S5 L2 Respiratory Failure Flashcards
Respiratory failure:
- Type 1 and type 2 explain…
- Hypoxia vs hypoxaemia - meaning of these
- Tissue damage is most likely to occur at…
• Hypoxaemia - low pO2 in arterial blood
• Hypoxia - O2 deficiency at tissue level
Tissues can be hypoxic without hypoxaemia (eg anaemia, poor circulation) - however, the term hypoxia is typically used to include hypoxaemia as well
• Tissue damage most likely when
– O2 saturation < 90%
– pO2 < 8 kPa
– These levels used to diagnose respiratory failure – the CLINICAL presentation will vary depending on whether acute respiratory failure or chronic- and an arterial blood gas may not always help to distinguish
Effects of hypoxaemia
Adaptions made in chronic hypoxaemia
Effects of hypoaxaemia:
• Impaired CNS function, confusion, irritability, agitation
• Tachypnaea
• Tachycardia
• Cardiac arrhythmias & cardiac ischaemia
• Hypoxic vasoconstriction of pulmonary vessels
• Central cyanosis (bluish discolouration of the skin and mucous membranes due to presence of 4 to 6 gm/dl of deoxyhaemoglobin (unsaturated Hb)
Cyanosis: Difference in symptoms and explain this difference
- Central cyanosis
- Peripheral cyanosis
5 Causes of hypoxaemia (list them)
- Low inspired pO2 e.g. high altitude
- V/Q mismatch
- Diffusion defect
- Shunt e.g. ARDs
- Hypoventilation
also:
6. Extra (outside of) -lung shunt - congenital heart defect
- Low inspired pO2 e.g. high altitude
- Ventilation-perfusion mismatch
Disorders with V/Q mismatch due to reduced ventilatiuon of parts of the lung
Ventilation - Perfusion Ratio
– optimal gas exchange when V/Q ratio is 1
V/Q matching must happen at alveolar level
Disorders which cause poor ventilation of some alveoli (but not all), include pneumonia, asthma (early/mid stages), COPD (early/mid stages) and Respiratory Distress Syndrome in the New Born.
Poorly ventilated alveoli have a V/Q ratio of < 1, as ventilation is low relative to perfusion. If a significant amount of lung tissue has a V/Q ratio of < 1, hypoxaemia results.
V/Q mismatch due to PE
How does the body react to hypoxaemia?
- Poor diffusion across alveolar membrane
Diffusion defects CO2 is more soluble \ CO2 diffusion less affected
than diffusion of O2
– pO2 low
– pCO2 normal or low
• Type 1 respiratory failure – initially- as disease progresses restrictive lung disease leads to hypoventilation - hypercapnia
Diffuse lung fibrosis
- What is affected
- Causes of this
- How could it improve?
- Intra-pulmonary shunt
- What is meant by ‘shunt’ in respiratory system
- Will providing oxygen improve levels of oxygen in the blood?
- Will giving oxygen improve oxygen levels in unaffected parts of the lungs?
Example of diffuse intra-pulmonary shunting - Acute Respiratory Distress Syndrome
- What is this syndrome/what happens
- What do lungs ‘look’ like?
- Characteristics/symptoms of this syndrome
- Why does shunt develop?
- Hypoventilation
- How does this lead to hypoxaemia
- Type 1 or type 2 Resp failure?
- How to treat
- Caveat with treating hypoventilation
Hypoventilation ALWAYS causes hypercapnia
•Therefore causes Type 2 Respiratory Failure with both hypoxaemia + hypercapnia
• Hypoxaemia secondary to hypoventilation will correct with added oxygen does not solve hypercapnia problem though as ventilation impaired
Acute vs Chronic hypoventilation
More than one mechamism may cause hypoxaemia in a given disease
- give an e.g.
How can type 1 progress into type 2?
- give an e.g.
Does giving oxygen always help with respiratory failure?
- give some caveats to this
Causes of hypoventilation disorders
Central disorders - examples of causes of hypoventilation
Motor disorders - how can this lead to hypoventilation?
Disorsder of neuromuscular junction - examples of disorders…
Muscle weakness or fatigue - examples of disorders…
DISORDERS OF NEUROMUSCULAR JUNCTION
•MG
•Organophosphate toxicity
•Botulism
MUSCLE WEAKNESS OR FATIGUE
Diseases/conditions
• COPD
• Asthma
• Malnutrition
• Diaphragmatic dysfunction e.g. damage to phrenic nerve
• Muscular dystrophy
• RDS
• Severe restrictive lung disease
Chest wall disordrs
- Example of some
- Why can this lead to hypoventilation?
Effects of hypercapnia - Acute and chronic
Review - Chronic CO2 rentention - effect on central chemoreceptors
- *Chronic type 2** respiratory failure and oxygen
- Why treatment of hypoxaemia may worsen hypercapnia - MAIN mechanisms
Reminder -
More than 1 mechanism may be responsible for respiratory failure, give example…
Summary:
- Number of causes of hypoxaemia?
- Which of these will be fully or partially corrected with oxygen?
- Which one of these will not be corrected with oxygen?
- Which type of respiratory failure will not be corrected with oxygen?
GW:
Haemoglobin-oxygen dissociation curve
- What conditions cause left shift, which conditions cause right shift?
How does chronic affect compensation?
Which conditions is ground glass opacities found?
What conditions can lead to ARDs?
How can ventilation cause problems with carbon dioxide?
In a baby who has hypoxaemia and hypercapnia - explain why the pCO2 level was normal but is now increasing?
Pulmonary embolism -signs and symptoms
Asthma - if the chest is silent, what does this mean?
Chronic - had time to compensate
Ground glass opacities - infections, interstitial lung disease, pulmonary oedema, neoplasm
ARDs: severe flu, severe COVID…
Ventilation: Ventilator is set at a higher respiratory rate e.g. 35, this is to improve oxygen level. This is as if someone is hyperventilating. However, a problem with this is increased carbon dioxide levels.
Baby is trying to open up chest
Hyperventilation due to low oxygen levels
Baby tires
This leads to baby hypoventilating (decompensation)
Hypoventilation leads to increased CO2
Pulmonary embolism:
- Sudden deterioration
- Tachycardia (most likely sign)
- Hypoxaemia
- ECG changes (most specific sign)
Asthma - means SEVERE asthma (very serious)
