Respiratory Failure Flashcards
What is respiratory failure?
PaO2 <8kPa and subdivided into two types according to the PaCO2.
What are the steps of normal ventilation?
- Diaphragm (and external intercostals) contract - in laboured breathing, the accessory muscles contract.
- Increases the volume and increases the negative intrapleural pressure - overcomes elastic recoil of lungs, pleural cavity filled with fluid which cannot expand.
- Lungs expand
- Diaphragm relaxes - quiet breathing = lung elastic recoil, increased ventilation = aided by internal intercostal and accessory muscles.
- Decreases the negative pressure and forces air out.
Which areas of the brain control ventilation and what specifically do they each control?
- Medulla - controls basic rhythm of respiration, respiratory pattern generator
- Apneustic centre - increases inspiration and prevents expiration
- Pneumotaxic centre - coordinates transition between inspiration and expiration (inhibits apneustic centre)
Where do the centres in the brain controlling respiration receive input from?
- Peripheral chemoreceptors - in the aortic arch (CN IX) and carotid body (CN X), they are stimulated by low oxygen and high CO2 and acidaemia.
- Central chemoreceptors - ventral medulla, stimulated by CO2 only in the CSF so cannot detect metabolic causes of acid-base imbalance, only respiratory.
What is a VQ mismatch?
Reduction in either perfusion (obstruction to blood supply) or ventilation (airway obstruction).
What is the extreme form of VQ mismatch where there is no blood perfusion?
Shunt
What are the early signs of respiratory failure?
Tachypnoea (more pronounced in type 1), agitation and decreased levels of consciousness.
What are the long term effects of hypoxia?
- Polycythaemia - decreased renal oxygenation, increased EPO.
- Cor pulmonale - hypoxic vasoconstriction of pulmonary vessels = pulmonary HTN, right heart hypertrophy, right sided heart failure.
- Fluid retention - decreased renal perfusion, RAAS upregulation.
What are the signs and symptoms of hypoxia?
Dyspnoea, restlessness, agitation, confusion, central cyanosis, polycythaemia (chronic), cor pulmonale (chronic).
What are the signs and symptoms of hypercapnia?
Headache, confusion, drowsiness, coma, peripheral vasodilation, bounding pulse, tremor/flap, papilloedema.
What are the long term effects of hypercapnia?
- Respiratory acidosis - compensated in chronic patients
2. Hypercapnic respiratory drive desensitised - partial switch to hypoxic drive.
What is type 1 respiratory failure?
A failure of oxygenation - hypoxia with a normal or low PaCO2.
What are the causes of type 1 respiratory failure and do they affect ventilation (V) or perfusion (Q)?
- Pneumonia (V)
- Pulmonary oedema (V)
- Pulmonary embolism (Q)
- Asthma (V)
- Emphysema (V)
- Pulmonary fibrosis (V)
What is the management for type 1 respiratory failure?
- Treat underlying cause
- O2 24-60% by facemask
- Assisted ventilation if PaO2 <8kPa despite 60% O2
What is type 2 respiratory failure?
A failure of pump - hypoxia with hypercapnia (alveolar hypoventilation)
What are the causes of type 2 respiratory failure?
- Pulmonary disease - asthma, COPD, pneumonia, end stage pulmonary fibrosis, OSA
- Reduced respiratory drive - sedative drugs, CNS tumour/trauma
- Neuromuscular disease - cervical cord lesion, diaphragmatic paralysis, myasthenia gravis, Guillain-Barre syndrome
- Thoracic wall disease - kyphoscoliosis
What is the management for type 2 respiratory failure?
- Treat underlying cause
- Controlled O2 therapy - start at 24%
- Recheck ABG after 20 mins, if PaCO2 steady then increased O2, if >1.5kPa then consider NIPPV (BiPAP)
- If NIPPV fails, intubation and ventilation
What is the key indication of non-invasive positive pressure ventilation?
COPD pH 7.25-7.35
What is non-invasive positive pressure ventilation and what are the two types?
Delivery of oxygen via tightly fitted mask:
- CPAP (continuous)
- BiPAP (bi-level positive airway pressure)
What ventilation is favoured in type 2 respiratory failure and why?
- BiPAP (CPAP for type 1)
2. Creates low pressure resistance for expiration
