Effects on Stones
Lumenis Pulse 120H UM-10012510 Rev. F
Page 26
repetition rate of the laser, depending upon the specific type of soft tissue,
the desired tissue effect (excision, ablation, or coagulation), and the speed
at which this effect should be achieved.
The Ho:YAG wavelength provides effective hemostasis without
damaging the surrounding or non-target tissues. Decreasing the laser
power density on vascularized tissue is an important tool in bleeding
control. This may be achieved in 3 ways:
• Increasing the pulse width/duration.
• Reducing the energy per pulse and repetition rate.
• Defocusing the beam without changing the system controls by
moving the tip of the fiber away from the target tissue
approximately 2 to 5 millimeters.
Effects on Stones
The holmium wavelength's high absorption in water and ability to
produce water vapor is also utilized for fragmenting stones. Urinary and
biliary stones contain a sufficient amount of water needed to absorb the
laser energy, heat and produce a vapor that causes enough pressure in the
specific location that will lead to the fracturing of the stone. The power
required to perform this application can be controlled by the pulse energy
that is delivered to the tissue and the frequency at which the pulses are
emitted. Both of these factors affect stone fragmentation.
The holmium wavelength's high absorption in water is advantageous
when working in a water filled environment, as it enables safe delivery of
energy without harming non-targeted tissue. Any water that interfaces
between the laser and the tissue absorbs the laser energy, therefore
distance between the laser and non-target tissue ensures its safety. Only
laser energy that is delivered directly to the target tissue, in contact, will
result in a significant tissue effect.
NOTE:
When treating calculi (e.g. urinary, biliary) migration of the stone may
occur due to the mechanical effect of the laser energy (retropulsion).
Migration may be avoided by several lasing techniques that are based on
the laser interaction with the stone. Firstly, decreasing the laser energy and
increasing the pulse frequency to maintain the required power output.
Secondly (in
Moses
mode), maintaining the energy and frequency and
increasing the pulse width.
Laser energy can be delivered to the tissue using various delivery devices.
These include straight-firing and side-firing fibers. Refer to the specific
delivery devices for detailed information.