Oxygen Measurements + Oximetry

Question 1

Define Oxygen capacity

Answer 1

the max quantity of O2 which can combine with Hb in a unit volume of blood

Question 2

Normal Hb levels for male:

Answer 2

160g/Litre

Question 3

Normal Hb levels for female:

Answer 3

135g/Litre

Question 4

How much can 1g of Hb combine with O2

Answer 4

1.34ml of O2

Question 5

maximum amount body can carry

Answer 5

201ml/L

Question 6

Explain Oxygen saturation

Answer 6

(SO2)
when O2 is fully saturated, 4 binding sites on HB all have O2 bound to them (100)%
normal O2 sat is 95-98%
Can be measured by an oximeter

Question 7

What is SaO2 and SpO2

Answer 7

arterial oxygen saturation
peripheral oxygen saturation

Question 8

Define oxygen content

Answer 8

is the total volume of oxygen carried by the blood
units ml per litre

Question 9

Oxygen content equation

Answer 9

O content= o2 carried by Hb + O2 in solution

Question 10

Calculate CaO2

Answer 10

(1.34xhb)x SaO2/100 +(0.225 xPaO2)
=201+3
=204ml of O2 per litre of blood

Question 11

Factors affecting O2 content

Answer 11

1. partial P of inspired O2
2. efficiency of ventilation and gas exchange
3. Hb level and affinity of Hb for O2
   PaO2 (partial arterial pressure) determines o2 saturation of Haemoglobin

Question 12

anemia:

Answer 12

The partial pressure of O2 is normal, low hemoglobin, has normal oxygen saturation, as sites that are available are saturated, just less sites for binding

Question 13

Define hypoxia, hypoxemia and cyanosis

Answer 13

Hypoxemia- lack of O2 in the blood
Hypoxia- reduced O2 to the tissues
Cyanosis- blue coloration of skin and mucus membranes resulting from raised levels of deoxyhemoglobin caused by hypoxemia

Question 14

Causes of Hypoxemia:

Answer 14

1. Hypoventilation (not breathing efficiently): causes raised CO2 in the blood (hypercapnia)
2. diffusion limitation: e.g., lung fibrosis, problem getting O2 across alveoli membrane, CO2 is more soluble
3. Shunt: blood that has gone through the lungs, but has not been ventilated
4. V/Q mismatch: Ventilation and perfusion,
   diseases cause large mismatch causing so areas to not be ventilated, but still perfused, leading to hypoxemia

Question 15

pH of blood:

Answer 15

7.35-7.45

Question 16

Standard partial pressure of CO2

Answer 16

4.8-6.0 kPa

Question 17

standard Partial pressure of O2

Answer 17

10.0-13.5

Question 18

Standard O2 saturation

Answer 18

95-98%

Question 19

Standard HCO3- concentration

Answer 19

22.0-26.0 mmol/L

Question 20

What is respiratory failure?

Answer 20

Where the patient is severely hypoxemic, PaO2 below 10kPa, below 8kPa is called respiratory failure

Question 21

Vital signs associated with oximetry

Answer 21

Temperature
Oxygen saturation
Pulse
Blood pressure
Respiratory rate

Question 22

What does arterial blood measure?

Answer 22

pH, PaO2, PaCO2, SaO2%, and HCO3- concentration
as well as creatine, hb, electrolytes, Hb, lactate and glucose levels

Question 23

How is arterial blood received and how is it analyzed

Answer 23

Arterial blood is collected from an artery in the wrist
It is measured by a blood gas analyzer

Question 24

Disadvantages of arterial blood gas sampling

Answer 24

The machines are very expensive and do not give instant results. There is a delay between taking the blood and analysing the results.
Individual components are costly,
For patients, it is an invasive and painful process
It needs to be carried out by specially trained staff

Question 25

Define and explain earlobe capillary blood gas sample

Answer 25

A sample of blood is taken from the earlobe, using a scalpel and a capillary tube. The ear needs to be well perfused (rubbed) to circulate blood flow, rub with a paper towel

Question 26

Advantages of the earlobe gas sample

Answer 26

It is less invasive and less painful

Question 27

Disadvantages of earlobe gas sampling

Answer 27

Needs specially trained staff It is slightly painful Not the most accurate form of blood sampling, tend to give an underestimate of O2 saturation, Too much compression may cause interstitial fluid to be collected alongside blood

Question 28

What is a pulse oximeter

Answer 28

It consists of a small probe which measures O2 saturation and pulse rate, it is not invasive nor painful

Question 29

Abnormal O2 saturation range

Answer 29

94-98%

Question 30

If it falls 55% or lower then..

Answer 30

Person is at risk of losing consciousness, this could lead to death, brain damage or organ failure

Question 31

oxygen saturation target for respiratory patients

Answer 31

88-92%

Question 32

Explain type 1 respiratory failure

Answer 32

This is a failure in oxygenation, there is low levels of oxygen in the blood with normal/ reduced PaCO2

Question 33

Explain type 2 respiratory failure

Answer 33

This is a failure in ventilation, this involves hypoxemia as well as hypercapnia, as movement of air out of the lungs is reduced, prevents CO2 from being eliminated from blood, so builds up, affecting blood pH

Question 34

Advantages of oximeters?

Answer 34

Non-invasive not painful no specialist training needed cheaper easier to use compact and portable can be used for continuous monitoring

Question 35

When would pulse oximeters be used?

Answer 35

Pre-op acute emergencies Hypoxia challenges excercise and sleep studies spot check measurements

Question 36

What is a spot check oximeter measurement?

Answer 36

used for a single test, measures O2 saturation and pulse rate. It can sometimes show us volume changes in blood,

Question 37

What is a bedside oximeter needed for?

Answer 37

Needed for continuous monitoring e.g., overnight

Question 38

What is a recording oximeter used for?

Answer 38

To measure oxygen saturation and pulse rate, over a period of time as it is able to store data, used mostly in sleep and exercise studies

Question 39

Limitations of Oximetry

Answer 39

Only measures O2 sat & PR, ignores pH, PaO2, PaCO2, HCO3- conc, Hb levels, can lack accuracy and precision as oximeters differ between manufacturers May suffer electromagnetic interference and light interference Artefacts may be produced if patient it moving Cannot distinguish between HbO2 and HbCO, this may give a falsely high reading, as CO binds better than O2, Skin pigmentation may affect reading, those with darker skin may get a false reading Probe applied incorrectly e.g., upside down

Question 40

How to perform an oximetry

Answer 40

1. wash your hands & apply PPE, introduce yourself, give patient details and check their identity, explain the procedure 2. obtain verbal consent & allow the patient to sit comfortably for 5+ mins 3. remove any nail polish, rings etc from the left index finger 4. make sure hands are warm & well perfused 5. Select probe and apply it correctly, note down date, time & site of probe 6. If patient on O2, record flow rate & make note of it 7. check pulsatile signal, if abnormal check patient's pulse on the wrist 8. compare against blood gas sample, allow reading to stabilize 9. record results, remove probe, clean probe 10. tell patient results & produce a written report which includes: date, time, your name & title, type of oximeter, SaO2 and pulse rate