exam 3 part 2 Flashcards
vaporizers
2 pathways of fresh gas flow in a variable bypass chamber
one stream flows directly through a bypass circuit, not contacting the anesthetic liquid,
the other stream enters the vaporizing chamber where it becomes saturated with anesthetic vapor by passing over the liquid anesthetic, acting as the “carrier gas” before rejoining the bypass stream to create the final anesthetic concentration
what is the splitting ratio
the proportion of fresh gas flow that enters the vaporizing chamber within a vaporizer, compared to the amount that bypasses it
splitting ratio of carrier gas to bypass gas depends on
ratio of resistances to their flow which is controlled by concentration control dial and temperature compensation valve
molecules from a liquid, like sevoflurane for example, escape into the atmosphere, this is dependent on what factor
temperature
vapor is a gas that is below it’s
critical temperature
vapor pressure
pressure of molecules in a closed container
SVP for inhalational anesthetics at 20 degrees C
Halothane
Nitrous
Isoflurane
Desflurane
Sevoflurane
H- 243
N - 38770
I - 238
D- 669
S- 157
Concentrations of inhalational anesthetics at there SVP at 20 degrees C for 1 MAC
H- 0.76
N- 104
I- 1.15
D- 6.0
S- 1.85
splitting ratio is calculated by
dividing the flow rate through the vaporizing chamber by the flow rate through the bypass pathway
examples of split ratio calculations
If the carrier gas flow is x ml/min, the bypass flow is 1000-x, and the splitting ratio is (1000-x)/x. For example, if x = 38 ml/min, the bypass flow is 962 ml and the splitting ratio is 25:1
If the dial is set to 1% concentration, the splitting ratio is 44.5:1. This means that if 5000 ml of fresh gas flows into the vaporizer, 110 ml will flow into the vaporizing chamber.
How does temperature and saturated vapor pressure influence the splitting ratio
Temperature directly influences the splitting ratio in a vaporizer by affecting the saturated vapor pressure (SVP) of the anesthetic agent; as temperature increases, the SVP rises, leading to a higher proportion of fresh gas flowing through the bypass channel (lower splitting ratio)
and vice versa
when temperature decreases, more fresh gas enters the vaporizing chamber due to a lower SVP, resulting in a higher splitting ratio to compensate for the reduced vaporization.
carrier gas
flows into the vaporizing chamber, becomes saturated with vapor and is a small % of total FGF
bypass gas
FGF into vaporizer that is not exposed to liquid agent, this is a high % of FGF
describe where and how the anesthetic agent is added to the carrier gas in the variable bypass chamber
anesthetic agent is added to the carrier gas within the “vaporizing chamber” where a portion of the incoming fresh gas flow (acting as the carrier gas) passes through, becoming saturated with the anesthetic vapor before mixing back with the bypassed gas stream
comparing the output of a variable bypass vaporizer using oxygen, air, and nitrous oxide as carrier gases
the output will be highest with pure oxygen, followed by air, and significantly lower with nitrous oxide
viscosity of nitrous as a carrier gas
nitrous oxide’s lower viscosity leads to less gas flowing through the vaporizing chamber, resulting in a reduced anesthetic agent delivery
N2O will initially _____ agent output for about 10 min
and vice versa - turning N2O off will ____ agent output for a short time
reduce
increase
oxygen results in a slightly ______output compared to air
higher
(50-10%)
the surface area of the vaporizer chamber is increased with the use of the
wick and baffle system
liquid agent is wicked into baffles which become wet with agent
in direct contact with vaporizing chamber walls constructed of metals with high specific heat and thermal conductivity (heat sink)
WICKS
ambient heat is conducted into chamber to minimize
cooling due to vaporization
agent output concentration of incorrectly filled vaporizer when a vaporizer calibrated for a low SVP agent is filled with a high SVP agent
the resulting agent output concentration will be significantly higher than the intended concentration due to the increased volatility of the high SVP agent, leading to a much greater proportion of vapor being delivered to the breathing circuit, even at a low dial setting on the vaporizer
concentration of agent delivered is NOT dependent on
FGF rate
the % output of variable-bypass vaporizers is relatively constant over FGF of
250ml/min - 15L/min
EXCEPTION:
All sevo vaporizers are _______ accurate at high FGF (>10L/min) and high vaporizer concentration settings, they would deliver ______ than the dial setting due to _______
less
less
low vapor pressure of the agent
output of agent is accurate within ____ of dial setting at _____degrees C
20%
20-35 degrees C
temperature and splitting ratio
lower temp - ratio adjusted to allow for more carrier gas flow
higher temp - ratio adjusted to less carrier gas flow
splitting ratio is calibrated for 760mmHg so at higher altitude (500mmHG) the % of agent delivered will be ____
higher than the set %, so MAC value delivered will be higher
going from sea level to higher altitudes affects the % output of the agent but this is somewhat offset by the
reduction in barometric pressure
for sevo at 1 atm (760mmHg) the SVP of 160mmHg =
21%
at high altitude of 500mmHg, sevo SVP of 160 mmHg =
32%
in a hyperbaric chamber tje % of agent delivered will be ____than the set % but it is somewhat offset by the increase in barometric pressure
lower
agent output concentration of incorrectly filled vaporizer when a vaporizer calibrated for a high SVP agent is filled with a low SVP agent
the output concentration of the anesthetic agent will be significantly lower than intended because the low SVP agent will not readily vaporize, resulting in a much smaller amount of anesthetic vapor being added to the fresh gas flow, even when the dial is set to a high concentration setting.
