Ferret anesthesia and analgesia (Proceedings)

Introduction

The ferrets are mammals in the Mustelid family. There are three species of them. Research is showing that pet ferrets are increasing every year. This means that more and more of them will be presented for medical care just as other domestic species. Managing the anesthetic period (including pain evaluation) should be just as it would in any other small animal.

Physiologic Terminology

An Intact Male is a Hob (1-2 kg). An intact Female- Jill (0.6-1 kg) A spayed female is a Sprite. A castrated male is a Gib. When a ferret is < 1yr old, we called these little ones, Kits. Males will be twice as big as females if allowed to reach maturity. This makes them more powerful and can defend the next better. The females stay small to be able to stay close to the nest and also be able to reserve food requirements for her kits. A group of Ferrets is known as a "Business". Their body is long and tubular and the spine is flexible. This allows them the mobility to move around into small areas, thus the reason for great hunting. They have short legs but long claws which makes them great at digging. They have seasonal wt change. They lose weight in the summer and gain it back in the winter. (up to 40% in intact Ferrets).

Breeding

Females will molt their coat after ovulation and if not bred, this coat may not come back in full. There could be patched of alopecia. They are induced ovulators and will ovulate 30-40 hrs post-copulation. If a Jill is not bred, she will have a pseudopregnancy and this can cause a hyperestrogenism.

Physiologic Terminology (normals)

Life span- 5-11 yrs, Sexually mature- 6-12 months, Gestation- 41-43 days, Litter size 1-18 kits (average 8), Wt at birth 6-12 g, Body temperature (100-104), HR-200-400, RR- 33-36, blood volume 60ml/kg

Ferret Dangers

There are a number of dangers that play a role in the life of a ferret. Special precautions must be taken to avoid this. Advise owner's to keep their ferret's habitat a safe one.

Restraint

Most ferrets are gentle enough and can be examined with a small amount of restraint. AS with dogs and cats, the more a ferret is handled in the home, the easier it will be to work on them. They bite more if not handled frequently. You can scruff the back of their neck while dangling the animal in the air, which is better for the more fractious ferret. You can securely hold them down on the exam table similar to a nice cat for a non-invasive examination. Remember not to coax a ferret with food if taking a blood glucose sample as this may alter your results. You can also use a Plexiglas tube and slide them down with the body part out that you want to examine.

Health Concerns

Ferrets hide sickness and pain. They are not a dog and make you feel sorry for them when they do not feel good. They may hide a lot or stop eating. Their eyes may appear half closed. The owner may notice that their grooming behavior has changed. Also, they may be quieter than usual or do not want to interact with you. They have a high metabolism therefore cancer and other disease can progress quickly. Neutering of male & female is recommended at maturity. Intact females can die of aplastic anemia (if not bred) due to this massive hyperestrogenism. Males are stinky. They can be descented at 5-6 weeks or. Neutering does help with this or you can bathe them frequently.

Common Anesthetic Procedures

Common procedures include ovariohysterectomy, castration, removal of pancreatic insulinoma. Ferrets can acquire lymphoma or adrenal disease (hyperplasia or cancer). Treatment may include surgery. They might have anal glands excised or melatonin implants placed. They chew on things so a laporotomy may be necessary to retrieve foreign bodies. Trauma is also common with all the dangers posed to ferrets as well as localized abscesses.

Preanesthetic Evaluation and Physical Exam

You should familiarize yourself with normal values of ferrets. Observe for attitude and alertness. Take weight with a gram scale to be more accurate.When evaluating hydration status (like a cat and dog) –mucous membranes, capillary refill time and skin turgor. Palpate abdomen gently for foreign bodies or abnormally sized organs. If the patient has been demonstrating bruxism (grinding of teeth), this can indicate a problem with the gastrointestinal tract. Heart and lung auscultation should be monitored for abnormal sounds. It is common to see a sinus arrhythmia. (Use a pediatric stethoscope). Assess nares and upper respiratory tract for noise or abnormalities.

Diagnostics

Minimal Diagnostics should include packed cell volume, total plasma protein, glucose, blood urea nitrogen and urine specific gravity. You will not need to obtain much blood for these tests. This is important as large samples may be difficult to obtain. If there is indication of disease, a full chemistry profile as well as a complete blood count should be performed as well as any other diagnostic needed such as ultrasound. Venipuncture can be performed through the jugular or anterior vena cava vein or the cephalic for small quantities.

