Acta Anaesthesiol Scand. 2020;00:1–7.
Received: 7 Januar y 2020
Revised: 19 Febr uary 2020
Accepted: 27 Februar y 2020
DOI : 10.1111/aas.135 71
Residual volatile anesthetics after workstation preparation and
activated charcoal filtration
Lukas M. Müller-Wirtz1 | Christine Godsch1 | Daniel I. Sessler2 | Thomas Volk1 |
Sascha Kreuer1 | Tobias Hüppe1
This is an op en access arti cle under the ter ms of the Creative Commons Attribution L icense, which pe rmits use, dis tribu tion and reprod uction in any med ium,
provide d the original wor k is properly cited.
© 2020 The Authors. Acta Anaesthesiologica Scandinavica published by John Wil ey & Sons Ltd on behalf of Acta A naesthesio logica Scand inavic a Foundation
The Cent er of Breath Rese arch is part of th e Outcomes Rese arch Consort ium, Clevelan d, OH, USA
1Center of Breath Research, Depar tment
of Anesthesiology, Intensive Care and
Pain The rapy, Saar land Uni versit y Medical
Center, Homburg, Saarlan d, Germany
2Depar tment of Outcomes Resea rch,
Anest hesiology Institute, Cleveland Clinic,
Cleveland, OH, USA
Lukas M. Müller-Wirtz, CBR-Center
of Breath Research, Department of
Anest hesiology, Intensive Care and Pain
Therapy, Saarlan d Univer sity Medical Center
and Saar land University Faculty of Medicine,
Hombur g, Saar land 66 421, Ger many.
The act ivated charcoal filter s were provided
by Medical Instrument s Corp oration
GmbH, G ermany. All other materials were
provide d solely from ins titut ional an d/or
Background: Volatile anesthetics potentially trigger malignant hyper thermia crises in
susceptible patients. We therefore aimed to identify preparation procedures for the
Draeger Primus that minimize residual concentrations of desflurane and sevoflurane
with and without activated charcoal filtration.
Methods: A Draeger Primus test workstation was primed with 7% desflurane or 2.5%
sevoflurane for 2 hours. Residual anesthetic concentrations were evaluated with five
preparation procedures, three fresh gas flow rates, and three distinct applications of
activated charcoal filters. Finally, non-exchangeable and autoclaved parts of the work-
station were tested for residual emission of volatile anesthetics. Concentrations were
measured by multicapillary column–ion mobility spectrometry with limits of detection/
qu a n t i f i c at i o n being <1 pa r t pe r bi llion (ppb) fo r de s f l u r a n e an d <2.5 ppb fo r se voflurane.
Results: The best preparation procedure included a flushing period of 10 minutes
between removal and replacement of all parts of the ventilator circuit which imme-
diately produced residual concentrations <5 ppm. A fresh gas flow of 10 L/minute
reduced residual concentration as effectively as 18 L/minute, whereas flows of 1 or
5 L/minute slowed washout. Use of activated charcoal filters immediately reduced
and maintained residual concentrations <5 ppm for up to 24 hours irrespective of
previous workstation preparation. The fresh gas hose, circle system, and ventilator
diaphragm emitted traces of volatile anesthetics.
Conclusion: In elective cases, presumably safe concentrations can be obtained by a
10-minute flush at ≥10 L/minute between removal and replacement all components of
the airway circuit. For emergencies, we recommend using an activated charcoal filter.
1 | INTRODUCTION
Malignant hyperthermia is rare and susceptible patients need spe-
cific anesthetic management.1 Volatile anesthetics are well-known
triggering agents, so exposure should be avoided.2,3 Anesthesia
workstations regularly used with volatile anesthetics can emit
potentially triggering residual concentrations of volatile anesthet-
ics. The Malignant Hyperthermia Association of the United States
(MHAUS)4 and the European Malignant Hyperthermia Group
(EMHG)5 recommend three possible options to use anesthesia work-
stations to provide “trigger-free” anesthesia. The first option is to
use a “vapor-free” workstation—a workstation that has never been
MÜLLER-WIRT Z ET aL.
