Vaporizer Services

Tec 4,Tec 5 and Tec 7 Vaporizer Exchange Service & Sales

The GAV Vaporizer from

Phone 812-305-3606

The GAV vaporizer provides an effective means
of controlling agent delivery over a broad spectrum of clinical situations.
It is designed for use in continuous flow techniques of general anesthesia and
has a finely graduated dial coupled with an output which remains largely unchanged
over a wide range of dial settings, flow rates and temperatures.

Safety features such as interlock, non-spill and
keyed filler are incorporated and many convenience features are also included
to provide reliable and trouble free operation. The vaporizers are agent specific
with clear labeling and color coding to identify the agent with which they are
designed to be used. The warranty period three years from day of supply. We
recommend that the calibration is simply checked on site each year after that.

Tec 7 Sevoflurane Vaporizer

Calibration

Each GAV vaporizer has a single control dial which is calibrated in percentage
of anesthetic agent vapor per total volume (% v/v).
The dials for Isoflurane and Halothane are calibrated to 5% v/v in steps
of 0.2% up to 1% and in steps of 0.5% from 1% to 5%.
The dial for Sevoflurane is calibrated to 8% v/v in steps of 0.2% up to
1% and in steps of 0.5% from 1% to 8%.

Accuracy

When the vaporizer is `Off’ it is isolated so it offers no resistance to
gas flow.
With the dial turned on, the resistance is 15-20cm H2O at a flow of 5 I/min
02.

Operating Temperature

18° – 35°C

Liquid Capacity

300 ml nominal—wicks dry
75 ml nominal retained by the wicks

Weight and Dimensions

Height: 240mm Width: 115mm Depth: 200mm Weight: 7Kg dry

Vaporizer
Technical Information:

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The Anesthesia Gas Machine

Michael P. Dosch CRNA MS
University of Detroit
Mercy Graduate Program in Nurse Anesthesiology
This site is http://www.udmercy.edu/crna/agm/.

ANESTHESIA GAS MACHINE> COMPONENTS & SYSTEMS> PROCESSING>
VAPORIZERS

Physical principles
Classification
Vaporizer interlock
Operating principles of variable bypass vaporizers
How to fill vaporizers
How much liquid agent does a vaporizer use per hour?
Hazards and safety features of contemporary vaporizers
Current models

Processing: Vaporizers

Physical principles

Vapor pressure Molecules escape from a volatile liquid to
the vapor phase, creating a “saturated vapor pressure” at equilibrium. Vapor
pressure (VP) increases with temperature. VP is independent of atmospheric
pressure, it depends only on the physical characteristics of the liquid,
and its temperature.

Latent heat of vaporization is the number of calories needed
to convert 1 g of liquid to vapor, without temperature change in the remaining
liquid. Thus, the temperature of the remaining liquid will drop as vaporization
proceeds, lowering VP, unless this is prevented.

Specific heat is the number of calories needed to increase
the temperature of 1 g of a substance by 1 degree C. Manufacturers select materials
for vaporizer construction with high specific heats to minimize temperature
changes associated with vaporization.

Thermal conductivity – a measure of how fast a substance transmits
heat. High thermal conductivity is desirable in vaporizer construction.

Classification

Dräger Vapor 19.1, Vapor 2000, Penlon Sigma, Datex-Ohmeda S/5 ADU Aladin
vaporizers, and Datex-Ohmeda Tec 4, 5 are classified as

Variable bypass: Fresh gas flow from the flowmeters enters the inlet of any vaporizer which
is on. The concentration control dial setting splits this stream into bypass
gas (which does not enter the vaporizing chamber), and carrier gas (also called
chamber flow, which flows over the liquid agent).
Flow over: Carrier gas flows over the surface of the liquid volatile agent in the vaporizing
chamber, as opposed to bubbling up through it (as in the copper kettle and
Vernitrol)
Temperature compensated: Equipped with automatic devices that ensure steady vaporizer output over
a wide range of ambient temperatures
Agent-specific: Only calibrated for a single gas, usually with keyed fillers that decrease
the likelihood of filling the vaporizer with the wrong agent
Out of circuit: Out of the breathing circuit, as opposed to (much) older models such as
the Ohio #8 (Boyle’s bottle) which were inserted within the circle system.

