Respiratory: Oxygen therapy Flashcards
In patients who are critically ill (anaphylaxis, shock etc) how should oxygen be delivered? [2]
In patients who are critically ill (anaphylaxis, shock etc) oxygen should initially be given via a reservoir mask at 15 l/min.
Why is the haemoglobin dissociation curve a sigmoid shape? [1]
Due to co-operative binding of oxygen to haemoglobin. Is difficult to bind first O2, but once it does, it chanages shape and becomes easier to bind. Once have 4 O2s bind, curves off again
What shifts oxygen haemoglobin to the right? [5]
What happens to oxygen release when this happens? [1]
Shift to right:
* Increased CO2
* Decreased pH
* Increased temperature
* Increased 2,3 DPG
* Exercise
When moves to right, becomes easier to release (Bohr Shift)
What is the difference betwen hypxoia and hypoxaemia? [2]
Hypoxia: failure of tissue oxygenation
Hypoxaemia: low arterial oxygen concentration (i.e. low partial pressure of blood oxygen)
What are the five causes of tissue hypoxia? [5]
Hypoxaemic hypoxia: due to hypoventilation, ventilation/perfusion (V/Q) mismatch, or pulmonary shunts
Circulatory hypoxia: due to inadequate cardiac output
Anaemic hypoxia
Histotoxic hypoxia: inability of the tissue to use oxygen (e.g. cyanide poisoning)
Oxygen affinity hypoxia: decreased oxygen delivery to tissue (i.e. haemoglobin holds onto oxygen)
What are the two major target saturations for patients being treated with oxygen? [2]
94-98%: patients NOT at risk of type 2 respiratory failure
88-92%: patients WITH, or at risk of, type 2 respiratory failure
Which patient groups are at risk of type 2 respiratory failure? [5]
Moderate-to-severe chronic obstructive pulmonary disease (COPD): may be undiagnosed
Cystic fibrosis
Severe obesity (i.e. obesity hypoventilation syndrome)
Neuromuscular disease (e.g. Motor neurone disease)
Severe chest wall deformity (e.g. kyphoscoliosis)
Previous episode of T2RF
What do need to consider with oxygen therapy and T2RF? [1]
In patients with, or at risk of, T2RF higher levels of oxygen can induce or worsen hypercapnia due to a combination of ventilation/perfusion mismatch and increased physiological deadspace.
Therefore, we can get oxygen-induced hypercapnia.
Name an AE of oxygen therapy? [1]
Can cause vasoconstriction
Which of the following is a non-rebreather reservoir bag
1
2
3
4
Which of the following is a non-rebreather reservoir bag
1
2
3
4
Which of the following is a simple face mask?
1
2
3
4
Which of the following is a simple face mask?
1
2
3
4
Which of the following is a venturi device?
1
2
3
4
Which of the following is a venturi device?
1
2
3
4
What is rate of oxygen nasal cannulae can delive? [1]
What oxygen rate should nasal cannulae not be given more than? [1]
Why? [1]
2 - 6 l/min
do not exceed 4L/min as will dry out the nasal passages, leading to irritation
When should nasal cannulae not be used? [1]
Do not use if the patient mainly breathes through their mouth
Which face masks are predominately used for T1RF? [1]
Simple face mask
Simple face masks deliver what oxygen flow between what range? [1]
What oxygen concentration does this cause? [1]
Delivers oxygen between 5-10L/min
Creates variable oxygen conc between 35-60%
What kPa is hypoxia defined as? [1]
< 8 kPa
Why is humidification of air important? [2]
Stops airways becoming dry: tissues become dry and have a risk of mucosal bleeding
Helps decrease amount secretion
When is humidified oxygen indicated in patients? [1]
If delivering more than 24hr for moderate to high flow rate oxygen systems
When is a non-rebreather / reservoir mask indicated? [1]
Critical illness / trauma patients
What oxygen flow rate does a non-rebreather mask deliver? [1]
What FiO2 does this equate to? [1]
Delivers up to 15L/min, which approximately equates to 70-90% FiO2 (does not deliver 100% FiO2 as some room air will escape into the mask due to the mask not being perfectly adherent to the face)
What is high flow nasal cannulae? [1]
Why is it particularly useful? [2]
High-flow nasal cannula (HFNC) therapy is an oxygen supply system capable of delivering up to 100% humidified and heated oxygen at a flow rate of up to 60 liters per minute.
Can provide PEEP 7.4cm H20 (PEEP: Positive end-expiratory pressure; stops airways from collapsing due to pressure)
What is the difference between venturi masks and other oxygen delivery methods? [1]
What is important to remember about venturi masks? [1]
Delivers specific concentration of oxygen
Increasing flow does NOT increase oxygen concentration
Explain how venturi masks work?
Where the oxygen is delivered, there is a constriction in the mask.
Arrives in the mask at low speed, and therefore high pressure.
As moves through the constriction point, the speed increases and causes decreases in pressure
But then moves into larger chamber, speed goes down and pressure goes up.
