Peritonitis in the Horse
Dr. Melissa Mazan
Diagnostic Tests Abdominocentesis. This procedure gives the definitive diagnosis of peritonitis. Your veterinarian inserts a needle into the abdominal cavity and withdraws fluid contained within the peritoneal space. Peritoneal fluid should be clear and straw-colored, with a low white cell count and protein level. Horses with peritonitis have a very high white cell count in the peritoneal fluid, and usually a high protein count in the peritoneal fluid. The fluid also has a serosanguinous appearance – it appears orange or red tinged.
In the case of an infectious peritonitis, there may also be bacteria in this fluid. The bacteria often consist of a mixed bag of gram negative, gram positive, and anaerobic (meaning existing without the presence of air). Your veterinarian will usually choose to culture this fluid in order to identify the bacteria, and test the resultant growth against a battery of antibiotics in order to determine which treatment will work the best. This test is a bacterial sensitivity test.
A rectal examination may reveal quiet intestines (ileus, or lack of forward movement of the intestines) or a mass that may be an abscess or a tumor. In cases of a catastrophic intestinal rupture, there may be a gritty feeling to the abdomen.
Nasogastric intubation may yield excessive fluid (reflux) which indicates the presence of ileus.
Bloodwork. A CBC may show signs of inflammation and infection, such as a high white cell count and high fibrinogen level. A chemistry profile may show dehydration or compromise to liver and kidney function. A chemistry profile may also show either a high protein level due to increased inflammatory molecules, or a low protein level due to loss into the abdomen.
Ultrasound examination will often show the presence of excessive amounts of peritoneal fluid, and may also allow the veterinarian to determine if there is a mass (such as an abscess or tumor) present that she wasn't able to feel on rectal examination. This may require referral to a specialist, although many veterinarians in the field are adept in the use of abdominal ultrasound.
Your veterinarian may also choose to perform an endoscopic examination of the stomach (gastroscopy) in order to look for gastric ulcers – especially in foals. This may require referral to a specialist, although it is becoming more common for veterinarians in the field to have access to a gastroscope.
Your veterinarian may choose to examine the peritoneal cavity using a laparascope – this essentially provides a small camera at long distance to view inside the horse's abdomen. If there is a mass present it may be possible for your veterinarian to perform a biopsy on the mass using laparoscopy. It is usually necessary to travel to a referral center for laparoscopy.
In small horses or foals, abdominal x-rays may be of use in finding a foreign body or a sand impaction. Except in young foals or miniature horses, abdominal x-rays can only be taken at a referral center.
In the majority of cases, the cause of peritonitis is a bacterial infection. The most effective weapon against bacterial infection is broad spectrum antibiotics. This is one reason why it is so helpful to get a good culture and bacterial sensitivity on the infected peritoneal fluid – it helps us to have a specifically directed therapy.
After broad spectrum antibiotics, supportive care is of utmost importance. If the horse has become dehydrated due to ileus or has such a high fever that he doesn't want to eat or drink, it is important to give him fluids, either intravenously or using a nasogastric tube, depending on the individual case. It is necessary to keep the stomach decompressed in cases of ileus. Other treatments, such as lavage and draining of the peritoneal cavity in order to decrease the number of bacteria and contaminants, may be helpful. In cases when we can identify a physical cause of the peritonitis – say, a foreign body – it is important to remove the cause.
Adhesions and laminitis are two of the most important complications of peritonitis, and they can cause a horse's death despite curing the original problem. We aren't sure if our treatments to prevent adhesions, such as heparin, are effective. Because adhesions can have such devastating consequences for horses, many veterinarians choose to treat with heparin nonetheless.
Treatment for potential laminitis consists of maintaining soft footing, and good supportive care, and anti-inflammatory medications. There are many, many treatments for laminitis – which tells us that we are still unsure of the best way to tackle this devastating problem. Some very good veterinarians choose to try to prevent laminitis, while other equally experienced practitioners are of the opinion that there is no good preventative other than good supportive care.
The mainstay of treatment for peritonitis is broad spectrum antibiotics. Ideally, your veterinarian can use the results of the peritoneal fluid culture to guide her antibiotic choice. Because it may take several days to get the results of culture and sensitivity, most veterinarians start with a combination of drugs, such as penicillin, gentocin, and metronidazole – this mix targets gram positive, gram negative, and aerobic bacteria, respectively.
Horses that have developed ileus due to the peritonitis will usually need to have a nasogastric tube in place for several days in order to empty the stomach of the fluid build-up. Horses are unable to vomit, and if there is too much fluid build-up, the stomach may rupture.
Horses with reflux due to ileus, are losing a lot of fluids into the intestines secondary to the peritonitis, or who are so colicky or feel so miserable that they don't drink, may need treatment with intravenous fluids.
In cases with a very high white cell and bacterial load in the peritoneal fluid, peritoneal lavage may be useful. Lavage refers to flushing the peritoneal cavity with sterile fluid in order help physically cleanse the peritoneal cavity.
Your veterinarian may also choose to use an indwelling drain, in order to physically remove some of the contaminated fluid.
Horses with peritonitis often need anti-inflammatories such as Banamine, as well.
It is important to remove the cause of the peritonitis if it can be found. In foals with peritonitis secondary to gastric ulceration, it will be of paramount importance to treat with stomach protectants and acid blockers. If there is a foreign body present, surgery may be necessary to remover the object.
Some veterinarians choose to use heparin in order to decrease the likelihood of adhesions forming.
It is important to remember that peritonitis is a very serious and potentially fatal condition for the horse. It can also be a very expensive disease – horses with acute disease may need to spend several weeks in a referral hospital.