Note: This article was published in June 2003.
Researchers at Louisiana State University (LSU) have reassuring news about the treatment of choke: Most of the medications typically used to relieve the condition, which occurs when food becomes lodged in the horse's esophagus, seem to have a desirable effect.
Because there is no prevailing drug treatment for choke, veterinarians generally choose a sedative, tranquilizer or muscle relaxant based on their own preferences and experiences. "Reduction of pressure is a primary objective in treating choke," says Anne Wooldridge, DVM, who coordinated the LSU study. "The thinking is that if the pressure around the esophagus can be reduced, the mass can be moved by the veterinarian or move on its own as saliva softens it."
Five medications--acepromazine (tranquilizer), guaifenesin (muscle relaxant), a xylazine-butorphanol combination (sedative), detomidine (sedative) and oxytocin (hormone)--are commonly used to achieve this effect, so the LSU team decided to investigate how each treatment affected the esophagus.
For the study, eight horses had pressure gauges placed in three key locations within the esophagus: just behind the pharynx, at the entrance to the thoracic cavity, and near the entrance to the stomach. Next, the researchers took baseline measurements of pressure at each location within each horse's esophagus and recorded how often the animals swallowed.
The horses were then injected with one of the five medications or a control treatment of saline, and the researchers collected pressure data from the gauges at regular intervals for 40 minutes, while also counting all spontaneous swallows during that time.
The data revealed that acepromazine, detomidine and guaifenesin all affected pressure in the esophagus at the thoracic inlet. Acepromazine was the only drug to affect pressure just in front of the stomach.
The sedatives and tranquilizers, as well as guaifenesin, also reduced the number of spontaneous swallows. "Less swallowing may actually help in cases of choke," says Wooldridge, "because it decreases pain and spasms, allowing lubricants to pool around the mass."
In contrast, the hormone oxytocin, a smooth-muscle stimulant, did not reduce esophageal pressure anywhere along the organ's length, nor did it affect frequency of swallowing. "There have been other studies conducted with different methods that did show some effect of oxytocin," says Wooldridge. "I suspect that means we still have more to learn about the drug."
This article originally appeared in the June 2003 issue of EQUUS magazine.
To read more about choke, see "How to Handle Choke" in the December 2007 issue of EQUUS.