Fasting

Fasting has not been shown to be beneficial on ferrets. They can still regurgitate even when fasted. Since hypoglycemia is an issue with Ferrets, try to minimize the fasting period to 1-4 hours prior to the induction period.

Stabilization

Try to correct any dehydration, hypoglycemia, anemia, electrolyte and or acid-base disturbance prior to anesthesia. Crystalloids and colloids are used frequently. If PCV is less than 25%, a whole blood transfusion may be required prior to surgery to aid in oxygen carrying capacity. A large healthy male ferret makes a good donor. You can take 6-12ml from the donor and add 1ml of an anticoagulant for every 6ml of whole blood. Oxyglobin, which is an oxygen carrying, hemoglobin based solution, has been used on Ferrets at 11-15mg/kg, once to twice daily. Each treatment is administed over 4 hours.

Prenanesthetic Evaluation

Failing to plan is planning to fail so work up your patient prior to anesthesia. Develop your anesthesia & analgesia protocol for a ferret and consider species differences, physiology as well as pathophysiology, behavior, procedure as well as complications anticipated from the procedure. Ferrets commonly acquire Insulinomas therefore expect hypoglycemia and take precautions to avoid this. Also, evaluate your diagnostics for abnormalities that will help you stabilize your patient or help chose appropriate drug protocol. Chose drugs based on all of this information.

Premedication

Premedication is advised just as any other species. This is to eliminate stress and anxiety, reduce the amount of drugs required for induction, maintenance and recovery. Pain management is essential. Preemptive analgesia should be considered as well and symptoms of pain and discomfort should be evaluated before the procedure all the way through recovery and into the post-operative period (multiple days after surgery).

Anesthetic Drugs

Consider sedation, tranquilization, muscle relation and analgesia. Some use anticholinergics to support bradycardia such as Glycopyrrolate 0.01mg/kg SC/IM. Keep in mind, there are indications where a lower dose may be necessary such as a sick ferret. Also, become familiar with pharmacology of these drugs before you administer them.

Sedation and muscle relaxation

Acepromazine 0.1- 0.3mg/ kg,

Diazepam 0.5-2 mg/kg

Midazolam 0.5-2 mg/kg

Medetomidine 0.08-0.2mg/kg (For intubation, add Ketamine 5-8 mg/kg)

Ketamine 5-15mg/kg (should be used w/ muscle relaxant)

Atipamazole (reversal of Medetomidine)

Analgesia

An opioid and or non-steroidal anti-inflammatory agent can be used. Local anesthesia can be performed. Ideally, analgesia should be on board prior to noxious stimulus.

Buprenorphine 0.01-0.03 mg/kg IM/SC

Butorphanol 0.1-0.5mg/kg IM/SC

Morphine 0.5mg/kg IM/SC

Hydromorphone 0.1-0.2mg/kg IM/SC

Meloxicam 0.2mg/kg SQ (can be administered PO the for 3 days following surgery SID at the same dose)

