Monitors

Question 1

What law is used to estimate oxyhemoglobin concentration in pulse oximetry?

Answer 1

The Lambert Beer Law

Question 2

What is the difference between SaO2 and SpO2?

Answer 2

SaO2 = HbO2/(HbO2+HHb+COHb+MetHb)

SpO2 = HbO2/(HbO2+HHb)

SpO2 is measured by pulse oximetry and used to estimate SaO2

Question 3

What wavelengths are measured in traditional pulse oximetry?

Answer 3

660 nm {red band, absorbed readily by HHb}

940 nm {infrared band, absorbed readily by HbO2}

Question 4

What two problems may affect the accuracy of pulse oximeters in patients with SPO2 < 70%?

Answer 4

1. Pulse oximeters were calibrated using healthy volunteers
2. The absorption spectrum of HHb is maximal at 600 nm, which means that small fluctuations in emitted light will cause large variations in measurement during states of hypoxemia, i.e. high HHb

Question 5

Which pulse oximeter probe location is fastest and which is slowest in terms of desaturation response time?

Answer 5

Ear - fastest (7.2-19.8 s)
Finger - middle (19.5-35.1 s)
Toe - slowest (41.0-72.6)

Question 6

Which two sites for pulse oximeter probe placement are least sensitive to decreased pulse?

Answer 6

Forehead & Earlobe

Question 7

What is the effect of COHb on the pulse oximeter reading and what is the mechanism?

Answer 7

COHb is interpreted as 90% HbO2 and 10% HHb; therefore the pulse oximeter will overestimate saturation if high levels of COHb are present

Question 8

What is the effect of metHb on the pulse oximeter reading and what is the mechanism?

Answer 8

MetHb is interpreted by the pulse oximeter as a saturation of 85% because it absorbs infrared and infrared light in a 1:1 ratio; therefore in cases of methomoglibinemia the SpO2 will appear to approach 85% regardless of the actual saturation

Question 9

List 8 medications or medication types that can cause methemoglobinemia

Answer 9

1. Anti-anginals, i.e. nitrates/nitrites (i.e. amyl nitrite, NTG)
2. Nitroprusside
3. Antimalarials
4. Local anesthetics (prilocaine, benzocaine, lidocaine)
5. Antibiotics (rifampin)
6. Anticonvulsants (phenytoin, valproate)
7. DMARDS (sulfasalazine, sulfonamides)
   processes)
8. Methylene blue

Question 10

Name three medical dyes that can affect the SpO2 reading (list from greatest to least change)

Answer 10

Methylene blue > Indocyanine green > Indigo carmine

Question 11

List 5 external/non-physiologic factors that can interfere with the pulse oximeter reading.

Answer 11

1. Ambient light changes
2. Skin pigmentation
3. Electrocautery interference
4. Motion artifact
5. Fingernail polish (acrylic alone does not usually interfere)

Question 12

What approach is associated with the highest success rate in placement of a pulmonary artery catheter?

Answer 12

Right IJ

Question 13

Name 6 parameters directly measured by a PAC.

Answer 13

1. CVP
2. PAP
3. PAOP
4. CO
5. MvO2
6. RVEF

Question 14

What equation is used to calculate CO using a PAC?

Answer 14

Modified Stewart-Hamilton Equation

Question 15

What technical and patient factors will affect the accuracy of a CO determined using a PAC?

Answer 15

TECHNICAL FACTORS:

• Change in volume of injectate
• Change in temperature of injectate
• Improper catheter tip location
• Long injection time

PATIENT FACTORS:

• Intracardiac shunt
• R sided valvular regurgitation
• Deep spontaneous respiration
• Valsalva maneuver
• Movement
• Arrhythmia