Use of the laryngeal mask airway in
rabbits: placement and efficacy
George M. Kazakos, DVM, PhD1, Tilemahos Anagnostou, DVM, PhD1, Ioannis Savvas, DVM, PhD1,
Dimitris Raptopoulos, DVM, PhD, DVA, DECVA1, Dimitra Psalla, DVM, PhD2 &
Irene M. Kazakou, MD3
The laryngeal mask airway (LMA) has been used in various animal species anesthetized
for the purpose of device evaluation, but the device has not been evaluated in rabbits
during surgery. The authors tested the feasibility and potential advantages of using
the LMA in 50 rabbits undergoing surgery under spontaneous-breathing inhalational
anesthesia, focusing mainly on the technique of insertion and its efficacy. The LMA
was easily inserted and no air leakage at the larynx was detected. Although four
rabbits developed lingual cyanosis, this was reversible and most likely due to lingual
vascular compression by the LMA. The authors conclude that the LMA is an attractive
alternative to endotracheal intubation, as the mask can be inserted easily and rapidly
and its correct placement is easily confirmed.
Intubation of the trachea in rabbits is technically
demanding and time-consuming even under expe-
rienced hands. As a result, administration of volatile
agents often proves to be difficult, especially when con-
trolled ventilation must be applied. Moreover, attempts
to intubate rabbits can lead to laryngospasm and subse-
quent airway trauma or obstruction1.
Special techniques and devices (such as optical fiber-
scopes and X-ray machines2,3) are often used to facili-
tate endotracheal intubation in rabbits; some workers
have even resorted to tracheostomy,4 while others try to
avoid intubation altogether by using alternative meth-
ods for anesthesia administration5. Recently, Imai et al.6
constructed a prototype of an airway device for use in
laboratory animals that is currently being evaluated.
The LMA is a device intended as an alternative to
face masks and endotracheal tubes. It consists of an
airway tube, a mask, and a mask inflation link (Figs. 1,
2). Following insertion over the laryngeal aperture and
into the pharynx, the mask forms a direct end-to-end
junction between the upper airway and an artificial tube
for supplying gas to the bronchial tree7. Since the LMA
became commercially available in 1988, many alterna-
tive techniques have been described to aid its insertion
in humans8,9. The use of the LMA offers some advan-
tages over tracheal intubation. The former is easier for
the inexperienced staff members to insert. In fact, the
ease of use makes the device an attractive alternative
especially in cases of emergency10. Moreover, deviation
from the ideal positioning does not preclude excellent
1Companion Animal Clinic, Faculty of Veterinary Medicine, Aristotle University of Thessaloniki, Greece. 2Laboratory of Pathology, Faculty
of Veterinary Medicine, Aristotle University of Thessaloniki, Greece. 3Internal Medicine Clinic, University General Hospital of Heraklion,
Greece. Correspondence should be addressed to G.M.K. (email@example.com).
FIGURE 1 | The concave side of the Laryngeal Mask Airway
device, showing the (a) airway tube, (b) mask, and (c) mask
Volume 36, No. 4 | APRIL 2007 29
functional results in human patients8,9. However, there
is concern about an incomplete seal between the LMA
and the larynx in humans10 and laboratory pigs11.
Furthermore, the inability of the device to completely
protect the airway against aspiration of gastric contents
is considered to be its main disadvantage when com-
pared with endotracheal intubation12. Laryngospasm,
sore throat, hoarseness, and dysphagia have been
reported following LMA use in people10.
Although it is designed for use in humans, the LMA
has been found suitable for dogs, cats, pigs, ferrets, and
rabbits anesthetized for the purpose of device evalua-
tion; however, it has never been evaluated for surgical
interventions in rabbits. The aim of the present study
was to examine the feasibility and potential advantages
of using the LMA in rabbit surgery, focusing on the
technique of insertion and its efficacy.
We used the LMA in 50 New Zealand white rabbits
weighing 2.3–4.5 kg. The animals were part of two
experimental projects approved by the Local Animal
Ethics Committee (license numbers 13/8015/08.07.2004
and 13/7908/05.07.2004). The projects involved either
soft tissue (autologous orthotopic and heterotopic
ovarian transplantation) or orthopedic surgery (exter-
nal fixation of a tibial fracture) and were carried out
at the Surgery Unit of the Companion Animal Clinic,
Faculty of Veterinary Medicine, Aristotle University of
Thessaloniki, Greece. All the animals had free access to
food and water for up to two hours before induction
Initially, cadaveric heads of two rabbits weighing 3.1
and 4.3 kg were sagitally dissected to expose the larynx,
the pharynx, the tongue, and the rest of the oral cav-
ity. The larynx and trachea were held intact (Fig. 3).