exposed to volatile anesthetics. The second option is the prepara-
tion of a workstation by the replacement of exchangeable parts of the
breathing circuit and flushing. And the third option is to use activated
Gi ven the co st of mod e rn an e sth e si a wor k stat ion s and the ra r ity of
malign an t hy per the rmia, it is usually imp rac tic al to re ser ve a dedica te d
“vapor-free” workstation. Thus, workstation preparation and flushing
are often performed. A most probably safe threshold of 5 parts per
million (ppm) was established based on expert opinions and a single
study performed in swine.6 So previous studies assessing the prepa-
ration of the Draeger Primus reported their results down to 5 ppm.7-9
We use the far more accurate technique of multicapillary column–ion
mobility spectrometry (MCC-IMS) which detects volatile anesthetics
down to concentrations of several parts per billion (ppb),10 thereby
allowing us to reliably distinguish residual anesthetic concentrations
after various preparation methods and identify the best.
We also evaluated activated charcoal filters.11 There is compel-
ling evidence that these filters effectively absorb volatile anesthet-
ics.11,12 However, published studies did not evaluate positioning a
sin gl e fi lter close to the patie nt wit ho ut a rep la ceme nt of the breath-
ing circuit which might save time in emergenc y situations.
At least non-exchangeable and non-disposable components of
the anesthesia workstation are apparently major sources of resid-
ual concentrations. Inert coating of the inner surface of a fresh gas
hose may reduce, but not totally exclude, absorbance and emission
of volatile anesthetics. Furthermore, it is unclear, whether autoclav-
ing completely eliminates the emission of residual concentrations.
We therefore investigated the ef fectiveness of Draeger Primus
machine component replacement, various fresh gas flows, and dif-
ferent applications of activated charcoal filters on residual concen-
trations of desflurane and sevoflurane, and finally investigated the
emission of residual concentrations by non-exchangeable and auto-
2 | MATERIAL AND METHODS
An anesthesia workstation (Primus, Draeger) was used with match-
ing accessories (breathing tubes: Draeger Anesthesia set VentStar®,
disposable, basic, 2 L, 1.8 m/1.5 m, latex-free; carbon dioxide absorber:
Draeger CLIC Abso rber 80 0+; test lung : Draeger SelfTestLung™; sam-
ple tube and water trap of the capnography: Draeger Waterlock® 2
and sample tube; heat and moisture exchanger: Gibeck Humid-Vent®).
The workstation was primed by ventilating a test lung with desflurane
(7%) or sevoflurane (2.5%) for two hours at a fresh gas flow of 1 L/
minute (100% oxygen). Ventilatory parameters were as follows: tidal
volume = 500 mL, ventilation frequency = 12/minute, PEEP 5 mbar.
Gas sampling was started within a maximum of 30 seconds
after preparation from the inspiratory limb of the workstation
and repeated at 5-minute intervals (sampling position 1, Figure 1).
The concentrations of desflurane and sevoflurane were mea-
sured by multicapillar y column–ion mobility spectrometry (MCC-
IMS by B&S Analytik, Dortmund, Germany). Visual Now 3.6 (B&S
Analytik) software was used to quantify peak intensity in volts.
Defined standards of desflurane and sevoflurane ranging from 1 to
7000 ppb (0.001 to 7 ppm) were used for calibration. Limits of de-
tection and limits of quantification were determined as previously
described by Maurer et al.13 Limit of detection/quantification was
0.8/0.9 ppb (0.0008/0.0009 ppm) for desflurane, and 2.2/2.4 ppb
(0.0022/0.0024 ppm) for sevoflurane.
2.1 | Assessment of different preparation
procedures and fresh gas flow rates
After priming, the vaporizer was removed, and the fresh gas flow
was set to 18 L/minute until the detection limit of the internal optical
This investigation presents a detailed description for how
one can minimize residual concentrations of desflurane
and sevoflurane to a safe level if the anesthesia worksta-
tion must be mad e ra pi dl y re ady for a malign an t hy pe rth er-
mia-susceptible patient. The simplest and quickest method
is to place an activated charcoal filter at the Y-piece.
