Capnography Flashcards
capnogrpahy
graph of C02 concentration over time
uses of capnogrpahy
- gold standard for ventilation
- detects circulatory abnormalities
- detects excessive aerobic metabolism (malignant hypothermia)
- detects proper placement of ETT or LMA with 3 consecutive end tidal breaths
- detects circuit disconnect
- helps determine adequate exchange of air during anesthesia without an airway
- can act as a guide for vent settings (ventilation)
- used to evaluate deadspace (increased beta angle)
capnogrpahy for circuit abnormalities
- pulmonary embolism (VEA will drop end tidal C02)
- occult hemorrhage
- hypotension
- decreased C0
- cardiac arrest
capnography vs PaC02
PaC02 > PaEtC02
2-5mmHg under
Methods of measuring C02
- Colorimetric
2. Infrared Absorption Spectrophotometry
Colorimetric
- rapid assessment of C02 present
- uses metacresol purple impregnated paper that changes color. when acid is present
*like a C02 scrubber
C02 + H20 = carbonic acid = paper changes color
Infrared absorption spectrophotometry
- Most common
- gas mixture is analyzed and each gas absorbs infrared radiation at different wavelengths
- C02 is measured by its absorption at specific wavelengths
- other gases absorption is filtered out
Measurement Techniques for infrared absorption
- Mainstream capnogrpahy
2. Sidestream capnogrpahy
Mainstream Capnography
AKA Flow through
- heated (40 degrees) infrared measuring device placed in circuit
- less time delay
- sensor window must be cleared of mucous
- adds weight and headspace to circuit (risk of kinking ETT)
- newer technology not as bad
- potential for burns with heated sensor
Sidestream capnography
- aspirates a fixed amount of gas/min (30- 500ml/min) via tube and send it to the sampling cell
- best if located as close to expiration port as possible
- sample must pass through filters and water traps
- time delay
- risk of disconnect
*keep in mind with pedi pt and closed-circuit bc you are aspirating volume
4 phases of capnogram
phase 1; inspiratory baseline, first part of expiration
phase 2; expiration
phase 3; alveolar plateau
phase 4; beginning of inspiration
Phase 1
- inspiratory baseline
- inspiration and first part of expiration
- deadspace gas is exhaled
- should have no C02 reading
- reflect no rebreathing
Phase 2
- expiration
- exhale alveolar gas
- upstroke represents rising C02
- slope is determined by evenness of alveolar emptying
- steeper slope more even emptying
- slanted air trapping (uneven emptying) asthma, COPD
-its a mixture of exhaled alveolar gas and deadspace gas (exhale in phase 1)
Phase 3
- alveolar plateau
- longest phase
- constant or slight upstroke
- peak at the end is where the reading is taken of a sample of alveolar gas
- normal value 30-40
Phase 4
- beginning of inspiration
- rapid decline to inspired value (zero)
5 characteristics of waveform tracing
- frequency (RR)
- Rhythm
- Height (C02 concentration)
- Baseline (rebreathing)
- Shape
Increased EtC02 with unchanged vent settings
- malignant hyperthermia
- release of tourniquet (ortho case) increased C0
- release of aortic/ major vessel clamp; increased C0
- IV bicarb administration
- C02 into peritoneal cavity; C02 very soluble (0.067) absorbed into blood)
- equipment defects
- unidirectional valves stuck open increases dead space, increased rebreathing
- exhausted C02 scrubber
Decreased EtC02
-hyperventilation; gradual decrease reflective of increased MV
- Pulmonary embolism (rapid decrease)
- increased difference between PaC02 and EtC02
- V/Q mismatch (rapid decrease)
- increased difference between Paco2 and Etco2
- we create a V/Q mismatch with positive pressure ventilations
- cardiac arrest
- sampling errors (dead space gas instead of alveolar gas)
