Gas Systems & Scavenging Flashcards
Carter/maggie+ bowman
link 25 proportioning system in newer machines is
internalized. As dials are electric, you cannot turn on nitrous oxide without oxygen flowing.
color of helium cylinder
brown
Full E sized oxygen cylinders have ___ volume and ___ pressure
625-700 L at 2000 - 2200 PSI
Full E sized air cylinders have ___ volume and ___ pressure
~625 L at 1900 PSI
In air and oxygen cylinders, pressure falls in
proportion to the volume remaining in the tank
Full E sized N2O cylinders have ____ volume and ____ pressure
1590 L and 745 PSI
purity of medical gases is specified and enforced by
Specified us US Pharmacopeia or national formulary
Enforced by FDA
Cylinder Label
each cylinder must have a label or decal on the side or on the shoulder. But not covering any permanent markings.
Cylinder Label shows (3)
the compressed gas association marking system.
Diamond shape, name of gas, signal word with statements of hazards and measured to be taken. Hazard Status Caution words
DOT permanent markings on cylinders (6)
Include: cylinder type, working PSI serial number date of manufacture neck rick identification restest markings
7 safe handling procedures for cylinders
- Never stand a cylinder upright without support
- Never leave empty cylinders on the machine
- Never leave the plastic tape on the port while installing the cylinder
- Never rely on the cylinders color for identification of its contents
- Never oil valves
- Before any fitting is applied to the cylinder valve, particulates of dust, metal shavings, and other foreign matter should be cleared from the outlet by slowly and briefly cracking the valve a way from you and/or other personnel
- The valve should always be fully open when a cylinder is in use. Marginal opening may result in failure to deliver adequate gas.
vapor pressure sevoflurane
160 mmHg
vapor pressure enflurane
172 mmHg
vapor pressure isoflurane
240 mmHg
vapor pressure halothane
244 mmHg
vapor pressure desflurane
669 mmHg
Tec 6 vaporizer maintains
a temp of 39 and atm of 2 for desflurane, constant temp/pressure
Gas-vapor blender =
tec 6 vaporizer
pressure regulating valve in Tec 6
down regulates the desflurane to 1.1 atm
Aladdin cassettes are
computer controlled variable by pass vaporizers
Copper Kettle is unique in that it (4)
has its own dedicated flow meter
is out of the circuit
non-agent specific
bubble through
Steps of gas through copper kettle (~4 steps)
Air flows from dedicated flow meter into copper kettle, into loving cup,
loving cup forces it back down,
then bubbles through the gas diffuser disk that is filled with anesthetic of your choice,
is laden with anesthetic gases, flows out o f copper kettle as a very highly concentrated anesthetic, joins rest of gas flow.
copper kettle calculation
(Carrier Gas x Vapor Pressure) / Barometric Pressure - Vapor Pressure = Vapor output in mL/min
then! [Vapor Output] in mL/min / [total gas] flow in mL/min
variables you can change in copper kettle calculation
Carrier gas and total gas flow
If you accidentally put an anesthetic with high vapor pressure in a low vapor pressure vaporizer
High- low -> High
higher concentration than set
If you accidentally put an anesthetic with low vapor pressure in a high vapor pressure vaporizer
Low - high ->
Lower concentrations than set
Definition of scavenging
COLLECTION of excess gases from equipment used in administering anesthesia or exhaled by patients and REMOVAL of these excess gases to an appropriate place of discharge outside the working environment.
NIOSH recommended levels of anesthetic gases in OR
volatile halogenated anesthetic alone = 2 ppm
nitrous oxide = 25 ppm
volatile anesthetic with nitrous oxide = 0.5 ppm
Basic Components of Scavenge (5)
- Gas collecting assembly
- Transfer means
- Scavenging interface
- Gas disposal tubing
- Gas disposal assembly
Size of connections in scavenging system is important so that
it is unable to connect to other components of the breathing system
Gas Collecting Assembly (Does)
captures excess gasses at the site of emission and delivers them to transfer tubing
Gas Collecting Assembly connection is usually
30 mm (19mm) in older machines and male fitting.
Transfer means of scavenge system
- also called:
- function
Also called exhausted tubing or transfer system.
function: conveys gas from the collecting assembly to the interface
Transfer means of scavenge system details (5)
usually a tube with female fitting connectors on both ends
tubing is short with a large diameter to carry a high flow of gas w/o a significant increase in pressure
must be kink resistance
must be different from breathing tubes
color coded yellow and stiffer plastic
problem with NIOSH recommended levels
“Theres no safe level of gas exposure and its questionable where these numbers came from”
Scavenging interface function (3)
prevents pressure increases or decreases the scavenging system from being transmitted to the breathing system
also called the balancing valve or balancing device
interface limits pressures immediately downstream of the gas collecting assembly to between -0.5 to 3.5 cmH2O.
