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Rectal Examination for the Equine Acute Abdomen: What Am I Really Feeling?
P.O.E. Mueller
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Take Home Message
A complete and thorough rectal examination is an essential component of a diagnostic evaluation when examining horses with abdominal pain. Rectal examination findings should always be considered in conjunction with the results of the physical exam and evaluation for the presence of nasogastric reflux. Occasionally, rectal examination findings clearly indicate the specific disease. However, more often, rectal examination does not yield a specific diagnosis, but yields information regarding the severity of the problem and the need for referral or surgical intervention.
Introduction
A complete and thorough rectal examination is an essential component of a diagnostic evaluation when examining horses with abdominal pain. Rectal examination findings should always be considered in conjunction with the results of physical examination, nasogastric intubation, abdominocentesis, and laboratory evaluation. A rectal examination should always be performed before abdominocentesis in order to recognize an extremely gas distended or ingesta-filled cecum or large intestine. If these abnormalities are identified, extreme care must be taken when performing an abdominocentesis to avoid accidental enterocentesis.
Occasionally, rectal examination findings clearly indicate the specific disease, such as a renosplenic entrapment, early ileal impaction, or herniation of small intestine through the inguinal ring in a stallion. Most often, however, rectal examination does not yield a specific diagnosis, but yields information regarding the severity of the problem and the need for surgical intervention. Abnormal rectal examination findings include abnormal positioning of the intestine, distention of the intestine with gas or ingesta, abnormally thickened intestinal wall, and the presence of intra-or extra-luminal masses.
The size and depth of the peritoneal cavity in the horse limit the examiner to palpation of the caudal 25-30% of the peritoneal cavity. Because of the inability to examine the entire peritoneal cavity, subtle abnormalities identified on examination are often used to make inferences concerning the more cranial regions of the peritoneal cavity. Consequently, the lack of abnormal rectal examination findings does not completely rule out an intestinal abnormality.
Technique
When performing a rectal examination, proper restraint is of the utmost importance to assure the safety of the horse and the examiner. Inadequate restraint may result in iatrogenic rectal tear, a potentially fatal complication of rectal examination, or serious injury to the examiner. A nose twitch should always be used to control the patient. Horses that resist rectal examination, or those with signs of unrelenting abdominal pain should be sedated with xylazine (0.3-0.5 mg/kg, IV) or detomidine (.01-.05 mg/kg, IV). The anticholinergic drug, N-butylscopolammonium bromidea may also be administered (0.3 mg/kg, IV or 7-ml/450-kg horse) to promote rectal relaxation. It should be noted that the anticholinergic actions of the drug cause a marked increase in heart rate that may last for up to 30 minutes after administration. Adequate lubrication of the examiner's hand and arm is necessary to minimize irritation to the rectal mucosa. Hydrated methylcellulose (Obstetric lube) is the most commonly used lubricant. Initial introduction of the examiner's hand through the anal sphincter is often met with great resistance. Therefore, this should be performed with a slow and steady motion. The fingers and thumb of the hand should be kept together in an extended position throughout the entire examination. Once the hand is through the anal sphincter, the feces within the rectum are evacuated. The amount and consistency of fecal material in the rectum should be noted. Absence of fecal material, or the presence of dry, fibrin and mucous covered feces is abnormal and is consistent with delayed intestinal transit. Fetid watery, fecal material is often present in horses with colitis. Large amounts of sand within the feces may be indicative of a sand impaction or sand-induced colitis. After evacuation of feces from the rectum, intra-rectal administration of 50-60 ml of 2% lidocaine via a 60 cc catheter tip syringe may help promote further rectal relaxation and reduce straining. The syringe may also be used to administer additional lubrication into the rectum at this time.
The examiner’s arm is then re-introduced into the rectum and advanced slowly and steadily as far as comfortably possible. The arm is left in this position without excessive movement for 20 to 30 seconds. In most cases, this initial delay in internal palpation will allow the rectum to relax around the examiner's arm, facilitating a more thorough palpation of the more cranial aspects of the abdomen. Initial examination of the caudal aspects of the abdomen with a half-inserted arm is not recommended because it usually results in straining and excessive peristaltic contraction of the rectum.
The most severe complication associated with rectal palpation is an iatrogenic rectal tear. Although rare, tears usually occur dorsally between the 10 and 12 o'clock positions. Most rectal tears can be avoided by proper restraint, adequate lubrication, and steady and careful palpation technique. If a peristaltic contraction or increased resistance is felt during examination, the hand should immediately be withdrawn from the rectum to avoid potential rectal injury.
The examination should be performed in a consistent, systematic manner to assure a complete and thorough examination and minimize the chance of missing a lesion. I prefer a clockwise approach, starting with the spleen in the left dorsal abdominal quadrant. This is followed by examination of the right dorsal, right ventral, and left ventral quadrants. The pelvic canal and more caudal structures are examined just before removal of the hand from the rectum. [...]
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