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
What are venturi masks? Colours and oxygen?
Provides a precise percentage or fraction of O2 at high flow rates Blue = 24% White = 28% Yellow = 35% Red = 40% Green = 60%
What is non-rebreathing mask?
Have reserver bag and deliver high concentrations of O2 (60-90%), determined by the inflow (10L-15L/min) and the presence of flap valves on the side
Used in emergency but are imprecise
What are other ways to increase oxygenation?
Treat anaemia - transfuse if essential
Improve CO - treat heart failure
Chest physio to improve VQ mismatch
How do you interpret ABG?
pH - acidosis/alkalosis pCO2 - high > 6 or low/normal < 4.7 does - If high and acidotic --> respiratory - if low and alkalotic --> respiratory HCO3 - high >26 or low <22 - low and acidotic --> metabolic - high and alkalotic --> metabolic pO2 - is this normal? Is there any compensation - renal compensation of respiratory or respiratory compensation o metabolic Calculate the base excess (anion gap): (Na + K) - (Cl + HCO3)
What is oxygen for patients who are acutely unwell?
15L/min via a non-rebreathable mask aim for 94-98% if pCO2 is normal
For COPD: 28% venturi mask at 4L/min and aim for 88-92%
What are SaO2 targets?
94-98% in acutely ill patients
Patients at risk of hypercapnia (COPD) : 88-92%
When not to use O2 therapy if there is no evidence of hypoxia
MI and ACS
Stroke
Obstetric emergency
Anxiety related hyperventilation
What causes respiratory acidosis?
COPD
Decompensation in asthma/pulmonary oedema
Sedative drugs - benzodiazepines, opiate overdose (hypoventilation leads to CO2 retention)
What causes respiratory alkalosis?
Anxiety leading to hyperventilation PE Salicylate poisoning CNS disorders - stroke, SAH, encephalitis Altitude Pregnancy
