Cataract Extraction Units, Phacoemulsification

1. Cataract Extraction Units,Phacoemulsification

2. Purpose • Phacoemulsification systems are used to break upand remove the cataractous lenses of eyes. • A cataractis a fogging of the normally transparent lens that inhibits the transmission of light to the retina, causing a painless blurring of vision

3. Cataracts are caused by: • changes in the chemical composition of the lens associated with many factors: • environment, • drugs, • Systemic diseases, • age, • traumatic eye injuries, • Certaindiseases of the eye, • and genetic or birth defects If cataracts arenot treated, progressive visual loss, leading to significantlyimpaired sight, can occur.

4. Phacoemulsification • widely used by ophthalmicsurgeons because the entire procedure — cataract extractionand implantation of an intraocular lens (IOL) —canbedone througha single small incisionthat may helpcontrol surgically induced astigmatism, quicken visual rehabilitation, and decrease surgical complications.

5. Principles of operation • Phacoemulsification is one type of extracapsularcataract extraction, a procedure that removes the lensnucleus, surrounding cortex, and the enclosing anteriorcapsule; the zonules and posterior capsule are leftintact to help support an IOL implant During a phacoemulsification procedure, the surgeonperforms several steps with the aid of an operating microscope

6. A 2.8 to 3.5 mm incision is made to gain access tothe eye’s anterior chamber. A viscoelastic material isthen infused to deepen the anterior chamber and protectthe corneal endothelium.

7. the surgeon inserts a phaco-emulsificationprobe, which consists of a hollow, cylindricaltip 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 ofthe phacoemulsifier. Remaining cortex is aspirated viathe I/A attachment. Either a polymethyl methacrylate (PMMA) or a foldable silicone IOL is inserted throughthe incision and into the bag of the capsule, which isthen sutured; however, self-sealing, sutureless corneal incisions are becoming more widely used for phacoemulsification procedures.

8. Typical phacoemulsification systemsintegrate 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 capabilitiesby depressing a single footpedal.

9. A bottle of balanced salt solution is used as theirrigant; mounted on an adjustable intravenous (IV)pole, its pressure head can be controlled by adjustingits height.

11. 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, ormixtures of the two with other additives.

12. 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.

13. Centrifuges, Blood Bank • Centrifuges, Cell Washing • Centrifuges, Cytological • Centrifuges, Floor • Centrifuges, Microhematocrit • Microcentrifuges • Ultracentrifuges

14. Three general types • the low-speed centrifuge, • the high-speed centrifuge, • and the ultracentrifuge.

15. the low-speed centrifuge, • general operatingrange of up to 10,000 rpm • Available in nonrefrigeratedor refrigerated versions, low-speed units are used primarily to centrifuge red blood cells or bulky precipitates;they cannot reach sufficient speed to adequatelyseparate ultrasmall particles (e.g., viruses, DNA) ormacromolecules or to perform density gradient centrifugation.

16. High-speed tabletop centrifuges • operate at12,000 to 25,000 rpm, are used for most preparativeapplications, and some are refrigerated to cool the rotor chamber.

17. Ultracentrifuges • used for high-resolution separation of subcellular components, have a general operatingrange of 30,000 to 120,000 rpm, with centrifugalforces of up to 700,000 g, where g is the standardacceleration of gravity. Ultracentrifuges must be refrigerated because air friction created at high speedsgenerates heat that could decompose the proteins, viruses, or other components being centrifuged. • Ultracentrifuges are special-purpose floor units that aretypically used in research laboratories.

18. Principles of operation • Centrifugation • Centrifugation is based on the fact that an objectmoving in a circular path at a steady angular velocityis subjected to an outwardly directed force. • The magnitude of this force depends on both the rotor radiusand the speed squared. • This force is called the relativecentrifugal force or relative centrifugal field (RCF). • It is expressed as a multiple of g, the standard accelerationof gravity (e.g., 13,000 g).

19. Centrifuge components • The basic components of a tabletop centrifuge include: • an electric motor, a shaft and rotor heads (ofteninterchangeable) on which the centrifuge head turns,and a motor drive assembly. If the centrifuge is refrigerated, a compressor and associated components areincluded. The entire system is housed within a chamber.

21. Incubators, Infant • Purpose • An infant incubator provides a closed, controlled environment that warms an infant by circulating heatedair over the skin. The heat is then absorbed into the body by tissue conduction and blood convection

22. At birth, an infant’s core and skin temperatures tendto drop significantly because of • heat loss fromconduction (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 withthe infant), • and water evaporation (heat loss from the infant’s lungs and skin surface).

23. Whereas termneonates naturally regulate their body temperature tosome extent, premature infants have • thinner skin,which allows surface blood vessels to more readily loseheat to the environment; • a large ratio of surface areato volume, resulting in greater heat losses from radiationand convection; • and almost no subcutaneous fat to either metabolize into heat or act as an insulator.

24. Prolonged cold stress in neonates can cause oxygendeprivation, hypoglycemia, metabolic acidosis, andrapid depletion of glycogen stores. Therefore, energyconservation provided by thermal support is critical.

25. 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 ornatural 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 temperaturemeasuring device, over a water reservoir used to humidify the air (if desired), and up into the infantcompartment

27. Oximeters, Pulse • Purpose • Pulse oximeters noninvasively monitor the oxygensaturation (expressed as a percentage or decimal) of arterial hemoglobin by measuring light absorbance changes resulting from arterial blood flow pulsations.

28. Principles of operation • Pulse oximeters provide a spectrophotometricassessment of hemoglobin oxygenation (SpO2) by measuring light transmitted through a capillary bed,synchronized with the pulse. The detection system consists of single-wavelength light-emitting diodes (LEDs) and microprocessors.

29. The pulse oximeter probe is applied to an area of thebody such as a finger, a toe, or an ear. • Two wavelengths of light (e.g., 660 nm [red] and 930 nm [infrared]) aretransmitted by the probe through the skin and are differentially absorbed by oxyhemoglobin, which is red andabsorbs infrared light, and deoxyhemoglobin, which isblue 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

31. Nebulizers, Heated; Ultrasonic • Purpose • Nebulizers provide aerosol treatment and/or medicine to patients with certain respiratory disorders • Nebulizertherapy is particularly effective in treating conditions such as cystic fibrosis, emphysema, croup, bronchitis, and severe asthma

32. Most nebulizers are either pneumatic (driven bycompressed air) or ultrasonic. Both types provide an effective aerosol mist for depositing medication into the lungs.

33. Heated nebulizers provide warmed aerosol mist tospontaneously breathing patients being treated with oxygen or compressed air, which, delivered cold, can cause severe bronchospasm in patients with hyperac-tive airways (asthma patients).

34. Principles of operation • Heated nebulizers • A heated nebulizer generally consists of • a reservoir, • a heating element, • a compressor, • and a nebulizer jet.

35. 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

36. To begin nebulization, a high-frequency (typically 1to 2 MHz) electrical voltage is applied to a piezoelectric crystal within the oscillator circuit, which changes the applied electrical signal into mechanical vibrations.

37. These vibrations, in turn, produce 1 to 2 MHzsound 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

38. During drug therapy,medication cupshold small quantities of medication such as albuterol; the water in the chamber serves only as a medium to transmit the ultrasonic energy

39. The size of the mist particles isdetermined 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;