Review Article

Advances in vaporisation: A narrative review

Address for correspondence: Pankaj Kundra, Shreya Goswami1, Aruna Parameswari2

Dr. Pankaj Kundra, Department of Anaesthesiology and Critical Care, Jawaharlal Institute of Postgraduate Medical
Department of Anaesthesiology Education and Research, Puducherry, 2Department of Anaesthesiology, Critical Care and Pain Medicine,
and Critical Care, Jawaharlal Sri Ramachandra University, Chennai, Tamil Nadu, India, 1Department of Anaesthesiology, Washington
Institute of Medical University School of Medicine, St Louis, MO, USA
Education and Research,
Puducherry ‑ 605 006, India.
E‑mail: p_kundra@hotmail.com ABSTRACT
Submitted: 19-Nov-2019
Revised: 08-Jan-2020 The output of inhalational agents from modern vaporisers are both electronically and pneumatically
Accepted: 24-Jan-2020 controlled. They are designed to deliver set agent concentrations accurately with low fresh gas
Published: 11‑Mar‑2020 flows and possess enhanced safety features. The purpose of this review article is to give an
overview of three modern vaporisers, namely, the Aladin cassette vaporiser, injection vaporisers
and AnaConDa™. The Aladin cassette is integrated with Datex Ohmeda S/5 ADU and GE Aisys
anaesthesia machines. The electronic vapour control unit is incorporated within the anaesthesia
machine. The agent specific cassettes act as a detachable vaporising chamber. The system can
Access this article online work as a variable bypass and measured flow vaporiser but requires a power supply to function.
Website: www.ijaweb.org Injection vaporisers can achieve the set end‑tidal agent concentration very rapidly with even
metabolic flow rates. Hence, anaesthetic depth can be rapidly altered with minimal wastage and
DOI: 10.4103/ija.IJA_850_19
theatre pollution. The two types of injection vaporisers, namely, Maquet and DIVA™ are customised
Quick response code
to function with Maquet FLOW‑i and the Drager Zeus anaesthesia machine, respectively.
AnaConDa™ is a combination of vaporiser and humidity and moisture exchange filter which can
be fitted in the ventilatory circuit. It is primarily designed for use in intensive care for sedation and
out of operating room use.

Key words: Aladin cassette, AnaConDa, anaesthesia machine, injection vaporiser, vaporisers

INTRODUCTION integration, operation and safety features incorporated

in modern vaporisers to yield to end‑user demands.
Vaporisers are a salient component of modern
anaesthesia workstation and are integrated with the A thorough literature search was done from
anaesthesia workstation to match the accuracy and inception till March 2019 using databases/search
safety standards. Since the evolution of the anaesthesia engines (Medline, Embase, Scopus, PubMed and
machine into a workstation, the vaporisers have Google Scholar). The articles were manually searched
evolved too; integrating electronics with pneumatics. by the authors for cross‑referencing. All the articles
These electronic vaporisers have been made very published in English were searched. We used
safe for use and have incorporated different priority the following keywords ‘anaesthesia machine’,
alarms to warn the end‑user whenever there is a ‘anaesthesia workstation’, ‘gas delivery’, ‘vaporisers’,
malfunction. In addition, with the use of more potent ‘Aladin cassette’, ‘injection vaporiser’ and ‘AnaConDa’.
volatile agents and agents with low boiling points, Amongst 2400 articles (review articles, primary
the modern vaporisers have the ability to control the
vapour output with extreme accuracy even when the This is an open access journal, and articles are distributed under the terms of
the Creative Commons Attribution‑NonCommercial‑ShareAlike 4.0 License,
anaesthesia machine fresh gas flows (FGF) are changed which allows others to remix, tweak, and build upon the work non‑commercially,
to alter the anaesthetic depth rapidly. The high‑end as long as appropriate credit is given and the new creations are licensed under
the identical terms.
anaesthesia workstations have an option to set the
For reprints contact: reprints@medknow.com
target end‑tidal anaesthetic concentration (ETAC)
and these vaporisers are designed to respond to such How to cite this article: Kundra P, Goswami S, Parameswari A.
demands with precision. Hence, this review aims to Advances in vaporisation: A narrative review. Indian J Anaesth
describe the components, electronics and pneumatic 2020;64:171-80.