The copper kettle and Vernitrol are measured-flow, bubble-through, non-temperature
compensated, multiple agent, and out of circuit.
cellpadding=”8″ width=”638″ align=”center”>

**Vaporizer Models**
size=”2″>Classification	Datex-Ohmeda Tec 4, Tec 5, SevoTec, and Aladin (AS/3 ADU); Dräger Vapor 19.n, Vapor 2000	Copper Kettle, Vernitrol	Datex-Ohmeda Tec 6 (Desflurane)
Splitting ratio (carrier gas flow)	Variable-bypass (vaporizer determines carrier gas split)	Measured-flow (operator determines carrier gas split)	Dual-circuit (carrier gas is not split)
Method of vaporization	Flow-over (including the Aladin for desflurane, which does not require added heat like the Tec 6)	Bubble-through	Gas/vapor blender (heat produces vapor, which is injected into fresh gas flow)
Temperature compensation	Automatic temperature compensation mechanism	Manual (i.e., by changes in carrier gas flow)	Electrically heated to a constant temperature (39ºC; thermostatically controlled)
Calibration	Calibrated, agent-specific	None; multiple-agent	Calibrated, agent-specific
Position	Out of circuit	Out of circuit	Out of circuit
Capacity	Tec 4: 125 mL Tec 5: 300 mL Vapor 19.n: 200 mL Aladin: 250 mL	200-600 mL (no longer manufactured)	390 mL

Vaporizer interlock

The vaporizer interlock ensures that

Only one vaporizer is turned on
Gas enters only the one which is on
Trace vapor output is minimized when the vaporizer is off
Vaporizers are locked into the gas circuit, thus ensuring they are seated
correctly.

Operating principles of variable bypass vaporizers

Total fresh gas flow (FGF) enters and splits into carrier gas (much less than
20%, which becomes enriched- saturated, actually- with vapor) and bypass gas
(more than 80%). These two flows rejoin at the vaporizer outlet. The splitting
ratio of these two flows depends on the ratio of resistances to their
flow, which is controlled by the concentration control dial, and the automatic
temperature compensation valve.

Effect of flow rate: The output of all current variable-bypass
vaporizers is relatively constant over the range of fresh gas flows from approximately
250 mL/min to 15 L/min, due to extensive wick and baffle system that effectively
increases surface area of vaporizing chamber. All sevoflurane vaporizers are
less accurate (due to the low vapor pressure of the agent) at high fresh gas
flows (> 10 L/min) and high vaporizer concentration settings typical after
induction, where they deliver less than the dial setting (Anesth Analg
2000;91:834-6 notes that this tendency is accentuated if the vaporizer is nearly
empty). Clinically this is relatively unimportant, since we titrate to effect
(end tidal agent concentration) using overpressure.

Effect of ambient temperature: The output of modern vaporizers
is linear from 20-35 degrees C, due to

Automatic temperature compensating devices that increase carrier gas flow
as liquid volatile agent temperature decreases
Wicks in direct contact with vaporizing chamber walls
Constructed of metals with high specific heat and thermal conductivity

Effect of intermittent back pressure transmitted from breathing
circuit : The pumping effect is due to positive pressure ventilation
or use of the oxygen flush valve. It can increase vaporizer output. Modern vaporizers
are relatively immune (older vaporizers are certainly not immune) due
to check valves between the vaporizer outlet and the common gas outlet, smaller
vaporizing chambers, or tortuous inlet chambers. Any of these design features
prevent gas which has left the vaporizers from re-entering it. The check valves
are why a negative pressure leak check is recommended by the FDA checklist (step
5), since it works for all machines. The S/5 ADU has check valves in the vaporizer
control mechanisms.

How to fill vaporizers

For either funnel or keyed filler types,

fill the vaporizer only to the top etched line within the sight glass. Do not
hold the bottle up on a keyed filler until it stops bubbling (this will overfill
the chamber, particularly if the concentration control dial “on”, or if leaks
are present). The only current vaporizer which can be filled while
it is operating is the Tec 6 (Desflurane).

