An ultrasonic aspirator, typically controlled by a footswitch, consists of a control unit and a handpiece. The control unit houses an ultrasound generator and a pump used for suction and irrigation. The ultrasound generator produces an ultrasonic signal, which is sent to a transducer. The signal is transformed into mechanical motion, vibrating the tip. Control units can have either a console or tabletop configuration; a combined cable and tubing set connects the control unit to the handpiece. The handpiece has either a piezoelectric or a magnetostrictive transducer, which causes the hollow titanium tip to oscillate, fragmenting cellular matter. Transducers are usually permanently housed inside the handpiece.
Handpieces are typically frequency specific, operating either at a low frequency (e.g., 23 kHz) or a high frequency (e.g., 55 kHz). A lower-frequency, higher-amplitude probe is more effective in removing calcified or elastic tissue as it has a broader tissue effect. A higher-frequency, lower-amplitude handpiece provides a more focused tissue effect, making it more effective for soft- and medium-density tissue and accommodating smaller tips for procedures that entail delicate dissections. When the vibrating tip of an ultrasonic aspirator handpiece comes into contact with cells of high water content, vapor pockets form within the cells, causing them to separate and eventually collapse. Due to the nature of the vibrations, low-water-content, collagen-rich tissues, such as blood vessels or ducts, will remain virtually intact when they encounter an ultrasonic aspirator. Therefore, encapsulated and invasive tumors can be delicately resected without injury to adjacent blood supplies. Manipulating the handpiece allows the surgeon to determine the consistency of the tissue touching the tip, allowing very precise removal.
Fluidic System
The ultrasonic aspirator has a fluidic system that controls irrigation, aspiration, and cooling. Irrigation is provided by a bottle of irrigant (saline or lactated Ringer’s) mounted on an adjustable intravenous pole. On most units, the irrigation tubing passes through a solenoid valve that opens when the footswitch is pressed. Fluid then flows through the irrigation tubing to the handpiece and through an irrigation sleeve, which surrounds the tip and provides a flow path between the tip and the surgical site. The irrigant cools the tip of the handpiece during surgery to prevent thermal trauma to the tissue and dilutes the fragmented tissue to prevent obstructions from flowing into the handpiece or tubing.
The aspiration line runs from the handpiece to a vacuum pump and a collection container. Suction is used to hold larger fragments to the tip, where they can be emulsified; irrigant and smaller fragments are then aspirated into a collection container through the aspiration line.
Irrigation/aspiration (I/A) systems commonly use peristaltic, diaphragm, and venturi pumps to create a vacuum. In most diaphragm and venturi pump systems, only the vacuum levels can be set; the rate at which objects are drawn to the tip – the aspiration flow – can be changed only by adjusting these levels. Peristaltic pump systems, on the other hand, can alter the flow by varying the pump speed; a separate vacuum control is used to adjust the maximum vacuum at the probe tip.
Handpiece Configurations
Ultrasonic aspirator handpieces are lightweight, typically between 113.4 and 284 g (4 and 10 oz). Most suppliers offer straight and angled configurations, often with extensions, which can facilitate access to areas that are difficult to reach or see (e.g., a deep-seated brain tumor). Some suppliers offer handpieces that fit through a laparoscopic trocar cannula, and some offer 55.5 kHz handpieces that can coagulate.
Some handpieces have a one-piece construction, while others can be disassembled for cleaning and routine maintenance. The transducers are either air- or water-cooled to prevent them from overheating. Irrigation and aspiration lines may run along the outside or the inside of the casing; most handpieces can be steam sterilized, while others are sterilized with ethylene oxide (EtO) or gas plasma sterilization. Ultrasonic aspirator tips can be either reusable or disposable and are generally flat.
The ability of a handpiece to emulsify tissue is determined by the amplitude (stroke length) and frequency of the vibrating tip; the shape and sharpness of the tip; the ability of the handpiece to maintain the resonance, or natural frequency, of the vibrating complex (consisting of the handpiece, the tip, and the object contacting the tip); and the level of aspiration. Most ultrasonic systems have a continuous autotuning feature that allows the generator to adjust its output signal to match the changing resonance of the handpiece system.