But having fixed sized apertures where air can enter allows specific amount of air into delivery device. Means you can deliver a fixed concentration of oxygen.
What are the differences between the different coloured venturi masks? [1]
NB: mechanics of the masks
Have different sized apertures to allow different volume of air into the mask
On a venturi mask, it states:
‘24% (set at 2L/min)’
What does this actually mean? [1]
The mask needs flow of 2L/min to deliver 24% oxygen concentration to a patient.
(If dial up more, will still only deliver 24%)
Explain the physiology of why delivering oxygen to COPD patients is different to normal patients [2]
COPD patients are used to being in a hypercapnic state, so their respiratory drive becomes determined by oxygen levels: aka they rely on their hypoxic drive (Normally respiratory drive, is detected in the carotid body by the levels of pCO2)
If give oxygen, you reduce the ventilatory drive and may become hypercapnic
Can cause CO2 retention leading to narcosis / respiratory arrest
What % of COPD patients are CO2 retainers? [1]
5-15%
What is more dangerous: hypercapnia or hypoxia? [1]
Why is this clinically significant? [1]
hypoxia
In absolute acute setting; give oxygen, but be really aware may be COPD patients and adapt
What should you do when admitting a COPD patient when starting O2 therapy? [1]
Baseline ABG and repeat in 30mins after starting O2 therapy
Would you prescribe oxygen? [1]
If so, what device? [1]
Yes, via face mask
Would you prescribe oxygen? [1]
If so, what device? [1]
Via venturi
Would you prescribe oxygen? [1]
If so, what device? [1]
Yes, non-rebreather
Would you prescribe oxygen? [1]
If so, what device? [1]
No
Would you prescribe oxygen? [1]
If so, what device? [1]
Nasal cannulae / face mask
Why is she hypoxic? [1]
PE
Shirley Bennett is a 75 year old lady admitted with an infective exacerbation of COPD. Initial investigations revealed that she was hypoxic. Supplemental oxygen was delivered via a 24% venturi mask. When would be the next time to repeat an ABG?
Question 2Select one:
a.
20 - 30 minutes after starting oxygen
b.
0-20 minutes after starting oxygen
c.
30 - 60 minutes after starting oxygen
d.
After 1 hour on oxygen
Shirley Bennett is a 75 year old lady admitted with an infective exacerbation of COPD. Initial investigations revealed that she was hypoxic. Supplemental oxygen was delivered via a 24% venturi mask. When would be the next time to repeat an ABG?
Question 2Select one:
a.
20 - 30 minutes after starting oxygen
b.
0-20 minutes after starting oxygen
c.
30 - 60 minutes after starting oxygen
d.
After 1 hour on oxygen
Aliya Fuentes is an 18 year old lady. She was admitted with an acute exacerbation of her asthma. SHe is a social smoker of 2 cigarettes a week, she has smoked for the last year. On examination, her oxygen saturations were 92%, BP 135/84mmHg, HR 95bpm, RR 24/min. On asculatation of her lungs she was found to have a bilateral polyphonic wheeze. What would be the next best oxygen device and oxygen flow rate to start?
Select one:
a.
Simple Face Mask, 2 L/min
b.
Nasal Cannulae 6 L/min
c.
Venturi Mask 35%
d.
Nasal cannulae, 2 L/min
e.
Reservoir mask,15 L/min
Aliya Fuentes is an 18 year old lady. She was admitted with an acute exacerbation of her asthma. SHe is a social smoker of 2 cigarettes a week, she has smoked for the last year. On examination, her oxygen saturations were 92%, BP 135/84mmHg, HR 95bpm, RR 24/min. On asculatation of her lungs she was found to have a bilateral polyphonic wheeze. What would be the next best oxygen device and oxygen flow rate to start?
Select one:
a.
Simple Face Mask, 2 L/min
b.
Nasal Cannulae 6 L/min
c.
Venturi Mask 35%
d.
Nasal cannulae, 2 L/min
e.
Reservoir mask,15 L/min
Which of the following oxygen concentrations are delivered by the simple face mask?
Question 4
a.
40-60%
b.
80-100%
c.
20-40%
d.
60-80%
Which of the following oxygen concentrations are delivered by the simple face mask?
Question 4
a.
40-60%
b.
80-100%
c.
20-40%
d.
60-80%
Steve Cummings is a 45 year old gentleman with a previous medical history of myasthenia gravis. He was admitted with difficulty in breathing. He has never smoked and has a normal BMI. His oxygen saturations are found to be 83%. What should his target oxygen saturations be?
Select one:
a.
100%
b.
90-94%
c.
≥85%
d.
88-92%
e.
94-98%
f.
90-92%
Steve Cummings is a 45 year old gentleman with a previous medical history of myasthenia gravis. He was admitted with difficulty in breathing. He has never smoked and has a normal BMI. His oxygen saturations are found to be 83%. What should his target oxygen saturations be?
Select one:
a.
100%
b.
90-94%
c.
≥85%
d.
88-92%
e.
94-98%
f.
90-92%
