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The Anesthesia Workstation

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Lee Chang

on 1 July 2018

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Transcript of The Anesthesia Workstation

Flow tubes are tapered, with the smallest diameter at the bottom of the tube and the largest diameter at the top.
The oxygen flow control knob is distinctively fluted and is larger in diameter.
All knobs are color coded for the appropriate gas
High Pressure



The Anesthesia Workstation

Break the machine up into systems…
temperature increases - more molecules enter the vapor phase, and the vapor pressure increases. Vapor pressure is
independent of atmospheric pressure
molecules bombard the wall of the container and create a pressure known as the

saturated vapor pressure

volatile liquids in a closed container - molecules escape from the liquid phase to the vapor phase until the number of molecules in the vapor phase is constant.
Lee Chang
Associate Professor
Department of Anesthesiology
What is the oxygen flush positive-pressure leak test?
(Draeger Apollo has an automated one)
When should you perform it?
What is the pressure of a full oxygen tank?

What is the pressure of a full nitrous oxide tank? 1/2 full?

What is the pressure following the pressure regulator?
Mapleson circuits are “semi-open”.
- lack unidirectional valves and CO2 absorbent.

Circle systems (semi-closed breathing circuits) have several advantages over Mapleson circuits:
- maintain heat and moisture in the airways
- allows the use of low flows
- minimizes rebreathing of CO2 while maximizing the rebreathing of volatile anesthetics
- minimizes contamination of the O.R. because they allow the use of scavenging systems.

- rugged, simple, compact, and cheap.

- low resistance to gas flow because they lack valves and CO2 absorbent.

- very low dead space.
helpful with small children and neonates, where you don't want a large amount of dead space relative to the patient's small tidal volumes

Spontaneous ventilation efficiency:
"All Dogs Can Bite"
A > D/E/F > C/B

Controlled ventilation efficiency:
"Dog Bites Can Ache"
D/F > B/C > A

What is the negative-pressure leak test?
What is the order of the flowmeters? Why does it make a difference?
Is it possible to deliver a hypoxic mixture with the fail safe valve intact?
What happens if you overfill or tip over the vaporizer?
Can you use desflurane in a traditional bypass vaporizer?
Two reasons:

1. High Vapor Pressure

2. High MAC requirements

A man lives on the twelfth floor of an apartment building. Every morning he takes the elevator down to the lobby and leaves the building. In the evening, he gets into the elevator, and, if there is someone else in the elevator -- or if it was raining that day -- he goes back to his floor directly. Otherwise, he goes to the tenth floor and walks up two flights of stairs to his apartment.

Cassette Vaporizers
Three formulations of carbon dioxide absorbant:

soda lime
80% calcium hydroxide
15% water
4% sodium hydroxide
1% potassium hydroxide (an activator)
calcium hydroxide lime
calcium hydroxide
calcium chloride

(a mixture of calcium hydroxide and barium hydroxide)
20% barium hydroxide
80% calcium hydroxide
Soda Lime
1. CO2 + H2O -> H2CO3
2. H2CO3 + 2NaOH (KOH) -> Na2CO3 (K2CO3) +
+ Heat
3. Na2CO3 (K2CO3) + Ca(OH)2 ->
+ 2NaOH (KOH)

1. Ba(OH)2 + 8H2O + CO2 -> BaCO3 +
+ Heat
2. 9H2O + 9CO2 -> 9H2CO3
3. 9H2CO3 + 9Ca(OH)2 ->
+ Heat
Pin Index Safety
was associated with operating room fires when used with
sevoflurane - discontinued by manufacturer in 2004

Carbon Monoxide
(Desflurane > Sevoflurane) and
Compound A

(Sevoflurane) are also concerns

What is the most common cause of carbon monoxide buildup and what day of the week are you most likely to encounter it?
Bain Circuit
Mapelson Circuits
What can cause the inspiratory CO2 levels to increase?
Direct connection between intermediate and low pressure systems

Potential for barotrauma in old machines if used during the venitlation cycle

APL Valve is no longer part of the circuit
technically part of the inspiratory limb
Which gases are interchangeable?
Main pipeline switched. What steps do you take?
Descending Bellows
(really, really old)
Dr. Mark Harbott
Ascending Bellows
What's all this have to do with the flush valve?
How are the bellows compressed?
Fresh Gas Decoupling Mechanism
GE Healthcare/Datex-Ohmeda machines have this. Drager machines do not.
Datex-Ohmeda's failsafe valve is all or nothing, while Drager's is proportional
Open Interface
Closed Interface
concern for compound A
and carbon monoxide
absolute amount of desflurane vaporized
is considerably greater than other drugs

heat is absorbed when changing from liquid
to gas (latent heat of vaporization)

in absence of external heat source, excessive
cooling of the vaporizer would occur, reducing output
Ohmeda "link" proportion limiting control system
Maximum nitrous oxide-oxygen
flow ratio of 3:1
Drager Oxygen Ratio Monitor Controller

Limits nitrous oxide flow to prevent delivery
of hypoxic mixture - unlike ohmeda which actively increases oxygen flow
shaft pushes to left
and opens the slave
control valve for
nitrous oxide
remember - vapor pressure
increases as temperature
hotter it gets, the less resistance there is and more will go through the bypass chamber
"T" on dial setting is for transport
Why is desflurane's vaporizer warm to touch?
Newer Dräger machines (like Apollo) use a
Sensitive Oxygen Ratio Controller

shuts off nitrous oxide if the oxygen flow is less than 200 mL/min, or if the oxygen fresh gas valve is closed.

audible and visible alarms sound if pipeline pressure is less than 20 psi

in case of complete oxygen pipeline failure, the machine will supply pipeline air so that some oxygen and agent can still be supplied to the patient.
a variable
bypass vaporizer
Vaporizer interlock system
When you put two vaporizers together, their pins touch.

When one vaporizer is turned on, it protrudes its pins which then pushes in the pins of adjacent vaporizers and locks them.

When this vaporizer is turned off, its pins retract and releases the pins on the adjacent vaporizers and thereby unlocks them. In this way,
only one dial can be turned on
at a given time
Draeger Apollo (and many of the newer anesthesia machines) uses litholyme.
No carbon monoxide production and Compound A production. And therefore no required flow levels.
Where are the bellows on our Draeger Apollo?
Electronic Flowmeters: everything is controlled by the computer - no proportion limiting control systems, etc.
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