Hypoxaemia Flashcards
Difference between hypoxaemia and hypoxia?
hypoxaemia is low oxygen in the blood whereas hypoxia is low in the tissues
2 ways to measure oxygen in the blood?
Pulse oximetry or ABG
What is the normal partial pressure of oxygen in the blood?
10-14 kPa
How does hypoventilation cause hypoxaemia?
Decrease removal of co2, co2 build up in alveoli, reduce o2 in alveoli, reduce gradient and therefore transfer of oxygen into blood, high PaCO2 in blood
How do you correct hypoxaemia caused by hypoventilation?
Supplement oxygen
What can cause hypoventilation?
CNS depression, drugs like opioids and sedatives, neuromuscular disorders, airway obstruction
How do changes in ventilation and perfusion effect levels of oxygen and co2 in the alveolar sacs?
If ventilation reduces but perfusion remains the same, alveoli will have low oxygen high co2
If ventilation remains the same but perfusion decreases then alveoli will have high oxygen and low co2
What 3 conditions causes ventilation perfusion mismatch
Obstructive lung disease, interstitial lung disease, pulmonary vascular disease
How do you correct hypoxaemia caused by ventilation perfusion mismatch
Moderate oxygen supplementation
What happens to the ventilation and perfusion in PE?
large areas of dead space
ventilation but not perfused
Alveoli have high oxygen and low CO2 but cant diffuse
Define what is meant by a shunt?
Shunt is when there is no ventilation but perfusion is maintained so hypoxic blood returns to heart
Causes of shunt in the lungs?
atelectasis collapsed lung pulmonary oedema secretions (infective or not) blood cancer
What are the main reasons for a shunt occuring?
Collapsed alveoli
Alveoli filled with a fluid
PE
Name 2 conditions cause abnormal diffusion and therefore hypoxaemia? When are symptoms noticed to be worse?
Interstitial lung disease
Fibrosis
Noticed to be worse on exercise as perfusion faster and ventilation isnt
reduced inspired o2 occurs in what conditions?
high altitudes
If a patient presents as hypoxaemic what are causative signs are you initially checking for whilst performing ABCDE?
Are they hypoventilating? sedatives? airway obstruction?
Mechanical issues/shunting? rib fractures? pneumothorax? atelectasis? collapsed lung? pleural effusion?
If the cause of hypoxaemia is by full or collapsed alveoli, what do you do instead of oxygen supplementation?
Sit patient upright deep breaths and cough pulmonary oedema - diuretics Infection - culture and antibiotics Incentive spirometer Physio Treat pain High flow nasal oxygen -airvo CPAP or NIV
When do you consider a referral to critical care for hypoxaemia?
IF they are on 60% FiO2/Airvo and remaining hypoxaemic or if they are failing
What 3 investigations would you consider in someone with hypoxaemia?
ABG, CXR, CTPA
How should the FiO2 correspond to the PaO2/sats
Their FiO2 should be 10 more than their PaO2
If a patient is on oxygen, what information is it important to give alongside their oxgen sats or PaO2?
The concentration of oxygen they are inhaling
Example of a high flow nasal oxygen that can be given?
Airvo
What does Airvo do? Who is it useful for?
Fills the upper airways with a low level CPAP system
Useful for short of breath who have increased minute ventilations of over 15l/min as supplementary oxygen wouldnt provide enough and they’d end up diluting with room air
Why is high flow nasal oxygen limited to 60% oxygen?
risk that using HFNO needs steadily increasing FiO2 as demands increase to the point that a sudden deterioration in patient condition wouldnt have any residual increase in oxygen left to help so limit unless emergency