Two silicone rubber reusable (autoclavable) LMAs
(size-1 and size-1.5, LMA-Classic, Intavent Orthofix
Ltd., Maidenhead, Berkshire, UK) were compared with
the laryngeal openings of the dissected rabbit heads to
determine which was most suitable for use in rabbits by
matching the size of the mask to the cadaveric laryngeal
aperture (Fig. 4).
Thirty-eight animals were premedicated with carprofen
(Rimadyl, Pfizer Hellas, Athens, Greece) and medeto-
midine (Domitor, Pfizer/Orion Co., Espoo, Finland).
Approximately 40 minutes later, anesthesia was induced
with thiopentone (Pentothal, Abbott Laboratories Hellas,
Athens, Greece). Additional doses of 1–2 mg/kg each
were administered if necessary until the palpebral and
ear-pinch reflexes were eliminated, at which point we
attempted insertion of the LMA. In each animal, the total
amount of thiopentone (in mg/kg) was recorded as the
total thiopentone dose. The other 12 animals were pre-
medicated with carprofen combined with either medeto-
midine or xylazine (Rompun, Veterin, Athens, Greece),
and anesthetized ~30 minutes later with ketamine
(Imalgene 1000, Merial, Lyon, France). Dosage details
for the drugs used in the three protocols are shown in
Table 1. In these animals, insertion of the LMA was
attempted ~10 minutes after administration of ketamine,
following demonstration of loss of reflexes as described
above. In order to lubricate the cornea during anesthesia,
we applied a mild ophthalmic ointment (Thilogel, Alcon
Laboratories Hellas S.A., Athens, Greece).
Routine preinsertion testing of the LMA cuff for leaks
was always performed immediately before use. The cuff
FIGURE 2 | The Laryngeal Mask Airway device. When properly
positioned, the dorsal black line of the airway tube (arrow)
should line up with the animal’s midline, keeping the convex
side of the tube against the hard palate.
FIGURE 3 | The larynx of a 3.1 kg cadaveric rabbit exposed
after sagittal dissection of the head.
www.labanimal.com30 Volume 36, No. 4 | APRIL 2007
was coated with a water-soluble lubricant containing
2% lidocaine. With the rabbit in left lateral recum-
bency, its head and neck were kept flexed dorsally at a
60-degree angle by an assistant, who at the same time
kept the mouth open by grasping the tongue and pull-
ing it forward. Initially, with the cuff fully deflated, we
introduced the LMA into the oral cavity through the
right interdentium with the aperture slightly advanced
and facing the right buccal wall. Then we rotated the
LMA 90 degrees counterclockwise so as to position the
dorsal black line on the tube of the LMA (Fig. 2) at the
midline, with the convex side against the hard palate.
These manipulations were considered necessary in order
to avoid laceration of the cuff by the rabbit’s teeth. At
that point in the procedure, we could feel resistance to
further advancement of the LMA, which was easily over-
come until we encountered a second point of unyielding
resistance. The cuff was then inflated while a check was
performed for signs considered indicative of success-
ful inflation of the cuff in humans, such as an outward
movement of the tube during inflation of the cuff or an
externally palpable cuff9. Finally, we secured the LMA in
place by using adhesive tape around the muzzle of the
animal and connected it to the anesthetic machine via a
Jackson-Rees modification of an Ayre’s T-piece system.
We initially administered 100% oxygen when
checking for correct placement of the device so as to
ensure normal breathing and avoid the breath-holding
sometimes associated with inhalant agents in rabbits13.