© 2020 Indian Journal of Anaesthesia | Published by Wolters Kluwer - Medknow 171

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 Kundra, et al.: Modern vaporisers

manuscripts, case reports, letter to the editors and cassettes are available with a colour‑coded, Easy‑Fil or
chapters from books) the relevant information Quik‑Fil mechanism. On the other hand, desflurane
pertinent to the topic were sorted out. The information cassettes have a filling mechanism that is compatible
available is very limited and only 14 references could with Saf‑T‑Fil desflurane bottles [Figure 1a]. These
be included. cassettes can hold up to 250 mL of liquid anaesthetic.

ALADIN CASSETTE VAPORISER The larger rear section of the cassette is the vaporising
chamber containing the liquid anaesthetic at its
Aladin cassette vaporiser electronically controls SVC (saturated vapour concentration). The cassette is a
the gas flow and vapour concentration. This system specially designed liquid sump that requires main power
is used in the Datex Ohmeda S/5 ADU and GE supply or battery backup and adequate oxygen and air
Aisys anaesthesia workstation.[1] The vaporiser pressure to work. It is filled with a synthetic material
system consists of an electronic vapour control unit soaked in liquid anaesthetic that is arranged as lamellae
internalised within the anaesthesia workstation and with metal plates interspersed between the lamellae.
coded agent cassettes that contain the anaesthetic They are so arranged to form a convoluted pathway for
liquid that serves as a detachable vaporising chamber. the FGF so that the surface area available for vaporisation
The cassettes are coloured and magnetically coded is maximised. The back panel has an inflow valve and
and are designed to deliver five different inhalational outflow valve which are spring‑loaded mechanical ball
anaesthetics (halothane, isoflurane, enflurane, valves to prevent agent leak during transport [Figure 1b].
sevoflurane and desflurane).
Functional Anatomy: The Aladin cassette vaporiser is
The structural and functional components: The concentration calibrated, flow over and electronically
Aladin cassette comprises of two parts, namely, thermo‑compensated that works both as variable
the agent‑specific vaporiser chamber (cassette) and bypass and measured flow vaporiser.[2,3]
the central processing unit (CPU) which is integrated
into the anaesthesia machine. The cassette is a Function as a variable bypass: Aladin cassette vaporiser
leakproof metal box which has a smaller front portion is in many ways similar to the other variable bypass
which is colour‑coded to the specific agent and a larger vaporisers such as Tec 4, Tec 5 and Tec 7 vaporisers,
rear portion that is black in colour. The front portion however, there are several important differences. The
has an agent‑specific filling system, a glass window vaporiser consists of (a) a bypass chamber which
to display the level of the anaesthetic liquid and a houses a backpressure regulator that builds pressure
handle with a lever for locking the cassette in the slot at the input to the vaporiser if necessary, to drive gas
provided on the anaesthesia machine. This portion through the cassette, and this is permanently housed
also houses the contact for the electronic temperature in the anaesthesia machine and (b) a detachable
sensor and liquid anaesthetic agent level. There are cassette that serves as the vaporising chamber. The
four copper coloured circles that can be seen on the two separate parts must come together to form a
top surface of the front of the cassettes. These are the functioning vaporiser. The liquid anaesthetic is
copper contacts of the electronic bus that power the filled in the front section and enters the rear section
capacitor plates which sense the level of the liquid through a one‑way valve. The FGF and the vaporiser
agent. Information from the liquid level sensor and output are electronically controlled with the necessary
vaporiser temperature data is transmitted by this hardware and software built into the anaesthesia
electronic bus to the anaesthesia workstation. There machine [Figure 2].
are also five agent identification magnets arranged in a
sequence in the front portion of the cassette, but these
are not visible externally. These signature magnets
allow the anaesthesia machine to identify the agent
cassette that is inserted into the machine slot.

