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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_605_Библиотеки_им_академика_М_И_Перельмана.pdf
251Classical (Open) Surgery
The consequence is a fast temperature rise within the cells above 100˚C
as well as a volume increase of the intracellular water leading to the bursting of the cells and tissue severance. The thermal expansion within the
tissue is directly correlating to the course of current density within the
tissue. It is assumed that while cutting tissue, the current density field distribution of every electrical arc impact is spherical. This assumption is
made as several electrical arcs are sparking along the cutting electrode at
the same time and the average distance between the electrical arcs are so
far apart, that the thermal impact of these events can be regarded as independent events. The current density and thermal effect decrease with the
fourth power of the distance from the active electrode. The current density
at the electrical arc striking point is very high and decreases strongly with
increasing distance into the tissue. Electrical arcs are only ignited when the
complete electrode is insulated from the tissue by a vapor film. The arcs
strike at the point where the vapor film is thinnest. Once the discharge has
taken place, the thickness of the vapor film at this spot increases and
the next electrical strike is at another position of the active electrode. The
electrical arcs spread out over the total length of the active electrode
[7].
The ignition of electrical arcs is polarity dependent. During the
sinusoidal voltage course only electrical arcs originating from the metal
electrode are ignited as it is easier to withdraw electrons from metal than
from the tissue. The intensity of the electrical arc is directly correlating
with the peak voltage and with increasing electrical arc intensity the
depth of the thermal defect increases.
The cutting and coagulation properties are furthermore affected by
the modulation of the voltage applied to the tissue. A sinusoidal unmodulated voltage results in a smooth cut with a minor hemostasis effect in the
cut edges. The application of strongly modulated voltage with duty cycles
of less than 10% of the same voltage amplitude is preferably used for
hemostasis purposes, due to the higher thermal impact.
A fast ignition of electrical arcs is of great importance for a safe cutting
process. For every cut there is a prevalence of a cut delay. Only when the
voltage of more than 200 V and an insulating layer between the electrode
and the tissue is present can electrical arcs be ignited. As long as ohmic
current flow is present, the ignition of arcs and therefore the start of the
cut is not possible. During this period an extensive thermal damage is
introduced to the surrounding tissue. The higher the initial power introduction chosen, the faster the intracellular water is evaporated to form an
252 Biomedical Engineering in Gastrointestinal Surgery
insulating vapor layer around the electrode. The cut delay duration is
therefore dependent on the initial introduced power level. Once the
vapor cushion is present and the cut is running, less than 10% of the initial current density is required to maintain the cut. In a worst case consideration, e.g., if the initial peak voltage is just below 200 V, a high power
density is introduced into the tissue—too high for coagulation purposes
but too low to initiate a cut. The tissue quickly dehydrates, coagulants are
formed, and a large extent of thermal damage is induced, causing perforations on the one hand and on the other hand the electrode can get stuck
within the tissue to be dissected. No further cut can be initiated.
6.2.14 Electrosurgical Unit
Modern ESUs convert the low-frequency alternating current from the
wall outlet to high-frequency alternating currents from 300 kHz to a
maximum 5 MHz according to the International Electrotechnical
Commission standard 60601-2-2. Today’s ESUs are controlled by microprocessors and are capable of producing a series of different current waveforms that are necessary for electrosurgery. Diverse current waveforms,
current blends, and predefined cutting and coagulation modes can be
selected by the means of monitor-based user interfaces. Furthermore,
manifold safety monitoring features, such as neutral electrode monitoring
and control algorithms in the form of impedance-controlled voltage
management, are implemented in state-of-the-art ESUs.
6.2.15 Clinical Aspects of Electrosurgery
Modern surgery would be inconceivable without electrosurgery.
However, it is also potentially dangerous, mainly through causing thermal
injuries, frequently leading to significant morbidity and mortality and
medicolegal actions.
According to surveys, 18% of general surgeons and gynecologists have
seen at least once visceral burns, and many of them admitted one or more
ongoing causes of litigations due to these burns
[18] plays a major role as well as burns due to the neutral electrode.
