1b Respiratory Failure Flashcards
What is the broad definition of respiratory failure?
Syndrome of inadequate gas exchange due to dysfunction of one or more components of the respiratory system
Which parts of the nervous system are involved in the respiratory system?
CNS / Brainstem
Peripheral NS
Neuro-muscular junction
What respiratory muscles are involved in respiratory infections?
Diaphragm and thoracic muscles
Extra-thoracic Muscles
Where in the lung will there be more ventilation? and why?
At the base - the alveoli are smaller and more compliant
Describe the difference in transmural pressure gradient between the apex and the base of the lung?
Greater gradient at the apex of the lung, much smaller at the bottom as the Pleural Pressure is LESS NEGATIVE AT THE BOTTOM
What is meant by compliance?
Compliance is the tendency to distort under pressure (change in volume/ change in pressure)
In which part of the lung are the alveoli more compliant?
Base of the lung
Which part of the lung has a LOWER INTRAVASCULAR PRESSURE?
APEX
Which part of the lung has a higher intravascular pressure?
Base
What are the effects of the high intravascular pressure at the base of the lung?
More recruitment
less resistance
higher flow rate
What are the effects of a lower intravascular pressure at the apex of the lung?
Less recruitment
Greater resistance
Lower flow rate
What is the pulmonary transit time?
0.75s
What is the time taken for gas exchange to occur through?
0.25s
What is elastance?
The tendancy to recoil to its original volume
What is the formula to calculate compliance?
Change in Volume / Change in pressuer
What is the formula to calculate elastance?
Change in pressure / change in volume
What is the biggest risk factor for males with chronic respiratory failure?
Smoking
What is the biggest risk factor for women with chronic respiratory failure?
Household air pollution from solid fuels
What is an acute presentation of respiratory failure?
Acute Respiratory Distress Sydrome
How would you diagnose someone with ARDS based on timing?
Within 1 week of known clinical insult or new or worsening respiratory symptoms
What would be seen on chest imaging of someone with ARDS?
bilateral opacities, not fully explained by effusions, lung collapse, or nodules
What is the origin of oedema in a patient with ARDS?
Respiratory failure not fully explained by cardiac failure or fluid overload.
Need objective assessment (e.g. echocardiography) to exclude hydrostatic oedema if no risk factor present
What are acute on chronic types of respiratory failure?
Infective exacerbation of COPD, CF
Myasthenic crisis
Post operative
What is the tidal volume?
The amount of air breathed in and breathed out in a normal cycle of breathes
What is the inspiratory reserve volume?
The volume of air which can be inspired on top of the tidal volume to reach maximum inspiration capacity
What is the inspiratory capacity a sum of?
Tidal volume + Inspiratory reserve volume
What is functional residual capacity?
Expiratory reserve volume + residual volume
What is the residual volume?
The volume of air which is kept in the lungs in order for the pressure to be balanced in the lungs and prevent them from collapsing
What is the vital capacity?
Inspiratory reserve volume + Expiratory reserve volume + tidal volume
What is meant by minute ventilation?
The volume of gas which is entering and leaving the lungs per minute
How do you calculate minute ventilation?
Tidal Volume x breathing frequency
What is alveolar ventilation?
The gas entering and leaving the alveoli per minute
How is alveolar ventilation measured?
(Tidal volume - dead space) x breathing frequency
What is type 1 respiratory failure?
Failure of oxygen exchange (Hypoxemic)
What is the level of PaO2 for respiratory failure to be considered type 1?
PaO2 less than 60
what happens to the shunt fraction in type 1?
Increased due to alveolar flooding
What are the pulmonary causes of acute respiratory failure?
Infection
Aspiration - when something accidentally enters your lungs
Primary graft dysfunction (Lung Tx) - severe lung injury occurs within first 72 hours of lung transplantation
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What would be the extra-pulmonary causes of acute respiratory failure?
Trauma
Pancreatitis - increased inflammatory chemicals secreted into the bloodstream
Sepsis
What are the neuromuscular causes of acute respiratory failure?
Myasthenia/ GBS - respiratory muscle weakness
What is meant by an increased shunt fraction?
Increased shunt fraction - percentage of blood put out by the heart that is not completely oxygenated (Q S)
Therefore less oxygenated blood in the body