How much liquid agent does a vaporizer use per hour?

Ehrenwerth and Eisenkraft (1993) give the formula:
3 x Fresh gas flow (FGF) (L/min) x volume % = mL liquid used per hour

Or one can determine the volume (mL) of saturated vapor needed to provide 1%
(ie 4000 x 0.01 = 40 mL); then use Avogadro’s hypothesis, the molecular weight,
the liquid density, and molar volume (22.4 L at 20 degrees C) to determine how
many mL of liquid become 40 mL vapor per minute. Typically, 1 mL of liquid volatile
agent yields about 200 mL vapor. This is why tipping is so hazardous- it discharges
liquid agent into the control mechanisms, or distal to the outlet. And minute
amounts of liquid agent discharged distal to the vaporizer outlet result in
a large bolus of saturated vapor delivered to the patient instantaneously.

Hazards and safety features of contemporary vaporizers

Hazards

Incorrect agent
Tipping
- If tipped more than 45 degrees from the vertical, liquid agent can obstruct
  valves.
- Treatment: flush for 20-30 minutes at high flow rates with high concentration
  set on dial. Please note that this is the recommended treatment for the
  Tec 4 vaporizer. The correct approach for other models differs, so their
  individual operating manuals must be consulted.
Simultaneous inhaled agent administration
- If removing the central vaporizer from a group of three on an Ohmeda
  Modulus machine, move the remaining two so that they are adjacent. On
  models which were manufactured prior to 1995, removing the center vaporizer
  of three defeats the interlock, and allows the outer two vaporizers to
  be turned on simultaneously.
Reliance on breath by breath gas analysis rather than preventive maintenance
- Problem: failure of temperature compensation device may result in a
  rapid onset, high output failure of the vaporizer
- Failure of renewable components such as seals and O-rings may have the
  same effect
Overfilling
- May be prevented by following the manufacturer’s guidelines for filling:
  fill only to the top etched line on the liquid level indicator glass,
  and fill only when the vaporizer is off. Anaesthesia 2002;57:288
Leaks
- Leaks are relatively common, often due to malposition of vaporizers
  on the back bar (Anaesthesia 2002;57:299-300), or loss of gaskets,
  and these leaks may not be detected with the standard checklist unless
  the negative pressure check is performed.
- Tec 6 vaporizers can also leak liquid while being filled, if the desflurane
  bottle is missing the white rubber O-ring near its tip. This can be mistaken
  for a defective vaporizer (Anesth Analg 2003;96:1534-5)
Electronic failure
- As vaporizers incorporate electronics, they are susceptible to electronic
  failure. Two case reports in 2000 detail ADU vaporizers failing due to
  “fresh gas unit failure”, and from copious emesis soaking the machine
  (Anaesthesia 2000;55:1214-5, Anaesthesia 2000;55:1215).

Safety features

Important safety features include:

Keyed fillers
Low filling port
Secured vaporizers (less ability to move them about minimizes tipping)
Interlocks
Concentration dial increases output in all when rotated counterclockwise
(as seen from above)

Current models

Variable bypass vaporizers

Ohmeda Tec 4, 5 With the center vaporizer removed (if three

are mounted side by side), one can activate both outer vaporizers simultaneously
(in machines manufactured after 1995, this fault is corrected). Vaporizer outlet
has check valve.

The Sevotec 5 is used in a similar fashion to the other Tec
5 vaporizers. Note that in December 1997 the product labeling was changed to
allow fresh gas flow as low as 1 L/min (for not greater than 2 MAC-hours).

Penlon Sigma is similar to the Tec vaporizers, and can be

found on either type (Ohmeda, Dräger) of machine. The Penlon Sigma
Delta sevoflurane vaporizer fits a SelectaTec interlock bar for Dräger
machines.