Scavenging interface details
inlet should be 30 mm male connector
should be situated as close to gas-collecting assembly as possible
3 basic components of the scavenging interface
positive pressure relief - protects pts and equipment in case of occlusion in system
negative pressure relief - limit sub atmospheric pressure
reservoir capacity - matches the intermittent gas flows rom gas collecting assembly to the continuous flow of disposal system
2 types of scavenging interfaces
open
closed
Open interface scavenging system
No valves!
Is open to the atmosphere via “relief ports” in reservoir, avoiding build up of positive and negative pressure
- must have high vacuum flow to prevent pollution of OR.
requires reservoir and vacuum
Positive Pressure Relief only closed scavenge system
Only positive pressure relief valve
Disposal is passive, no vacuum, pressure comes from expiration
Gas vents to a non circulating HVAC or a window,
No reservoir bag needed
Positive+ Negative relief closed scavenge system (5)
used with active disposal (vacuum)
has a reservoir bag
gas is vented to the atmosphere if pressure is over +5cmH2O
Room air is entrained if pressure is below -0.5cmH2O
BACKUP negative pressure valve at -1.8cmH2O if first one becomes occluded
In positive+negative relief closed scavenge system, adjust the vacuum control valve so that
the reservoir bag is appropriately inflated
i.e. neither overly distended or completely deflated
Reservoirs in scavenging systems should match the
intermittent volume from pt expiration/gas collecting assembly to the continuous flow of the disposal system
Gas disposal tubing that is connected to an active gas disposal system requires
a DISS
Gas disposal tubing for passive systems should be
short and wide (decrease resistance, increase flow)
Gas disposal tubing to ensure no kinks should be
running overheard to prevent accidental obstruction (stepping) or kinking
Gas Disposal Assembly consists of
Components used to remove waste gases from OR . Two types, active and passive
Active Disposal Assembly advantages/disadvantages
Vacuum! Connected from breathing system to hospital vacuum via an interface controlled by needle valve
advantage: convenient in large hospitals where many different machines are used in different locations
disadvantage: expensive to have network, needle valve may need continual readjustment
Passive Disposal Assembly advantages/disadvantages
Waste gas is directed out of building via open window, pipe passing to outside wall, fan to outside
advantage: Cheap! simple
disadvantage: may be impractical in some buildings
Scavenging System Check (3)
- Ensure proper connections between scavenging system and both APL VALVE and VENTILATOR RELIEF VALVE to waste gas vacuum
- Fully open APL valve and occlude Y-Piece, with minimal O2 flow collapse scavenger bag and ensure it reads 0 and not negative pressure (appropriate vacuum)
- Fully open APL valve and occlude Y-piece ,with high gas flow allow reservoir bag to distend and ensure that pressure does not rise to greater than 10 cmH2O.
Capnometry vs Capnography
Capnometry: quantification of carbon dioxide concentration
Capnography: actual graph of capnometry values over time
“Purposes” of capnograhy (8)
- gold standard to determine if patient is being ventilated, critical, life-saving monitor
- used to confirm ETT/LMA placement
- Without an airway, helps determine if pt is adequately exchanging air/oxygen
- Guide ventilator settings (avoids too much or too little ventilation )
- Detect circuit disconnections
- Detect CIRCULATORY abnormalities - (PE, occult hemorrhage/hypotension)
- Detect excessive aerobic metabolism (Malignant hyperthermia)
- Standard for VAE detection
contraindications to capnography
there are none
“Clinical uses” of capnography (2)
May be used as ESTIMATE of PaCo2
Used as an evaluation of dead space
EtCO2 compared to PaCo2
PaCo2 > EtCo2 by approx 2-5 mmHg
Methods of Measuring CO2 in Expired gases
- colorimetric
2. infrared absorption spectrophotometry (most common)
Colorimetric co2 detector uses
metacresol purple paper (turns color with present of carbonic acid)
Infrared Absorption Spectrophotometry works
- by analyzing the gas mixture
- determination by proportion of gas contents
- each gas in mixture absorbs infrared radiation at different wave lengths, amount of CO2 is measured by detecting its absorbable at specific wavelengths and filtering the absorbance related to other gases
measurement techniques of etco2 include (2)
main stream and side stream capnography
mainstream capnography
advantages
disavtanges
advantages: Less time delay
disadvantages: potential for burns r/t heated circuit,
increases dead space
heavy -> can kink ETT.
