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www.aana.com/aanajournalonline AANA Journal June 2013 Vol. 81, No. 3 169
Activated Charcoal Adsorp-
tion of Volatile Anesthetic
Agents for Anesthesia
Machine Preparation of
Malignant Hyperthermia
Susceptible Patients
To the editor: We would like to
share recent advancements regard-
ing the utilization of activated
charcoal filters to adsorb volatile
anesthetic agents (VAAs). Although
activated charcoal has been known
for many years to adsorb VAAs,
1-3
it
has only recently become commer-
cially available and endorsed by the
Malignant Hyperthermia Association
of the United States (MHAUS).
4
MHAUS has put forth updated
recommendations for the prepara-
tion of anesthesia workstations to
be used in malignant hyperthermia
(MH) susceptible patients. In these
new recommendations, MHAUS rec-
ommends longer flushing times and
the use of activated charcoal filters
for the absorption of VAAs.
4
“Recommendations (4 alternatives):
1. Flush and prepare worksta-
tion according to manufacturer’s
recommendations or published
studies; this may take 10 to >90
minutes. Most studies also physi-
cally disconnect vaporizers from the
workstation; use a new, disposable
breathing circuit; and replace the
carbon dioxide absorbent. During
the case, fresh gas flow (FGF)
should be kept at 10 liters per min-
ute to avoid ‘rebound phenomenon’
(increased release of residual vola-
tile anesthetic agent when fresh gas
flow is reduced after a set period of
flushing).
OR
2. Use commercially available
charcoal filters that have been
shown to remove trace levels of
volatile anesthetic agents within
10 minutes of application, without
additional preparation. These filters
may have to be regularly replaced
during the anesthetic (see below).
OR
3. If available, use a dedi-
cated ‘vapor free’ machine for
MH-susceptible patients. The
machine must be regularly main-
tained and safety-checked.
OR
4. If appropriate to the institu-
tion, use an ICU ventilator that has
never been exposed to volatile anes-
thetic agents.”
4
The reasons for these updated
recommendations are twofold: the
commercial availability of activated
charcoal filters and the variability of
flush out times in newer anesthesia
machines. In the past, anesthesia
machines were designed and manu-
factured relatively the same from
year to year, and model to model.
Preparation of anesthesia machines
in the past was relatively simple and
straight forward, remove vaporizers
and flush (cleanse) with high flow
oxygen. The goal of flush has been
to reduce the patient’s exposure
levels of VAAs to under 5 parts per
million (ppm).
4-7
Meeting the rec-
ommendation of VAAs under 5 ppm
can be accomplished by a variety of
methods. A commonly employed
technique is to remove or disable
vaporizers (by taping them in the
“OFF” position), flush the machine
with high-FGF greater than or equal
to 10 L/min using the ventilator for
at least 20 minutes, and replace the
fresh gas outlet hose, CO
2
absor-
bent, and breathing circuit.
5
Unfortunately, many of the
internal breathing components in
modern anesthesia machines utilize
more plastic and rubber parts than
older traditional machines. As a
result, a significant reservoir exists
that retains VAAs and therefore
are particularly difficult in “cleans-
ing”.
4-6
A review of the literature
has shown that past recommenda-
tions for preparing the anesthesia
machine for an MH susceptible
patient are outdated and unreliable.
Previous guidelines were devel-
oped for, now “older”, anesthesia
machines that utilized simpler
internal breathing circuits and were
free from the highly soluble reser-
voirs for VAAs that are common
in modern machines.
5-6
Studies
demonstrate that in order to achieve
a safe level of VAAs under 5 ppm,
modern machines should undergo
washout with high-FGF rates at 10
L/min for a minimum of 122 min-
utes.
8-13
It should be noted that
this minimum of 122 minutes flush
with high-FGF is assuming that the
ventilator diaphragm and ventila-
tor hose have been autoclaved.
8-10
Without meeting this step, the flush
time increases to a minimum of
151 minutes.
8
Regardless of time
spent in preparing the anesthesia
machine in washout mode, the lat-
est studies also point out a common
occurrence, the rebound effect.
5-8
This rebound effect occurs when
modern anesthesia machines, that
have been prepared using the tradi-
tional recommendations, have the
FGF rate reduced to under 10 L/
min. When flow is reduced to 3 L/
min, a surge in VAA concentra-
tion occurs exceeding 50 ppm, well
LETTERS
170 AANA Journal June 2013 Vol. 81, No. 3 www.aana.com/aanajournalonline
above the safe level of 5 ppm.
