Respiratory - CXR, ABGs and Lung Function Tests Flashcards
Which details should be checked when beginning X-ray interpretation?
Patient details: name, date of birth and unique identification number.
Date and time the film was taken.
Previous imaging (useful for comparison)
How can the quality of the CXR be assessed?
Comment upon the rotation, inspiration, projection and exposure of the CXR (RIPE).
Rotation: the medial aspects of each clavicle should be equidistant from the spinous processes, with the spinous processes vertically orientated against the vertebral bodies.
Inspiration: 5-6 anterior ribs, lung apices, both costophrenic angles and the lateral rib edges should be visible.
Projection: note if the film is AP or PA; if there is no label, assume it’s a PA film.
Exposure: the left hemidiaphragm should be visible to the spine and the vertebrae should be visible behind the heart.
What mnemonic can be used to interpret a CXR, after assessing quality?
The ABCDE approach can be used to carry out a structured interpretation of a chest X-ray:
Airway: trachea, carina, bronchi and hilar structures.
Breathing: lungs and pleura.
Cardiac: heart size and borders.
Diaphragm: including assessment of costophrenic angles.
Everything else: mediastinal contours, bones, soft tissues, tubes, valves, pacemakers and review areas.
What are some causes of tracheal deviation?
True tracheal deviation can either be from ‘pushing’ or ‘pulling’ of the trachea:
Pushing of the trachea secondary to large pleural effusion or tension pneumothorax; pulling of the trachea secondary to lobar collapse.
Apparent tracheal deviation occurs due to rotation of the patient.
What is the carina and its significance on CXR?
The carina is cartilage that is situated at the point the trachea bifurcates into its left and right main bronchi.
The carina is an important landmark when assessing nasogastric (NG) tube placement, as the NG tube should bisect the carina if it is correctly placed in the gastrointestinal tract.
Into which bronchus are you more likely to aspirate and why?
Most likely to aspirate into the right main bronchus, as this bronchus is wider and more vertical than the left main bronchus.
What are the hilar and their significance on CXR?
The hilar consist of the main pulmonary vasculature and the major bronchi.
Each hilar also has a collection of lymph nodes which aren’t usually visible in healthy individuals.
The hilar are usually the same size, so asymmetry should raise suspicion of pathology.
The hilar point is also a very important landmark; anatomically it is where the descending pulmonary artery intersects the superior pulmonary vein. When this is lost, consider the possibility of a lesion here (e.g. lung tumour or enlarged lymph nodes).
Give some causes of hilar enlargement.
Bilateral symmetrical enlargement is typically associated with sarcoidosis.
Unilateral/asymmetrical enlargement may be due to underlying malignancy.
Give some causes of abnormal hilar position.
You should inspect for evidence of the hilar being pushed (e.g. by an enlarging soft tissue mass) or pulled (e.g. lobar collapse).
How can the lungs be inspected for abnormalities on CXR?
Divide each lung into three zones (upper, middle and lower).
Compare each zone between lungs, noting any asymmetry (some asymmetry is normal and caused by the presence of various anatomical structures e.g. the heart).
Some lung pathology causes symmetrical changes in the lung fields, which can make it more difficult to recognise, so it’s important to keep this in mind (e.g. pulmonary oedema).
Increased airspace shadowing in a given area of a lung field may indicate pathology (e.g. consolidation/malignant lesion).
The complete absence of lung markings should raise suspicion of a pneumothorax.
What is the pleura and its significance on CXR?
The pleura are not usually visible in healthy individuals. If the pleura are visible it indicates the presence of pleural thickening which is typically associated with mesothelioma.
Inspect the borders of each lung to ensure lung markings extend all the way to the edges of the lung fields (the absence of lung markings is suggestive of pneumothorax).
Fluid (hydrothorax) or blood (haemothorax) can accumulate in the pleural space, resulting in an area of increased opacity on a chest X-ray. In some cases, a combination of air and fluid can accumulate in the pleural space (hydropneumothorax), resulting in a mixed pattern of both increased and decreased opacity within the pleural cavity.
How is the heart assessed on CXR?
Calculate cardiothoracic ratio (cardiomegaly >50%) ONLY on PA X-ray
The heart borders may also become difficult to distinguish from the lung fields as a result of pathology which increases the opacity of overlying lung tissue (e.g. pneumonia, effusion).
What are some causes of cardiomegaly?
- valvular heart disease
- cardiomyopathy
- pulmonary hypertension
- pericardial effusion.
When assessing the diaphragms on CXR, what are the important clinical signs?
Presence of free air under a hemi-diaphragm is pneumoperitoneum, which is suggestive of bowel perforation.
In healthy individuals, the costophrenic angles should be clearly visible, with a well defined acute angle; costophrenic blunting suggests consolidation in the area, or hyperinflation of the lungs.
Which mediastinal contours should be assessed in CXR?
Aortic knuckle - if there is reduced definition, it is suggestive of an aneurysm.
Aortopulmonary window - if there is reduced definition, it is suggestive of mediastinal lymphadenopathy.
What is forced vital capacity?
The volume of air forcibly expired from the lungs from a maximum inspiration.
In obstructive lung disease, give the typical FEV1/FVC ratio.
Obstructive lung disease can be diagnosed when FEV1 is less than 75% of FVC (FEV1/FVC <75%).
This means the person has a good lung volume, but air can only move out of the lungs slowly due to obstruction (e.g. asthma, COPD).
On spirometry, how is asthma differentiated from COPD?
Asthma and COPD will both show an obstructive pattern on spirometry (FEV1/FVC <75%).
To distinguish you can test for reversibility by giving a bronchodilator (e.g. salbutamol); the FEV1/FVC ratio will improve ≥12% in asthma, but will not be reversible in COPD.
In restrictive lung disease, give the typical FEV1/FVC ratio.
FEV1/FVC will remain >75%, however both FEV1 and FVC will be reduced in comparison to normal.
This means there is a restriction to the ability of the lungs to expand and take air in, however the patient is still able to expire normally.
What is peak expiratory flow rate?
The fastest point of a persons expiratory flow of air during a forced expiration.
Measured using a peak flow meter - technique is to stand tall, take a deep breath in, make a good seal around the device with the lips and blow as fast and hard as possible into the device. Take three attempts and record the best result.
Measured in L/min
