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What is Pulse Oximetry?
A noninvasive & continuous means estimating the percentage of Hb saturated with oxygen in arterial blood at the peripheral capillary level: SpO2 = Estimation of SaO2.
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What is the normal SpO2 reading in healthy adults?
94-100%
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What are the benefits of Pulse Oximetry?
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What is Oxyhemoglobin?
97% of O2 in blood is bound to Hb, only 3% is dissolved in plasma.
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What is Deoxyhemoglobin?
Hemoglobin without oxygen bound (HHb).
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What should be audible during pulse oximetry usage?
The variable pitch pulse tone and the low threshold alarm.
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What is the objective of oxygenation during anesthesia?
To ensure adequate oxygen concentration in the inspired gas and the blood.
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What is SpO2?
SpO2 = O2 saturation measured by pulse oximetry, an indirect estimation of arterial O2 saturation (SaO2).
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Why is pulse oximetry important?
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How does pulse oximetry work?
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What are the saturation levels of hemoglobin?
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What does a pulse oximeter sensor do?
It emits light using red (660 nm) and infrared (940 nm) diodes to measure O2 saturation.
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What does Beer's Law state?
The amount of absorbed light is proportional to the solution concentration.
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What does Lambert's Law describe?
Amount of light absorbed is proportional to the length of the path that light travels in the absorbing substance.
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What wavelengths are used for deoxyhemoglobin and oxyhemoglobin?
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What is the calibration curve in pulse oximetry?
It relates SpO2 reading to R:IR ratio and corrects expected errors from Beer-Lambert law.
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What is a limitation of pulse oximeters below 70% saturation?
They are less accurate below saturations of ~70%.
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What is the formula for the Beer-Lambert Law?
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What does pulse oximetry calculate?
It calculates the ratio of deoxyhemoglobin to oxyhemoglobin.
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How do we differentiate arterial blood?
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What is the function of Photoplethysmography?
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What does the Pulse Oximetry Calibration Curve indicate?
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What is a normal SpO2 reading for a healthy adult?
94-100% (hypoxia = below 94%)
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What does pulse oximetry actually measure?
It calculates an R value and uses a calibration curve to estimate the SaO2.
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What is the accuracy range of pulse oximetry?
Accurate from 70-100% with a standard deviation of +/- 2%.
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What causes inaccuracies in pulse oximetry readings?
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How can ambient light affect pulse oximetry readings?
Increased DC signal can lead to falsely high readings.
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What is a common cause of low perfusion affecting pulse oximetry?
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What is a motion artifact in pulse oximetry?
Artifactual large AC signal caused by excessive movement, mimicking arterial pulse.
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How can you minimize ambient light interference in pulse oximetry?
By covering the pulse oximeter with opaque material (e.g., blanket).
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What does the pleth waveform indicate in pulse oximetry?
It detects cyclical changes in volume and size of arteries, affecting SpO2 accuracy.
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What are the effects of low perfusion on pulse oximetry?
Low AC signal leads to low pleth amplitude and inaccurate SpO2 readings.
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What can excessive movement during pulse oximetry lead to?
It can create a motion artifact, resulting in falsely low readings.
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What should be monitored to ensure pulse oximetry accuracy?
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What does a SvO2 of 75% indicate?
Increased R:IR ratio; unable to distinguish between arterial and venous blood.
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What is a significant effect of Methylene blue on pulse oximetry?
Causes short-lived falsely low SpO2 reading (85%) lasting 10-60min with large doses.
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What is the difference between Functional and Fractional SaO2?
Functional SaO2: fraction of effective hemoglobin oxygenated. Fractional SaO2: fraction of total hemoglobin oxygenated.
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What is the effect of Dyshemoglobins on pulse oximetry?
Most do not carry oxygen but can still absorb light, leading to inaccurate readings.
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What is the role of Indocyanine green (ICG)?
Used in tissue perfusion tests; similar effect to Methylene blue but more transient (~30s).
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What does the O2 content equation assume about hemoglobin?
Assumes all Hb types are capable of carrying oxygen, which is not always true.
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What does the noise artifact in pulse oximetry indicate?
