Gastrointestinal stasis is one of the most common clinical disorders of pet rabbits and can be primary or secondary in nature.1–4 Underlying or contributing pathological conditions can include gastric impaction, gastric gas accumulation, intestinal impaction, intestinal gas accumulation, intestinal obstruction, primary gastroenteritis, intestinal adhesions, neoplasia such as uterine adenocarcinoma, pancreatitis, and liver abnormalities such as hepatic lipidosis, torsion, and cholangiohepatitis.1,2,4 Associated clinical signs are generally attributable to secondary alterations in fluid balance, gastrointestinal motility, or both1–4 and are often nonspecific.
Rabbits with gastrointestinal stasis typically need supportive care and a diagnostic workup to determine underlying causes. Gastrointestinal obstruction needs to be ruled out whenever possible because of the need for surgical management in most cases and because the prognosis for rabbits undergoing gastrointestinal surgery is guarded owing to the high risk of peritonitis, postoperative gastrointestinal stasis, endotoxemia, or acute renal failure, even with prompt foreign body removal.4,5
Abdominal radiography is useful in the evaluation of rabbits with gastrointestinal stasis, and serial radiography can be used to monitor response to treatment.4–6 Drawbacks of radiography include distress to the rabbit, risk of injury or radiation exposure to the rabbit or handler, possible need for sedation, lack of quantitative results, and inability to distinguish between mechanical and paralytic ileus.5 A more sensitive and specific imaging modality is needed to better guide treatment recommendations for affected rabbits and avoid unnecessary surgery whenever possible.
Ultrasonography, which lacks ionizing radiation, has been diagnostically useful for human and veterinary patients with gastrointestinal disorders. For example, in a prospective study7 of people with ileus and gastrointestinal obstruction, abdominal ultrasonography revealed abnormalities in 25% of people with normal radiographic findings, and the cause of the obstruction was identified in 13% of those patients. Furthermore, in a study8 of dogs and cats with confirmed gastrointestinal foreign bodies, only 9 of 16 foreign bodies were identified via radiography, whereas all 16 were identified via ultrasonography.
Although ultrasonography can be helpful to identify gastrointestinal obstructions and foreign bodies, its use for rabbits has previously been limited because of perceived difficulty obtaining images owing to gastrointestinal gas accumulation.4 To the authors’ knowledge, the sole report9 of ultrasonography of the gastrointestinal tract in rabbits consists of descriptions of normal ultrasonographic features in 21 healthy rabbits, including those of the ventral aspect of the stomach wall, pylorus, descending duodenum, jejunum, sacculus rotundus, appendix, cecum, spiral loop of the ascending colon, and descending colon.
Traditional B-mode ultrasonography is commonly used in small animal practice and generates a grayscale image based on the amplitude and depth of returning echoes.10 Doppler ultrasonography identifies an apparent shift in the sound frequency of a moving target within an imaged area and is quantitative, providing velocity of returning echoes. Pulsed-wave Doppler ultrasonography allows identification of that Doppler shift from a specific depth or location, with the Doppler shift displayed as a graph mapping velocity over time.
Duplex Doppler ultrasonography, which consists of simultaneous display of real-time B-mode and PWD images, has been used to provide subjective (B-mode) and more quantitative (PWD) analysis of gastrointestinal peristalsis in humans, horses, and dogs and can be used to differentiate between mechanical and paralytic ileus.11–14 This noninvasive technique analyzes Doppler signals produced by placing the PWD ultra-sonography sample volume on the wall or within the lumen of the gastrointestinal tract. Doppler signals are displayed on a graph, with the x-axis representing time and the y-axis representing velocity. Distinction of peristaltic contractions from nonprogressive movements is based on degree of amplitude and duration of the PWD signal. More specifically, when crescendo-decrescendo waveforms or organized large excursions from baseline (the emitting frequency of the ultrasound transducer) are observed (indicating large shifts of the contents within the sample volume), activity is described as probably peristaltic. Alternatively, when no or minimal deviation from baseline is detected, the gastrointestinal tract is classified as having no peristaltic activity.13 In rabbits, gastrointestinal activity is reported to infrequently involve true aborad peristaltic motion and more frequently segmentation motion throughout the intestinal tract,15 although such observations have not been confirmed via ultrasonography.
Given findings in humans, horses, and dogs, duplex Doppler ultrasonography could provide a minimally stressful and objective technique for assessing gastrointestinal activity in rabbits and has potential as an additional diagnostic technique for differentiating between obstructive and nonobstructive gastrointestinal disease. At the authors’ institution, abdominal ultrasonography has typically been performed on nonsedated rabbits, which generally appear to tolerate the procedure well. However, distressed rabbits brought for evaluation have typically been sedated prior to any extensive handling or diagnostic testing, which may affect gastrointestinal motility. For example, xylazine, ketamine, and acepromazine have different effects on small intestinal motility in horses and dogs.11,14
The purpose of the study reported here was to explore the usefulness of duplex Doppler ultrasonography for evaluation of gastrointestinal activity in healthy nonsedated and sedated rabbits and to evaluate agreement between B-mode and PWD ultrasonographic measurements. We believed that focused ultrasonography of the gastrointestinal tract would be well tolerated by nonsedated and sedated rabbits. We hypothesized that the number of peristaltic contractions as measured via B-mode and PWD ultrasonography would not differ significantly, regardless of sedation status, and that there would be no difference in the number of peristaltic contractions between non-sedated and sedated rabbits.
Funded by the Association of Exotic Mammal Veterinarians 2016 Benjamin and Bella Rabbit Research Grant.
Presented in abstract form at the 15th Annual Conference of the Association of Exotic Mammal Veterinarians, Dallas, September 2017.
The authors thank Dr. Joanna Webb for data collection and patient recruitment.
Philips EPIQ 7, Philips, Bothell, Wash.
Carestream Health Inc, Rochester, N Y.
Epiphan DVI2USB, Epiphan Systems Inc, Palo Alto, Calif.
Wirecast, Telestream LLC, Sterling, Va.
Camtastia, TechSmith Corp, Okemos, Mich.
Quicktime, Apple, Cupertino, Calif.
Torbugesic, Fort Dodge Animal Health, Overland Park, Kan.
Midazolam, West-Ward Pharmaceutical Corp, Eatontown, NJ.
Putney Inc, Portland, Me.
SAS, version 9.4, SAS Institute Inc, Cary, NC.
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