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Year 3 - CR > Oxygen Therapy > Flashcards

Oxygen Therapy Flashcards

1
Q

what is the percentage of oxygen in the air

A

21%

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2
Q

why does the oxygen decrease from the atmosphere into the lung

A
  • mixing with dead space gases

- water vapour

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3
Q

describe the oxygen cascade

A
  • Oxygen starts as dry atmospheric gas at 21 kPa
  • it becomes humidified tracheal gas at 19.8 kPa
  • alveolar gas it turns to 14 kPa due to mixing with dead space
  • in arterial gas it goes down to 13.3 kPa
  • in capillary blood it is 6-7 kPa
  • and in the mitochondria it is 1-5 kPa
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4
Q

What does the oxygen bind to in haemoglobin

A

haem

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5
Q

Describe how oxygen binds to haemoglobin

A
  • its difficult for the first oxygen to bind to the haemoglobin
  • once that first oxygen molecule binds there is a conformation change and then oxygen binds to the haemoglobin more easily
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6
Q

describe what the oxygen haemoglobin dissociation curve shows you

A
  • shows the change in saturation with the change in partial pressure of oxygen
  • sigmoid shape due to the binding of oxygen to haemoglobin - first oxygen molecule is hard to bind but the conformation change makes it easier to bind
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7
Q

What shifts the oxygen dissociation curve right

A
  • high carbon dioxide
  • increase in temperature
  • pH - increase in acid (lower pH)
  • exercise
  • 2,3- DPG
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8
Q

What shift the oxygen dissociation curve to the left

A
  • lower CO2
  • higher pH
  • lower temperature
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9
Q

What happens when the oxygen dissociation curve is shifted to the right

A
  • oxygen release is easier
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10
Q

What are the two ways in which oxygen is delivered in a hospital setting

A
  • wall oxygen

- cylinder oxygen

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11
Q

how do you classify what oxygen supply patients should receive

A
  • Critical patients
  • most patients
  • selected COPD patients
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12
Q

What should the oxygen saturation not be below

A
  • below 90/94
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13
Q

If patients have an oxygen saturation above …

A

94% then you don’t need to deliver oxygen

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14
Q

what is the target oxygen stats for patients with COPD

A
  • 88-92%

- these patients are at risk of hypercapnia respiratory failure

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15
Q

What is the target stats for all other patients

A
  • greater than 94%
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16
Q

How should you administer oxygen in patients with COPD

A
  • venturi masks in patients with COPD
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17
Q

How do you measure oxygen saturations

A
  • pulse oximetry
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18
Q

What are the BTS oxygen prescribing guidelines

A
  • Critical illness requires high levels of oxygen supplementation
  • serious illness requires moderate level of oxygen if the patient is hyperaemic
  • COPD and other conditions require controlled or low-dose oxygen therapy
  • conditions for which patients should be monitored closely but oxygen therapy is not required unless the patient is hypoxaemic
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19
Q

What are the dangers of oxygen

A
  • free radicalisation - oxygen toxicity
  • flammable - explosive
  • loss of hypoxic drive
  • cause vasoconstriction
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20
Q

Name the 4 oxygen delivery devices

A
  • venturi mask
  • face mask
  • nasal cannulae
  • resovoir bag with face mask
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21
Q

Who is the nasal cannulae suitable for

A
  • for most patients with type 1 or type II respiratory failure
22
Q

How much oxygen can the nasal cannulae give

A
  • 2-5L a minute gives approximately 24-50% FIO2

- range as its not a fixed performance device - breath through your mouth

23
Q

What does the FIO2 depend on in nasal cannulae

A
  • oxygen flow rate
  • patients minute volume
  • inspiratory flow
  • pattern of breathing
24
Q

What are the benefits of nasal cannulae

A
  • comfortable and easily tolerated
  • no re-breathing
  • low cost
25
Q

Who do you use a simple face mask for

A

Type 1 respiratory failure

26
Q

What is type 1 respiratory failure

A

hypoxia less than 8 kPa but no hypercapnia

27
Q

What is type 2 respiratory failure

A

Hypoxia and hypercapnia

28
Q

Describe what flow the simple face masks gives

A
  • variable oxygen concentration between 35% and 60%
  • flow rate is 5-10L/min
  • flow must be at least 5L/min to avoid carbon dioxide build up
29
Q

