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Rigid endoscopes are more convenient than flexible endoscopes for examining and performing procedures in body cavities [7–9]. Rigid scopes (i.e., telescopes) are also much simpler in design and less expensive than flexible endoscopes. Despite their lens system and fiber optics, they do not contain flexible materials, are easier to clean and maintain, and have a longer working lifespan [10]. Some models may include a working channel, integrated instrument, or a variable viewing angle, which allows a wider viewing field, in narrow deep anatomical regions. State‐of‐the‐art rigid telescopes are constructed with high‐quality optical glass rod lenses (HOPKINS^® rod lenses), producing high‐quality images that are bright, magnified, wide angle, and of high resolution and contrast [1–5, 9]. No single model of rigid endoscope is universally suitable. The appropriately sized telescope should be selected based on the surgical procedure, size, and morphology of the patient and ultimately by the preference and experience of the surgeon. Although smaller scopes tend to be more versatile, they are also more prone to breakage, and their illumination capacity is limited when used in larger, more light‐absorptive cavities such as the abdomen or thorax of large breed dogs.

Table 3.1 Image troubleshooting guide.

Problem	Possible cause	Resolution
Image is not clear	Fogged or dirty lens	Blot distal lens of telescope on live tissue or apply antifog agent to lens.
	Fogged distal lens	Immerse telescope in warm sterile water or apply antifog agent to lens.
	Dirty eyepiece, camera, or adapter	Clean using cotton swab moistened with sterile water.
	Lens not adjusted to operator's eyesight	Rotate focus adjustment ring on camera head until image is clear.
	Internal fluid damage or cracked rod lens	Moisture within telescope will permanently cloud lens in distal end or eyepiece (repair by manufacturer).
	Misconnected camera on telescope eyepiece	Check for proper coupling and positioning of camera head to telescope by adjusting adapter.
Image is too dark or too bright	Dirty light guide	Clean light‐guide connector and distal tip using gauze moistened with sterile water.
	Improper light source or camera settings	Adjust brightness control knob, camera gain, or manual aperture setting.
	Old or improperly installed lamp	Properly install lamp; replace old lamp.
Image is too blue	White balance improperly done or not done before telescope insertion into patient	Remove telescope from patient, clean distal lens, and perform white balance correctly.
Deficient illumination	Bulb lifespan ending	Check working hours on light source; replace bulb or activate alternate bulb inside light source.
	Improperly connected light cable	Check for correct and full insertion of light‐transmitting cable.
	Worn light cable (broken fibers)	If >30% of light‐transmitting capacity is lost, then substitute cable.
	Light source on stand‐by mode	Check and press stand‐by button to activate light output.
	Light source is turned down	Increase light source output.
Loss of pneumoperitoneum	Empty tank or closed valve from gas supply	Check gas remaining in tank; replace tank; open valves of general gas supply.
	Open Luer‐lock on one or more trocars, leaking gas	Check and close all stopcocks except the one coming from the insufflator.
	Blockage of line going to patient	Be sure the tip of the Veress needle is not blocked by tissue and that the valve on the Veress needle or gas input cannula is open to incoming gas.
	Leaky cannula valve or sealing cap	Assure proper assembly and functioning of each cannula and replace any worn sealing caps.
	Leakage around portal sites	Check for leakage around wounds and suture closed where necessary.
No image on screen or monitor or black and white image only	Connector into front of the camera control unit (CCU) is not fully inserted, dirty, or wet	Clean and dry the connector and replace securely.
	Video cables between the CCU and monitor are faulty or not tightly connected	Tighten connections and replace cables, if necessary.
	Camera head cable that connects to CCU is damaged	Send to the manufacturer for repair.
	One or more devices in the video chain are not activated or damaged	Check that all devices in the video chain are turned on and have proper and tightly connected power cords.

Figure 3.2 Rigid endoscopes used in laparoscopy and thoracoscopy. From bottom to top: 4 mm 30°; 5 mm 0°; 10 mm 0° and 10 mm ENDOCAMELEON variable angle laparoscope.

Source: © KARL STORZ SE & Co. KG, Germany.

Standard surgical telescopes come in a variety of sizes (Figure 3.2). The most versatile and popular rigid telescopes used in small animal laparoscopy and thoracoscopy are 5 mm in diameter and approximately 30 cm in length. Smaller rigid endoscopes, 2.7 or 3 mm in diameter and 14–18 cm long are ideal for cats, puppies, and toy breeds. With a smaller diameter and shorter shaft, these are easier to maneuver in smaller patients but too short in larger patients, and their light‐carrying capacity may be inadequate in larger cavities, due to the small diameter of the telescope. Telescopes larger than 5 mm in diameter have decreased in popularity, mostly because of the improvements in image size and brightness of 5‐mm and smaller telescopes [1–5, 8, 9].

Conversely, the 10 mm diameter operating laparoscope has become popular. It contains optics similar to that of a 5‐mm telescope but has an integrated working channel that allows passage of 5‐mm instruments down the same shaft. Operating scopes are available in two types: right angled or oblique (Figure 3.3). Some surgeons prefer this style of telescope for certain routine procedures such as biopsies, ovariectomies, and lately natural orifice translumenal endoscopic surgery (NOTES) because the instruments are always under visual control. For this reason, an operating telescope may also be recommended for novice endoscopic surgeons [1–5].