FIGURE 1 Experimental setup during measurement period. Residual concentrations were measured at sampling position 1 to evaluate different
preparation procedures, dif ferent rates of fresh gas flow and activated charcoal filters at filter position 1. Sampling position 2 was only used for the
assessment of one activated charcoal filter at the y-piece (filter position 2). exp./insp., expiratory/inspirator y limb of the circle system; HME, heat
and moisture exchanger; MCC-IMS, multicapillary column–ion mobility spectrometer [Colour figure can be viewed at wileyonlinelibrary.com]
MÜLLER-WIRT Z ET aL.
sensors was reached (approximately 90 seconds). The respective
preparation procedure was subsequently performed (Table 1). After
each preparation procedure, a compliance and leak test was carried
out. The sample tube of the MCC-IMS was connected to the inspira-
tory limb by a t-piece and measurements were starte d (sampling posi-
tion 1, Figure 1). During the measurement period, fresh gas flow was
set to 18 L/minute and a new test lung was ventilated with the same
ventilatory settings used for priming. Each preparation procedure was
test ed th re e tim es for 10 0 0 mi nutes . Fin ally, th e bes t pre pa r at ion pro -
cedure was evaluated once with each fresh gas flow of 1, 5, and 10 L/
minute. Experimental setup, priming, and preparation remained the
2.2 | Assessment of activated charcoal filters
Priming of the workstation was done as already described above. A
fresh gas flow of 10 L/minute, a new heat and moisture exchanger
and a new test lung was used during the measurement period. Three
different filter applications (Vapor-Clean, Dynasthetics) were as-
sessed, each with desflurane and sevoflurane.
1. The best tested preparation was combined with the additional
placement of activated charcoal filters at the inspirator y and
expiratory limb of the circle system (filter position 1, sampling
position 1, Figure 1).
2. Filter application was performed according to the manufac turer's
recommendations, which includes replacement of the breathing
tubes, breathing bag and the placement of activated charcoal
filters at the inspiratory and expiratory limb of the circle system
(filter position 1, sampling position 1, Figure 1).
3. Only one filter was placed at the y-piece of the breathing tubes
without other changes to the breathing circuit than the heat and
moisture filter. The t-piece for sampling was therefore moved
from the inspiratory limb of the circle system to the test lung (fil-
ter position 2, sampling position 2, Figure 1).
Compliance and leak test was omitted during the second and
third method, as these approaches were designed for emergency
use when time is limited.
2.3 | Assessment of trace concentrations emitted by
different parts of the workstation
Our local technician provided a used fresh gas hose removed dur-
ing inspection of a Draeger Primus. The inner diameter was 6 mm
with a leng th of 70 cm resulting in a volume of approximately 20 mL
and a surface area of 130 cm2. The circle system and ventilator dia-
phragm were cleaned according to the local hygiene protocol (1-hour
thermodesinfector, minimum exposure time to 93.7°C of 5 minutes;
autoclaving at 134°C). Fresh gas hose and ventilator diaphragm
were placed in a perfluoroalkoxy alkane container (2.7 L) at 20°C.
The container was flushed with purified air (ALPHAGAZ™ 1 LUFT,
Air Liquide) for two minutes and repeated headspace samples were
subsequently taken by MCC-IMS over one hour. The circle system
was investigated by taking samples from the inspiratory limb placed
in a climatized room at 20°C over one hour. The highest measured
concentration was taken as the emitted concentration.
2.4 | Statistics
Statistics were calculated with SigmaPlot 12.5 (Systat Software
GmbH). Data are presented as means ± SDs. After testing for nor-
mality by Shapiro-Wilk test, comparisons were performed by a one-
way ANOVA followed by multiple comparisons with Bonferroni
correction. P < .05 was considered as statistically significant.
Washout curves were fitted by nonlinear regression to appropriate
3 | RESULTS
Initial tests before finalization of the study design showed that
ventilation of a test lung is critical to allow a sufficient washout.
