Respiratory Investigations
Investigations
In respiratory medicine, there are several investigations available, ranging from simple testing to more invasive procedures. To explain these procedures to their patients, all respiratory nurses should understand what tests are available, how the tests are conducted, and any preparation necessary before and after the test.
Peak expiratory flow rate (PEFR)
PEFR is the maximum flow of air that a patient can expel from their lungs from a full inspiration.
Spirometry
Spirometry is a method of assessing lung function by measuring the volume of air that a patient can expel from their lungs following maximal inspiration. It also measures the flow rate and gives far more information than PEFR alone.
Respiratory function tests
Respiratory function tests In secondary care, a systematic combination of lung function tests are carried out in lung function laboratories. The two tests of lung function that are often carried out routinely, in addition to spirometry, are the measurement of lung volumes and diffusing capacity. The gas held by the lungs is thought of in terms of subdivisions, or specific lung volumes.
Exercise testing
One of the main symptoms of respiratory disease is breathlessness, especially on exertion.
Breathlessness rating
Breathlessness is a subjective term; it is important to determine how the breathlessness affects the individual. There are several scales for assessing it subjectively. Those most commonly used are: The Medical Research Council (MRC) dyspnoea scale The ‘oxygen cost’ diagram The Borg scale.
Body mass index (BMI)
The simplest measure of nutritional status is body weight, from which BMI can be calculated. The formula to calculate an individual’s BMI is: BMI = Weight (in kg) / Height2 (in metres)
Arterial blood gas (ABG)
ABG analysis evaluates gas exchange in the lungs by measuring the acidity or alkalinity of the blood (pH), respiratory function (oxygen and carbon dioxide) and metabolic measures (bicarbonate and base excess).
Arterial blood sample
Arterial blood samples can be obtained by an arterial puncture or ‘stab’, or they can be taken from an indwelling arterial cannula.
Capillary blood samples
Blood can also be taken from the earlobe or a digit for occasional ABG samples; this technique is considered less invasive and painful than an arterial stab.
Pulse oximetry
Arterial oxygenation can be easily measured, and provides an estimate of the level of oxygenation of the blood arterial oxygen saturation (SaO2). It is measured with a pulse oximeter placed either on a finger or an earlobe. The oximeter uses a red and infrared light to detect the absorbed characteristics of oxygenated and deoxygenated haemoglobin.
Blood tests
Many routine blood tests are performed when a patient has either an acute or a chronic respiratory disease.
Radiological investigations
Chest X-ray A chest X-ray is the basic screening test for patients with respiratory symptoms. It is regarded as standard for patients presenting with chronic problems or acute potentially serious symptoms.
Bronchoscopy
Bronchoscopy is the direct inspection of the trachea and larger bronchi. It can be used to sample lung tissue via brushings, lavage or biopsy. There are two types of bronchoscopes used: fl exible fi breoptic bronchoscopes and rigid bronchoscopes
Skin-prick testing
A skin-prick test can help to identify whether someone is allergic to a compound. The primary function of the test is to confirm a diagnosis of atopy, to confirm the clinical history and to allow for correct advice and treatment to be given. It is used most frequently in patients with a history of asthma and allergic rhinitis.
Sputum tests
Sputum is the material expectorated from the lungs and bronchi during coughing. Analysis of a sputum sample helps diagnose respiratory disease, determine the cause of respiratory infection, and identify abnormal lung cells.