Capnography And Pulse Oximetry

Question 1

Oxygen dissociation curve landmarks

Answer 1

PaO2 of 60mmHg = SaO2 of 90%
PaO2 of 40mmHg = SaO2 of 75%
The P50 is 27mmHg. The Hb has a saturation of 50% at a PaO2 of 27mmHg

Question 2

Oxyhemoglobin dissociation curve; affinity

Answer 2

The strength of noncovalent binds between two substances, as measured by the dissociation constant of the complex

Question 3

Oxyhemoglobin dissociation curve; left shift

Answer 3

Increased affinity for O2
Low pCO2, H+, 2,3-DPG, temp

Question 4

Oxyhemoglobin dissociation curve; right curve

Answer 4

Decreased affinity for O2
High pCO2, H+, 2,3-DPG, temp
Low pH

Question 5

Haldane effect

Answer 5

Describes the ability of hemoglobin to carry increased amounts of carbon dioxide in the deoxygenated state
A high concentration of CO2 facilitates dissociation of oxyhemoglobin

Question 6

Bohr effect

Answer 6

An increase in CO2 results in a decrease in blood pH, resulting in hemoglobin releasing their load of oxygen
A decrease in CO2 provokes an increase in pH, which results in hemoglobin picking up more oxygen

Question 7

Three types of pulse oximetry

Answer 7

-Photoelectric (optical) plethysmography
-Spectrophotometry
-Light emitting diodes (LEDs)

Question 8

Machine can determine a baseline absorption

Answer 8

Tissue, venous blood flow

Question 9

Dependent on pulsatile flow

Answer 9

Absorption changes due to increased arterialized blood flow, determine baseline absorption, subtracting this baseline, the machine is able to determine absorption by arterial blood

Question 10

Photoelectric (optical) plethysmography

Answer 10

-Uses light absorption to produce waveforms from the blood pulsating in the vascular beds
-The amount of light absorbed is proportional to amount of blood flow
-Maximum absorption during systole and minimum during diastole

Question 11

Spectrophotometry

Answer 11

-uses light wavelengths to measure light absorption through a substance, in our case blood
-the two wavelengths that are used in pulse oximetry are; red light - wavelength of 660nm, infrared light - wavelength of 920nm

Question 12

Light emitting diodes (LED)

Answer 12

2 types of oximeter sensors are used; transmission, reflective

Question 13

Measurement in pulse oximetry

Answer 13

-The saturation that we see is calculated
-This is called a functional saturation
-Functional saturation is the ratio of HbO2 to the total Hb available for binding with O2

Question 14

Indications for using oximetry

Answer 14

-Noninvasive
-For continuous monitoring of arterial oxyhemoglobin saturation
-To monitor the adequacy of oxyhemoglobin saturation

Question 15

Advantages of pulse oximetry

Answer 15

-Noninvasive
-Saturations can be monitored continuously at the bedside in real time
-Little training or knowledge is required to use the equipment
-Safe and usually quite accurate

Question 16

Disadvantages of pulse oximetry

Answer 16

-Abnormal forms of Hb can not be measured
-HbCO is measured as HbO2 therefore false SpO2 readings
-Not as accurate as co-oximetry

Question 17

Appropriate oximetry sites

Answer 17

-Finger, toe
-Ear
-Bridge of nose
-Forehead
-Infant; across the foot or hand

Question 18

Factors that effect the accuracy of pulse oximetry

Answer 18

-Motion
-Low perfusion
-External lights
-False nails / nail polish
-Wring types of sensor or incorrect placement
-Dysfunctional Hb, anemia
-Vascular dyes

Question 19

Accuracy of pulse oximetry

Answer 19

-Accurate witching 2-4% until SpO2 of 80
-False high readings with SpO2 <80

Question 20

PaCO2

Answer 20

Partial pressure of CO2 in arterial blood

Question 21

EtCO2

Answer 21

Measurement of the concentration of CO2 at the end of exhalation

Question 22

A-ADCO2

Answer 22

Difference between ETCO2 and PaCO2 (normally 2-5 mmHg)

Question 23

Capnometry

Answer 23

Measurement and the numerical display of CO2 at the patient’s airway

Question 24

Capnography

Answer 24

Measurement and waveform display of CO2 concentration at the patient’s airway

Question 25

Capnogram

Answer 25

Waveform display of CO2 throughout respiration

Question 26

Indications for ETCO2; intubated applications

Answer 26

-verifying ETT placement, monitoring ETT position during transport, head injury, CPR (effectiveness of cardiac compressions, earliest sign of ROSC, predictor of survival)

Question 27

Indications for ETCO2; non-intubated applications

Answer 27

-Bronchospastic disease; asthma, COPD -Hypoventilation states -Shock states; sepsis, hypovolemia, anaphylaxis, cardiogenic -Hyperventilation

Question 28

Types of ETCO2 monitoring devices

Answer 28

-Spectrophotometry -Colorimetric -Mainstream -Slidestream -Microstream

Question 29

ETCO2 Spectrophotometry

Answer 29

Infrared absorption Increased CO2 = increased absorption

Question 30

ETCO2 mainstream

Answer 30

-In-line with subjects exhaled gas via ETT -Can pull on the airway (heavy) -Slight increase in dead space

Question 31

ETCO2 slidestream

Answer 31

-Sample rate -150mL / min -Slight lag in response time -Slight increase in dead space -Sample line can occlude with condensation

Question 32

ETCO2 microstream

Answer 32

-Newer units have a reduced sample rate - 50mL / min; reduces secretion aspiration -Smaller bore sample line; quicker response time -Incorporate nafion tubing to minimize H2O content -Small sample cell (15uL); quick response time

Question 33

ETCO2 Capnogram; phase 1

Answer 33

Respiratory baseline -Flat -No CO2 present -Corresponds with late inspiratory / early expiration part of respiratory cycle

Question 34

ETCO2 Capnogram; phase 2

Answer 34

Respiratory upstroke -Mixture of dead space and alveolar gases

Question 35

ETCO2 Capnogram; phase 3

Answer 35

Respiratory plateau -Represents air from ventilated alveoli -Nearly constant CO2 level -Highest point = ETCO2 -Recorded by capnometer

Question 36

ETCO2 Capnogram; phase 4

Answer 36

Inspiratory phase -Sudden downstroke to baseline as atmospheric air is inspired

Question 37

Normal values

Answer 37

PaCO2: 35-45 mmHg ETCO2: 35-45 mmHg Difference between PaCO2 and ETCO2 is approx 2-5 mmHg

Question 38

Causes of Low ETCO2

Answer 38

-Mechanical; circuit disconnect, leaks -Respiratory; airway obstruction, Bronchospasm, displaced ET tube, hyperventilation, mucous plug -Circulatory; cardiac arrest, embolism, sudden hypovolemia -Metabolic; hypothermia

Question 39

Causes of High ETCO2

Answer 39

-Mechanical; excessive mechanical dead space, faulty valve -Respiratory; COPD, respiratory depression or insufficiency -Circulatory; increased cardiac output -Metabolic; hyperthermia, malignant hyperthermia

Question 40

Verifying ETT placement

Answer 40

-Sensitivity and specifics are up to 100% -Can’t be used to detect bronchial or some hypopharyngeal misplacements -Time to detect esophageal intubation using capnography; 1.6 +/- 2.4 sec -Time to detection of esophageal intubation using clinical signs; 97 +/- 92 sec

Question 41

ETCO2 during CPR

Answer 41

-Square box waveform -ETCO2 10-15 mmHg (possibly higher) with adequate CPR -Change rescuers if ETCO2 falls below 10 mmHg -Will detect ROSC