There are three types of Aladin 2 cassettes (which are a b

currently used in modern anaesthesia workstations) Figure 1: Desflurane Aladin Cassette Vaporiser. (a) Front panel
showing the Saf‑T‑filling mechanism compatible with Desflurane
filler systems. Enflurane and isoflurane use a bottles (b) Rear panel with inflow and outflow spring‑loaded mechanical
colour‑coded, Easy‑Fil mechanism. Sevoflurane valves

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 Kundra, et al.: Modern vaporisers

Figure 2: Schematic illustration explaining the components and basic functional aspect of Aladin 2 cassette vaporiser. FGF = Fresh gas flow

Gas flow: The FGF is first split into two portions; the flow to the cassette [Figure 3b]. The excess pressure
bulk of the FGF passes through the bypass chamber in the cassette is then brought down by metering
and a smaller portion passes through a mechanical out some of the gas containing inhalational agent
one‑way valve and an electronic inflow close valve. from the cassette pressure relief valve attached to the
It then enters the cassette by passing through the scavenging system. Once the cassette pressure falls
open mechanical ball valve in the rear panel of the below the mixer output pressure some of the FGF is
cassette. This cassette inflow valve only opens when again routed through the cassette [Figure 3c]. Hence,
the cassette is plugged into the slot in the anaesthesia the control loop will differ depending upon whether
machine. The FGF enters the vaporising chamber to the entire FGF is routed through the bypass chamber
pick up vapour at its saturated vapour pressure (SVP). or to split between cassette and bypass chamber.
The gas saturated with anaesthetic vapour exits the When the entire FGF is through the bypass chamber,
cassette/vaporising chamber through the cassette the control loop depends on mixer flow. On the other
outflow valve and passes sequentially through an hand, when FGF is split between the cassette and the
electronic outflow close valve, a liquid flow prevention bypass chamber, the control loop for delivery of the
valve and a proportional flow valve. Finally, it passes volatile agent depends on the reported mixer flow,
through the agent flow measurement device and into cassette flow, cassette pressure and temperature.
the outlet of the control unit, gets mixed with the
bypass chamber gas and is delivered at the common The flowmeters: The inflow and outflow flowmeters
gas outlet [Figure 2]. determine the flow by detecting the pressure
drop across a fixed flow restrictor (pressure drop
Function as a measured flow vaporiser: To deliver is proportional to gas flow over fixed resistance).
the requested concentration of the volatile agent, the A zeroing valve is incorporated into each of the
outflow from the cassette (the variable control of flow flowmeters that temporarily will short the pressure
through the cassette) is controlled by a proportional transducer’s ports together for an accurate zero
valve. Hence, the control loop of the system measurement. These zeroing valves also prevent agent
depends upon the cassette flow and not the agent condensation as they are energised during standby to
concentration (that amount of cassette flow is added heat the flowmeter manifold.
to the bypass chamber flow to meet the desired set
concentration of the volatile agent) which is delivered Temperature control and compensation: Vapour
to the common gas outlet [Figure 3a]. concentration of the volatile agent is determined by
SVP divided by the total cassette pressure (SVP/Total
Delivery of the set agent concentration: Volatile cassette pressure).[2] Hence, if the temperature falls
anaesthetic agent is delivered from the cassette‑based the SVP of the volatile agent will fall and therefore
on the mixer output pressure and the cassette pressure. the proportional valve will accordingly govern the gas
When the cassette pressure exceeds the mixer output flow output from the cassette. Finally, temperature
pressure the entire FGF is directed through the bypass compensation is achieved by the central processing
chamber and inflow valve closes to prevent any gas unit. The microprocessor receives input from multiple

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 Kundra, et al.: Modern vaporisers

a b

c
Figure 3: Interplay of the cassette of cassette pressure and mixer output pressure in Aladin cassette function. (a) Cassette pressure and mixer
output pressure regulating agent delivery from cassette, (b) Cassette pressure exceeds mixer output pressure and the gas flow to the cassette
is stopped (c) Cassette pressure is lowered down as agent is metered out to the scavenging system and cassette pressure falls below mixer
output pressure and the gas is routed through the cassette. FGF = Fresh gas flow, F = Flowmeter, P = Pressure sensor, Cassette pr. relief
valve = Cassette pressure relief valve