Therefore, washout was investigated under standardized ventilation
of a test lung. Washout was best described by an exponential decay
function with three variables: [Concentration] = y0 + a*e−b[Time].
3.1 | Assessment of different preparation
procedures and fresh gas flow rates
Washout times were faster when the circle system and ventilator
diaphragm were replaced (Table 2). Further analyzes were therefore
restricted to procedures 3-5 to identify the best (Table 3). Procedure
5 showed the lowest residual concentrations, especially during early
washout times (Figure 2). The influence of the fresh gas flow rate
after performing the best tested preparation (procedure 5) is shown
TABLE 1 Definition of preparation procedures
Procedure Exchanged parts of the ventilator circuit
2Breathing tubes/bag, carbon dioxide absorber
3Breathing tubes/bag, carbon dioxide absorber, circle
system, ventilator diaphragm
4 Breathing tubes/bag, carbon dioxide absorber, circle
system, ventilator diaphragm, sample tube, and
water trap of the capnography
5Additional 10-minute flush between removal and
replacement of the same par ts as in procedure 4
Note: Circle system and ventilator diaphragm were replaced by
autoclaved part s. All other par ts were replaced by new parts. Humid
and moisture exchanger was changed in all procedures. W ith each
procedure, a new non-contaminated test lung was ventilated during the
MÜLLER-WIRT Z ET aL.
in Table 3. A prolonged washout was obser ved for both volatile an-
esthetics when lower fresh gas flows were used (Figure 3). Even
after 100 0 minutes, some residual volatile anesthetic remained.
3.2 | Assessment of activated charcoal filters
All applications of activated charcoal filters reduced and maintained
residual concentrations of volatile anesthetics <5 ppm (= 500 0 ppb)
for 24 hours immediately after filter placement (within a maximum
of 30 seconds after placement). No volatile anesthetic was detect-
able for 24 hours when preparation procedure 5 was combined with
activated charcoal filters at the inspiratory and expiratory limb of the
workstation. Carrying out manufacturer's recommendations, desflu-
rane concentrations ranged from 0.9 to 2 ppb (0.0009 to 0.002 ppm)
and sevoflurane concentrations were below the limit of detection
(<2.2 ppb, 0.0022 ppm) for 24 hours. Even a single filter at the y-
piece of the breathing tubes with no other changes than the heat and
moisture filter reduced desflurane concentrations to a range from 1
to 1.8 ppb (0.001 to 0.0018 ppm), and sevoflurane concentrations
to a range from 2.2 to 5.6 ppb (0.0 022 to 0.0056 ppm) for 24 hours.
3.3 | Assessment of trace concentrations emitted by
different parts of the workstation
The fresh gas hose emitted residual concentrations of 1 ppb
(0.001 ppm) desflurane and 6.7 ppb (0.0067 ppm) sevoflurane. The
ventilator diaphragm emitted 0.9 ppb (0.0009 ppm) desflurane and
5.1 ppb (0.0051 ppm) sevoflurane. Residual concentrations in the
inspiratory limb of the circle system were 0.9 ppb (0.0 009 ppm) of
desflurane and below the limit of quantification for sevoflurane.
4 | DISCUSSION
4.1 | Assessment of different preparation
procedures and fresh gas flow rates
All preparation procedures that included a change of circle system
and ventilator diaphragm resulted in residual concentrations <5 ppm
for either anesthetic immediately after preparation (within a maxi-
mum of 30 seconds after preparation). Washout was faster with an
additional 10-minute flushing period between removal and reas-
sembly of all exchangeable par ts of the ventilator circuit. Our results
are consistent with Crawford et al who also showed that replacing
circle system and ventilator diaphragm markedly reduced residual
Prinzha use n et al reported much longer me an wa sho ut times for
sevoflurane, needing 65 minutes to reach concentrations <5 ppm.9
The key distinction appears to be that Prinzhausen et al did not
TABLE 2 Washout times to reach concentrations <5 ppm
Time to [desflurane]
<5 ppm in min
<5 ppm in min
1115 ± 30 (95-150) 107 ± 20 (85-125)
2103 ± 19 (90-125) 110 ± 20 (90-130)
33 ± 3 (0-5) 3 ± 3 (0-5)
4 3 ± 3 (0-5) 3 ± 3 (0-5)
50 ± 0 (0) 0 ± 0 (0)
Note: Data presented as means ± SDs (minimum-maximum). Each
procedure was per formed three times.
