Anesthesia Gas Monitoring Flashcards
How is oxygen measured since it cannot be measure through infrared analysis?
- Oxygen is monitored through paramagnetic or fuel-cell oxygen
Infrared Analysis
- Based on the principle that gasses with two or more dissimilar molecular atoms in the molecule have specific and unique absorption spectra
- N2O, halogenated agents
- NOT OXYGEN
What is diverting (sidestream sampling)?
Continuously aspirates a sample of gas from the patient circuit (near where the breathing circuit connects to airway device)
- 50-250 ml/min are aspirated
- To quantify and identify multiple gases simultaneously, multiple optical filters are required
What are the advantages to diverting (sidestream sampling)?
- Automatic calibration and zeroing
- Minimal added dead space
- Low potential for cross-contamination between patients
What are some disadvantages of diverting (sidestream sampling)?
- Multiple places leaks could occur
- More variability in CO2 readings than with in-line sampling
- Slower response to changes than with in-line sampling
What is non-diverting (in-line sampling)?
Measures gas concentration by using a sensor that is located directly in the gas stream
*only oxygen and CO2 are being monitored by this method currently
What are the 2 ways to measure oxygen?
- Inline sampling using the fuel cell
2. Diverting sampling using the paramagnetic oxygen analysis
What is Paramagnetic Oxygen Analysis?
- When oxygen passes through a magnetic field, it goes to the strongest portion of that field.
- Expansion, contraction of the gas creates a pressure wave that is proportional to the oxygen’s partial pressure
- This mechanical signal is converted into an electrical one and is displayed as volume percent
What is Electrochemical Oxygen Analysis?
- Usually placed in the inspiratory limb
- Oxygen diffuses through sensor, the rate at which oxygen enters the cell and generates current is proportional to the partial pressure of the gas outside the membrane
- NEEDS CALIBRATION Q8HRS
Why is ETCO2 used in anesthesia?
- Validation of proper ETT placement
- Detection & monitoring respiratory depression
- Hyper/Hypoventilation
- Cardiac function
- Adjustment of parameter settings in mechanically ventilated pts
Capnography: Infrared Absorption
- a beam of infrared light energy is passed through a gas sample containing CO2
- CO2 molecules absorb specific wavelengths of infrared light energy
- Light emerging from the sample is analyzed
- A ratio of the CO2 affected wavelengths to the non=affected wavelengths is reported as ETCO2
What things that can increase ETCO2?
- Increased muscular activity (Shivering)
- Malignant Hyperthermia
- Increased Cardiac Output
- Bicarbonate Infusion
- Tourniquet release
- Effective drug therapy for bronchospasm
- Decreased minute ventilation
What things will decrease ETCO2?
- Decreased muscular activity
- Hypothermia
- Decreased cardiac output
- Pulmonary embolism
- Bronchospasm
- Increased minute ventilation
What are normal ETCO2 values?
30-43 mmHg
Why is ETCO2 levels lower than arterial?
CO2 is lost in the dead space of the circuit
