Capnography

Question 1

What’s the difference between capnography and capnometry?

Answer 1

graphy - graphic display of exhaled and inhaled CO2 over time

metry - numeric representation of CO2

Question 2

What are some uses of capnography? (10)

Answer 2

confirm placement of ETT/LMA, GA case w/out advanced aw (adequate exchange of air and O2), procedural sedation, guide vent settings, detect disconnects, detect resp. disease/abnorm. (COPD, bronchospasm), detect circ. abnorm. (embolism, hypoperf.), detect increase in metabolic rate (MH), estimate PaCO2 ( > etCO2 by 2-5 mmHg under GA), detect critical events, can evaluate dead space

Question 3

What are the contraindications of capnography?

Answer 3

none

Question 4

What is dead space?

Answer 4

area of ventilation but no gas exchange occurring

Question 5

How many types of dead space are there? What are they?

Answer 5

3, anatomic, alveolar and equipment deadspace

Question 6

Where does deadspace start in the airway?

Answer 6

nose, mouth

Question 7

What is the portion of the airway that is deadspace called and what structures are in it?

Answer 7

conducting zone: trachea, bronchi, bronchioles

Question 8

What is the portion of the airway that gas exchange occurs called and what structures are in it?

Answer 8

respiratory zone: respiratory bronchioles, alveolar ducts, alveolar sacs

Question 9

About how much volume of inspired air is dead space and how much is volume is involved in gas exchange?

Answer 9

350 mL gas exchange

150 mL dead space

Question 10

How is etCO2 measured? (4)

Answer 10

infrared absorption spectrophotometry (most common) via sample line
raman spectrography, mass spectrography, colorimetric

Question 11

What two types of measurement techniques are there for capnography?

Answer 11

Mainstream and sidestream

Question 12

What things increase etCO2?

Answer 12

[^ CO2 production and delivery to Lungs]
^ metabolic rate, fever, sepsis, MH, thyrotoxicosis (excess thyroid hormone), increased CO, bicarbonate admin.

[V Alveolar ventilation]
hypovent., resp. center depression, partial muscle paralysis, neuromusc. disease, high spinal anesthesia, COPD

[Equipment malfunction]
rebreathing, exhausted CO2 absorber, leak in ventilator circuit, faulty insp/exp valves

[other]
release of tourniquet, release or aortic/other major vessel clamp, insufflation of CO2 in peritoneal cavity - lap. surgery, ROSC

Question 13

What things decrease etCO2?

Answer 13

[V CO2 production and delivery to lungs]
hypothermia, pulm hypoperfusion, cardiac arrest, PE, hemorrhage, hypotension

[^ alveolar ventilation]
hypervent. - gradual decrease indicates increased VE

[Equipment malfunction]
vent disconnect, esophageal intub, complete aw obstruction, poor sampling, leak around ETT cuff

Question 14

Mainstream capnography is also called ______.

Answer 14

Flow Through

Question 15

What is mainstream capnography? What are its disadvantages? (4)

Advantage?

Answer 15

heated infrared measuring device placed in circuit to measure CO2, sensor must be free of mucous

potential for burns, heavy, increases equipment dead space

Less of a delay

Question 16

Describe Sidestream capnography. Advantage? Disadvantages? (4)

Answer 16

Aspirates fixed amount of gas/minute (30-500 mL/min), gas goes to sampling cell

most common

pediatric populations - sampling can cause low Tv, results in dilution, time delay for reading, potential for disconnection, water vapor can be an issue d/t condensation - need for traps/filters

Question 17

How many phases in the inspiratory phase on a capnogram, name/s? How many phases is the expiratory phase, name/s?

Answer 17

1, Phase 0

3 (4), Phase I, II, III, occasionally IV

Question 18

Describe Phase I of capnography waveform.

Answer 18

Inspiratory baseline, CO2 should be at 0, end of inspiration beginning of expiration, deadspace gas expired

Question 19

Describe Phase II of capnography waveform.

