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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_605_Библиотеки_им_академика_М_И_Перельмана.pdf
292 Biomedical Engineering in Gastrointestinal Surgery
a sensation of dizziness, nausea, and convulsions (visually induced motion
sickness). Even heart attacks have been described after 3D visualiza tion
[4]. This is due to the fact that the human brain is very sensitive to
irregularities in mistakes of the level of coherence and in differences of
the stereo images in contrast, color, and brightness. Unstable positioning of the camera as well as the so-called “cross-talk” are additional
factors. In the beg inning of stereoscopy, these failures were poorly
understood. Only step by step, were these problems overcome.
Further, the wide range of high imaging modalities offering HD or
even superior optics at a comparably low price, compared to 3D technology, has negatively influenced adoption
[5]. Another factor limiting endo-
stereoscopic imaging is the limitation in field of view (FOV) relative to
the FOV of 2D HD endoscopy
[6].
An approach toward a more application-friendly technology are autostereoscopic displays. Autostereoscopic 3D displays would offer severe
improvements. They allow to output 3D data without the use of special
3D glasses, creating additional benefits like speedier diagnosis, reductions
of human errors and improved training and education
[7].
Autostereoscopic displays were limited by a small viewing angle and low
resolution, due to spatial multiplex techn ology being employed.
Nowadays, 3D displays with a resolution of up to 4K are available. The
next step will be 8K, realizing a huge improvement of the currently
available full-HD images.
In a study recently published it was shown that the use of state-ofthe-art 3D technology in endoscopes is actually found beneficial by
surgeons. Even with the most experienced physicians, who were very
skeptical toward 3D technology in the past, perfor mance gains were
observed
[8].
Currently, research is being conducted on increasing the viewing
angle, while maintaining or even improving the resolution. The potential
is great and the field offers many chances for technological improvements
and innovations to be introduced. However, the promotion of such solutions has been complicated, due to the prevailing uncertainty in industries
according to the current state-of-the-art and future development of
3D display technology. Competitors in the market include Richard
Wolf GmbH (Knittlingen, Germany), Olympus, and Visionsense Ltd
(Philadelphia, PA, the United States) and many others.
In the future, further “fine-tuning” on stereoscopic technology in
general will help to underline the benefits of 3D endoscopy. In particular,
Operative (Surgical) Laparoscopy
293
research on autostereoscopic displays is required. The displays offer the
possibility to boost the popularity of 3D systems in surgical application
as they overcome the current necessity to use glasses.
7.1.6 Light Source and Transmission
An adequate illumination of the surgical site is always a crucial element in
surgery. Due to the specific conditions, illumination is a condition sine
qua non in operative laparoscopy. Looking into the closed abdominal
cavity without a light source is impossible. Accordingly, numerous
attempts were made to provide adequate illumination, beginning with
bulbs at the tip of the laparoscope as mentioned above. Because of the
limited efficiency of light sources which result in heat production, “cold
light sources” have been used since about 1960 to minimize the heat
generated at the tip. This means that the light source is outside the
endoscope, with filters for the infrared wavelengths to reduce heat transmission. The light then travels through fiber bundles into the laparoscope
and exits at the tip.
Currently, powerful light sources are available using either xenon,
halogen, or metal halide (
in light-emitting diodes (LED), this technology will soon replace the
current light sources because of the improved energy-efficiency, and
therewith less waste heat, and the increased lifetime for LED of about
30,000 hours, compared to recommended lamp exchanges after 500 hours
for the current light sources.
Fig. 7.29). However due to the developments
Figure 7.29 Light source: a, main switch; b, standby button; c, light intensity
adjustment buttons; d, controls for main/spare light bulb; e, intensity of light; f,
manual/automatic light intensity adjustment; g, light cable connector; h, optional air
pump switch and connector to reduce fog on telescope lens. From MITI.
294 Biomedical Engineering in Gastrointestinal Surgery
7.1.6.1 Halogen Lamps
Halogen lamps consist of a transparent quartz bulb filled with gas including a halogen. Halogen bulbs produce cr isp white light with excellent
color rendering. They need comparatively low voltage. A color temperature of about 5000 K is achieved. The life span is ca. 2000 hours.
Halogen lamps are comparatively cheap.
7.1.6.2 Xenon
Xenon is a highly unreactive gas which is used to fill the bulb which contains a cathode and an anode (arc lamp). The color temperature is about
6000 K. Lifetime is approximately 1500 hours.
As compared to the halogen lamp; the xenon light has a slightly bluish
tint, but it is more natural. Most modern cameras, however, are able to
analyze and eliminate these variations by an automatic equalization of
white. Luminance is excellent
[9].