6
All
the current studies conclude that
in order to keep the VAAs under
the concentration of 5 ppm, high-
FGF of at least 10 L/min must be
maintained for the entire anes-
thetic.
5-8
Due to variations in newer
anesthesia machine component
parts and effectiveness of flush out
times, recent research has shown a
one time flush-out approach to all
anesthesia machine preparation for
MH susceptible patients no longer
applies.
5,8-13
Therefore, previous
recommendations based on older
anesthesia machine VAA flush out
times should not be considered reli-
able. Updated recommendations
need to be used. High flow oxygen
(10 L/min) for at least 122 minutes
with continued 10 L/min carrier
gas flow rate during anesthesia
machine use for an MH susceptible
patient is one such recommenda-
tion. A separate anesthesia machine
that is kept VAA free or a critical
care ventilator are also options
although not necessarily feasible
for all facilities. Activated charcoal
filter adsorption of residual VAA
is a recently re-introduced option
that studies have shown to be both
quick and efficient.Vapor-Clean fil-
ters (Dynasthetics Inc) are activated
charcoal filter disks that are placed
between the breathing circuit and
the anesthesia machine inspiratory
and expiratory ports, shown in the
Figure.
6,14-15
Adsorption of VAAs
occurs immediately within the fil-
ters, and circuit carrier gases will
contain VAAs of less than 5 ppm
within 90 seconds and maintain this
low level for up to 12 hours.
14
High
FGF rates are not necessary with
Vapor Clean charcoal filter disks.
How Carbon Absorption
Works
Activated charcoal is simply
charcoal that has been prepared
with a maximum amount of
pore space to increase surface
area. The increased surface area
ensures that aromatic, uncharged,
organic molecules passing over or
through the charcoal will come
in contact with the charcoal sur-
face and be adsorbed. Adsorption
[emphasis added] is surface
attachment of a fluid (gas is con-
sidered a fluid) whereas absorption
[emphasis added] is dispersal of
a fluid throughout the absorbent.
Activated charcoal adsorption sur-
face binds VAAs through Van der
Waals thermodynamic forces.
16
These forces are weak noncova-
lent forces but strong enough to
remove the VAAs from the carrier
gas flow and prevent their reaching
the patient. Greater surface area
equals greater adsorptive ability.
The average carbon surface area
is 10-15 m
2
/g, activated charcoal
averages a surface area of 700 and
1,200 m
2
/g which is up to 120
times increase.
16
Conclusion
We share current developments and
MHAUS recommendations regard-
ing VAA adsorption by activated
charcoal and preparation of anes-
thesia machines for MH susceptible
patients. This newly re-introduced
option of carbon filter adsorp-
tion of residual VAA in anesthesia
machines in preparation for MH
susceptible patients fulfills a need
for newer anesthesia machines and
addresses the shortcoming of previ-
ous recommendations. Regarding
the use of activated charcoal
adsorbers to assist in removing the
volatile anesthetic triggering agent
in the event of a MH occurrence,
we cannot point to any definitive
recommendations. The significant
drop in VAA ppm with the use of
activated carbon filters suggests
that their use may also be useful
in the event of a MH episode but
current treatment for MH remains
unchanged.
REFERENCES
1. Holscher Fr. Zur beseitigung der aus-
geatmeten Narkosagase. Zib F Chir.
1927;25:1558-89.
2. Holscher Fr. Zum schtze des operateurs.
Dtsch Med Wochenschr. 1928;38:794-95.
3. Epstein HG, Berlin DP. Removal of
ether vapour during anesthesia. Lancet.
1944;243(6282):114-16.
4. Preparation of anesthesia workstations
to anesthetize MH susceptible patients.
Malignant Hyperthermia Association of
the United States website. Available from:
http://www.mhaus.org/recommendations/
anesthesia-workstation-preparation/#.
UI9CjbS9xSM. Accessed October 21, 2012.
5. Kim TW, Nemergut ME: Preparation of
modern anesthesia workstations for malig-
nant hyperthermia-susceptible patients: A
review of past and present practice. Anes-
thesiology. 2011;114:205-12
Figure. Activated Charcoal Filters Attached to the Inspiratory and Expira-
tory Limbs of the Anesthesia Workstation
www.aana.com/aanajournalonline AANA Journal June 2013 Vol. 81, No. 3 171
6. Birgenheier N, Stoker R, Westenskow D,
Orr J. Technical communication: Activated
charcoal effectively removes inhaled anes-
thetics from modern anesthesia machines.
