Flipped Classroom - Pulse Ox

Question 1

What does pulse oximetry measure?

Answer 1

Pulse oximetry measures pulse rate and the oxygen saturation of hemoglobin (SpO2) in a noninvasive, continuous basis.

Question 2

What does pulse oximetry not measure?

Answer 2

Pulse oximetry does not measure the quantity of hemoglobin (can’t measure anemia) or the total oxygen content bound to hemoglobin.

Question 3

How does pulse oximetry indirectly assess perfusion?

Answer 3

Pulse oximetry indirectly assesses perfusion through the measurement of oxygen saturation.

Question 4

What are the two types of pulse oximeter devices?

Answer 4

The two types of devices are Transmittance and Reflectance.

Question 5

What is the accuracy range of modern pulse oximeters?

Answer 5

Does not require calibrating. Modern pulse oximeters have an accuracy of within 2% to 3% at 70% - 100% saturation and +3% at 50% - 70% saturation.

Question 6

Where are common sites for pulse oximetry measurements?

Answer 6

Common sites include the finger, earlobe, forehead, nose, and toes.

Question 7

What principle does pulse oximetry utilize to determine oxygen saturation?

Answer 7

Pulse oximetry utilizes spectrophotometry based on Beer-Lambert’s law.

Question 8

What is Lambert’s law?

Answer 8

the absorption of light is proportional
to the concentration of the absorbing substance and
the path length).

Question 9

What are the two different wavelengths used in pulse oximetry?

Answer 9

Deoxyhemoglobin absorbs more red light (660 nm), while Oxyhemoglobin absorbs more infrared light (940 nm).

Question 10

What does the photodetector do in pulse oximetry?

Answer 10

The photodetector collects transmitted light, converts it into electrical signals, and displays a waveform on a monitor.

Question 11

What is the Beer-Lambert law?

Answer 11

The Beer-Lambert law is a mathematical relationship that relates changes in absorbed light intensity transmitted through a solution and the concentration of the solute in the solvent.

Question 12

How do pulse oximeters measure light absorption?

Answer 12

Pulse oximeters measure the amount of light absorption of two specific wavelengths many times a second to determine a ratio.

Question 13

What can cause inaccuracies in pulse oximetry readings?

Answer 13

Inaccuracies can occur in low perfusion states, motion artifacts, and environmental interference (ambient light sources).

Question 14

What must CRNAs recognize regarding pulse oximetry readings?

Answer 14

CRNAs must recognize unreliable pulse oximetry readings and confirm oxygenation via arterial blood gas analysis.

Question 15

What dangers during anesthesia can pulse oximetry detect?

Answer 15

Pulse oximetry can easily detect hypoxemia and hypoventilation during anesthesia.

Question 16

What is hypoxemia?

Answer 16

Hypoxemia is defined as low arterial oxygen levels (PaO2 < 60 mmHg).

Question 17

What are clinical signs of hypoxemia?

Answer 17

Clinical signs of hypoxemia include tachycardia and altered mental status, which are often masked during anesthesia.

Question 18

What does the oxyhemoglobin dissociation curve represent?

Answer 18

It represents the relationship between loosely bound oxyhemoglobin expressed as percent saturation and oxygen tension.

Question 19

What is the SpO2 at a PO2 of 40 mmHg?

Answer 19

The SpO2 correlates to 75% of O2 bound to hemoglobin.

Question 20

What happens to SpO2 after a PO2 of 60 mmHg?

Answer 20

SpO2 starts to plateau after 60 mmHg.

Question 21

What occurs when PaO2 is greater than 75 mmHg?

Answer 21

The SaO2 reaches a plateau and no longer reflects changes in PaO2.

Question 22

What is the clinical significance of the oxyhemoglobin dissociation curve for CRNAs?

Answer 22

It provides real-time monitoring of oxygenation to enhance patient safety and outcomes.

Question 23

How does pulse oximetry help in clinicals?

Answer 23

It allows for early detection of hypoxemia and hypoventilation, decreasing perioperative morbidity and mortality rates.

Question 24

Where should the pulse oximeter probe be placed in neonates?

Answer 24

It should preferably be placed on the right hand or earlobe to measure preductal oxygen saturation.

Question 25

How can pulse oximetry be utilized before radial artery cannulation?

Answer 25

It can be used in place of the Allen’s test to test for adequate perfusion.

Question 26

Who benefits from pulse oximetry monitoring?

Answer 26

Patients with cardiac or pulmonary disorders/diseases benefit from monitoring.

Question 27

What is a limitation of pulse oximetry regarding ventilation?

Answer 27

It is a poor indicator of adequate ventilation; desaturation may take several minutes to detect.

Question 28

What should be monitored during descending aorta aneurysm repairs?

Answer 28

Pulse oximetry monitoring should occur on the right side if impingement of the left subclavian artery occurs.

Question 29

How do ventricular assist devices (VADs) affect pulse oximetry?

Answer 29

The function of pulse oximeters with VADs depends on the patient’s residual cardiac function that produces a pulsatile reading.

Question 30

What alters pulse oximetry readings?

Answer 30

Carboxyhemoglobin and methemoglobin alter pulse oximetry readings.

Question 31

What can interfere with pulse oximetry during surgery?

Answer 31

Electrocautery can interfere if the photodetector senses the radiofrequency emissions.

Question 32

What should be done to mitigate ambient light interference with pulse oximetry?

Answer 32

Provide a cover to decrease risk.

Question 33

What is a limitation of pulse oximetry in certain physiological states?

Answer 33

There is a limitation in detecting pulsatile flow in low perfusion, hypothermic, or vasoconstrictive states.

Question 34

What are strategies to minimize interference in pulse oximetry?

