Gas Monitoring Flashcards
Delay time of gas monitor
Time to achieve 10% of a step change in reading at the gas monitor
Rise time of gas monitor
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
What is a sensor in terms of gas monitoring?
Part of a respiratory gas monitor that is sensitive to the gas being measured
In-Line gas sampling
“non-diverting” Measures gas concentration by using sensor located directly in gas stream.
Sidestream sampling- what does it do?
“Diverting” - Continuously aspirates sample of gas from patient circuit near where breathing circuit is connected to airway device. 50-250 mL/min aspirated.
Sampling tube
Conduit for transferring gas from the sampling site to the sensor in a diverting gas monitor
Partial Pressure of a Gas
Pressure that a gas in a gas mixture would exert if it alone occupied the volume of the mixture at the same temperature
Volume Percent
Volume of a gas in a mixture
Nondiverting gas monitor
Measures gas concentration by using a sensor located directly in the gas stream- only measures oxygen and CO2
Infrared analysis measures what?
CO2, N2O, volatiles - not O2 or Nitrogen- must be able to measure 2 or more dissimilar molecular atoms
Paramagnetic oxygen analysis measures what & how?
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
Electrochemical oxygen analysis measures what & how?
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
Chemical carbon dioxide detection measures what
CO2- when the indicator is exposed to carbonic acid from CO2+H2O it becomes more acidic and changes color
Increase in ETCO2 from what?
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
Decrease in ETCO2 from what?
Hypothermia, increased depth of anesthesia, decreased muscular activity, decreased Cardiac Output/cardiac arrest, pulmonary embolism, bronchospasm, increased minute ventilation
What can diverting sample be used for?
If multiple optical filters are used, can identify multiple gases simultaneously
Pros & cons of diverting sampling
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)
What can non-diverting sampling be used for?
oxygen & CO2 (CO2 uses infrared technology, oxygen uses electrochemical technology placed in inspiratory limb)
What is Dfend?
The water trap on the unit that keeps water vapor, liquid & patient secretions isolated from the system
Calibration of oxygen analyzer
Each day before use & every 8 hours, expose the sensor to room air & make sure it reads 21%
Why do we monitor End-Tidal CO2***
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
How does capnography work?
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
Average end-tidal CO2 in non-survivors of cardiac resuscitation (association with poor outcomes)
4-10 mmHg
Average end-tidal CO2 in survivors of cardiac resuscitation (association with good outcomes)
>30 mmHg
What can an end-tidal CO2 waveform tell someone in resuscitation?
If pulmonary ventilation is consistent with bagging, ETCO2 will directly reflect CO - flat waveform = PEA, increasing ETCO2 = possible return of spontaneous ventilation, increased CO..
Normal arterial CO2 level
35-45 mmHg
Normal ETCO2 from capnograph
30-43 mmHg(dead space)
Capnography
Measurement & display of both ETCO2 value & capnograph, measured by a capnograph
Capnometry
Measurement & display of ETCO2 value (no waveform), measured by capnometer
Explain deadspace
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)
Name A-B, B-C, C-D, D, D-E
A-B is baseline, B-C is expiratory upstroke, C-D is expiratory plateau, D is ETCO2 value, D-E inspiration begins
What is this waveform?
Sudden loss of waveform, #1 thought- airway disconnect! Apnea, airway obstruction (severe bronchospasm), dislodged airway, vent malfunction, cardiac arrest
Esophageal intubation, mauybe have little or no CO2
Inadequate seal around ETT from leaky/deflated ETT or tracheostomy cuff or artifical airway too small for patient
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
Hyperventilation (decrease ETCO2) from increased RR, increase TV, decrease in metabolic rate (CO), fall in body temperature
Rebreathing (not exhaling off all CO2.. stair stepping), from faulty expiratory valve, inadequate inspiratory flow, insufficient expiratory flow, malfunction of CO2 absorber**
What number signifies you need to change CO2 absorber?
5-10 inspired CO2
Obstruction from: partially kinked/occluded artifial airway, presence of foreign body in airway, obstruction in expiratory limb of breathing circuit, bronchospasm, asthma
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…)
Faulty ventilator one way circuit valves - baseline will elevate, abnormal descending limb of capnogram, allows patient to rebreath exhaled gas
Colorimetric CO2 detector
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”
Sidestream sampling - how it works, specifically
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.