Anesth Analg. 2011;112:1363-70.
7. Larach MG, Gronert GA, Allen GC,
Brandom BW, Lehman EB. Clinical pre-
sentation, treatment, and complications
of malignant hyperthermia in North
America from 1987 to 2006. Anesth Analg.
2010;110:498-507.
8. Whitty RJ, Wong GK, Petroz GC, Pehora
C, Crawford MW. Preparation of the
Dräger Fabius GS workstation for malig-
nant hyperthermia-susceptible patients.
Can J Anaesth. 2009;56:497-501.
9. Shanahan H, O’Donoghue R, O’Kelly P,
Synnott A, O’Rourke J. Preparation of the
Dräger Fabius CE and Dräger Zeus anaes-
thetic machines for patients susceptible to
malignant hyperthermia. Eur J Anaesthe-
siol. 2012;29(5):229-34.
10. Crawford MW, Prinzhausen H, Petroz
GC. Accelerating the washout of inhala-
tional anesthetics from the Dräger Primus
anesthetic workstation. Anesthesiology.
2007;106:289-94.
11. Prinzhausen H, Crawford MW, O’Rourke
J, Petroz GC. Preparation of the Dräger
Primus anesthetic machine for malignant
hyperthermia-susceptible patients. Can J
Anaesth. 2006;53:885-90.
12. Gunter JB, Ball J, Than-Win S: Preparation
of the Dräger Fabius anesthesia machine
for the malignant-hyperthermia susceptible
patient. Anesth Analg. 2008;107:1936-45.
13. Shinkaruk KS, Nloan K, Crossan M.
Preparation of the Datex-Ohmeda Aestiva
anesthetic machine for malignant hyper-
thermia cases (abstract A279). Presented
at the Annual Meeting of the American
Society of Anesthesiologists 2008.
14. Vapor-Clean Brochure. Dynasthetics. Salt
Lake City, Utah. Available at: http://www.
dynasthetics.com/Vapor-Clean/index.html.
Accessed January 8, 2013.
15. Vapor-Clean Instructions for Use. Dyn-
astetics. Salt Lake City, Utah. Available
at: http://www.dynasthetics.com/Vapor-
Clean/Vapor-Clean-IFU.pdf. Accessed
January 20, 2013.
16. Activated Carbon: Manufacture, Structure
& Properties. Cameron Carbon Incorpo-
rated. Havre de Grace, Maryland. Avail-
able at: http://www.cameroncarbon.com/
documents/carbon_structure.pdf. Accessed
January 12, 2012.
Joseph W. Martin, RRNA, BSN, BA
Texas Christian University
Fort Worth, Texas
Mark D. Welliver, CRNA, DNP, ARNP
Texas Christian University
Fort Worth, Texas
3-in-1 Block: Are We Still
Using This Misnomer?
To the editor: I would like to com-
ment on the study by Wallace et
al,
1
“Comparison of Fascia Iliaca
Compartment Block and 3-in-1
Block in Adults Undergoing Knee
Arthroscopy and Meniscal Repair”.
As the authors state, the term
“3-in-1” refers to the ability of one
high-volume block to cover the
lateral femoral cutaneous (LFC)
and obturator as well as the femo-
ral nerves. Unfortunately, this has
never proven out scientifically, as
coverage of the LFC and obtura-
tor nerves is inconsistent, and now
this technique is thought of as just
a femoral nerve block.
2
We do our-
selves a disservice by continuing to
use this misnomer in light of evi-
dence to the contrary.
The authors may have mis-
taken the ability of their blocks
to anesthetize the obturator nerve
because of the way they evaluated
the blocks’ onset and quality—sen-
sory changes in the corresponding
dermatomes. The success of an
obturator nerve block cannot be
evaluated by sensory distribution,
as there is overlap with the medial
cutaneous branch of the femoral
nerve.
3
Motor blockade was mea-
sured in the study, but it was not
used as the sole determinant of
blocking the obturator nerve.
Finally, I agree with the authors
that the fascia iliaca compartment
block (FICB) has a role in the field
or in austere environments, where
availability of a nerve stimulator
or ultrasound and a practitioner
skilled in using them may be limited.
This study and others
4,5
show that
the FICB is an efficacious analge-
sic modality for arthroscopic knee
surgery, but so is the femoral nerve
block, which is a basic block and easy
to learn. Therefore, I do not agree
that in the OR setting, the FICB is
a preferred technique for teaching
trainees or inexperienced providers
over the femoral nerve block. In my
experience with trainees, they master
the femoral nerve block without diffi-
culty and having an “easier” block to
teach them is unnecessary.
