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Laparoscopic Ultrasound in the Evaluation of Abdominal Structures in the Horse
Transcutaneous ultrasonography is considered as a very valuable tool in examining abdominal organs in horses but has several anatomical limits. The utilization of a laparoscopic ultrasound probe using minimal invasive methods (like in human medicine) is documented in this report.

Laparoscopic examination and treatment in horses has achieved considerable acceptance in recent years [1-9]. While many advances have been made in the routine applications of this modality, there remain many unanswered questions as a result of the anatomic limitations inherent to the species.

The utilization of transcutaneous ultrasonography, while remaining a very valuable tool, has certain restrictions and cannot be used to its full potential due, at least in part, to the inherent limitations of size of the structure to be examined, location of specific structures within the abdominal cavity, presence of gas filled intestinal structures, lungs and ribs, which all interfere with ultrasonographic evaluation using the transcutaneous approach. Based on the restrictions described above, it is logical to consider the possibility of combining these two modalities to maximize their potential in veterinary medicine. The concept of laparoscopic ultrasonography (LUS) has been well established in human medicine for a considerable time. Intra-operative ultrasonography (IOUS or IUS) refers to the utilization of ultrasonic examination during the course of a conventional operation and implies the direct application of an ultrasound probe head to an intra-abdominal organ or structure while maintaining a sterile field. Laparoscopic ultrasonography involves the utilization of the principle of minimal invasive surgery combined with ultrasonography whereby the ultrasound head in the form of a laparoscopic probe is inserted through a laparoscopic trochar and placed directly on the organ to be examined. The application of these methods in this manner was named invasive ultrasound by Hölscher in 1995 [10].

This report documents the utilization of an ultrasound probe currently used in human medicine using minimal invasive methods to examine abdominal structures in the horse. Specific information is presented relative to operative positioning and examination of horses of various sizes, an aspect of particular interest to practitioners.

Method
Whenever possible, feed should be withheld from patients for 24 hours in preparation for the examination, water may be offered ad libitum. The operative site is prepared in a standard manner as for conventional surgery. The procedure may be performed in either the standing or recumbent patient. In standing patients, sedation with an alpha-2 agonist (detomidine 0.02 mg/kg body weight, or with Sedivet® romifidine 0.08 mg/kg body weight). Levomethadon (Polamivet® 0.1 mg/kg body weight) is used as analgesic medication.

The two trochar sites in the center of the flank on the upper limit of the internal abdominal oblique muscle and 10 cm directly ventral to this site are infused with Lidocaine 2% at subcutaneous and intramuscular levels to desensitize the animal, allowing placement a laparoscopic trochar. Following placement of the rigid optic and insufflation of the peritoneal cavity with CO2 to a pressure of 8 - 10 mm Hg, inspection of the abdominal structures is performed in a systematic manner. Investigations on recumbent animals are accomplished under general anesthesia by means of isoflurane and O2 using intermittent positive pressure ventilation. The intra-abdominal pressure in recumbent animals may be raised to as high as 15 mm Hg. Following insufflation, the abdomen is explored according to the method of Scharner et al., [11]. Using this technique in decumbency allows for placement of the optic in the midline and the ultrasound probe in either left and/or right flank locations thus optimizing the placement of the ultrasound probe on a wider spectrum of organs.
Positioning the body in a head-down or head-up position may be used to improve the visibility of organs in selected abdominal and pelvic regions [12] and may also facilitate sonographic probe placement and evaluation.

The initial laparoscopic examination of all visible organs is followed by insertion of the ultrasonic probe through a separate port and direct placement on all available organs under laparoscopic visualization. The endoscopic tower (monitor on the top) should be positioned on the opposite side of the horse and oriented in the same axis as the optic channel.

An additional person operating the ultrasound equipment and associated instruments greatly facilitates the collection and optimal documentation of images. The coordination of laparoscopic and ultrasound images, enhancement of ultrasound images (focus, penetration, contrast) and video-endoscopic images can thus be managed to maximize and optimize all data collection.

Equipment
The ultrasound machine was combined with a laparoscopic linear transducer settings of 5.0, 7.5 and 8.0 MHz (Toshiba, Eccocee SSA-34A/3E, working length 40 cm). The laparoscopic sonography requires a twin video system for mixing two pictures on the monitor with a port for the telescope and a second for the ultrasound machine (Twin video, Storz).
The authors worked with a three-chip camera (Storz) and a light source (300 watt xenon light source). Standard endoscopic / laparoscopic technique was utilized in combination with a rigid endoscope 57 cm in length with a viewing angle of 30º. Standard surgical equipment was used to facilitate minimal invasive approaches and closures of the abdomen. Video images were stored on SVHS videotape, on black / white photographs (Sony) or on a still recorder (Sony).

Results
It was possible to complete all abdominal investigations in the standing horse without difficulty. Following a short initial learning phase, it was possible to easily apply the ultrasound probe to the desired abdominal organ which is considered to be an advantage over the transcutaneous method, which requires constant vigilance to obtain ultrasound (US) imaging of the desired organ or organ part. This is particularly so in those organs which must be visualized between the ribs using the larger transcutaneous probes which often provide limited visual fields. In addition, the relatively large image field obtained provides improved tissue details and better orientation relative to the complete organ thus further facilitating the examination. A further advantage of LUS is related to the reduced effect of movement which normally interferes with constant, prolonged imaging of a specific organ or tissue using the transcutaneous method. Using direct application of the probe head to the selected surface under direct vision establishes controlled imaging despite moderate animal body, abdominal wall or organ movements relative to body positioning, respiratory or intra-abdominal organ position changes. The ability to examine organs in multiple planes under visualization significantly increases the amount of information collected due to the utilization of the previously described three dimensional effect of internal organs which now become Laparoscopic Ultrasound in the Evaluation of Abdominal Structures in the Horse possible using the addition of the laparoscopic modality but which are not feasible using the transcutaneous technique.

Source: K. Gerlach and J. G. Ferguson: Laparoscopic Ultrasound in the Evaluation of Abdominal Structures in the Horse (Last Updated: 23-May-2003 )
In: Recent Advances in Laparoscopy and Thoracoscopy, Ferguson J.G. (Ed.)
International Veterinary Information Service, Ithaca NY (www.ivis.org), 2003; A1108.0303








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