sources every 200 ms including FGF rate, carrier gas is bigger in Aladin 2 and the handle has a locking
composition, set vapour concentration, liquid level lever. There is also an additional liquid level sensor
and temperature in the vaporising chamber (sump) which gives input back to the anaesthesia workstation
and controls vapour output electronically. To maintain via an electronic bus, which also conveys vaporiser
cassette temperature, there is a fan mounted beneath temperature data. Aladin DES and all Aladin 2
the Aladin cassette housing operating at cassette cassettes have electronic agent level sensing. Aladin
temperatures below 17°C. This serves to heat the 1 and Aladin 2 both measure temperature. While
cassette when large amounts of volatile anaesthetic are Aladin 1 had very simple temperature measurement
being vaporised and heat is lost. Aladin 2 cassettes are more advanced having internal
temperature sensing mechanism. A symbol indicating
The difference in the delivery of desflurane vapour enhanced temperature sensing is seen on the front of
compared to other agents: The desflurane Aladin cassette the cassette [Figure 2].
works differently compared to that of other agents. When
the temperature of desflurane inside the cassette is less Salient features of Aladin Cassette
than 22.8 , it functions as a flow over variable bypass The vapour output is not influenced by atmospheric
vaporiser just as it is for the other agents. However, pressure changes since the vapour concentration is
when the cassette temperature is above 22.8°C, which is determined by the separate environment that is the
the boiling point of desflurane, the inflow valve closes total cassette pressure. The electronic control in the
and no fresh gas enters the cassette. The vaporiser now cassette allows for automatic record keeping and
behaves as an injector and calculated amount of vapour usage calculation. Agent control is monitored by the
is injected out of the proportional valve to mix with the microprocessor up to 200 ms during operation. Aladin
fresh gas from the bypass. cassette vaporiser is electronically controlled hence, it
cannot function in the presence of power failure when
Aladin 1 and Aladin 2 cassettes: There are some the workstation battery gets depleted.
differences between the originally introduced Aladin
1 cassettes [Figure 4] and the currently used Aladin 2 Aladin cassette is featured with specific safety features
cassettes [Figure 2]. The liquid level display window to ensure safe and constant delivery of vapours to the

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pollution. Injection vaporisers were introduced with

high‑end anaesthesia workstations (Maquet FLOW‑i and
Drager Zeus).

It is worthwhile to know how the injection vaporiser

can achieve the set targets of rapidly altering
anaesthetic depth in 1 min with exceptionally low FGF.
Rapid anaesthetic depth titration with low FGF can be
achieved by first calculating the amount of sevoflurane
vapour required to achieve 2% ETAC of sevoflurane
Figure 4: Schematic illustration explaining the components and basic in approximately 6000 mL capacity reservoir which is
functional aspect of Aladin 1 cassette vaporiser. FGF = Fresh gas flow, 120 mL of vapour (120/6000 × 100 = 2%) where the
Cassette ID = Cassette identification
reservoir comprises of patient’s functional residual
patients. The cassette features with accurate overfill capacity of 2000 mL and the anaesthesia circle breathing
protection and the level sensing are electronic and system capacity of 4000 mL. With a sevoflurane
more accurate than only visual sensing. There is vaporiser set at 2%, the splitting ratio is 12:1. With FGF
a liquid spill prevention valve that prevents the of 6000 mL/min, 5538 mL/min flows through the bypass
anaesthetic liquid in the vaporising chamber from chamber and 462 mL/min flows through the vaporising
entering the fresh gas line. There is no risk of agent chamber and picks up 120 mL/min of sevoflurane
spilling if the cassette is tilted as the inlet valve will vapour. The total vaporiser output is 6120 mL/min and
close preventing any spillage. The vaporiser undergoes sevoflurane will represent ~2% of that output.[7]
a daily self‑check automatically when the anaesthesia
workstation is switched on. Aladin cassette also has Hence, the percentage of sevoflurane vapour that
a pressure relief valve that works as a safety valve a vaporiser should deliver to achieve 2% ETAC
that opens whenever the pressure inside the Aladin of sevoflurane in 1 min with 180 mL of FGF is
cassette is greater than 2.5 bar. equal to sevoflurane vapour/total FGF that is,
120/(180 + 120) = 0.4 or 40% where 180 mL is the near
Foong et al.[4] reported an accidental over‑delivery of metabolic FGF (3.5 mL/kg in a 50 kg person ~180 mL)
desflurane via Aisys Carestation Aladin 2 Cassette™ and 120 mL is the sevoflurane vapour added to FGF.
vaporiser. The inspired fraction of desflurane (FiDes) Thus, a vaporiser will have to deliver 40% sevoflurane
went up to 17.5% and 19.5% on two occasions during in FGF of 180 mL to achieve the 2% ETAC of sevoflurane
a procedure in end‑tidal control delivery mode. Both in 1 min. None of the vaporisers except the injection
episodes were managed by temporarily switching vaporisers can achieve this target in such a short time
off desflurane and washing off desflurane with high with near metabolic FGF.
FGF (6 l/min). The patient developed hypotension and
tachycardia and required pharmacological intervention Working principle: The anaesthetic agent is dispensed
for restoration of haemodynamic parameters. Changing as liquid and that liquid has to be converted into the
the cassette did not resolve the issues. However, similar vapour state. Thus, the working principle involves
situations could not be simulated later except on one the calculation of how much vapour will be generated
occasion and it was classified as an intermittent error. by 1 mL of an anaesthetic agent. For example, the
Hence, vigilance is necessary while using automated molecular weight of isoflurane is 184.5 and its specific
drug delivery devices. gravity is 1.5 g/mL. Hence, applying Avogadro’s
hypothesis 184.5 g/moles of isoflurane will occupy
INJECTION VAPORISERS 22.4 L at 273 K or 0and 760 mmHg. Therefore, 1 g/mole
at 20 will occupy 22400/184.5 × 293/273 and 1 mL
Injection vaporisers[5,6] inject a known amount of liquid will give 22400/184.5 × 293/273 × 1.5 = 194 mL of
agent or pure vapour into the gas stream to provide desired isoflurane vapour.[8]
concentration. The hallmark of injection vaporiser is that
it enables rapid titration of anaesthetic depth with highly MAQUET INJECTION VAPORISER
conservative low gas flows (metabolic flow) in a very
short time (as short as 1 min), as a result, they minimise The structural and functional components [Figure 5]:
the wastage of the anaesthetic agents and prevent theatre This is an electronically controlled injection type of

