cause light to travel in all directions within the

The wavelength of the laser of the tissue

laser cavity. Different laser source mediums

and characteristics impact the laser effect.

emit photons in different distinct wavelengths.

Hemoglobin and water absorb light at different

Laser light differs from natural light in that it

wavelengths. These interactions result in differ-

must have photons in phase, known as coher-

ent degrees of depth of penetration, absorption,

ence, they must travel in parallel, known as col-

reflection, and scattering of laser energy. In

limation,and all must have the same wavelength

addition, the denser the tissue is or becomes

or color in the visible light spectrum, known as

during treatment, the greater the degree of

monochromaticity. These properties allow the

absorption of light energy and the transforma-

laser light to be targeted accurately and with

tion to heat, resulting in decreasing penetration

into tissue. Blood flow also acts as a sink to

The performance of a laser is based on the

absorb thermal energy, thus reducing the power

power output and the mode of emission. Three

of the laser at the site of action.15

types of lasers are important in clinical urologic

There are many different types of lasers that

surgery. Continuous wave lasers emit a steady-

are used by urologists. Lasers are named after

state beam. Pulsed lasers produce higher peak

the laser medium generating a specific wave-

power than continuous as power output is built

length. The section below focuses on the differ-

up between pulses. This allows for more precise

ent lasers and their applications to treat urologic

control and less lateral heat conduction, and

diseases: condylomata acuminata, urolithiasis,

pulsed lasers are commonly used for tissue

benign prostatic hyperplasia, and ureteral and

coagulation.ThethirdtypeistermedQ-switched,

urethral strictures. Table 21.1 describes a guide

a pulsing technique that produces high-peak

to lasers and their applications.

There are 4 physical properties of a laser,

Clinical Application of Lasers

which impacts the type of laser used for differ-

ent procedures. Energy is the amount of work

Condylomata Acuminata

produced (Joules). Rate is described as cycles/s

(Hertz). Power is the rate of energy expenditure

The CO2 laser is often used to treat condylomata

(measured in Watts = Joules/s). Fluence is the

acuminata on the skin or urethral meatus. This

area

laser emits light

in the far infrared portion

(J/cm2), which determines the magnitude of the

(10,600 nm) and has a very short extinction

lasers interaction on the tissue. Thus, the smaller

length. Absorption of energy at the surgical site

the area, the more energy delivered to the tissue.

causes thermal coagulation to a depth of approx-

Irradiance or power density is the intensity of

imately 0.5 mm. Infected epithelium from the

the laser beam (W/cm2) and plays a critical role

papillomavirus (HPV) should be ablated pre-

cisely to a shallow depth, so that the virus is

Tissue interaction can be classified as either

killed and rapid

healing

can occur.16 Most

electromechanical, photoablative, photochemi-

patients can be

effectively

treated with low

cal, or photothermal. Electromechanical causes

morbidity.

dielectric breakdown in tissue by shock wave

plasma expansion resulting in localized mechan-

ical rupture. Urologists employ the electrome-

Urolithiasis

chanical property of laser energy for stone

fragmentation by spallation and cavitation.15

Endoscopic laser lithotripsy is the most com-

or

mon intracorporeal procedures performed by

breaking of molecular bonds in tissue. Photo-

urologists to treat urolithiasis. Pulsed lasers are

chemical causes light-induced chemical reac-

effective in stone fragmentation by producing

tions to destroy tissue. Finally, photothermal

high power density at the stone surface with

converts light energy into heat energy causing

minimized heat dissipation. The pulsed laser

tissue heating and vaporizing. Surgeons com-

causes the release of electrons and the forma-

monly use the thermal effect of laser energy to

tion of “plasma” bubbles, which then collapse

incise, coagulate or ablate tissues and fragment

generating a shockwave.17 The first pulsed laser

for lithotripsy was the coumarin green dye

Benign Prostatic Hyperplasia

continuous flow resectoscope. Eye protection is

necessary to filter the harmful radiation emitted

The use of lasers for the treatment of benign

from the KTP laser.

prostatic hyperplasia (BPH) has cycled dramati-

Gilling et al. are one of the first groups to

cally over the past decade. The two mechanisms

describe the technique of using the holmium

by which lasers function to relieve the obstruc-

laser to treat BPH.28 The Ho:YAG laser is highly

tion caused by the adenoma are coagulation and

absorbed by water and causes tissue vaporization.