Irregular, high-frequency fluctuations in the photoplethysmogram (pleth) waveform.
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What is the significance of absorbance at 668nm in pulse oximetry?
Close to 660nm, it mimics deoxy-Hb, affecting SpO2 readings.
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What does the diagram illustrate about oxygen content (CaO2)?
Shows the progression from SpO2 to SaO2 and finally to CaO2 and DO2.
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What does Fluorescein do to pulse oximetry readings?
It does not affect pulse-oximetry readings.
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What happens to Fe++ in methemoglobinemia?
Fe++ is oxidized to Fe+++, which cannot bind O2.
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What is the effect of one Fe+++ molecule on other Fe++ molecules?
It increases their binding affinity for oxygen, preventing release to tissues.
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What does pulse oximetry show in methemoglobinemia?
It trends towards 85% regardless of actual saturation, causing under/overestimation.
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What are the clinical signs of methemoglobinemia?
SpO2 ~85% that does not respond to 100% FiO2; severity correlates with MetHb levels.
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What symptoms occur at 10-20% MetHb concentration?
Mild symptoms, cyanosis, chocolate brown blood.
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What is the treatment for symptomatic methemoglobinemia?
Methylene Blue 1-2 mg/kg over 3-5 minutes; begins at 20% MetHb.
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What is a common cause of acquired methemoglobinemia?
Drug-induced, often from local anesthetics or overdose.
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What does the graph show about SpO2 and SaO2 versus methemoglobin concentration?
SpO2 (blue) remains at 85% while SaO2 (red) indicates hypoxia.
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What are the symptoms at >50% MetHb concentration?
CNS hypoxia, seizures, coma, tachypnea.
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What is the goal of treatment for methemoglobinemia?
To reduce Fe+++ to Fe++.
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What is the effect of carbon monoxide (CO) on hemoglobin?
CO binds to hemoglobin with an affinity >210x that of O2, decreasing oxygen delivery and utilization.
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How does carboxyhemoglobin affect pulse oximetry readings?
It overestimates SpO2, registering COHb as 90% oxygenated hemoglobin, leading to false readings.
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What are common sources of carbon monoxide exposure?
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What is the treatment for carboxyhemoglobinemia?
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What can cause falsely low readings in pulse oximetry?
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What is the appearance of patients with carboxyhemoglobinemia?
They may appear red/pink, resembling oxygenated blood, despite being hypoxic.
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Why doesn't anemia affect SpO2?
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What happens if Hct reaches <15%?
SpO2 reading may fail or be inaccurate due to low perfusion.
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What effect does Carboxyhemoglobin (COHb) have on SpO2?
Slight reduction in assessment of oxygen saturation; overestimates Hb available for O2 transport.
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What is the effect of Methemoglobin (MetHb) at high levels?
SpO2 approaches 85%, independent of actual Sao2.
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What is the effect of Hemoglobin S (Sickle cell) on SpO2?
No significant effect on SpO2.
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What is the effect of Indocyanine green on SpO2?
Transient decrease in SpO2.
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What does the diagram show about Hb content and SpO2?
Left: Hb ~15g/dL, SpO2 = 100%. Right: Hb ~8g/dL, SpO2 = 100%.
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What is the effect of Isosulfan blue on SpO2 at high doses?
Prolonged reduction in SpO2
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What happens to SpO2 readings with Methylene blue?
Transient, marked decrease in SpO2 lasting several minutes
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How does hemoglobin concentration affect SpO2 during hypoxemia?
Underestimation of actual SaO2 if Hb < 14.5 g/dL
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What is the effect of acrylic fingernails on SpO2 readings?
No significant effect
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How does ambient light interfere with SpO2 readings?
Bright light can falsely elevate SpO2 readings
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What is the relationship between plethysmograph amplitude and vascular tone?
Amplitude is directly proportional to vascular distensibility and inversely proportional to vascular tone
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What does pulse oximetry monitor?
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What are the limitations of clinical observation for oxygenation?
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How does amplitude relate to vascular tone?
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What is the effect of phenylephrine on pulse oximeter waveform?
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What is the effect of nitroprusside on pulse oximeter waveform?
