Principles of Minimally Invasive Surgery

Chapter 13

Principles of Minimally Invasive Surgery

Minimally invasive surgery (i.e., endoscopy) is an important diagnostic and therapeutic tool in veterinary medicine. This chapter provides a brief overview of endoscopic techniques, including underlying principles and a description of equipment. Specific techniques (e.g., thoracoscopic pericardiectomy and removal of osteochondritis dissecans [OCD] lesions) will be found in the relevant chapter(s) for that system, disease, or condition.

Definitions and Terminology

Endoscopy is the use of an instrument (i.e., an endoscope) to visualize the interior of an organ or body cavity that otherwise cannot be examined without surgery. Flexible endoscopy uses an endoscope that can bend to look and/or move around corners. The degree of flexibility depends on the instrument, but the ability to make bends ≥180 degrees is typical for most flexible scopes. Flexible endoscopes have a handle (where the scope is held by the operator), an insertion tube (the part that is inserted into the patient), and an umbilical cord (the part that attaches the scope to the light source and video processor). The biopsy channel is a passage that allows one to place instruments through the scope (e.g., biopsy forceps, foreign body retrieval forceps, aspiration tubes, cytology brushes) and aspirate air or liquids. Immersible scopes can have their handles placed in water without risk of damage.

Rigid endoscopy uses a plastic or metal scope that cannot bend. Sometimes a lens at the tip of the scope may allow one to look at various angles, even back on oneself. An obturator is a device placed through a hollow endoscope to facilitate insertion of the scope into the organ desired (e.g., esophagus, colon). When the obturator has a sharp point designed to facilitate penetration through tissue, it is termed a trocar.

Equipment is inserted into the body through the skin and soft tissue or a natural orifice. Insertion through the skin is done through portals. Portals are defined by their use. The scope is inserted through a scope or camera portal, whereas power and hand tools are inserted through an instrument portal. Cannulas are metal tubes that maintain the portals and protect the instruments. Triangulation refers to successful visualization of the instruments through the scope in a manner that is conducive to performing biopsies or therapeutic procedures within the body cavity.

Gastroduodenoscopy is endoscopy of the esophagus, stomach, and duodenum (and occasionally the upper jejunum). Colonoscopy is endoscopy of the colon. Ileoscopy is endoscopy of the ileum and is performed in conjunction with colonoscopy. Proctoscopy refers to examination of the anus and rectum. Bronchoscopy is endoscopy of the trachea and bronchi, whereas laryngoscopy is examination of the pharynx and larynx. Rhinoscopy generally refers to placing an endoscope through the anterior nares and examining the nasal passages. It may or may not include using an endoscope to examine the choanae. Cystoscopy is endoscopy of the urinary bladder and may be retrograde cystoscopy (advancing the scope through the urethra and into the bladder) or transabdominal cystoscopy (placing the scope through a cannula that has been inserted through the abdominal wall and the bladder wall). Vaginoscopy is endoscopy of the vagina. Laparoscopy is endoscopy of the peritoneal cavity and may be diagnostic (i.e., concerned with biopsy of organs) or interventional (i.e., used to perform minimally invasive surgery, such as gastropexy or placement of a jejunostomy tube). Thoracoscopy is endoscopy of the pleural cavity and likewise may be diagnostic or interventional.

Arthroscopy is endoscopy of a joint. Arthroscopes are always used through cannulas. Other instruments and fluid outflow devices may be used with or without cannulas. Instrumenting refers to the insertion of an endoscope, arthroscope, or other tool into the joint. Triangulation refers to successful visualization of the instruments through the scope in a manner that is conducive to performing biopsies or therapeutic procedures within the joint. The scope is inserted through a scope or camera portal, whereas power and hand tools are inserted through an instrument portal. Fluid flowing into the joint is referred to as inflow or ingress; fluid flowing out of the joint is referred to as outflow or egress. Repeat arthroscopic examination of a joint that has been previously scoped is referred to as second-look arthroscopy. In all endoscopies, a “red out” or a “white out” refers to having the viewing tip of the endoscope so close to the surface of what is being examined that one cannot focus on the surface (i.e., a blur occurs) or to having debris on the viewing end of the scope.

Endoscopy: General Principles, Equipment, and Techniques

Endoscopy is used to biopsy organs, remove foreign objects, examine the interior surface of hollow structures, and perform procedures typically done by more invasive surgery. This technique is valuable only when it is successful and eliminates the need for more invasive surgery. However, if for any of a number of reasons tissue samples obtained endoscopically are inadequate for diagnosis, unacceptable trauma occurs during endoscopic removal of foreign objects, or mucosal surfaces cannot be adequately examined endoscopically, then endoscopy ceases to be useful. Unfortunately, endoscopy sometimes has become more of a “hobby” than an important procedure to be learned and practiced diligently. Flexible endoscopy of the upper gastrointestinal tract in particular is much more difficult to properly perform than is widely appreciated, especially with regard to biopsying the mucosa. Much as is the case for a hemilaminectomy or a tibial plateau leveling osteotomy (TPLO), if the veterinarian is not sufficiently trained or is not going to perform the procedure often enough to maintain expertise, then it is probably best if patients are referred for this procedure.