We confirmed that there was an effective airway by not-
ing whether the movements of the reservoir bag were
in sync with the chest wall movements and by detect-
ing a normal capnogram. Then, we administered the
volatile anesthetic. A few minutes later, we squeezed the
reservoir bag manually for a few consecutive breaths
(peak inspiratory airway pressure 15 cm H2O) to check
for any gas leakage. We used three criteria to determine
the absence of a gas leak: whether the LMA generated
and maintained peak inspiratory airway pressure for
a few seconds without audible noise of gas escaping
into the oral cavity, whether the anesthetic gas ana-
lyzer (Capnomac Ultima, Datex-Engstrom, Helsinki,
Finland), with its probe placed inside the rabbits’ oral
cavity, detected any anesthetic agent, and whether
the capnogram was normal. Anesthesia was main-
tained with halothane (Halothane liquid, Concord
Pharmaceuticals, Avonmouth, Bristol, UK) or isoflu-
rane (Forenium, Abbott Laboratories Ltd., Kent, UK)
in oxygen with a gas flow of 1.5 l/min.
We continuously monitored intraoperative heart rate,
SpO2 (sensor placed on tongue), arterial blood pres-
sure (indirectly, oscilometric method), respiratory rate,
tidal volume, airway pressure, concentration of inspired
and end-tidal O2, and inhalant agent (isoflurane or
FIGURE 4 | Application of a size-1 LMA on the larynx of a 3.1 kg cadaveric rabbit. (a) Mid-lateral view of the larynx. Forceps hold
the device in place for the photography. (b) Dorsal view of the application of a size-1 LMA on the larynx of a 3.1 kg cadaveric rabbit.
TABLE 1 | Anesthetic protocols used in 50 rabbits
Protocol Premedication Induction Maintenance Na
1 Carprofen 4 mg/kg, s.c.b,
Medetomidine 0.5 mg/kg, s.c.
15 mg/kg, s.c.
2 Carprofen 4 mg/kg, s.c.,
Xylazine 10 mg/kg, s.c.
40 mg/kg, s.c.
3 Carprofen 4 mg/kg, s.c.,
Medetomidine 0.5 mg/kg, s.c.
9.98 ± 1.9 mg/kg, i.v.c
aN, number of animals; bs.c., subcutaneous; ci.v., intravenous
Volume 36, No. 4 | APRIL 2007 31LAB ANIMAL
halothane), as well as partial pressure of inspired and
end-tidal CO2. We recorded those values every 5 min-
utes using the Capnomac Ultima and PC Scout (PC
Scout, SpaceLabs Medical Inc., Redmond, WA) moni-
tors. We discontinued anesthesia administration after
closure of the surgical incision. Four rabbits were not
allowed to recover and were euthanatized by using KCl
i.v. while still at a surgical plane of anesthesia. In the rest
of the animals (which were euthanatized 4–6 months
later in accordance with the requirements of the rel-
evant experimental protocols), we removed the LMA
when either the palpebral or ear-pinch reflexes were
present, and allowed the animals to recover on heating
pads set to 37 °C. After its removal, we checked the LMA
for the presence of gastric content or blood. Moreover,
we observed the animals for any complications during
recovery. During necropsy of the above-mentioned
four sacrificed rabbits, we also examined the pharynx
and larynx for macroscopic lesions.
Our preliminary rabbit cadaver head specimens sug-
gested that the size-1 LMA was appropriate for the rab-
bit weighing 3.1 kg (Figs. 3, 4). However, for the 4.3-kg
rabbit, the size-1.5 LMA fit better.
In all rabbits, there was slight resistance to advance-
ment of the device just before reaching its final position
and while the cuff was still visible in the oral cavity. This
resistance, however, could easily be overcome until the
device met an unyielding resistance at the end of the
insertion, thereby preventing further advancement. In
no rabbit did we find any outward movement of the
mask upon inflation of the cuff; the black line on the
LMA was always maintained at the midline.
In all cases, the movements of the reservoir bag
corresponded with the chest wall movements during
both spontaneous and manual ventilation. Moreover,
all animals had normal capnograms. We were able to
manually ventilate all rabbits without gross gas leaks (as
assessed by the absence of sound caused by escaping gas
during pressure maintenance) until we reached a peak
airway pressure of 15 cm H2O. Also, in no instance did
the anesthetic gas analyzer detect the anesthetic agent
in the oral cavity.
The mean total thiopentone dose was 9.98 ± 1.9 mg/
kg. Mean anesthesia time was 26.6 ± 12.1 min (range
10–75 min). All monitored cardiorespiratory param-
eters were within normal limits. In particular, mean
ETPCO2 was 4.59 ± 1.44 kpa and the average mean
arterial blood pressure was 60.11 ± 10.41 mmHg.
