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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.
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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. (gkdvm@vet.auth.gr).
FIGURE 1 | The concave side of the Laryngeal Mask Airway
device, showing the (a) airway tube, (b) mask, and (c) mask
inflation link.
Volume 36, No. 4 | APRIL 2007 29
LAB ANIMAL
TECHNIQUE
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.
METHODS
Animals
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
of anesthesia.
Device choice
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).
Anesthesia induction
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).
Device placement
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
TECHNIQUE
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.
Monitoring
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
ba
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.
Ketamine
15 mg/kg, s.c.
Halothane
(to effect)
6
2 Carprofen 4 mg/kg, s.c.,
Xylazine 10 mg/kg, s.c.
Ketamine
40 mg/kg, s.c.
Halothane
(to effect)
6
3 Carprofen 4 mg/kg, s.c.,
Medetomidine 0.5 mg/kg, s.c.
Thiopentone
9.98 ± 1.9 mg/kg, i.v.c
Isoflurane
(to effect)
38
aN, number of animals; bs.c., subcutaneous; ci.v., intravenous
Volume 36, No. 4 | APRIL 2007 31LAB ANIMAL
TECHNIQUE
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.
RESULTS
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.
DISCUSSION
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
undergoing surgery.
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
TECHNIQUE
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
further investigation.
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.
CONCLUSIONS
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
TECHNIQUE
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
movements;
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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www.labanimal.com34 Volume 36, No. 4 | APRIL 2007
TECHNIQUE
... Lingual cyanosis was noted in six rabbits, three weighing < 2.5 kg. Lingual cyanosis is commonly reported when using Vgel and laryngeal masks, especially in small rabbits (Bateman et al. 2005;Kazakos et al. 2007;Wenger et al. 2017). The size of the device may occlude blood flow in the lingual artery (Varga 2017); normal lingual coloration returns 30 seconds after removing the laryngeal mask (Kazakos et al. 2007). ...
... Lingual cyanosis is commonly reported when using Vgel and laryngeal masks, especially in small rabbits (Bateman et al. 2005;Kazakos et al. 2007;Wenger et al. 2017). The size of the device may occlude blood flow in the lingual artery (Varga 2017); normal lingual coloration returns 30 seconds after removing the laryngeal mask (Kazakos et al. 2007). The relatively large size of the endoscope device (5.5 mm) and the lack of experience with the device may favor transient lingual ischemia, especially in small rabbits; however, removal of the device from the oral cavity and provision of oxygen supplementation immediately after intubation corrected the cyanosis. ...
Article
Objective: To compare between blind and smartphone-based endoscope-assisted techniques for endotracheal intubation in rabbits. Study design: Prospective clinical study. Animals: A total of 34 rabbits. Methods: Rabbits were assigned to four groups: intubation by a veterinary anesthesiologist (VA) or an exotic pet medicine specialist (EPS) using blind or endoscope-assisted techniques. Propofol dose, number of attempts until successful intubation, total time for intubation, duration of the successful attempt and occurrence of lingual cyanosis/laryngeal lesions were recorded. Data were analyzed by t test, Wilcoxon-Mann-Whitney U test or chi-square test. Pearson correlation for body weight was performed. Results: The success rate of blind intubation was 88.9% and 77.8% for VA and EPS, respectively. Propofol dose, total and median number of attempts, total time for intubation and duration of the successful attempt were 3.1 (0-6.2) mg kg-1, 19, 2 (1-5), 79 ± 65 and 30 ± 20 seconds for VA and 1.5 (0-4.5) mg kg-1, 24, 3 (1-5), 136 ± 92 and 38 ± 16 seconds for EPS. The success rate of endoscope-assisted intubation was 87.5% for both operators. Propofol dose, total and median number of attempts, total time for intubation and duration of the successful attempt were 2.5 (1.3-7.4) mg kg-1, 22, 3 (1-5), 170 (65-368) and 46 (22-150) seconds for VA and 3.2 (0-6) mg kg-1, 11, 1 (1-4), 56 (27-432) and 55 (26-79) seconds for EPS. VA performed blind intubation more quickly, propofol dose was lower and cyanosis was less frequent than in the endoscope-assisted group. Conclusions and clinical relevance: Both techniques were reliable for rabbit endotracheal intubation. Best results were achieved when the operator was experienced in the technique. The smartphone-based endoscope is a useful aid for rabbit intubation.