explain what would happen if you fill a sevo vaporizer with iso
vaporizer designed for sevoflurane (high SVP) is mistakenly filled with isoflurane (lower SVP). Even if the dial is set to deliver a high concentration of isoflurane, the actual output concentration will be much lower than intended because the lower SVP of isoflurane will not produce enough vapor in the vaporizing chamber.
relationship between SVP and vaporization
A high SVP means the agent readily vaporizes, while a low SVP means it evaporates less easily
Volatile Anesthetics SVP from high to low
D-H-I-S
Volatile anesthetics are…..
liquids with low boiling points and high SVPs.
administered through inhalation, which allows them to enter the bloodstream through the pulmonary alveolar capillaries
the “pumping effect” in anesthesia refers to a situation where
pressure from a ventilator during inhalation, particularly with positive pressure ventilation or when using an oxygen flush valve, is transmitted backwards into the vaporizer, potentially causing an inaccurate delivery of anesthetic agent by forcing already vaporized gas back into the bypass channel, leading to a higher concentration than intended
how do modern anesthesia machines prevent the pumping effect from occurring
Check valves: Most modern vaporizers incorporate a check valve between vaporizer and CGO, which allows gas to flow out but prevents it from flowing back into the vaporizer.
Smaller Chamber Design: minimizing the volume of gas that can be pushed back into the chamber during pressure changes.
Tortuous Inlet pathway design: A long, serpentine inlet tube helps to dampen pressure fluctuations before they reach the vaporizing chamber
The interlock function on an anesthesia vaporizer ensures that
only one vaporizer can be turned on at a time
FGF only enters the vaporizer that is on
that agent is out of circuit when it’s vaporizer is off
To activate the interlock mechanism,
press the dial release inward while the vaporizer lever is locked, and turn the dial to the desired concentration
what is the risk of filling vaporizer with the wrong agent
it can lead to unintended anesthetic delivery, potentially causing overdose or underdose due to inaccurate concentration readings on the monitor
if you overfill the vaporizer what can happen
increase in vaporizer output which could lead to dangerous concentrations of the agent being delivered to the patient.
Tipping an anesthesia vaporizer more than 45 degrees from vertical can
cause a potentially lethal amount of anesthetic to be delivered to a patient
Liquid anesthetic flow: Liquid anesthetic can flow into the bypass chamber, increasing the amount of anesthetic delivered and creating toxic levels.
Obstructed valves: Liquid anesthetic can obstruct valves.
Cardiovascular collapse: An accidental overdose of anesthetic can lead to cardiovascular collapse.
how to treat a tipped vaporizer
you can flush it with high flow rates (5-10L/min) and a high concentration setting for 10–20 minutes. The correct treatment for other models may differ, so you should consult the vaporizer’s operating manual.
if tipped for a long time, drain sump and then flush
tipped vaporizers are not an issue with
Aladdin style vaporizers
instead of a variable bypass vaporizer, deflurane has to be used with a _________, ___________ ________ due to its very low boiling point of 22.8 degrees C and high SVP of 669.
temperature-controlled, pressure-regulated vaporizer
Tec 6 vaporizer is designed for
desflurane
desflurane is heated to _____ to allow predictability
above room temp
Tec 6 does not have any _____ through the vaporizing chamber
FGF
Tec 6 heats agent to specifically _____ which produces a vapor pressure of around ______
39 degrees C
1550mmHg
concentration control with Tec 6
dial adjusts a transducer, which injects pure vapor into the FGF, the FGF rate is sensed by the transducer and adjusts the vapor accordingly
tec 6 vaporizer is calibrated with
100% O2
tec 6 and nitrous
the viscosity of N2O is less so FGF with high % of N2O will have reduced des concentration
(air is less than O2 but more than N2O)
(better carriers)
tec 6 at high altitude
7% of des will be a lower partial pressure than sea level (because 7% of 500mmHg is 35 and 7% of 760mmHg is 53)
if des is at a lower partial pressure at higher altitudes then it then it would be ______potent
less!
need higher % to reach the same MAC as sea level
variable bypass models
datex-ohmeda Tec 4, 5, 7ADU
Drager Vapor 19, 20000
Injector (des) vaporizers
Datex-ohmeda Tec 6
Drager D-vapor
Aladin vaporizer is adaptable to all agents due to the
two components
1- part integrated into the anesthesia machine
2- agent specific cassette or sump
splitting ratio: variable bypass vs injector
variable bypass - vaporizer splits fresh gas flow
injector- dual circuit - FGF does not split
splitting ratio with the Aladin is decided by
the sump/cassette used, then electronic controls implement appropriate setting
Aladin vaporizer will not allow FiO2 to fall below ____ at common gas outlet
25%
method of vaporization: variable bypass vs injector
variable bypass- flow over
injector - gas/vapor blender (heat creates vapor than is injected into fresh gas)
temperature compensation: variable bypass vs injector
variable bypass- automatic
injector- electronically heated to 39 degrees C
calibration and position for both variable bypass and injector
agent specific and out of circuit
which type of vaporizer has elevation compensation
variable bypass
(injector need intervention)
how does the aladin vaporizer work with Des
has a low agent alarm for des
hypoxic guard takes the des and N2O concentration into account
des cassette does not have a heater, so if temp < 22.8 degrees C then it functions as a variable bypass with splitting ratio
if the temp >22.8 degrees C the n no FGF enters cassette and des is released into the FGF like normal