We successfully inserted the LMA on the first and
only attempt in every case. Recovery was uneventful in
all animals. In four rabbits, the tongue became cyanot-
ic soon after insertion of the LMA, but all monitored
respiratory and cardiovascular parameters, including
mucosal color (Fig. 5) and SpO2 (sensor placed on the
ear), were within normal limits in these animals. The
first action we took in response to tongue cyanosis was
deflation of the cuff. Cyanosis disappeared in two rab-
bits after this maneuver, while it persisted in the other
two animals. In one of the latter, we resolved the cya-
nosis by repositioning the device with the cuff deflated;
however, in the other animal, neither deflation nor
repositioning were effective, and we restored normal
tongue colour only after use of a smaller-size mask.
Postmortem examination of the pharynx and larynx in
the four euthanatized rabbits did not reveal any lesions.
There have been a few reports evaluating the LMA in
rabbits14–16. However, none of these studies evaluated
the LMA during surgical interventions. In this study, we
investigated the feasibility of using the LMA in rabbits
The cadaver heads showed that although laryngeal
anatomy of the rabbit differs from that of humans, the
LMA fits well on the rabbit’s larynx and provides a good
seal around the laryngeal opening. In the present study,
we used the size-1 LMA in rabbits weighing less than
4 kg and the size-1.5 in larger animals. However, on
one occasion the size-1 LMA had to be used for a rab-
bit weighing more than 4 kg because tongue cyanosis
appeared with the use of a size-1.5 LMA.
Insertion of the LMA requires a lighter plane of
anesthesia than that required for endotracheal intu-
bation14,17. Moreover, Wemyss-Holden et al.18 found
it easy to insert LMAs in pigs following the intramus-
cular administration of ketamine/xylazine, without
the need to reach a near surgical plane of anesthesia as
required for endotracheal intubation following intra-
venous induction. Although the purpose of the present
study was not to compare the various anesthetic pro-
tocols with respect to the feasibility of using the LMA,
FIGURE 5 | Cyanosis of the tongue observed soon after
insertion of a size-1 LMA in a rabbit weighing 2.4 kg. Note the
normal buccal mucosal color (arrow).
www.labanimal.com32 Volume 36, No. 4 | APRIL 2007
the latter was successfully inserted at the first and only
attempt in all the rabbits in which anesthesia had been
induced with subcutaneous injection of a combination
of an α2-adrenergic agonist (medetomidine or xylazine)
with ketamine. This may be viewed as an advantage of
the technique in cases where, for various reasons, intra-
venous induction is difficult or must be avoided.
Two points should be emphasized concerning the
process of mask insertion. First, the device must be
protected from the rabbit’s teeth while in the limited
space of its oral cavity. The cuff also needs protection,
as previously described for LMA use in dogs and cats19.
In the present study, this was achieved by inserting the
mask through the right interdentium with the aperture
facing the upper buccal wall (animal in lateral recum-
bency) and by advancing it slightly before rotating it so
that the teeth would be bypassed and lacerations of the
cuff avoided; a similar technique was also followed by
Smith et al.15. Second, there is an easily overcome mild
resistance, possibly due to the narrow caudal oral cav-
ity, encountered as the device is advanced beyond the
molars but before the final position, at which point there
is an unyielding resistance to further advancement.
In four rabbits, we observed cyanosis confined to the
tongue; tongue color returned to normal after deflation
of the cuff, repositioning of the mask, or removal and
use of a smaller size mask. Although arterial blood gas
measurements were not performed, the color of the rest
of the mucous membranes was normal, SpO2 (when the
sensor was positioned on the ear) was more than 95%,
and other monitored cardiorespiratory parameters were
within normal limits. Hence, we postulate that the likely
cause of the cyanosis was the compression of the lin-
gual artery. This phenomenon has also been observed in
humans20 and in ferrets after prolonged (more than six
hours) anesthesia21. The possibility that tongue cyanosis
was caused by a substantial increase in cuff pressure dur-
ing the course of inhalational anesthesia, as described
by van Zundert et al.22 in humans, should probably
be excluded, since cyanosis appeared soon after LMA
positioning. Based on the findings of the present study,
the possibility of tongue cyanosis should always be kept
in mind. Placing the sensor of a pulse oximeter on the
tongue soon after insertion of the LMA may greatly
facilitate early diagnosis of lingual cyanosis. In cases of
lingual cyanosis, capnography, and buccal tissue perfu-
sion, monitoring may also be used to assess pulmonary
and cardiovascular function. During device placement,
we paid special attention to avoiding over-extension of
the tongue, as it might result in lingual trauma.
