Oxygen Therapy Flashcards
What are the indications for oxygen therapy
- known hypoxaemia
- acutely unwell patients when hypoxaemia is likely
What are the two ways to measure oxygen levels
- oxygen saturation
- partial pressure of oxygen
How much percentage of oxygen in blood is bound to haemoglobin
97%
How can you measure the oxygen saturation levels
- Pulse oximetry (SpO2)
- direct from arterial blood sample - SaO2
how can you monitor the remain 3% of oxygen that is not bound to haemoglobin
- this is the partial pressure of oxygen in the blood referred to as PaO2 (kPa) or in mmHg
even if the SpO2 is 100% the PaO2 can continue to rise above normal why is this
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.
what factors shift the oxyhemoglobin curve right
- drop in pH
- hypercapnia (rise in CO2)
- rise in temperature
What factors shift the oxyhaemoglobin curve left
- drop in temperature
- decrease in CO2
- rise in pH
What information does the ABG give
- dissolved CO2
- pH
- amount of bicarbonate
- base excess
What is type 1 respiratory failure
If the PO2 is < 8KPa and the PaCO2 is normal, then refer to this as Type 1 Respiratory failure.
What is type 2 respiratory failure
If the PO2 is < 8KPa and the PCO2 is high, then we refer to this as Type 2 Respiratory failure.
What is pH
This is a measure of the amount of hydrogen ions
the more hydrogen ions….
the more acidotic the solution and the lower the pH
What is PaCO2
This is a ‘respiratory parameter’3 and measures the dissolved carbon dioxide in the blood.
what does reduced ventilation do
Reduced ventilation would lead to a rise in CO2, which creates more acid, lowering the pH
What does increased ventilation do
Increased ventilation would lead to a reduction in CO2, which reduces the amount of acid, raising the pH
how long do bicarbonate changes take to happen
The kidneys can retain or excrete HCO3- in response to pH, but changes in bicarbonate levels tend to take more time (hours to days).
A high level of bicarbonate ions…
indicate alkalosis
What is base excess
Base excess (BE) is ‘the amount of base that would have to be removed (or balanced with H ) to order to correct the pH’
What does a low base excess indicate
A low BE (< 2) indicates acidosis
What does a high base excess indicate
A high BE (> 2) indicates alkalosis.
What is compensation
This is how the body tries to keep the pH within normal limits.
What are the normal values
- pH
- PCO2
- PO2
- HCO3-
- base excess
- SaO2
- 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%
if the patient is critically ill how much oxygen do you give them and in what way
give 15Litres of oxygen via a non- re-breathe mask
what device gives the maximum amount of oxygen to a patient
non rebreathe mask
what is the stimulus to breath in most people
- high carbon dioxide is the stimulus to breath
describe how COPD patients have there drive to breath
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
What oxygen levels do you give in patients who are vulnerable to hypercapnia respiratory failure
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.
name the different types of venturi masks
- there colour
- litres a minute
- percentage of oxygen
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
What oxygen litres do nasal cannulae give
- 1 l/min
- 2 l/min
- 4 l/min
What oxygen litres do nasal cannulae give
- 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%
What do you do if the patients oxygen concentration is 100% and 15 l/min
titrate the oxygen dow
- allow at least 5 minutes at each dose before adjusting further upwards or downwards
what devices supply a variable oxygen concentration
- face mask
- nasal cannula
how do you not rebreath carbon dioxide in a non-rebreathe reservoir mask
- 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