Tramadol 5mg/kg PO q12hrs

Lidocaine <2mg/kg SC

Induction

Common induction techniques

Propofol 3-6mg/kg IV

Ketamine 5-8 mg/kg IV & Diazepam 1-2mg/kg IV

Thiopental 2% 8-12 mg/kg IV

Mask induction or via Plexiglas tube

Maintenance and Equipment

Isoflurane (MAC is 1.52% for ferret) and sevoflurane are both excellent volatile anesthetics, although with sevoflurane, it has been noted that uptake and elimination is quicker. Ferrets should be intubated. You can use old IV tubing to prop open the mouth as mouth gags. They will often have a lot of jaw tone. Use cat size ET tubes. Lidocaine can be used to avoid laryngospasm. It is common to have endotracheal tubes kink due to their small size. Also, ferrets have long, flexible necks. Patient's can extubate quite easily. Tie them in well and pre-measure the length. Do not use cut tubes. Capnography (a measurement of end tidal carbon dioxide) is a nice monitor to have for troubleshooting airway problems. Intravenous access is ideal for support of tissue perfusion as well as emergency access. A 22, 24 or 26 gauge can be used on most ferrets. When placing an intravenous catheter, the cephalic or lateral saphenous vein can be used. For sick animals, jugular catheters are often placed. An intraosseous catheter has been recommended for shocky or dehabilitated animals and can be left in for a couple of days. This can be placed in the humerus, femur or tibia. Always use an Elizabethan collar for awake ferrets as they are big chewers. Administer fluids at a rate of 10ml/kg/hr. WATCH VOLUME! For example, a 1kg ferret will receive 10ml of crystalloid an hr. This can be measured with a microdrip set (60drops.ml) or a syringe driver can be used to be more precise as well as a Buretrol. Since ferrets have many disorders that involve glucose homeostasis, the blood glucose levels are monitored and Dextrose 2.5% or 5% is placed in maintenance fluid. If injectable drugs were used to maintain anesthesia, an endotracheal tube should still be placed and oxygen should be delivered to avoid any hypoxemic episode. If intubation is not possible, then a faze mask with supplemental oxygen should be used. It is desirable to use a non-rebreathing system on your anesthesia machine. There may be increased resistance to breathing on a rebreathing system. Small patients are more prone to hypothermia under anesthesia. It is essential to support body temperature as much as possible. Minimize your surgical prep solution to just a few milliliters. Do not drench a ferret, as this will bring core body temperature down along with the anesthetic drugs. Some will warm the prep solution prior to applying. A Bair Hugger or warm water blanket underneath the body should be used as well as warmed IV fluids. Support this throughout the recovery period. When monitoring these little animals, an anesthesia record should be kept and vitals such as blood pressure, oxygen saturation, heart rate and respiration should be monitored every five minutes. Capnography is used to measure ventilation, pulse oximetry- oxygenation. For non-invasive blood pressure, a Doppler or oscillimetric device can be used. It may be a challenge to place these instruments on ferrets. Cuff size is important in anesthesia. Chose a cuff that is a third of the circumference of the patient's limb and keep in mind that the size of the patient (less than 5kg); as measurements can read lower than what they really are. Use them for trends. Invasive blood pressure would be more accurate but difficult to obtain due to the size of the patient. The NIBP cuffs can be placed on the front legs as well as the tail. Pulse oximeter probes do not work well on the tongue; therefore they are placed on the front legs. Electrocardiogram can be used for electrical function of the heart and measurement of blood gases can be obtained through arterial blood gas sampling. This is reserved for more compromised patients.

Post-op Management

In 1999, a UK study showed 22% of exotics receive peri-op analgesia. This is too low and unacceptable. Support body temperature. Dry your patient. Keep them warm. Observe for pain.

When evaluating pain in a ferret, they can be relatively quiet and difficult to assess but if you know normal ferret behavior, you can observe changes. Acute pain is easier to recognize than chronic pain. If a ferret is experiencing chronic pain, it is most likely coming from arthritis, cancer or dental pain. A ferret in pain may curl up, hide, or have a hunched posture. They may foam at the mouth, shiver, droop their eyes, vocalize, grind their teeth or lose weight. Opioid drugs are still the best for surgical trauma or pain. When used in combination with non-steroidal anti-inflammatory drugs (NSAID) as well as local anesthetics, we can target pain receptors effectively. Meloxicam is commonly used as an NSAID. Lidocaine and Bupivicaine are commonly used local anesthetics. Opioids commonly used are Butorphanol, Buprenorphine, Morphine, Hydromorphone and Fentanyl. They can be administered as a single dose and many of them can be delivered through a constant rate infusion by itself or with Ketamine.

References

Cantwell S: Ferret, Rabbit and Rodent Anesthesia, The Veterinary Clinics of North America Exotic Animal Practice Analgesia and Anesthesia, Philadelphia, Saunders, Vol 4, number 1,Jan 01, pages 169-191

Hrapkiewicz K, Medina L: Clinical Laboratory Animal medicine 3rd ed. Iowa, Blackwell Publishing 2007

Matos R, Morrisey J: Common Procedures in the Ferret:The Veterinary Clinics of North America Exotic Animal Practice Analgesia and Anesthesia, Philadelphia, Saunders, Vol 9, number 2,May 06, pages 347-365

Muir W, Hubbell J, Bednarski R: Handbook of Veterinary Anesthesia, 4th ed. St. Louis, Mosby, 2007

Johnston M: Exotic Animal Analgesia, Unified Against Pain, Montreal, Canada, Nov 1-3, 0, 287-295

Seymour C, Gleed R: Manual of Small Animal Anaesthesia and Analgesia, Shurdington, UK, BSAVA, 1999

Quesenberry K, Carpenter J: Ferrets, Rabbits and Rodents 2nd ed., St. Louis, Saunders 2007

In Proc: Johnston M: Exotic Animal Analgesia, Unified Against Pain, Montreal, Canada, Nov 1-3, 07