Pulse Oximetry Flashcards by Renee DeAngelis

What are the 2 phases of respiration?

oxygenation - oxygen added to RBCs and plasma then into the cells
ventilation - removal of carbon dioxide

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What is pulse oximetry? What 2 things does it establish? When is it not considered safe?

non-invasive and continuous measurement of RBC saturation with oxygen - SpO2

pulse presence
oxygenation adequacy

long surgeries, MRI

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What is arterial blood gas analysis? What does it establish? What does it not give information on?

invasive and intermittent measurement of RBC saturation with oxygen - PaO2, SaO2

respiration adequacy - oxygenation, ventilation

cardiac output

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What oxygen content variables are typically measured?

SaO2
SpO2
PaO2

oxygen content = (Hb x 1.34 x SaO2) + (PaO2 x .003)

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What is the differences between SaO2, SpO2, and PaO2?

SaO2 and SpO2 are both measurements of hemoglobin’s saturation with oxygen - SaO2 is obtained through analysis of an arterial blood sample and SpO2 is obtained indirectly through pulse ox

PaO2 is the partial pressure of oxygen dissolved in plasma, related to the saturation of hemoglobin through the dissociation curve

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What are the 2 forms of blood oxygen?

on hemoglobin
in plasma

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How does pH affect oxygen dissociation from hemoglobin?

alkaline = increased oxygen affinity for Hb = high saturation

acid = decreased oxygen affinity for Hb = low saturation

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What is the relationship between PaO2 and oxygen saturation?

sigmoid - plateaus at a PaO2 of 60-100 mmHg, which is where a rise in O2 in blood provides only a small increase in the extent to where Hb is bound to O2 molecules

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What is the largest limitation of pulse oximetry?

insensitive - when SaO2 is greater than 90% PaO2 there is a highly variable reading

steep part of the curve provides most correlation between PaO2 and SaO2

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What is the difference between hypoxemia and hypoxia?

HYPOXEMIA = blood partial pressure or tension of oxygen below normal, PaO2 < 80-100 mmHg and SaO 80-85%

HYPOXIA = failure of oxygenation of tissues

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What are the 5 classic causes of hypoxemia?

low FiO2
high CO2
increased diffusion barrier
ventilation/perfusion mismatch
shunt

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How does pulse oximetry work?

light-emitting diode emits red and infrared light at specific wavelengths through a vascular bed, where the percentage of oxyHb are determined by ratio of infrared and red light transmitted

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What are 5 advantages to pulse oximetry?

continuous estimation of oxygen saturation of Hb (SpO2)
noninvasive
required nor calibration
portable monitors
identified and evaluated pulse rates (HR!)

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What 6 factors affect the accuracy of pulse oximetry readings?

dyshemoglobinemias and temperature changes cause curve shifting left and right
hyperbilirubinemia
poor perfusion
motion
ambient light
skin pigmentation

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What are the normal values for SpO2?

on 100% oxygen (intubated) = >95-97%, due to technical error >93% is accepted
on 20% oxygen (room air) = >85% expected, >90% ideal

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What are 3 non-pathologic causes of mildly decreased SpO2 levels?

recumbency
tracheal tube insertion length with increased dead space
upper airway issues (brachycephalics)

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What are 3 hypoxia differentials?

hypoxemia hypoxia: low FiO2, high CO2, low barometric pressure, diffusion issues, V/Q mismatch, shunting
circulatory hypoxia: decreased CO
anemic hypoxia: low PCV (very low)

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What should be done first if a low pulse ox reading is established?

INTUBATED = technical vs. non-respiratory
NOT INTUBATED = true hypoxia

TACHYCARDIC or TACHYPNEIC = true hypoxia
NOT = technical vs. non-respiratory

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What are rule outs for the 5 causes of true hypoxemia?

low FiO2 - oxygen not getting to patient, ET tube needed, clogged ET tube or malpositioned
high CO2 - hypoventilation, too deep, ET tube issues, sodasorb usage
diffusion problems - too much fluids, inflammation
V/Q mismatch - recumbency, atelectasis
shunt - large portion of lungs not working well

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What are some technical reasons for low pulse oximetry readings?

probe slipping (site is wet)
ambient light
too much overhead light
pigmented skin
probe compressing vessels = been in one place too long

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What are some non-respiratory reasons for low pulse oximetry readings?

hypothermia
vasoconstriction
poor perfusion due to deep planes of anesthesia or loss of sympathetic tone

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How can inconsistent pulse waves and signal issues be fixed?

move probe
warm patient and probe site
perfusion issue: check BP, volume status, albumin, and pressor use

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How can low oxygenation readings be fixed?

move probe
check oxygen supply and flow meter
confirm ET tube patency
treat overhydration
alter recumbency
check ventilation
anything affecting cheat - pneumothorax

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What is the proper placement of the pulse oximeter? How can slippage be avoided?