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 Kundra, et al.: Modern vaporisers

the supply of the pressurised liquid to the vaporiser

injector device when the vaporiser or the system is
off or on standby. The vaporiser injector delivers the
pressurised liquid anaesthetic in the form of spray into
the vaporising chamber. A nozzle plate is placed in
front of the injector to convert the liquid into a spray.
The injector’s opening is pulse controlled to achieve
the set concentration of the anaesthetic. This pulsed
liquid anaesthetic spray is monitored by the optical
vaporiser injection device (OVID). The vaporising
chamber is heated by the vaporising heating foil for
uniform heating and converts the vapour spray into
gas. The vaporising chamber has an inlet and an outlet
Figure 5: Schematic representation of components and function of for FGF. The FGF enters the vaporising chamber and
Maquet injection vaporiser. VC temp. sensor = Vaporising chamber gets mixed with the vaporised anaesthetic agent. The
temperature sensor, Heating foil temp. sensor = Heating foil mixed FGF exits the vaporiser and is routed through
temperature sensor, S = sensor, R = Receiver
the patient cassette.
vaporiser that is used exclusively with the Maquet
Functional Anatomy: Drive gas from the anaesthesia
FLOW‑i anaesthesia machine. The vaporisers weigh
workstation enters the liquid anaesthetic container
3.2 kg and are available for isoflurane, sevoflurane and
from the top at 120 kPa and forces the pressurised liquid
desflurane.
anaesthetic through a safety valve into the vaporiser
injector. The vaporiser injector injects the liquid
The vaporiser consists of a liquid fill reservoir (container)
anaesthetic in a pulsed, intermittent manner into the
with an agent capacity of 300 mL but at 260 mL it gives
heated vaporising chamber depending upon the set and
an indication of being 100% full. The electronic level
the measured concentration. The spray is delivered in
indicator shows the anaesthetic liquid level with the
short pulses of 0.8 mL of agent per ms and the pulse
help of a float in the illuminated metered tube. There
time varies from 2–10 ms for isoflurane/sevoflurane
are LEDs mounted at 6 different levels corresponding
and 5–10 ms for desflurane. Hence, the volume of agent
to 5, 10, 25, 50, 75 and 100%. The low and medium
injected per pulse is 1.6–8 mL for isoflurane/sevoflurane
priority alarm is triggered at the level of 10 and 5%,
and 4–8 µL for desflurane. The OVID contains 2 PC
respectively. However, the vaporiser does not switch boards i) vaporiser spray LED and ii) vaporiser spray
off when it is empty. The vaporiser does not have a detector which detects the presence of the spray
concentration control dial. The liquid container can of the anaesthetic agent into electronically heated
be filled with an anaesthetic agent via filling port that vaporising chamber. The temperature of the vaporising
has a safety fill valve to handle the pressure inside the chamber is monitored and maintained at 47°C for
liquid container. The safety valve is designed to handle isoflurane/sevoflurane and 37°C for desflurane.
different manufacturer’s specifications and filling Temperature of the vaporising chamber and heating
systems (Isoflurane: Key fill, Sevoflurane: Key fill and foil is measured by separate temperature sensors. 1)
Quick Fil™, Desflurane: Saf‑T‑Fil™). The vaporiser lid The vaporising chamber temperature is monitored
covers the safety valve and the filling port. Vaporiser by 2 vaporising temperature sensors. The vaporiser
lid position is monitored by a lid sensor and it must be gets switched off if the temperature of the vaporising
closed to activate the vaporiser. The liquid container chamber rises above 60°C or when the temperature
is also connected to a drive gas inlet to allow entry of difference of more than 5°C is detected between the
a driving gas and pressurise the liquid in the reservoir. 2 sensors, 2) When the temperature of the heating foil
The liquid container is connected to the vaporising goes beyond 140°C the heating foil is switched off, no
chamber via a vaporiser injector. The liquid container alarms are activated and the heating is restarted once
is provided by a gas escape pipe which helps to the temperature falls. But if the temperature exceeds
evacuate gas bubbles from the pressurised liquid 170°C the vaporiser is switched off and a technical
anaesthetic before it reaches the vaporiser injector. The alarm is activated. The liquid rapidly evaporates in
vaporiser pressure transducer measures the pressure the vaporising chamber and this vapour is carried by
of the liquid anaesthetic and a safety valve cuts off the FGF coming in through the inlet valves. The mixed

