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JW: Principles of Anesthesia I > Exam 1- Capnography (6/13/23) > Flashcards

Exam 1- Capnography (6/13/23) Flashcards

1
Q

Effects of Hypercarbia

A
  • Respiratory acidosis can develop over time
  • Increases cerebral blood flow (CBF)
  • Increases ICP in susceptible patients
  • Increases pulmonary vascular resistance, vasoconstriction
  • Potassium shifts from intracellular to intravascular
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2
Q

Effects of Hypocarbia

A
  • Respiratory alkalosis
  • Decreases CBF
  • Decreases pulmonary vascular resistance, vasodilation
  • Potassium shifts to the intracellular space
  • Blunts normal urge to breathe
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3
Q

Capnography provides information primarily on ventilation but can give info on:

A
  • Pulmonary blood flow
  • Aerobic metabolism
  • Placement of ETT/LMA (presence of ETCO2)
  • Integrity of breathing circuit
  • Estimates the adequacy of cardiac output
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4
Q

What is the Bohr equation used to calculate?

A
  • Physiological dead space
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5
Q

Define dead space.

A
  • Volume of each breath inhaled that does not participate in gas exchange
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6
Q

Differentiate anatomical and physiological dead space.

A
  • Anatomic – conducting zones of the airway (nose, trachea, bronchi)
  • Physiologic – airway dead space + alveolar dead space
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7
Q

Define alveolar dead space

A
  • Portion of the physiologic dead space that does not take part in gas exchange but is within the alveolar space
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8
Q

Conditions that increase alveolar dead space (V/Q mismatching)

A
  • Hypovolemia
  • Pulmonary hypotension
  • Pulmonary embolus
  • Ventilation of nonvascular airspace
  • Obstruction of precapillary pulmonary vessels
  • Obstruction of the pulmonary circulation by external forces
  • Overdistension of the alveoli
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9
Q

Measurement and quantification of inhaled or exhaled CO2 concentrations.

A
  • Capnometry
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10
Q

What is capnography?

A
  • Method of CO2 measurement and a graphic display of time
  • Detection of CO2 breath-by-breath
  • Best method to confirm endotracheal intubation
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11
Q

What is time capnography?

A
  • Pressure vs time plot; most common representation
  • CO2 concentrations digitally reported as ‘inspired’ and ‘end tidal’
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12
Q

High-speed vs. low-speed time capnography.

A
  • High-speed – user can interpret information about each breath
  • Slow-speed – appreciation of the expired and inspired trend
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13
Q

What is the most common gas sampling system?

A
  • Side-stream gas analyzer (time delay)
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14
Q

What phase on a capnograph will an ETCO2 be measured at?

A
  • ETCO2 measured at the end-point of phase 3.
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15
Q

What can increase ETCO2?

A
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16
Q

What can decrease ETCO2?

A
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17
Q

Difference between PaCO2 and ETCO2 is approx ____ mmHg.

A
  • 5 mmHg

Ex: ETCO2 of 35 mm Hg = PaCO2 of approx. 40 mm Hg

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18
Q

Problems that increase the difference between PaCO2 and ETCO2.

A
  • V/Q mismatching increases the difference between PaCO2 and PACO2 (PE, endobronchial intubation)
  • Breathing patterns that fail to deliver alveolar gas at the sampling site, increases the difference between PACO2 and true ETCO2 (alveolar gas) - COPD
  • Problems with the capnograph increase the difference between true ETCO2 (alveolar gas) and measured ETCO2 (capnograph)
19
Q

CO2 measurement most commonly relies on _____ light absorption techniques.

A
  • Infrared (IR)

The greater the CO2 in the sample, the less IR light that reaches the detector

20
Q

Describe the color change with a CO2 chemical indicator.

A
  • Purple – No CO2
  • Yellow – CO2

Sensitive to low levels of CO2
ETT placement still needs verification by alternative means

21
Q

What are the CO2 monitor requirements/ standards?

