These devices (for surgery) use energy generated from ultrasonic vibration.
Ultrasonic energy is an efficient alternative to electrosurgery and the basis for an efficient surgical instrument. The device cuts and coagulates by using lower temperatures than those used by electrosurgery or lasers. No electricity goes to or through the patient.
The ultrasonically activated scalpel (UAS) is characterized by its ability to cut and coagulate tissues simultaneously with relatively low heat and limited lateral thermal injury. The UAS has been used routinely in a number of general surgeries, including laparoscopic surgeries and open surgeries of the lung and liver.
The basic mechanism for coagulating bleeding vessels by UAS is similar to that of electrosurgery or lasers, in that vessels are sealed and occluded with denatured protein. However, the manner in which protein is denatured is different for each modality. Electrosurgery and lasers denature protein by heating the tissues with electric current in the former and light in the latter at a very high temperature. The UAS denatures protein by transferring mechanical energy to ultrasonic high frequency vibration (25Khz - 55KHz). The vibration breaks hydrogen bonds and produces frictional heat. This frictional heat produces lower maximum temperature and slower increase in tissue temperature than the heat from electrocautery. The cutting mechanism for the UAS is also different from that observed with electrosurgery or laser surgery. UAS cuts tissues by a relatively sharp blade vibrating at 25Khz - 55Khz over a distance of up 100µm.
In contrast, cutting with electrocautery or lasers is achieved when the cell temperature is elevated until the concomitant gas pressure explodes the cells.
UAS is a surgical device utilizing ultrasonic energy to cut and coagulate tissues simultaneously, instead of using electrical or laser energy. UAS has been reported to achieve effective coagulation and safe cutting of tissues with relatively small thermal injury. Actually, UAS has been used routinely in a number of clinical settings such as laparoscopic surgery and open surgeries of the lung and liver.
Use of the ultrasonic surgery offers surgeons some important benefits:
- Minimal lateral thermal tissue damage
- Minimal charring and desiccation
- Ultrasonic technology can reduce the need for ligatures with simultaneous cutting and coagulation
- Fewer instrument exchanges simplify procedure steps
- No electricity to or through the patient
- Greater precision near vital structures
- Minimal smoke for improved visibility in the surgical field
When the effect is prolonged, secondary heat is produced that seals larger vessels. (Pressure exerted on tissue with the blade surface collapses blood vessels and allows the coagulum to form a haemostatic seal). The precision of cutting and coagulation is controlled by the surgeon by adjusting the power level, blade edge, tissue traction and blade pressure. Converting ultrasonic vibrations into energy through a surgical instrument can minimize bleeding by coagulating as they cut. Simultaneous coagulation and cutting means procedures can be performed quickly. Coagulation is performed at a low temperature without delivery of electrical current through the patient's body.
By contrast, electrosurgery and lasers coagulate by burning (obliterative coagulation) at higher temperatures (150ºC to 400ºC). Blood and tissue are desiccated and oxidized (charred), forming eschar that covers and seals the bleeding area. Re-bleeding can occur when blades removed during electrosurgery stick to tissue and disrupt the eschar.
Other ultrasonic devices are used to grip organs or blood vessels with a holder at the tip of the probe and also to cut organs or blood vessels while blood coagulates and bleeding is stopped by heat generated from the mechanical vibration.
References:
http://www.jnjgateway.com/home.jhtml?loc=USENG&page=viewContent&contentId=09008b9880a2ba17
http://www.endocrinesurgeon.co.uk/news/harmonic.htm
John Sandham IEng MIIE MIHEEM