Answer 34

Secure placement and choosing appropriate sites.

Question 35

What should be recognized and troubleshot in pulse oximetry?

Answer 35

Signal artifacts or false readings.

Question 36

What is important to understand when interpreting SpO2 and waveform readings?

Answer 36

The clinical context, especially with dyshemoglobinemia.

Question 37

Where should the oximetry site be moved in low perfusion states?

Answer 37

To a central location such as the nose, ear, or forehead. ## Footnote Nagelhout et al., 2023. p. 320.

Question 38

What technology improves accuracy in measuring carboxyhemoglobin and methemoglobin?

Answer 38

Multi-wavelength technology.

Question 39

How do new pulse oximeters perform during patient movement and low-perfusion states?

Answer 39

They may measure SpO2 more accurately than current pulse oximeters. ## Footnote Barash et al, 2024. p. 669.

Question 40

What technology shows promise in reducing inaccuracies related to vasoconstriction?

Answer 40

Pulse oximeters utilizing reflectance technology. ## Footnote Nagelhout et al., 2023. p. 320.

Question 41

Are there any contraindications to pulse oximetry?

Answer 41

No, there are no contraindications.

Question 42

What is important regarding documentation in anesthesia records?

Answer 42

Accurate readings must be documented.

Question 43

What must be ensured about electronic readings in pulse oximetry?

Answer 43

They must be accurate.

Question 44

What role does pulse oximetry play in patient safety and liability?

Answer 44

It is a standard of care that ensures patient safety and reduces liability risks. ## Footnote Barash et al, 2024. p. 669.

Question 45

What should be noted in charting regarding false readings?

Answer 45

Any false readings should be documented.

Question 46

What light does deoxyhemoglobin absorb more of?

Answer 46

More red light (660 nm).

Question 47

What light does oxyhemoglobin absorb more of?

Answer 47

More infrared light (940 nm).

Question 48

What do arterial oxygen monitors not ensure?

Answer 48

They do not ensure adequacy of oxygen delivery to or utilization by peripheral tissues.

Question 49

What is required for pulse oximeters to function properly?

Answer 49

A pulsatile waveform to distinguish absorption of light by hemoglobin from other tissues.

Question 50

How can CRNAs ensure safe and effective anesthesia care?

Answer 50

By understanding hemoglobinopathies and practicing vigilance.

Question 51

What will accurate monitoring and charting ensure?

Answer 51

Patient safety and positive outcomes, while decreasing liability risks.

Question 52

1. Why is pulse oximetry not a reliable indicator of ventilation adequacy? A. It is affected by ambient light. B. It detects oxygen saturation but not carbon dioxide levels. C. It does not work during apnea. D. It cannot detect low perfusion states.

Answer 52

B. It detects oxygen saturation but not carbon dioxide levels. Rationale: Pulse oximeters only measure oxygen saturation (SpO₂) and do not assess ventilation or CO₂ levels, making them unreliable for detecting hypercapnia or hypoventilation (Barash et al., 2024. p. 670).

Question 53

2. Which strategy minimizes pulse oximetry inaccuracies in low perfusion states? A. Increase the oxygen flow rate. B. Use a central monitoring site (e.g., forehead, nose, ear). C. Change to a different wavelength. D. Remove ambient light sources in the operating room.

Answer 53

B. Use a central monitoring site (e.g., forehead, nose, ear). Rationale: Low perfusion affects central sites less than peripheral sites like fingers or toes, ensuring more reliable readings (Nagelhout et al., 2023. p. 320).

Question 54

3. Which of the following wavelengths is absorbed more by deoxygenated hemoglobin? A. 940 nm B. 660 nm C. 800 nm D. 500 nm

Answer 54

B. 660 nm Rationale: Deoxygenated hemoglobin absorbs more red light (660 nm), whereas oxygenated hemoglobin absorbs more infrared light (940 nm), as per the Beer-Lambert Law (Barash et al., 2024. p. 669).

Question 55

4. At what PaO₂ does the oxygen dissociation curve plateau, indicating minimal changes in SpO₂? A. 20 mmHg B. 40 mmHg C. 60 mmHg D. 75 mmHg

Answer 55

: D. 75 mmHg Rationale: The oxygen dissociation curve flattens at a PaO₂ of around 75 mmHg, where further increases in oxygen tension have minimal impact on hemoglobin saturation (SpO₂). This means the pulse oximetry no longer reflects the partial pressures of arterial oxygen at pressures higher than 75 mmHg (Barash et al., 2024. p. 669).

Question 56

5. What happens to the SpO2 when the oxyhemoglobin dissociation curve has a rightward shift? A. Hemoglobin binds oxygen more tightly, increasing SpO2 B. Hemoglobin releases oxygen more readily, decreasing SpO2 C. Oxygen saturation increases for a given PaO₂. D. The curve flattens significantly at all PaO₂ levels.

Answer 56

Correct Answer: B. Hemoglobin releases oxygen more readily. Rationale: A rightward shift (e.g., due to acidosis, hypercapnia, or increased temperature) facilitates oxygen release to tissues, reducing hemoglobin’s oxygen affinity. This shows a decrease in pulse oximetry saturation on the displayed monitor (Nagelhout et al., 2023. p. 320).

Question 58

6. What effect does methylene blue have on pulse oximetry readings? A. Causes falsely high SpO₂ readings. B. Causes falsely low SpO₂ readings. C. Does not affect SpO₂ readings. D. Stops the device from functioning.

Answer 58

: B. Causes falsely low SpO₂ readings. Rationale: Methylene blue absorbs light in the red and infrared wavelengths, interfering with pulse oximetry and causing transiently low SpO₂ readings (Nagelhout et al., 2023. p. 243).