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
Capnography: Method of Measuring CO2
Colorimetric:
Rapid assessment of CO2 presence.
Changes color in presence of acid.
CO2 + H2O = carbonic acid = paper changes color
Infrared Absorption Spectrophotmetry
Gas mixture analyzed
Determination of proportion of its contents
Each gas in mixture absorbs infrared radiation at different wavelength
Amount of CO2 measured by detecting is absorbance at specific wavelength and filtering the absorbance related to other gas
Capnography: Measurement Techniques
Mainstream Capnography
Sidestream Capnography
Capnography: Mainstream
Adapter near the Y piece = near the patient’s mouth
Similiar to respirometer
Advantage: real time reading
Disadvantage: sensor heats up and component can cause burn on neck or chest
Sensor window must be clear of mucus
Weight kinks ETT
Capnography: Sidstream
Aspirates fixed amount of gas/minute (50-500 mL)
Transports expired gas to sampling cell via tubing
Also uses IR analysis
Best location for sampling: near ETT
Disadvantage: time delay
Potential disconnect source
Pediatric sampling = lower ventilation = dilution
Water vapor condensation = traps/filters used
Capnogram: Phase I
An inspiratory baseline
No CO2
Inspiration and first part of expiration
Dead space gas exhaled
Capnogram: Phase II
An expiratory upstroke
Sharp upstroke represents rising CO2 levels in sample
Slope determined by evenness of alveolar emptying
Mixture of dead space and alveolar gas
Capnogram: Phase III
Alveolar Plateau Constant or slight upstroke Longest phase Alveolar gas sampled Peak at the end of the plateau is where the reading is taken = end tidal partial pressure of CO2 (PEtCO2) Reflection of PACO2 and PaCO2
Capnogram: Phase IV
Beginning of Inspiration
CO2 concentration - rapid decline to inspired value
Capnogram: Tracing Interpretation
Inspection of whole curve - 5 Characteristics:
1) Frequency
2) Height
3) Baseline
4) Shape
5) Rhythm
Primary use: verify ETT in the trachea
Presence of stable CO2 waveform for 3 breaths indicates tracheal intubation
Does NOT indicate proper position within the trachea. Listen to Bilateral breath sounds!
Capnogram: Trace Interpretation
Determine adequacy of Ventilation
Disconnect indicator
Assess quality of CO2 absorption
Monitor changes in perfusion and dead space
Capnogram Waveform: Obstructive Lung Disease
COPD, asthma, Bronchoconstriction, acute obstruction
Slow rate of rise in Phase II
Little or no Phase II
Problems with exhaling CO2
Make sure obstruction wasn’t from excess secretions
Capnogram Waveform: Esophageal Intubation
Get CO2 initially, but more breaths it will decrease
Capnogram Waveform: Rebreathing
If value remains above baseline (0) at the end of Phase IV: inspiration Causes of rebreathing: 1) Equipment Dead Space 2) Exhausted CO2 absorber 3) Inadequate fresh gas flows
Spontaneous Ventilation/Recovery from Neuromuscular Blockade
Anesthetics can paralyze the patient with no spontaneous respiratory effort
Muscle relaxant wears off = muscular tone and diaphragm moves and start to take their own breaths
Curary cleft: old neuromuscular medication. Respiratory effort and in-training some air and not enough to count a breath of their own
Capnogram Waveform: Cardiac Oscillations
Sensing the vibration of the heart beat = cardiac impulses from the back side
They don’t mean anything
Capnogram Waveform: Rising CO2 when ventilation unchanged
MH
Release of Tourniquet: building up lactic acid and byproducts. All these substances are released suddenly and then breathing faster to get rid of the byproducts
Release of Aortic/Major Vessel clamp
IV Bicarb Administration
Insufflation of CO2 into peritoneal cavity
Equipement defects: expiratory valve stuck or CO2 absorbent exhausted)
Capnogram Waveform: Decrease in EtCO2