In simple face masks what must the flow rate be above

A
  • flow must be at least 5L/min to avoid carbon dioxide build up
30
Q

What are the benefit and disadvantages of a simple face mask

A

+
- low cost

  • uncomfortable
31
Q

Who do you use humidified oxygen in

A
  • reasonable to use humidified oxygen for patients who require moderate to high flow oxygen systems for more than 24 hours or who report upper airway discomfort due to dryness
32
Q

Why do we humidify oxygen in the body

A
  • stops drying out the mucoua if this happened it would bleed
  • helps with secretions and prevents mucous plugging
33
Q

who do you use a high concentration reservoir mask in

A
  • non re-breathing reservoir mask
  • critical illness/trauma patients
  • post-cardiac or respiratory arrest
34
Q

What is the oxygen concentration in a high concentration reservoir mask

A
  • oxygen concentrations between 70-80% or above

- highest concentration of oxygen in non invasive delivery

35
Q

Who do you use a high flow nasal cannulae for

A
  • critical illness - non compliant with face masks

- effective longer term use if high concentrations of oxygen are required

36
Q

describe the flow and oxygen concentration in a high flow nasal cannulae

A
  • humidified and warmed for increased tolerance
  • oxygen concentrations range between 20-100%
  • flow rate is up to 60L/min
  • can provide PEEP 7.4cm H20 at 60L/min
37
Q

What is a PEEP

A

Positive end expiratory pressure (PEEP), is a pressure applied by the ventilator at the end of each breath to ensure that the alveoli are not so prone to collapse
- KEEPS ALVEOLI OPEN WHEN YOU EXPIRE

38
Q

What is a normal PEEP

A

5cm of water

39
Q

What is a venturi mask used for

A

COPD

40
Q

describe how venturi masks work

A
  • colour coded
  • deliver constant oxygen concentration
  • increasing flow does not increase oxygen concentration
41
Q

In an venturi mask increasing flow does not….

A

increase oxygen concentration

42
Q

describe the difference between a 24% and a 28% Venturi mask

A

For 24% Venturi mask, the typical oxygen flow of 2 l/min gives a total gas flow of 51 l/min

For 28% Venturi mask, 4 l/min oxygen flow, gives a total gas flow of 44 l/min

43
Q

What is the worry with COPD patients and oxygen

A
  • potential CO2 retention leading to narcosis and respiratory arrest
44
Q

What percentage of COPD patients are CO2 retainers

A

5-15%

45
Q

describe the pathophysiology in regards to COPD retainer patients

A
  • if too much oxygen is given patients loose their drive to breathe and can become hypercapnia and may be at risk of respiratory arrest
46
Q

what is worse hypoxia or hypercapnia

A

hypoxia

47
Q

How long does it take for a COPD patient to develop significant hypercapnia?

A
  • in an acute setting with a COPD patient you should give the oxygen as hypoxia is worse
  • takes 15 minutes to become hypercapnia
48
Q

what is the recommended treatment for COPD patients

A
  • initially on assessing acutely unwell patient - use 15L non rebreathe mask
  • target stats of 88-92%
  • use a venturi mask to titrate oxygen
  • take a baseline ABG and repeat it 30 minutes after starting oxygen therapy
49
Q

How do you measure shifts to the right on the oxygen haemoglobin dissociation curve

A
  • use P50 marker
50
Q

what is the normal for

  • PO2
  • PCO2
  • HCO3-
  • standard HCO3-
  • base deficit
A
  • PO2 = 10.6-13.3 kPa (80-100mmHg)
  • HCO3- (22-26mmol/l)
  • PCO2 ( 4.8-6.1 kPa) (36-46mmHg)
  • standard HCO3- = 22-26mmol/l
  • base deficit +- 2.5
51
Q

Why do you use a non breathe face mask

A
  • higher concentration of oxygen - gives you 60-80 % whereas a rebreather face mask gives you 40-60%

Year 3 - CR (44 decks)

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