and Hugh W. Grant1
(1)
Department of Paediatric Surgery, Oxford University Hospitals NHS Foundation Trust, Oxford Children’s Hospital, John Radcliffe Hospital, Oxford, UK
Abstract
Minimal access surgery (MAS) differs from traditional open surgery in that it accesses and visualizes the operative field via small skin incisions. The small access points minimize the morbidity and unsightly scars caused by larger open wounds. The endoscopic visualization can also offer additional views by reaching deeper within the body cavity. The procedure can still be invasive and traumatic, and therefore it is more appropriate to describe the approach as “minimal access” instead of “minimally invasive.”
Keywords
ErgonomicsOperative fieldTask performance2.1 General Information
Minimal access surgery (MAS) differs from traditional open surgery in that it accesses and visualizes the operative field via small skin incisions. The small access points minimize the morbidity and unsightly scars caused by larger open wounds. The endoscopic visualization can also offer additional views by reaching deeper within the body cavity. The procedure can still be invasive and traumatic, and therefore it is more appropriate to describe the approach as “minimal access” instead of “minimally invasive.”
The three interrelated performance-enhancing elements in optimizing operative surgery are technology, ergonomics, and training (Fig. 2.1). The innate abilities of the surgeon and patient factors also influence surgical outcomes. The interaction ergonomics and psychomotor skills are even more evident in pediatric MAS, where there is often a limited operative workspace.
In this chapter we provide an overview of the basic equipment used in pediatric MAS, the ergonomic constraints, and optimization strategies.
Specific requirements in operative procedures and developments in techniques such as single incision laparoscopic surgery (SILS) and robotic surgery are described in other chapters.
Fig. 2.1
Three interrelated performance enhancing elements
2.2 Working Instruments
The equipment and instruments used in pediatric MAS are mostly the same as those used in adult MAS with some specifically designed for surgery in infants. It is important for the surgeon to understand how the equipment works and to know how to trouble-shoot basic problems.
2.2.1 Creation of the Operative Workspace
An insufflator is used to create, maintain, and control an adequate operative workspace during MAS. The machine regulates and monitors the flow rate, volume, and pressure of CO2 transported into the body cavity from the CO2 cylinder. A filter is used to prevent back flow of fluid from the patient. The ambient air within the tube should be purged and filled with CO2 prior to connecting it to the patient. The desired pressure and flow rate can be set by the user (Fig. 2.2). The insufflations are given in short pulses and not continuously (although set as liters per minute). When the measured pressure is less than the set pressure, another pulse of insufflation is given, and the process is repeated until the set pressure is reached. Most machines are designed for adult use. In a large body cavity, leakage can be easily compensated for by setting the machine at a higher flow rate to maintain pressure. Leakage poses a problem in small infants because each pulse of insufflation (if set at a high rate) could result in a pressure surpassing the set pressure before the negative feedback occurs that stops further insufflation. This can be particularly dangerous when insufflation is used in the neonatal chest. The initial pressure and flow rate settings should be at low levels to start (e.g., a pressure of 6–8 mmHg and a flow rate of 1 L/min).
Fig. 2.2
Insufflator displaying preset and measured pressure and flow rate. Some machines only display the preset values temporarily after adjustments are made
2.3 Visualization of the Operative Field
It is crucial that the surgeon understands the imaging chain (Fig. 2.3). Any disruption of this chain results in suboptimal visualization.
Fig. 2.3
Imaging chain. A clear understanding of this interlinked chain would allow trouble-shooting when the displayed image is absent or poor
2.3.1 Light
Most modern light sources use 300 watt xenon bulbs that emit white light transmitted via a fiberoptic light cable to the light post of the endoscope. Problems arise if there is a size mismatch between the light cable and the endoscope size, loose connections, or plus or minus broken fibers within the light cable (Fig. 2.4). Light is transmitted along the optical fibers within the endoscope, which provides illumination from its tip. These were called “cold” light sources because of the color temperature of 5000–6500 K. They generate a significant amount of heat, which can cause thermal damage to tissue; the temperature at the distal end of the tip of the endoscope can reach up to 95 °C.
Fig. 2.4
Broken fibers in the light cable are shown as black dots on close inspection
2.3.2 Optical Image
The traditional endoscope, the Hopkins rod lens endoscope, contains optical lenses in the center and illumination fiberoptics in the periphery. The endoscopes come in various sizes and lengths, with a viewing angle of 0–70°. Generally, smaller endoscopes have lower optical resolution, lower light transmission, and greater distortion compared with larger ones (Fig. 2.5a, b). The optical image at the eyepiece of the endoscope is captured by the camera head, which contains the charge coupled device (CCD). It converts the optical information into electrical signals for processing in the camera box. Single chip cameras have been replaced by three-chip cameras, which have one channel for each of the three primary colors. Some cameras are also equipped with a parfocal zoom, which allows enlargement of the image without moving the endoscope. However, zooming results in less resolution, illumination, and perception of depth.
