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Nurse Anesthesia Summer 19 > Capnography > Flashcards

Capnography Flashcards

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1
Q

capnogrpahy

A

graph of C02 concentration over time

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2
Q

uses of capnogrpahy

A
  1. gold standard for ventilation
  2. detects circulatory abnormalities
  3. detects excessive aerobic metabolism (malignant hypothermia)
  4. detects proper placement of ETT or LMA with 3 consecutive end tidal breaths
  5. detects circuit disconnect
  6. helps determine adequate exchange of air during anesthesia without an airway
  7. can act as a guide for vent settings (ventilation)
  8. used to evaluate deadspace (increased beta angle)
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3
Q

capnogrpahy for circuit abnormalities

A
  1. pulmonary embolism (VEA will drop end tidal C02)
  2. occult hemorrhage
  3. hypotension
  4. decreased C0
  5. cardiac arrest
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4
Q

capnography vs PaC02

A

PaC02 > PaEtC02

2-5mmHg under

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5
Q

Methods of measuring C02

A
  1. Colorimetric

2. Infrared Absorption Spectrophotometry

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6
Q

Colorimetric

A
  • 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

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7
Q

Infrared absorption spectrophotometry

A
  • 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
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8
Q

Measurement Techniques for infrared absorption

A
  1. Mainstream capnogrpahy

2. Sidestream capnogrpahy

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9
Q

Mainstream Capnography

A

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
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10
Q

Sidestream capnography

A
  • 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

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11
Q

4 phases of capnogram

A

phase 1; inspiratory baseline, first part of expiration

phase 2; expiration

phase 3; alveolar plateau

phase 4; beginning of inspiration

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12
Q

Phase 1

A
  • inspiratory baseline
  • inspiration and first part of expiration
  • deadspace gas is exhaled
  • should have no C02 reading
  • reflect no rebreathing
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13
Q

Phase 2

A
  • 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)

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14
Q

Phase 3

A
  • 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
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15
Q

Phase 4

A
  • beginning of inspiration

- rapid decline to inspired value (zero)

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16
Q

5 characteristics of waveform tracing

A
  1. frequency (RR)
  2. Rhythm
  3. Height (C02 concentration)
  4. Baseline (rebreathing)
  5. Shape
17
Q

Increased EtC02 with unchanged vent settings

A
  1. malignant hyperthermia
  2. release of tourniquet (ortho case) increased C0
  3. release of aortic/ major vessel clamp; increased C0
  4. IV bicarb administration
  5. C02 into peritoneal cavity; C02 very soluble (0.067) absorbed into blood)
  6. equipment defects
    - unidirectional valves stuck open increases dead space, increased rebreathing
    - exhausted C02 scrubber
18
Q

Decreased EtC02

A

-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)

Nurse Anesthesia Summer 19 (11 decks)

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