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101 Cards in this Set
- Front
- Back
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most common absorbent
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Soda Lime
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Soda Lime can absorb
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23-26 L per 100g of absorbent
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Soda Lime hardeners
mesh size |
(silica and kieselguhr) added
minimize formation of dust size 4 to 8 mesh |
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Soda Lime water content
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(15%)
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Soda Lime main ingredient (80%)
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calcium hydroxide
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Soda Lime
lesser ingredient |
sodium hydroxide and potassium hydroxide (5%)
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Soda Lime exhausted
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exhausted when all hydroxides have become carbonates
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Soda Lime regeneration or peaking
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seen with soda lime
soda lime appears to be reactivated with rest color will revert back to white but absorptive capacity will be low and purple color will reappear quickly after brief exposure to CO2 ***there is no true regeneration of activity occurring |
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Baralyme
activator and content |
activator is barium hydroxide (20%)
calcium hydroxide (80%) small amount of water present no hardeners needed |
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Baralyme
slightly less efficient than soda lime but |
less likely to dry out if stored under poor conditions
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baralime absorptive capacity
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9-18 L
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CARBON DIOXIDE ABSORPTION
Indicators |
acid or base whose color depends on pH
added to absorbent to indicate when exhaustion has occurred due to regeneration, may not be able to rely on color change solely for granule exhaustion |
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CARBON DIOXIDE ABSORPTION
most important indicator granule exhaustion |
***use of capnometry to detect rising inspired CO2 is most important
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Blast furnace in anesthesia machine?
Adequate oxygen form |
Byproduct = non-toxic
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Blast furnace in anesthesia machine
Inadequate oxygen In form of low H2O |
Byproduct CO
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High COHgb in Swine Study
48 hrs |
48 hour drying time @ 10 LPM
H2O decreased from 12% to 3% 3 pigs died due to 80% COHgb after 20 minutes Reservoir bag removed |
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High COHgb in Swine Study
24 hrs |
: H2O dec and inc temp and inc CO
CO peaked at 8,800 to 13,600 ppm Reservoir bag removed |
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High COHgb in Swine Study
5 LPM |
Not dry enough
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High COHgb in Swine Study
conclusion |
if bag off change canister
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When to Change the Canisters
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recommended Q 24 hours
Most follow manufacturer recommendation No indication when dessication occurs |
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Consult WR Grace
H2O content stable for |
one month after plastic wrapping removed
OK to leave on machine for 1 month Change if we suspect flows left ON |
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cannot use CO2 granules with
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flammable anesthetics
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Halothane + soda lime =
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metabolite BCDFE
nephrotoxic in rats only |
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Enflurane + soda lime
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carbon monoxide
at elevated temperatures only |
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soda lime degrades (most and least)
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sevoflurane most, desflurane least
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Degradation of Sevoflurane
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Each of the compounds are quite toxic in relatively low concentrations.
