Equipment Flashcards
Gas Chromatograph
Absorption type analyzer
Measures Ne, O2, N2, CO
Measures multiple gases via a separator column
Requires carrier gas- He or Ne
Not very fast- not breath to breath
Affected by moisture and CO2
Mass spectrometer
Measures mass of gases
Measures multiple gases at the same time
Very fast- breath to breath
Very expensive and large
Gas analyzer troubleshooting
Add the gasses and if not 100% there is an error- adjust the gain until the total equals 100%.
Infrared absorption analyzer
Measures CO, CO2 & methane
Uses a “chopper” motor/blade
Very fast- breath to breath
Calibration with room air (low), a known concentration of CO or CO2 (high), the room air again.
If calibration is off adjust the gain
Affected by moisture and long sampling line (delay)
Helium Analyzer
AKA thermal conductivity analyzer
AKA Wheatstone bridge analyzer
Helium passes over and cools hot wires and changes the resistance
Can’t be uses around combustible gases
Calibrate with room air, then a known concentration (around 10%), then room air again
Nitrogen Analyzer
Gas sample pumped into a chamber where it’s ionized
Ionized nitrogen emits light- photo tube detects light
Very fast response, breath-to-breath
Troubleshooting: pump malfunction, leaks or excess moisture (causes erratic readings or spikes of nitrogen)
Calibrate with 100% O2, then known N2 concentration
ABG Analyzers: severinghaus electrode
Measures PCO2
Nylon spacer + teflon membrane
CO2 passes through into electrode to cause reaction
ABG Analyzers: Clark electrode
Measures PO2
Most complicated and most cause for errors
Platinum cathode + silver chloride anode
Polypropylene membrane- rough surface that can trap blood particles
Requires polarizing voltage
Cleaned periodically with pumice
ABG Analyzers: pH electrodes
Consist of reference and measuring electrodes
Reference electrode has constant electrical potential
Introducing a sample causes an electrical potential (charge) to develop between the electrodes
The voltage changes proportional to the pH
Calibrating ABG Analyzers
PH electrode: add a sample of known pH and compare
CO2- low=5%, high=10%
O2- low=0%, high=12% or 20%
To read results, need to convert % into mmHg (713 x % as decimal)
Troubleshooting ABG analyzers
Ensure gas tanks aren’t empty
Unstable, erratic or noisy readings: worn out or ruptured membrane, clots (protein remover + flushes to clear)
Galvanic fuel cell analyzer
AKA zirconium fuel cell
Expose to O2 to create reaction & analyze
Fast and accurate
Measures PO2 and converts to %
Affected by changes in pressure or altitude
Troubleshooting- only malfunction if fuel runs out- replace
Polarographic O2 analyzer
Uses a Clark electrode to measure PO2 converted to FiO2
Affected by water on sensor, changes in pressure or altitude
Troubleshooting: check batteries, electrolytes, membrane
Calibrating O2 sensors
FiO2: 21% & 100% O2
FeO2: 12-14% & 21% O2
Tonometer
Used to QC ABG analyzers
Creates a precise gas mixture in a buffering solution or blood
Adds known PO2 or PCO2 to QC blood sample to check analyzers
Valves & sampling devices
Ensure proper function: observe the flaps or diaphragms aren’t sticking
Should have low dead space, low resistance, low compliance (stiff), easy to clean
To determine dead space- fill with water and drain out into a graduated beaker
CO2 absorber
AKA CO2 scrubber or sodium/barium hydroxide canister
Removes CO2 from air and converts to water
Only necessary for tests requiring rebreathing
Malfunctioning CO2 absorber can cause: flushing, dizziness, light-headedness, increased RR (stop testing and check system)
Color change= chemical used up and should be replaced (usually brow->white or cream->purple)
Water absorber
AKA desiccant
Calcium sulfate (dry-rite)
Placed inline after CO2 scrubber
Blue -> pink = used up
Perma Pure tubing
AKA Nafion tubing
Allows humidity in tube to equilibrate with room air
Wright respirometer
Measures flow and estimates volume
Exhaled flow spins a vane and turns gears that then turn dial to show volume
Convenient but also delicate and not very accurate
Pressure differential pneumotach
Measures a pressure differential and converts to volume
Contains resistive elements (typically capillary tubes)- flow over the elements changes the pressure on one end vs the other
Quick and accurate
Moisture in the capillary tubes can cause high volume errors- heating element helps minimize moisture
Troubleshooting- check for moisture, check or replace heating element
Thermal element pneumotach
Heated wire cools as air passes and converts to flow
Contains a screen with heated wire behind it- damaged or blocked screen causes errors
Pilot tube
Not affected by moisture
Contains two tubes to measure inspiratory and expiratory flow
Disposable
