Scavenging Systems, Capnography and CO2 Absorption Flashcards
Scavenger
Collection of excess gas from equipment used in administering anesthesia or exhaled by the patient
Removal of excess gases to an appropriate place of discharge outside the working environment
Also prevent pressure buildup in the system
NIOSH Recommendation Levels of Anesthetic Gas in OR
Volatile Anesthetics alone = 2 ppm
Nitrous Oxide = 25 ppm
Volatile Anesthetics with Nitrous Oxide = 0.5 ppm
Over a period of 8 hours and then sampled
Components of Scavenger: 5 Components
1) Gas collecting assembly
2) Transfer Means = tubing from where it collects it and takes it to the interface
3) Scavenging interface
4) Gas Disposal Tubing = completely away from the machine
5) Gas Disposal assembly
Components of Scavenging System
Gas collecting assembly: APL valve, Ventilator relief valve
Transfer means: 19 mm tubing or 30 mm tubing
Scavenger interface: open or closed
Gas disposal assembly: active (vacuum) and passive
Scavenger: Gas Collecting Assembly
1) Ventilator Relief valve
2) APL
3) Gas Analyzer
Scavenger: Transfer Tubing
Different color and diameter to prevent accidentally connecting to the breathing system.
Breathing Circuit: 22 cm
Transfer tubing: 30 cm
Scavenger: Transfer Means
Exhausting tube or hose and transfer tube
Conveys gas from the collecting assembly to the interface
Usually a tube with female-fitting connectors on both ends
Tubing is short and large diameter, to carry a high flow of gas without significant increase in pressure
Must be kink resistant
Must be different from breathing tubes = color coded yellow and stiffer plastic
Scavenger Interface
Prevent pressure increases or decreases in the scavenger system from being transmitted to the breathing system
Also called the balancing valve or device
Interface limits pressure immediately downstream of the gas-collecting assembly to between -0.5 to 5 cm H2O
Positive pressure: exhale and creates pressure in the system
Negative pressure: created by a vacuum or too much vacuuming.
Scavenger Interface: 3 Basic Elements and 2 Types
1) Positive pressure relief protects patient and equipment in case of occlusion of system
2) Negative pressure relief limits subatmospheric pressure
3) Reservoir capacity matches the intermittent gas flow from the gas collecting assembly to the continuous flow of disposal system
Reservoir = capture exhalation volume that comes out
Open or closed
Scavenger Interface: Pressure and Holes
Excess positive pressure = blow out the holes
Problem: putting in the environment
Need enough vacuum or suction to take the volume out of the canister before it has time to go to the environment
Too much vacuum: train air into the system.
Requires vacuum or evacuation system to work or it would spill into the environment
No valves to adjust for positive or negative pressure = just holes
Scavenger Interface: Open Interface
No valve = is open to the atmosphere via holes in reservoir, avoiding buildup of positive or negative pressure
Require use of central vacuum system and a reservoir (open canister) should allow for high waste gas flows
Gas enters the system at the top of the canister and travels through a narrow inner tube to the base
Vacuum control valve can be adjusted - varies with the level of suction on the canister/reservoir must be > excess gas flow rate to prevent OR pollution
Scavenger Interface: Closed Interface - 2 Types
Positive pressure relief only:
1) Single positive pressure relief valve opens when a maximum pressure is reached
2) Passive disposal - no vacuum used, no reservoir bag needed
Positive and Negative Pressure Relief
1) Has positive and negative relief valve and reservoir bag
2) Used with an active disposal systems - vacuum control valve adjusted so that the reservoir bag is over distended or completely deflated
3) Gas is vented to the atmosphere if the system pressure exceeds +5 cm H2O
4) Room air is entrained if the system is less than -0.5 cm H2O
Scavenger Interface: Closed Interface
Balancing valve = black cap on top and adjust how much positive pressure allow out of the system.
Make sure volume in reservoir bag takes is equal to breathing system
Too much positive pressure = it will get bigger and see an increase
Negative pressure = collapse on itself for the reservoir bag
Scavenger: Gas Disposal Tubing
Connects the scavenging interface to the disposal assembly
Should be different in size and color from the breathing system
With passive system, the hose would be short and wide
Tubbing running overhead ideal to prevent acidentally obstruction and kinking
Scavenger: Gas Disposal Assembly: 2 Types
Components used to remove waste gases from the OR
2 Types:
Active: a mechanical flow inducing device moves the gas (produces a negative pressure in disposal tubing) must have negative pressure relief
Passive: pressure is raised above atm by the patient exhaling, manual squeezing of the reservoir bag or ventilator (needs positive pressure)
Scavenger: Passive System
The waste gases is directed out of the building via:
1) Open window
2) A pipe passing through an outside wall
3) Extractor fan vented to the outside air
Advantage: inexpensive to set up, simple operation
Disadvantage: may be impractical in some buildings
Scavenger: Active System
Connect the exhaust of the breathing system to the hospital vacuum system via an interface controlled by a needle valve
Advantage: convenient in large hospitals where many machines are used in different locations
Disadvantage: vacuum system and pipework is major expense.
Scavenger: System Check
Ensure proper connections between the scavenger system and both APL valve and ventilator relief valve and waste gas vacuum
Fully open APL valve and occlude Y piece
With minimal O2 flow, allow scavenger reservoir bag to collapse completely and verify that pressure gauge reads zero
With the O2 flush activated, allow scavenger reservoir bag to distend fully, and then verify that pressure gauge reads less than 10 cm H2O
Capnography Purposes
Confirm ETT placement: gold standard
Determine if patient is ventilating: Moving air
Guide ventilator settings
Detect abnormalities: embolism, MH, disconnect obstructive airway
THERE ARE NO CONTRAINDICATIONS
Capnography: Clinical Purpose
Estimate of PaCO2
PaCO2 > PEtCO2
Average gradient = 2-5 mm HG under general anesthesia
Used an an evaluation of dead space
Dead space: The Y piece. Add things on or get away from that piece = gradient is increasing
Due to dead space = diluting it out so that why there is lower value than arterial PaCO2
Capnography: Increase in CO2
Hypoventilation: TV too low or RR is low Wrong I/E ratio: wrong obstructive lung disease Increase metabolism: MH, fever, sepsis Rebreathing CO2 from the system Washout = high flow system
Capnography: Decrease in CO2
Hyperventilation
Leak in the system = train air in the system = maybe artificial
