this is unclear.
A Cochrane review of the use of procalcitonin to guide initiation and duration of antibiotic treatment in people with acute respiratory tract infections found it lowered the risk of mortality, and led to lower antibiotic consumption and lower risk for antibiotic-related side effects in all patients, including those with acute exacerbation of COPD.[109] Further research is required to establish its use in clinical practice. In a separate analysis of 1656 patients, 826 were randomly assigned to a group where the decision on whether to provide antibiotics was based on the results of a procalcitonin assay (830 patients were given usual care).[110]
The assay results did not result in less use of antibiotics.
There was no significant difference between the procalcitonin group and the usual-care group in antibiotic-days (mean 4.2 and 4.3 days, respectively; difference −0.05 day; 95% CI −0.6 to +0.5; P = 0.87) or the proportion of patients with adverse outcomes (11.7% [96 patients] and 13.1% [109 patients]; difference −1.5 percentage points; 95% CI −4.6 to +1.7; P <0.001 for non-inferiority) within 30 days.[110]
Result
higher levels of procalcitonin have been detected in severe bacterial infections[109]
point-of-care CRP
Test
Point-of-care CRP testing safely reduces antibiotic use in patients with acute exacerbations of COPD.[111]
Raised levels of CRP suggest the presence of bacterial infection.
In the community, it is difficult to rapidly determine whether an acute exacerbation is due to an infection, and antibiotics are often prescribed in case there is an underlying bacterial infection.
A a randomised controlled trial of the use of point-of-care CRP testing to guide antibiotic prescribing for COPD exacerbations found it reduced unnecessary antibiotic use, without compromising safety or patient outcomes.[111]
Result
elevated CRP suggests presence of infection
eosinophil count
Test
Eosinophil count may become a useful indicator of likelihood of benefit from inhaled corticosteroids.[1]
Corticosteroids (generally a 5-day course of oral prednisolone) can shorten recovery time from a COPD exacerbation.
Recent studies suggest that systemic corticosteroids may be less effective in treating exacerbations in patients with lower levels of blood eosinophils.[58][112][113][114]
After stabilisation of the acute episode, blood eosinophil level can also help to guide the decision on whether the patient will benefit from inhaled corticosteroids to reduce the risk of further exacerbations.
Result
corticosteroids may be less effective in treating exacerbations in patients with lower levels of blood eosinophils
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