7.1.6.3 Halide Lamps
Metal halide vapor lamps are high intensity discharge lamps which are frequently used for commercial and residential purposes. They deliver a light
which is perceived as a “natural white” by the human eye. Halide lamps
need a warming up time. Life span is about 600015,000 hours. Up to
6000 K may be achieved.
7.1.6.4 Condensing Lens
The light produced by the lamp is collected by mirrors and converged to
the area of light cable input by means of the condensing lens.
7.1.6.5 Illumination Control
The intensity of light (luminosity) needed varies depending upon several
conditions: Distance to the object, dimension of the area, absorption by
tissue, etc. Close-up view produces reflections, whereas a more distant
view is too dark. Manual adjustment is helpful to adapt luminosity to the
respective conditions.
Modern light sources, however, are equipped with an automatic
intensity adjustment function. This is enabled by analyzing the luminance
signal of the camera which is sent to the CCU. If the signal is too high
(if the image is overexposed), power of the light source is reduced and
vice versa.
Operative (Surgical) Laparoscopy
295
7.1.6.6 Light Cables
Light transmission is provided by liquid crystal gel cables or fiber bundles.
Fluid light cables permit a more even transmission of light across the
spectrum, but the loss of brightness is higher as compared to fiber transmission. Glass fiber cables are currently predominating.
In both instances, light is transmitted over the distance due to total
internal reflection (
Figs. 7.30 and 7.31).
Figure 7.30 Total internal reflection in a fiberoptic cable: Due to the great angle of
incidence, the refracted light cannot leave the fiber, as long as the bending of the
cable is not too sudden. From MITI.
Figure 7.31 Fiberoptic light cable. Black spots indicate that some optical fibers are
broken (inset). From MITI.
296
Biomedical Engineering in Gastrointestinal Surgery
Light transmission cables are very sensitive to mechanical damage.
Accordingly they have to be handled with special care. Steam sterilization, however, is possible.
7.1.7 Suction/Irrigation Device
In almost all surgical interventions, minor or major bleedings occur.
Major blood collections in the surgical site obscure the view and should
be avoided or removed (
The suction/irrigation device provides the vacuum to aspirate fluid
and enables to flush the abdomen with cleansing fluid (saline or Ringer’s
solution). Most frequently, roller pumps are used. Disposable hose/bag
systems are used to avoid direct contact with the rinsing/aspiration fluid
(
Fig. 7.33).
Fig. 7.32).
Figure 7.32 Suction/irrigation device: a, main switch; b, maximum flow adjustment
and display; c, maximum pressure adjustment; d, minimum aspiration vacuum
adjustment and display; e, standby button; f, instillation tube notch; g, aspiration
tube connection. From MITI.
Figure 7.33 Suction/irrigation unit during surgery. From MITI.
Operative (Surgical) Laparoscopy
297
7.1.8 Documentation
At the beginnings of laparoscopic surgery, video documentation was quite
common, resulting in millions of videotapes which never hav e been watched
again and were thrown awa y. Pr oper administration and storage has alw a ys
been a problem, which only could be lessened with the advent of more
recent technologies. Originally, standard video formats were in use, such
as S-VHS, Betacam, and U-matic. Nowadays, digital data make storage and
handling significantly easier. With the introduction of digital storage, digital
storage devices replaced tapes. Today, typically surgeries are recorded on hard
disks and then exported to CD, DVD, or USB and other portable media.
The quality of the recorded video is dependent on two main condi-
tions: The quality of the video source and the compression.
The video source is dependent on the laparoscopic camera and its processor; this video signal is transferred for digital storage to a frame-grabbing device
and then compressed (
produce big file sizes and would need extremely fast or special hard disks. The
uncompressed size for an image or a video can be calculated with Eq. (7.1).
After compression the video file is stored (temporarily) on a device connected
directly to the CCU, where archiving and copying can be made by CD,
D VD, or other portable devices. Newer systems allow also a direct connection
to the hospital information system for archiving over network connections.
Fig. 7.34), since uncompressed (raw) video would
Equation (7.1): Calculation of image and video file sizes.
Ten minutes of a surgical HD 1080p50 video would then produce a
video file with a size of approximately 1.49 TB (Eq. (7.2)).
Equation (7.2): Example calculation for a 10 minutes 1080p50 video of a HD camera
with three color channels and color depths of 8 bit, respectively, 256 shades for each
color channel.
Figure 7.34 Processing of the video stream for documentation. From MITI.