There is no uniform policy concerning the inflation
of the cuff when the LMA is used for inhalational anes-
thesia in rabbits; although Cruz et al.14 inflated it, for
instance, Bateman et al.16 did not. In the present study,
we did not detect any gas leaks and found all cardiore-
spiratory parameters within normal limits in the two
animals in which the cuff was deflated to resolve tongue
cyanosis, which supports the contention that the LMA
works adequately even when the cuff is not inflated.
Three of the rabbits that exhibited tongue cyanosis
weighed 2.3–2.5 kg, and the fourth one, which eventu-
ally required the use of a size-1 LMA instead of a size-
1.5, weighed 4 kg. It may be argued that compression of
the lingual artery was caused by the use of a relatively
large LMA. Thus, 2.5 kg may represent the lower body
weight limit for use of size-1 LMA in rabbits without
the risk of tongue cyanosis. Moreover, the use of a size-1
LMA in rabbits weighing more than 4 kg may also be
appropriate. The appropriate body weight ranges for
the use of LMA size-1 or size-1.5 and whether full infla-
tion of the cuff is necessary are two subjects which need
In humans, the current recommended practice is to
leave the LMA inflated in situ until the patient regains
consciousness. In the present study, we removed the
mask when either the palpebral or ear-pinch reflex was
present but before full recovery, so as to avoid both bites
on the tubing/cuff and destruction of the device. This
practice has also been reported by Wemyss-Holden et
al.18 in pigs anesthetized for experimental purposes.
Based on the fact that stridor was not observed during
or after recovery, nor was there any vomiting or regurgi-
tation, the early removal of the LMA seems to be a good
practice. All rabbits that were allowed to recover did so
without incident. Moreover, necropsy performed on four
animals did not reveal any macroscopic lesions (trauma,
edema, congestion) at the pharynx and/or larynx.
Smith et al.15 compared the LMA to cuffed and
uncuffed endotracheal tubes with respect to their
capacity to limit waste anesthetic gases during spon-
taneous ventilation. By using a portable infrared spec-
trophotometer, the LMA was found to be inferior to
entotracheal tubes because of gas leakage. However,
Fujita et al.19 detected no leakage of anesthetic gas with
a urinary catheter which was inserted into the esopha-
gus during spontaneous ventilation of anesthetized
cats via an LMA. In the present study, no gas leaks were
detected during either spontaneous or manual bag ven-
tilation. Studies in humans using fiberoptic examina-
tion, computed tomography, or magnetic resonance
imaging have shown that the airway can be functionally
patent and clinically acceptable although placement of
the LMA is less than perfect8. Besides this, according to
Fujita et al.5 rabbits seldom require intermittent posi-
tive pressure ventilation during surgery for anatomical
reasons, even when the chest is open. This reduces the
concern expressed by Smith et al.15 about the complete
seal of the larynx by the LMA.
We conclude that the use of the LMA device offers an
attractive alternative to endotracheal intubation or to
Volume 36, No. 4 | APRIL 2007 33LAB ANIMAL
the use of a face mask for maintenance of anesthesia in
rabbits undergoing surgery under spontaneous-breath-
ing inhalational anesthesia. Useful clinical indices for
correct LMA placement are:
• Detection of unyielding resistance to further
advancement during insertion;
• Vigilant positioning of the black line of the LMA
at the midline;
• Close monitoring of the synchronization of the
movements of the reservoir bag with chest wall
• Observation of sufficient chest wall movements
during manual ventilation; and
• Absence of sound caused by gas escaping in the
oral cavity during manual ventilation.
Effective ventilation can ideally be confirmed by
using capnography. Finally, early removal of the LMA
seems to be a good practice. The only complication,
occuring in four rabbits, was cyanosis confined to the
tongue, which was easily resolved by either deflation or
repositioning of the cuff, or through the use of a smaller
LMA. SpO2 monitoring through a sensor on the tongue
soon after the insertion of the LMA is advisable.
COMPETING INTERESTS STATEMENT
The authors declare that they have no competing financial interests.
Received 20 October 2006; accepted 21 November 2006.
Published online at http://www.labanimal.com
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