How to Perform Hysteroscopy in the Mare

1. Introduction

Hysteroscopy is not a common procedure in broodmare practice. A thorough breeding soundness examination that includes transrectal palpation and ultrasonography, endometrial cytology, endometrial biopsy, endometrial culture, and vaginal/cervical speculum examination will detect many reproductive maladies frequently encountered in the mare. However, in some circumstances, these more commonly employed techniques are insufficient to clearly identify or ameliorate the problem, and hysteroscopy has been used to achieve this end. In an early study, 17 of 40 mares admitted to a veterinary teaching hospital with a history of infertility had reproductive tracts that were considered normal on palpation, yet hysteroscopy revealed abnormalities in 26 of these 40 mares.¹ Since that time, abnormalities observed through the use of transrectal ultrasonography have either obviated the need for or alternatively prompted the use of hysteroscopy to render a more definitive diagnosis or treatment.

The use of hysteroscopy in the mare was described as early as the 1960s.² Subsequently, many authors have published articles on the use of hysteroscopy in the mare for a variety of purposes.^1,3–9 While the term hysteroscopy will be used throughout this manuscript, it is also called uteroscopy and has been referred to as examination of the uterus via fibroscopy, endoscopy, and videoendoscopy in other publications. 

2. The Equipment

A flexible videoendoscope, 100 cm in length and 1 to 1.4 cm in diameter, is commonly used for hysteroscopy. The unit should have sufficient light intensity and image quality to optimize visualization of the uterine lumen. Most modern units are equipped with a video monitor, which enhances the examination. The use of recording equipment to capture still and video images is highly recommended to enable review of the procedure and to provide a record of the examination. Ideally, the insertion tube should have a working channel that accommodates ancillary equipment such as catheters, grasping forceps, biopsy forceps, electrocautery loops, and laser fibers.

Since endoscopy equipment is used for examination of a variety of body cavities, it is important that it be thoroughly cleaned and sterilized according to the manufacturer’s instructions between uses. Particular attention should be paid to areas where moisture may accumulate, as these sites provide an environment that facilitates the growth of Pseudomonas aeruginosa. Persistent endometritis with Pseudomonas as well as growth of other organisms has been reported following hysteroscopic procedures.¹⁰ If the equipment has undergone chemical sterilization, it is also imperative that the insertion tube, including all of its channels and the water reservoir, be thoroughly rinsed to remove the disinfecting solutions as these chemicals can be very caustic to mucosal tissues.

3. Preparation of the Mare

The mare should be placed in stocks with the tail wrapped and deviated away from the perineal area. Feces should be evacuated from the rectum and the perineum of the mare should be cleansed in an aseptic manner. Sedation and analgesia should be administered. Most practitioners have a favorite sedation protocol, and the following is the author’s preferred method. Depending on the size and temperament of the mare, she is administered detomidine HCL^a (0.006–0.01 mg/kg, IV), and a catheter is placed in the jugular vein. Depending on the anticipated length of the procedure, 5 or 10 mg of detomidine HCL is added to a 500 or 1000 mL bag of saline, respectively, which is then connected to the catheter in a routine manner. The detomidine/saline mixture is then administered by slow drip until the desired level of sedation is achieved. If necessary, more can be administered during the procedure as needed. The author prefers this method because it maintains a more even level of sedation and avoids the wide fluctuations in sedation that can occur over time with repeated larger boluses of sedative. After the mare is sedated and just prior to the start of the procedure, butorphanol tartrate^b (0.01– 0.02 mg/kg) is administered intravenously thought the catheter.

4. Basic Procedure

Under ideal circumstances, at least three people should be present to perform the hysteroscopic procedure; one person remains at the head of the mare for restraint as well as monitoring and administering sedation, one person inserts and maintains the position of the insertion tube through the cervix, and one person operates the steering controls of the insertion tube and directs the overall procedure.

After the insertion tube has been rinsed thoroughly, the image should be “white balanced” to optimize visualization. It is easy to become disoriented once the insertion tube enters the uterus, especially if rotation of the tube has occurred. Therefore it is helpful, prior to inserting the instrument into the mare, for the operator to select a point of reference and become familiar with the directional controls of the steering tube.

A small amount of sterile lubricant is applied to the end of the insertion tube, avoiding contact with the lens, and the assistant wearing a sterile glove and sleeve carries the insertion tube through the vulva and vestibule into the vagina so that the cervix can be visualized (Fig. 1). The cervix is then penetrated and slightly dilated with the index finger, and the insertion tube is passed through the cervix into the uterus. Once inside the uterus, the lumen needs to be distended to allow visualization. While the hysteroscopic procedure can be performed at any time in the mare’s cycle, diestrus is preferable because, at that time, the cervix is of sufficient length to be grasped around the insertion tube and maintain uterine distention. Administering progestogens to estrous or anestrous mares for 5 to 7 days prior to the procedure can also accomplish this. In periovulatory mares, the cervix may be sufficiently relaxed that the entire hand carrying the insertion tube can be placed though the cervix into the uterine body and then the hand pulled back against the internal cervical os to act as a plug to maintain distention.
 

Distention of the uterine lumen can be accomplished by insufflation with filtered air administered via the endoscopic equipment or by a sterile, isotonic fluid such as saline or lactated Ringer’s solution (LRS). Note that insufflation with air can cause endometrial hyperemia, which should not be misinterpreted as inflammation. The method of distention depends on clinician preference and the purpose of the procedure. Regardless of which method is chosen, over distention of the uterus should be avoided so as not to cause significant discomfort to the patient or damage to the uterus. One study determined that a hysteroscopy can be performed safely and efficiently within a pressure range of 12.8 to 28.6 mm Hg and that clinical or cardiac signs of discomfort or effects on the circulatory system were only registered after pressures significantly exceeded 100 mm Hg.¹¹ Precise monitoring of intraluminal pressures is not practical in most clinical environments, so it is recommended to use only the amount of distention necessary to optimize visualization and to continuously monitor the mare for signs of discomfort. [...]