Comparison of preparation procedures
Flow [L/min] 18
Procedure 345 3 45
10 min 383 ± 41* 320 ± 42* 215 ± 32 366 ± 141 374 ± 134 268 ± 63
100 min 214 ± 92 244 ± 30* 70 ± 6 112 ± 32 108 ± 24 75 ± 42
1000 min 28 ± 11* 22 ± 6 6 ± 2 8 ± 2 9 ± 2 7 ± 1
Comparison of different fresh gas flow rates
Flow [L/min] 1 5 10 1 5 10
10 min 2661 916 141 6707 1658 204
100 min 2297 345 72 5653 14 5 89
1000 min 72 41 13 3 5 5
Note: The upper part of the table compares different preparation procedures. Procedure 5 was
identif ied to lead to the lowest residual concentrations of both volatile anesthetics. The lower part
of the table shows the influence of different fresh gas flow rates on washout after performing
procedure 5. *P < .05 vs procedure 5, one-way ANOVA, multiple comparisons Bonferroni
corrected. Dat a presented as means ± SDs. Values are given in ppb (1 ppb = 0.001 ppm).
TABLE 3 Residual concentrations
of desflurane and sevoflurane 10, 100
and 1000 min after preparation of the
workstation (Draeger Primus)
MÜLLER-WIRT Z ET aL.
perform an exchange of the ventilators diaphragm during prepara-
tion. Cottron et al also report long washout times for sevoflurane
at a median of 42 minutes to reach concentrations below 5 ppm.7
Fresh gas flow was identical with our approach at 18 L /minute, but
the ventilators diaphragm was apparently unchanged. Available
data therefore suggest s that replacing all exchangeable parts of
the ventilator circuit is critical to speed washout. Our results fur-
ther show that additional 10 minutes of flushing between part re-
moval and reassembly further reduces residual volatile anesthetic
Washout after the best preparation was considerably faster
with a fresh gas flow of 10 L/minute than with 1 or 5 L/minute,
but increasing flow to 18 L/minute did not further speed washout.
We thus recommend using a fresh gas flow of 10 L/minute after
preparing the machine. An alternative strategy is to use a high gas
flow such as 10 L/minute until presumably safe concentrations
are reached, and then continue with a lower flow. However, pre-
vious studies detected a significant rebound in the concentration
after changing to low flow rates.8 ,9 A fresh gas flow of 10 L/min-
ute should thus be used for washout, and then maintained during
4.2 | Assessment of activated charcoal filters
Activated charcoal filters immediately reduced residual volatile
anesthetic concentrations below 5 ppm (within a maximum of
FIGURE 2 A and B, Washout curves for desflurane (top, A)
and sevoflurane (bottom, B) following preparation procedures 3-5
(1 ppb = 0.001 ppm). Procedure 3: exchange of breathing tubes/
bag, carbon dioxide absorber, circle system, ventilator diaphragm;
procedure 4: exchange of breathing tubes/bag, carbon dioxide
absorber, circle system, ventilator diaphragm, sample tube and
water trap of the capnography; procedure 5: additional 10-min
flush bet ween removal and replacement of the same parts as in
procedure 4. Nonlinear regression was performed using the mean
values of the three measurement runs of each procedure. The
coefficient of determination (R2) describes the fit of the mean
values and the respective regression model [Colour figure can be
viewed at wileyonlinelibrar y.com]
FIGURE 3 A and B, Washout curves for desflurane (top,
A) and sevoflurane (bottom, B) following the best tested
preparation procedure (5) with 1, 5, and 10 L/min fresh gas flow
(1 ppb = 0.001 ppm). Each fresh gas flow rate was tested once.