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FGF exits the vaporising chamber through the outlet The dosing chamber, whose pressure is monitored, is
valves.[5] connected to the heated vaporising chamber through
a dosing valve. This dosing valve is controlled by an
DRAGER DIVA (DIRECT INJECTION OF VAPOUR electronic computer‑controlled feedback control unit,
ANAESTHETIC) VAPORISER which receives information about the FGF rate and
set anaesthetic agent concentration (either fresh gas
The Drager DIVA vaporiser which is integrated into the or ETAC). The feedback control unit thus controls the
Zeus anaesthesia machine allows for target‑controlled amount of liquid injected through the dosing valve
anaesthesia with closed‑loop quantitative control of into the heated vaporising chamber. The gas supply
the delivery of oxygen, carrier gas and anaesthetic module [Figure 6c] is part of the anaesthesia machine.
vapour. It consists of propellant gas (air) inlet, a non‑return
valve, a pressure buffer and pressure reducer and
Structural and functional components: The Drager DIVA a supply valve through which gas (air) enters the
injection vaporiser can be categorised as measured metering module [Figure 6].[6]
flow vaporiser. The carrier gas and the anaesthetic
agent is uncoupled and both are delivered separately Functional anatomy: When the vaporising module is
into the system [Figure 6a]. The vaporiser integrated placed in its slot it gets integrated with the gas supply
with the anaesthesia machine consists of 2 modules, module. The propellant gas (air) enters the metering
a detachable vaporising or metering module that module and propels the liquid anaesthetic through
is anaesthetic specific and a fixed non‑specific gas the liquid gate into the dosing chamber. The pressure
supply module that is inbuilt in the Zeus anaesthesia in the dosing chamber is transmitted to the feedback
machine. The metering module [Figure 6b] stores control unit. Depending on the set agent concentration
the liquid anaesthetic in a reservoir with a coded (that is transmitted electronically from the feedback
filling system, liquid level indicator window and a control unit to the dosing valve) a fixed amount of
ventilation outlet. It also houses a dosing chamber liquid anaesthetic is injected into the heated vaporising
that is connected to the reservoir through a liquid gate. chamber. The liquid anaesthetic is vaporised in the

a b

c
Figure 6: Gas flow schematic illustration of Zeus/Zeus IE rebreathing system. (a) Illustration showing uncoupled carrier gas and direct injection
volatile agent (DIVA), both delivered separately into the circle system. (b) Schematic illustration showing the components and function of the
metering module of DIVA vaporiser. (c) Schematic illustration of the gas module within the anaesthesia machine that gets integrated with the
metering module of DIVA vaporiser during use. FGF = Fresh gas flow, APL = Adjustable pressure limiting, P = Pressure sensor