Dräger Vapor 19.1 is similar to Ohmeda Tec 4, 5: all

are variable bypass types. The interlock on Dräger machines continues to
function if any vaporizers are removed, but one must attach a short-circuit
block to prevent leaks if any vaporizer is removed. There is no outlet check
valve- the tortuous inlet arrangement protects from the pumping effect. The
Dräger site has a
href=”http://www.nad.com/8aaa_vaporizers.htm”
target=”_top”>description of the Vapor 19, with operating principles and clinical
guidelines.

The Vapor 2000 is one of two tippable vaporizers (ADU Aladin
cassettes are the other). The dial must first be rotated to a “T” setting (“transport”
or “tip”) which is beyond zero (clockwise).

Datex-Ohmeda Aladin vaporizer Cassettes containing each volatile

liquid anesthetic are inserted into a port containing the central electronic
control mechanism, which recognizes the contents of the cassette and dispenses
agent into the stream of fresh gas flow. Because each cassette is only a liquid
sump without control mechanisms, they can be tipped in any orientation without
danger, and they are maintenance free. The cassette and the control mechanisms
are checked as part of the electronic equipment checklist daily. The Aladin
will not deliver volatile agent without mains power or battery backup, and adequate
oxygen (or air) pressure. The output of older vaporizers varies slightly with
changes in fresh gas mixture, whereas the Aladin compensates for this automatically.
The S/5 ADU features a low agent alarm for desflurane, the hypoxic guard system
takes the desflurane concentration into account along with nitrous oxide, and
the desflurane cassette works without added heat. The cassettes are extremely
light, and may be removed with one hand. For a study of this vaporizer’s performance,
see Anesth Analg 2001;93:391-5.

Gas/vapor blenders

Tec 6 Suprane^TM (desflurane) vaporizer: Because

of the volatility of this agent, it requires new systems to contain, transfer,
and vaporize it. The saturated vapor pressure at room temperature (20 degrees
C) is 664 torr- 87% of one atmosphere. This means that desflurane is nearly
boiling at room temperature. The vaporizer is a gas/vapor blender, not a variable
bypass type.

Classification (from Anesth Analg 1993;76:1338-41):

electrically heated, dual circuit gas/vapor blender, constant-temperature, agent
specific, and out-of-circuit. Function: Heats agent to 39 degrees
C, which produces a vapor pressure of around 1550 mm Hg. Electronic controls
inject pure vapor into the fresh gas flow from the flowmeters, controlled by
the concentration control dial, and a transducer (which senses the fresh gas
flow rate, and adjusts the vapor output accordingly). Requires electrical power
(it shuts off in power failures!), and has alarms; two unusual aspects compared
to other contemporary vaporizers. In use it is similar to variable bypass vaporizers:
it fits in the interlocks, and is mounted on the back bar in a similar way.
It is accurate at low flows (ie considerably less than 1 L/min total FGF). It
may be filled during use. A mark on a liquid crystal display indicates when
the liquid level is one bottle low (250 mL). The user must replace a battery
which powers the alarms periodically. There is an alarm for low liquid level.
The unit requires a warm-up period. Datex-Ohmeda has moving pictures on their
site to help in
href=”http://www.us.datex-ohmeda.com/products/anesth_tec6_trouble.htm”> troubleshooting
the Tec 6.

Checkout procedure for the Tec 6

Press and hold the mute button until all lights and alarms activated.
Turn on to at least 1% and unplug the electrical connection. A “No Output”
alarm should ring within seconds. This tests battery power for the alarms.
This step is crucial in relation to the quick emergence characteristics
of this agent- any interruption in its supply must be noted and responded
to at once.

A calibrated throttle valve is opened or closed by the user. The more it is
closed, the greater the pressure exerted by the fresh gas flow on the surface
of the liquid anesthetic. This pressure tends to force liquid to atomize at
the injector nozzle. The number of molecules of liquid injected is proportional
to the resistance to gas flow at the throttle valve (controlled by the concentration-control
dial). The liquid droplets vaporize in the flowing fresh gas stream. Thus, since
the liquid is not vaporizing (at least within the vaporizer), no thermal compensation
is required.

A desflurane vaporizer for the Kion is not available.

The GAV vaporizer is a direct replacement for the Ohmeda select-a-tec vaporizer.