Respiratory: Respiratory Failure Flashcards
What is the definiton of hypoxia? [1]
PaO2 below 8.0 kPA
Define Type 1 & Type 2 respiratory failure [2]
Type 1 respiratory failure (T1RF): is characterised by hypoxaemia (PaO2 < 8 kPa) and a normal or low CO2.
Type 2 respiratory failure (T2RF): is characterised by hypoxaemia (PaO2 < 8 kPa) and hypercapnia (PaCO2 > 6.5 kPa).
State 5 main causes of hypoxaemia [5]
V/Q mismatch
Shunt
Diffusion limitation
Hypoventilation
Increased dead space
Why does pneumonia lead to respiratory failure? [1]
Pleural effusion / empyema blocks gas exchange
Describe V/Q mismatch in normal health [4[
Normal health:
- there is a mismatch in V/Q that differs depending on location of lung
- When standing, perfusion is b to the bases due to gravitational forces
- Ventilations is higher at the bases compared to the apices BUT by far less than perfusion
- Therefore V/Q ratio at the apices is 3.3; bases is 0.6
Describe what is meant by low and high V/Q mismatch in hypoxia [2]
State what could cause each [2]
Hypoxaemia usually caused by:
Low V/Q:
- alveoli with poor ventilation compared to perfusion
- Caused by: airway disease or interstitial lung disease where ventilation is reduced
- Therefore, hypxoxia induced v/c occurs and redirects blood to better ventilated areas
High V/Q:
- Poor perfusion c.f ventilation
- Caused by: PE
What is a shunt (with regards to hypoxia)? [1]
How does this occur in pathological conditions? [1]
Blood entering the left side of the heart without first having travelled through pulmonary capillaries and participating in gaseous exchange.
This can be thought of as an extreme version of V/Q mismatch (V/Q = 0)
In pathological conditions this occurs due to pulmonary arteriovenous malformations
State 4 conditions that cause pulmonary shunts [4]
pneumonia
ARDS
pulmonary oedema
alveolar collapse
What is meant by diffusion limitation (causing hypoxia?)
Describe two pathophysiological causes of diffusion limitation [2]
Diffusion limitation refers to the impairment of gaseous exchange across the alveolocapillary membrane.
Causes:
Reduced surface area:
- reduced surface area of alveoli due to pathological destruction limits the amount of lung tissue available for gaseous exchange.
Alveolocapillary membrane changes:
- inflammation and fibrosis of the alveolocapillary membrane impairs diffusion across it.
State common causes of diffusion limitation [3]
Emphysema
Lung fibrosis
Oedema
State 6 causes of hypoventilation [6]
Respiratory depressants (e.g. opiates, alcohol)
Neurological disorders (e.g. ALS, GBS, Myasthenia gravis)
Myopathies
Chest wall disease (e.g. kyphoscoliosis)
Exacerbation of COPD
Severe asthma attack
Describe what is meant by increased dead space causing hypoxaemia [1]
Areas of the lung that are ventilated but not perfused and therefore do not contribute to gaseous exchange.
(It can be thought of as an extreme V/Q mismatch and the opposite of a shunt)
Name two pathologies that cause increased dead space [2]
emphysema (COPD) and interstitial lung disease destroying pulmonary capillaries
What is the most common cause of T1RF? [1]
V/Q mismatch
Describe how T1RF can present [1]
Why is this clinically significant when investigating T1RF? [1]
Can be acute or chronic; but can‘t differentiate between the two on an ABG
State 5 common causes of T1RF [6] (and the cause of hypoxia)
Diffusion abnormality:
- Pulmonary fibrosis
- Emphysema in COPD
V/Q mismatch: reduced V
- Pneumonia
- Pulmonary oedema
- Pneumothorax
V/Q mismatch: reduced Q
- Pulmonary embolism
Low inspired oxygen
Hypxoxia = increased V
More CO2 exhaled
Hypoxia but not hypercapnic
State common consequences of chronic T1RF [5]
These indicate oxygen treatment
Polcythaemia (increase in RBC)
Development of cor pulmonale
Peripheral oedema
Poor sleep
Fatigue
Pulmonary hypertension
How much oxygen is required to be given to see reduction in mortality in chronic T1RF? [2]
Daily for 16hrs for more than one year
T2RF is seen in conditions that cause what changes to alveoli? [1]
T2RF is seen in conditions that result in alveolar hypoventilation.
