Endoscopy has been under-utilized in rabbits for many years, despite their popularity as pets.
Recently, the usefulness of endoscopy has been recognized and a variety of papers concerning the applications of clinical endoscopy in the companion rabbit can be found.
Patient evaluation
Endoscopic procedures are usually performed under general anaesthesia, so careful attention to the clinical condition of the patient before perform-ing anaesthesia is important. Stabilization may be necessary. Pre-anaesthetic assessment is des-cribed in Chapter 1. Given that rabbits hide signs of disease, a clinical profile, including complete blood count and routine urinalysis, may be useful to high-light possible metabolic problems. A chest radio-graph may help to exclude subclinical cardiac or respiratory problems. Careful examination of the skull, including different radiographic views, is man-datory when endoscopic procedures are intended for exploration of the nose, mouth, throat or ear.
Anaesthetic considerations
Anaesthetic protocols for endoscopy are related to the nature of the disease that is under investigation, as well as to the clinical condition of the patient. In most cases, premedication with a benzodiazepine combined with an opioid is indicated, followed by induction with ketamine and medetomidine or with sevoflurane delivered by facemask.
When the patient is in an optimal state of relax-ation, intubation can be performed and an appropri-ate plane of anaesthesia can be maintained using isoflurane in oxygen. Tracheal intubation should be performed for surgery and invasive procedures.
A nasal mask may be sufficient for faster or less invasive procedures.
Instillation of lidocaine into the nasal cavity is helpful to reduce sensitivity during rhinoscopy.
Some authors (Divers, 2010b) suggest the use of neuromuscular blockers (e.g. atracurine) that inhibit reflex movements. The use of these agents means that lower concentrations of inhalational anaesthet-ics are required, but careful monitoring and ventila-tion are necessary (see Chapter 1).
Equipment
Most endoscopic procedures can be performed with a basic set of instruments, a good source of light, a camera, a monitor and a rigid endoscope.
Rigid endoscopes
The most useful rigid endoscope is 2.7 mm × 18 cm with a 30 degree oblique view. This allows investiga-tion of several organ systems and the body cavities of most companion rabbits, and a wide variety of tools can be used through its service channel. With its sheath, the diameter of a 2.7 mm endoscope increases to 4.8 mm, and this can be a problem with investigation of delicate structures in small rabbits, especially the nasal cavities. For this indication a 1.9 mm endoscope with a sheath built to give a total diameter of 3.3 mm is more appropriate for rabbits that weigh <1 kg, but this has the disadvantage of only being able to work with a reduced range of dedicated tools.
Flexible endoscopes
A 3 mm fibreoptic endoscope is appropriate for the majority of flexible endoscopic procedures in the rab-bit. The most frequently used ancillary instruments are i ps rceps and cr c dile teet ’ rceps e applications of flexible endoscopy in rabbits are limited, partly because of their small size and partly because the primary indication for flexible endos-copy is gastrosendos-copy and duodenosendos-copy in carni-vores. These procedures are severely limited in rabbits because their stomach is never empty. There are descriptions of flexible tracheobronchoscopy procedures in rabbits and the endoscopic anatomy of the respiratory system has also been published, but such applications in daily practice are very rare.
Light sources
The endoscope is connected via a fibreoptic cable to a light source. A xenon source is recommended for its bright and intense light, even though cheaper halo-gen light sources may also provide acceptable results for most simple procedures and in animals <2 kg.
Cameras and monitors
Direct observation through the eyepiece of the lens is acceptable for short procedures and manipulation is easy, but the position does not allow the freedom of movement that is needed for minimally invasive
surgery. The use of a camera and a monitor is considered essential for the surgical procedures described in this chapter, and optional for diagnostic procedures such as rhinoscopy or tracheoscopy. An additional advantage of video equipment is the ability to collect and store images, which are useful both for teaching and for communication with the owner.
Carbon dioxide
Insufflation is beneficial for the visualization of many structures through an endoscope. Laparoscopic pro-cedures require CO2 insufflation. A special (dedi-cated) pump can be used but compressed ambient air insufflated with an aquarium pump or a syringe is acceptable, although there is a small risk of introduc-ing air. The gas is introduced through the valves of the operating sheath, and it is also possible to use this channel to introduce irrigation fluids, such as saline, to dilate orifices such as the nasal conchae or urethra.
Ancillary instruments
In order to work on the structures that can be visual-ized with endoscopy, it is necessary to use instru-ments that can pass through the operating sheath.
The most frequently used devices in rabbit medicine are biopsy forceps and grasping forceps, which are useful for debridement and/or to retrieve foreign bodies from ears and nostrils. A flexible needle is useful to aspirate the contents of cystic structures and/or to irrigate cavities that are hard to reach.