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What is the primary use of pulse oximetry?
Monitoring circulation, HR & rhythm analysis, detecting cardiac arrhythmias.
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How does pulse oximetry assist in ECG interpretation?
Helps interpret ECG artifact; if pulse oximeter is normal, ECG may be erroneous.
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What can pulse oximetry detect during shoulder surgery?
Can alert to brachial artery compression.
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What does the pulse oximeter waveform correlate with?
Correlates well with arterial blood pressure waveform.
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What does a return-to-flow method measure?
Blood pressure by squeezing arm, cutting blood flow, then slowly deflating.
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What is the effect of ventricular tachycardia on pulse oximetry?
Pleth pulse perfusion is present; not pulseless v tach.
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What can photoplethysmography detect?
Sensitive to pulsatile flow; can detect compromised circulation.
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What is the significance of respiratory variability in vascular volume monitoring?
Indicates changes in vascular volume.
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What is sympathetic block's effect on blood flow?
It increases blood flow.
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What happens to perfusion during ventricular fibrillation?
No perfusion occurs during V-Fib.
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What does a large variation in pleth amplitude indicate?
It suggests low volume due to compression of SVC and IVC.
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What does a plethysmograph with > 12% variation suggest?
The patient may benefit from a fluid bolus.
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Which body site is most accurate for pulse oximetry?
Finger is more accurate than earlobe.
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What effect does nail polish have on pulse oximetry readings?
Dark colors, especially blue, can affect readings.
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What is the response time of pulse oximetry at the toe?
Greater delay than finger or central location.
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What is the accuracy of pulse oximetry at the nose?
Accuracy questioned, but useful under hypothermia, hypotension, vasoconstrictor drugs.
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What is a key advantage of using pulse oximetry at the ear?
Faster response time than finger, relatively immune to vasoconstriction.
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What is the accuracy of pulse oximetry at the tongue?
Very accurate with a disposable probe wrapped around the tongue.
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Which method of pulse oximetry is more accurate than finger?
Buccal pulse-oximetry detects increases and decreases more quickly.
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What are the two types of plethysmography mentioned?
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What is a disadvantage of using forehead pulse oximetry?
Do not use in patients in trendelenburg; inaccurate due to venous congestion.
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What do new technology pulse-oximeters measure?
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What is a key feature of reflective pulse oximetry on the forehead?
Easily accessible, less affected by vasoconstriction, quicker saturation detection than finger.
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What can cause low readings in forehead pulse oximetry?
Pooling of venous return may cause low readings in supine patients.
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What does the Pleth Variability Index (PVI) indicate?
It measures fluctuations in plethysmographic amplitude during the respiratory cycle and evaluates volume status.
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What technology does Rainbow Set Technology use?
It uses 8 wavelengths of light to measure HbO2, DHb, MetHb, and COHb.
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What is P50 in oxyhemoglobin dissociation?
It is the PaO2 at which hemoglobin is 50% saturated, approximately 27 mmHg.
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What is the saturation of mixed-venous blood?
About 75% at a PaO2 of 40 mmHg.
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What are the limitations of SpO2?
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What is the accuracy of SpO2 readings above 70%?
±2% (1 SD) 68% of the time, ±4% (2 SD) 95% of the time.
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How does response time vary between finger and ear oximetry?
Finger response is 24-50 seconds slower; ear response is 10-20 seconds.
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What happens if a patient is hypoxic regarding SpO2 readings?
You may see a low reading due to delay, which could worsen.
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What is the relationship between PaO2 and SpO2?
SpO2 of 95% corresponds to a PaO2 of approximately 75 mmHg.
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What does the oxygemoglobin dissociation curve illustrate?
It shows the relationship between PaO2 and SpO2, including left and right shifts.
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What is the initial step in pulse oximetry?
Various light intensities try to find a strong enough signal to transmit through tissue.
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What does a good waveform on the Pleth indicate?
The reading will be accurate.
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What can cause misinterpretation of pulse oximetry data?
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What is a potential complication of pressure on the sensor?
Do not tape the sensor too tightly, especially in low perfusion cases.
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What skin damage can occur from pulse oximetry?