Controls
Front-panel controls for the ultrasonic aspirator are used to select power setting, vacuum limits, and irrigation rates. These modes are used simultaneously during active ultrasonic aspiration; some models also have a standby mode that allows for constant low-level irrigation and aspiration. In the ultrasonic (or vibration) mode, the unit delivers the preset aspiration vacuum and ultrasound output levels immediately with footswitch activation (preset control). In addition, by using the footswitch, the surgeon can individually control the vacuum or ultrasound output level (linear control). For example, in the linear mode, the handpiece output is directly proportional to the displacement of the footswitch in the ultrasound position.
Most ultrasonic aspirators control and display the status of irrigation, aspiration, and vibration. Many specify error code messages for troubleshooting; these messages include clogged or damaged tips and handpiece malfunctions, as well as suction, electronics, and footswitch problems. Many systems offer a touch screen user interface.
Reported Problems
Some ultrasonic aspirator handpieces need to be disassembled for cleaning and routine maintenance. Special accessories such as a torque wrench or handpiece holder are typically required for proper disassembly and reassembly. Improper use of these accessories or improper reassembly can compromise the handpiece, resulting in inefficient operation. Using an inappropriate handpiece for a given tissue density can also result in inefficient operation.
There have been reports that ultrasonic aspirators can produce a fine mist or aerosols that may travel upward and potentially contaminate the environment and the staff. It is therefore advisable that the surgical team wear protective eyewear and take other effective measures for infection control. Risks of contamination can also be minimized by using adequately upgraded instruments at optimal irrigation and aspiration settings.
Purchase Considerations
ECRI Institute Recommendations
Included in the comparisons are ECRI Institute’s recommendations for minimum performance requirements for ultrasonic aspirators. Both ultrasonic aspirator transducer assemblies should be housed permanently in the handpieces. An piezoelectric oscillation system capable of operating at an amplitude of 300 µm and a frequency of 20 to 80 kHz for ultrasonic aspirators.
Ultrasonic aspirator fluidic systems should be capable of operating at a maximum vacuum of 600 mm Hg. The footswitch control should possess both preset and linear modes. The aspirator should include power, vacuum, irrigation levels, and application time displays, as well as irrigation, aspiration, and ultrasound controls. The unit should also display error code messages.
Other Considerations
Some ultrasonic aspirator systems are self-contained; they incorporate a vacuum pump and a standard suction canister for holding aspirated tissue. Other systems may require the use of the hospital’s central vacuum or irrigation system.
Some systems require manual tuning before the tip is used. Once the tip encounters a change in mass, the unit may no longer be tuned to resonance. Other systems have a continuous autotuning function and may or may not have a pre-use tuning button. Autotuning enables the ultrasonic generator to constantly change its output to match the changing resonance of the handpiece, thereby eliminating the need for manual tuning and increasing the efficiency of the ultrasound circuit and tip.
Because of the complexity of the technology, clinical evaluations should be performed before a purchase decision is made to ensure that the surgeon is comfortable with the ultrasonic aspiration system. Handpieces are generally chosen for particular clinical procedures on the basis of the size and weight of the handpiece and tip, the consistency of the tumor or tissue to be removed, and the importance of minimizing damage to surrounding tissues and structures. Each system has different performance characteristics, and its effectiveness depends on the surgeon’s comfort level and familiarity with the system.
Cost Containment
The cost of ultrasonic aspiration systems varies greatly, not only because of differences in the initial price, but also because of vast differences in the cost per procedure, which can include such items as handpiece tips and I/A tubing sets. Many suppliers offer disposable handpiece tips, while others offer reusable tips that usually have a limited number of uses.
Because ultrasonic aspirators entail ongoing maintenance and operational costs, the initial acquisition cost does not accurately reflect the total cost of ownership. Therefore, a purchase decision should be based on issues such as the average cost per procedure, cost of disposables, initial cost of reusables, cost per procedure for sterilization of reusables, cost of additional handpieces, discount rates and non-price-related benefits offered by the supplier, and local service support.
ECRI Institute recommends that hospitals negotiate pricing for service contracts before the system is purchased. Discounts may be available for multiyear agreements or advance payments.
This article is adapted from ECRI Institute’s Healthcare Product Comparison System (HPCS), a searchable database of technology overviews and product specifications for capital medical equipment. The source article is available online to members of ECRI Institute’s HPCS; learn more at www.ecri.org/components/HPCS.