Oxygen Therapy

Question 1

What are the indications for oxygen therapy

Answer 1

• known hypoxaemia

- acutely unwell patients when hypoxaemia is likely

Question 2

What are the two ways to measure oxygen levels

Answer 2

• oxygen saturation

- partial pressure of oxygen

Question 3

How much percentage of oxygen in blood is bound to haemoglobin

Answer 3

97%

Question 4

How can you measure the oxygen saturation levels

Answer 4

• Pulse oximetry (SpO2)

- direct from arterial blood sample - SaO2

Question 5

how can you monitor the remain 3% of oxygen that is not bound to haemoglobin

Answer 5

• this is the partial pressure of oxygen in the blood referred to as PaO2 (kPa) or in mmHg

Question 6

even if the SpO2 is 100% the PaO2 can continue to rise above normal why is this

Answer 6

When PaO2 drops, with will SaO2. When PaO2 rises, so does SaO2. When the SaO2 (or SpO2) reaches 100%, the haemoglobin is fully saturated. But more oxygen can still dissolve into the blood.

Question 7

what factors shift the oxyhemoglobin curve right

Answer 7

• drop in pH
• hypercapnia (rise in CO2)
• rise in temperature

Question 8

What factors shift the oxyhaemoglobin curve left

Answer 8

• drop in temperature
• decrease in CO2
• rise in pH

Question 9

What information does the ABG give

Answer 9

• dissolved CO2
• pH
• amount of bicarbonate
• base excess

Question 10

What is type 1 respiratory failure

Answer 10

If the PO2 is < 8KPa and the PaCO2 is normal, then refer to this as Type 1 Respiratory failure.

Question 11

What is type 2 respiratory failure

Answer 11

If the PO2 is < 8KPa and the PCO2 is high, then we refer to this as Type 2 Respiratory failure.

Question 12

What is pH

Answer 12

This is a measure of the amount of hydrogen ions

Question 13

the more hydrogen ions….

Answer 13

the more acidotic the solution and the lower the pH

Question 14

What is PaCO2

Answer 14

This is a ‘respiratory parameter’3 and measures the dissolved carbon dioxide in the blood.

Question 15

what does reduced ventilation do

Answer 15

Reduced ventilation would lead to a rise in CO2, which creates more acid, lowering the pH

Question 16

What does increased ventilation do

Answer 16

Increased ventilation would lead to a reduction in CO2, which reduces the amount of acid, raising the pH

Question 17

how long do bicarbonate changes take to happen

Answer 17

The kidneys can retain or excrete HCO3- in response to pH, but changes in bicarbonate levels tend to take more time (hours to days).

Question 18

A high level of bicarbonate ions…

Answer 18

indicate alkalosis

Question 19

What is base excess

Answer 19

Base excess (BE) is ‘the amount of base that would have to be removed (or balanced with H ) to order to correct the pH’

Question 20

What does a low base excess indicate

Answer 20

A low BE (< 2) indicates acidosis

Question 21

What does a high base excess indicate

Answer 21

A high BE (> 2) indicates alkalosis.

Question 22

What is compensation

Answer 22

This is how the body tries to keep the pH within normal limits.

Question 23

What are the normal values

• pH
• PCO2
• PO2
• HCO3-
• base excess
• SaO2

Answer 23

• pH: 7.35 to 7.45
• PCO2: 4.6 – 6.4 kPa
• PO2: 10.6 to 13.5 kPa
• HCO3-: 22 to 28 mmol/l
• BaseExcess: -2 to +2 mmol/l
• SaO2: >96%

Question 24

if the patient is critically ill how much oxygen do you give them and in what way

Answer 24

give 15Litres of oxygen via a non- re-breathe mask

Question 25

what device gives the maximum amount of oxygen to a patient

Answer 25

non rebreathe mask

Question 26

what is the stimulus to breath in most people

Answer 26

- high carbon dioxide is the stimulus to breath

Question 27

describe how COPD patients have there drive to breath

Answer 27

Traditionally we thought that patients with COPD developed a hypoxic (low O2) drive due to chronically high levels of CO2. It was thought that if high levels of oxygen were administered to these patients, they would lose their hypoxic drive, causing a respiratory depression2, 6 hypoventilation and dangerous hypercapnia - studies have now shown that reduction in respiratory drive is not a major contribution to oxygen induced hypercapnia in patient with acute exacerbation of COPD - much of the rise in CO2 occurs during high dose oxygen therapy is due to deterioration in the matching of blood flow and gas flow in the lungs

Question 28

What oxygen levels do you give in patients who are vulnerable to hypercapnia respiratory failure

Answer 28

In patients who are vulnerable to hypercapnic respiratory failure (e.g. in COPD), give 24 to 28% oxygen therapy to maintain oxygen saturation at 88 – 92%. Monitor O2 and CO2 levels with repeat ABGs.

Question 29

name the different types of venturi masks - there colour - litres a minute - percentage of oxygen

Answer 29

Blue - 24% - 2-4L/min White - 28% - 4-6l/min Yellow - 35% - 8-10 l/min Red - 40% - 10-12 l/min Green - 60% - 12-15l/min

Question 30

What oxygen litres do nasal cannulae give

Answer 30

- 1 l/min - 2 l/min - 4 l/min

Question 31

What oxygen litres do nasal cannulae give

Answer 31

- 1 l/min - should increase inspired oxygen by about 3-4% (from 21% at room to 24% - 2 l/min - 4 l/min - for each additional litre the oxygen concentration should go up by 4%

Question 32

What do you do if the patients oxygen concentration is 100% and 15 l/min

Answer 32

titrate the oxygen dow | - allow at least 5 minutes at each dose before adjusting further upwards or downwards

Question 33

what devices supply a variable oxygen concentration

Answer 33

- face mask | - nasal cannula

Question 34

how do you not rebreath carbon dioxide in a non-rebreathe reservoir mask

Answer 34

- a non-rebreathe mask has a one way valve between the reservoir bag and the mask - this means that exhaled carbon dioxide does not enter the bag