... Modern developments in medical technology have created less strenuous means of maintaining airways during general anesthesia. Since its approval in 1999, the conventional Laryngeal Mask Airway (LMA TM ), invented by Archibald Brain, represented the first non-invasive method of airway management [4][5][6]. However, the continued usage of the LMA TM presented evident restrictions in its application to various patient populations [7]. ...
... 3 The LMA, originally developed for human use as an alternative to the ET tube for maintaining airway patency during general anesthesia for short-duration or ambulatory procedures, 20 consists of a tube connected at one end to a leaf-shaped inflatable silicone mask that is designed to cover the entrance of the larynx and provide a secure airway. 20 In veterinary medicine, the human LMA has been used for maintaining general anesthesia in rabbits, 4,8,9,16,25 cats, 1,6,22 swine, 11,12,24 and dogs. 5 More recently, species-specific supraglottic devices have been developed for use in rabbits, 7,9,25 cats, 2,22 and rats. ...
Article
Orotracheal intubation carries greater difficulty in rodents than in most domestic species. The human laryngeal mask airway (LMA) was compared with an endotracheal tube (ETtube) for maintaining airway patency in anesthetized capybaras (Hydrochoerus hydrochaeris). Six capybaras (24-52 kg) were remotely darted with intramuscular ketamine, midazolam, and acepromazine on two occasions (7-day intervals). After isoflurane mask induction for random placement of an ETtube or a LMA during each episode, anesthesia was maintained with isoflurane in oxygen under spontaneous ventilation for 90-120 min. Computed tomography of the pharynx and larynx was performed in two of six animals and three of six animals with the ETtube and LMA, respectively. End-tidal isoflurane [median (range)] was not significantly different between ETtube [0.6% (0.5-1.5%)] and LMA [0.6% (0.4-0.9%)]. Heart rate [67 6 11 beats/min (ETtube) and 67 6 18 beats/min (LMA)], mean arterial pressure [74 6 13 mm Hg (ETtube) and 74 6 14 mm Hg (LMA)], arterial CO2 tension [41 6 2 mm Hg (ETtube) and 43 6 4 mm Hg (LMA)], and arterial O2 tension [360 6 59 mm Hg (ETtube) and 360 6 63 mm Hg (LMA)] were not significantly different between treatment groups. Computed tomography showed gas in the esophagus with the LMA (three of three animals); the fit of the LMA to the larynx was adequate in two of three animals and fair in one of three animals. Recovery from anesthesia was uneventful. The LMA is a feasible alternative to the ETtube for maintaining airway patency during inhalant anesthesia in spontaneously breathing capybaras. However, the LMA may be dislodged during movement of the animal.
... Gastric tympany is a reported complication of SGAD use in rabbits and humans but has not been reported in other species (Varga 2017;Skarbek & Borland 2019). In rabbits, gastric tympany has mainly been associated with the use of human laryngeal mask airways rather than the commercial rabbit SGAD model used in this study (Bateman et al. 2005;Kazakos et al. 2007;Varga 2017). Further studies assessing the safety of the SGAD use in hedgehogs are warranted. ...
