Transcript Cataract Extraction Units, Phacoemulsification

Cataract Extraction Units,
Phacoemulsification
Purpose
 Phacoemulsification systems are used to
break up and remove the cataractous lenses
of eyes.
 A cataract is a fogging of the normally
transparent lens that inhibits the
transmission of light to the retina, causing a
painless blurring of vision
Cataracts are caused by:
 changes in the chemical composition of the lens
associated with many factors:
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environment,
drugs,
Systemic diseases,
age,
traumatic eye injuries,
Certain diseases of the eye,
and genetic or birth defects
If cataracts are not treated, progressive visual loss, leading to significantly
impaired sight, can occur.
Phacoemulsification
 widely used by ophthalmic surgeons
because the entire procedure — cataract
extraction and implantation of an intraocular
lens (IOL) —can be done througha single
small incisionthat may help control surgically
induced astigmatism, quicken visual
rehabilitation, and decrease surgical
complications.
Principles of operation
 Phacoemulsification is one type of
extracapsular cataract extraction, a
procedure that removes the lens nucleus,
surrounding cortex, and the enclosing
anterior capsule; the zonules and posterior
capsule are left intact to help support an
IOL implant During a phacoemulsification
procedure, the surgeon performs several
steps with the aid of an operating
microscope
 A 2.8 to 3.5 mm incision is made to gain
access to the eye’s anterior chamber. A
viscoelastic material is then infused to
deepen the anterior chamber and protect
the corneal endothelium.
 the surgeon inserts a phaco-emulsification probe,
which consists of a hollow, cylindrical tip surrounded
by an irrigation sleeve.
 When electrically activated, the probe tip oscillates
rapidly,creating ultrasonic waves that cut tissue.
 The surgeon emulsifies the cataractous lens using
shaving or scooping motions of the probe tip.
 The lens fragments are then aspirated from the eye
through the hollow tip of the phacoemulsifier.
Remaining cortex is aspirated via the I/A
attachment. Either a polymethyl methacrylate
(PMMA) or a foldable silicone IOL is inserted
through the incision and into the bag of the capsule,
which is then sutured; however, self-sealing,
sutureless corneal incisions are becoming more
widely used for phacoemulsification procedures.
Typical phacoemulsification systems
integrate into a single handpiece the I/A and
US capabilities needed to break up and
remove a cataractous lens from the eye. The
surgeon typically activates these
capabilities by depressing a single
footpedal.
A bottle of balanced salt solution
is used as the
irrigant; mounted on an
adjustable intravenous (IV)
pole, its pressure head can be
controlled by adjusting
its height.
Centrifuges, Tabletop
 Purpose
Centrifuges apply centrifugal force to
separate suspended particles from a liquid
or to separate liquids of different densities.
These liquids can be bodily fluids (e.g.,
blood, serum, urine), commercial eagents,
or mixtures of the two with other additives.
In the clinical laboratory, centrifugation is one
of several sample preparation steps
commonly required before measuring
analytes in a patient sample.
By creating forces many times greater than
gravity, centrifuges can greatly accelerate
separations that occur naturally as a result
of differences in density.
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Centrifuges, Blood Bank
Centrifuges, Cell Washing
Centrifuges, Cytological
Centrifuges, Floor
Centrifuges, Microhematocrit
Microcentrifuges
Ultracentrifuges
Three general types
 the low-speed centrifuge,
 the high-speed centrifuge,
 and the ultracentrifuge.
the low-speed centrifuge,
– general operating range of up to 10,000 rpm
– Available in nonrefrigerated or refrigerated
versions, low-speed units are used primarily to
centrifuge red blood cells or bulky precipitates;
they cannot reach sufficient speed to
adequately separate ultrasmall particles (e.g.,
viruses, DNA) or macromolecules or to perform
density gradient centrifugation.
High-speed tabletop centrifuges
 operate at 12,000 to 25,000 rpm, are used
for most preparative applications, and some
are refrigerated to cool the rotor chamber.
Ultracentrifuges
 used for high-resolution separation of subcellular
components, have a general operatingrange of
30,000 to 120,000 rpm, with centrifugal forces of
up to 700,000 g, where g is the standard
acceleration of gravity. Ultracentrifuges must be
refrigerated because air friction created at high
speeds generates heat that could decompose
the proteins, viruses, or other components being
centrifuged.
 Ultracentrifuges are special-purpose floor units
that are typically used in research laboratories.
Principles of operation
 Centrifugation
– Centrifugation is based on the fact that an object
moving in a circular path at a steady angular
velocity is subjected to an outwardly directed
force.
– The magnitude of this force depends on both the
rotor radius and the speed squared.
– This force is called the relative centrifugal force or
relative centrifugal field (RCF).
– It is expressed as a multiple of g, the standard
acceleration of gravity (e.g., 13,000 g).
