Shadow was close to having it.  From a feeding tube that wedged into
the wall of his stomach and prevented it from being removed in the
normal way.  Other than that, I don't know much about it.

Stacey,

Peritonitis almost always occurs secondary to some other disease or trauma
or penetrating wounds to the abdominal cavity or following surgery where the
intestines were damaged.  Peritonitis is a particulary dangerous disease
because the infection can quickly spread to the blood and other organs.

Some of cases of peritonitis that we've had over the years were usually in
females with pyometra or infected or abscessed uterine stumps, cats with
gastrointestinal foreign objects such as bones, needles attached to
swallowed tread, or other objects that perforated the intestines, or string
that pleated and cut through the intestinal wall, and male cats with
ruptured urinary bladders caused by urethral obstructions.

If the damage causing the peritonitis is repaired and the inciting cause is
removed or treated in time, and antibiotic therapy is begun early enough,
many cats recover and go on to live long, normal and healthy lives.
Unfortunately, we don't always get the sick cats in time.

The first priority of treatment is determining and removing the inciting
cause.
Has the cause been determined?

Best of luck.

Phil.