Anesthesia machine 3 Flashcards
In the context of Thorpe tube flow dynamics, a low fresh gas flow will favor a ________ flow pattern
laminar
At a higher fresh gas flow, the annular space acts like an orifice, creating a _________ flow pattern
turbulent
Laminar flow is dependent on
gas viscosity (Poiseuille equation)
Turbulent flow is dependent on
gas density (graham’s law)
You are administering air 1 L/min and oxygen 3 L/min. Calculate the fraction of inspired oxygen.
80%
Describe how to calculate the FiO2 when using a flowmeter.
FiO2= (air flow rate x 21) + (oxygen flow rate x 100)/ total flow rate
Describe how to calculate fIo2 when using a nasal cannula.
add 4% FiO2 for every liter of O2 administered (up to a max of 44% FiO2 at 6 L/min)
You are using an anesthesia machine that couples fresh gas flow to tidal volume and fully compensates for circuit compliance. Calculate the total tidal volume delivered to the patient.
oxygen= 3 L/min.
air = 1 L/min.
I:E= 1:2
bellows= 500 mL
RR= 10 bpm
632 mL
What is the tidal volume delivered to the patient equation?
Vt set on ventilator + FGF during inspiration- volume lost to circuit compliance
In flow-coupled anesthesia machines, changes in _________________ impacts the total tidal volume delivered to the patient.
respiratory rate, I:E ratio, FGF, and the height of the bellows
If an anesthesia machine does not couple FGF to tidal volume, then
what’s set on the ventilator is what’s delivered to the patient
Older anesthesia machines couple FGF to the tidal volume set on the ventilator which
may lead to errors in predicted Vt and minute ventilation
Vent changes that increase delivered tidal volume include
decreased RR
increased I:E ratio (from 1:2 to 1:1)
increased FGF
increased bellows height
Vent changes that decrease delivered tidal volume include
increased RR
decreased I:E ratio
Decreased FGF
decreased bellows height
Increasing the FGF will increase
tidal volume
minute ventilation
and peak inspiratory pressure
should see EtCo2 decrease
Decreasing the FGF will decrease
tidal volume
minute ventilation
peak inspiratory pressure
should see EtCo2 increase
A ventilator is programmed to deliver a tidal volume of 600 mL. If the breathing circuit compliance is 5 mL/cm H2O and the peak pressure is 25 cmH2O, what is the total tidal volume delivered to the patient?
a. 425 mL
b. 450 mL
c. 475 mL
d. 500 mL
c. 475 mL
Define compliance.
compliance is a change in volume for a given change in pressure- it’s a measure of distensibility
What is the compliance equation?
compliance= volume/pressure
Many modern ventilators ________________ for fresh gas lost to circuit compliance.
automatically compensate
When the ventilator produces pressure inside the breathing circuit, some of this gas causes the circuit to expand. Since this doesn’t reach the patient,
it doesn’t contribute to the tidal volume that the patient receives
Compliance is a measure of
distensibility
The isoflurane dial is set to 2%. What percent of fresh gas exiting the vaporizing chamber is saturated with isoflurane?
100%
When you consider the variable bypass vaporizer, think
variable bypass, flow-over, temperature compensated, out-of-circuit, and agent-specific
Describe what out of circuit means.
the variable bypass vaporizer is positioned outside of the breathing circuit
Describe what is meant by variable bypass.
when fresh gas enters the vaporizer, some of it encounters the liquid anesthetic while the rest bypasses the liquid anesthetic.
With a variable bypass vaporizer, by setting the concentration on the dial, you determine
the splitting ratio (i.e. how much fresh gas contacts the liquid anesthetic)
Describe what is meant by flow-over.
As the fresh gas enters the vaporizing chamber (liquid anesthetic is here), it flows over a series of baffles and wicks.
Baffles and wicks increase _________ & _______________
surface area and turbulence
Baffles and wicks ensure that fresh gas inside the vaporizing chamber becomes
100% saturated with the anesthetic agent
Variable bypass vaporizers _______________ at changes in elevation
automatically compensate vaporizer output
Describe agent-specific.
Each vaporizer is calibrated to one anesthetic agent- filling a vaporizer with the incorrect anesthetic can lead to catastrophic errors in output
Describe temperature-compensated.
The temperature compensating valve adjusts the ratio of vaporizing chamber flow to bypass flow and guarantees a constant vaporizer output over a wide range of temperatures
Setting a higher concentration directs more fresh gas towards _____________
the liquid anesthetic
Setting a lower concentration directs
less fresh gas towards the liquid anesthetic
Flows less than _________ or greater than __________ can lead to reduced vaporizer output
200 mL/min or greater than 15 L/min.
If the vaporizer is tipped over some of the liquid anesthetic may enter
the bypass chamber leading to increased vaporizer output
1 mL of liquid anesthetic produces _________ of anesthetic vapor
200 mL
If the vaporizer is tipped, then you should run a high FGF through it for
20-30 minutes before it can be used for a patient
The pumping effect can
increase vaporizer output
Anything that causes gas that has already left the vaporizer to re-enter the vaporizing chamber can cause
the pumping effect
The pumping effect is enhanced by
low fresh gas flows, low concentration dial setting, low levels of liquid anesthetic in the vaporizing chamber, positive pressure ventilation, and the use of the oxygen flush valve
The pumping effect is minimized by
modern vaporizer design
The most common cause of a vaporizer leak is
a loose filler cap
The most common location for a leak to occur in the low-pressure system is
an internal leak in the vaporizer
A leak can only be detected when
the vaporizer is turned off
What is the equation to calculate how much liquid anesthetic is used?
mL of liquid anesthetic used per hour= Vol% x FGF (L/min) x3
Setting the vaporizer to __________ eliminates the worry of tipping the vaporizer during transport or removal
transport mode (T)
