Respiratory Failure Flashcards
Define type 1 respiratory failure
Hypoxia PaO2<8kPa with a normal or low paCO2.
What are normal values for PaO2, PaCO2 and pH and HCO3
PaO2 = 10.6-13.3 kPa PaCO = 4.7-6.0 kPa ph = 7.35-7.45 HCO3 = 22-26mmol/L
What causes type I respiratory failure?
Ventilation perfusion VQ mismatch Hypoventilation Abnormal diffusion Right to left cardiac shunts VQ mismatch can be caused by pneumonia, pulmonary oedema, PE, asthma, emphysema, pulmonary fibrosis, ARDS
What is VQ mismatch? What happens to compensate?
Ventilation to perfusion ratio is ideally 1:
ventilation rate is 5L/min, perfusion rate is 5L/min,
The ratio vaires dye to position of heart in relation of the lungs - and is on average 0.8
Increased ventilation and perfusion at base of lungs
Decreased ventilation and perfusion at apex of lung - gravity
If there is mismatch between alveolar ventilation and blood flow, VQ ratio may fall - thus, perfusion is greater than ventilation = pO2 will fall and pCO2 will rise.
Hypoxic vasoconstriction can occur to divert blood to better ventilated part of lungs however this is limited.
As a result pO2 is still low, causing hyperventilation –> normal or low CO2 levels
What is type 2 respirator failure?
Hypoxia (PO2 < 8kPa) and hypercapnia PCO2>6kPA)
What causes T2RF?
Alveolar hypoventilation with or without VQ mismatch.
Causes:
Pulmonary: asthma, COPD, pneumonia, pulmonary fibrosis, OSA
Reduced respiratory drive: sedative drugs, CNS tumour, trauma
Neuromuscular disease - cervical cord lesion
MSK - kyphoscoliosis
Where are chemoreceptors located and what do they detect?
Peripheral chemoreceptors are located at:
Aortic bodies detect changes in blood oxygen and CO2
Carotid body detect changes in O2, CO2 and pH
Central chemoreceptors are loaded on th ventrolateral surface of the medulla oblongata and detect changes in pH of CSF - respond to hypercapnic hypoxia (T2RF) but eventually desnsitise
Signal to respiroty centrer in the medulla oblongata to send impulses to intercostal muscles and diaphragm via intercostal and phrenic nerves to increase/decrease breathing rate/volume of lunges during inhalation
What are the clinical features of hypoxia?
Dyspnoea, restlessness, agitaiton, confusion, central cyanosis.
If long standing: polycythaemia, pulmonary hypertension, cor pulmonale
What are the clinical features of hypercapnia?
Headache, peripheralvasdilation, tachycardia, bounding pulse, CO2 retention flap/tremor, papilloedema, confusion, drowsiness, coma
What investigations for RF?
Bedside: SaO2 BP Bloods: FBC, ABG, U&E, CRP Imaging: CXR Micro: sputum and blood cultures Other: spirometry
What is management for T1RF?
Treat underlying cause
Give oxygen (24-60%) by facemask
Assisted ventilation if PaO2<8kPa despirte 60% O2
What is the management for T2FR?
Treat underlying cause
Controlled oxygen - respiration could be driven by hypoxia so be careful
Start at 24% O2
Recheck ABG after 20 mins
If pCO2 is steady or lower, increase O2 to 28%
If pCO2 has risen >1.5kPa consider NIV
If this fails intubation and ventilation
What are the options for delivering oxygen?
Nasal cannulae
Simple face mask
Venturi mask
Non-rebreathing mask
What is the flow rate in nasal cannulas and what is their use?
1-4L.min
O2 conc of 24-40%
Used to Maintain SaO2 when neb are run using air
What are simple face masks for?
Deliver a variable amount of O2 depending on the rate of inflow
Less precise than venturi masks - so don’t use if hypercapnia or T2FR as risk fo CO@ accumulation within mask and so in inspired gas if flow rate < 5L/min