Operator positioning
The best position in which to use the endoscope is determined, within certain limits, by the individual operator, who will develop working practices in accordance with his/her individual abilities and pref-erences. Secure control over the endoscope is essential because the equipment is expensive and fragile. Flexion of the endoscope easily breaks the cylindrical lenses inside the device.
In order to perform endoscopy, it is necessary to master the technique of maintaining the rigid endo-scope with a single hand. For a right-handed opera-tor the left hand holds the lens, placing it between the extended thumb and palm, and wrapping it with the other fingers; the right hand remains free to use the ancillary tools. At first, it may be useful to have the help of a second person, but to be efficient it is necessary to learn to do it alone. It should be stressed that even the most modern cameras have most of their weight at the upper end of the endo-scope, so it is necessary to hold the equipment in two places. The camera is held with the whole hand, with the thumb and forefinger at the point of entry into the body of the patient.
Direct observation through the eyepiece of the lens can be used for fast procedures but does not allow a suitable ergonomic position to be maintained during prolonged observation. A camera and a moni-tor are necessary. It is essential that the monimoni-tor is directl in r nt t e perat r’s e es and ideall the endoscope should be directed toward the
monitor itself. This simple practice can help to maintain an ergonomic position and facilitates rapid mental association between hand movements and images on the monitor.
For minimally invasive surgery, when several sites of access on both sides of the patient are needed, the use of two monitors is preferred.
Alternatively, an assistant can be instructed to move the monitor when the surgeon changes position, but effective collaboration of the surgical assistant with the procedure is then compromised.
Patient positioning
The rabbit can be placed in dorsal, sternal or lateral recumbency, according to the procedure that is to be performed. It is helpful to have the ability to tilt t e patient’s ead p ards in rder t ain d access to the liver during laparoscopy, or down-wards to improve access to the caudal organs such as the bladder or intra-abdominal testes, or to facili-tate the flow of irrigation fluid during rhinoscopy.
Endoscopic examination of the ear The prevalence of subclinical otitis in rabbits, espe-cially in lop-eared breeds (see Chapter 16), war-rants special attention to endoscopy of the ear. It is always better to sedate the rabbit, in order to avoid sudden movements that may cause damage to the ear canal or the instrument. The patient may be maintained in sternal or lateral recumbency. The normal ear canal contains wax. Often there is a mild degree of inflammation, which produces a large amount of debris, so mechanical cleaning is required before introducing the endoscope.
Irrigation with sterile saline is preferred because this will allow sample collection for bacteriology.
The endoscope is inserted along the length of the ear canal down to the eardrum; the examination may reveal generalized or localized inflammation (Figure 10.1), foreign bodies, mites or tumours. If the tympanic membrane is ruptured or perforated by infection, syringotomy to collect material for analy-sis, and to decrease pressure and relieve clinical signs, may be helpful.
An endoscopic view of an inflamed ear canal containing a wa plug and pus.
10.1
Endoscopic evaluation of the pharynx and larynx
The larynx in rabbits is covered by the soft palate, which needs to be lifted in order to visualize the glottis, to insert an endotracheal tube or to obtain a tracheal swab sample. Foreign bodies may be visualized in the larynx.
Endoscope-guided endotracheal intubation
Unlike in dogs, cats and ferrets, in rabbits it is not possible to visualize the glottis directly simply by opening the mouth; endotracheal intubation is t ere re re di ic lt lt lind’ int ati n is possible, endoscopy-guided intubation is faster and safer. A small-gauge paediatric laryngoscope that is slightly curved is particularly useful because it provides a route for an oxygen supply, which reduces the risks associated with the procedure. It is recommended that lidocaine gel be applied to the endotracheal tube prior to intubation to reduce the risk of laryngeal spasm.
Alternatively, a 2.7 mm 0 degree straight probe may be employed, either by inserting it inside the tube or by placing it adjacent to the tube. Inserting the endoscope into the tube is usually only possible in rabbits large enough to be intubated with 3 mm tubes, unless a 1.9 mm endoscope is available that can be used in smaller rabbits. It may be necessary to shorten the endotracheal tubes: their length should not be greater than that of the endoscope, otherwise steam or saliva can accumulate in the tip, obstructing vision.
To insert an endotracheal tube alongside an endoscope, the anaesthetized rabbit is placed in sternal recumbency with its head and neck raised and extended. The head is supported dorsally to avoid compression of the trachea. It may be convenient to place the animal on a mobile dental platform or to use a dental gag. The tongue is pulled out to aid progression of the endoscope through the oral cavity, following the median groove to maintain the correct direction. If the endoscope is oriented ventrally to the larynx, the larynx will be visible through the transparent soft palate. At this point, the tube is advanced to the side of the endoscope until it enters the visual field.