A
  • CO2 reading within +/- 12% of actual value
  • Manufacturers must disclose interference caused by ethanol, acetone, halogenated volatiles
  • Must have a high CO2 alarm for inhaled and exhaled CO2
  • Must have an alarm for low-exhaled CO2
22
Q

Information that can be interpreted from a time capnograph?

A
  • Interpreting CO2 values
  • Approximate blood CO2 levels
  • Pulmonary blood flow
  • Alveolar ventilation
  • Differential diagnosis of loss of exhaled CO2 (esophageal intubation, cardiac arrest)
23
Q

What are the inspiratory and expiratory segments of a normal capnograph?

A
  • Inspiratory – Phase 0
  • Expiratory – Phases I, II, and III
24
Q

Describe Phase I of a normal capnograph.

A
  • Baseline
  • Exhalation of anatomic dead space and the apparatus (ETT, LMA)
  • Essentially no CO2
  • 1/3 of tidal volume is exhaled
25
Q

Describe Phase II of a normal capnograph.

A
  • Expiratory upstroke begins (CO2-rich alveolar gas)
  • Sampling of alveolar gases
  • Normally steep uprise
26
Q

Describe Phase III of a normal capnograph.

A
  • Alveolar Plateau phase
  • Normally representative of CO2 in alveolus
  • Can be representative of ventilation heterogeneity, slightly increasing slope
27
Q

Describe Phase 0 of a normal capnograph.

A
  • Sometimes called phase IV
  • Inspiration of fresh gas, remaining CO2 washed out
  • Downstroke returns to baseline
28
Q

Describe the Occasional Phase IV (Phase IV Prime) of a capnograph.

A
  • A sharp upstroke in PCO2 at the very end of phase III
  • Upstroke probably results from the closure of lung units with lower PCO2
  • Allows for regions with higher CO2 to contribute to more of the exhaled gas sample
  • Seen in pregnant and obese pts
  • Decreased FRC and lung capacity
29
Q

Describe the alpha angle of the capnograph.

A
  • Separates phase II and phase III
  • 100 – 110 degrees
  • Angle increases with an expiratory airflow obstruction
  • Ex: COPD, bronchospasm, or kinked ETT
30
Q

Describe the beta angle of the capnograph.

A
  • Separates phase III and phase 0
  • 90 degrees
  • Angle increases with malfunctioning inspiratory unidirectional valves, rebreathing, and low tidal volume with rapid respiratory rate
31
Q

Describe the capnograph

A
  • Normal Capnograph
  • Mechanical Ventilation
32
Q

Describe the capnograph

A
  • Normal Capnograph
  • Spontaneous Ventilation
33
Q

What is the issue with this capnograph?

A
  • Inadequate Seal around ETT
34
Q

What is causing this capnograph?

A
  • Faulty Inspiratory Valve (top capnograph)
  • Rebreathing (bottom capnograph)
35
Q

What is causing this capnograph?

A
  • Sample line leak
    Take note that this a small wave form and that ETCO2 does not even reach 40 mmHg
36
Q

What is causing this capnograph?

A
  • Hyperventilation
  • Gradually decreasing waveforms
37
Q

What is causing this capnograph?

A
  • Hypoventilation
  • Gradually increasing waveforms
38
Q

What is causing this capnograph?

A
  • Airway obstruction
39
Q

What is causing this capnograph?

A
  • Cardiac oscillation
  • Often seen in pediatric patients, the heart is close to the trachea
40
Q

What is causing this capnograph?

A
  • Re-breathing soda lime exhaustion
    Take note that rebreathing is occurring. The capnograph does not return to baseline.
41
Q

What is causing this capnograph?

A
  • NMBD’s wearing off
  • Presence of a “curare cleft”
42
Q

What is causing this capnograph?

A
  • Over-breathing
  • Notice the spontaneous breath between the mechanical breath
43
Q

What is causing this capnograph?

A
  • Esophageal intubation

JW: Principles of Anesthesia I (61 decks)

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