Gas Monitoring

Question 1

Delay time of gas monitor

Answer 1

Time to achieve 10% of a step change in reading at the gas monitor

Question 2

Rise time of gas monitor

Answer 2

Time required for a change from 10% to 90% of the total change in a gas value with a change in concentration at the sampling site

Question 3

What is a sensor in terms of gas monitoring?

Answer 3

Part of a respiratory gas monitor that is sensitive to the gas being measured

Question 4

In-Line gas sampling

Answer 4

“non-diverting” Measures gas concentration by using sensor located directly in gas stream.

Question 5

Sidestream sampling- what does it do?

Answer 5

“Diverting” - Continuously aspirates sample of gas from patient circuit near where breathing circuit is connected to airway device. 50-250 mL/min aspirated.

Question 6

Sampling tube

Answer 6

Conduit for transferring gas from the sampling site to the sensor in a diverting gas monitor

Question 7

Partial Pressure of a Gas

Answer 7

Pressure that a gas in a gas mixture would exert if it alone occupied the volume of the mixture at the same temperature

Question 8

Volume Percent

Answer 8

Volume of a gas in a mixture

Question 9

Nondiverting gas monitor

Answer 9

Measures gas concentration by using a sensor located directly in the gas stream- only measures oxygen and CO2

Question 10

Infrared analysis measures what?

Answer 10

CO2, N2O, volatiles - not O2 or Nitrogen- must be able to measure 2 or more dissimilar molecular atoms

Question 11

Paramagnetic oxygen analysis measures what & how?

Answer 11

Oxygen- expansion & contraction of the gas creates a pressure wave proportional to oxygen’s partial pressure which is sensed & converted from mechanical to electrical signal

Question 12

Electrochemical oxygen analysis measures what & how?

Answer 12

oxygen, usually in inspiratory limb, oxygen diffuses through sensor - rate at which oxygen enters generates a current proportional to the partial pressure of the gas outside the membrane… NEEDS CALIBRATION EVERY 8 HOURS

Question 13

Chemical carbon dioxide detection measures what

Answer 13

CO2- when the indicator is exposed to carbonic acid from CO2+H2O it becomes more acidic and changes color

Question 14

Increase in ETCO2 from what?

Answer 14

absorption of CO2 from peritoneal cavity, injection of NaHCO3, pain, anxiety, shivering, increased muscle tone, convulsions, (malignant) hyperthermia, restoration of peripheral circulation after it has been impaired – tourniquet (ortho procedures), effective drug therapy for bronchospasm, decreased minute ventilation

Question 15

Decrease in ETCO2 from what?

Answer 15

Hypothermia, increased depth of anesthesia, decreased muscular activity, decreased Cardiac Output/cardiac arrest, pulmonary embolism, bronchospasm, increased minute ventilation

Question 16

What can diverting sample be used for?

Answer 16

If multiple optical filters are used, can identify multiple gases simultaneously

Question 17

Pros & cons of diverting sampling

Answer 17

Good: automatic calibration/zeroing, minimal added dead space, low potential for cross-contamination between patients. Bad: Multiple places that leaks may occur, more variability in CO2 readings, slower response to changes, cannot be used with infants (high flow rate impedes inspiratory/expiratory flows)

Question 18

What can non-diverting sampling be used for?

Answer 18

oxygen & CO2 (CO2 uses infrared technology, oxygen uses electrochemical technology placed in inspiratory limb)

Question 19

What is Dfend?

Answer 19

The water trap on the unit that keeps water vapor, liquid & patient secretions isolated from the system

Question 20

Calibration of oxygen analyzer

Answer 20

Each day before use & every 8 hours, expose the sensor to room air & make sure it reads 21%

Question 21

Why do we monitor End-Tidal CO2***

Answer 21

Validation of proper ETT placement, detection & monitoring of respiratory depression, hyper/hypoventilation, cardiac function (poor mans cardiac output monitor), adjustment of parameter settings in mechanically ventilated patients

Question 22

How does capnography work?

