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SUMMER 2015 ISSUE
EQUINE MATTERS
6
Veterinary surgeon
Sally Hodgson
XLEquine practice
Hook Norton
Veterinary Group
PER I TONI T I S
What is peritonitis?
The peritoneum is the thin membrane that
lines the abdominal cavity. Its job is to
secrete the small volume of peritoneal fluid
that lubricates the abdomen. The term
‘peritonitis’ means inflammation of the
peritoneum. The cause may be mechanical,
chemical or infectious. Mechanical causes
include trauma, breeding or foaling
accidents and abdominal surgery. Chemical
peritonitis arises from irritation from leaking
body fluids such as urine, lymphatic fluid,
blood, pus or gut contents, and from drugs
administered into the peritoneal cavity.
Leakage of urine from a ruptured bladder
or abnormalities of the lymphatic drainage
from the intestines (lymphangiectasia) are
seen almost exclusively in very young foals
(Figure 1)
.
Secondary bacterial infection usually
accompanies mechanical or chemical
causes. Other causes of infectious peritonitis
include abscesses within the abdomen,
parasite migration and some viral infections.
Clinical signs
Symptoms of peritonitis include colic,
dullness and inappetance. The abdominal
wall is often tensed or ‘guarded’ and is
painful to external palpation. The horse may
be reluctant to move. Examination by a vet
will usually find decreased gut motility,
dehydration and fever. Chronic cases may
show weight loss, ventral oedema and
exercise intolerance. Some will have
excessive amounts of peritoneal fluid, which
causes the abdomen to swell up and makes
the horse look bloated. Peritonitis can be
confirmed or ruled out by taking a sample
of peritoneal fluid through the body wall
with a needle, a procedure called a
peritoneal tap or ’belly tap’. The peritoneal
fluid can then be examined to determine the
types and numbers of cells present and the
protein levels. This information helps the vet
to determine whether or not peritonitis is
present, and in some cases can help identify
the cause.
Normal peritoneal fluid is clear and
straw-coloured. Cloudy or dark/red
peritoneal fluid is abnormal. It is also very
useful to send a sample for culture and
sensitivity testing. This identifies the type
of bacteria involved and checks which
antibiotics should treat them and which
they are resistant to.
Treatment
Pain relief and intravenous antibiotics (most
commonly penicillin, gentamicin and
metronidazole) are essential for the treatment
of septic peritonitis. Antibiotic treatment must
be started straight away, and may need to
be altered depending on the results of culture
and sensitivity testing of the peritoneal fluid
sample. Peritonitis caused by abdominal
abscesses need antibiotic treatment for
weeks to months depending on the types of
bacteria involved. Aggressive intravenous
fluid therapy may be needed to correct
dehydration. Abdominal drainage and
lavage can help to remove bacteria and
toxins from the abdominal cavity in severe
septic peritonitis.
(Figure 2)
.
Figure 1: Lymphangiectasia
Figure 2: Abdominal drain/tapped
abscess
Prognosis
The prognosis varies depending
on the cause. If the primary cause
(e.g. ruptured bladder) can be
identified and corrected, the
prognosis for survival is reasonably
good, however survival in horses with
septic peritonitis after abdominal
surgery is less than 50%. If there is a
gastrointestinal rupture the prognosis
is very grave indeed.
Sally Hodgson VetMB BA BSc MRCVS,
Hook Norton Veterinary Group
Peritonitis
in horses