Progressing gently, the tip of the endoscope will lift the soft palate and release the larynx, so the tube can be inserted during inhalation (see Technique 1.2).
Proper placement of the tube is confirmed by direct observation, by the sight of vapour in the transparent t e r i t e sc pe in t e t e’
technique is used, by observation of the tracheal rings. The advantages of this technique are the ability to use endotracheal tubes of the widest calibre possible, the security of not introducing foreign material into the trachea and the ability to intubate a rabbit who is not breathing.
Rhinoscopy
Rhinitis is a common problem in rabbits, and has a varied and multifactorial aetiology. Treatment is often frustrating and an early aetiological diagnosis is important to guide appropriate therapy, otherwise the problem tends to become chronic. Rhinoscopy is an invaluable aid in making a diagnosis: it permits irriga-tion of the nasal cavities, which removes excess secretions; it is used to detect infection or neoplasia and to collect biopsy samples for bacteriology, cyto-logy and histopathocyto-logy; and can aid removal of foreign bodies. Some endoscopic views of the nose, throat, mouth and trachea are shown in Figure 10.2.
(a) Endoscopic views of the nose. (continues) 10.2
Pus in nasal conchae
Pus in nasal conchae
Pus and granuloma in nasal conchae
opening the mouth; endotracheal intubation is t ere re re di ic lt lt lind’ int ati n is possible, endoscopy-guided intubation is faster and safer. A small-gauge paediatric laryngoscope that is slightly curved is particularly useful because it provides a route for an oxygen supply, which reduces the risks associated with the procedure. It is recommended that lidocaine gel be applied to the endotracheal tube prior to intubation to reduce the Alternatively, a 2.7 mm 0 degree straight probe may be employed, either by inserting it inside the tube or by placing it adjacent to the tube. Inserting
(a)
Given that the nasal mucous membranes are very sensitive, a deep plane of anaesthesia is required as well as local analgesia, such as a lido-caine spray. The intubated animal is placed in ster-nal recumbency with the head slightly lower than the body (10–20 degrees). As an uncuffed endotracheal tube is normally used, it is important to fill the mouth with soft gauze to absorb any liquid and prevent its inhalation. Placing a towel under the animal is also useful, because of the extensive irrigation that is required for this examination.
In rabbits <2 kg, a 2.7 mm endoscope with its sheath is too large to reach the deep nasal cavity. A 1.9 mm endoscope with a built-in sheath is prefer-able. Alternatively, a 2.7 mm endoscope can be used without the sheath, irrigating the nasal pas-sages using a syringe intermittently, but the results are much less satisfactory.
After introduction of the endoscope, the lens is guided gently through the nasal passages (Figure 10.3). The endoscope needs to be placed medially (continued) (b) Endoscopic views of the throat.
(continues) 10.2
Catheter for tracheal wash Taking swab from trachea Entrance to larynx Tonsil
(b)
(continued) (c) Endoscopic views of the trachea.
10.2
Normal trachea
Pus in trachea (c)
Tooth fragment in the ma illary sinus. The sinuses can be e plored endoscopically after trephining a hole through the bone.
10.4
There are three meatuses in the nasal cavity dorsal middle and ventral. The endoscope needs to be directed into the middle meatus because the dorsal and ventral meatuses are blind ended. n order to e plore the delicate nose of smaller rabbits a fi ne scope . mm with built in sheath is advisable. Some bleeding is to be e pected.
oreign bodies chronic infections and complications from odontogenic abscesses are common fi ndings in this region.
10.3
because the mucosa of the turbinates is fragile, especially if inflamed, and may bleed profusely. It is almost impossible not to cause minor bleeding, even if the procedure is conducted carefully.
It is also possible to access the nasal cavity and paranasal sinuses by rhinotomy or facial osteotomy to explore the cavity before a major surgical pro cedure (Figure 10.4). This application can be particularly useful in cases of odonto -genic abscesses involving the nasal region (Divers, 2010c).
Tracheoscopy. sing a rigid endoscope of appropriate si e with some care and attention the rabbit trachea can be e plored down to the bronchial bifurcation. The normal tracheal mucosa is a bright red colour which can be confused with infl ammation.
Tracheal stenosis and obstruction cause severe respiratory distress and it is mandatory to provide e tra o ygen to the rabbit during the whole procedure.