Article
In Press, Veterinary Anaesthesia and Analgesia, 04 Mar 2021 Objective: To evaluate the feasibility of a commercial supraglottic airway device (SGAD) designed for rabbits for use in African pygmy hedgehogs (Atelerix albiventris) during inhalation anesthesia. Study design: Prospective, randomized, blinded experimental study. Animals: A total of 12 adult African pygmy hedgehogs (seven male, five female). Methods: Hedgehogs were placed in a chamber and anesthesia was induced using isoflurane in oxygen. Oropharyngeal rigid endoscopy was performed and observations recorded. A SGAD (v-gel R1, Docsinnovent, UK) was inserted and time to placement was recorded. A Mapleson D circuit was used for anesthetic maintenance. Capnography, pulse oximetry, physiologic variables and the feasibility of holding the lungs inflated at 10 and 20 cmH2O were assessed at routine intervals during anesthesia. Anesthetized hedgehogs were randomly positioned into right and left lateral, dorsal and sternal recumbency to evaluate the effect of a change in body position on SGAD displacement; the anesthetic circuit was detached from the SGAD during animal repositioning. At the end of anesthesia, the SGAD was removed and oropharyngeal endoscopy performed. The SGAD was reinserted, placement confirmed and isoflurane discontinued. Recovery time was recorded. Pre- and post-SGAD placement endoscopy videos were retrospectively reviewed and scored (0-3 scale) for observed gross trauma by an observer blinded to treatment. Results: The median (interquartile range [IQR]) time to successful SGAD placement was 38 (16–68) seconds. A total of 50% of hedgehogs required repositioning of the device to successfully perform lung inflation or maintain capnography readings; a median (IQR) of 2.5 (1-3.5) adjustments were performed during the anesthetic period for this group of six hedgehogs. Lung inflation at 10 cmH2O was successfully performed without leakage in all animals, although readjustment was needed beforehand for 1-2 time points in three animals. Inflation at 20 cmH2O was successfully performed without an air leak in six animals, but only at a single time point for each animal. Changes in heart rate and fR during anesthesia were not clinically relevant. Median endoscopic scores were 0 (no lesions) for both pre-and postplacement. Conclusions and clinical relevance: The SGAD was relatively quickly and easily placed, permitted lung inflation and caused no significant oropharyngeal damage. The SGAD is a practical option for airway management in African pygmy hedgehogs.
... We hypothesized that LMA would be compatible with several animal species and that they would have higher efficiency in securing a tight airway, with minimal risk for aspiration of gastric contents, compared to the endotracheal intubation technique. This assumption was based following reports for the use of LMA with a socalled 'blind-technique', both in human (4) and animal species (5,6). In some animal species, endotracheal intubation can be challenging due to anatomical specificities. ...
Article
Full-text available
Providing a secure airway management during general anesthesia could be problematic in some medical cases, especially when there is a risk of regurgitation and aspiration of the gastric content due to increased intragastric pressure. The current study aimed to test the applicability of two types of LMA in several animal species and to compare its effectiveness to the endotracheal intubation method in securing sealed airway respiration as an alternative to using endotracheal tubes. The study was conducted in dogs (n=33), cats (n=9), swine (n=9), rabbits (n=5), sheep (n=7) and roe deer (n=1). One or both types of laryngeal masks were used for each animal species: LMA Classic™-cLMA and LMA ProSeal™-PLMA. The assessment of each laryngeal mask was performed by determining the insertion technique, the possibilities of first-attempt insertion and malposition, the compliance with various animal species, ventilation time, cuff pressure, and sealing capacity. The highest LMA size compatility in dogs (23,87±14,30 kg) was size-3 in six and size-4 in forteen subjects; In swine (43,22±12,32 kg), size-4; In rabbits (3,84±0,36 kg) size-1; and in sheep (48,29±4,65 kg) size-3 and size-4. Ventilation time was highest in swine and roe deer (121,11±42,85 min and 300,00 min, respectively) and lowest in cat (28,33±16,96 min). First-attempt LMA insertion success was lowest in rabbits (60%), and highest in sheep and roe deer (100%). Malposition was with highest rate in rabbits (40%) and lowest in cat, sheep and roe deer (0%). Gastric reflux was most frequently observed in sheep (71,4%) and roe deer (100%). The usage of LMA in the veterinary anesthetic practice significantly improves airway management in animals during general anesthesia. The inflated LMA cuff does not prevent its disposition. Therefore, both the drain and respiratory tubes must be fixed. The usage of LMA in rabbits was associated with higher incidence of malposition and other complications. Our findings suggest that LMA designed for humans can be used for airway management in veterinary medicine.
With the increasing frequency of rabbits as veterinary patients, the expectation for high-quality, intensive veterinary care, and resultantly an understanding of anesthesia has been increasing. Sedation and general anesthesia are commonly required for many routine and emergency procedures in rabbits, and this results in the need for a strong awareness of anesthetic principles, knowledge of limitations of anesthesia, and maintenance of high standards of anesthesia.
