Respiratory Investigations Flashcards
What respiratory investigations are commonly used?
- Oxygen saturation
- Vital signs
- Blood gases
- Oxygenation index
- Spirometry
What is the purpose of measuring oxygen saturation’s?
For detection of hypoxaemia and monitoring of response to oxygen therapy
What are the advantages of saturation monitors?
Non-invasive and allows continuous monitoring
What do blood gases measure?
Direct measurement of arterial pH, PaO2, and PaCO2
When is measurement of blood gases particularly important?
In intensive care for patients on respiratory support q
Where is the ideal place to get blood gases from?
Arterial line
What is the limitation of blood gases from a peripheral artery?
They need to be interpreted in conjugation with clinical features, as will be affected by the infant crying
Where is spirometry widely used?
Outpatient settings
What does a peak expiratory flow meter and spirometer allow the measurement of?
- Peak expiratory flow rate (PEFR)
- Forced viral capacity (FVC)
- Forced expiratory volume in 1 second (FEV1)
- Forced exploratory flow (FEF25-75)
What is the forced expiratory flow?
The mean maximal flow in the middle of the FVC (forced expiration)
How does FEF25-75 compare to FEV1 or PEFR?
FEF25-75 is more sensitive but more variable than FEV1 or PEFR in assessing obstruction of the small to moderate sized airways
How is PEFR measured?
A child must give a short sharp expiration into the device
What does the measured value reflect in PEFR?
The maximal flow able to be generated (in L/min)
What is the limitation of PEFR?
It is a much less sensitive a marker of airway obstruction than FEV1 or the shape of a flow-volume curve, and is used less than in the past
How is a flow-volume curve generated?
A child must take a maximal inspiration and then exhale into a mouthpiece as hard as possible and for as long as possible. The volume and flow of exhaled breath are measured
How is reproducibility in the generation of a flow-volume curve ensured?
There should be 3 attempts producing results within less than 5% error
At what age are most children able to perform good quality spirometry/flow-volume loops?
5 years
What % of expiration is effort dependant?
The first 25-35%
What is spirometry good for?
Sensitive way to assess airway narrowing
What are the two main patterns of spirometry recognised?
- Obstructive
- Restrictive
What is the most common pattern of spirometry?
Obsturctive
What effect does asthma have on spirometry?
It causes reversible obstruction
What is the clinical relevance of asthma causing reversible obstruction on spirometry?
Diagnosis is made based on spirometry before and after salbutamol usage to show improvement in the post-salbutamol measurement
What bronchodilator reversibility is considered significant and can confirm a diagnosis of asthma?
More than 8-12%
At what age is airway smooth muscle seen from?
Birth
At what age is functional ß-adrenoceptor activity documented?
From infancy
What happens to FEV1 and FEF25-75 in obstructive airway disease?
They are both reduced, FEF25-75 more so
Why is the ratio of FEV1 to FVC a useful measure?
It gives an indication of severity, and ‘tracks’ throughout life
