Paediatrics: Investigations

Investigations

Chest X-ray

CXR is a key investigation in respiratory disease. It will give you informa-tion about lung volume (e.g. hyperinflation in asthma), signs of chronic in-flammation (e.g. peribronchial cuffing), and evidence of congenitial lesions (e.g. lung cysts). However, it is an investigation that can be overused. It should not replace a thorough clinical examination, and think hard before requesting repeat studies.

A CXR is used to glean more clinical evidence about what the child’s underlying problem is. So, in each presentation consider why you have requested the test. Here are some examples.

Wheeze

A CXR is not needed every time a patient presents with ‘asthma’. However, if that child has never had an X-ray, or there is something atypical about the history, consider other possibilities:

·  Suspected foreign body inhalation: i.e. inspiratory and expiratory film (object often radiolucent).

·  Suspected gastro-oesophageal reflux with aspiration, or aspiration from abnormal swallowing: i.e. looking for different lobes affected at different times.

·  Monophonic wheeze: i.e. looking for hilar lymph nodes compressing on the right main-stem bronchus, or a large left atrium compressing the left main-stem bronchus, or mediastinal mass.

Stridor 

Suspected tracheal lesion around the thoracic inlet.

Cough

·  Suspected typical and atypical pneumonia, or empyema.

·  Suspected bronchiectasis.

Breathlessness

·  Suspected pulmonary parenchymal disease.

·  Pneumothorax.

·  Suspected heart disease, e.g. heart failure.

Snoring with sleep apnoea 

Suspected cardiopulmonary disease or cor pul-monale from chronic upper airway obstruction.

Bedside tests in respiratory medicine

Four tests are frequently performed at the bedside or in the laboratory are lung function testing, sweat test, and arterial blood sampling.

Lung function testing

Spirometry can be achieved in 5-yr-olds, but measurements are easier in >=7 year olds. Peak expiratory flow rate (PEFR) monitoring is useful in asthma. Other measurements include:

·FEV₁/FVC: the forced expired volume in 1s as a fraction of forced vital capacity.

·Exercise testing.

·Bronchodilator responsiveness (i.e. reversibility).

Sweat test

This test is used in the diagnosis of cystic fibrosis. Sweating is induced in an area of the forearm using pilocarpine, and a capillary tube is used to collect the sweat. A minimum of 15µL (and preferably >30µL) of sweat should be collected. In cystic fibrosis abnormal function of the sweat glands results in higher concentrations of chloride in the sweat:

·Suspicious: >40mmol/L (>30mmol/L in newborn screened babies).

·Diagnostic: >60mmol/L.

Pulse oximetry 

Assessment of oxygen saturation (SpO₂) using a pulse oximeter is a non-invasive way of assessing a child’s oxygenation using a probe attached to a finger or toe.

Arterial blood gas 

Assessment of blood O₂, CO₂, and acid–base are impor-tant in critically ill children, or in those where you suspect significant lung disease.

Further investigations

Sometimes more detailed investigations are needed before you can select the best treatment for your patient. These include the following:

Imaging

·Chest computed tomography: useful for assessing abnormalities in airways as well as abnormalities in parenchymal tissue density.

·Thoracic MRI: useful for looking at airway–blood interface, and vascular and mediastinal anatomy.

·Nuclear imaging: useful for assessing regional ventilation (V) and perfusion (Q), as well as V/Q matching.

Direct visualization of structure

Flexible bronchoscopy: used to assess directly the airway from nose to distal bronchus; used to lavage the lung for microscopy and culture