Oximetry Flashcards
What are the vital signs we look for when assesing?
-pulse
-blood pressure
-temperature
-respiratory rate
-oxygen saturation
what is the standard method of assessing blood gases?
arterial blood gas samping
what are standard measurement of arterial blood gas?
-Ph
-PaO2
-Paco2
-Sao2
-bicarbonate (HCO3-)
What are some other measurement s of arterial blood gas?
-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
How do we analyse arterial blood gas measurements?
blood gas analysis
(need a hepronised sample)
What are some disadvantages of blood gas measurements?
-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
Whats the visual difference between arterial and venous blood?
-arterial is a brighter red that venous blood
What is the other technique we use instead of arterial blood gas measurements?
earlobe cappilary blood gas sampling
What are some disadvantages of earlobe cappilary blood gas sampling?
-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
what is a pulse oximeter?
-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
What does a pulse oximeter measure?
-indirect,non invasive estimate of arterial oxygen saturation
-detects hypoxaemia earlier than cyanosis can be seen
what are normal rates for a pulse oximeter?
SpO2- 95%-98%
Pulse-60-100BPM
what is the oxygen saturation os someone at risk of type 2 respiratory failure?
88-92%
At what oxygen level will patients loose conciousness?
55%
-in danger of dying or having permanent brain damage or organ failure
Why do we use pulse oximeters?
-non invasive
-rapid result
-cheap
-easy to use
-portable
-continuouse monitoring
What are some clinical applications of pulse oximetry?
-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
describe a recording oximeter
-used in excersise testing
-stores information which can be downloaded for analysis
-commonly used for overnight analysis
Describe a bedside oximeter
-inpatient use
-continuous monitoring
What are some limitations of oximetry?
-equiptment
-patients
-what it doesnt measure- eg ph, paO2 ect
What are some equiptment limitations of pulse oximetry?
-artefacts and innacuracies
-calibration
-memory
accuracy and prescion
sampling rates for trend data storage
-electromagnetic interference
-external light interference
How are oximeters calibrated?
-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
Describe the relationships between accuracy and prescions
low accuracy and high prescion
high accuracy and low prescion
high accuracy and high prescion
What are some patient limitations of pulse oximeter?
-movement artefacts
-incorrect sitting of probe
-poor perfusion
-substance interference
-carbon dioxide
-carbon monoxide
-anaemia
-abnormal haemoglobins
What substance interferences can affect an oximetry reading?
-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
Why does CO interfere with oximeters?
-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
what is the equation for O2 saturation?
O2 bound to Hb (ml/l)/ o2 capacity (ml/l) all x100
What is methaemoglobin?
-unable to bind to O2
-normally 1-2% of haemoglobin
-metHb increased in inherited or aquired methaemoglobinaemila
How does acquired methaemoglobinaemia occur?
from exposure to toxins, for example due to a high levels of nitrates in water or food