Great care has to be taken to avoid these specific risks of electrosurgery, e.g., through continuous training and education. In order to
improve the surgeons knowledge
[19], some specific programs like the
“Fundamental use of surgical energy (FUSE) certification" were developed
[20].
[17]. Insulation failure
Classical (Open) Surgery
253
6.3 ULTRASOUND DISSECTION
Dissection of living tissue is inevitably accompanied by bleeding and
surgeons dreamed of “dry” cutting. Electrocautery was the first step
forward, but the effect of vessel occlusion (hemostasis) was very limited.
More effective tools were required. It was about 40 years ago that a new
principle was introduced into clinical practice to dissect living tissue: cavitation. The phenomenon of cavitation and its effects was originally
detected in early tests of naval propellers: high-frequency vibrations cause
the creation, expansion, and implosion of cavities in liquids. The gases
inside these cavities are compressed and the local temperature is significantly elevated leading to fast corrosion of the propellers. In living tissue,
cavitation leads to the well-known effects of overheating. Fat is melted
away and proteins are transduced from the gel to the sol state (
Under practical conditions, the cavitation effect during surgery is
generated by ultrasound dissection devices.
In medicine, ultrasound is also the denomination of an imaging
technique using sound waves. Ultrasonic dissection (and coagulation),
however, has nothing to do with imaging but is derived from the vibration frequency.
The principle of ultrasonic tissue manipulation is to exert relatively high
amplitude vibrations (80360 μm)tothetissueinafrequencyrange
between 23.5 and 60 kHz. The vibrations are pr oduced by electrical energy,
predominantly by piezoelectric crystals. In an electric field, piezos deform in
a linear and reversible manner. The generator induces a potential difference
Fig. 6.33).
Figure 6.33 (A) The protein of a raw egg is resilient and cannot easily be divided by
force. (B) As soon as it is heated it becomes friable and can be cut easily. All from MITI.
254
Biomedical Engineering in Gastrointestinal Surgery
across the crystal, and polarity changes lead to vibrations. The vibrational
energy is, then, transmitted via the steel rod to the tip of the instrument.
The system consists of the power supply and control unit which is
connected with a cable to the hand piece. The latter consists of the piezoelectric vibration generator and the (exchangeable) instrument tip
(
Fig. 6.34). The instrument tip is most commonly designed as a scissors
(either curved or straight bladed). One blade is shaped by the vibration
steel rod. The correspondent jaw is deflectable with a silicone cushion.
By means of the deflectable arm, tissue can be squeezed against the
vibrating steel rod. Vibration energy initiates collagen denaturation and
breaks tertiary hydrogen bonds between collagen and other extracellular
matrix proteins
[21]. This produces a viscous coagulum which leads to
the sealing effect. Tissues and vessels become an amorphous, condensed
necrotic structure which prevents bleeding out of the cutting edge.
Mechanical pressure and cavitation finally lead to complete dissection.
The process is very similar to baking an egg. By heating the egg protein,
the state is changed from gel to sol. Under surgical conditions this leads
to a reliable occlusion of vessels up to a diameter of 57 mm. Surgical
dissection is facilitated, but a significant reduction of OR time cannot
(yet) be observed
[22].
Ultrasonic dissection devices are provided by several companies, either
as reusable or as partly disposable systems. Most frequently, the scissors are
for single use, whereas the part of the piezoelectric elements can be
Figure 6.34 Tip of reusable laparoscopic ultrasound scissors. The tissue is pressed
against the vibrating steel rod. After mechanical coagulation, it will fall into its two
parts. From MITI.
Classical (Open) Surgery
255
sterilized (Fig. 6.35). The control units are available as stand-alone systems
or embedded into a multifunctional power station (
Fig. 6.36).
As in other energetic soft-tissue treatment modalities, collateral thermal damage is an issue in ultrasonic dissection as well. Though data from
the literature vary, clinically relevant injury may only be expected in the
immediate vicinity of the rod.
