anesthesia machine Flashcards
anatomy of the cylinder valve
what to do if you open the cylinder and hear a hissing sound
- tighten connection
- if that doesn’t work, replace washer (gasket)
what happens if theres no cylinder or yoke plug present and check valve fails
gas that should be going to patient will exit anesthesia machine
MRI safe cylinder will have
two colors. most of tank is silver and top of tank is color of gas that it contains. has to be aluminum.
name 2 oxidizers
O2 and nitrous oxide
safety relief devices to prevent cylinder explosion include
-fusible plug that melts at elevated temperatures. typically made from woods metal (bismouth, lead, tin, cadmium- remember BLT with cheese)
-valve that opens at elevated pressurs
-frangible disc that ruptures under pressure
role of american society for testing and materials (ASTM)
sets standards for required components of anesthesia machine. standard document is ASTM F1850
role of FDA
created 1993 anesthesia machine pre use check out procedures
role of OSHA
sets standards for acceptable occupational exposure to volatile anesthetics
role of DOT
sets standards for compressed gas cylinders
(tests cylinder at 1.66 x PSI ex: O2 is 1900 PSI so is tested at 3,154 PSI)
USDOT requires the following info on the cylinder label (7)
- government agency (DOT)
- type of metal used to construct cylinder
- max filling pressure PSI
- serial number
- manufacturer
- owner
- date of last inspection
which pressure system does the O2 fail safe device reside in
intermediate pressure system
two components of the intermediate pressure system
- threshold alarm that sounds when O2 pipeline pressure falls between 28-30 PSI
- pneumatic device that reduces or stops the flow of N2O when the pressure in the O2 tank falls below 20 PSI (less O2 will put less pressure on the spring to keep it down and then it ultimately blocks flow of N2O)
2 types of O2 fail safe devices based on machine
- GE Datex Ohmeda- O2 falls below 20 PSI, N2O flow is not allowed
- Drager- as O2 pipeline pressure decreases, there is a proportionate decrease in N2O flow
How can you tell O2 pressure failure device is working?
If you d/c O2 when machine is on, N2O should stop before O2 goes to 0 and should be restored once O2 is re connected
can the O2 fail safe device detect a flow meter leak?
no, since it is up stream from the flow meters
the hypoxia prevention safety device on the gas machine will
limit the ratio of N2O to 3x O2 flow (O2 never drops below 25%)
compare and contrast O2 pressure failure device with hypoxia prevention safety device
describe link 25 (on GE datex ohmeda)
O2 and N2O flow meter are mechanically linked by a chain
-incorporates second stage regulator for N2O and O2 (pneumatic component)
-gear engages to ensure titrated gases adjust as needed
O2 ratio monitor controller (Drager)
-O2 and N2O are connected pneumatically
when can the proportioning devices not handle a hypoxic mixture?
- O2 pipeline cross over
- leaks distal to flow meter valves
- administration of a third gas (ex helium)
- defective mechanic or pneumatic components
describe annular space in flow meter
between indicator and flow meter wall
O2 flow meter is always furthest to the
right aka closest to the patient
4 types of flow meter floats and where to measure
high flow versus low flow in flow meter
type of flow and what it is dependent upon
re < 2000 = laminar flow, dependent on peusoilles law (viscosity)
re >2000 = turbulent flow, dependent on grahams law (density)
reynolds number =
density * diameter * velocity / viscosity
how to calculate FiO2
(air flow rate x .21) + (O2 flow rate x 100) / total flow rate
how much % O2 delivered through NC for each liter of O2 being administered?
add 4% for each liter of O2 administered up to 44% (6L/min)
with fresh gas coupling, total Vt delivered to patient equals
Vt set on ventilator + FGF during inspiration - volume lost to compliance
if using a vent that couples FGF to Vt, name some vent changes that increase delivered Vt
decreased RR
increased I:E ratio (from 1:2 to 1:1)
increased FGF
increased bellows height
if using a vent that couples FGF to Vt, name some vent changes that decrease delivered Vt
increased RR
decreased I:E ratio (from 1:2 to 1:3)
decreased FGF
decreased bellows height
if your Vt is set to 600mL, your PEEP is 5cmH2O and your peak pressure is 25cmH2O, how much Vt is the patient actually getting? (this is for machines that couple FGF)
475mL because 5X25=125
600-125=475
how the splitting ratio in a variable bypass chamber is determined
setting higher concentration of agent directs more FGF towards anesthetic
how to ensure fresh gas gets 100% saturated with agent when it enters the vaporizing chamber
flows over a series of baffles and wicks which increases surface area and turbulence.
what to do if a vaporizer is tipped over
- drain vaporizer to remove all liquid anesthetic
- run high FGF for 20-30m before it can be used on a patient (end tidal amount of agent should decrease to zero
define latent heat of vaporization
number of calories needed to convert 1g of liquid into vapor without a change in temperature
what is the role of the temperature compensating valve in the variable bypass chamber
adjusts ratio of vaporizing chamber flow too bypass flow and guarantees a constant vaporizer output over a wide range of temperatures.