Figure 3.3 Operating laparoscopes. (A). Right angled. (B). Oblique.

Source: © KARL STORZ SE & Co. KG, Germany.

The viewing angle of a telescope is an important consideration because it affects both orientation and visual access (Figure 3.4). Standard forward‐viewing telescopes (0°) provide the simplest spatial orientation, centered on the axis of the telescope, but they present a relatively limited viewing field. A 30° distal tip angle allows the surgeon to view a larger area by simply rotating the shaft of the telescope on its longitudinal axis [8, 9]. With experience, the operator becomes proficient at using angled telescopes, thus gaining a wider viewing field. Telescopes with more acute tip angulations are also available (70, 90, and 120°), but they are rarely used in small animal laparoscopy and thoracoscopy [1–5].

Relatively new dynamic‐range rigid telescopes are available with a variable viewing angle, allowing the surgeon to control angulation from 0 to 120°, with a mechanical twisting mechanism near the eyepiece: ENDOCAMELEON – Karl Storz SE & Co. (Figure 3.5). These newer telescopes are currently used for selected procedures, mainly because of their versatile viewing abilities [10–12].

Figure 3.4 Telescope viewing angles. (A). 0°. (B). 30°.

Source: © KARL STORZ SE & Co. KG, Germany.

Figure 3.5 ENDOCAMELEON^® telescope with variable viewing angle, adjusted by turning the collar on the eyepiece.

Source: © KARL STORZ SE & Co. KG, Germany.

These variable angle scopes are available in 4 and 10 mm diameter, for different size patients, the smaller size also being used for arthroscopy in humans. These newer scopes provide the surgeon with the ability to evaluate more thoroughly and maneuver the scope more easily, with an emphasis on thoracoscopic surgery. A recent study conducted at NCSU College of Veterinary Medicine demonstrated the advantages of the variable‐angle rigid scopes by providing an optimal alternative to circumvent the visual impediments of lung expansion during thoracoscopy when one‐lung ventilation is not feasible [10]. This study reveals that the use of an ENDOCAMELEON^® significantly shortens exploratory thoracoscopic procedures, compared to the use of a standard fixed 30° angle telescope, while ventilating both lungs. The variable‐angle lens was also found to minimize iatrogenic injuries due to reduced maneuvering in the cavity compared to standard scopes [10–12].

Although fluorescence specific scopes exist (see next section on fluorescence imaging), the standard scopes can also be used, by adding a “snap‐on” dedicated filter between the ocular of the scope and the camera head lens, thus filtering the image to make visible the specific desired wavelengths. The subtracted light is eliminated from the picture, and a specific contrast obtained for the final image displayed on the screen. However, it is highly suggested for routine work with NIR that NIR‐dedicated scopes with integral filters be used since the snap‐on filters do not provide the same quality.

Using a telescope and instruments of the same diameter (i.e., 5 mm) is convenient for maximum flexibility during surgery and allows for exchanging location of the telescope and instruments during a procedure without exchanging ports [1–5, 9]. Nevertheless, trocar cannula can be fitted with a reducer to accommodate smaller diameter instrumentation without loss of pneumoperitoneum [9].

The development and adoption by surgeons of smaller diameter endoscopes has resulted in the detail provided by full HD miniature laparoscopy and the increasing trend toward needlescopy and associated instrumentation sets. That stated, miniature laparoscopy and needlescopy techniques make use of any rigid scope with a diameter equal to or smaller than 3.3 mm. The most common scope range used in clinical practice includes the 2.0, 2.4, 2.7, 3.0, and 3.3 mm. Therefore, the instrumentation varies from 2.0 to 3.5 mm. These scope lengths range from 14 to 25 cm allowing complete surgical access to deeper anatomic structures, even in medium‐sized patients.

Despite the wide range of smaller scopes available on the market, the most common choices for surgical procedures in dogs and cats are 2.4 mm × 18 cm × 30°, 2.7 mm × 18 cm × 30°, and the 3.0 mm × 14 cm × 0°. For those scopes, the trocar diameter ranges from 2.5 to 3.9 mm according to the size and accessory instruments.

The increasing demand for more advanced and complex procedures, which lead many surgeons to choose a VALS (video‐assisted laparoscopic surgery) or VATS (video‐assisted thoracic surgery) approach, has also resulted in the increasing use of exoscopes. An exoscope vastly improves visibility without occupying space inside the cavity being operated and also offers magnification abilities that provide up to 26 times the real structures' dimensions. The ergonomics and extended possibilities of exoscopes in combination with fluorescence technologies or 3D imaging put these surgical aids among the top requested trends, both in open and endoscopic‐assisted surgical procedures. The standard exoscope is 10 mm in diameter and 11 cm long and has high‐powered special illumination components. A 90° angle of view exoscope is available, which interferes as little as possible with the surgeon's instrumentation and range of motion, when enhanced ergonomics are desired. Special fluorescence technology exoscopes exist as well, which help map either vascular or neoplastic tissues, thus enabling the surgeon to identify the safest surgical margins.