Page 810 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Gastrointestinal system: 4.2 The lower gastrointestinal tr act 785

VetBooks.ir be useful in certain circumstances. It is very useful curves have been reported in normal horses, and car-
Cytological examination of peritoneal fluid can
bohydrate absorption tests should be considered in
for differentiation of enterocentesis versus intestinal
diagnostic findings. ‘Normal’ test results do not nec-
rupture. Intracellular bacteria and degenerate neu- the context of the animal’s clinical state and other
trophils should be present if intestinal rupture has essarily indicate normal small intestine; segmental
occurred. Total nucleated cell count should be <5 × disease may not be identified if the remaining small
10 /l. Bacterial culture should be performed if sep- intestine has a normal absorptive capacity.
9
tic peritonitis or chronic inflammation is suspected.
Results of a Gram stain may be useful in guiding Rectal mucosal biopsies
initial antimicrobial therapy in cases of suspected Rectal mucosal biopsies are a useful adjunctive diag-
peritonitis. nostic tool in the evaluation of chronic GI disease,
although their limitations should be recognised and
Carbohydrate absorption tests they are rarely diagnostic in isolation. Instead they
Carbohydrate absorption tests are used to assess should be performed as part of a thorough diagnostic
small-intestinal absorption, mainly in horses with work-up of chronic GI disease alongside haematol-
chronic weight loss or hypoproteinaemia, or in ogy, ultrasonography, gastroscopy, radiography and
cases of suspected inflammatory bowel disease. The carbohydrate absorption tests.
principle of the test is that monosaccharides (i.e. Rectal mucosal samples can be readily collected
D-xylose, glucose) are normally readily absorbed in using uterine biopsy forceps. The horse is sedated,
the small intestine. These tests involve oral admin- and, after faecal matter is removed, 20–50 ml of 2%
istration of the carbohydrate, followed by analysis of lidocaine is infused into the rectum. The biopsy
serial blood samples for the specific carbohydrate. forceps are then inserted into the rectum shield by
The main advantage of xylose over glucose is that a gloved hand. Sampling is performed at approxi-
unlike glucose, xylose is not metabolised, so blood mately 15–20 cm of depth and at the 10 o’clock and
levels more closely represent intestinal absorp- 2 o’clock positions. To sample, a small tag of mucosa
tion. However, xylose is more expensive, and glu- is pulled ventrally, and the biopsy forceps applied.
cose is more readily available. Both tests should be The remaining mucosa is then separated, and the
performed following an 18–24 hour fast. Extended forceps removed. This procedure is repeated 3–4
fasting beyond 24 hours should be avoided as it times. Rectal mucosal biopsy is well tolerated when
potentially impacts on the test results. A base- performed correctly and no specific aftercare (i.e.
line blood sample is collected, then xylose or glu- antimicrobials) is required. Histopathological evalu-
cose (0.5–1.0 g/kg as a 10–20% solution in water) ation of rectal mucosal biopsies should be performed
is administered via a NG tube. Sedation should be by a pathologist experienced with mucosal pathology
avoided because of the effects on gastric emptying. in the horse.
Blood samples are then collected every 30 minutes
for 3 hours, or until an adequate increase in blood USE OF ANALGESICS IN COLIC
carbohydrate level is observed. Blood glucose levels
should increase by at least 85%, while blood xylose The goal of analgesic therapy in colic is to relieve
levels should reach 1.33–1.68 mmol/l (20–25 mg/dl) pain to facilitate examination, to benefit animal
in most horses. A peak in glucose or xylose typically welfare, to prevent self-induced trauma, to lessen
occurs within 60–90 minutes. A flattened absorption pain-induced ileus or to allow for safe transporta-
curve suggests impaired small-intestinal absorption; tion to a referral facility. A ‘standard’ regime for
however, delayed gastric emptying can cause the analgesia is not available and analgesic admin-
same result. A decrease of blood glucose levels of istration should be tailored towards each case
<15% is considered complete malabsorption and may (Table 4.2). Overly aggressive analgesic therapy
be a poor prognostic indicator. Care should be taken should be avoided so that deterioration of disease
in interpreting results because attenuated absorption is not masked, particularly where early surgical