With their continuously growing teeth, these pets present a particular challenge. They suffer from periodontal disease, malocclusions, and fractured teeth that can all result in the formation of abscesses. Here again, they do not behave as other mammals; their purulent secretions are caseous in nature and cannot be drained easily. They have to be treated as one would a tumour - surgically. Moreover, only a few systemic antibiotics are safe and efficacious. We will review ways of successfully dealing with dental abscesses.
Multiple protocols are in use for preanesthetics:
Medetomidine - 100 to 500 mcg/kg SC or IP
Midazolam - 1 to 2 mg/kg IM, IV, IP
Ketamine/medetomidine - 15 mg/kg + 0.25 mg/kg IM
Ketamine/midazolam - 15 mg/kg + 0.2 mg/kg IM
Ketamine/acepromazine - 10 mg/kg + 0.05 mg/kg IM. Premed with glycopyrrolate 0.1 mg/kg IM; SC is recommended with this drug combination
Domitor - 0.1 to 0.5 ml/kg IM, SC. Antisedan reversal 0.2 to 0.4 ml/kg IM
At present, we induce rabbit and guinea pig patients with a mixture of Dexdomitor (150 µg/kg) and ketamine (15 mg/kg), given subcutaneously. With chinchillas, we decrease the dosage of the mixture to Dexdomitor 100 µg/kg and ketamine 10 mg/kg. Wait 10 to 15 minutes or until the animal is unable to maintain its righting reflex. If the patient needs more injectable drugs during the procedure, we use ketamine (5 to 10 mg/kg) and Valium (0.2 mg/kg) intravenously. Once the patient has been sedated, an intravenous catheter is placed in an ear vein. The ear is taped to the contralateral one or to a syringe case to prevent its bending and resulting kinking of the catheter. The use of a small extension set connected to the catheter makes injecting more comfortable. The patient is then loaded with subcutaneous fluids (10 ml/kg).
If necessary, the patient is intubated or masked. The mask is placed over the nose while keeping the mouth accessible. As those patients are nose breathers, it is sufficient to maintain anesthesia. Intubation is reputed to be difficult, but with a bit of practice, it is actually not that hard. It is usually reserved for larger rabbits (> 2 kg).
It is also always prudent to have your emergency drugs ready:
Epinephrine - 0.1 mg/kg (1:1000 concentration)
Atropine - 0.1 to 0.2 mg/kg SC, IM, IV
Glycopyrrolate - 0.005 mg/kg IV, repeat in 2 to 5 minutes in necessary
Glycopyrrolate - 0.1 mg/kg SC
Lidocaine - 2 mg/kg IV (dilute 1:1 NaCl)
Dexamethasone - 1 to 2 mg/kg IV
Doxapram - 1 mg/kg IV
Furosemide - 2.2 mg/kg IV
Diphenhydramine - 1 to 2 mg/kg IV, IM, PO (Some rabbits produce anticholinesterase, which will break down atropine. Glycopyrrolate is the anticholinergic of choice.)
As far as equipment is concerned, one should have the following: surgical pack and drapes, surgical lights, surgical loupes, high-speed hand piece, burs (round #0 and #2, or pear shape #329 or #330), retractors. A laser scalpel is definitely helpful to control hemostasis. A radio-cautery unit can be used, but there is more risk of causing injuries to the soft tissues.
The area is shaved and surgically prepared. A cutaneous incision is made over the swelling and the edges are spread apart using a pair of Gelpi retractors or a ring retractor system (Lone Star Medical Products Inc.a). Bluntly dissect the abscess sac, trying not to rupture the membrane. The base of the sac is usually deep around the affected tooth. The dissection is time consuming and hazardous, as there are many vital structures in the immediate area of the surgery. Facial and mandibular veins and arteries run dangerously close. The author often uses a laser scalpel to maintain better homeostasis. Dental abscesses often require the extraction of the affected tooth/teeth below. They also require thorough cleaning of the infected area. Best is to try to remove the whole abscess "en bloc" to increase the chance of success. Unfortunately, in the large majority of cases the abscess wall ruptures during removal or the abscess is multichambered, and one has to deal with an infected site. Once the area is as clean as possible, marsupialize the opening by suturing the skin edges to the subcutaneous tissues below. A 5-0 poliglecaprone suture swaged on a fine reverse cutting needle is perfect for the job (Ethicon,b Monocryl). Then it is time to select the antibiotic. Pack the antibiotic into the defect right up to the opening and allow the patient to recover.
Only a few systemic antibiotics are safe: chloramphenicol and enrofloxacin, but unfortunately their spectrum is not adequate. Recently the use of injectable penicillin G benzathine (Bicillin®, Duplocillin®) has shown promise, but it is not enough to cure the infection alone. It is sent home as subcutaneous injections of 75,000 U every 48 h for patients less than 2 kilos and 150,000 U every 48 h for patients more than 2 kilos of body weight. When confronted with cases of severe infection, the injections can be given at 24-hour intervals. The patients are usually sent home with 7 to 14 injections. The main goal of the procedure remains the cleaning and sterilizing of the locally infected area.