Tracheobronchoscopy 10.5
This is one of the few applications for flexible endoscopy in the rabbit, although a rigid endo-scope will reach the tracheal bifurcation. For tracheobronchoscopy, the head and the neck must
be kept extended and aligned, to avoid any trauma to the sensitive tracheal mucosa. To avoid prob-lems with gas exchange, only small diameter endoscopes should be used and only for short periods of time, or oxygen can be introduced through the instrument channel of the endoscope (Figure 10.5).
Tracheobronchoscopy is useful for removing for-eign bodies and to obtain an aetiological diagnosis in cases of severe respiratory disease. Chronic inflammatory processes may be caused by mucosal injury and complicated by tracheal stenosis followed by severe respiratory failure.
n male and female rabbits the urethra is very elastic and easily allows the passage of the endoscope. This may be the only way to retrieve stones lodged in the pelvic stretch of the urethra. iopsy samples of bladder mucosa can be taken in a relatively non invasive way.
10.7
arcinoma in left cervi
pening of right cervi
ass in right cervi
ass in right cervi
(a) ndoscopic views of the cervi . continues
10.8
Vaginoscopy, urethroscopy and cystoscopy
Haematuria is a frequent clinical sign in rabbits and, although other diagnostic imaging techniques (radio-logy, ultrasonography) are commonly used to deter-mine the cause, endoscopy is a valid aid for ex amination of the vagina (Figure 10.6), urethra (Figure 10.7), bladder and cervix. With a rigid endoscope, it is possible to manipulate urethral stones that would otherwise be unreachable because, for example, they are in the pelvic stretch of the urethra. Endoscopy can also be used to take biopsy samples and remove small papillomas. The patient is usually positioned in dorsal recumbency with the perineum at the edge of the table. Dilation of the urethra is facilitated by irrigation with warm saline. Some endoscopic views of the urogenital tract are shown in Figure 10.8.
ndoscopic e amination of the vagina is straightforward. The openings of the urethra separate the vaginal vestibulum and the long soft uterine vagina. n this image a mass can be seen in the vaginal wall. Although ultrasonography is more frequently used to diagnose uterine diseases in does hysteroscopy allows the surgeon to obtain biopsy samples of pathological tissue before surgery and to obtain a more precise prognosis.
10.6
(a)
Endoscopy of the digestive tract Although this is the most commonly used endo-scopic technique in domestic carnivores, in rabbits gastroscopy is almost impossible because the stom-ach is never empty. It is possible to use the endo-scope for colonoscopy and rectoscopy (see Figure 10.8b) and, in cases of papillomatosis, endoscopy can be used to rule out the presence of papillomas in areas not visible following simple protrusion of the rectal mucosa (Figure 10.9).
ectal papillomatosis is quite common in rabbits and colonoscopy can help to locate masses not immediately evident on simple evagination of rectal mucosa. These masses can be e cised using traditional surgery cryosurgery or surgical laser see
hapter . 10.9
(b) continued ndoscopic views of the bladder and rectum.
10.8
ladder wall
Sediment in urine
aecal pellet in rectum (b)
Laparoscopy
Laparoscopic investigation (see also Chapter 13) and minimally invasive abdominal surgery are in their early days in the rabbit, but several authors have emphasized the advantages in terms of reduced tissue trauma, less pain and faster postoperative recovery. However, the owner must be informed that, in the case of complications, access by trad itional open surgery may still be necessary.
Laparoscopic procedures in rabbits include ova-riectomy (Divers, 2010a), liver and kidney biopsy, and endoscope-assisted cystotomy for removal of small uroliths. Laparoscopy requires additional care when compared with endoscopic examination of natural orifices. A pneumoperitoneum must be gen-erated to visualize the abdominal organs and to move among them. This is usually achieved by insufflation with carbon dioxide, which is consid-ered safer than ambient air because there is less risk of embolization or combustion if electrocautery is used. Creating a pneumoperitoneum increases the pressure in the abdominal compartment and hinders diaphragmatic excursion so it is essential to work only with intubated rabbits receiving mechan-ical ventilation. The increased intra-abdominal pres-sure also alters haemodynamics as a result of compression of the aorta and the vena cava.
Although this problem is marginal in large rabbits, in patients <5 kg it is recommended not to exceed an intra-abdominal pressure of 8 mmHg.
For most procedures, the patient is placed in dorsal recumbency. The fur is shaved and the skin prepared as for conventional surgery. Insufflation of gas takes place through a special cannula with a trocar (Veress needle) that is inserted in the caudal midline. It is advisable to ensure that the rabbit has an empty bladder because it is possible to traumatize viscera with the Veress needle.
Other causes of organomegaly (gastric dilatation, pregnancy, pyometra, abscess, neoplasm) should