Products of this pathway (methanol, formaldehyde, formate or formic acid) |
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Compound A
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Sevoflurane Degradation
Nephrotoxic in rats Controversial renal effect in humans Increase levels for 1-2 hours Level plateaus, then declines |
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Compound A
highest |
DURING LOW FLOW
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Sevoflurane reacts with CO2 granules
recommendation |
recommend using higher FGF’s with Sevo (2-5 L/min) to flush absorber of toxic compounds
product insert does not recommend sevoflurane at total FGF’s of less than 1L/min for more than 2 Mac-hours |
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Phosgene formation
5 points |
Toxicity arise from inhalation
Reacts with water, forms hydrochloric acid Symptoms appear 2-24 hours later Pulmonary edema, pneumonia, abscess, death Break down product of chloroform |
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strong bases (NaOH, KOH) implicated in
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CO and compound A
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New Absorbents goal
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goal is to maintain efficiency while lessening production of byproducts
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Dragersorb 800 and Medisorb are used now
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(contain less NaOH and no KOH)
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FDA recommends: when circuit is pressurized, release pressure through
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through APL valve and not through elbow near patient’s face
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inhaled dust is
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caustic and is an irritant
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USP Standards 4 to 8 mesh
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85% 4 to 8 mesh’
‘7% oversized’ ‘7% undersized ‘< 65% 6-8 mesh’ |
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Goal Air Space in Canister
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65% of canister as airspace
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Size of absorber must match
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patient TV
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2 compounds when sevo starts to degrade
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compound A and methanol, and formic acid
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Match TV to Absorber Capacity
If absorber capacity = 1400 ml |
Airspace = 700 – 910 ml
Appropriate for patient up to 90 Kg Assuming 10 ml/kg for TV |
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Channeling
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Gas flows in characteristic pattern through absorber..path of least resistance
Top center Down the sides To the bottom |
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Efficiency Breakpoint
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inspired CO2 = .1%
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Efficiency Exhaustion
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inspired CO2 .5%
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Efficiency Rebreathing
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if inspired CO2 goes higher than 0.5
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Efficiency Varies with
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Hardness
Porous granules absorb more |
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Hard granules
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absorb less
100% hard rock absorbs nothing O% hard sponge absorbs everything Compromise between absorption and dust |
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Additives to decrease dust
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Silica added to dust-clogs the granules
Kieselguhr (diatomaceous earth) hardens |
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Exhaustion
breakpoint is defined |
which the first trace of unabsorbed CO2 is detected in inspiratory port of the absorber
approx 0.1% |
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exhaustion is the time at which
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which the CO2 level at the inspiratory port reaches 0.5%
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sevo always use xx flows
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2
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CARBON DIOXIDE ABSORPTION
Replace Canisters: 4x |
when inspired CO2 is > 3-5 mmHg
when ETCO2 is increased when 50-75% color is changed when temperature of canister is cool |
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Sodalime more caustic than
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Baralyme
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Dust implicated in patient injury
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Facial burns
Bronchospasm Irritation to mucous membrane |
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Direction of gas flow in absorber decreased what
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dust expulsion
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Baffles
3 points |
annular rings that serve to direct gas flow toward central part of canister
placed at top and bottom of absorber increase path of travel for gases along sides and help compensate for wall effect |
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Side Tube
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external to canisters
conducts gases either to or from bottom of absorber main flow of gases passing through absorber will be opposite to gases passing through side tube |
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only 2 reasons for increase in inspired CO2:
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absorbent granules are exhausted
unidirectional valves are faulty |
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if inspired CO2 is more than 3-5 mm Hg,
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FGF should be increased to 5-8 L/min
this converts system to semi-open where rebreathing of exhaled gases is minimized |
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Sodasorb manufacturer recommends changing the absorbent if left in machine for
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> 48 hrs
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Drager recommends their absorbent in Fabius GS be changed if machine has been idle for
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48 hrs. or at least every Monday morning
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2 reasons for these cautious guidelines:(Replacement absorber)
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gas flows may be left on overnight or all weekend which dries out granules (they do not regenerate)
ethyl violet indicator may be inactivated by intense light |
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Humidity is a general term used to describe
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the amount of water vapor in a gas
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Absolute humidity
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mass of water vapor present in a volume of gas
Changes when temperature changes |
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Humidity at Saturation
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maximum amount of water vapor that can be carried in a volume of gas
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Relative Humidity
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The amount of water vapor at a particular temperature expressed as a percentage of the amount that would be held if the gases were saturated
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The amount of water that can be held as a vapor depends
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on the ambient temperature
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The warmer the temperature
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the more water vapor a gas can hold.
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As temperature decreases i.e water vapor
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amount of water the air holds goes down.
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Water begins to condense out of the air at
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cooler temperatures.
