LUNG FUNCTION TESTS, NON-INVASIVE VENTILATION, OXYGEN Flashcards
What is FEV1?
forced expiratory volume in 1 second.
This is the amount of air a person can exhale as fast as they can in 1 second. This is a measure of the ability of air to freely flow out of the lungs
It will be reduced if there is any obstruction to the air flow out of the lungs
What is FVC?
forced vital capacity
This is the total amount of air a person can exhale after a full inhalation. This is a measure of the total volume of air that the person can take in to their lungs.
It will be reduced if there is any restriction on the capacity of their lungs.
How is obstructive lung disease diagnosed using spirometry?
when FEV1 is less than 75% of FVC (FEV1:FVC ratio < 75%).
This suggests that there is some obstruction slowing the passage of air getting out of the lungs. The person may have a relatively good lung volume but air is only able to move in and out of the lungs slowly due to obstruction.
How is restrictive disease diagnosed using spirometry?
If FEV1 and FVC are equally reduced and FEV1:FVC ratio > 75% this suggests restrictive lung disease.
Restrictive lung disease is where there is a restriction to the ability of the lungs to expand and take air in.
What is peak flow?
Measures the fastest point of a persons expiratory flow of air
It demonstrates how much obstruction to airflow is present in the patients lungs - particularly useful in asthma
What is non-invasive ventilation?
involves using a full face mask or a tight fitting nasal mask to blow air forcefully into the lungs and ventilate them without having to intubate them. It is not pleasant however it is much less invasive than intubation and ventilation and acts as a useful middle point between basic oxygen and intubation.
It can either be BiPAP or CPAP
What is BiPAP?
bilevel positive airway pressure
This involves a cycle of high and low pressure to correspond to the patients inspiration and expiration.
What is BiPAP for?
Type 2 respiratory failure, typically due to COPD
Whats the criteria for initiating BiPAP?
Respiratory acidosis (pH < 7.35, PaCO2 >6) despite adequate medical treatment.
What are the contraindications of BiPAP?
Untreated pneumothorax
Structural abnormalities or pathologies affecting the face, airways or GIT
What should be done before initiating BiPAP?
CXR to exclude pneumothorax
Plan should be put in place in case NIV fails - i.e. do they want intubationand ventilation or palliative care
What is IPAP?
Inspiratory positive airway pressure - forcing air into lungs
What is EPAP?
Expiratory positive airway pressure - provides some pressure during expiration so that the airways don’t collapse
What is CPAP?
continuous positive airway pressure - provides continuous air blowing into the lungs to keep the airways expanded so the air can more easily travel in and out i.e. it adds positive end-expiratory pressure - used to maintain airways in conditions prone for collapse
What are indications for CPAP?
Obstructive sleep apnoea
Congestive cardiac failure
Acute pulmonary oedema
What is PEEP?
Positive end-expiratory pressure
What is end-expiratory pressure?
the pressure that remains in the airways at the end of exhalation.
How can you add positive end-expiratory pressure?
High-flow nasal cannula
Non-invasive ventilation
Mechanical ventilation
What are benefits of prone positioning?
Reducing compression of the lungs by other organs
Improving blood flow to the lungs, particularly the well-ventilated areas
Improving clearance of secretions
Improving overall oxygenation
Reducing the required assistance from mechanical ventilation
What flow rates can high-flow nasal cannula give?
Up to 60L/min
What is mechanical ventilation?
Using a ventilator machine to move air into and out of the lungs
Often used when other forms of ventilators support are inadequate or contraindicated
What is extracorporeal membrane oxygenation?
ECMO
the most extreme form of respiratory support and very rarely used
Only used when respiratory failure is not adequately managed by intubation and ventilation
Blood is removed from the body, passed through a machine where oxygen is added and carbon dioxide is removed, then pumped back into the body. The process is similar to haemodialysis but for respiratory support rather than renal support.
ECMO is only used short-term, where there is a potentially reversible cause of respiratory failure. It is not a long-term treatment. It is only provided in specialist ECMO centres and is not available in most intensive care units. Patients need to be transferred to a specialist centre for ECMO.
What form should oxygen be given to critically ill patients?
Non-rebreath mask at 15L/min
What form should oxygen be given for COPD patients?
28% Venturi mask at 4L/min