298
Biomedical Engineering in Gastrointestinal Surgery
To overcome the necessity of the special video hard disks and the large
storage, compression is applied to the videos. The aim of video compression is to represent a sequence of images using as few bits as possible while
maintaining its visual appearance. This is possible because most frames
contain highly redundant data, i.e., adjacent pixels are highly correlated.
Therefore, today several video codec (compression/decompression) standards and algorithms are available to not store all complete frames, instead
only changes of the pixels between the frames. Currently, MPEG-4 and
related codecs as standardized by the International Organization for
Standardization (ISO) are mainly used, which provide a sufficient compression with acceptable quality loss. The decompressors for these compressed
videos are also available as standard on most operating systems, which
is why these are preferable. Nevertheless, there are more effective video
compression techniques available; however, these can only be used on
dedicated systems or require further processing.
Common video recording systems allow to change different parameters to adjust the recorded videos to the specific needs. Reducing the
resolution is the most effective way to reduce file size by maintaining the
content of the video, while with higher compression rates the video loses
details due to missing/imprecise data of pixel information which result in
blurry images (
Fig. 7.35).
The increasing use of 3D camera systems demands different recording
strategies. For documentation of the surgery, the use of only one channel
of the camera is sufficient, if, however, the 3D information is to be maintained, both channels are necessary. The best quality could then be
achieved by parallel recording of both video streams for the left and right
eye with same parameters; however, synchronicity is the precondition for
further use and postprocessing of the video. In common, only one mixed
video stream of the left and right video channel (side-by-side) is recorded,
which can be decompressed by several present video players.
Figure 7.35 Uncompressed versus strong compression with blurring and loss of
details. All from MITI.
Operative (Surgical) Laparoscopy
299
7.1.9 Equipment Cart
The various devices as mentioned above are usually positioned on
a trolley to permit flexible use in different OR theaters (
For practical reasons, a central power supply (terminal strip) is
provided by most carts. By pushing the main switch, all devices can be
activated simultaneously which saves time.
Laparoscopic trolleys are equipped with antistatic rollers and
locking brakes. Laparoscopy-specific devices are located on several
shelves. In addition, one or mo re drawers are integrated to store the
accessories.
To increase flexibility of monitor positioning an additional screen is
fixed to a side arm.
In dedicated laparoscopic OR suites, the equipment is positioned on
a rack mounted to a boom. Ceiling-mounted racks are ergonomically
better and need less space (
Fig. 7.37).
Fig. 7.36).
Figure 7.36 Mobile laparoscopy cart: Containing the whole range of laparoscopic devices,
it enables to perform laparoscopic surgery at any surgical OR available. From MITI.
300
Biomedical Engineering in Gastrointestinal Surgery
Figure 7.37 “Integrated operating room.” Specially designed for minimally invasive
surgery, the suite has ceiling-mounted towers. A central provision of CO
gas tank superfluous. The laparoscopy unit can be moved freely into the optimal
position. From MITI.
makes the
2
7.2 HAND INSTRUMENTS
Laparoscopic hand instruments are conventional hand instruments
modified according to the specific conditions in laparoscopic surgery.
They have to have a long shaft for being suitable for introduction through
the port. The diameter is limited by the inner diameter of the trocar
(usually 5 and 10 mm).
Some types of hand instruments must have a holding position during
use, such as needle holders or graspers. Various arresting mechanisms are
available, all of them based, in principle, upon the saw-tooth design.
Similar to trocars, almost every type of hand instrument is available
as reusable or disposable issues.
Disposable instruments are expensive and produce garbage. Reusable
instruments require much effort due to the need for resterilization. To
Operative (Surgical) Laparoscopy
301
facilitate the recycling, they should have a minimum of hinges and bolts
and must be easily dismountable for cleaning (
Fig. 7.38).
On the other hand, high quality reusable hand instruments can be
produced in fine craftsmanship, whereas disposable instruments are
machined mass products.
7.2.1 Forceps/Graspers
The central push rod can be moved forward and backward by opening or
closing the handle. By the appropriate joint at the tip of the instrument,
the axial force can be translated into the specific function required. Either
one or both branches of the tip are activated. The tip is designed for the
particular functionality (
Fig. 7.39).
Figure 7.38 Typical hand instrument for laparoscopic surgery: a, tip; b, insulated
outer tube; c, insufflation channel; d, rotator; e, dismantling knob; f, attachment for
electrosurgical cable (monopolar). From MITI.
Figure 7.39 Different graspers/forceps: (A) Unilateral, powerful grasper for secure fixation; (B) bilateral forceps with straight branches; (C) grasper with bent branches.
The function is similar to the Overholt clamp in open surgery (also suitable for tissue
dissection). From MITI.