Chapter
Oxygen therapy is an extremely valuable and critical treatment tool in exotic companion mammals (ECM) to allow for institution of a rapid life‐saving measure. Not only the importance of oxygen therapy but also the need to recognize situations where oxygen therapy is needed are discussed. Diagnostic tools to recognize hypoxemia and oxygen toxicity are also discussed. Oxygen administration techniques and their advantages and disadvantages are reviewed, as well as how techniques to administer oxygen. The chapter also briefly reviews common respiratory diseases of ECMs. The overarching goal of this chapter is to provide the reader with an understanding of the importance of oxygen therapy, situations where it has utility, and methods of administration of oxygen in ECMs.
Article
Background Due to the technical difficulties with endotracheal intubation of rabbits, a prospective, randomised, controlled study was performed to compare a rabbit-specific supraglottic airway device (SGAD), the v-gel, with endoscopic endotracheal intubation (EEI) in spontaneously breathing rabbits undergoing ovariohysterectomy. Methods Fourteen adult female New Zealand white rabbits were randomly allocated to one of two groups based on the method of airway establishment: EEI or v-gel SGAD. Anaesthesia was induced with ketamine and xylazine and maintained using isoflurane in 100 per cent oxygen. Comparisons were made between groups based on placement time of endotracheal tube/SGAD, number of attempts and adjustments, the necessity to increase isoflurane concentrations to maintain a surgical plane of anaesthesia, arterial blood gas values, gross laryngeal evaluation, and laryngotracheal histopathology. Results Both techniques resulted in elevated arterial pCO 2 levels, but the v-gel was associated with more elevated pCO 2 in comparison with EEI (P=0.045). Airway trauma was histologically present but clinically negligible in both groups, with no statistically significant differences observed between techniques (P>0.05). Placement time of the v-gel was significantly faster (P=0.003) and required less technical skill than EEI, but was more easily displaced when changing the animal’s position (P=0.004). Conclusion The v-gel is a practical alternative to EEI for securing the airway of healthy spontaneously ventilating rabbits, provided a capnograph is utilised to ensure continuous placement. Both airway techniques appear safe and effective with few complications, as long as intermittent positive pressure ventilation can be employed to correct hypercapnia.
Article
A seven-year-old female spayed dwarf rabbit (Oryctolagus cuniculus) was evaluated for respiratory distress 12 days after an ovariohysterectomy and mammary mass removal. Severe inspiratory stridor and open-mouth breathing were observed on presentation. Results of whole body radiographs revealed an intrathoracic tracheal stricture 12.5-cm distal to the nose. A 5-mm × 30-mm nitinol self-expanding metallic stent was placed under fluoroscopic guidance across the tracheal stricture. The patient was discharged the next day on a tapering course of prednisone over a week and a short course of a bronchodilator (terbutaline) and an antibiotic (enrofloxacin). On follow-up examinations from 10 days to 21 months after stent placement, no associated respiratory signs or stent complications were observed. At present, the rabbit remains otherwise healthy with an intact tracheal stent and no recurrent episodes of dyspnea over 24 months after placement. Tracheal stent placement in this rabbit allowed for emergent treatment of life threatening tracheal stricture formation utilizing a minimally invasive technique. Tracheal stenting resulted in rapid resolution of respiratory distress with favorable long-term outcome. This is the first reported clinical case of tracheal stent use in a rabbit, and supports the tolerance of tracheal stents in this species long term.
Chapter
Airway management reflects the need to provide an adequate path for airflow to go from the upper airway to the lower airways. For the clinician, airway management requires rapid and accurate patient assessment and early intervention as required.
Chapter
This chapter reviews the topic of anesthesia and analgesia as it pertains to the rabbit. It also discusses biomethodology, pre-, intra-, and postoperative considerations, as well as special anesthetic procedures. Rabbits should be subject, at a minimum, to a physical examination prior to inclusion in an anesthetic protocol. The chest should be auscultated carefully for evidence of pulmonary or cardiovascular disease and rectal temperature should be determined. Baseline laboratory evaluation including a complete blood count and serum biochemistry may be useful in animals that have been subject to prior manipulation. Rabbits with pasteurellosis are not good anesthetic candidates. Thoracic radiography is advisable in rabbits from colonies with enzootic pasteurellosis to identify latent pulmonary consolidation and abcessation. Specialized studies may require additional preoperative diagnostics. Constant vigilance must be observed; one person who is trained in appropriate decision making should be assigned the task of monitoring anesthesia. Patient monitoring can be considered to be composed of three areas—reflexes, cardiopulmonary parameters, and body temperature. These three areas should be evaluated with regard to presurgical baseline and response to surgical stimuli or intraoperative events.