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What should be checked if there is no signal from the pulse oximeter?
Check connection, cable, or probe for defects.
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What can improve a low quality signal in pulse oximetry?
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What is Pulse Oximetry?
A noninvasive & continuous means estimating the percentage of Hb saturated with oxygen in arterial blood at the peripheral capillary level: SpO2 = Estimation of SaO2.
What is the normal SpO2 reading in healthy adults?
94-100%
What are the benefits of Pulse Oximetry?
What is Oxyhemoglobin?
97% of O2 in blood is bound to Hb, only 3% is dissolved in plasma.
What is Deoxyhemoglobin?
Hemoglobin without oxygen bound (HHb).
What should be audible during pulse oximetry usage?
The variable pitch pulse tone and the low threshold alarm.
What is the objective of oxygenation during anesthesia?
To ensure adequate oxygen concentration in the inspired gas and the blood.
What is SpO2?
SpO2 = O2 saturation measured by pulse oximetry, an indirect estimation of arterial O2 saturation (SaO2).
Why is pulse oximetry important?
How does pulse oximetry work?
What are the saturation levels of hemoglobin?
What does a pulse oximeter sensor do?
It emits light using red (660 nm) and infrared (940 nm) diodes to measure O2 saturation.
What does Beer's Law state?
The amount of absorbed light is proportional to the solution concentration.
What does Lambert's Law describe?
Amount of light absorbed is proportional to the length of the path that light travels in the absorbing substance.
What wavelengths are used for deoxyhemoglobin and oxyhemoglobin?
What is the calibration curve in pulse oximetry?
It relates SpO2 reading to R:IR ratio and corrects expected errors from Beer-Lambert law.
What is a limitation of pulse oximeters below 70% saturation?
They are less accurate below saturations of ~70%.
What is the formula for the Beer-Lambert Law?
What does pulse oximetry calculate?
It calculates the ratio of deoxyhemoglobin to oxyhemoglobin.
How do we differentiate arterial blood?
What is the function of Photoplethysmography?
What does the Pulse Oximetry Calibration Curve indicate?
What is a normal SpO2 reading for a healthy adult?
94-100% (hypoxia = below 94%)
What does pulse oximetry actually measure?
It calculates an R value and uses a calibration curve to estimate the SaO2.
What is the accuracy range of pulse oximetry?
Accurate from 70-100% with a standard deviation of +/- 2%.
What causes inaccuracies in pulse oximetry readings?
How can ambient light affect pulse oximetry readings?
Increased DC signal can lead to falsely high readings.
What is a common cause of low perfusion affecting pulse oximetry?
What is a motion artifact in pulse oximetry?
Artifactual large AC signal caused by excessive movement, mimicking arterial pulse.
How can you minimize ambient light interference in pulse oximetry?
By covering the pulse oximeter with opaque material (e.g., blanket).
What does the pleth waveform indicate in pulse oximetry?
It detects cyclical changes in volume and size of arteries, affecting SpO2 accuracy.
What are the effects of low perfusion on pulse oximetry?
Low AC signal leads to low pleth amplitude and inaccurate SpO2 readings.
What can excessive movement during pulse oximetry lead to?
It can create a motion artifact, resulting in falsely low readings.
What should be monitored to ensure pulse oximetry accuracy?
What does a SvO2 of 75% indicate?
Increased R:IR ratio; unable to distinguish between arterial and venous blood.
What is a significant effect of Methylene blue on pulse oximetry?
Causes short-lived falsely low SpO2 reading (85%) lasting 10-60min with large doses.
What is the difference between Functional and Fractional SaO2?
Functional SaO2: fraction of effective hemoglobin oxygenated. Fractional SaO2: fraction of total hemoglobin oxygenated.
What is the effect of Dyshemoglobins on pulse oximetry?
Most do not carry oxygen but can still absorb light, leading to inaccurate readings.
What is the role of Indocyanine green (ICG)?
Used in tissue perfusion tests; similar effect to Methylene blue but more transient (~30s).
What does the O2 content equation assume about hemoglobin?
Assumes all Hb types are capable of carrying oxygen, which is not always true.