-its either a bimetallic strip or an expansion element
define the pumping effect
increases vaporizer output due to things that cause back flow of agent. ex) PPV or the use of an O2 flush valve. enhanced by low FGF, low concentration dial setting, low levels of liquid anesthetic in vaporizing chamber.
most common cause of vaporizer leak
loose filler cap
most common location for a leak to occur in the low pressure system
internal leak in the vaporizer
how to calculate how long your liquid anesthetic will last (equation)
mL of liquid anesthetic used per hour = Vol% * FGF (L/min) * 3
vaporizers approved for the use of Des include
DE datex ohmeda tec 6 and drager D vapor
how does tec 6 work
injects a precise amount of agent directly into FGF
compared to sevo and iso, the absolute volume of des that must be vaporized is
higher (because desflurane is much less potent). plus heat in the form of energy is lost when molecules are vaporized (and des’ vapor pressure is close to atmospheric pressure)
-heating and pressurizing to 39c and 2 atmospheres
does the tec 6 compensate for changes in elevation
no
in lower ambient pressures (high altitudes), what should you set the dial to for des?
in higher ambient pressures (low altitudes), what should you set the dial to for des?
high altitudes (low ambient pressure): increase the setting on the dial
low altitudes (high ambient pressures), decrease the setting on the dial
required dial setting equation for desflurane =
normal dial setting (%*760) / ambient pressure in mmHg
are vaporizers positioned in circuit or out of circuit
all are positioned out of circuit
which device would be the first to detect an O2 pipeline cross over? (and where is it located)
O2 analyzer (which resides in the inspiratory limb of the breathing circuit)
if the O2 pipeline supply fails, you must do these 2 crucial steps
turn ON O2 cylinder
d/c pipeline O2 supply
pressing the O2 flush valve exposes the patient to an O2 flow of __________ and an O2 pressure of __________
O2 flow of 35-75mL/min and 50 PSI (pipeline pressure)
the drive gas on a pneumatic ventilator serves two functions
- compresses the bellows (during inspiration, drive gas flow creates a pressure gradient to push gas towards lungs. during exhalation, drive gas is stopped)
- drive gas opens and closes ventilator spill valve (during inspiration, drive gas closes spill valve. during exhalation, after circuit pressure exceeds 3cmH2O, spill valve opens and gas exits the scavenger.
amount of gas that drives bellows in a pneumatic circuit =
sum of Vt exhaled + FGF during expiration
will descending bellows continue to rise and fall with patient disconnect
yeah, the older ones will
fresh gas coupling (piston driven ventilator) total Vt delivered to patient =
Vt set on ventilator + FGF during inspiration - small volume lost to compliance
if FGF is 10L/min, the RR is 10, the I:E is 1:2 and the Vt=500 on the FGF coupled ventilator, what’s the real Vt being delivered to the patient?
500mL/min + 333mL =833mL
10,000mL/min divided by 10 RR = 1000 mL min.
I:E is 1:2 which for a 6 second breath (based on RR) is 2/6 seconds or 1/3.
1000 x 1/3 = 333
“fresh gas during I time is added to Vt from I:E”
what are the patient implications of a bellow leak
may transmit high gas pressure to the breathing circuit which may cause barotrauma
anesthetic vapor could also escape leading to anesthetic awareness
bellows uses air or air/O2 mixture- if you are running high FiO2, the FiO2 getting to patient may decrease
if theres a bellows leak and O2 is used as ventilator drive gas, FiO2 in breathing circuit may increase
will the piston ventilator consume tank O2 in the event of a pipeline failure?
no, but pneumatic may
describe two pressure relief valves in piston ventilator
- positive pressure relief valve opens at 75cmH2O which prevents excessive pressure build up in anesthesia circuit
- negative pressure relief valve opens at -8cmH2O. when the circuit pressure falls below this value, negative pressure relief valve opens and entrains room air
piston ventilators do what to fresh gas
de couple FGF from ventilator!!
