Friday, February 19, 2010

Fri 2/19/10 - Colic - Clinical Case

Vet Tip of the Day: Fatal Colic
Key Words: Ischemia, Shock, Banamine, Heart Rate, Pain

My assistant Jessie and I had a hectic day - three emergencies, each in a different geographic area, on top of scheduled calls.  Our third emergency was the horse pictured here, who had an acute onset of abdominal pain.  Unfortunately, the outcome was not positive.  I am going to share this case with you so that perhaps by learning from this lovely old horse we can give some small value to his death.  The education he provides will be his last gift to us.

Chance was a 23 year old gelding.  His nutrition and preventive health care were excellent, and he was in very good condition.  He was used as a school horse for beginning riders and had no previous history of colic.  He was normal this morning, but suddenly around 2 PM began to look back at his abdomen  and paw at the ground.  Within 20 minutes these signs had progressed to the point that Chance would crumple to the ground and roll unless one person led him forward while a second person encouraged him to stay up with a longe whip.  We arrived 30 minutes after the onset of signs.

Chance's behavior is classic for acute, severe colic.  Mild signs of abdominal pain include looking back at the abdomen,  standing in a stretched out posture as if trying to urinate, loss of appetite, occasional pawing and spending unusual amounts of time lying down.  Moderate pain is characterized by persistent pawing, and frequent lying down and getting up.  As pain becomes severe, signs include falling suddenly to the ground and rolling violently.

When we arrived, it was impossible to perform a physical examination on Chance because as soon as he stood still he would attempt to throw himself down.  I administered a mild sedative intravenously as he was walking.  After 10 minutes this medication had had no effect so a second, more powerful sedative/analgesic combination was given.  Five minutes later Chance would stand without trying to roll, but was heavily sedated and not normally responsive to stimuli.  At this time his heart rate was moderately elevated (52 beats per minute/normal range 28-40), he had no gut sounds, and his gums were pale pink.  On rectal examination I could palpate an increased quantity of heavy ingesta in the large colon, which was displaced from its normal position.  A stomach tube was passed through the nose into Chance's stomach, and when a siphon was applied it was determined that there was no build up of fluid in the stomach.

Although I had not felt anything too alarming on rectal exam, at the time of our initial evaluation Chance has only been showing signs of discomfort for 30 minutes.  And in this time his degree of pain had escalated rapidly.  At this point my assessment was that Chance was suffering from an acute, severe colic.  Based on the severity of pain (which was only controlled temporarily by a very potent pain relieving injection) and the rapid progression of signs I was suspicious of a strangulating obstruction, or a twist in the bowel that had cut off blood supply to a section of the intestine.  These sudden strangulating lesions cause the most immediate, severe, and unrelenting pain of all forms of colic.  The strangulation can occur in either the large or small intestine.  Eventually the normal bowel becomes very distended in front of the strangulation, but this takes a few hours to develop, and during this time the rectal exam may be deceptively normal.  Unfortunately I couldn't accurately assess Chance's heart rate because I had to sedate him before I could listen to his heart and the sedative lowers heart rate significantly.  To answer one of yesterday's questions, of all the information we can gain from a colic, including sophisticated laboratory data, the two most sensitive indicators of the severity of the situation are heart rate and degree of pain.

At this point, Chance becomes a surgical candidate.  The only hope for horse's with strangulating lesions is rapid surgical intervention.  Once a significant portion of bowel looses blood supply,  endotoxic shock (see yesterday's blog) sets in very rapidly. Cardiovascular collapse and death can occur within 4-6 hours in the most severe cases. Because of Chance's age and economic constraints, surgery was not an option.  The only hope was that my assessment was incorrect.  I gave Chance a dose of flunixin meglumine (Banamine), a powerful anti-inflammatory medication which relieves gastrointestinal pain and combats the effects of endotoxemia, and we waited.

Within 30 minutes, when the sedative/pain killer was wearing off, Chance became very painful again.  With the recurrence of pain now Chance also exhibited an elevated heart rate (80 beats per minute), muscle tremors, a continued abscence of gut sounds, and deteriorating mucous membrane color.  His gums took on a grey/purple hue, which is hallmark indicator of cardiovascular compromise, or shock (see picture).

Euthanasia was performed 3 hours after the onset of Chance's colic.  Within that short time he had progressed from a healthy horse to one with multiple signs of severe endotoxic shock, the result of a strangulating intestinal lesion.

Long term (over 1 year) survival of horses with severe strangulating lesions after surgery ranges from 30 - 60%, depending on what study you read.  Estimated cost of surgery and hospitalization for these severe cases is 7,000 to over 10,000 dollars.  These are the worst case scenario colics, and they are by far the least common.  Colics requiring surgery that do not involve dead bowel, such as simple large colon displacements, have 85 - 90% long term survival rates, with cost estimate around 6,000 dollars.  And while Chance's story is a tragic one, remember that the vast majority of colics do not require surgery, and respond well to medical therapy.

The key to preventing colic is regular preventive health care, excellent quality diet, and a regular exercise program.  Unfortunately, colic can be an  indiscriminant killer, and as Chance showed us today, even horse's receiving the best of care can be stricken.  Chance was a wonderful horse, and will be sorely missed.  Hopefully by sharing his story he will help bring veterinary assistance to another horse with the chance for a better outcome.

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