What does the noise artifact in pulse oximetry indicate?
Irregular, high-frequency fluctuations in the photoplethysmogram (pleth) waveform.
What is the significance of absorbance at 668nm in pulse oximetry?
Close to 660nm, it mimics deoxy-Hb, affecting SpO2 readings.
What does the diagram illustrate about oxygen content (CaO2)?
Shows the progression from SpO2 to SaO2 and finally to CaO2 and DO2.
What does Fluorescein do to pulse oximetry readings?
It does not affect pulse-oximetry readings.
What happens to Fe++ in methemoglobinemia?
Fe++ is oxidized to Fe+++, which cannot bind O2.
What is the effect of one Fe+++ molecule on other Fe++ molecules?
It increases their binding affinity for oxygen, preventing release to tissues.
What does pulse oximetry show in methemoglobinemia?
It trends towards 85% regardless of actual saturation, causing under/overestimation.
What are the clinical signs of methemoglobinemia?
SpO2 ~85% that does not respond to 100% FiO2; severity correlates with MetHb levels.
What symptoms occur at 10-20% MetHb concentration?
Mild symptoms, cyanosis, chocolate brown blood.
What is the treatment for symptomatic methemoglobinemia?
Methylene Blue 1-2 mg/kg over 3-5 minutes; begins at 20% MetHb.
What is a common cause of acquired methemoglobinemia?
Drug-induced, often from local anesthetics or overdose.
What does the graph show about SpO2 and SaO2 versus methemoglobin concentration?
SpO2 (blue) remains at 85% while SaO2 (red) indicates hypoxia.
What are the symptoms at >50% MetHb concentration?
CNS hypoxia, seizures, coma, tachypnea.
What is the goal of treatment for methemoglobinemia?
To reduce Fe+++ to Fe++.
What is the effect of carbon monoxide (CO) on hemoglobin?
CO binds to hemoglobin with an affinity >210x that of O2, decreasing oxygen delivery and utilization.
How does carboxyhemoglobin affect pulse oximetry readings?
It overestimates SpO2, registering COHb as 90% oxygenated hemoglobin, leading to false readings.
What are common sources of carbon monoxide exposure?
What is the treatment for carboxyhemoglobinemia?
What can cause falsely low readings in pulse oximetry?
What is the appearance of patients with carboxyhemoglobinemia?
They may appear red/pink, resembling oxygenated blood, despite being hypoxic.
Why doesn't anemia affect SpO2?
What happens if Hct reaches <15%?
SpO2 reading may fail or be inaccurate due to low perfusion.
What effect does Carboxyhemoglobin (COHb) have on SpO2?
Slight reduction in assessment of oxygen saturation; overestimates Hb available for O2 transport.
What is the effect of Methemoglobin (MetHb) at high levels?
SpO2 approaches 85%, independent of actual Sao2.
What is the effect of Hemoglobin S (Sickle cell) on SpO2?
No significant effect on SpO2.
What is the effect of Indocyanine green on SpO2?
Transient decrease in SpO2.
What does the diagram show about Hb content and SpO2?
Left: Hb ~15g/dL, SpO2 = 100%. Right: Hb ~8g/dL, SpO2 = 100%.
What is the effect of Isosulfan blue on SpO2 at high doses?
Prolonged reduction in SpO2
What happens to SpO2 readings with Methylene blue?
Transient, marked decrease in SpO2 lasting several minutes
How does hemoglobin concentration affect SpO2 during hypoxemia?
Underestimation of actual SaO2 if Hb < 14.5 g/dL
What is the effect of acrylic fingernails on SpO2 readings?
No significant effect
How does ambient light interfere with SpO2 readings?
Bright light can falsely elevate SpO2 readings
What is the relationship between plethysmograph amplitude and vascular tone?
Amplitude is directly proportional to vascular distensibility and inversely proportional to vascular tone
What does pulse oximetry monitor?
What are the limitations of clinical observation for oxygenation?
How does amplitude relate to vascular tone?
What is the effect of phenylephrine on pulse oximeter waveform?
What is the effect of nitroprusside on pulse oximeter waveform?
What is the primary use of pulse oximetry?