Study These Flashcards

use on distal areas (NOT meaty tissue), like lips, ears, flank fold, prepuce, triceps fold, and toes while changing frequently —> warming site increases blood flow

gauze
no moisture or lube

How does the available oxygen determine accuracy of the pulse oximeter?

100% O2 = pulse rate and oxygenation accurate, gives good information about tissue perfusion less than 100% O2 = pulse rate accurate, reflects respiration status

How can respiratory function be determined when pulse oximeter measures adequate SpO2?

- waveform - presence of other issues: tachypnea, changed respiratory pattern, waking, tachycardia - capnography - arterial blood gas sample for analysis

What are the 2 major ways of assessing ventilation?

1. arterial blood gas analysis: invasive, intermittent, gold standard 2. capnogrpahy: non-invasive, continuous, very accurate due to the relationship of CO2 and ventilation

What is PaCO2?

measure of CO2 production and ventilation, inversely proportional to ventilation ---> higher ventilation = lower PaCO2

What is end tidal capnometry?

measurement of the amount of carbon dioxide in exhaled air made via sampling expired gas and subjecting it to infrared spectrophotometry

How is absorption spectrophotometry used in capnography?

CO2 absorbs infrared light and a beam of light is split and passes through the sample and control - energy absorbed is compared to the control, which displays concentration oc CO2

What is a normal ETCO2? What is expected in real patients?

35-45 mmHg usually 6-10 mmHg lower than PaCO2 - can be very low in severely compromised patients

What is the path of CO2 in an intubated patient?

- produced by tissues - transferred to blood across membranes - carried by blood to lungs - transferred across membrane to alveoli - exhaled from body - cleaned out of system by high flow oxygen flows or sodasorb - sensed at the end of the ET tube

What are 5 reasons to used capnography?

1. monitor for tissue perfusion and metabolism 2. ideal monitor for appropriated respiration and ventilation 3. monitor for technical issues with used sodasorb or one way valves 4. assess success of CPR 5. identify correct placement of ET tube

How do pulse oximetry and capnographs compare in identifying cardiovascular status?

PULSE OX - pulse presence and characteristics CAP - perfusion of tissues allows CO2 exchange, ventilatory status of cells = metabolism

How do pulse oximetry and capnographs compare in identifying respiratory status?

PULSE OX - oxygenation, O2 saturation, may appear adequate in hypoxic patients CAP - ventilation, CO2, and PaCO2

How is capnogrpahy used to determine technical and equipment status?

- appropriated intubation - life at the cellular level - appropriate functioning of anesthesia machine

What is a colorimetric CO2 detector? What is it used for?

detector where purple color changes to yellow when exposed 15 mmHg of CO2 confirms intubation - small kittens, exotics

What is the difference between mainstream and sidestream capnography?

MAIN = gas sampled near the end of the ET tube, tends to be cumbersome, bulky, heavy, and increase dead space SIDE = gas is aspirated and measured distantly, condensation and secretions can block tube, induced a lag time

What is the difference between real-time and trend waveform displays?

RT = shows changes in individual breaths TREND = shows changes in waveform across time

What are 4 common causes of decreasing ETCO2 readings and waveform height?

1. hyperventilation 2. hypothermia 3. hypovolemia 4. vasoconstriction

What are the most common causes of sudden drops to zero, progressive drops to zero, and progressive stops to near zero seen on waveform capnographs?

total disconnect or obstruction, incorrect intubation PTE, cardiopulmonary arrest, massive bleed partial disconnect or obstruction

What are the 3 most common causes of increasing ETCO2 readings and waveform height with baseline elevation?

1. rebreathing old sodasorb or one way valve sticking 2. low sampling rate of capnograph 3. bicarbonate administration

What are the 2 most common causes of increasing ETCO2 readings and waveform height without baseline elevation?

1. hypoventilation 2. increased CO2 production by hypermetabolism or malignant hyperthermia

What are 6 causes of abnormal waveforms?

1. ventilator or breathing circuit leak 2. partial airway obstruction 3. spontaneous respirations between ventilatory delivered breaths 4. pleural space disease 5. hiccups 6. cardiogenic oscillations - vascular underload

What are causes of equipment and physiologic dead space?