Article
The laryngeal mask airway LMA-Classic has been used widely in clinical practice. A new disposable supraglottic airway device, the Soft Seal LM, has been introduced recently. In a randomized study, the authors compared the LMA-Classic and the disposable Soft Seal LM in terms of their clinical performance, cuff pressures during nitrous oxide anesthesia, position of the laryngeal mask in situ by fiberoptic evaluation, and morbidity in a wide range of routine general surgery procedures. A total of 200 adult patients were randomly assigned to a size 4 laryngeal mask in two equal-sized groups for airway management during surgery: (1) LMA-Classic (Intavent Orthofix Ltd., Maidenhead, Berkshire, United Kingdom); or (2) Soft Seal LM (Portex Ltd., Hythe, Kent, United Kingdom). Anesthesia was administered with fentanyl, propofol, nitrous oxide, oxygen, and sevoflurane. The variables studied were ease of insertion, fiberoptic view, time in situ, incidence of blood on the laryngeal mask at the time of removal, and the incidence of postoperative sore throat at 2 and 24 h. The laryngeal mask cuff pressures were measured continuously. Intracuff pressure limitation was not attempted. The LMA-Classic and the Soft Seal LM showed similar clinical performances, as shown by their insertion time (successful insertion at first attempt was achieved within 20 s in 97% with LMA-Classic trade mark vs. 95% with Soft Seal LM), fiberoptic evaluation of the anatomic position of the laryngeal mask, and satisfactory anesthesia conditions. Laryngeal mask cuff pressures increased from 45 to 100.3 mmHg in the LMA-Classic and from 45 to 46.8 mmHg in the Soft Seal LM (P < 0.001). Macroscopic blood was seen on only four occasions in the LMA-Classic group. The incidence of sore throat was significantly increased at 2 h postoperatively when using the LMA-Classic, although there was no difference at 24 h after surgery. In spontaneously breathing adult patients requiring a size 4 laryngeal mask airway, the new disposable Soft Seal LM device is an acceptable alternative to the reusable LMA-Classic trade mark, resulting in a good laryngeal seal and offering similar clinical performance. Cuff pressures increase substantially when the LMA-Classic is used but not when using the Soft Seal LM. There was less trauma to patients using the Soft Seal LM, as assessed by the incidence of sore throat in the early postoperative period.
Article
Endotracheal intubation may be difficult in rabbits and airway obstruction due to laryngospasm is common under these circumstances. This study compared the use of a laryngeal mask (LM) and endotracheal tube (ET) for administration of inhalation anaesthesia in rabbits under spontaneous ventilation.Eight female Norfolk rabbits (2.7 ± 0.4 kg) were anaesthetized twice, at least one week apart. Pre-anaesthetic medication was with methotrimeprazine (2 mg kg−1) IM. Thirty minutes later, anaesthesia was induced with thiopentone IV and 5 ml of radiographic contrast (barium sulphate) was introduced into the stomach via an intragastric tube. On one occasion, trachea were intubated blindly using a number 2 cuffed ET (4 mm external diameter) inflated to a pressure of 100 mm Hg. On another occasion, a number 1 LM was introduced blindly over the larynx and the cuff was inflated to a pressure of 60 mm Hg. Inflation pressures, based on a previous study in dogs, avoided leakage and local histological changes. The same inexperienced operator attempted to intubate all rabbits, after two attempts an experienced person intubated the animals. Anaesthesia was maintained for 60 minutes with FÉhal 1.4 V% in 100% O2 (400 mL kg−1min−1) using a Bain circuit. Heart rate, ECG, direct arterial blood pressure (auricular artery), arterial blood gases (pH, PaO2, PaCO2), arterial haemoglobin O2 