Flexible Endoscopy

Although flexible endoscopy of the alimentary and respiratory tracts occasionally is performed to dilate a stricture, control hemorrhage, remove part or all of an organ, insert a tube, or remove a foreign object, its primary use in veterinary medicine is to visualize and obtain tissue or cytologic samples (Box 13-1). Biopsy should always be performed regardless of the gross mucosal appearance unless there is a specific reason not to biopsy (e.g., coagulopathy, increased risk of perforation). Tissue samples obtained by flexible endoscopy are limited to the mucosa and adjacent submucosa as opposed to the full-thickness samples obtained surgically. However, endoscopic samples are typically adequate for diagnosis in probably >90% of patients (personal observation of author M.D.W.) with gastric or intestinal infiltrative disease (e.g., inflammatory bowel disease, histoplasmosis, neoplasia), assuming the operator has been well trained. Endoscopy cannot diagnose disorders beyond its reach (e.g., focal carcinoma of mid-jejunum). Nor can endoscopy reliably diagnose infiltrates that are too deep in the mucosa for the endoscopic biopsy forceps to reach or those that are hard, densely fibrotic lesions (e.g., pythiosis, scirrhous carcinoma).

image Box 13-1   Primary Indications for Endoscopic Procedures in Dogs and Cats

Cytologic studies from endoscopic brushings or washes are occasionally diagnostic for disorders such as cancer, histoplasmosis, protothecosis, and eosinophilic enteritis. Histoplasmosis occasionally has been diagnosed cytologically when it was missed histologically. However, most inflammatory bowel diseases (especially lymphocytic-plasmacytic infiltrates) cannot be definitively diagnosed cytologically. Washings are especially useful in the respiratory tract to diagnose inflammatory or infiltrative problems, but they may also be useful in the search for gastric Ollulanus tricuspis infestation or duodenal giardiasis.

Rectal and gastric polyps can be removed endoscopically, although endoscopic snares fitted for electrocautery are required. However, because rectal polyps usually are found close to the rectum, surgical removal typically is easier and more certain to remove the entire polyp. Endoscopic polypectomies should be attempted only if the practitioner has been trained in endoscopic electrocautery; inappropriate use of electrocautery can damage or destroy the endoscope and/or video processor.

Percutaneous placement of gastrostomy feeding tubes can be done with or without endoscopy (see p. 107). Endoscopic placement of such tubes is indicated when the nonendoscopic apparatus for placement cannot be safely passed through the esophagus (e.g., esophageal stricture, esophageal dilation), when the operator is inadequately trained in the use of nonendoscopic apparatus, or when the endoscope is already in the stomach for other purposes. Endoscopic placement includes insufflation of the stomach, which is advantageous because insufflation helps prevent other abdominal organs from becoming trapped between the stomach and the abdominal wall.

Endoscopic dilation of benign esophageal strictures caused by post-esophagitis scarring is preferred to surgical resection. Strictures can recur after either method, but surgery may be associated with greater postprocedural morbidity and mortality and has a higher recurrence rate.

Severe upper gastrointestinal hemorrhage and persistent vaginal hemorrhage are indications for endoscopy. Endoscopy may help determine whether surgery is indicated and ensure that all bleeding sites are located. Intraoperative endoscopy can find bleeding gastric mucosal lesions if the surgeon cannot identify them at surgery; large ulcers may be missed when the stomach is examined only through a gastrostomy incision. Severely hemorrhaging lesions may require endoscopic electrocautery or injection with alcohol. Endoscopy may also detect small mucosal tumors undetectable from the serosal surface.


Flexible Endoscopes

Endoscopes: The equipment needed depends on the type of endoscopy and the body system to be investigated. Rigid and flexible endoscopes are available in a large assortment of sizes and lengths; both types have advantages and disadvantages (Box 13-2). Flexible endoscopes most often used in veterinary medicine are gastroduodenoscopes, bronchoscopes, and colonoscopes. Flexible scopes have a handle, an insertion tube, and an umbilical cord (Fig. 13-1). Bronchoscopes usually have a 2- to 6-mm outer diameter, gastroduodenoscopes a 7.9- to 10-mm outer diameter, and colonoscopes a 10- to 16-mm outer diameter. All scopes should have a biopsy-suction channel (usually 2 mm in diameter for bronchoscopes and 2- to 3.2-mm for gastroduodenoscopes and colonoscopes). Gastroduodenoscopes and colonoscopes have four-way deflection of the tip of the scope and an air-water channel that is used to insufflate air and wash off the viewing lens; bronchoscopes and ultrathin gastroduodenoscopes typically have only two-way deflection of the tip. Bronchoscopes do not have an air-water channel. The insertion tube typically has a working length of 40 to 60 cm in bronchoscopes, 100 to 135 cm in gastroduodenoscopes, and 130 to 220 cm in colonoscopes.