Side stream capnography works by
aspirating a fixed amount of gas/minute to analyze in the sampling cell via tubing
side stream capnography should be
as close to ETT as possible
Potential problems with side stream capnography
time delay
potential disconnect
water vapor condensation, traps/filters used
capnogram =
Pco2 vs time
has 4 phases
Phase 1 of capnogram (4)
Should have no CO2 reading,
represents inspiration and beginning of expiration.
Dead space gas exhaled.
Inspiratory baseline
Phase 2 of capnogram (3)
An expiratory upstroke!
Sharp upstroke represents rising CO2 level in sample
mixture of dead space and alveolar gas
Slope of line in phase 2 of capnogram represents (~3)
evenness of alveolar emptying
straight = healthy, no air trapping
sloped = air trapping
Phase 3 of capnogram (5)
Alveolar plateau
Constant or slight upstroke
Longest phase
Alveolar gas is sampled
Peak at the end of plateau is where reading is taken
Reading of ETCO2 is taken at
peak of phase 3 (alveolar plateau)
Phase 4 of capnogram (2)
Beginning of inspiration
co2 concentration has rapid decline to inspired value
5 characteristics of capnogram
frequency height rhythm baseline shape
Primary use of capnogram is to
verify ETT placement in the trachea vs esophagus
Indications of tracheal intubation on capnogram
presence of stable CO2 waveforms for 3 breaths >30mmHG
Causes of rebreathing = (3)
equipment dead space
exhausted CO2 absorber
inadequate FGF
Contributors to rising CO2 when ventilation unchanged (6)
- malignant hyperthermia
- release of tourniquet
- release of aortic/major vessel clamp
- IV bicarb administration
- insufflation of CO2 into peritoneal cavity
- equipment defects, (expiratory valve stuck CO2 exhausted)
Gradual Decrease in ETCO2
likely hyperventilation, reflects increased minute ventilation
Rapid decrease in ETCO2
- PE, V/Q mismatch
- Cardiac arrest
? Sampling error
Sampling errors in ETCO2
disconnects, high sampling rate with elevated FGF
Capnogram pattern in obstructive lung disease
COPD/Asthma/Bronchoconstriction/Acute obstruction
- slow rate of rise in Phase ii
- steep upslope of phase iii (in extreme cases may not see phase iii)
Spontaneous ventilation/recovery from neuromuscular blockade on a capnogram
tugging the middle of plateau
Carbon dioxide absorber works by (~5)
chemical neutralization of cO2 Base neutralizes an acid acid:carbonic acid (formed by CO2/H2O) base: some hydroxide (alkali or alkaline earth metal) end product: water, a carbonate, heat
Older CO2 absorbers (2 canisters) were a problem because (2)
- couldn’t change during the case because disturbs circle system integrity
- common sources of leaks
Modern single canister models have
bypass feature so you can change during case
4 common absorbents
- soda lime (sodium hydroxide lime)
- amsorb plus (calcium hydroxide lime)
- baralyme
- litholyme (lithium hydroxide)
Soda lime contains %
Sodium Hydroxide Lime
4% sodium hydroxide 1% potassium hydroxide 15% H2O 0.2% silica 80% calcium hydroxide
Characteristics of soda lime
silica added for hardness to prevent dust
capable of absorbing 26 L of CO2 for 100 g of absorbent granules
water is present as thin film on granule surface
MOISTURE IS ESSENTIAL reaction makes place between ions that only exist in presence of water
a pound of CaOH can absorb 0.59 lb of CO2
Soda Lime Reaction
formula
CO2+H2O H2CO3 + 2NAOH(KOH) NA2CO3(K2CO3) + 2H2O + HEAT
^predominant reaction b/c faster^
slower reaction:
CO2 + Ca(OH)2 CaCo3 + h2o + heat
Soda Lime Rxn in words
“Carbon dioxide combines with water to form carbonic acid, carbonic acid reacts with the hydroxides to form sodium (or potassium) carbonate, water, and heat.
Some carbon dioxide reacts CaOh2 but this reaction is much slower.