Figure 6.35 (A) Hand piece with cable bound power supply. (B) Battery driven ultrasonic dissection device. From (A) MITI and (B) Medtronic GmbH.
Figure 6.36 Power supply and control unit. (A) Stand-alone device; (B) integrated
into a multifunctional unit. All from MITI.
256 Biomedical Engineering in Gastrointestinal Surgery
Plume—or mist—production during ultrasonic dissection is nasty but
immanent to the procedure. In laparoscopic surgery, visualization is deteriorated (see Chapter 7.2.9: Laparoscopic Ultrasound Dissection). The particles
produced are larger than electrosurgery smoke. They consist of fat or, in rare
cases, even of vivid material
[23].However,uptonow,norelevantside
effects have been reported upon.
Conclusively, ultrasonic dissection is an essential pillar of modern open
and minimally invasive surgery.
6.4 WATER JET
Cutting with a high pressure water jet was initially used in industrial applications. At pressure levels about 20,000 bar the water beam reaches supersonic speed enabling it to cut wood without the development of heat or to
remove rubber from airplane landing strips. The first applications in surgery
were attempted in the 1980s. It soon became clear that parenchymal organs,
in particular the liver, were best suited to this technique (
Using the thin laminar liquid-jet effect (
Fig. 6.37B), liver cells can be
removed without destroying cord-like fibrous structures such as the bile
ducts or blood vessels. These decisive structures can be excellently visualized and severed after occlusion (
Fig. 6.38).
Water jet dissection has also been successfully employed in procedures
concerning the prostate, kidney, and parotid gland.
Despite the clear advantages of hydro jet dissection, the initial euphoria was lost in the last couple of years. The large amount of water
combined with cell spillage is not without problems, in particular in the
case of malignant disease.
Pulsed water jet is today gaining interest in endoluminal endoscopic
interventions such as endoscopic submucosal dissection.
Fig. 6.37A).
6.5 STAPLING DEVICES
Reliable closure of anatomical structures or joining visceral organs is crucial in surgery. Over the long history of surgery, hand stitched sutures
were the single option. Surgical sutures need special skills and are timeconsuming, in particular when bowel anastomoses have to be created.
Not surprisingly, numerous approaches were attempted in the history of
modern surgery to develop mechanical assistance in the forming and closing procedures. First, the concept of mating cylinders in various design
variants was developed. H. Hu¨ltl is considered as the father of the stapling
Classical (Open) Surgery
Figure 6.37 Water jet dissection: (A) Helix Hydro-Jet pressure generator [24];
(B) nozzle tip of the instrument with the thin, sharp water jet (arrow). From (A) Rau
HG, Duessel AP, Wurzbacher S. The use of water-jet dissection in open and laparoscopic
liver resection. HPB (Oxford) 2008;10(4):275-80 and (B) MITI.
257
Figure 6.38 Water jet dissection of liver parenchyma: Removal of the parenchymal
cells. Small bile ducts and blood vessels are left over. Occlusion and cutting of the
remaining canalicular structures can then be performed. From MITI.
principle. He disclosed in 1908 the idea of approximating the two wound
edges by means of an U-shaped metallic clip: By pressing it against a staple forming bucket, the typical B-shape is created and adequate compression is exerted on the tissue to provide healing. By combining several
258
Biomedical Engineering in Gastrointestinal Surgery
lines of multiple clips, effective tissue sealing could be achieved. A. von
Petz introduced an improved version in 1921 and the “Petz clamp” found
moderate success in clinical surgery over the next decades. The real
breakthrough of the stapling devices, however, began in 1967, when the
United States Surgical Corporation introduced the first reliable circular
stapler. It was a significantly improved version of former Russian developments
[25]. Today, various companies provide a wide range of different
stapling devices
mature and reliable
[26]. They are slightly different in design, but all of them
[27].
There are three main modern stapler types:
Linear staplers,
Linear cutting staplers,
Circular staplers.
6.5.1 Linear staplers
This type of a stapler, in its numerous variants, joins the tissue by inserting a linear, staggered double or triple row of staples into it. After closure,
the tissue protruding between cartridge and anvil is cut off with a scalpel
(
Fig. 6.39).