Answer 22

Beam of infrared light energy passed through gas sample containing CO2, CO2 molecules absorb specific wavelengths of infrared light energy, light emerging from sample is analyzed, ration of CO2 affected wavelengths to the non-affected wavelengths is reported as ETCO2

Question 23

Average end-tidal CO2 in non-survivors of cardiac resuscitation (association with poor outcomes)

Answer 23

4-10 mmHg

Question 24

Average end-tidal CO2 in survivors of cardiac resuscitation (association with good outcomes)

Answer 24

>30 mmHg

Question 25

What can an end-tidal CO2 waveform tell someone in resuscitation?

Answer 25

If pulmonary ventilation is consistent with bagging, ETCO2 will directly reflect CO - flat waveform = PEA, increasing ETCO2 = possible return of spontaneous ventilation, increased CO..

Question 26

Normal arterial CO2 level

Answer 26

35-45 mmHg

Question 27

Normal ETCO2 from capnograph

Answer 27

30-43 mmHg(dead space)

Question 28

Capnography

Answer 28

Measurement & display of both ETCO2 value & capnograph, measured by a capnograph

Question 29

Capnometry

Answer 29

Measurement & display of ETCO2 value (no waveform), measured by capnometer

Question 30

Explain deadspace

Answer 30

wasted ventilation - areas which do not participate in gas exchange. Anatomic - airways leading to alveoli, alveolar - ventilated areas in the lungs without blood flow (PE), mechanical - artificial airways including ventilator circuits (rebreathing)

Question 31

Name A-B, B-C, C-D, D, D-E

Answer 31

A-B is baseline, B-C is expiratory upstroke, C-D is expiratory plateau, D is ETCO2 value, D-E inspiration begins

Question 32

What is this waveform?

Answer 32

Sudden loss of waveform, #1 thought- airway disconnect! Apnea, airway obstruction (severe bronchospasm), dislodged airway, vent malfunction, cardiac arrest

Question 33

Answer 33

Esophageal intubation, mauybe have little or no CO2

Question 34

Answer 34

Inadequate seal around ETT from leaky/deflated ETT or tracheostomy cuff or artifical airway too small for patient

Question 35

Answer 35

Hypoventilaion (ETCO2 increasing) from decrease in RR, decrease in TV, increase in metabolic rate (thyroid storm, seizing, malignant hyperthermia, increased CO), rapid rise in body temperature

Question 36

Answer 36

Hyperventilation (decrease ETCO2) from increased RR, increase TV, decrease in metabolic rate (CO), fall in body temperature

Question 37

Answer 37

Rebreathing (not exhaling off all CO2.. stair stepping), from faulty expiratory valve, inadequate inspiratory flow, insufficient expiratory flow, malfunction of CO2 absorber**

Question 38

What number signifies you need to change CO2 absorber?

Answer 38

5-10 inspired CO2

Question 39

Answer 39

Obstruction from: partially kinked/occluded artifial airway, presence of foreign body in airway, obstruction in expiratory limb of breathing circuit, bronchospasm, asthma

Question 40

Answer 40

Muscle relaxants “curare cleft” - appears when muscle relaxant begins to subside - depth of cleft is inversely proportional to degree of drug activity (never measure depth…)

Question 41

Answer 41

Faulty ventilator one way circuit valves - baseline will elevate, abnormal descending limb of capnogram, allows patient to rebreath exhaled gas

Question 42

Colorimetric CO2 detector

Answer 42

Not a monitor - uses chemicallyt reated paper that changes color when exposed to CO2, must match color ot a range of values, requires 6 breaths before determination can be made “gold is golden”

Question 43

Sidestream sampling - how it works, specifically

Answer 43

Sample is directed to a place between infrared emitter, optical filter, and infrared detector, which outputs a signal proportional to remaining infrared energy not absorbed by the gases.. for multiple gases - multiple optical filters are required. The detected signal is amplified and interpreted via microprocessors.