Oximetry

Question 1

What are the vital signs we look for when assesing?

Answer 1

-pulse
-blood pressure
-temperature
-respiratory rate
-oxygen saturation

Question 2

what is the standard method of assessing blood gases?

Answer 2

arterial blood gas samping

Question 3

what are standard measurement of arterial blood gas?

Answer 3

-Ph
-PaO2
-Paco2
-Sao2
-bicarbonate (HCO3-)

Question 4

What are some other measurement s of arterial blood gas?

Answer 4

-electrolytes such as calcium,sodium,potasium,chloride

-metabolites such as glucose,creatine and lactate

-haemoglobin level
-different forms of haemoglobin such as oxyhaemoglobin, deoxyhaemoglobin and carboxyhaemoglobin

Question 5

How do we analyse arterial blood gas measurements?

Answer 5

blood gas analysis

(need a hepronised sample)

Question 6

What are some disadvantages of blood gas measurements?

Answer 6

-invasive procedure
-uncomfortable for patient
-need specially trained staff
-equiptment is expensive
-delay between sampling and availability of results
-analysers are usually hospital based
-consumables are very expensive

Question 7

Whats the visual difference between arterial and venous blood?

Answer 7

-arterial is a brighter red that venous blood

Question 8

What is the other technique we use instead of arterial blood gas measurements?

Answer 8

earlobe cappilary blood gas sampling

Question 9

What are some disadvantages of earlobe cappilary blood gas sampling?

Answer 9

-must be skilled/trained
-sometimes you dont stab the ear so it doesnt bleed as well, then they squeeze the ear which causes more interstital fluid to arise

Question 10

what is a pulse oximeter?

Answer 10

-small probe usually attached to finger
-can be used for a single check of oxygen saturation or long term monitoring
-probe measures SpO2 or pulse rate

Question 11

What does a pulse oximeter measure?

Answer 11

-indirect,non invasive estimate of arterial oxygen saturation
-detects hypoxaemia earlier than cyanosis can be seen

Question 12

what are normal rates for a pulse oximeter?

Answer 12

SpO2- 95%-98%
Pulse-60-100BPM

Question 13

what is the oxygen saturation os someone at risk of type 2 respiratory failure?

Answer 13

88-92%

Question 14

At what oxygen level will patients loose conciousness?

Answer 14

55%
-in danger of dying or having permanent brain damage or organ failure

Question 15

Why do we use pulse oximeters?

Answer 15

-non invasive
-rapid result
-cheap
-easy to use
-portable
-continuouse monitoring

Question 16

What are some clinical applications of pulse oximetry?

Answer 16

-acute emergencies
-hypoxic challenges
-ambulatory oxygen walk test
-long term oxygen therapy assesment
-theatre
-spot check
-cardiopulmonary excersise test
-overnight sleep studies
-excersise tolerance test

Question 17

describe a recording oximeter

Answer 17

-used in excersise testing
-stores information which can be downloaded for analysis
-commonly used for overnight analysis

Question 18

Describe a bedside oximeter

Answer 18

-inpatient use
-continuous monitoring

Question 19

What are some limitations of oximetry?

Answer 19

-equiptment
-patients

-what it doesnt measure- eg ph, paO2 ect

Question 20

What are some equiptment limitations of pulse oximetry?

Answer 20

-artefacts and innacuracies
-calibration
-memory
accuracy and prescion
sampling rates for trend data storage
-electromagnetic interference
-external light interference

Question 21

How are oximeters calibrated?

Answer 21

-during manufacture they check against blood samples from healthy volunteers at differing FIO2 levels

-should periodically check SpO2 against an arterial blood gas measuremetn for quality assurance

Question 22

Describe the relationships between accuracy and prescions

Answer 22

low accuracy and high prescion
high accuracy and low prescion
high accuracy and high prescion

Question 23

What are some patient limitations of pulse oximeter?

Answer 23

-movement artefacts
-incorrect sitting of probe
-poor perfusion
-substance interference
-carbon dioxide
-carbon monoxide
-anaemia
-abnormal haemoglobins

Question 24

What substance interferences can affect an oximetry reading?

Answer 24

-Nail polish and artifical nails may affect the accuracy of SpO2 and reduce the rading

-intravenous dye such as methylene blue used in imaging and during surgery can interfere with the accuracy of SpO2

-skin pigmentation may alter readings -established using caucasian subjects

Question 25

Why does CO interfere with oximeters?

Answer 25

-CO has a greater affinity for HB than O2
-pulse oximeters cant distinguish between carboxyhaemoglobin and oxyhaemoglobin
-o2 saturation would be falsely high
-smokers may have high levels of carboxyhaemoglobin-so SpO2 will be overestimated

Question 26

what is the equation for O2 saturation?

Answer 26

O2 bound to Hb (ml/l)/ o2 capacity (ml/l) all x100

Question 27

What is methaemoglobin?

Answer 27

-unable to bind to O2
-normally 1-2% of haemoglobin
-metHb increased in inherited or aquired methaemoglobinaemila

Question 28

How does acquired methaemoglobinaemia occur?

Answer 28

from exposure to toxins, for example due to a high levels of nitrates in water or food