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Dew point
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: a measure of the temperature of the gas when liquid water will appear
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Tracheal intubation or the use of an LMA bypasses the upper airway, modifying the pattern of heat and moisture exchange leaving
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the tracheobronchial mucosa to assume the burden of heating and humidifying gases
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Cold, dry air from anesthesia machine is warmed to
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to patient
Warm moist 100% relative humidity alveolar air from patient at 37 C |
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Travels into breathing circuit at room temp 20 C is it
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‘rains out’ inside breathing circuit
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3 Effects of Inhaling Dry Gases and Damage to the respiratory tract
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Reduced mucous flow
Interference with mucociliary transport Decreased ciliary activity, twisting, tangling |
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adults when breathing dry unhumidified air
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body temp falls 3 times faster than adults
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Ciliary Depression Occurs as early as
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30 minutes after induction
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Ciliary Depression is
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Complete cessation of ciliary activity after exposure to gases with absolute humidity of 22 mg/H2O/L
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Ideal Humidity Levels is
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inspired absolute humidity of 28-32mgH2O/L is associated with minimum heat loss and minimal damage to tracheal epithelium when anesthesia lasts longer than 1 hour
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ISO set the following humidification characteristics for HMEF:
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Should at least provide a moisture output of 25.4 mgH2O/L
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Excessive Humidity also a problem, associated with 8x
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Condensed water in the circuit is a perfect home for bacterial growth
Heat and water gain which is hazardous in infants and small children Degeneration of the cilia Increased secretions Atalectasis Decreased FRC Diminished surfactant activity hyperthermia |
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4 Ways to increase humidity in the breathing circuit
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Pass the anesthetic gases through a carbon dioxide absorber (they contain 15% water)
Decrease the fresh gas flowrate, the lower the FGF the higher the inspired humidity Add a heat and moisture exchanger to the breathing circuit Use of a heated humidifier – rare |
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Heat and Moisture Exchange Filters 2 Types
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Hydrophobic Membrane
Composite Hygroscopic |
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Hydrophobic Membrane
5 points |
high surface area= low resistance
moderate moisture output efficient viral and bacterial filters Consistently prevents passage of Hep C Stop particles because of the small size of their pores but allow passage of water vapor not liquid |
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Composite Hygroscopic
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a hygroscopic layer plus a thin membrane that has been subjected to an electric field to increase polarity which improves filtration efficiency and hydrophobicity
Usually used in dry environments Contain a wool, foam , or paper like material coated |
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HMEs are most useful during
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short-term ventilation in patients who are adequately hydrated
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HME Should be used in a patient with
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a known infectious disease
(may be used with a trach) |
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HME Contradindications for use
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thick of bloody secretions
an expired tidal volume less than 70% of delivered tidal volume (e.g.,leaking or absent tracheal tube cuff body temperatures less than 32C a bronchopleurocutaneous fistula |
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type of HMEs have better heat and moisture exchanging properties than
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hygroscopic HMEs have better heat and moisture exchanging properties than hydrophobic
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Inspiratory/expiratory flows – the faster the gas passes through the HME
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the less time there is to absorb or deposit moisture so an increased tidal volume will cause humidity of the inspired gas to fall
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Continuity of the system – a leak around the tracheal tube or between the tube and the HME will
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will decrease inspired humidity
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The greatest inspired relative humidity occurs with the HME positioned
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next to the tracheal tube or LMA, RH declines as the space between the tracheal tube and HME increases
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HME
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HME
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HME best for nebs meds
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Hydrophobic
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HME
max efficient with long case |
hydroscopic
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HME Hazards
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1. Excessive resistance (If peak airway pressures increase, measure with and without HME in place)
2. Airway obstruction (The lungs get over expanded possibly causing a tension pneumothorax) 3. Aspiration of Particles 4. Rebreathing 5. Interference with Monitoring 6. Leaks and Disconnections |
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HME The most common fault is
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a plastic defect that causes a partial or complete obstruction
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Advantages of Active Humidification 2
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Provides 100% humidity
Maintains temperature |
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Disadvantages of Active Humidification 8
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Over/under hydration
Hypo/Hyperthermia –problematic in infants Melting of disposable circuits Aspiration Infection Costly May not produce as much humidity as assumed Increased chance of malfunction |
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most frequently isolated pathogen
i.e. Incidence of Nosocomial Pneumonia |
Gram negative bacteria
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a vector for cross contamination
3 most frequently contaminated |
Facemask, elbow, breathing circuit are the most frequently contaminated
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anesthesia (typical filter)
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0.3 microns
Eventually pores fill up and resistance increases as filter gets clogged or water breeches filter |
