Capnography Flashcards
What’s the difference between capnography and capnometry?
graphy - graphic display of exhaled and inhaled CO2 over time
metry - numeric representation of CO2
What are some uses of capnography? (10)
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
What are the contraindications of capnography?
none
What is dead space?
area of ventilation but no gas exchange occurring
How many types of dead space are there? What are they?
3, anatomic, alveolar and equipment deadspace
Where does deadspace start in the airway?
nose, mouth
What is the portion of the airway that is deadspace called and what structures are in it?
conducting zone: trachea, bronchi, bronchioles
What is the portion of the airway that gas exchange occurs called and what structures are in it?
respiratory zone: respiratory bronchioles, alveolar ducts, alveolar sacs
About how much volume of inspired air is dead space and how much is volume is involved in gas exchange?
350 mL gas exchange
150 mL dead space
How is etCO2 measured? (4)
infrared absorption spectrophotometry (most common) via sample line
raman spectrography, mass spectrography, colorimetric
What two types of measurement techniques are there for capnography?
Mainstream and sidestream
What things increase etCO2?
[^ 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
What things decrease etCO2?
[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
Mainstream capnography is also called ______.
Flow Through
What is mainstream capnography? What are its disadvantages? (4)
Advantage?
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
Describe Sidestream capnography. Advantage? Disadvantages? (4)
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
How many phases in the inspiratory phase on a capnogram, name/s? How many phases is the expiratory phase, name/s?
1, Phase 0
3 (4), Phase I, II, III, occasionally IV
Describe Phase I of capnography waveform.
Inspiratory baseline, CO2 should be at 0, end of inspiration beginning of expiration, deadspace gas expired
Describe Phase II of capnography waveform.
expiratory upstroke, represents CO2 level in sample, slope is dependent on evenness of alveolar emptying, represents a mixture of deadspace and alveolar gas
Describe Phase III of capnography waveform.
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)
Where is the etCO2 value measured in the capnography waveform? What is a normal value?
peak at the end of Phase III, 30-40 mmHg
Describe Phase 0 of capnography waveform.
beginning of inspiration, CO2 value rapidly declines to inspired value (inspiratory downstroke), sometimes called Phase IV by some books
Describe Phase IV of capnography waveform.
sharp upstroke at end of Phase III’s plateau, seen in obese and pregnant pts.
Describe alpha angle of capnography waveform.
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.