Explain how T2RF causes acidosis? [4]
pO2 < 8
BUT: Failure of ventilation;
Can’t blow off CO2;
CO2 rises in blood to produce carbonic acid
pH falls
Describe the difference between acute and chronic T2RF presentation
Acute T2RF:
- Significant hypoxaemia
- New respiratory acidosis with normal bicarbonate
- Electrolyte disturbances
- CV instability
- LOC
- Cardiac arrest
Chronic T2RF:
- Increase in bicarbonate levels in setting of chronic respiratory acidosis
Remember T2RF is caused by alveolar hypoventilation
Explain what is meant by NIV / BIPAP treatment? [3]
Non-invasive ventilation (NIV) involves using a full face mask, hood (covering the entire head) or a tight-fitting nasal mask to blow air forcefully into the lungs and ventilate them.
Much less invasive than intubation and ventilation.
BiPAP is a specific machine that provides NIV. BiPAP stands for Bilevel Positive Airway Pressure.
Involves a cycle of high and low pressure to correspond to the patient’s inspiration and expiration:
- IPAP (inspiratory positive airway pressure) is the pressure during inspiration – where air is forced into the lungs
- EPAP (expiratory positive airway pressure) is the pressure during expiration – stopping the airways from collapsing
Describe the difference in pressures between CPAP and NIV / BIPAP
CPAP:
- One continous pressure
BIPAP:
- Two pressures: high pressure when you breath in and low pressure when you breath out. Difference in pressure helps ventilation
Why does NIV (BIPAP) help to treat acute T2RF? [2]
In acute T2RF:
- Hypoxia causes increase in ventilation
- Unable to increase ventilation
- NIV helps to increase ventilation
Which of the following would this CXR cause hypoxaemia?
V/Q mismatch
Shunt
Diffusion limitation
Hypoventilation
Increased dead space
Lobar pneumonia causing V/Q mismatch
Out of which of the following would this CXR cause hypoxaemia?
V/Q mismatch
Shunt
Diffusion limitation
Hypoventilation
Increased dead space
Diffusion abnormality: patient has sarcoidosis
Out of which of the following would this CXR cause hypoxaemia?
V/Q mismatch
Shunt
Diffusion limitation
Hypoventilation
Increased dead space
Hypoventilation: patient has TB
Out of which of the following would this CXR cause hypoxaemia?
V/Q mismatch
Shunt
Diffusion limitation
Hypoventilation
Increased dead space
Hypoventilation: lobar collapse
Out of which of the following would this CXR cause hypoxaemia?
V/Q mismatch
Shunt
Diffusion limitation
Hypoventilation
Increased dead space
Diffusion limitation:
Pulmonary fibrosis
Out of which of the following would this CXR cause hypoxaemia?
V/Q mismatch
Shunt
Diffusion limitation
Hypoventilation
Increased dead space
Hypoventilation: COPD
Can be T1 or T2RF
Out of which of the following would this cause hypoxaemia?
V/Q mismatch
Shunt
Diffusion limitation
Hypoventilation
Increased dead space
Hypoventilition: motor neuron disease - can’t use muscles / diaphragm to breathe
Out of which of the following would this CXR cause hypoxaemia?
V/Q mismatch
Shunt
Diffusion limitation
Hypoventilation
Increased dead space
VQ mismatch: pneumothroax
Out of which of the following would this cause hypoxaemia?
V/Q mismatch
Shunt
Diffusion limitation
Hypoventilation
Increased dead space
Morbid obesity: hypoventilation
Out of which of the following would this CXR cause hypoxaemia?
V/Q mismatch
Shunt
Diffusion limitation
Hypoventilation
Increased dead space
Shunt: eisenmenger syndrome