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heating chamber and passes through a flow sensor out AnaConDa VAPORISER
of the metering module [Figure 6b]. AnaConDa™ or Anaesthetic conserving device
was the brainchild of Giebeck AB and introduced
The anaesthetic vapours can take one of the two in the market by Sedana Medical, Stockholm,
pathways once they exit the metering module, Sweden.[10] It is a miniature anaesthetic vaporiser and
depending on the mode set on the Zeus anaesthesia HME (humidified moisture exchanger) filter combined
machine. If it is set at fresh gas control mode, the together. The device is meant to be used mainly for
vapours pass through a fresh gas valve to a mixing sedation in the intensive care unit (ICU) and outside
chamber, where they mix with the FGF and the operating rooms. It is designed to deliver only
mixture is directed to the breathing system. If it is isoflurane and sevoflurane [Figure 7].
set in auto control mode, the vapours exit through
another pathway, pass through the saturated vapour The structural and functional components: The
valve directly to the breathing system, where they mix AnaConDa™ the device has a colour‑coded patient
with the FGF. Thus, in auto control mode, anaesthetic side (transparent) and a ventilator side (black)
vapours and FGF are injected separately into the separated by a bilayer filter. It is a unique oval‑shaped
breathing system while in the fresh gas control device where the ventilator inlet and the patient outlet
mode; the system emulates a classical system with are aligned parallel to the filter medium to facilitate
flowmeter and vaporiser. The electronic feedback laminar airflow. The device is customised to fit
control unit thus determines the amount of liquid between the Y‑piece and endotracheal tube (ETT) like
that would be dosed through the dosing valve into an HME filter. The patient end has an outlet which
the heated vaporisation chamber and controls the can be connected directly to the ETT or a connector.
vapour output. Hence, quantitative closed‑system The patient’s end has a gas sampling port connected
anaesthesia or target‑controlled anaesthesia can be with a standard Leur lock through which end‑tidal
achieved. The blower unit (TurboVent2) is the crucial gas monitoring can be performed. AnaConDa™
component that creates the gas flow (inspiration) to does not require any additional power supply for its
the patient. operation [Figure 7]. The vaporiser should be placed at
an angle of 45°. Internally in the vaporiser, the first layer
Salient features of injection vaporisers of the bilayer filter is an electrostatic polypropylene
Injection vaporisers are electronically and filter, a protective layer situated towards the patient
pneumatically operated with safety features that side, which prevents the ventilator from bacterial and
switch off the vaporiser with an audiovisual technical viral contamination. The second layer is a thick 3–4 mm
alarm when there is a malfunction of temperature and activated carbon felt adsorptive layer which adsorbs
pressure. The vaporiser is not vulnerable to tipping as and reflects inhalational anaesthetics and moistures
it has no wicks to saturate and agent cannot spill into in the circuit. However, for proper functioning, the
the vaporising chamber. Filling of the vaporiser can be device should be replaced daily [Figure 8a].
performed while the vaporiser is in use (though agent
delivery does not happen during filling). AnaConDa™ is available presently in two different
internal volumes of 100 and 50 mL to be used in
Struys et al.[9] compared time to reach desired ETAC,
initial overshoot and stability at target ETAC and
washout time using agents desflurane and sevoflurane
between Zeus (Dräger, Lübeck, Germany) apparatus
using direct injection of inhaled anaesthetics and
Primus apparatus (Dräger, Lübeck, Germany) using a
classic out‑of‑circle vaporiser. The authors observed
that electronic control allows instantaneous changes
in vapour concentrations to achieve set ETAC values
even with very low FGF. In Zeus, the wash‑out times
were faster, inhaled anaesthetic concentration was
the lowest, no overshoot at the target was seen and
the time course of sevoflurane and desflurane was
minimally influenced by changes in FGF. Figure 7: Set up of AnaConDa™ vaporiser for use

