SURGICAL SOLUTIONS FOR GERBILS: ANALGESIA AND ANAESTHESIA IDEAS

Blood sampling is not easy and if blood is obtained, it is usually in very small amounts, such as 0.7ml to 1.0ml.

Radiographs provide a limited amount of information about abdominal organs. Ultrasound is used more frequently, and it may be possible to make some interesting diagnoses.

In this article, I will focus on anaesthesia, analgesia and common surgical procedures.

It is essential to weigh patients accurately to calculate the correct dose of medication. Gram scales that measure up to 1.0g are essential. They are also useful to monitor responses to treatment, or to detect the onset of a disease process if weight loss has occurred. They can be obtained for less than £20.

Vacutainers are useful for diluting drugs to a lower concentration, such as 0.1ml ketofen one per cent plus 0.9ml water will provide a concentration of 0.1 per cent. Always discuss product dilution with drug companies before diluting their products, to confirm what you should dilute with and how long it remains stable.

Dropper bottles contain 0.05ml in each drop and, therefore, substances can be diluted so that one drop is given each time a dose is needed. For example – dosing a 125g gerbil with fluoroquinolone at 10mg/kg:

• 125/1,000 = 0.125kg × 10mg = total dose of 1.25mg required.

• 1.25 divided by 25 = 0.05ml = one drop.

Therefore, if the patient weighs 62g, it would need 0.025ml; in effect, half a drop. Therefore, dilute 50: 50 with water and provide one drop.

Antibiotics to avoid, especially by oral route, include:

• penicillin;

• lincomycin;

• ampicillin;

• amoxicillin;

• clindamycin;

• cephalosporin; and

• erythromycin.

Anaesthesia

Anaesthesia for gerbils is no longer as risky as it used to be, and it is extremely rare to lose a patient under anaesthesia.

A number of actions can decrease the risks associated with anaesthesia. These include keeping the patient warm, pre-oxygenating it, providing subcutaneous fluids and ensuring adequate analgesia. Limiting blood loss is another important factor.

So, how do we achieve all this? We use small portions of plastic air-bubble packaging or recovery blankets, and wrap as much of the animal’s body as possible to prevent heat loss. Special attention is paid to the feet. Heat mats may also be used. Warm fluids are injected subcutaneously. This is obviously not as good as intravenous fluids, but it will be beneficial.

I like to give analgesia as soon as possible. This can either be done a few hours pre-operatively or at the time of induction. NSAIDs and/or opioids may be administered, depending on how painful the procedure is likely to be. It is essential to weigh patients prior to administering either opioids or NSAIDs.

Induction using isoflurane in oxygen can take place in a custom-made induction chamber or in an inverted large dog mask. This requires a smaller amount of gas and allows rapid induction.

A smaller mask or blue connector is then used to maintain anaesthesia. This method can be problematic if the surgical procedure involves the head. Options are to either use injectable combinations of drugs, or to constantly remove and replace the mask. I prefer the latter method, as the patient can be woken more quickly after the surgical procedure. See the Formulary panel for doses of injectable anaesthetic combinations.

Blood loss can be minimised by careful surgical technique and the use of electrocautery or radiosurgery. About one per cent of the bodyweight can be safely lost as blood. We use sterile cotton buds as swabs, and these can be weighed during or after surgery to get some idea of the amount of blood loss.

Surgical procedures

We perform four surgical procedures on gerbils fairly regularly. It is useful to be familiar with them.

• Tail slip and tail amputation. If gerbils are picked up by the tip of their tails, there is a real risk of the skin slipping off, leaving the raw, exposed tissue underneath. If left untreated, this will eventually become necrotic and slough off.

Presumably, this is an evolutionary adaptation as a prey species. If this occurs, it is preferable to amputate the tail at the point where the skin has been broken. I try to leave the skin a little longer at the ventral surface and fold it up so the suture line is not dragged along the ground. Bone cutters or scissors can be used to transect the tail.

Any bleeding should be cauterised to limit blood loss. I prefer using fine sutures in the order of 5/0 or 6/0.

Analgesia and antibiotic cover should be provided.

• Scent gland infection/neoplasia. The ventral scent gland is more prominent in males than females, and is androgendependent. It would be wise to familiarise yourself with the normal appearance of the gland to make it easier to discern when a gland is exhibiting pathology. Infections with Staphylococcus and Streptococcus are common, and will usually respond to topical and/or systemic antibiotics.

A one per cent chlorhexidine solution can be used, and topical fusidic acid may be effective. If the infection does not resolve, or some other inflammatory or neoplastic condition is suspected, excision is indicated.

A simple incision is made around the gland. The gland is then elevated and can be quite easily dissected free of the subcutaneous tissue. Take care not to lacerate the abdominal wall, as the tissue is very thin and delicate. Intradermal sutures of 5/0 are placed to prevent mutilation of the wound.

Tumours of the scent gland include adenomas, adenocarcinomas, squamous cell carcinomas and basal cell carcinomas.

• Cystic ovaries/ovarian neoplasia. Abdominal distension should make the clinician suspicious of ovarian disease. Cystic ovaries are the most commonly encountered disorder, but neoplasia may also occur. The symptoms are usually quite dramatic, with a bilaterally distended abdomen that often compromises breathing. Radiography and ultrasonography may provide additional information.

Aspirating the mass may confirm the presence of fluid and may improve the patient’s respiratory ability prior to surgery. Ideally, these cases should be taken to surgery for a routine ovariohysterectomy. It is helpful to drain the cysts once the abdomen has been opened, as this makes exteriorisation and removal of the ovaries a lot easier. I usually excise the scent gland at the same time, as it eases skin suturing afterwards.

I once removed a granulosa cell ovarian tumour from one gerbil and, the following day, removed one from its sister, which would implicate a genetic basis for these tumours.

• Aural masses. Masses on the vertical ear canal can include polyps, papillomas, melanomas and cholesteatomas (cholesteatomas occurred in nearly seven per cent of gerbils in one study; they are only found in humans and gerbils). Any mass in the ear canal tends to cause a lot of irritation, and may lead to bleeding or infection. Under isoflurane anaesthesia, it is usually possible to visualise a mass using an auroscope.

A lateral wall resection can be quite easily performed, resulting in the removal of the irritating mass. I use 5/0 fine sutures, which alleviate the need for suture removal at a later date.

Summary

All the above procedures are well within the capabilities of any vet with basic surgical skills. Small instruments, good lighting, a steady hand and some common sense are all that are required.

Further reading

• Longley L (2009). Rodents: dermatoses. In: Keeble E and Meredith A (eds). BSAVA Manual of Rodents and Ferrets, Wiley-Blackwell.
• Bennett R A (2009). Rodents: soft tissue surgery. In: Keeble E and Meredith A (eds). BSAVA Manual of Rodents and Ferrets, Wiley-Blackwell.
• Meredith A (2006). Skin diseases and treatment of gerbils. In Paterson S (ed), Skin Diseases of Exotic Pets, Blackwell.
• Greenacre C B (2004). Spontaneous tumours of small mammals, Veterinary Clinics of North America: Exotic Animal Practice 7(3): 627-651.
• Keeble E (2002) Gerbils. In: Meredith A and Redrobe S (eds), BSAVA Manual of Exotic Pets (4th edn), BSAVA.
• Donnelly T M. Disease problems of small rodents. In Queensberry K E and Carpenter J W (eds), Ferrets, Rabbits and Rodents: Clinical Medicine and Surgery (2nd edn), Saunders.
• Carpenter J W (2005). Exotic Animal Formulary (3rd edn), Elsevier Saunders.