Материал: Oxford American Handbook of Urology ( PDFDrive )

602 CHAPTER 16 Urological surgery and equipment

Box 16.3 Pacemakers and diathermy: problems and their prevention

•Pacemaker inhibition. The high frequency of diathermy current may simulate the electrical activity of myocardial contraction so the pacemaker can be inhibited. If the patient is pacemaker dependent, the heart may stop.

•Phantom reprogramming. The diathermy current may also simulate the radiofrequency impulse by which the pacemaker can be reprogrammed to different settings. The pacemaker may then start to function in an entirely different mode.

•The internal mechanism of the pacemaker may be damaged by the diathermy current if this is applied close to the pacemaker.

•Ventricular fibrillation. If the diathermy current is channeled along the pacemaker lead, ventricular fibrillation may be induced.

•Myocardial damage. Another potential effect of channeling of the diathermy current along the pacemaker lead is burning of the myocardium at the tip of the pacemaker lead. This can subsequently result in ineffective pacing.

It was formerly recommended that a magnet be placed over the pacemaker to overcome pacemaker inhibition and to make the pacemaker function at a fixed rate. This can, however, result in phantom reprogramming. For demand pacemakers, it is better to program the pacemaker to a fixed rate (as opposed to demand pacing) for the duration of the operation. Consult the patient’s cardiologist for advice.

Other precautions

•The patient plate should be sited such that the current path does not go right through the pacemaker. Ensure that the indifferent plate is correctly applied, as an improper connection can cause grounding of the diathermy current through the ECG monitoring leads, and this can affect pacemaker function. The indifferent plate should be placed as close as possible to the prostate (e.g., over the thigh or buttock).

•The diathermy machine should be placed well away from the pacemaker and should certainly not be used within 15 cm of it.

•The heartbeat should be continually monitored, and a defibrillator and external pacemaker should be at hand.

•Try to use short bursts of diathermy at the lowest effective output.

•Give antibiotic prophylaxis (as for patients with artificial heart valves).

•Because the pacemaker-driven heart will not respond to fluid overload in the normal way, the resection should be as quick as possible, and fluid overload should be avoided.

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604 CHAPTER 16 Urological surgery and equipment

Sterilization of urological equipment

Techniques for sterilization

Autoclaving

Modern cystoscopes and resectoscopes, including components such as light leads, are autoclavable. Standard autoclave regimens heat the instruments to 121°C for 15 minutes or 134°C for 3 minutes.

Chemical sterilization

This involves soaking instruments in an aqueous solution of chlorine dioxide (Cidex), an aldehyde-free chemical (there has been a move away from formaldehyde because of health and environmental concerns). Chlorine dioxide solutions kill bacteria, viruses (including HIV and hepatitis B and C), spores, and mycobacteria.

Cameras cannot be autoclaved. Use a camera sleeve or sterilize the camera between cases.

Sterilization and prion diseases

Variant Creutzfeldt Jacob disease (vCJD) is a neurodegenerative disease caused by a prion protein (PrP). Other examples of neurodegenerative prion diseases include classic CJD, kuru, sheep scrapie, and bovine spongiform encephalopathy (BSE). Variant CJD and BSE are caused by the same prion strain and represent a classic example of cross-species transmission of a prion disease.

There has been much recent concern about the potential for transmission of vCJD between patients via contaminated surgical instruments. Classic CJD may be transmitted by neurosurgical and other types of surgical instruments because normal hospital sterilization procedures do not completely inactivate prions.1 It is not possible at present to quantify the risks of transmission of prion diseases by surgical instruments. To date, iatrogenic CJD remains rare, with 267 cases having been reported worldwide, up to the year 2000.2

The risk of transmission of CJD may be higher with procedures performed on organs containing lymphoreticular tissue, such as tonsillectomy and adenoidectomy, because vCJD targets these tissues and is found in high concentrations there. For this reason there was a move toward the use of disposable, once-only-use instruments for procedures such as tonsillectomy. However, these instruments have been associated with a higher postoperative hemorrhage rate.3

Prions are particularly resistant to conventional chemical (ethylene oxide, formaldehyde, and chlorine dioxide) and standard autoclave regimens, and dried blood or tissue remaining on an instrument could harbor prions that will not then be killed by the sterilization process. Once

1 Collinge J (1999). Variant Creutzfeldt-Jakob disease. Lancet 354:317–323.

2 Collins SJ, Lawson VA, Masters CL (2004). Transmissible spongiform encephalopathies. Lancet 363:51–61.

3 Nix P (2003). Prions and disposable surgical instruments. Int J Clin Pract 57:678–680.

606 CHAPTER 16 Urological surgery and equipment

Telescopes and light sources in urological endoscopy

There are three types of modern urological telescopes—rigid, semi-rigid, and flexible. These endoscopes may be used for inspection of the urethra and bladder (cystoscourethroscopes, usually simply called cystoscopes), the ureter and collecting system of the kidney (ureteroscopes and ureterorenoscopes), and, via a percutaneous access track, the kidney (nephroscopes).

The light sources and image transmission systems are based on the innovative work of Professor Harold Hopkins, University of Reading.

The Hopkins rod-lens system

The great advance in telescope design was the development of the rodlens telescope, which replaced the conventional system of glass lens with rods of glass, separated by thin air spaces that essentially were air lenses (Fig. 16.13). By changing the majority of the light transmission medium from air to glass, the quantity of light that could be transmitted was doubled. The rods of glass were also easier to handle during manufacture, and therefore their optical quality was greater.

The angle of view of the telescope can be varied by placing a prism behind the objective lens. 0°, 12°, 30° and 70° scopes are available.

Lighting

Modern endoscopes (urological and those used to image the gastrointestinal tract) use fiber-optic light bundles to transmit light to the organ being inspected. Each glass fiber is coated with glass of a different refractive index so that light entering at one end is totally internally reflected and emerges at the other end (Fig. 16.14).

These fiber-optic bundles can also be used for image (as well as light) transmission, as long as the arrangement of the fibers at either end of the instrument is the same (coordinated fiber bundles are not required for simple light transmission). The fiber bundles are tightly bound together only at their end (for coordinated image transmission). In the middle, the bundles are not bound—this makes the instrument flexible (e.g., flexible cystoscope and flexible ureteroscope).