Respiratory failure Flashcards
What is respiratory failure
when the lungs fail to adequately oxygenate arterial blood, and/or fail to prevent CO2 retention
What is seen in bloods with type 1?
type 1 known as oxygenation failure
Low PaO2 (hypoxaemia), Low or normal PaCO2
Type 1 respiratory failure is associated with?
Damage to lung tissue which prevents adequate oxygenation of the blood. However, the remaining normal lung is still sufficient to excrete carbon dioxide.
- gas exchange problem
Commonest mechanism to cause type 1 respiratory failure?
V/Q mismatch
possible to recognise a VQ mismatch or shunt because the arterial blood gases will not fit the alverolar gas equation (PaO2 is reduced, PaCO2 is normal) - type 1
Some common causes of type 1 respiratory failure?
- Pneumonia
- Pulmonary oedema
- Pulmonary embolism
- Asthma
- Emphysema
- Pulmonary fibrosis
- Acute respiratory distress syndrome
Treatment for type 1 respiratory failure
improve oxygenation: nasal cannula, hudson mask, venturi mask, non-rebreathe mask, high flow nasal cannulae
recruit alveoli
In type 2, what is seen in bloods?
Low PaO2 (hypoxaemia), high PaCO2 (hypercapnea)
Commonest mechanism to cause type 2 respiratory failure?
Alveolar hypoventilation
Some common causes of type 2 respiratory failure
Lung problems (restrictive eg FLD, obstructive eg COPD)
Respiratory generator problems (drugs, hypothyroidism, CVA)
Chest wall/neuromsc junction (obesity, kyphoscoliosis, myasthenia gravis)
Problems with just oxygenating more?
will not ventilate the patient more, only oxygenate the patient better
Treatment of type 2 respiratory failure?
Positive pressure ventilation
- Bilevel positive airway pressure (BIPAP)
– Inspiratory positive airway pressure (IPAP)
– Positive end expiratory pressure (PEEP/EPAP)
- Set backup respiratory rate
- Can be volume controlled
- CPAP = continuous positive airway pressure,
not ventilation, can splint upper airway (in
obstructive sleep apnoea), aids oxygenation
Treating the underlying cause
Difference between invasive and non-invasive PPV
Positive pressure ventilation can be delivered in two forms: non-invasive positive pressure ventilation (NIPPV), which is delivered through a special face mask with a tight seal (air travels through anatomical airways), or invasive positive pressure ventilation (IPPV), which involves the delivery of positive pressure to the lungs through an endotracheal tube or tracheostomy (or any other device that delivers gas bypassing parts of the anatomical airway).
Non-invasive postive pressure ventilation
- NPPV is used to treat both acute and chronic respiratory failure
- In the patient with chronic respiratory failure, NPPV can be used to provide 24-hour ventilatory support
- Acute exacerbation of COPD most evidence/successful
Why might giving uncontrolled O2 therapy to someone in type 2 failure may indeed worsen their condition?
chronic pulmonary disease usually causes the patient to be reliant on hypoxic drive (as opposed to hypercapnic drive) for breathing; therefore, giving them O2 could obliterate this hypoxic drive and cause them to go into respiratory arrest.
What is V/Q mismatch mechanism?
Ventilation/perfusion ratio is off
Lead to compensatory vasoconstriction
Extremes:
Ventilation, no perfusion =dead space
Perfusion, no ventilation =shunt
Common causes of V/Q mismatch?
- Alveolar filling e.g. pneumonia, pulmonary oedema
- Poor ventilation COPD
- Pneumothorax
- Pulmonary embolus
What is shunt? causes of shunt?
- the passage of deoxygenated blood from the right side of the heart to the left without participation in gas exchange in the pulmonary capillaries.
- may not respond to supplemental oxygenation
- if extreme will affect CO2
Causes:
Extensive atelectasis/Severe pneumonia/ARDS
Can be anatomic e.g. Intracardiac defects (Eisenmengers) and intrapulmonary (AV malformations)
What is impaired diffusion?
Impaired if distance between alveoli and capillary increased, e.g. in fibrotic lung disease
What is Hypoventilation?
occurs when ventilation is inadequate to perform respiratory gas exchange
- breathing too little
- causes increased CO2 (hypercapnea) and respiratory acidosis
Arterial hypoxaemia an important cause of
tissue hypoxia but not the only cause as
also influenced by:
Tissue blood flow
Cardiac output
Haemaglobin O2 affinity
Oxygen carrying capacity of blood
Low pH occurs in?
primary respiratory acidosis
If arterial PCO2 is decreased what does it mean?
Hyperventilation
If PaO2 fits the alveolar PO2 → hyperventilation problem only (e.g. panic attack)
If PaO2 less than calculated alveolar PO2 → hyperventilation problem + gas exchange problem)
If arterial PCO2 is decreased what does it mean?
Hyperventilation
If PaO2 fits the alveolar PO2 → hyperventilation problem only (e.g. panic attack)
If PaO2 less than calculated alveolar PO2 → hyperventilation problem + gas exchange problem)
If arterial PCO2 is elevated what does it mean?
hypoventilation
If the PaO2 fits the alveolar gas equation → hypoventilation only (e.g. respiratory depressant drug e.g. morphine)
If PaCO2 elevated and PaO2 less than calculated alveolar PO2 → hypoventilation problem and gas exchange problem e.g. COPD
Why do we use PaO2’s reference range of >10.6kPa?
the point where 98% saturation of Hb is achieved on the HbO2 dissociation curve
what is PaO2 ?
partial pressure of O2, measurement of oxygen pressure in arterial blood. Reflects how effective oxygen is able to move from the lungs into the blood.