Centrifuge components
 The basic components of a tabletop
centrifuge include:
– an electric motor, a shaft and rotor heads (often
interchangeable) on which the centrifuge head
turns,and a motor drive assembly. If the
centrifuge is refrigerated, a compressor and
associated components are included. The entire
system is housed within a chamber.
Incubators, Infant
 Purpose
– An infant incubator provides a closed, controlled
environment that warms an infant by circulating
heated air over the skin. The heat is then
absorbed into the body by tissue conduction
and blood convection
 At birth, an infant’s core and skin
temperatures tend to drop
significantly because of
– heat loss from conduction (heat loss to
cooler surfaces in direct contact with the
infant),
– convection (heat loss to air moving past
the infant),
– radiation (heat loss to cooler objects not
in direct contact with the infant),
– and water evaporation (heat loss from
the infant’s lungs and skin surface).
 Whereas term neonates naturally regulate
their body temperature to some extent,
premature infants have
– thinner skin, which allows surface blood
vessels to more readily lose heat to the
environment;
– a large ratio of surface area to volume,
resulting in greater heat losses from radiation
and convection;
– and almost no subcutaneous fat to either
metabolize into heat or act as an insulator.
Prolonged cold stress in
neonates can cause oxygen
deprivation, hypoglycemia,
metabolic acidosis, and
rapid depletion of glycogen
stores. Therefore, energy
conservation provided by
thermal support is critical.
Principles of operation
 The neonate lies on a mattress in the infant
compartment, which is enclosed by a clear plastic
hood.
 Most incubators warm the infant by a forced or
natural flow of heated air
 Heating and humidification systems are located
beneath the infant compartment. A fan or natural
flow circulates air past the heater and the
temperature measuring device, over a water
reservoir used to humidify the air (if desired), and
up into the infant compartment
Oximeters, Pulse
 Purpose
– Pulse oximeters noninvasively monitor the
oxygen saturation (expressed as a
percentage or decimal) of arterial
hemoglobin by measuring light absorbance
changes resulting from arterial blood flow
pulsations.
Principles of operation
 Pulse oximeters provide a
spectrophotometric assessment of
hemoglobin oxygenation (SpO2) by
measuring light transmitted through a
capillary bed, synchronized with the pulse.
The detection system consists of singlewavelength light-emitting diodes (LEDs) and
microprocessors.
 The pulse oximeter probe is applied to an area
of the body such as a finger, a toe, or an ear.
 Two wavelengths of light (e.g., 660 nm [red] and
930 nm [infrared]) are transmitted by the probe
through the skin and are differentially absorbed
by oxyhemoglobin, which is red and absorbs
infrared light, and deoxyhemoglobin, which is
blue and absorbs red light.
 The ratio of red to infrared light is used to derive
oxygen saturation.
 The photo-detector on the other side of the
tissue converts the transmitted light into
electrical signals proportional to the absorbance
Nebulizers, Heated; Ultrasonic
 Purpose
– Nebulizers provide aerosol treatment and/or
medicine to patients with certain respiratory
disorders
– Nebulizer therapy is particularly effective in
treating conditions such as cystic fibrosis,
emphysema, croup, bronchitis, and severe
asthma
 Most nebulizers are either pneumatic
(driven by compressed air) or
ultrasonic. Both types provide an
effective aerosol mist for depositing
medication into the lungs.
 Heated nebulizers provide warmed
aerosol mist to spontaneously
breathing patients being treated with
oxygen or compressed air, which,
delivered cold, can cause severe
bronchospasm in patients with
hyperac-tive airways (asthma
patients).
Principles of operation
 Heated nebulizers
– A heated nebulizer generally consists of
 a reservoir,
 a heating element,
 a compressor,
 and a nebulizer jet.
Ultrasonic nebulizers
 An ultrasonic nebulizer consists of several
compo-nents:
– an electronic oscillator,
– an ultrasound transducer (piezoelectric crystal),
– a coupling basin,
– a nebulizer chamber (also called a cup),
– and a fan
To begin nebulization, a high-frequency
(typically 1 to 2 MHz) electrical voltage
is applied to a piezoelectric crystal
within the oscillator circuit, which
changes the applied electrical signal
into mechanical vibrations.
These vibrations, in turn, produce 1 to 2 MHz
sound waves in the coupling basin.
The coupler (water or saline) transmits the sound
waves to the solution in the nebulizer chamber.
The ultrasonic waves induce cavitation (formation
of partial vacuums in a liquid), which causes
bubbles to form when the low-pressure phase of
the wave is lower than the liquid’s vapor pressure.
When the sound waves reach the liquid/air
interface, the liquid forms a geyser and disperses
into an aerosol mist
During drug therapy,
medication cups hold small
quantities of medication such as
albuterol; the water in the
chamber serves only as a
medium to transmit the
ultrasonic energy
The size of the mist particles is
determined primarily by the
vibrating frequency; the higher
the frequency, the smaller the
particles.
Ultrasonic nebulizers produce
particles in the range of 0.5 to
35 mm;