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respiratory system > Oxygen Measurements + Oximetry > Flashcards

Oxygen Measurements + Oximetry Flashcards

1
Q

Define Oxygen capacity

A

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

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2
Q

Normal Hb levels for male:

A

160g/Litre

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3
Q

Normal Hb levels for female:

A

135g/Litre

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4
Q

How much can 1g of Hb combine with O2

A

1.34ml of O2

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5
Q

maximum amount body can carry

A

201ml/L

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6
Q

Explain Oxygen saturation

A

(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

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7
Q

What is SaO2 and SpO2

A

arterial oxygen saturation
peripheral oxygen saturation

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8
Q

Define oxygen content

A

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

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9
Q

Oxygen content equation

A

O content= o2 carried by Hb + O2 in solution

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10
Q

Calculate CaO2

A

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

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11
Q

Factors affecting O2 content

A
  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
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12
Q

anemia:

A

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

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13
Q

Define hypoxia, hypoxemia and cyanosis

A

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

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14
Q

Causes of Hypoxemia:

A
  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
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15
Q

pH of blood:

A

7.35-7.45

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16
Q

Standard partial pressure of CO2

A

4.8-6.0 kPa

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17
Q

standard Partial pressure of O2

A

10.0-13.5

18
Q

Standard O2 saturation

A

95-98%

19
Q

Standard HCO3- concentration

A

22.0-26.0 mmol/L

20
Q

What is respiratory failure?

A

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

21
Q

Vital signs associated with oximetry

A

Temperature
Oxygen saturation
Pulse
Blood pressure
Respiratory rate

22
Q

What does arterial blood measure?

A

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

23
Q

How is arterial blood received and how is it analyzed

A

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

24
Q

Disadvantages of arterial blood gas sampling

A

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

25
Q

Define and explain earlobe capillary blood gas sample

A

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

26
Q

Advantages of the earlobe gas sample

A

It is less invasive and less painful

27
Q

Disadvantages of earlobe gas sampling

A

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

28
Q

What is a pulse oximeter

A

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

29
Q

Abnormal O2 saturation range

A

94-98%

30
Q

If it falls 55% or lower then..

A

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

31
Q

oxygen saturation target for respiratory patients

A

88-92%

32
Q

Explain type 1 respiratory failure

A

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

33
Q

Explain type 2 respiratory failure

A

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

34
Q

Advantages of oximeters?

A

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

35
Q

When would pulse oximeters be used?

A

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

36
Q

What is a spot check oximeter measurement?

A

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

37
Q

What is a bedside oximeter needed for?

A

Needed for continuous monitoring e.g., overnight

38
Q

What is a recording oximeter used for?

A

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

39
Q

Limitations of Oximetry

A

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

40
Q

How to perform an oximetry

A
  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

respiratory system (10 decks)

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