Medical or veterinary device

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Disposable trocars Laparoscopic instruments for insertion through trocars

A trocar (or trochar) is a medical or veterinary device used in minimally invasive surgery. Trocars are typically made up of an awl (which may be metal or plastic with a pointed or tapered tip), a cannula (essentially a rigid hollow tube) and often a seal.[1][2] Some trocars also include a valve mechanism to allow for insufflation. Trocars are designed for placement through the chest and abdominal walls during thoracoscopic and laparoscopic surgery, and each trocar functions as a portal for the subsequent insertion of other endoscopic instruments such as grasper, scissors, stapler, electrocautery, suction tip, etc. — hence the more commonly used colloquial jargon "port". Trocars also allow passive evacuation of excess gas or fluid from organs within the body.

Etymology

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The word trocar, less commonly trochar,[3] comes from French trocart or trocar, itself either from trois-quarts 'three fourths' or from trois carres 'three sides';[4][5][6] in any case referring to the instrument's triangular point. First recorded in the Dictionnaire des Arts et des Sciences, 1694,[7] by Thomas Corneille, younger brother of Pierre Corneille.

History

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Trocar, c. 1850

Originally, doctors used trocars to relieve pressure build-up of fluids (edema) or gases (bloating). Patents for trocars appeared early in the 19th century, although their use dated back possibly thousands of years. By the middle of the 19th century, trocar-cannulas had become sophisticated, such as Reginald Southey's invention of the Southey tube.[8]

Applications

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Medical/surgical use

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Trocars are used in medicine to access and drain collections of fluid such as in a patient with hydrothorax or ascites.

In modern times, surgical trocars are used to perform laparoscopic surgery. They are deployed as a means of introduction for cameras and laparoscopic hand instruments, such as scissors, graspers, etc., to perform surgery hitherto carried out by making a large abdominal incision, something that has revolutionized patient care. Today, surgical trocars are most commonly a single patient use instrument and have graduated from the "three-point" design that gave them their name to either a flat bladed "dilating-tip" product or something that is entirely blade free. This latter design offers greater patient safety due to the technique used to insert them.

Trocar insertion can lead to a perforating puncture wound of an underlying organ resulting in a medical complication. Thus, for instance, a laparoscopic intra-abdominal trocar insertion can lead to bowel injury leading to peritonitis or injury to large blood vessels with hemorrhage.[9]

Embalming

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Trocars are also used near the end of the embalming process to provide drainage of bodily fluids and organs after the vascular replacement of blood with embalming chemicals. Rather than a round tube being inserted, the three-sided knife of the classic trocar would split the outer skin into three "wings" which was then easily sutured closed. In a less obtrusive way, a trocar button can be used in place of a suture. It is attached to a suction hose, usually attached to a water aspirator, but an electric aspirator can also be used. The process of removing gas, fluids, and semi-solids from the body cavities and hollow organs using the trocar is known as aspiration. The instrument is inserted into the body two inches to the (anatomical) left and two inches up from the navel. After the thoracic, abdominal, and pelvic cavities have been aspirated, the embalmer injects cavity fluid into the thoracic, abdominal and pelvic cavities, usually using a smaller trocar attached via a hose connected to a bottle of high-index cavity fluid. The bottle is held upside down in the air so as to let gravity take the cavity fluid through the trocar and into the cavities. There is a small thumb hole attached to the fluid injector to control the flow of liquid. The embalmer moves the trocar in the same manner used when aspirating the cavities. In order to fully and evenly distribute the chemical, it is recommended to use 1 bottle of cavity fluid for the thoracic cavity and 1 for the abdominal cavity.

After cavity embalming has been finished, the puncture is commonly sealed using a small plastic object resembling a screw, called a trocar button.