Monitoring circulation, HR & rhythm analysis, detecting cardiac arrhythmias.
How does pulse oximetry assist in ECG interpretation?
Helps interpret ECG artifact; if pulse oximeter is normal, ECG may be erroneous.
What can pulse oximetry detect during shoulder surgery?
Can alert to brachial artery compression.
What does the pulse oximeter waveform correlate with?
Correlates well with arterial blood pressure waveform.
What does a return-to-flow method measure?
Blood pressure by squeezing arm, cutting blood flow, then slowly deflating.
What is the effect of ventricular tachycardia on pulse oximetry?
Pleth pulse perfusion is present; not pulseless v tach.
What can photoplethysmography detect?
Sensitive to pulsatile flow; can detect compromised circulation.
What is the significance of respiratory variability in vascular volume monitoring?
Indicates changes in vascular volume.
What is sympathetic block's effect on blood flow?
It increases blood flow.
What happens to perfusion during ventricular fibrillation?
No perfusion occurs during V-Fib.
What does a large variation in pleth amplitude indicate?
It suggests low volume due to compression of SVC and IVC.
What does a plethysmograph with > 12% variation suggest?
The patient may benefit from a fluid bolus.
Which body site is most accurate for pulse oximetry?
Finger is more accurate than earlobe.
What effect does nail polish have on pulse oximetry readings?
Dark colors, especially blue, can affect readings.
What is the response time of pulse oximetry at the toe?
Greater delay than finger or central location.
What is the accuracy of pulse oximetry at the nose?
Accuracy questioned, but useful under hypothermia, hypotension, vasoconstrictor drugs.
What is a key advantage of using pulse oximetry at the ear?
Faster response time than finger, relatively immune to vasoconstriction.
What is the accuracy of pulse oximetry at the tongue?
Very accurate with a disposable probe wrapped around the tongue.
Which method of pulse oximetry is more accurate than finger?
Buccal pulse-oximetry detects increases and decreases more quickly.
What are the two types of plethysmography mentioned?
What is a disadvantage of using forehead pulse oximetry?
Do not use in patients in trendelenburg; inaccurate due to venous congestion.
What do new technology pulse-oximeters measure?
What is a key feature of reflective pulse oximetry on the forehead?
Easily accessible, less affected by vasoconstriction, quicker saturation detection than finger.
What can cause low readings in forehead pulse oximetry?
Pooling of venous return may cause low readings in supine patients.
What does the Pleth Variability Index (PVI) indicate?
It measures fluctuations in plethysmographic amplitude during the respiratory cycle and evaluates volume status.
What technology does Rainbow Set Technology use?
It uses 8 wavelengths of light to measure HbO2, DHb, MetHb, and COHb.
What is P50 in oxyhemoglobin dissociation?
It is the PaO2 at which hemoglobin is 50% saturated, approximately 27 mmHg.
What is the saturation of mixed-venous blood?
About 75% at a PaO2 of 40 mmHg.
What are the limitations of SpO2?
What is the accuracy of SpO2 readings above 70%?
±2% (1 SD) 68% of the time, ±4% (2 SD) 95% of the time.
How does response time vary between finger and ear oximetry?
Finger response is 24-50 seconds slower; ear response is 10-20 seconds.
What happens if a patient is hypoxic regarding SpO2 readings?
You may see a low reading due to delay, which could worsen.
What is the relationship between PaO2 and SpO2?
SpO2 of 95% corresponds to a PaO2 of approximately 75 mmHg.
What does the oxygemoglobin dissociation curve illustrate?
It shows the relationship between PaO2 and SpO2, including left and right shifts.
What is the initial step in pulse oximetry?
Various light intensities try to find a strong enough signal to transmit through tissue.
What does a good waveform on the Pleth indicate?
The reading will be accurate.
What can cause misinterpretation of pulse oximetry data?
What is a potential complication of pressure on the sensor?
Do not tape the sensor too tightly, especially in low perfusion cases.
What skin damage can occur from pulse oximetry?
What should be checked if there is no signal from the pulse oximeter?
Check connection, cable, or probe for defects.
What can improve a low quality signal in pulse oximetry?
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