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26 Cards in this Set
- Front
- Back
What kinds of hgb is the pulse ox sensitive to? |
-All types |
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How is SaO2 calculated? |
HbO2 / (HbO2 + Hb) x 100 |
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How does the pulse oximeter work? |
-estimates spO2 from differential absorption of red and infrared light -Differentiates oxy v reduced hgb, reduced absorbs more red light, oxy more infrared -red and infrared lights pulsed several hundred times /sec -photodiode collects light and converts it to electrical signal which is amplified and displayed |
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What is optical plethmography? |
The recording of changes in the size of a vessel as modified by the circulation of blood through it -waveforms are produced from pulsatile flow that occurs |
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What is spectrophotometry? |
-quanitative measurement of hgb O2 sat by using 2 wavelengths of light -uses the measurement of light absorbance to determine the concentrations of various solutes in a clear solution |
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What are the wavelengths of the two different LED lights emitted from the pulse ox? |
-Red light at 660nm -infrared at 940nm -Photodiode measures the amount of each type that passes through the tissues |
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How can the lights in the room affect the pulse ox? |
-Can cause erroneous readings -photodiode detects extraneous light |
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Where can a pulse ox probe be placed? |
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What are the benefits of a pulse ox? |
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What are some limitations of the pulse ox? |
-Delay in reading, late sign of hypoxia -Penumbra effect -venous pulsations -slippage/movement -no pulse -vasoconstriction/cold -dyes |
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What is the penumbra effect? |
Pulse ox is positioned so that light shines at a grazing angle which may give correct HR but erroneous saturation |
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What are some situations where a no/diminished pulse situation occurs? |
-CP bypass -tourniquet/BP cuff -Vasoconstriction/shock -hypovolemia/decreased CO -anemia -Hypothermia |
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What can cause slippage/movement of the pulse ox? |
-seizures -shivering -restlessness -induction/emergence |
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What dyes can affect pulse ox reading? Which has the most profound effect? |
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Describe the effect of Methylene blue on the pulse ox reading. |
-greater concentration in the blood, the lower the spo2 -dose is 2-5mg/kg and will lower spo2 for 10-60 min -may get as low as 65% |
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Describe the effect of indigo carmine, isosulfan blue and indocyanine green on pulse ox. |
Indigo carmine: small decreases in spo2, 0.5-2 mg/kg distorts values for 1 to 15min Isosulfan blue: used for sentinel node mapping, spo2 decreased after 15 min - 6hours Indocyanine green: least likely to distort spo2 |
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What are normal values of carboxyhemoglobin? How do increased values affect spo2? |
-Normal <2%, smokers may have up to 10% -Causes falsely high spo2 |
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What is methemoblobin? What is the normal value? How does it affect spo2? |
-iron in heme is oxidized from ferrous to ferric and cannot carry O2 -Normal <3% -Causes over estimation of functional saturation however spo2 decrease with increasing MetGb to plateau of 85% |
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What are the different types of methemoglobinemia? |
-congenital (deficiency of NADH methemoglobin reductase or abnormal hemoglobins: HbM, HbH -Acquired: oxidizing drugs |
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What types of drugs can cause methemoglobinemia? |
-Antimalarials -EDTA -Local anesthetics (prilocaine, lidocaine, benzocaine) -Nitrates |
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What is sulfhemoglobin? What is the treatment for it? |
-occurs with administration of sulfonamides (sulfanilimide, sulfamylon) -more rare than MetHb -Sulfur in porphyrin ring gives Hb blue-green hue -Cyanosis-not good transporter of O2 -Treatment: O2, methylene blue, exchange transfusion |
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What nail polish has the greatest effect on spo2 reading? |
-Blue has the greatest effect -Red may cause overestimation of spo2 |
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Below what spo2 level is O2 sat likely to be inaccurate? |
may be inaccurate when O2 sat < 40-70% |
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What type of ambient light interferes with spo2 the most? |
flourescent light in 660nm range causes distortion -if ambient light is flickering it may interfere |
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What must you consider with pulse ox in MRI? |
-MRI may interfere with reading -pulse ox cable can generate granular MRI images |
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What are the dangers when only monitoring pulse ox? |
-hypoventilation: spo2 may be normal but CO2 could still be elevated -endobronchial intubation: spo2 could still be normal |