Veterinary use

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Trocars are widely used by veterinarians not only for draining hydrothorax, ascites, or for introducing instruments in laparoscopic surgery, but for acute animal-specific conditions as well. In cases of ruminal tympany in cattle, a wide-bore trocar may be passed through the skin into the rumen to release trapped gas.[10] In dogs, a similar procedure is often performed for patients presenting with gastric dilatation volvulus in which a wide-bore trocar is passed through the skin into the stomach to immediately decompress the stomach. Depending on the severity of clinical signs on presentation, this is often performed after pain management has been administered but prior to general anaesthesia. Definitive surgical treatment involves anatomical repositioning of the stomach and spleen followed by a right-sided gastropexy.[11] Depending on the severity, partial gastrectomy and/or splenectomy may be indicated if the relevant tissues have necrosed due to ischemia caused by torsion/avulsion of the supplying vasculature.

In popular culture

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In the movie Far from the Madding Crowd (1967) Gabriel Oak, played by Alan Bates, uses a trocar to aspirate abdominal gasses from Bathsheba Everdene's herd of sheep who had strayed into a field of clover and were bloated.

In the movie True Lies, Arnold Schwarzenegger's character, having picked the lock on his handcuffs, uses a Patterson trocar to kill his guard prior to breaking the neck of his torturer.

Citations

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General and cited references

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• Janet Amundson Romich. An illustrated guide to veterinary medical terminology, Volume 1
• Mayer, Robert (2006). Embalming: History, Theory, and Practice (4th ed.). McGraw-Hill. ISBN 0-07-143950-1.

Laparoscopic Trocars

In its simplest form, a trocar is a pen-shaped instrument with a sharp triangular point at one end, typically used inside a hollow tube, known as a cannula or sleeve, to create an opening into the body through which the sleeve may be introduced, to provide an access port during surgery. 

Different Materials and Different Function

The tip design of trocar instrumentation is something that is constantly evolving. The materials, edge design and transparency are factors that may facilitate placement inside the abdominal or thoracic cavity. The clear tip in the trocar above aids laparoscopic entry. Metal robot ports sit next to it on the right.

Such devices have been in use for thousands of years: Aulus Cornelius Celsus detailed the use of trocar-like instruments in his six-volume medical encyclopaedia De Medicina in c.30AD, and Arab physician Albucasis (936–1013) described a similar surgical tool in his own thirty-volume encyclopaedia of medicine, the Kitab al-Tasrif. Use of the term “trocar” was not recorded until the early 1700s and it is most likely a derivation of the French trochart,from trois, meaning “three” and carré, meaning “edge”.

Robotic Trocars as Simple Metal Tubes

Robotic trocars are very minimalistic. They are simple metal tubes that serve as entry points for the robotic instruments. The metal trocars have a disposable plastic valve which maximizes their reusability. There are various inserts (also called Stylets) of different design that allow placement into the body cavity with minimal trauma.

Originally used as a means of draining fluids or gasses from the body, by the mid-18th century, urologists had begun to use trocars to guide surgical scopes into the bladder.  George Kelling is credited with performing the first documented laparoscopic procedure in 1901, during which the German doctor and early advocate of minimally invasive surgery used a trocar and scope to examine the abdominal organs of a dog. In his 1920 paper on diagnostic laparoscopy, American Radiologist Benjamin Henry Orndoff described a pyramidal trocar tip of the kind still in use today.

The 1950s saw the introduction of a dual trocar method, with German gastroenterologist Heinz Kalk among the first surgeons to routinely apply such an approach. Kalk went on to make a number of refinements to the technique, establishing it as a safe and efficient surgical practice, thus laying the foundations of modern laparoscopic surgery. Modern techniques continue to make use of multiple trocars. Most commonly, a primary trocar is used to create a port through which the laparoscope is introduced, with between one and three secondary trocars used to create additional ports of entry for surgical instruments such as scissors and graspers, or to assist in drainage of fluids, as required by the specific procedure.