Procedure 5:10-min flush between removal and replacement
of breathing tubes/bag, carbon dioxide absorber, circle system,
ventilator diaphragm, sample tube, and water trap of the
capnography. Nonlinear regression was performed to obtain
washout curves. The coefficient of determination (R2) describes the
fit of the measurement values and the respective regression model
[Colour figure can be viewed at wileyonlinelibrary.com]
MÜLLER-WIRT Z ET aL.
30 secon ds) and remained the m below 5 ppm for 24 ho ur s. Volatile
anesthetics were no longer detectable, even at parts-per-billion
concentrations when optimal workstation preparation was com-
bined with two activated charcoal filters. Our results are generally
co ns iste nt Ne ira et al who sho we d that th e com bin ati o n of Dr aeger
Zeus workstation preparation and charcoal filters was more ef-
fective than workstation preparation alone.14 The first study that
used FDA-approved activated charcoal f ilters reported an immedi-
ate reduc tion of volatile anesthetics within 2 minutes and concen-
trations remaining below 5 ppm for 60 minutes.11 Further studies
showed the reduction of residual concentrations below 5 ppm by
filter placement over 1212 and even up to 24 hours.15 We extend
previous results by showing that the application of a single acti-
vated charcoal filter at the Y-piece was as ef fective as the recom-
mended use which includes replacement of breathing tubes and
bag and the placement of two filters at inspiratory and expiratory
limb of the circle system. Taken altogether, every use of activated
charcoal filters that we assessed maintained residual concentra-
tions below 5 ppm for at least 24 hours. Positioning a single filter
at the y-piece appears to be perfectly effective—and is both fast
4.3 | Assessment of trace concentrations emitted by
different parts of the workstation
Optimal preparation and flushing massively reduced emission of
anesthetics, but residual concentrations remained detectable even
after 16 hours of flushing. The reason appears to be that non-ex-
changeable and autoclaved components continue to release trace
concentrations of volatile anesthetics. The fresh gas hose emitted
the highest concentrations, presumably due to its strong exposure
to volatile anesthetics, as it connects vaporizers to the circle sys-
tem. While autoclaving helped, it did not fully eliminate trace con-
centrations. Both, circle system and ventilator diaphragm emitted
desflurane and sevoflurane. It seems unlikely that parts-per-billion
residual anesthetic concentrations trigger malignant hyperthermia.
But to totally avoid exposure to volatile anesthetics, use of acti-
vated charcoal filters or a never-exposed “vapor-free” workstation
5 | CONCLUSION
Optimal preparation of a Draeger Primus workstation for patients
susceptible to malignant hyperthermia differs—with the replace-
ment of workstation components for elective and the use of acti-
vated charcoal filters for emergency cases. The best preparation
procedure includes a 10-minute flush ≥10 L/minute between re-
moval and reassembly of all parts of the ventilator circuit. In case
of emergencies, when malignant hyperthermia is suspected or ur-
gent anesthesia for susceptible patients is indicated, we recom-
mend using an activated charcoal filter. The first option (intended
use) includes the replacement of breathing tubes and bag, and
insertion of two activated charcoal filters on the inspiratory and
expiratory limbs. Alternatively, the placement of a single activated
charcoal filter at the y-piece is fast, inexpensive, and equally ef-
fective—but an of f-label use. Workstation preparation or filter use
should be followed by a fresh gas flow of 10 L/minute during the
subsequent procedure. Finally, the very lowest concentrations will
be obtained when machine preparation and activated charcoal
filters are combined, or by using a workstation never exposed to
This study contains data taken from the thesis presented by Christine
Godsch as par t of the requirement s for the obtention of the degree
“Doctor of Medicine” at Saarland University Medical Center and
Saarland University Faculty of Medicine.
CONFLICT OF INTEREST
The authors have no conflicts of interest.
Lukas M. Müller-Wirtz https://orcid.org/0000-0002-7984-1798
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How to cite this article: Müller-Wirtz LM, Godsch C, Sessler
DI, Volk T, Kreuer S, Hüppe T. Residual volatile anesthetics
after workstation preparation and activated charcoal
filtration. Acta Anaesthesiol Scand. 2020;00:1–7. ht t p s : //d oi .