Abscesses carry a guarded prognosis in some reports, but the author thinks that the chance of cure can be improved by being more surgically aggressive and by packing antibiotics directly into the affected sites. The goal is to first thoroughly debride the infected area and then to maintain a constantly high level of antibiotics at the local level. Debridement consists of flushing the area with saline solution and cutting out diseased tissues. There is now a laser activated free radical releasing solution that can greatly help in the sterilization of the surgical site. An infected cavity is filled with the free radical holding solution, died blue for easy visualization. A laser rod is introduced in the cavity and activated. The wavelength of the laser light stimulates the release of free radicals; they in turn damage the cell walls of bacteria, viruses, protozoa, etc. After a full minute of stimulation, the illuminated area is now sterile. The advantages are many: no resistance, nothing for the client to do, you control the treatment, minimal chance of allergic reactions, ease and speed of treatment. Two disadvantages: 1) Cost of laser; if the light does not penetrate to an area, the area does get sterilized; 2) The product is new, but no longer experimental on the human side; it is therefore still not easily obtained and is expensive. Various products have been used to maintain a high level of antibiotics locally; a partial list is as follows: tetracycline slurry, clindamycin slurry, doxycycline-soaked gauze, Doxirobe®, Ca(OH)2 slurry, or amikacin/ gentamycin/tobramycin impregnated beads. The results vary from one author to the next; each has its favorite product.
The crucial point remains surgical intervention. Anesthesia is most often the limiting factor. Better anesthesia increases safety to the patient and allows more thorough surgical debridement. This results in a successful outcome rather than a failure. Thus, anesthesia becomes the first area that the practitioner should concentrate on when dealing with rodents and lagomorphs. We start with IM sedation in order to place an IV catheter. Ear veins are not that hard to catheterize with a little patience. Even in a chinchilla, one can pluck hair and access the saphenous vein. Obtain 24-ga and 26-ga catheters to make your life easier. Connect the catheter to an extension line and tape the apparatus to the ear using a syringe casing as a stent to keep the ear from bending. Place the syringe casing inside the ear pinna and wrap the ear and the catheter around the casing. Hold the line in place with some white tape. The IV line allows you to use injectable drugs to maintain and to modify anesthesia, rather than just inhalants. We can then inject small doses of ketamine hydrochloride when a painful procedure is being done. Its action is immediate and more important than most believe. Warm up the fluids to prevent severe cooling of the patients. These patients are also prone to hypoglycemia, and it is prudent to obtain a blood glucose level at the beginning of the procedure to monitor their levels.
Inhalants are administered through intranasal tubes or via a small mask, placed on the nose. Both rodents and lagomorphs are nose breathers; thus the mouth does need to be covered during surgery. It is a blessing, as the surgical area is small enough as it is and would be totally unmanageable with an endotracheal tube added to it. Keep the patient warm without covering the body so that monitoring of respiration is still possible. You can use heat disc, bean bags, circulating water blankets, bubble bags, etc. Next, one needs good lights and magnification. Surgical loupes are a must. Finally, a set of rodent dental instruments are necessary.
Now to come back to the surgery: make the initial incision wide enough, dissect bluntly and try to get the abscess lining intact. If the abscess ruptures, flush copiously. Debride thoroughly, pack your antibiotics in the defect and leave it open. Recommend to the owner to clean the incision daily and to make sure it stays open. I send them home on injections of Duplocillin® (Bicillin®) q24h to q48h for 2 to 4 weeks. Analgesia is also very important; we use a variety of products depending on the patient and on the procedure (buprenorphine, meloxicam, codeine, meperidine). If the pain is controlled, return to self-feeding is rapid and easy. A recheck is set at 10 to 14 days to change the dressing. In most of the cases a superficial necrosis is present once the product has been removed. The devitalized tissue needs to be removed. Ensure that only healthy tissue is left. Replace the dressing. I usually alternate between 2 or 3 different antibiotics. Send the patient home with the same recommendations for another 2 weeks. Most cases require two dressing changes before the area is healthy and clean enough to let it granulate by secondary intention. The second biggest mistake, after not being aggressive enough during the surgery, is trying to close the incision too early. Do not rush; the patients do very well with open wounds for 6 to 8 weeks. If teeth were involved, obtain more X-rays at recheck time to ascertain that they are not regrowing abnormally. When you think the cure is complete, set up a recheck visit for 6 to 8 weeks later to verify that there is no recurrence.
a. Lone Star Medical Products Inc.; 11211 Cash Rd.; Stafford, TX, USA 77477.
b. Ethicon, Johnson & Johnson Co.; Guaynabo, Puerto Rico, 00969.
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