Answer 19

expiratory upstroke, represents CO2 level in sample, slope is dependent on evenness of alveolar emptying, represents a mixture of deadspace and alveolar gas

Question 20

Describe Phase III of capnography waveform.

Answer 20

alveolar plateau, constant or slight upstroke, it is the longest phase, when alveolar gas is sampled, peak at end of plateau is where value is taken (normal 30-40 mmHg)

Question 21

Where is the etCO2 value measured in the capnography waveform? What is a normal value?

Answer 21

peak at the end of Phase III, 30-40 mmHg

Question 22

Describe Phase 0 of capnography waveform.

Answer 22

beginning of inspiration, CO2 value rapidly declines to inspired value (inspiratory downstroke), sometimes called Phase IV by some books

Question 23

Describe Phase IV of capnography waveform.

Answer 23

sharp upstroke at end of Phase III’s plateau, seen in obese and pregnant pts.

Question 24

Describe alpha angle of capnography waveform.

Answer 24

between expiratory upstroke (Phase II) and alveolar plateau (Phase III), normal 100-110 degrees, can use to assess V/Q, if angle is larger than normal (not as sharp expiratory upstroke) can indicate a prolonged expiratory phase: COPD, bronchospasm, kinked ett.

Question 25

Describe beta angle of capnography waveform.

Answer 25

between alveolar plateau (Phase III) and inspiratory downstroke (Phase 0), normal is 90 degrees, larger angle (not as sharp inspiratory downstroke) can indicate: faulty inspiratory valve or CO2 absorbent exhausted

Question 26

What are 5 characteristics to a capnography waveform?

Answer 26

Frequency
Rhythm
Height
Baseline
Shape

Question 27

How does one confirm ETT placement in trachea w/ capnography?

Answer 27

presence of stable CO2 waveform for 3 breaths, CO2 at > 30 mmHg

Question 28

Does capnography indicate proper placement of ETT in trachea?

Answer 28

No, need to auscultate.

Question 29

What can indicate Right bronchial intubation?

Answer 29

Increased PIP

Question 30

What is a shark fin shape on a capnography waveform indicate? Describe traits seen in waveform.

Answer 30

obstructive lung disease (COPD, asthma, bronchoconstriction, acute obstruction)

slow rise Phase II, large alpha angle, steep Phase III (or absent)

Question 31

Describe what an esophageal intubation would look like on capnography.

Answer 31

Initial CO2 reading that decreases and disappears, initial reading may be from insufflation caused by preoxygenation

Question 32

Describe what rebreathing would look like on capnography. What are some causes of rebreathing?

Answer 32

if CO2 does not return to baseline (0 mmHg) at end of inspiration

causes: inadequate FGF, faulty expiratory valve, equipment deadspace, exhausted CO2 absorbent

Question 33

Describe what spontaneous vent. after NMBD would look like on capnography. What’s it indicate?

Answer 33

camel hump shaped, not perfect CO2 waveform, indicates pt may be waking up or that they no long paralyzed - test twitches

Question 34

Describe what cardiac oscillations would look like on capnography. What’s it indicate? Does it require intervention?

Answer 34

Ripples on Phase 0, inspiratory downstroke
More noticeable in peds, w/ decreased Tv and RR
Nothing wrong, no intervention needed.

Question 35

How can you tell you have a faulty inspiratory valve using capnography?

Answer 35

Phase 0, inspiratory downstroke has a part of it where CO2 stays the same (doesn’t decrease) and creates a step pattern

Question 36

What is a Curare Cleft and what can it indicate? What interventions?

Answer 36

during Phase III there may be a decrease in CO2 (instead of steady upward slope)

could indicate: pt attempted spont breath - may need more paralytic or sedation, increase RR

could be: surgeon manipulating pt (depends on surgical site)

check train of four

Question 37

What 4 things can etCO2 indicate changes in?

Answer 37

metabolism, circulation, ventilation, equipment

Question 38

ANY change in etCO2 waveform warrants _______.

Answer 38

investigation