Biomedical Engineering Reference
In-Depth Information
plume evacuator. It is best not to keep the fi re extinguisher in
the laser room, because should the room fi ll with plume, it
may not be possible for the staff to fi nd it (Fig. 17.7). If it is
positioned just outside the room, it is quickly available for
someone either inside or outside the room. All staff should be
inserviced and have current knowledge of how to operate the
fi re extinguisher.
When patients present for procedures at the hairline, the
area must be washed free of any cosmetic preparation (hair
spray, gels, mousse, nail polish, etc.) that may contain alco-
hol. This should be a standard nursing procedure to be com-
pleted at the time of pretreatment patient admission and
preparation.
All sources of oxygen (nasal cannulas) need to be eliminated
from the laser target site. Flammable gases of any kind should
not be used in the laser room.
Refl ection is a hazard, when exposed refl ective or specular
materials, instruments, or surfaces are allowed to interfere in
the beam path. The beam path extends from the aperture
(point of emission from the delivery device) to the target. It is
unlikely that a beam can cause a refl ection hazard from a wall
or cabinet, unless it is directed at that surface. The LSO should
assess the potential for hazards from any metal cabinets, wall
coverings, or furniture in the laser treatment room, before rec-
ommending the costly removal or replacement of such
equipment.
Specular surfaces may include speculum blades, retractors,
non-anodized black instruments, foil masks, or front surface
glass lenses. Surface dulling (sandblasting, anodizing, etching),
NOT blackening or ebonizing, will result in diffusion of the
incident laser beam and prevent refl ection. If anodized instru-
ments are not available, the exposed surfaces should be cov-
ered with wet drapes or towels to prevent refl ection and
unintended burn hazards.
All nonrefl ective coatings or processes should be tested by
the LSO to determine whether or not they are truly effective,
before instruments are sent off to be resurfaced or new ones
purchased. Some ebonized (blackened) coatings come off
quickly during instrument cleaning and sterilization, and
some are just as refl ective as silver colored fi nishes. Companies
should supply testing materials at no charge.
Plastic or rubber devices (teeth guards, mouth gags, tongue
blades, etc.) should not be used in the beam path, unless they
are tested for safety by the LSO with the intended laser wave-
length, and at surgical levels of power intended to be used.
If testing specifi cations are not available from the manufac-
turer, the LSO must conduct appropriate tests and verify safety
of such devices and instruments.
External, nontargeted tissues in the direct beam path should
be draped with wet towels. Metal foil material or any other
device that may refl ect the beam or heat up upon laser impact
should not be used.
Testing and Calibration
It is important to test fi re or calibrate a laser prior to use. Infra-
red lasers with coaxial visible aiming beams must be tested
for alignment and for the presence of an appropriate beam
mode, whereas fi beroptic lasers must be calibrated for ade-
quate transmission across the fi ber, in order to assure accurate
and consistent power density delivery to tissue.
Infrared testing consists of fi ring the beam at a dampened
tongue depressor, and watching to see that a burn appears in
the same spot where the aiming beam is visible. The test must
be done in the delivery system intended for use (handpiece,
microscope, etc.) and the delivery system must be held at right
angles to the target in order to allow for assessment of the
beam mode. No more than 5 W is necessary for this test.
Beam mode must be TEM00 (fundamental mode) indicated
by a clean circle without distortion. It is critical to being able to
maintain power density.
Testing should be done before the fi rst patient of the day,
and then repeated if the laser is moved or if the delivery system
is changed (Fig. 17.8 and 17.9). The nurse or operator can test
however, should there be a question of suitability; the user
must decide whether it can be used on the patient.
Electrical Hazards
Lasers are electrical devices and should be treated with the
same caution. This may be overlooked by individual users,
especially those using hand-held or small mobile devices. It
must be remembered that all electrical safety procedures
should be followed, and an occupational health and safety
plan for response to fi re should be in place and included in
staff education programs.
Figure 17.8
Infrared lasers are tested prior to use, to assess whether or not the
working beam and the visible aiming beam are properly aligned, and to deter-
mine whether or not the beam is in the TEM00 mode.
Figure 17.7
Correct placement of fi re extinguisher and fi re blanket outside the
laser procedure room.