Comparison of fibreoptic-guided intubation through the ILMA versus
fibreoptic-guided intubation using the LMA Classic plus the Aintree Intubating
Catheter: a manikin study in a simulated difficult airway
A.M.B. Heard,1 D.A. Lacquiere,2 and R.H. Riley.1
1 Department of Anaesthesia and Pain Medicine, Royal Perth Hospital, Perth, Australia
2 Department of Anaesthesia, Taunton and Somerset NHS Foundation Trust, Taunton, UK
Introduction
Results
Many types of supraglottic airway
device have been used as a conduit
for tracheal intubation. The technique
may be useful in difficult airway
scenarios and the likelihood of
success increases if fibreoptic
guidance is used.
The median (IQR [range]) number of
years experience in anaesthesia of
the participants was 6 (3.5-8.75 [018]) years. Two participants had no
experience with fibreoptic intubation,
eight described their experience as
minimal, thirteen as moderate, and
three as extensive. Participants’ prior
experience in the use of the two
intubating techniques examined is
outlined in the table below:
In this randomised cross-over manikin
study of a simulated difficult
intubation, 26 anaesthetists attempted
to intubate the trachea using two
techniques:
a
fibreoptic-guided
technique using an Aintree Intubating
Catheter (AIC) via an LMA ClassicTM
(cLMA), and a fibreoptic-guided
technique via an Intubating Laryngeal
Mask Airway (ILMA).
We hypothesised that intubation
success rate would be higher using
the former technique than with the
latter. If correct, use of the cLMA
would appear to be preferable to use
of the ILMA when faced with a failed
intubation.
Table 1. Number of times participants had
performed the two intubating techniques,
prior to the study. Values are numbers
(proportion)
Why is the cLMA + AIC
technique superior?
In 18 of the 21 failures to intubate in
the ILMA group, the vocal cords were
never reached with the fibrescope.
This suggests that the primary reason
for the superiority of the cLMA
technique is that it is easier to locate
the larynx with a fibrescope from the
end of the cLMA than from the end of
the ILMA, when there is abnormal
perilaryngeal anatomy.
In the case of the ILMA, the
fibrescope (or rather, the tracheal
tube that surrounds it) has to lift, and
thus pass beyond the EEB, before the
larynx is revealed. In normal airways,
with good ILMA positioning, this is not
a
problem,
and
may
be
advantageous, as the EEB lifts the
epiglottis out of the way. However in
the difficult airway it may not be
possible to position the EEB directly
beneath the epiglottis, and so the
EEB
itself
may
distort
the
perilaryngeal anatomy as it is lifted.
Moreover if the larynx is anterior
and/or distorted, a ‘wide-angled’ view
of the larynx is desirable. The need
to pass beyond the EEB reduces the
angle available, thus limiting the
ability of the operator to locate the
vocal cords.
Methods
The
Local
Research
Ethics
Committee waived the need for formal
approval for this study. Prior to
participant involvement a size three
cLMA was positioned in an Airsim
airway manikin (Trucorp Ltd, Belfast,
UK), and a size three ILMA was
positioned in an identical manikin. In
both cases the larynx of the manikin
was lifted anteriorly and laterally by
tube ties, to simulate a difficult airway.
Intubation
was
completed
successfully in all 26 cases using the
AIC with cLMA technique, and in five
cases using the ILMA technique
(p<0.0001).
The former technique also proved
quicker (mean [95% CI]) in terms of:
Ferson et al. have reported use of the
ILMA in 48 FO-guided intubations, in
patients with airway distortion3. All
these were successful at the first
attempt, however the operators were
experienced in the use of the ILMA
This expertise may help to explain
Ferson’s high success rates, and the
low success rates with the same
technique in our study. A FO-guided
technique needs to be easy to
perform
despite
minimal
prior
exposure. Proficiency in the use of
the ILMA may require 20 attempts4,
whereas safe use of the cLMA + AIC
technique can be achieved with
considerably less experience5,6.
We have shown that FO-guided
tracheal intubation can be achieved
more often and faster using an AIC
via a cLMA than using an ILMA, in the
simulated difficult airway. Even in this
scenario the technique appears easy
to perform by those with limited
experience. Given the familiarity most
anaesthetists have with the cLMA and
the limited experience they have with
the ILMA7 we suggest most
anaesthetists, when facing a possible
airway crisis, consider using the cLMA
as the first choice conduit for
oxygenation and subsequent FOguided intubation, if conventional
intubation techniques have failed.
