Anesthesia Gas Monitoring

Question 1

Why do we care?

Answer 1

• inadvertent agent OD
• timing to reach MAC/MAC awake
• error detection in vaporizer filling
• monitor uptake/distribution
• monitor low-flow anesthesia

Question 2

How is gas monitoring measured?

Answer 2

Infrared analysis- gasses with 2+ dissimilar molecular atoms in molecule have specific/unique infrared absorption spectra

Question 3

Can O2 be measured with infrared analysis?

Answer 3

NO! 2 similar atoms in molecule.

Question 4

How is O2 monitoring measured?

Answer 4

-requires paramagnetic/fuel-cell analysis

Question 5

Infrared photospectrometry

Answer 5

• amt of IR rays absorbed is proportional to the concentration of the absorbing molecules
• compared to known standard
• calculated

Question 6

Diverting =

Answer 6

Sidestream sampling

Question 7

How does diverting: sidestream sampling function?

Answer 7

• continuously aspirates a sample of gas from patient circuit near the breathing circuit and airway device connection (as close to the patient as possible)
• detects inspired/expired gases simultaneously

Question 8

How many mls aspirated from diverting: sidestream sampling?

Answer 8

50-250 mls

Question 9

Diverting: Sidestream sampling

Answer 9

• sample directed between infrared emitter, optical filter, & infrared detector -> outputs a signal proportional to remaining infrared E not absorbed by gases -> detected signal amplified/interpreted via microprocessors
• multiple optical filters required if identifying multiple gases simultaneously

Question 10

Advantages of diverting: side stream sampling

Answer 10

• automatic calibration/zeroing
• minimal dead-space
• minimal cross contamination between patients

Question 11

Disadvantages of diverting: side stream sampling

Answer 11

• multiple places leaks could occur
• more variability in CO2 reading
• slower response to changes

Question 12

Non-diverting =

Answer 12

in-line gas sampling

Question 13

How does non-diverting: in-line sampling function?

Answer 13

-measures gas concentration by using sensor that is located DIRECTLY in the gas stream

Question 14

What gases are measured with non-diverting: in-line sampling?

Answer 14

O2 & CO2

Question 15

How does non-diverting: in-line sampling measure CO2?

Answer 15

infrared analysis with sensor between breathing system and patient

Question 16

How dose non-diverting: in-line sampling measure O2?

Answer 16

electrochemical analysis with sensor in the inspiratory limb of breathing circuit

Question 17

Issues with diverting: side stream sampling monitoring

Answer 17

• high sample flow (200 ml/min)
• high flow rate impedes use with infants d/t inspiratory/expiratory flows similar to analyzer
• water vapor, liquid, secretions remain isolated from system (Dfend water trap)

Question 18

Answer 18

Increase EtCO2:

• increased muscular activity (shivering)
• MH
• increased CO (resuscitation)
• Bicarb infusion
• Tourniquet release
• effective bronchospasm therapy (bronchodilation)
• decreased minute ventilation (hypoventilation)

Question 19

Answer 19

Decrease EtCO2:

• decreased muscular activity (NMBA)
• hypothermia
• decreased CO (cardiac arrest)
• pulmonary embolism
• bronchospasm
• increased minute ventilation (hyperventilation)

Question 20

Answer 20

Esophageal intubation- little or no CO2 present

Question 21

Answer 21

Inadequate seal around ETT

possible causes:

1. leaky/deflated cuff
2. airway too small for patient

Question 22

Answer 22

Hypoventilation

possible causes:

1. decreased RR
2. decreased TV
3. increase metabolic rate
4. hyperthermia

Question 23

Answer 23

Hyperventilation

possible causes:

1. increased RR
2. increased TV
3. decreased metabolic rate
4. hypothermia

Question 24

Answer 24

Rebreathing

possible causes:

1. faulty expiratory valve
2. inadequate inspiratory flow
3. insufficient expiratory flow
4. malfunction of CO2 absorbant

Question 25

Answer 25

Obstruction

possible causes:

1. kinked/occluded airway
2. foreign body in airway
3. obstruction in expiratory limb of circuit
4. bronchospasm

Question 26

Answer 26

Muscle relaxants

“curare cleft” appears when NMBA begin to subside

depth of cleft is inversly proportional to degree of blockade

Question 27

Answer 27

faulty ventilator/one way circuit valves

• baseline elevated
• abnormal descending limb of capnogram
• patient rebreathing exhaled gas

Question 28

Answer 28

post-bronchospasm

“shark fin” waveform

Question 29

What are the normal EtCO2 values?

Answer 29

30-43 mmHg

Question 30

What is capnography?

Answer 30

• measurement and display of EtCO2 value and capnogram (waveform)
• measured via capnograph

Question 31

What is capnometry?

Answer 31

• measurement and display of EtCO2 value
• measured via capnometer

Question 32

What is deadspace?

Answer 32

ventilated areas that do not participate in gas exchange

total deadspace = anatomic + alveolar + mechanical

Question 33

Normal EtCO2 waveform (A-E)

Answer 33

A-B- baseline

B-C- expiratory upstroke

C-D- expiratory plateau

D- EtCO2 value

D-E- inspiration begins

Question 34

Sudden loss of EtCO2 waveform

Answer 34

Airway disconnection

apnea

airway obstruction

disloged airway (esophageal)

ventilator malfunction

cardiac arrest

Question 35

Qualitative measure of EtCO2

Answer 35

Colorimetric “detector”

chemically treated paper changes color when exposed to CO2

requires 6 breaths before determination made

gold is “golden”