The ideal assortment of flexible scopes depends on the expertise of the operator and what procedures are anticipated. Ideally, a bronchoscope (4- to 5-mm diameter), a pediatric gastroduodenoscope (≤7.9-mm diameter with a 2-mm channel), and a regular gastroduodenoscope (8.5- to 9.8-mm diameter with a 2.8-mm channel) allow one to perform almost all procedures. Other flexible scopes that might be considered depending on one’s needs are a 1.6-meter pediatric colonoscope (helpful in extremely large animals and large, exotic cats) and an ultrathin bronchoscope or ureteroscope for small birds, pocket pets, and flexible cystoscopy or rhinoscopy. If you can purchase only two scopes, which will be used for both alimentary and respiratory tract work, consider a bronchoscope (4- to 5-mm diameter) and a gastroduodenoscope (8.5- to 9-mm outer diameter with a 2.8-mm channel). If you want only one scope and your clinic wishes to perform both respiratory and alimentary tract endoscopy, a 7.9-mm outer diameter pediatric gastroduodenoscope may be the best compromise. If you wish to obtain only one scope and it will be used only for alimentary tract endoscopy, an 8.5-mm outer diameter scope with a 2.8-mm channel is preferable.

Biopsy/cytology equipment: Biopsy and foreign body retrieval forceps for flexible scopes come in various shapes. The size of the forceps depends on the size of the biopsy aspiration channel; the larger the channel, the bigger and stronger the biopsy or retrieval device that can be used. If possible, a scope with a 2.8-mm channel should be used for most alimentary tract endoscopy in dogs and in cats weighing more than 3 to 4 kg. The tissue sample obtained through a 2.8-mm channel can be more than twice the size of a sample obtained through a 2-mm channel. These larger pieces of alimentary tissue can easily contain the full thickness of the mucosa and often some submucosa. The author (M.D.W.) prefers fenestrated biopsy forceps in an ellipsoid, alligator jaw configuration without a needle (Fig. 13-2); however, other endoscopists have other preferences that work for them. Disposable biopsy forceps are widely used in human medicine but seem to offer no real advantage in veterinary medicine.

Equipment used to obtain samples for cytology and culture typically consists of a stiff brush in a plastic tube. This brush is manually extended out the tip of the plastic tube once the tip of the brush assembly has been advanced through the endoscopic biopsy channel and is near the tissue to be sampled. However, such brush assemblies can be contaminated as they are passed through the endoscopic channel. Brush assemblies are made for when it is absolutely critical that a noncontaminated sample be obtained (i.e., culture). These brushes consist of an extendable brush that is within an extendable tube that is in yet another tube. The tip of the outermost tube is typically plugged so there is no chance of contamination when the scope is passed through the biopsy channel of the endoscope. Once the tip of the brush assembly is near the site to be cultured, the innermost tube is extended out the end of the outermost tube, and then the brush is extended out the tip of the innermost tube. Brushes for diagnostic purposes should never be cleaned and reused, as opposed to biopsy forceps, which can be used repeatedly.

Interventional tools for flexible endoscopes: A variety of special retrieval instruments are necessary to reliably remove most commonly encountered foreign objects. The most useful devices are a coin retrieval (W-type) forceps, a shark’s tooth forceps (especially useful for firmly grabbing cloth), an alligator jaw forceps, and a four- or six-wire basket (Fig. 13-3). The basket should be made of very flexible wire to facilitate passage over and around an object; however, this quality also makes it easier to bend the wire and ruin the basket. Other retrieval devices include wire snares, three-wire grabbers, magnetic-tip probes, and forceps with nonskid rubber; these instruments are seldom required.

Balloons and bougies have been designed to dilate esophageal strictures. Despite rhetoric that ballooning is superior to bougienage, success is more dependent on the skill and training of the operator than on the equipment used. Esophageal dilation balloons come in two major configurations: “over the wire” or “through the endoscope channel.” It is important to use these as opposed to a round balloon as is found on endotracheal tubes.

Other equipment includes sheathed needles that allow aspiration or intralesional injection of various lesions through the endoscope. A variety of flexible endoscopic biopsy instruments, snares, knives, and probes have electrocautery capability. Electrocautery snares are most commonly used because they allow removal of esophageal, gastric, and colonic polyps; they can also be used to make three or four quadrant “cuts” into esophageal strictures to aid in ballooning difficult lesions.

Sep 11, 2016 | Posted by in SMALL ANIMAL | Comments Off on Principles of Minimally Invasive Surgery
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