References
1.Time taken in seconds to reach the
vocal cords with the fibrescope (17.8
[15.0-21.2] versus 81.9 [50.7-132.5],
p = 0.0008)
2.Time until a device was railroaded
into the trachea (40.7 [35.9-46.2]
versus 91.0 [49.7-166.4] p = 0.01)
3.Time to first ventilation (89.8 [81.599.1] versus 113.5 [69.6-185.3], p =
0.0038).
1
2
3
4
Discussion
Figure 1. Manikin with tube
ties looped around the
larynx to simulate a difficult
airway
Care was taken to ensure that the
anatomical relationship between the
airway device and the larynx was
identical in each manikin (see Figure
2). After being shown written and
video instruction, the participants
attempted to intubate the trachea of
each manikin. Successful intubation
was the primary endpoint and these
data were evaluated using the Sign
test. Timings were also recorded, and
analysed using paired t-tests.
We found that in a simulated difficult
intubation, FO-guided intubation can
be achieved more quickly and reliably
using a cLMA with an AIC, than using
an
ILMA.
We
suspect
most
anaesthetists would choose a cLMA
over an ILMA to oxygenate the patient
when faced with an airway crisis,
because of the cLMA’s ubiquity and
the familiarity anaesthetists have with
its use. Our findings of increased
speed and, more importantly, success
of tracheal intubation if a cLMA is
chosen, represent another reason to
select a cLMA in this situation.
5
Figure 3. The need to pass the fibreoptic
bronchoscope beyond the Epiglottic Elevating
Bar of the ILMA reduces the angle available to
view the larynx.
(a) view via the cLMA. (b) view via the ILMA.
6
7
McNeillis NJD, Timberlake C, Avidan
MS, Sarang K, Choyce A, Radcliffe JJ.
Fibreoptic views through the laryngeal
mask and the intubating laryngeal
mask. European Journal of
Anaesthesiology 2001; 18: 471–5.
Keller C, Brimacombe J. Pharyngeal
mucosal pressures, airway sealing
pressures, and fibreoptic position with
the intubating versus the standard
laryngeal mask airway. Anesthesiology
1990; 90: 1001–6.
Ferson D, Rosenblatt W, Johansen M,
Osborn I, Ovassapian O. Use of the
intubating LMA-Fastrach in 254 patients
with difficult-to-manage airways.
Anesthesiology 2001: 95: 1175-81Scott,
E.C. 2005.
Chan YW, Kong CF, Kong CS, Hwang
NC, Ip-yam PC. The intubating
laryngeal mask (ILMA): initial
experience in Singapore. British Journal
of Anaesthesia 1998; 81:610–11
Atherton DPL, O’Sullivan E, Lowe D,
Charters P. A ventilation-exchange
bougie for fibreoptic intubations with the
laryngeal mask airway. Anaesthesia
1996; 51: 1123-6
Higgs A, Clark E, Premraj K. Low-skill
fibreoptic intubation: use of the Aintree
Catheter with the Classic LMA.
Anaesthesia 2005; 60: 915–20
Hodzovic I, Wilkes AR, Gataure P, Latto
IP. Survey of experience with the more
advanced components of the 2004
Difficult Airway Society guidelines.
Anaesthesia 2005; 60: 834A
Are our findings supported by
the literature?
Other authors have also reported inferior
fibreoptic positioning of the ILMA
compared to the cLMA.
(a)
(b)
Figure 2. (a) Endoscopic view via the cLMA.
(b) Endoscopic view via the ILMA (epiglottic
elevating bar removed)
•Like us, McNeillis et al. blame the
increased depth of insertion of the
bronchoscope, necessary to lift the EEB1.
•Keller and Brimacombe suggest that the
fixed length of the airway tube of the ILMA
may be responsible2. However we
controlled for this by ensuring that the
distance between the point at which the
bronchoscope emerged from the airway
tube and the vocal cords was identical in
the two manikins.
Acknowledgements
The authors would like to thank Michael
Phillips for his help with the statistical
methods employed, and LMA PacMed for
supplying the manikins.