Organ replacement in animals

When an animal experiences organ failure organ replacement therapies can be used to treat diseased or injured pets. Veterinarians now use many of the same types of therapies that are used in human medicine.

Total hip replacement
A good candidate for Total Hip Replacement (THR) must be at least 9-12 months old to be sure he has finished developing and weigh at least 30 lb. The hip implant for dogs is similar to its human counterpart, but it is much smaller. X-rays are used to determine the dimensions of an appropriately-sized implant. The femoral stem is usually made of cobalt chrome or stainless steel, while the cup is made of ultra high molecular weight polyethylene. Polymethyl methacrylate is the cement used with cemented implants, whereas 250-micrometres (diameter) titanium beads usually cover the stem surface of the press-fit implants.

The THR is expected to last 10-15 years, which usually surpasses the remaining lifetime of the dog. In less than 5% of cases, the THR will malfunction through loosening of the acetabular cup or femoral fracture. However rare these failures are, they must be corrected immediately with revision surgery.

Pacemaker implants
The first pacemaker surgery on a dog was performed in 1968. About 300 pacemakers are implanted in dogs each year, even though about 4000 dogs are in need of one. There are no pacemakers made specifically for use in dogs, but human pacemaker users are often outlasted by their pacemakers, leaving behind a functioning pacemaker with less battery power left than a new pacemaker which could be implanted into a dog. One difficulty in implanting used pacemakers is the removal from the deceased human - the pacemaker leads often experience accumulation of surrounding heart muscle tissue and become difficult to remove after death. If the leads are cut in order to remove the pacemaker donation is not possible. If a pacemaker has not been used by a human but has reached its expiry date it will not be suitable for use in a human but could still be used in a dog.

Blood transfusion
For a blood transfusion to take place the donor and recipient must be of compatible blood types. Dogs have eleven blood types but are born without antibodies in their blood. For this reason, first time transfusions will not have a reaction, but further transfusions will cause severe reactions if the dog has a mismatch in the DEA1.1 blood type. Because the immune systems of dogs are so fierce, cross-match tests must be performed upon each dog blood transfusion. Only about one in every 15 dogs is negative for all antigens and thus, a universal donor. Cats have A, B, and AB blood types with specific factors, but there is no universal donor type Recipient and donor blood must be properly cross-matched. Red cells from the donor are mixed with the serum of the recipient in major cross-matching. In a minor cross-match, the recipient's red cells are compared with the donor's serum. Blood donors must meet specific requirements in order to qualify to donate. They must weigh at least 50 lb for dogs and 10 lb for cats, have high enough blood component values, and have no infectious diseases. One donation could be used by up to two animals.

Heart valves
Open-heart surgery for dogs requires a six- to eight-person team to carefully monitor the patient before and during the invasive surgery. The entire surgery lasts five hours, during which time the dog is connected to a blood oxygenator and the heart is bypassed. The defective heart valve is removed and the replacement valve, typically from bovine pericardium, is precisely sewn into place. The dog’s heart is then restarted and monitored for at least two hours after the surgery is completed. Due to the expense, this is not a common procedure.

Prosthetic limbs
While small dogs and cats can survive comfortably with three legs, larger dogs, horses, and farm animals require the limb to support their weight. Surgery has also been done on birds that are used for breeding purposes. Each prosthetic limb is custom-made to fit the individual needs of the specific animal.

Orthopedic implants
UC Davis’ equine orthopedic surgery program has developed an implant that has been successful in human surgery for a long time. The intermedullary interlocking nail is used to treat horses with long leg bone fractures. The nails are positioned within the medullary cavity and can be secured to the proximal and distal fracture segments using transcortical screws which penetrate both cortices of the bone, as well as pass through holes in the nail. The nail is placed centrally in the axis of the bone to give full support unlike bone plates that only give exterior support. In an attempt to aid horses with bowed tendons, research has been done using carbon fiber implants that consist of about 40,000 fibers in total each of which is 8 micrometres in diameter. These fibers induce tissue growth and result in a structure of carbon and tissue about 8 mm in diameter.