Principles 1: Test 4: Pulse Oximetry

Front 1

What kinds of hgb is the pulse ox sensitive to?

Back 1

-All types

Front 2

How is SaO2 calculated?

Back 2

HbO2 / (HbO2 + Hb) x 100

Front 3

How does the pulse oximeter work?

Back 3

-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

Front 4

What is optical plethmography?

Back 4

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

Front 5

What is spectrophotometry?

Back 5

-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

Front 6

What are the wavelengths of the two different LED lights emitted from the pulse ox?

Back 6

-Red light at 660nm

-infrared at 940nm

-Photodiode measures the amount of each type that passes through the tissues

Front 7

How can the lights in the room affect the pulse ox?

Back 7

-Can cause erroneous readings

-photodiode detects extraneous light

Front 8

Where can a pulse ox probe be placed?

Back 8

• fingers, toes
  
• nose, lip
  
• earlobe
  
• palm, foot, arm of neonate
  
• tongue
  
• cheek
  

Front 9

What are the benefits of a pulse ox?

Back 9

• no pressure necrosis/burning
  
• no skin prep or calibration
  
• continuous instantaneous reading of HR/spo2
  
• multiple monitoring sites
  
• wide variety of sensors available
  
• accurate and reliable
  

Front 10

What are some limitations of the pulse ox?

Back 10

-Delay in reading, late sign of hypoxia

-Penumbra effect

-venous pulsations

-slippage/movement

-no pulse

-vasoconstriction/cold

-dyes

Front 11

What is the penumbra effect?

Back 11

Pulse ox is positioned so that light shines at a grazing angle which may give correct HR but erroneous saturation

Front 12

What are some situations where a no/diminished pulse situation occurs?

Back 12

-CP bypass

-tourniquet/BP cuff

-Vasoconstriction/shock

-hypovolemia/decreased CO

-anemia

-Hypothermia

Front 13

What can cause slippage/movement of the pulse ox?

Back 13

-seizures

-shivering

-restlessness

-induction/emergence

Front 14

What dyes can affect pulse ox reading? Which has the most profound effect?

Back 14

• Methylene blue (most profound)
  
• Indigo Carmine
• Indocyanine gree
• Flouroscein (no effect)
• Isosulfan Blue

Front 15

Describe the effect of Methylene blue on the pulse ox reading.

Back 15

-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%

Front 16

Describe the effect of indigo carmine, isosulfan blue and indocyanine green on pulse ox.

Back 16

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

Front 17

What are normal values of carboxyhemoglobin? How do increased values affect spo2?

Back 17

-Normal <2%, smokers may have up to 10%

-Causes falsely high spo2

Front 18

What is methemoblobin? What is the normal value? How does it affect spo2?

Back 18

-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%

Front 19

What are the different types of methemoglobinemia?

Back 19

-congenital (deficiency of NADH methemoglobin reductase or abnormal hemoglobins: HbM, HbH

-Acquired: oxidizing drugs

Front 20

What types of drugs can cause methemoglobinemia?

Back 20

-Antimalarials

-EDTA

-Local anesthetics (prilocaine, lidocaine, benzocaine)

-Nitrates

Front 21

What is sulfhemoglobin? What is the treatment for it?

Back 21

-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

Front 22

What nail polish has the greatest effect on spo2 reading?

Back 22

-Blue has the greatest effect

-Red may cause overestimation of spo2

Front 23

Below what spo2 level is O2 sat likely to be inaccurate?

Back 23

may be inaccurate when O2 sat < 40-70%

Front 24

What type of ambient light interferes with spo2 the most?

Back 24

flourescent light in 660nm range causes distortion

-if ambient light is flickering it may interfere

Front 25

What must you consider with pulse ox in MRI?

Back 25

-MRI may interfere with reading

-pulse ox cable can generate granular MRI images

Front 26

What are the dangers when only monitoring pulse ox?

Back 26

-hypoventilation: spo2 may be normal but CO2 could still be elevated

-endobronchial intubation: spo2 could still be normal