BODY CAVITY SONOGRAPHY IN THE FIELD
Assessment with Sonography in the Horse) (Bevevino et al., 2023 ) evaluations. These protocols, like the FLASH protocol for colic, are designed to identify specific abnormalities such as the presence of effusions, evidence of cardiac compromise and lung pathology (Bevevino et al., 2023 ; Eberhardt & Schwarzwald, 2022 ). The pro- tocols have been evaluated for clinical relevance and efficiency, as well as the ability of clinicians to learn them rapidly (Bevevino et al., 2023 ; Eberhardt & Schwarzwald, 2022 ). In addition to evaluating the interior of the thoracic cavity, ul-
trasonography is an effective modality for detecting rib fractures. Rib fractures can be a source of local pain and swelling or may be an occult cause of behaviour change or poor performance (Hall et al., 2023 ). Thoracic trauma resulting in rib fractures can also be a cause of acute haemo- and/or pneumothorax (Reef, 2012 ). Radiographic evaluation is limited in the identification of rib frac- tures in adult horses due to body size and superimposition of the cardiac silhouette and other structures. Ultrasonographic evaluation was shown to be superior to radiography (98% vs. 42% detected) in a study of 59 horses in which rib fractures were confirmed by nuclear scintigraphy (Hall et al., 2023 ). Because the rib surfaces are located 2 to 4 cm deep to the skin surface, they are best evaluated with a 7.5–15.0 MHz linear transducer at a depth setting of 5 to 6 cm. Keeping the transducer face on the rib can be facilitated by placing a finger on either side of the transducer within the intercostal spaces cranial and caudal to the rib of interest. Regardless of the type of examination, proper, thorough patient
preparation is essential for the acquisition of high- quality images. For ideal image quality, as much of the hair coat as possible should be removed by clipping with a #40 blade, and the skin washed with soap and warm water. It may not be practical in all cases to clip the entire abdomen or thorax (horses that live out in the winter time especially); in this case, clipping small windows in areas of interest can be useful to improve the image. Application of acoustic gel to the skin provides a coupling substrate. Warming the gel prior to
(a)
| 599
application promotes vasodilation in the skin, facilitating the trans- mission of sound waves. If clipping is not possible (or prohibitively impractical, as in the
case of the FLASH exam), the hair coat should at least be brushed thoroughly to remove dirt and debris, as these will block the trans- mission of sound waves. If not clipping, isopropyl alcohol or warm water is used instead of gel to wet the hair and provide a coupling substrate (Figure 1 ). When using alcohol, especially in cool environ- ments, evaporation will cause piloerection and impede further im- aging through the resultant trapping of air at the skin surface, even when alcohol is re- applied. Thus, applying alcohol to one small area at a time as that area is being evaluated is strongly recommended over dousing the entire side of the horse at the beginning of the examination. In addition to external preparation of the patient, sometimes it
is possible to improve examinations by fasting the patient for 12–24 h prior to evaluation. Visceral gas is a major impediment to visu- alisation of the abdominal contents of the horse. Additionally, the small intestine is a common site for digestive dysfunction resulting in weight loss, protein loss and chronic intermittent colic, but is poorly visualised in the horse due to colonic gas, its anatomic location and the presence of ingesta within the small intestinal lumen. Fasting has been shown to have the effects of decreasing gas in the large colon, slowing peristalsis of the small intestine and reducing the overall size of the stomach (Epstein & Hall, 2022 ; Mitchell et al., 2005 ; Norman et al., 2010 ). Diminishing the size of the colon and stomach and emptying the small intestine favours descent of the jejunum to the ventral abdomen where it can be more readily examined (Epstein & Hall, 2022 ; Mitchell et al., 2005 ; Norman et al., 2010 ). This effect has been demonstrated to improve measures of small intestinal vis- ibility and definition (Norman et al., 2010 ). Especially in the inguinal area, small intestine adjacent to the body wall may allow interroga- tion with higher frequency transducers, thus yielding more detailed information about intestinal wall thickness and layering.
(b)
FIGURE 1 Effect of patient preparation for equine abdominal sonography. These images were obtained minutes apart from the same horse with no change in machine settings. (a) Obtained with isopropyl alcohol applied to clean, unclipped hair. (b) Obtained with ultrasound coupling gel applied to skin after clipping with a #40 blade.
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