E1- Capnography 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
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
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
4
Q
What is the Bohr equation used to calculate?
A
- Physiological dead space
5
Q
Define dead space.
A
- Volume of each breath inhaled that does not participate in gas exchange
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
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
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
9
Q
Measurement and quantification of inhaled or exhaled CO2 concentrations.
A
- Capnometry
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
11
Q
What is time capnography?
A
- Pressure vs time plot; most common representation
- CO2 concentrations digitally reported as ‘inspired’ and ‘end tidal’
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
13
Q
What is the most common gas sampling system?
A
- Side-stream gas analyzer (time delay)
14
Q
What phase on a capnograph will an ETCO2 be measured at?
A
- ETCO2 measured at the end-point of phase 3.
15
Q
What can increase ETCO2?
A
16
Q
What can decrease ETCO2?
A
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
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
Describe Phase II of a normal capnograph.
* Expiratory upstroke begins (CO2-rich alveolar gas)
* Sampling of alveolar gases
* Normally steep uprise
26
Describe Phase III of a normal capnograph.
* Alveolar Plateau phase
* Normally representative of CO2 in alveolus
* Can be representative of ventilation heterogeneity, slightly increasing slope
27
Describe Phase 0 of a normal capnograph.
* Sometimes called phase IV
* Inspiration of fresh gas, remaining CO2 washed out
* Downstroke returns to baseline
28
Describe the Occasional Phase IV (Phase IV Prime) of a capnograph.
* 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
Describe the alpha angle of the capnograph.
* Separates phase II and phase III
* 100 – 110 degrees
* Angle increases with an expiratory airflow obstruction
* Ex: COPD, bronchospasm, or kinked ETT
30
Describe the beta angle of the capnograph.
* 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
Describe the capnograph
* Normal Capnograph
* Mechanical Ventilation
32
Describe the capnograph
* Normal Capnograph
* Spontaneous Ventilation
33
What is the issue with this capnograph?
* Inadequate Seal around ETT
34
What is causing this capnograph?
* Faulty Inspiratory Valve (top capnograph)
* Rebreathing (bottom capnograph)
35
What is causing this capnograph?
* Sample line leak
*Take note that this a small wave form and that ETCO2 does not even reach 40 mmHg*
36
What is causing this capnograph?
* Hyperventilation
* Gradually decreasing waveforms
37
What is causing this capnograph?
* Hypoventilation
* Gradually increasing waveforms
38
What is causing this capnograph?
* Airway obstruction
39
What is causing this capnograph?
* Cardiac oscillation
* Often seen in pediatric patients, the heart is close to the trachea
40
What is causing this capnograph?
* Re-breathing soda lime exhaustion
*Take note that rebreathing is occurring. The capnograph does not return to baseline.*
41
What is causing this capnograph?
* NMBD's wearing off
* Presence of a "curare cleft"
42
What is causing this capnograph?
* Over-breathing
* Notice the spontaneous breath between the mechanical breath
43
What is causing this capnograph?
* Esophageal intubation
