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