Flipped Classroom - Pulse Ox Flashcards
What does pulse oximetry measure?
Pulse oximetry measures pulse rate and the oxygen saturation of hemoglobin (SpO2) in a noninvasive, continuous basis.
What does pulse oximetry not measure?
Pulse oximetry does not measure the quantity of hemoglobin (can’t measure anemia) or the total oxygen content bound to hemoglobin.
How does pulse oximetry indirectly assess perfusion?
Pulse oximetry indirectly assesses perfusion through the measurement of oxygen saturation.
What are the two types of pulse oximeter devices?
The two types of devices are Transmittance and Reflectance.
What is the accuracy range of modern pulse oximeters?
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.
Where are common sites for pulse oximetry measurements?
Common sites include the finger, earlobe, forehead, nose, and toes.
What principle does pulse oximetry utilize to determine oxygen saturation?
Pulse oximetry utilizes spectrophotometry based on Beer-Lambert’s law.
What is Lambert’s law?
the absorption of light is proportional
to the concentration of the absorbing substance and
the path length).
What are the two different wavelengths used in pulse oximetry?
Deoxyhemoglobin absorbs more red light (660 nm), while Oxyhemoglobin absorbs more infrared light (940 nm).
What does the photodetector do in pulse oximetry?
The photodetector collects transmitted light, converts it into electrical signals, and displays a waveform on a monitor.
What is the Beer-Lambert law?
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.
How do pulse oximeters measure light absorption?
Pulse oximeters measure the amount of light absorption of two specific wavelengths many times a second to determine a ratio.
What can cause inaccuracies in pulse oximetry readings?
Inaccuracies can occur in low perfusion states, motion artifacts, and environmental interference (ambient light sources).
What must CRNAs recognize regarding pulse oximetry readings?
CRNAs must recognize unreliable pulse oximetry readings and confirm oxygenation via arterial blood gas analysis.
What dangers during anesthesia can pulse oximetry detect?
Pulse oximetry can easily detect hypoxemia and hypoventilation during anesthesia.
What is hypoxemia?
Hypoxemia is defined as low arterial oxygen levels (PaO2 < 60 mmHg).
What are clinical signs of hypoxemia?
Clinical signs of hypoxemia include tachycardia and altered mental status, which are often masked during anesthesia.
What does the oxyhemoglobin dissociation curve represent?
It represents the relationship between loosely bound oxyhemoglobin expressed as percent saturation and oxygen tension.
What is the SpO2 at a PO2 of 40 mmHg?
The SpO2 correlates to 75% of O2 bound to hemoglobin.
What happens to SpO2 after a PO2 of 60 mmHg?
SpO2 starts to plateau after 60 mmHg.
What occurs when PaO2 is greater than 75 mmHg?
The SaO2 reaches a plateau and no longer reflects changes in PaO2.
What is the clinical significance of the oxyhemoglobin dissociation curve for CRNAs?
It provides real-time monitoring of oxygenation to enhance patient safety and outcomes.
How does pulse oximetry help in clinicals?
It allows for early detection of hypoxemia and hypoventilation, decreasing perioperative morbidity and mortality rates.
Where should the pulse oximeter probe be placed in neonates?
It should preferably be placed on the right hand or earlobe to measure preductal oxygen saturation.
How can pulse oximetry be utilized before radial artery cannulation?
It can be used in place of the Allen’s test to test for adequate perfusion.
Who benefits from pulse oximetry monitoring?
Patients with cardiac or pulmonary disorders/diseases benefit from monitoring.
What is a limitation of pulse oximetry regarding ventilation?
It is a poor indicator of adequate ventilation; desaturation may take several minutes to detect.
What should be monitored during descending aorta aneurysm repairs?
Pulse oximetry monitoring should occur on the right side if impingement of the left subclavian artery occurs.
How do ventricular assist devices (VADs) affect pulse oximetry?
The function of pulse oximeters with VADs depends on the patient’s residual cardiac function that produces a pulsatile reading.
What alters pulse oximetry readings?
Carboxyhemoglobin and methemoglobin alter pulse oximetry readings.
What can interfere with pulse oximetry during surgery?
Electrocautery can interfere if the photodetector senses the radiofrequency emissions.
What should be done to mitigate ambient light interference with pulse oximetry?
Provide a cover to decrease risk.
What is a limitation of pulse oximetry in certain physiological states?
There is a limitation in detecting pulsatile flow in low perfusion, hypothermic, or vasoconstrictive states.
What are strategies to minimize interference in pulse oximetry?
Secure placement and choosing appropriate sites.
What should be recognized and troubleshot in pulse oximetry?
Signal artifacts or false readings.
What is important to understand when interpreting SpO2 and waveform readings?
The clinical context, especially with dyshemoglobinemia.
Where should the oximetry site be moved in low perfusion states?
To a central location such as the nose, ear, or forehead.
Nagelhout et al., 2023. p. 320.
What technology improves accuracy in measuring carboxyhemoglobin and methemoglobin?
Multi-wavelength technology.
How do new pulse oximeters perform during patient movement and low-perfusion states?
They may measure SpO2 more accurately than current pulse oximeters.
Barash et al, 2024. p. 669.
What technology shows promise in reducing inaccuracies related to vasoconstriction?
Pulse oximeters utilizing reflectance technology.
Nagelhout et al., 2023. p. 320.
Are there any contraindications to pulse oximetry?
No, there are no contraindications.
What is important regarding documentation in anesthesia records?
Accurate readings must be documented.
What must be ensured about electronic readings in pulse oximetry?
They must be accurate.
What role does pulse oximetry play in patient safety and liability?
It is a standard of care that ensures patient safety and reduces liability risks.
Barash et al, 2024. p. 669.
What should be noted in charting regarding false readings?
Any false readings should be documented.
What light does deoxyhemoglobin absorb more of?
More red light (660 nm).
What light does oxyhemoglobin absorb more of?
More infrared light (940 nm).
What do arterial oxygen monitors not ensure?
They do not ensure adequacy of oxygen delivery to or utilization by peripheral tissues.
What is required for pulse oximeters to function properly?
A pulsatile waveform to distinguish absorption of light by hemoglobin from other tissues.
How can CRNAs ensure safe and effective anesthesia care?
By understanding hemoglobinopathies and practicing vigilance.
What will accurate monitoring and charting ensure?
Patient safety and positive outcomes, while decreasing liability risks.
- 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.
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).
- 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.
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).
- Which of the following wavelengths is absorbed more by deoxygenated hemoglobin?
A. 940 nm
B. 660 nm
C. 800 nm
D. 500 nm
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).
- 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
: 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).
- 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.
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).
- 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.
: 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).