saturation, respiratory rate, tidal and minute volume, F éCO2 and rectal temperature were measured every 15 minutes during inhalation anaesthesia. Cervical and thoracic radiographs were taken immediately after anaesthesia when the ET or LM had been removed, to investigate the occurrence of regurgitation and aspiration of the contrast. Data (expressed as mean ± SD) were analysed using anova for repeated measures followed by Dunnett’s t-test to investigate temporal differences within each group. Factorial anova followed by Fisher's test was used to compare differences between groups. Differences were considered significant when p < 0.05.A significantly higher dose of thiopentone was necessary to introduce the ET (36 mg kg−1) compared to the LM (24 mg kg−1). Trachea were successfully intubated (ET) in three out of eight animals at the first attempt and the LM successfully placed in eight out of eight animals. There were no significant differences between groups in any variable. The PaCO2 ranged from 4.6 ± 0.8 to 5.7 ± 1.2 kPa [35 ± 7 to 43 ± 9 mm Hg] (LM) and from 4.5 ± 0.6 to 5.6 ± 0.6 kPa [34 ± 5 to 42 ± 5 mm Hg] (ET) before and at 60 minutes during anaesthesia, respectively. The PaO2 ranged from 11.8 ± 1.6 to 44.6 ± 7.0 kPa [89 ± 12 to 335 ± 53] (LM) and from 10.5 ± 2.1 to 37.0 ± 11.3 kPa [79 ± 16 to 278 ± 85 mm Hg] (ET) at these times. Haemoglobin O2 saturation remained above 95%. No regurgitation was identified.An LM may be recommended as an airway for administration of inhalation anaesthesia in rabbits undergoing spontaneous respiration. When compared to endotracheal intubation, it was easier to introduce and a lower dose of the anaesthetic induction agent was required. Gas exchange was comparable with both methods and airways appeared to be properly maintained although regurgitation was not observed.Acknowledgements: FAPESP and Fundunesp for financial support.
Article
The purpose of this study was to find out if an LMA (#1 LMA-Classic) would provide a better airway than a face mask in spontaneously breathing anesthetized rabbits, and to test if it could be used for mechanically controlled ventilation. Sixteen rabbits (4.1 ± 0.8 kg, mean ± SD) were assigned randomly to three treatment groups; face mask with spontaneous ventilation (FM-SV; n = 5), LMA with spontaneous ventilation (LMA-SV; n = 5), and LMA with controlled ventilation (LMA-CV; n = 6). Rabbits were anesthetized in dorsal recumbency using a circle circuit at constant ET isoflurane (2.3%, Datex airway gas monitor) and constant rectal temperature (38.85 °C) for 2 hours. PaCO2, PaO2, minute volume, tidal volume (Wright's respirometer), and PeCO2 were measured at 15 minute intervals. Two individuals in the FM-SV group had PaCO2 >100 mm Hg (>13.3 kPa). One rabbit in the FM-SV had PaO2 <80 mm Hg (<10.7 kPa). All FM-SV rabbits showed signs of airway obstruction and two were withdrawn from the study at 45 and 90 minutes, respectively, because of cyanosis. Tidal volume could not be measured in the FM-SV group. No signs of airway obstructions were observed in either of the LMA groups. Four rabbits in the LMA-CV group developed gastric tympany, and one of these refluxed after 110 minutes. The significance of differences between the two spontaneously breathing groups and between the two LMA groups were measured using Wilcoxon's rank sum test (with significance assumed at p < 0.05). There were no statistical differences between FM-SV and LMA-SV in any variable tested. PaCO2 and Pe′CO2 were less in the LMA-CV group than in the LMA-SV group, while PaO2, tidal volume, and minute volume were all more. We conclude that biologically, the LMA provides a better airway than the face mask during spontaneous breathing and that it can be used for IPPV, but that gastric tympany is likely to occur during IPPV.
