Capnograph Flashcards
What are the 2 types of capnographs
- Mainstream
- Sidestream
How does sidestream Capnography work
- Sampling tube placed between ET tube & breathing circuit
- Sampling tube transmits gases to measurement device, located away from breathing circuit
How does Mainstream capnograph work?
- Measurement device between ET tube & breathing circuit
- Infrared light within sensor traverses respiratory gases & detected by photodetector
- Sensors are heated to prevent condensation of water vapor
- What is the Optimal rate of sampling for a sidestream capnograph?
- Why is this important to know?
- 50 - 200 ml/min
- If you have a low flow of oxygen (machine can go as low as 200ml/min) your patient can become hypoxemic since the capnograph is taking a lot of the oxygen
What are the different parts of the capnograph
also include the downslope
- (A), Carbon dioxide cleared from the anatomic dead space;
- Phase I (expiratory baseline) is the beginning of exhalation and corresponds to exhalation of CO2-free dead space gas from the larger conducting airways. The CO2 value during this phase should be zero
- (B), dead space and alveolar carbon dioxide
- Phase II (expiratory upstroke) involves exhalation of mixed alveolar and
decreasing dead space gas, which rapidly increases the CO2 concentration
- Phase II (expiratory upstroke) involves exhalation of mixed alveolar and
- (C), alveolar plateau
- Phase III (expiratory plateau) occurs when all the dead space gas has
been exhaled, resulting in exhalation of completely alveolar air. The highest point of phase III corresponds with the actual ETCO2 value. The
plateau has a slight positive slope because of the continuous diffusion of
CO
2 from the capillaries into the alveolar space.
- Phase III (expiratory plateau) occurs when all the dead space gas has
- (D), end-tidal carbon dioxide tension (ETCO2)
- Phase 0 (inspiratory downstroke)—
- Because of inhalation of CO2-free
gas, the CO2 concentration rapidly declines to zero.
- Because of inhalation of CO2-free
What part of the graph is the end-tidal carbon dioxide number that the capnograph shows you?
(D), end-tidal carbon dioxide tension (ETCO2)
What are the advantages and disadvantages of a sidestream capnograph?
- Advantages
- lightweight sampler
- ease of manipulation near the patient
- smaller sample chamber
- ability to sample other gases (i.e. inhaled anesthetics)
- Disadvantages
- plugging of sample line by secretions/condensation
- 2- to 3-second delay
- Need to scavenge aspirated gases***
- dilution of sample from leaks in breathing circuit
What are the Advantage/Disadvantages of a mainstream capnograph
- Advantages
- Real-time measurement (response rate of <100 ms)
- NO scavenging of aspirated gases needed
- Disadvantages
- excessive dead space in patient breathing circuit produced by sensing chamber can lead to false readings
- Weight can cause kinking of ET tube
- Sensing chamber may be contaminated by secretions/condensation
- patients may be burned by heated cuvette
What is the normal difference of EtCO2 and PaCO2 in horses?
can be 10-15 mmHg difference!
Other than EtCO2, what can a capnograph show you
- esophageal intubation,
- airway disconnection,
- airway obstruction,
- leak in endotracheal tube cuff,
- exhaustion of CO2 absorbent**,
- incompetent one-way valve of anesthetic circle system**,
- inadequate O2 flow rate for non-rebreathing (NRB) circuit ** =>∗∗ ↑Inspired CO2
- Capnogram demonstrating a gradual increase in baseline and ETCO2.
- Rebreathing of exhaled gases is the primary reason that the inspiratory phase does not return to the zero baseline
- Capnogram of a nonrebreathing anesthetic system.
- During inspiration, a small rebreathing wave can result from inhalation of CO2.
- The extent of rebreathing depends on fresh gas flow, the tidal volume, and the respiratory rate
Upward sloping plateau representing a bronchospasm or another expiratory obstructive process that prevents complete alveolar emptying.
Capnogram of a patient emerging from neuromuscular blockade
and demonstrating a curare cleft
- Capnogram demonstrating a normal shape but decreased plateau height.
- This can be the result of hypovolemia, hyperventilation, hypothermia, and increased dead space ventilation.
Capnogram demonstrating dilution of ETCO2 by fresh gas flow,
which produces a terminal dip in the plateau.
- Capnogram displaying oscillations during the inspiratory phase.
- They result from cardiac pulsations or fluttering of the inspiratory valve in a rebreathing circuit.
Capnogram with an abnormal plateau and inspiratory downstroke, representing endotracheal tube cuff leakage
Normal time base capnogram demonstrating the waveform after a patient has been mask ventilated with esophageal intubation.
Trend capnogram showing a progressive decrease in ETCO2 associated with onset of cardiopulmonary arrest followed by a progressive increase in ETCO2 with successful CPCR and ROSC
