Capnography

Question 1

-What is the purpose of capnography

Answer 1

• confirms ETT and LMA placement
• determines adequate ventilation
• guides ventilator setting changes
• detects circuit disconnections
• detects circulatory abnormalities
• detects excessive aerobic metabolism
• *there are no contraindications

Question 2

What are clinical use of capnography

Answer 2

-may be used to estimate the PaCO2-pETCO2 gradient
(Usually 2-5 mmHg under general anesthesia)
-used as an evaluation of dead space

Question 3

What increases the PaCO2 > pETCO2 gradient?

Answer 3

• anything that inhibits the removal of CO2, or leak in the system
• V/Q mismatch
• increased dead space
• R to L shunt
• upper airway obstruction
• leak in the sample line, ETT, or LMA
• poor seal from ETT or LMA

Question 4

What are two methods of measuring CO2 in expired gases

Answer 4

• colorimetric

- infrared absorption spectrophotometry (most common)

Question 5

How does colorimetric assessment work?

Answer 5

-purple impregnated paper changes color to gold in the presence of acid (CO2 +H2O = H2CO3)

Question 6

What is infrared absorption spectrophotometry work?

Answer 6

• analyzes mixtures of expired gas (CO2, volatile anesthetic etc)
• each gas absorbs infrared radiation at different wavelengths
• the amount of CO2 is measured by detecting its absorbance at specific wavelengths and filtering the absorbance related to other gases

Question 7

What is Mainstream Capnography

Answer 7

• heated infrared measuring device placed in circuit

Question 8

What are some issues with mainstream capnography?

Answer 8

• can cause potential burns/fire to the patient because it is heated
• adds weight and dead space to the breathing circuit
• sensor must be clear of mucous in order to work properly

Question 9

What are some advantages to mainstream capnography?

Answer 9

-creates faster results than side stream

Question 10

What is sidestream capnography?

Answer 10

-port that comes off the elbow of the ETT, that aspirates (30-550mL) of exhaled gas and transports to sampling cell for analysis (CO2, anesthetic gas)

Question 11

What are some disadvantages of sidestream capnography?

Answer 11

• pulling off 30-500mL of gas is a lot of gas
• this large sample size may result in dilution of the ETCO2 sample
• there is a time delay (~30 sec) between exhalation and result
• *(if you are using sidestream in OR for confirmation of placement—utilize this time delay to listen for BBL, chest rise ETT fogging)
• potential for disconnection from source
• water vapor can get in the tube creating condensation —> traps or filters are sometimes required to prevent this

Question 12

Capnography waveform

Answer 12

• has 4 phases

- displays PCO2 vs time

Question 13

Phase I

Answer 13

• an inspiratory baseline
• should have zero mmHg
• reflects inspiration and first part of exhalation
• the exhalation is zero due to dead space

Question 14

Phase II

Answer 14

• exploratory upstroke
• beginning portion of slope is dead space ventilation
• latter portion of the slope is alveolar ventilation
• slope determined by evenness of alveolar emptying
• prolonged in obstruction of exhalation: COPD, ETT kink, asthma, bronchospasm, acute obstruction

Question 15

Phase III

Answer 15

• alveolar plateau
• constant or slight upstroke
• longest phase
• alveolar gas sampled
• peak portion at the end of plateau is where the reading is actually taken from
• normal value = 30-40 mmHg
• reflection of the PACO2 and PaCO2

Question 16

Phase IV

Answer 16

• beginning of inspiration

- CO2 concentration experiences a rapid decline

Question 17

Alpha Angle of CO2 waveform

Answer 17

• normally 100-110 degree

- if increased indicates airflow obstruction COPD, bronchospasm, kinked ETT

Question 18

Beta angle CO2 waveform

Answer 18

• normal 90 degrees

- if increased, would signify rebreathing (faulty inspiratory valve, exhausted CO2 absorber)

Question 19

What five characteristics do you interpret in an ETCO2 waveform?

Answer 19

• frequency (RR)
• height (how much CO2)
• shape (obstruction of exhalation or rebreathing)
• rhythm (abnormal - phase II of emergence)
• baseline (rebreathing)

Question 20

What is the primary use of the ETCO2 waveform?

Answer 20

-confirm ETT placement

Question 21

What indicates tracheal intubation?

Answer 21

3 waveforms > 30mmHg

Question 22

Does it indicate proper placement in the trachea?

Answer 22

-NO! Listen for BBS

Question 23

COPD, asthma, kinked ETT, bronchospasm waveform

Answer 23

• gradual rise in Phase II
• steep upslope of Phase III
• increased alpha angle

Question 24

Esophageal intubation ETCO2 morphology

Answer 24

• little blips which indicate presence of acid

Question 25

Rebreathing waveform

Answer 25

- baseline is above zero - increased beta angle - (think exhausted CO2 absorber or faulty inspiratory valve)

Question 26

Spontaneous ventilation/recovery from NMBA on ETCO2 waveform

Answer 26

- create a QRA “cleft” in phase 3 - this might indicate they can be pressure supported - this might indicate the patient needs more NMBA or sedative

Question 27

Cardiac oscillations

Answer 27

- transient waves from heart beats - as the heart is beating it motions the esophagus lying behind the trachea; cardiac oscillations are translated to the ETCO2 waveform

Question 28

What factors affect the proper ETCO2

Answer 28

- CO2 production - transport of CO2 to lungs via pulmonary (Q) - ventilation to transport CO2 to the breathing circuit - proper functioning equipment

Question 29

What are some causes of elevated ETCO2?

Answer 29

Malignant hyperthermia (increased production) Release of tourniquet (sudden increased in perfusion) Release of aortic or major vessel clamp (sudden increase in perfusion) IV Bicarb administration (increase production) Insufflation of CO2 in abdominal cavity (increased production) CO2 absorber exhausted (rebreathing) Valve malfunction (rebreathing) Increased dead space (decreases ventilation) Hypoventilation (decreases ventilation)

Question 30

How does IV sodium Bicarb increase ETCO2

Answer 30

- acidotic state = increased circulating H+ ions - add base (NaHCO3-) to bind with H+ - creates H2CO3 which is a weak acid - H2CO3 disassociates into H2O and CO2

Question 31

What are some causes of depressed ETCO2

Answer 31

- hypothermia (decrease production) - cardiac arrest (decrease production) - V/Q mismatch (decrease perfusion or ventilation) (rapid) - P.E (decrease perfusion) (rapid) - hyperventilation (transient decrease) - vent disconnect (equipment issue) - sample line leak or high sample rate (equipment issue) - esophageal intubation (equipment issue) - poor ETT/LMA seal (equipment issue)