Article
Objective: To determine whether a laryngeal mask airway (LMA) provides a better airway than a facemask in spontaneously breathing anesthetized rabbits, and to test if it can be used for mechanically controlled ventilation. Study design: Randomized prospective experimental trial. Animals: Sixteen young, healthy, specific pathogen-free Giant Flemish cross Chinchilla rabbits (10 females and 6 males) weighing 4.1 +/- 0.8 kg. Methods: Rabbits were assigned randomly to one of three treatment groups: facemask with spontaneous ventilation (FM-SV; n = 5), LMA with spontaneous ventilation (LMA-SV; n = 5), and LMA with controlled ventilation (LMA-CV; n = 6). In dorsal recumbency, and at 2.3% end-tidal isoflurane concentration, Fé isoflurane, Fi isoflurane, partial pressure of expired isoflurane (PECO(2)), partial pressure of inspired carbon dioxide (PiCO(2)), heart rate, respiratory rate, minute volume, arterial oxygen tensions (PaO(2)), arterial carbon dioxide tensions (PaCO(2)), arterial pH (pH(a)), arterial standard base excess (SBE(a)) values were measured for 120 minutes. Results Two individuals in the FM-SV group had PaCO(2) > 100 mm Hg. One rabbit in the FM-SV had PaO(2) < 80 mm Hg. All FM-SV rabbits showed signs of airway obstruction, and two were withdrawn from the study at 45 and 90 minutes, respectively, because cyanosis was observed. No signs of airway obstruction were observed in either LMA group. Four rabbits in the LMA-CV group developed gastric tympanism, one of which refluxed gastric contents after 110 minutes. There were no differences between FM-SV and LMA-SV in any variable tested. PaCO(2) and PECO(2) were decreased, while PaO(2) and minute volume were increased in the LMA-CV group compared to the LMA-SV group. Conclusions: An LMA provided a better airway than a facemask during spontaneous breathing in rabbits, as the use of a facemask was associated with hypercapnia and low partial pressures of oxygen. Although an LMA can be used for intermittent positive pressure ventilation (IPPV), gastric tympanism may develop, especially at a peak inspiratory pressure of 14 cm H(2)O. Clinical relevance: The LMA can be used in rabbits but further work is needed before it is applied routinely.
The history of the invention and development of the Laryngeal Mask in the East End of London during the years 1981-88 is briefly described. The concept evolved from home-made prototypes built from the Goldman Dental Mask through a complex series of one-off latex models culminating in a primitive factory-made silicone cuff in 1986. This work defined the design parameters necessary to reconcile the needs for safety, reliability and ease of insertion while at the same time exploring the limits to possible use. In early 1988 the final version was tested by the inventor who had by this time used the device in more than 7500 patients undergoing routine surgery. From this experience a number of important lessons were learned relating to safe and effective use, which are summarized in the inventor's Instruction Manual. The importance of referring to this volume before use is stressed.
Article
After a short training programme 11 naval medical trainees inserted a laryngeal mask airway (LMA) and a tracheal tube (ETT) in random order in a total of 110 anaesthetised patients. They were allowed 40 s for each attempt. Success was defined as the detection of expired carbon dioxide within 40 s of Guedel airway removal which subsequently rose to an end-tidal value of at least 4 kPa, together with satisfactory lung expansion and ventilation, without other airway intervention by the anaesthetist. 104 LMA insertions were successful compared with 56 of ETTs (p less than 0.01). All first attempts at LMA insertion were successful, whereas satisfactory ETT placement was progressive. Insertion was also quicker with the LMA (20 s) than with the ETT (35 s) (p less than 0.01). Further studies are indicated to assess the value of the LMA in emergencies.
Article
The Laryngeal Mask Airway (LMA) is a new type of oropharyngeal airway that provides an alternative to endotracheal intubation and standard mask anaesthesia in certain cases. Once the patient is adequately anaesthetised, it can be inserted blindly, without recourse to laryngoscopy or muscle relaxants. Anaesthetists of all grades, given minimum instruction, were able to provide a clinically satisfactory airway in 49 out of 50 spontaneously breathing, anaesthetised patients. The advantages over standard mask anaesthesia are: better airway control, minimal leakage of anaesthetic gases, secure airway during transport to the recovery ward, and it frees the anaesthetist's hands, as no mandibular support is needed. Postoperative problems were minimal and 97.6% of our patients said that they would prefer a similar anaesthetic in future. LMA does not guarantee against the risk of aspiration and it is not recommended for use in patients who may have a full stomach.