Prior to use, white balancing should be performed by keeping a white object in front of the endoscope and activating the appropriate button on the camera box or camera head. This is used as a white reference to adjust to the three primary colors.
With advances and miniaturization of imaging technology, some manufacturers place the CCD at the tip of the endoscope (“chip-at-tip”) rather than at the eyepiece end without the need of Hopkins rod lenses. This construction also allows pivoting at the tip in larger endoscopes.
Whatever type of endoscope is used, the processed electronic signal of the image is then transmitted to the viewing monitor. Previously large cathode-ray tube (CRT) monitors were placed on top of other equipment in the MAS tower. Most hospitals now use flat panel monitors attached to the MAS tower or suspended from the ceiling; they are usually adjustable to allow changes in position. High definition (HD) camera systems and monitor displays are increasingly used in the operating theater. It is important to note that a compatible processor connecting cables and monitor is essential for the superior imaging from three-chip CCD or HD cameras.
Fig. 2.5
(a, b) Barrel distortion is less marked using a larger endoscope
2.4 Instruments
Instruments are available in disposable or reusable forms. Disposable instruments are always new, clean, sterile, and work well as manufactured. However, they are expensive. Reusable instruments are generally more economical but have to be cleaned, sterilized, packed, and serviced. It is essential that the cleaning/sterilization department knows the exact requirements of each instrument.
Instrument access into a body cavity in MAS is usually via a port that consists of the cannula and trocar. The cannula is also commonly referred to as the port. There are various types of trocar tips (Fig. 2.6), the commonest being pyramidal, conical (sharp or blunt), or with a retractable blade. Insertion using a pyramidal or blade tip should avoid any twisting action in order to minimize tissue damage. Specialized ports such as those used for bariatric surgery have a bladeless trocar with a transparent trocar tip, allowing for insertion of an endoscope to visualize entry during insertion. Disposable radially expandable sheath ports are popular with some surgeons.
The size of the port depends on the instruments to be used. Most ports have a side stopcock for insufflation and an internal valve to prevent gas leakage when the instrument is removed (Fig. 2.7); some allow instruments of different sizes to be used without the need for adaptors/reducers. The rubber bung at the outer end maintains the gas seal when the instrument is inserted.
The length of the port is important: Long ones are heavy and can limit the surgeon if they are inserted too deeply into the body cavity. On the other hand, short ports increase the risk of dislodging owing to the thin body wall of infants.
There are various ways to fix a port after insertion into the body, and some ports have been designed to prevent slippage, such as the screwing-in shaft, the radially expanding sheath, or the Hasson port (Fig. 2.8). In small children and infants, instruments can be inserted without a port, especially if frequent instrument changes are unlikely, such as in a pyloromyotomy. The incision needs to be small and tight around the instrument to minimize the leakage of gas.
Commonly used working instruments in MAS include graspers/dissectors, scissors, retractors, clippers/staplers, ligature placing devices, suction/irrigation devices, energy supplying devices, and tissue retrieving bags. Some of these instruments are only available in disposable form (e.g., staplers). Several manufacturers have modular design instruments to allow interchangeable handles (e.g., various ratchets) with different tips. The diameter of the shaft is usually 3 mm or 5 mm. Generally, 3-mm instruments are preferable in patients weighing less than 10 kg.
Fig. 2.6
Trocars with conical (10 mm) and pyramidal (5 mm) tips are shown
Fig. 2.7
Internal valve mechanisms when an instrument is inserted. (a) Silicon valve. (b) Metal valve
Fig. 2.8
Hassan port system for port fixation. It can be secured at variable internal lengths
2.5 Energy Devices
Electrosurgical devices are used extensively for hemostasis and dissection in MAS. Minor bleeding can obscure the view and reduce light reflection within the operative field. The general principles of monopolar and bipolar diathermy are the same as those for open surgery and are controlled by a foot pedal. Extra care must be taken when using monopolar diathermy to avoid hazards caused by insulation failure, capacitive coupling, and inadvertent direct (coupling) touching of another metal instrument within the operative field. All plastic or all metal port systems can be used but avoid ports that are made from a combination of materials (i.e., hybrid ports). The hook monopolar diathermy instrument is most commonly used for dissection. Bipolar diathermy uses special forceps without the need for use of the patient return plate in monopolar diathermy. In general, bipolar instruments are preferable because the electrical circuit passes between the tips of the instruments, not through the patient’s body.
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