The exchangeable cartridge containing the clips is mounted in the
stapler exactly opposite to the anvil. The tissue to be dissected is
positioned in-between. With the first squeeze of the firming handle (or
trigger) the tissue is approximated. A pen is pushed forward to prevent
any escape of the tissue. At this point, the process is still reversible. Using
the release button, the stapler can be opened again and readjusted. If the
trigger is squeezed for the second time, the staples perforate the tissue
layer and are shaped into the “B” form thus inducing a water- and
\airtight closure. A scalpel is used to divide the tissue from the side of the
specimen. Now, the trigger is released and the device can be removed.
Figure 6.39 Linear stapler. From MITI.
Classical (Open) Surgery
259
Originally, staplers were provided as reusable instruments with reload-
able cartridges. They were high precision tools made of steel.
Today, staplers are disposable instruments primarily made of plastics.
The cartridges can still be reloaded for multiple use on the same patient.
Initially, the clips were made of silver. Later on, surgical steel was
used. Today, titanium is preferred.
“Simple” linear staplers are used if a certain part of the GI tract has to
be resected, i.e., to be removed completely. The removal of a Zenker’s
diverticulum is one typical example (
Fig. 6.40).
6.5.2 Linear Cutting Devices
As opposed to simple “linear” staplers, linear cutting devices are designed
to seal both edges of the anatomical structure to which it is applied.
Accordingly, two parallel, linear, staggered double or triple rows of clips
are inserted and dissection is performed in-between. Formerly, tissue separation was achieved by a scalpel inserted into the slit between the middle
of the rows of staples. Today, a knife is simultaneously driven between the
staple rows, dividing them up to one and one half staple lengths from the
distal end (
Linear cutters consist of two separate assemblies which are inserted
independently into the respective segment of the GI tract. Then, they are
mated together and locked during tissue approximation. The stapler is fired
by pushing the firing knob forward toward the distal end of the instrument.
Fig. 6.41).
Figure 6.40 (A) The linear stapler is used to occlude just one edge of the tissue.
Here: Removal of a so-called Zenker’s diverticulum (small bag of the esophagus). The
communication with the esophagus has to be occluded with three stapler lines,
whereas the specimen is removed. (B) After excision of the diverticulum, the stapler
is released and removed. All from MITI.
260
Biomedical Engineering in Gastrointestinal Surgery
Figure 6.41 Linear cutting device: (A) It consists of two branches which can be
inserted independently of each other into the respective tubular structure. (B) In
the next step, they are mated together and locked. If the firing knob is moved
forward to the distal end, the staple lines are closed and, simultaneously, divided.
All from MITI.
This knob drives the knife and, simultaneously, the staple pusher along the
cartridge, thus inserting the staple lines and dividing them.
The devices are disposable and provided in various lengths (315 cm).
Should more than one firing be required, the device can be reloaded by
a new cartridge.
Linear cutting devices were intelligently adapted to various applications.
Linear cutters do not only f acilitate (
Fig. 6.42) resection but also
facilitate the creation of side-to-side anastomoses (see Chapter 3.2.3:
Steps of the Operation).
Special designs of cutting staplers are available for laparoscopic surgery
(see Chapter 7: Operative (Surgical) Laparoscopy).
6.5.3 Circular Staplers
Circular staplers are designed to perform anastomoses between the two
ends of a hollow organ (see Chapter 3.2.3: Steps of the Operation).
Circular staplers consist of the head, a slightly bent tubular body, and
the handle (
a detachable anvil unit. The cartridge contains two or three staggered concentric arrays of numerous staples and a circular knife, which is positioned
radially inward from the staples. The bucket of the anvil, which forms
the staples, forms an annular array so that each staple in the cartridge
has a corresponding bucket in the anvil. A plastic ring is located inside
the array of buckets in alignment with the knife in the cartridge. Turning
the wing nut approximates or separates the head and the anvil (
Fig. 6.43). The head encompasses the staple cartridge and
Fig. 6.44).