gas driven bellows ventilators do what to fresh gas
they couple it and Vt relies on FGF!
compare and contrast piston ventilator to gas driven bellows vent and PEEP
the piston ventilator does not add PEEP while the gas driven bellows ventilator adds 2-3cmH2O auto PEEP due to design of ventilator spill valve
breathing bag and pressure ventilator
-incorporated during MV
-deflates during expiration (WEIRD)
-bag will not move if patient breathes spontaneously on the ventilator
VCV
describe Pinsp, PIP, inspiratory flow
Pinsp varies based on compliance
if aw resistance rises or compliance decreases, PIP will rise
inspiratory flow is held constant during inspiration
-fixed Vt, inspiratory flow rate, inspiratory time
PCV
describe Pinsp, PIP, inspiratory flow
inspiratory flow varies based on compliance. usually uses decelerating pattern. begins high to achieve set inflation pressure then slows down to keep it constant
-fixed PIP, inspiratory time
things that decrease Vt based on compliance issue or resistance issue
compliance: pneumo, trendelenburg
resistance: kinked ETT, bronchospasm
things that increase Vt based on resistance change
bronchodilator therapy or removing secretions
situations when PCV is better than VCV
low compliance patient (obese, pregnant, lap procedure, ARDS)
cant have high PIP (LMA, neonate, emphysema)
need to compensate for a leak (LMA, uncuffed ETT in kids)
what does an assisted versus controlled versus spontaneous breath look like on the vent
if patient initiates breath in AC, do they get pre set Vt
yes they get the Vt that is set
describe BiPAP (biphasic positive aw pressure)
pressure #1 inspiratory positive aw pressure (think pressure support for spontaneous breath)
pressure #2 expiratory positive aw pressure (think CPAP on exhalation)
define APRV (aw pressure release ventilation)
-used for spontaneous ventilation
-like BiPAP but there’s a high level of CPAP throughout resp cycle
-high level pressure is released at pre set intervals to facilitate exhalation
-useful in patient with ARDS
what is the risk with IRV (inverse ratio ventilation)
breath stacking or dynamic hyperinflation (auto PEEP)
all halogenated anesthetics react with soda lime to produce
carbon monoxide
(des>iso>sevo)
how does compound A get produced
soda lime plus sevo
(1-2L/min for up to 2 MAC hours minimum then increase to >2L/min after 2 MAC hours)
describe the reaction of carbon dioxide with soda lime
CO2 + H2O = H2CO3
H2CO3 + 2NaOH –>Na2CO3 + 2H2O + heat
Na2CO3 + Ca(OH)2 –> CaCO3 + 2NaOH
how small versus large granule mesh affects airflow resistance and surface area
small granule: increase air flow resistance and surface area
large granule: decrease air flow resistance and surface area
2 problems with soda lime that occur
- absorbent is exhausted and unable to neutralize CO2 (pH >10.3, turns purple)
- absorbent is desiccated aka too dry
what is the best indicator of expired soda lime
presence of inspired CO2 in breathing circuit (remember when soda lime is not in use, it can turn back to white from purple/blue and be deceiving)
best thing to do in the middle of the case when you cant change the soda lime
increase FGF to create a semi open system. baseline on capnograph should return to 0
methods to minimize risk of carbon monoxide and compound A
-utilize low FGF to preserve water content of soda lime
-turn of FGF in between cases
-change all absorbents at one time
-change canisters if ethyl violet
-change canisters if unsure about hydration (FGF left on overnight or something)
benefits of silica addition to soda lime
decreases dust and therefore bronchial irritation
decreases flow resistance
(does reduce efficiency of granules)
describe the reaction of CO2 with calcium hydroxide lime (amsorb plus)
CO2 + H2O = H2CO3
H2CO3 + 2Ca(OH)2 –> CaCO2 +2H2O + heat
does calcium hydroxide lime contain a strong base? silica?
no, it contains calcium hydroxide to neutralize carbonic anhydrase.