Today, a very wide range of precision-engineered laparoscopic trocars exists, with instruments available in a variety of lengths and diameters, and with many different styles of tip. Most modern trocars comprise an outer housing assembly, a sleeve that fits inside the housing assembly and a piercing stylus which slots into the sleeve such that the tip protrudes from the lower end of the instrument. The stylus is used to create an opening in the abdominal wall through which the sleeve is inserted and fixed into place, following which the stylus is removed through an opening in the upper end of the instrument to allow insertion of a laparoscope or other surgical tools through the sleeve. Where it was once used to refer solely to the piercing stylus, the term “trocar” is now generally used to refer to the whole assembly.

Gateways for Minimally Invasive Instrumentation

Planning a minimally invasive operation involves an understanding of the steps of the operation and the progression of the different technologies and devices involved. Combined robotic and laparoscopic or thoracic cases require that dissection can start with one technology and allow resection with another. Often times it is necessary to switch camera angles, points of view and a variety of other tools as the operation proceeds. Trocars serve as the gateways that allow minimally invasive instruments to pass.

One of the fundamental techniques of laparoscopy involves creation of a pneumoperitoneum by inflating the abdomen with carbon dioxide to create separation between organs and increase the internal space available for manipulation of surgical instruments. Insufflation, as it is known, can be performed using a Veress needle prior to placement of the primary trocar, or via the trocar itself, through a gas intake port, typically located on the side of the outer housing. Once the laparoscope has been introduced, secondary trocars can be placed under direct laparoscopic observation, to minimise risk of injury.

A gas-tight valve is located at the top of the trocar to allow instruments to be inserted and removed during a procedure without permitting the insufflated carbon dioxide escape. Various types of valve are available, offering different characteristics in terms of leakage, mode of operation and location on the trocar. Spring loaded or magnetic trap-door valves can be operated single-handedly, whereas manually retractable types such as trumpet valves offer low levels of leakage, but require the use of both hands and can sometimes cause damage to instruments during insertion or removal if not fully opened. Flexible silicone seals can be used to minimise gas leakage if instruments of differing diameter need to be inserted through the same port during a procedure. Alternatively, some designs allow for the attachment and removal of a separate outer valve during use, such that the diameter of the valve opening can be matched to that of the required instrument. More recently, a valveless trocar has been designed that makes use of a pressurised curtain of gas at the top of the instrument, eliminating the need for a valve altogether. This approach has the dual benefit of significantly reducing carbon dioxide leakage and smudging of the laparoscope lens, which is problem commonly associated with traditional valve types.

Various designs of single-use and reusable trocar are available. Although the initial cost of a reusable trocar is high, the per-use cost is significantly less than that of disposable types. However, reusable trocars can be difficult to sterilise due to the number of small parts that comprise the valve and gas inlet assemblies. Additionally, over time, the tips can become blunt, and the valves leaky and stiff. Some manufacturers now offer a combination type, employing a reusable sleeve and piercing stylus, in conjunction with a single-use valve assembly.

Sleeves are available with diameters in the range 3mm to 30mm, with 5mm and 10mm being the most commonly used. Sleeves may be metal or plastic, and smooth or threaded, with the latter offering more secure placement within the abdominal wall. Additionally, the end of the sleeve through which the trocar extends may be straight or angled. Optical trocars have a transparent plastic sleeve, into which the laparoscope may be fitted prior to insertion of the trocar, enabling the surgeon to monitor the passage of the instrument through the layers of the abdominal wall. The internal surface of the sleeve must be non-reflective, to avoid light from the laparoscope interfering with the surgeon’s view.

The pointed pyramidal tip from which the trocar gained its name is now one of several different types available, with outer diameters ranging from around 2mm to 15mm. Other designs include flat double-edged blades, and pointed conical tips. Bladed trocars reduce the amount of force needed for the instrument to pass through the abdominal wall. For increased safety, some designs now include a spring-loaded plastic shield that automatically covers the blade as it enters the abdominal cavity. Conical tips can be either metal or plastic and require a small initial incision to be made using a scalpel. They pass through the tissues of the abdominal wall by stretching rather than cutting them. This leads to improved sleeve retention as it is surrounded by intact tissue layers that help hold it in place. The main potential advantages, however, are reduced patient discomfort and recovery time.

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