EQUIPMENT = malfunciton, inappropriate, ET tube beyond nose and Y-piece PHYSIOLOGIC = alveoli not perfused, larger airways that do not participate in gas exchange (trachea)

What does dead space look like on a capnograph?

What are some consequences to increased dead space?

- respiratory acidosis (increased CO2) - sympathetic stimulation - cardiac arrhythmias - variable peripheral vasoconstriction followed by vasodilation - CNS depression, narcosis - increased cerebral blood flow and ICP - tachypnea and increased work associated with breathing - arterial O2 levels decrease to hypoxemia - interferes with adjustments in anestehtics levels

Capnography monitors ventilation and this is based on a basic physiology rule: As ventilation increases, PaC02 and ETC02... a. both decrease b. increase and decrease c. decrease and increase d. both increase

The sample is obtained and the patient is turned off isoflurane allowed to breath 100% oxygen and the as the patient begins to move, blink, swallow and spit out the ET tube, you notice that the Sp02 drops from 98% to 90%. The patient is NOT dyspneic or tachypneic or appears to simply be waking. Which of the following category of issue is likely the cause of the drop in Sp02? a. there is non-respiratory or technical issues b. due to pigmentation not fomerly noticed c. due to low FiO2 d. true hypoxia e. due to an increase in diffusion barrier within lung parenchyma

Which of the following is the correct equation for determining the oxygen content (Ca02) of blood? a, (Hb x 1.34 x CaO2) + (PaO2 x .003) b. (Hb x 1.34 x SaO2) + (PaO2 x .005) c. (Hb x 1.34 x SaO2) + (PaO2 x .003) d. (Hb x 1.34 x SaO2) + (SpO2 x .003) e. (Hb x 1.54 x SaO2) + (PaO2 x .003)

During the procedure when the patient is on 100% oxygen with isoflurane 1.5% and the internist is obtaining her BAL, filling the right middle lung lobe with 50ml of saline for sampling via a small 5 french foley catheter down the ET tube…you notice again that the pulse ox drops precipitously from 95% to 75% as the flush is being administered. The reason for this drop in Sp02 was likely due to which of the 5 classic hypoxemia causes? a. low FiO2 b. V/Q mismatch or shunting c. low albumin d. hypoventilation e. diffusion barrier increase

T three most objective means to assess adequate breathing include which of the following? a. RR and character, pulsoximetry b. pulse oximetry, capnography, and arterial blood gas analysis c. arterial blood gas analysis, pulse ox, oxygen content analysis d. pulse ox, capnography, respiratory character analysis e. BP monitoring, ECG, echo

Five classic causes of hypoxemia include all of the following EXCEPT: a. hypoventilation b. pulmonary shunt c. obstructed ET tube d. increased diffusion barrier e. low FiO2

Which of the following suggest normal readings for a mix breed DSH under general anesthesia, intubated and on sevoflurane in 100% oxygen, with adequate cardiovascular and respiratory status and in a steady safe stage III, plane 2 anesthesia? a. SpO2 88%, ETCO2 37 mmHg b. SpO2 90%, ETCO2 15 mmHg c. SpO2 95%, ETCO2 20 mmHg d. SpO2 94%, ETCO2 45 mmHg e. SpO2 95%, ETCO2 60 mmHg

You are attempting to sell your boss on getting a capnography for the practice. All of the following are reasons he/she should invest in one EXCEPT: a. identified successful resuscitation from cardiopulmonary arrest b. confirms adequate oxygenation c. troubleshoots ventilation and tissue perfusion/metabolism issues d. identifies appropriate intubation e. verifies used sodasorb

If you obtain a low pulse oximeter reading, the three categories of problems which can cause this reading include: a. CV issues, technical issues, metabolic issues b. non-respiratory, hypoxia, shuting c. low FiO2, diffusion barrier, shunting d. non-respiratory (CV), technical, hypoxia e. CV, technical, V/Q mismatch

The largest limitation of the pulse oximeter is which of the following: a. high readiny may indicate a great PaO2 or a really poor PaO2 b. PaO2 and SaO2 are linearly related, nut the curve is sigmoid c. oxygen content is more due to total Hb concentration d. Hb saturation is related more to Hb amounts vs. PaO2 e. SpO2 and SaO2 are often greatly different

Which of the following best describes the advantages of pulse oximetry and capnography over arterial blood gas analysis? Pulse oximetry and capnography (both) are: a. invasive, intermittent, and safe b. invasive, continuous, safe c. safe, noninvasive, continuous d. risky, essential to establish pulse presence e. noninvasive, intermittent, risky

Pulse Oximetry Flashcards

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