Hyperventilation: GRADUAL decrease reflects increased i minute ventilation RAPID decrease: PE (thrombus, fat, amniotic fluid) VQ mismatch Increase in PACO2 - PEtCO2 gradient Cardiac arrest Sampling error Disconnect High sampling rate with elevated fresh gas flow
Carbon Dioxide Absorber
Chemical neutralization of CO2
Base neutralizes an acid
Acid: carbonic acid formed by reaction of CO2 + H2O = H2CO3
Base: hydroxide of an alkali or alkaline earth metal
End product: water, CO3 (carbonate) and heat
During inspiration phase
Carbon Dioxide Absorber: Flow
Flow into the absorber: top to bottom
Usually on the top = exhausted earlier than bottom
Flow through it very irregular
Carbon Dioxide Absorbents: 2 Types
Soda Lime Amsorb Plus (Calcium hydroxide lime)
Carbon Dioxide Absorbents: Soda Lime
4% NaOH 1% KOH 15% H2O 0.2% Silica 80% CaOH
Carbon Dioxide Absorbents: Soda Lime
Silica added for hardness to prevent dust
Capable of absorbing 25 Liters of CO2/100 g of absorbent granules
Water is present as thin film on granule surface
Moisture is essential. Reaction takes places between ions that exits in presence of water: CO2 + H2O = H2CO3
Average non-stressed CO2 released per hour: 12L
Water is added outside to the granules to react with CO2
Carbon Dioxide Absorbents: Soda Lime Reaction
CO2 + H2O = H2CO3
H2CO3 + 2NaOH (KOH) = Na2HCO3 (K2CO3) + 2H2O + heat
Na2CO3 (K2CO3) + Ca(OH)2 = CaCO3 + 2NaOH (KOH)
Carbon Dioxide Absorbents: Calcium Hydroxide Lime
Aka Amsorb Plus
80% CaOH
16% H2O
1-4% CaCl
Calcium sulfate and polyvinlypyrrolidine added for hardness
Absorb 10L of CO2/100 g of absorbent granules
Carbon Dioxide Absorbents: Calcium Hydroxide Reaction
CO2 + H2O = H2CO3
H2CO3 + Ca(OH)2 = CaCO3 + 2H2O + heat
Carbon Dioxide Absorber: Indicators
An acid or base whose color depends on pH
Color conversion signals absorber exhaustion
Color reverts back with rest
Replace absorbent with 50-70% color change
Ethyl violet = most common indicator
Size of Absorbent Granules
4-8 mesh Irregular shape: increased surface area Small granules increase resistance Provide greater surface area Blend of large and small minimizes resistance with little sacrifice in absorbent capacity
Diagram of a Carbon Dioxide Absorber
Head plate Granules of absorbent Double Canisters Base Plate Dust Trap Lever Release
Carbon Dioxide Absorber: Granule Hardness
Excessive powder = channeling resistance and caking
Soda Lime: silica added to increase hardness
Tested with steel ball bearings and screen pan
% original remaining = hardness number
Hardness number should be> 75
Carbon Dioxide Absorber: Channeling
Preferential passage of exhaled gas flow through absorber via pathways of low resistance
Results from loosely packed granules
Air space occupies 48-55% of the volume in the canister
Absorbent along channels may exhaust
CO2 may filter through channels not visible
CO2 monitoring
Degradation of Inhaled Anesthetics
Soda Lime
Desiccated (dry) soda lime may degrade sevolfurane, isoflurane, enflurane, desflurane to carbon monoxide
Degrades sevoflurane and halothane to unsaturated nephrotoxic compounds
Fires
Inhalation
During inhalation phase of respiration, gas flows through the absorber and follow its course
High flow like O2 flush or through flow meters.
Gas into the common gas outlet and goes out the inspiration.
Flows are high: retrograde into the CO2 absorber and gets dried out
Exhalation
During exhalation, gas flow through the mask, into the rebreathing bag, and out the APL valve
Fresh gas continues to flow from the common gas outlet at the machine into the common gas inlet at the absorber
Recommendation on Safe Use of Carbon Dioxide Absorbents
Turn off all gas flow when the machine is not in use
Change absorbent regularly
Change absorbent whenever the color change indicates exhaustion
Change all absorbent, not just the canister
Change absorbent when uncertain of the state of hydration such as FGF
Low flows preserve humidity in the granules