vaporization. Coagulative necrosis is caused by

The laser can be used to either vaporize or enu-

focused laser energy heating the tissue to tem-

cleate the prostate. Advantages of the holmium

peratures between 70°C and 100°C. Coagulation

laser include its pulsed nature and minimal tissue

may put tissues not being treated, like the

penetration, which provides rapid tissue vapor-

sphincter, at risk due to its imprecise mecha-

ization, less tissue coagulation, and less injury to

nism.Vaporization occurs at temperatures of up

surrounding tissues.29 The laser has excellent

to several 100°C. The power density is high, but

hemostatic properties. Holmium laser ablation of

it is delivered through a narrow beam, limiting

the prostate (HoLAP) is performed with a 550-

injury to surrounding tissues.

mm side-firing laser fiber at 80–100 W power in a

Initially, the Nd:YAG laser was used for coag-

near-contact mode, creating a channel within the

ulation of the prostate. The combination of neo-

prostatic fossa.30 Contact with the tissue can cause

dymium and yttrium aluminum garnet crystal

overheating, which degrades the fiber tip and

has high efficiency, increased rate of repetition,

reduces the energy output. The procedure is eas-

thermal conductivity, and good optical quality.

ily learned, as it does not require resection and

It emits light at 1,064 nm (poorly absorbed by

retrieval of the tissue. Length of procedure is gen-

both hemoglobin and water), which has a tissue

erally dictated by prostatic size. Thus, HoLAP is

penetration of 10 mm and causes deep coagula-

best reserved for glands less than 50 g.

tion and coagulative necrosis of the adenoma.15

Holmium laser enucleation of the prostate

It can be used to coagulate up to 5 mm blood

(HoLEP) is a minimally invasive alternative to

vessels with hemostasis. Treatment of BPH with

TURP and simulates the open simple prostatec-

the Nd:YAG laser typically resulted in extended

tomy. The prostate is divided into 3 anatomic

periods of tissue sloughing and unacceptable

lobes, the two lateral lobes and the median lobe.

rates of irritative voiding symptoms and pro-

The high-powered 100 W Holmium laser and a

longed catheter time.25 The deep tissue penetra-

550-mm end-firing holmium laser fiber are used

tion of the Nd:YAG laser made it effective for

to delineate the natural tissue plane between the

BPH, but caused a high rate of tissue injury

prostate adenoma and the prostatic capsule.

when applied for lithotripsy.

Once the three lobes are enucleated in a retro-

An alternative technology is the potassium-

grade fashion, morcellation is carried out to

titanyl phosphate (KTP) “green light” laser,

remove the tissue from the bladder.31 The main

which utilizes the 1,064 nm Nd:YAG laser light

advantage of the procedure is that the same

that is emitted or passed through a KTP crystal

amount of tissue is removed as with the open

resulting in a green light.26 This laser technology

simple prostatectomy but in a minimally inva-

causes photoselective vaporization of the pros-

sive technique. Multiple randomized controlled

tate. The KTP crystal doubles the frequency and

clinical trials comparing HoLEP to TURP and

halves the wavelength to 532 nm, which is highly

open simple prostatectomy have demonstrated

absorbed by hemoglobin. This results in less

HoLEP to have equal efficacy, improved AUA SS,

depth of penetration (3 mm) as compared to the

flow rates with shorter hospital stay, catheteriza-

Nd:YAG laser (10 mm), which is much safer to

tion time, and less blood loss.32,33 A disadvantage

use in the prostatic cavity. In addition, it can be

of the procedure has been the perception of a

delivered at a higher power,either 80 W or 120 W

challenging learning curve and translation of

(new HPS system) maximizing the vaporization

the technique to practicing community urolo-

effect. The technique has decreased bleeding,

gists, although Shah et al. have demonstrated

making photoselective vaporization feasible in

that an endourologist inexperienced in HoLEP

patients on anticoagulation.27 Vaporization is

can perform the procedure with reasonable effi-

achieved through a side-firing laser in a near

cacy after about 50 cases with comparable out-

contact sweeping technique through a 24 F

comes to that of experienced physician.34