Complication rate in dogs and cats is about 10.5%, which is about 10 times higher than in people. The most common failure is blockage of the tubing or port so that material can neither be injected nor extracted. This can be prevented by properly flushing the port with heparinized saline after each use. Complications are higher for those in leg veins than in neck veins in cats.
Also, because of the need to use special needles and have special training to inject into these ports, at the present, these ports are only being used by researchers and a few select cancer treatment centers. Since most cats do not need repeated blood draws or injections, the usefulness of these ports is unclear.
From "Vascular Access Ports in Cats", Alane Kosanovich Cahalane, pp585-591, Feline Internal Medicine, vol. 7, 2015