Oximetry and Pulse Ox Flashcards
What is the respiratory quotient?
Amount of CO2 produced / % of O2 consumed
Why is oximetry measured?
Der b/c we need O2 to live
What is the normal O2 consumption of a 70 kg patient?
3.3 mL / kg
On room air (21% FiO2) what is the normal FeO2 and that means we consume approximately how much O2?
Normal FeO2 = 18%
so that means we consume about 3% of minute ventilation
According to the normal O2 consumption of a 70 kg patient, how much O2 is that per min?
3.3 mL / kg and 70 kg
= 250 mL of O2 / min
Hypoxemia and hypoxia both give a determination of what?
Amount of O2 in the blood and tissues
What is an easy deadspace calculation?
The pt’s weight in lbs
What is the minimum tidal volume to maintain oxygenation and to reduce amount of atelectysis?
3-4 x deadspace
What is the minimum oxygen percent you can give to your patient that has 0 V/Q mismatch and no circuit leaks of any kind?
5%
What is carboxyhemoglobin?
Who does this occur in?
Carbon monoxide bound hemoglobin
Smokers
What is methemoglobin?
Where the heme molecule losses an electron of iron (Fe) and causes hemoglobin molecule to lose its shape
What is sulfhemoglobin? Who does this occur in?
Sulfar bound Hb
Diabetics
What is sickle cell hemoglobin?
Sickled Hb which decreases the O2 carrying capacity
What is fetal Hemoglobin?
haha according to Biggs, the fetal people Hb
What is the oxygen content equation?
CO2 = 0.0031 x PO2 + 1.31 x O2 Hb x SO2
What does your minute ventilation approximately need to be equal to?
Cardiac output
What is oxyhemoglobin?
O2 bound hemoglobin
What is deoxyhemoglobin?
Reduced O2 bound hemoglobin
What is the standard for measuring oximetry? (we don’t use in OR)
Laboratory Bench Co-oximeters
What do we use in the OR for measuring oxygen saturation?
Pulse Oximeter
What is the fractional SaO2 formula used in the Co-oximeters?
O2 Hb /
O2 Hb + Deoxy Hb + CO Hb + Met Hb + HbF
What is the functional SaO2 formula used in pulse ox?
O2 Hb / O2 Hb + deoxy Hb
What are the 2 wavelenths used in pulse ox readings?
Red @ 660 nm
Infrared @ 940 nm
KNOW THE GRAPH ON PAGE 6 which is of the Hemoglobin extinction curves. If someone knows how to put pics in please do on the answer part of this question.
INSERT YOUR THINGY HERE
What does someone who has carboxyhemoglobin read on the pulse ox?
90%
What does someone who has methemoglobin read on the pulse ox?
85%
What kind of pulse ox is used in adults?
Transmission
LED and photodetectors on opposite sides
What kind of pulse ox is used in fetal monitoring?
Reflectance
LED and photodetectors on same side and reflects off bone
Where can you put the pulse ox we use in the OR?
Any protuberance \:fingers \:ears \:tongue \:nose \:toes \:lip \:penis
Which light wavelength is shown on the screen when using a pulse ox and why?
Infrared (940 nm) because it shows the greatest amplitude and is stronger at 100% O2 sat
What is the assumed difference between what the screen shows and what the actually saturation may be?
+/- 2%
What is the isobestic point?
Point at which frequency the two wavelengths absorb exactly the same amount of two hemoglobins
What is the isobestic point of oxyhemoglobin and deoxyhemoglobin?
800 nm
What causes right shifts in the oxygen-hemoglobin dissociation curve?
R (rightward) I (increase of CO2) G (2,3 DPG increase) H (H+ increase) T (Temp increase)
What does a rightward shift indicate on the curve?
A decreased affinity for O2 binding or increased oxygen uploading
What causes left shifts in the oxygen-hemoglobin curve?
Exact opposite of right \:Decreased CO2 \: decreased 2,3 DPG) \: decreased H+ \: decrease in temp But also: \:Fetal hemoglobin \:CO poisoning
What does a leftward shift indicate on the curve?
Increased affinity for O2 binding and therefore decreased oxygen unloading
In white patients, SpO2 of >92% predicted PaO2 of 60 mmHg. However in black patients SpO2 of _______ predicted PaO2 of 60 mmHg
> 95%
What are some causes of low perfusion?
Vasoconstriction
Severe PVD
Hypothermia
Hypovolemia
What kind of lights obscure pulse ox readings?
Fluorescent
What causes blood to become a very bright red color?
Carbon monoxide
Will anemia have any affect on pulse ox readings?
No because just because there are fewer Hb molecules available does not change the saturation of the ones that are present
In the masimo SET instrument, what does the SET stand for and what does it do?
Signal extraction technology
Separates the signal from noise
Of the dyes that effect Pulse ox, which has the greatest effect?
Methylene blue
What are the dyes that have effects on pulse ox in order from greatest distortion to least?
Methylene blue Lympharzurine blue Indocyanine green Indigo carmine Fluorescein (no effect)
What colors of nail polish may effect absorbance of pulse ox?
Blues and blacks
How much lower of a SO2 will wearing nail polish produce because of low signal strength?
What can be done to alleviate this problem?
6% lower
Rotate probe 90* from normal so it is looking across the finger
What is the only real hazard of pulse ox today?
Pressure necrosis
What is PI?
Perfusion Index
is a relative assessment of the pulse strength at the monitoring site
CO binds hemoglobin how many more times than 02 binds?
240 x
On page 26 and 27, read the Clinical moments part , biggs said there would be 1 or 2 questions from these.
Again if someone wants can copy and paste them into here
What is NIRS?
Near infrared spectroscopy
What does NIRS give you?
Will give you absorption of the brain tissue but not the blood, so is referred to rSO2
What is difference of rSO2 and tSO2?
regional SO2 and tissue SO2
rSO2 is for brain
tSO2 is for other tissues in the body
How many probes come with Cerebral oximetry and why?
2 probes so you can measure oxygenation of both hemispheres at same time
Most anesthetics increase or decrease cerebral blood flow ?
Increase
What are the average values for cerebral oximetry?
55 - 75 %
What are the main problems with cerebral oximetry ?
Depends on partition of arterial and venous blood which depend on:
PaCO2
Hypoxia
pH
What is SvO2?
Mixed venous oxygen saturation
Where do you usually obtain SvO2?
PA catheter advanced near a capillary
What are some variables that affect SvO2?
Q (blood flow)
Hb concentration
SaO2 (arterial oxygenation)
VO2 (oxygen uptake - metabolic rate - perfusion)
What does SjvO2 measure?
Jugular venous saturation
Which way do you place the catheter that reads SjvO2?
Towards the brain