REFERENCES
1. Wallace JB, Andrade JA, Christensen JP,
Osborne LA, Pellegrini JE. Comparison of
fascia iliaca compartment block and 3-in-1
block in adults undergoing knee arthros-
copy and meniscal repair. AANA J. 2012;
80(4 Suppl):S37-44.
2. Enneking et al. Lower-extremity periph-
eral nerve blockade: essentials of our cur-
rent understanding. Region Anesth Pain M.
2005;30(1):4-35.
3. Choquet et al. A new inguinal approach
for the obturator nerve block: anatomical
and randomized clinical studies. Anesthesi-
ology. 2005;103(6):1238-45.
4. Farid et al. Comparison of femoral
nerve block and fascia iliaca block for
analgesia following reconstructive knee
surgery in adolescents. J Clin Anesth.
2010;22(4):256-259.
5. Capdevila et al. Comparison of the three-
in-one and fascia iliaca compartment blocks
in adults: clinical and radiographic analysis.
Anesth Analg. 1998;86(5):1039-44.
Roland A. Flores, Jr., MD
Houston, Texas
ACKNOWLEDGMENT
I want to acknowledge Amy Toups, CRNA, for
her contribution to the letter.
Response: I would like to respond
to the comments to the AANA
Journal by Dr Roland Flores with
regard to our article, “Comparison
of Fascia Iliaca Compartment
Block and 3-in-1 Block in Adults
Undergoing Knee Arthroscopy
and Meniscal Repair”. Dr Flores
questions our use of the term “3:1
block”, stating that this is a misno-
mer because it frequently fails to
anesthetize the femoral nerve (FN),
obturator (ON) and lateral femoral
cutaneous nerve (LFC). The term
“3:1 block” as described by Winnie
et al
1
uses a single injection tech-
nique that aims to block all 3 nerves
(FN, ON, and LFC). In our study,
we were interested in comparing the
outcomes of the fascia iliaca block
and the 3:1 block because there
was a paucity of literature for this
172 AANA Journal June 2013 Vol. 81, No. 3 www.aana.com/aanajournalonline
comparison. Though we agree that
this block has variable results in
achieving an adequate block of all
three nerves, it consistently achieves
blockade of the femoral nerve.
Unfortunately since both of these
blocks are femoral nerve blocks, it
was necessary for us to utilize ter-
minology that could differentiate
between the blocks for the reader.
Our intent with this article was
to describe the use of the fascia
iliaca block, a block that does not
require technology and has been
shown to be useful in situations
outside of the traditional operating
room environment.
2
Many practitio-
ners use ultrasound technology to
place blocks in an effort to get the
needle as close to the nerve as pos-
sible in an effort to increase block
efficacy and duration. However, one
of the interesting findings noted in
our study was that the duration of
action was noted to be longer in the
fascia iliaca block despite the fact
that the needle injection point is
at a considerable distance from the
FN. This was the point that we were
attempting to emphasize and the use
of a comparison with the 3:1 block
technique was chosen since this is a
block that is well known and is still
used by many practitioners.
Dr Flores’s comment is inter-
esting because it brings to light
the confusion created when using
terminology that has been used to
describe skin marking techniques
to refer to a block under ultrasound
guidance. We do not disagree with
Dr Flores’s assertion that the 3:1
block may be a misnomer and sim-
ply chose this block for comparison
because of its long history and use
among anesthesia practitioners.
We also agree that both the fascia
iliaca block and the 3:1 block are
simply different approaches to block
primarily the FN and perhaps it is
time to develop terminology for the
subtle differences in approach for
ultrasound-guided blocks because
the same problem exists for other
extremity blocks as well.
REFERENCES
1. Winnie AP, Ramamurthy S, Durrani Z,
Radonjic R. Plexus blocks for lower
extremity surgery. Anesthesiology Rev.
1974;1:11-16.
2. DeBuck F, Devore S, Missant C, Van
de Velde M. Regional anesthesia out-
side the operating room: indications
and techniques. Curr Opin Anaesthesiol.
2012;25(4):501-7.
CDR Lisa A. Osborne, CRNA, PhD,
NC, USN
Bethesda, Maryland
The views contained herein are the private ones
of the authors and are not to be construed as
official or reflecting the views of the Depart-
ment of Defense or the Uniformed Services
University of the Health Sciences.