Amsorb Plus (Calicum Hydroxide Lime) contains
80% calcium hydroxide
16% water
1 -4 % calcium chloride
Characteristics of calcium hydroxide lime/Amsorb Plus (2)
- calcium sulfate and polyvinlyprrolidine added hardness to prevent dust
- capable of absorbing 10L of CO2/100g of absorbent granules
Calcium Hydroxide Lime/Amsorb Plus Reaction Formula
CO2 + H2O H2CO3 + Ca(OH)2 CaCO3 + 2H20 + heat
Calcium hydroxide rxn in words
carbonic acid + calcium hydroxide calcium carbonate + water + heat
Baralyme was voluntarily pulled from market b/c of
risk of fire
Baralyme (Barium Hydroxide) consists of
20% Barium Hydroxide
80% Calcium Hydroxide
Characterstics of Baralyme (7)
Small amounts of sodium/potassium hydroxide may be added
Granules are 4-8 mesh
No hardening agent is needed
It is slightly less efficient than Soda lime but is less likely to dry out
No water
Implicated in fires
Absorptive capacity similar to soda lime of 26 L co2 / 100 g granules
Baralyme Reaction formula
BaOH + 2(8H2O) + CO2 -> BaCO3+ 9H2O + heat.
9h2o + co2 -> 9H2CO3
9H2CO3 + 9Ca(OH)2 -> 9CaCO3 + 18H2O + heat
Litholyme (Lithium Hydroxide Monohydrate) components
75% lithium hydroxide (LiOH)
12-19% H2O
<3% lithium chloride
Characteristics of litholyme
also comes in anhydrous form
1 pound of LiOH absorbs 0.91 lb of CO2
Litholyme reaction formula
2LiOH + H2O + CO2 Li2CO2 + 3H2O - heat
Indicators (5 things to know)
- An acid or base whose colors depends on pH
- Color conversion signals absorber exhaustion
- Replace absorbent with 50 - 70% color change
- Color reverts back with rest, especially in NaOH containing formulas
- Ethyl violet - most common, critical pH 10.3
Phenolphthalein
fresh; white
used; pink
Ethyl Violet
fresh; white
used; purple
Clayton Yellow
fresh; red
used; yellow
Ethyl Orange
fresh; orange
used ; yellow
mimosa 2
fresh; red
used; white
Size of absorbent granules (4)
4-8 mesh in size
irregular shape -> increased surface area
small granules increase resistance but also provide greater surface area
blend of large and small minimize resistance with little sacrifice in absorbent capacity
Granule hardness (3)
Not enough hardness = excessive powder which can lead to channeling and caking
Hardness is tested with steel ball bearings and screen pan
& of original remaining = hardness number,
hardness number should be >75
Silica in soda lime
is to increase hardness
Channeling results from
loosely packed granules
Some manufactures may now use
a polymer to bind the granules in pre-formed channels to prevent channeling
Air space in the co2 absorber occupies
48 to 55%
Strong bases capable of degrading volatile gases
absorbents containing KOH and also NaOH
Compound A has been found
to cause nephrotoxic effects In rats
To prevent theoretical formation of compound A
Manufactures recommend not more than 2 MAC hours at flow rates <2 L/min
Carbon monoxide has been known to accumulate
in desiccated (Dry) NaOH and KOH containing absorbents when they are not used for 24 to 48 hours.
With dried out absorbents a slow
reaction occurs with the volatile agents and absorbents that produces carbon monoxide, can result in critically high levels of carboxyhemoglobin in exposed patients .
Desflurane is associated with
highest accumulation of carbon monoxide
Anesthesia Safety Foundation Recommendation on Safe Use of Carbon Dioxide Absorbents (6)
- Turn of 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 one canister
- Change absorbent when uncertain of the state of hydration, such as if FGF
- Low flows preserve humidity in granules
DISS and PISS are required
for all anesthesia machines
KISS
key index safety system, part of vaporizer
At altitude, you need to increase concentration of
tec-6 vaporizer, desflurane.
because tec 6 will heat des to 39 / 2 atm regardless of ambient temperature to deliver a constant percentage that will be lower at 350 mmHG thats 750 mmHg
Vaporizers are made of metals with
high specific heats and high thermal conductivity to maintain uniform internal temp
Most vaporizers are (3)
temperature compensated
agent specific
variable by-pass
Potential Vaporizer Hazards (7)
Wrong agent in the vaporizer
(high - low high or low - high - low)
Contamination (leaving it open)
Tipping
Overfilling
Simultaneous administration of vapors
leaks
pumping effect
(alternating pressure in pipeline that ends up giving more gas than expected)
Not enough hardness =
Not enough hardness = excessive powder which can lead to channeling and caking