calcium chloride keeps it moist
calcium sulfate and polyvinylpyrrolidone are used in place of silica to increase hardness
benefits of calcium hydroxide lime (amsorb)
- does not create carbon monoxide
- little to no compound A production
- lower risk of fire when compared to soda lime
draw backs of calcium hydroxide lime (amsorb)
- cannot absorb as much CO2 as soda lime (26L per 100g versus 10.6L/100g)
- therefore, requires replacement more often (and is more expensive)
active scavenger system relies on
suction to remove gas (safer for patient but not safer for OR personnel because it communicates with OR environment)
-needs negative pressure relief valve to ensure barotrauma does not occur
passive scavenger system relies on
positive pressure to remove gas
OSHA guidelines exposure to halogenated anesthetics
control of FGF going into scavenger: spontaneous ventilation versus mechanical ventilation
spontaneous ventilation: APL valve controls
MV: spill valve controls
5 components of scavenger system
- gas collecting assembly (collects waste gas, located at APL and spill valve)
- transfer tubing (directs gas to interface)
- interface (open or closed)
- gas disposal tubing
- gas disposal system
open system interface on scavenging system
can only be used with active systems (connected to suction)
no need for positive or negative pressure relief valves
removes risk of barotrauma or FGF from breathing circuit
too much suction entrains room air in scavenger
too little suction vents scavenged gas into OR
contains reservoir
higher risk of exposing OR personnel to waste gas
closed system interface scavenging system
communicates to atmosphere with pressure valves
passive system (not connected to suction), must have positive pressure relief
since there is no suction, will not remove excess gas from circuit
if an active system is used, must have positive and negative pressure relief
contains a reservoir
closed system interface scavenging system
communicates to atmosphere with pressure valves
passive system (not connected to suction), must have positive pressure relief
since there is no suction, will not remove excess gas from circuit
if an active system is used, must have positive and negative pressure relief
contains a reservoir
4 ways to monitor for circuit disconnect
pressure, volume, EtCO2, vigilance
(nothing electronic, like O2 analyzer, is mentioned because it is electronic and will alert on a delay versus real time)
high pressure system location and components
begins at cylinder, ends at cylinder regulators
components: hanger yoke, yoke block with check valves, cylinder pressure gauge, cylinder pressure regulators
intermediate pressure system location and components
begins at pipeline, ends at flow meter valves.
components: pipeline inlets, pressure gauges, oxygen pressure failure device, oxygen second stage regulator, oxygen flush valve, ventilator power inlet, flow meter valves
low pressure systems, locations, components
begins at flow meter tubes, ends at common gas outlet
components: flowmeter tubes (thorpe tubes), vaporizers, check valve (if present), common gas outlet.
intermediate pressure system pipeline and tank PSI
pipeline= 50 PSI
tank= 45 PSI
SPDD
supply (cylinder)
processing (vaporizor)
delivery (circle system)
disposal (scavender)
5 tasks of O2 in anesthesia machine
- O2 pressure alarm
- O2 pressure device
- O2 flow meter
- O2 flush valve
- ventilator drive gas
DISS
prevents wrong gas hose from being attached to the anesthesia machine
how to calculate how long your O2 will last based on how much O2 is left in your cylinder:
1: How much O2 is left in cylinder? 660L/2000 PSI x contents remaining (L) /500 PSI
2: how long will it last? contents remaining (L) / FGF rate in L/min = minutes left before tank expires
O2
liters
PSI
PISS
660L
1900 PSI
PISS 2,5
Air
liters
PSI
PISS
625L
1900 PSI
PISS 1,5
N2O
liters
PSI
PISS
1590L
745 PSI
PISS 3,5
piston ventilator considerations
more accurate Vt
uncoupled from FGF
doesnt use tank O2 (because it doesnt use it as a bellows drive gas)
artificial sound can mimic bellow ventilator
high pressure system
begins and ends at
includes
begins at cylinder, ends at cylinder regulators
includes hanger yoke, yoke block with check valves, cylinder pressure gauge, cylinder pressure regulators
intermediate pressure system
begins and ends at
includes
begins at pipeline, ends at flow meter valves
includes pipeline inlets, pressure gauges, oxygen pressure failure device, oxygen second stage regulator, O2 flush valve, ventilator power inlet, flowmeter valves
low pressure system
begins and ends at
includes
begins at flow meter tubes, ends at common gas outlet
flow meter tubes (thorpe tubes)
vaporizers
check valve (if present)
common gas outlet
PISS use
prevent use of wrong gas cylinder
DISS use
gas hoses
the bourdon pressure gauge on an O2 cylinder reads 500 PSI. how long will the tank last if youre administering 2L/min
75 (or 83 or 87 depending on liters of O2)
O2 fail safe device resides in which pressure system
intermediate
minimum FiO2 permitted by a proportioning device
25%