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 Kundra, et al.: Modern vaporisers

unique thread different in diameter and look from

other commonly used medical threads so that they are
exclusively keyed to each other. Specially designed
polyoxymethylene bottle adaptors are available for
filling the syringe attached to the AnaConDa™. During
inspiration [Figure 8b], the gas in the inspiratory limb
a
picks up vapour from the evaporator rod and delivers
it to the patient. During expiration [Figure 8c], the
unabsorbed part of the anaesthetic vapour is absorbed
by the thick carbon filter. A major portion (as high
as 90%) of this absorbed vaporiser is delivered to
the patient again (or ‘reflected’ back) in the next
b
inspiration. The small amount of vapour which
reaches the expiratory limb gets scavenged eventually.
The rate of infusion of anaesthetic vapour depends on
the type of vapour used (isoflurane and sevoflurane),
patients’ mass and tidal volume used. Pharmacokinetic
models for manually adjusted infusion rates have been
tried with some success [Figure 8].[12]
c
Figure 8: Schematic cross‑section of AnaConDa™ vaporiser The AnaConDa™ devices are validated by the
(a) Schematic cross‑section illustrating the inner components of
AnaConDa™ vaporiser when switched off. (b) The flow of gases manufacturers in bench‑top tests as per ISO‑9360
during inspiration through the AnaConDa™ vaporiser. (c) The flow of standards for HME and HME filters.[13] The
gases during the expiration phase through the AnaConDa™ vaporiser. AnaConDa™ has a keyed system in the form of a
HME = Humidity moisture exchanger
unique thread that connects the adaptor and the
patients with high and low tidal volumes, respectively. syringe. Neither AnaConda™ can be connected to
AnaConDa™ (50 ml) is for the patients with less than any other syringe than the customised one nor the
50 kg body weight and a tidal volume of fewer than syringe can be attached to any other Luer lock or other
350 mL as a dead space of 100 mL will lead to inadequate intravenous devices. AnaConDa™ by its recycling
carbon dioxide washout and thus may give rise to mechanism (activated carbon) saves anaesthetic
deleterious hypercapnia. The 50 mL device can be used vapours as well as prevents environmental pollution.
even in patients with a tidal volume as low as 200 mL. Nishiyama et al. demonstrated that AnaConDa™
While the 100 mL AnaConDa™ is recommended for could save anaesthetic vapour consumption and
tidal volumes ranging from 350–1200 mL. The 50 ml fasten emergence from general anaesthesia versus
device is slightly less efficient (by approximately 2%) conventional TEC vaporisers.[11] However, the device
than the 100 mL device, therefore, requiring a slightly has certain limitations. AnaConDa™ creates a dead
higher infusion rate for a desired end‑tidal vapour space effect larger than its internal volume due to
concentration. reflection of carbon dioxide hence, it is used in patients
with acute respiratory distress syndrome and other
Functional anatomy: AnaConDa™ delivers constant respiratory illness is questionable as it limits giving
inhalational agents to the patients despite having low tidal volume ventilation as well as increases the
no measurement dials.[11] A porous polypropylene physiological dead space.[14]
evaporator rod is mounted to the patient’s end of the
device [Figure 8a]. The rod has an external agent line Summary: The modern vaporisers have both electronic
made of polyethylene connected to a 50 mL specially and pneumatic control and can deliver set or target
modified syringe mounted on a syringe pump. The anaesthetic agent concentration accurately. The FGF
agent line has an adaptor with a small spring valve rates through the vaporisers may vary as in Aladin or
which only opens when the syringe is fully fitted to constant as in Flow‑I and DIVA to achieve the target
the adaptor. This safety feature prevents anaesthetic agent concentration with minimal wastage and theatre
agents from leaking backwards into the device at pollution. They are designed to alleviate hazards
the time of syringe disconnection of the syringe for and ensure safe, constant and effective delivery of
refilling. The device adaptor and the Syringe share inhalational anaesthetics to the patients.

Indian Journal of Anaesthesia | Volume 64 | Issue 3 | March 2020 179

Page no. 19
 Kundra, et al.: Modern vaporisers

Financial support and sponsorship Philadelphia: Elsevier Saunders; 2013. p. 752‑820.

Nil. 8. Eisenkraft JB. Anaesthesia vaporizers. In: Ehrenwerth J,
Eisenkraft JB, Berry JM, editors. Anaesthesia Equipment:
Principles and Applications. 2nd ed. Philadelphia: Elsevier
Conflicts of interest Saunders; 2013. p. 64‑94.
There are no conflicts of interest. 9. Struys MM, Kalmar AF, De Baerdemaeker LE, Mortier EP,
Rolly G, Manigel J, et al. Time course of inhaled anaesthetic
drug delivery using a new multifunctional closed‑circuit
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180 Indian Journal of Anaesthesia | Volume 64 | Issue 3 | March 2020

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