Ensuring the efficiency of extracorporeal lithotripsy equipment

There are various operational parameters (varying from the electrode being currently used to the calculi tracking system) which can directly interfere with the efficiency of electro-hydraulic shock wave extracorporeal lithotripsy procedures.

Find a description of each of those factors below, as well as tips to nullify them.

1 – WATER: The water used to fill up the ellipsoid during an extracorporeal lithotripsy procedure should be distilled and mixed with physiological serum on a 10:1 ratio (1 unit of serum for every 10 units of water). This measure makes the water adequate for the maximum performance of the electrical discharge which will generate the shock wave. This water should be replaced daily since it contains electrode particles resulting from procedures – these particles alter the water characteristics. The use of tap water’s not advisable because it has too many variable and unfavorable characteristics to be able to achieve great performance in shock wave generation;

2 – FOCUS: The reflectors used to generate electro-hydraulic shock waves are ellipsoid. This geometrical shape is characterized by having 2 focuses, F1 and F2, arranged in such a way that the sum of the distances from each focus to any point on the elliptical curve is always constant. This consists of the basic property which allows the electrical discharge energy on F1 to be converged by means of a mechanical wave to F2. Therefore, users should be careful about the following factors:

a. ELECTRODES: The electrodes have been designed so that the electrical discharge occurs on F1. A significant deviation (above 1mm) of F1 prevents the shock wave from converging to F2, lowering equipment efficiency. Thus, it’s important that electrodes ensuring the discharge on F1 be used. Whenever an electrode is reconditioned (not advisable, but common practice), it’s necessary to check the distance between its poles, as well as its relative position in relation to F1. The space between the electrodes should be precisely located on F1. When the poles are only approached, the position of the space between them won’t be aligned with F1, resulting in lower performance.

 

b. F2 POSITIONING: Calibration of F2 should be performed before every procedure to ensure that the target calculus is precisely positioned on F2. Calibration procedures vary among equipment models.

3 – ELECTRODES: The electrodes being used are an important factor in the efficiency of Extracorporeal Lithotripsy equipment. Besides their geometrical characteristics, already mentioned in the previous item, their electrical features play a vital role in maximizing performance in shock wave generation. The materials in use have got certain conductivity characteristics which directly influence the electrical discharge responsible for generating shock waves. Therefore, lots of care should be taken in the purchase of electrodes destined to Extracorporeal Lithotripsy treatments.
                                   
4 – SHOCK WAVE GENERATOR: The shock wave generator constitutes the main element in shock wave generation. All of its original characteristics must be preserved. Most generators used in electro-hydraulic devices contain an electronic apparatus which transfers the stored energy from the generator to the electrode. This electronic apparatus ensures maximum efficiency in this energy transfer process. Once this equipment is replaced with mechanical actuators for energy transfer, equipment efficiency falls dramatically. Therefore, before purchasing a generator, check whether it’s electronic or mechanical with your supplier.

5 – MAINTENANCE: Lithotripsy equipment maintenance should be performed by specialized personnel. This is the only way to ensure that other shock wave generation parameters will keep working properly. There are many cases in which maintenance procedures are carried out by non-specialized professionals. After such occurrences, the equipment apparently still works, but there is a noticeable decrease in efficiency because certain working parameters have not been respected.

6 – PROCEDURE: Many precaution measures must be taken during treatment as found below:

a. FOCUS: As described above, before every procedure one should verify whether F2 is calibrated so as to ensure the correct positioning of the calculus.

b. AIR BUBBLES: It’s common practice to fill up the ellipsis without checking whether there are air bubbles inside. In case that happens, the shock wave is not transferred to the calculus and, therefore, the stone is not broken. Thus, once filling up the ellipsis, checking for air bubbles is necessary.

c. CONTACT GEL: The contact gel between the membrane and patient skin is really important for maximizing the shock wave transfer to the calculus to be broken. In case there is little or no gel, the shock wave can be dissipated on the membrane surface as soon as it gets in contact with the surrounding air.

d. CHECKING THE CALCULUS LOCATION: The operator must periodically make sure, during treatments, whether the calculus is located on F2 on two different levels (generally 0º and 30º for XR focusing). The check rate will depend upon how much the patient is moving. On average, calculus location should be checked every 500 shots.

To maximize the efficiency of Extracorporeal Lithotripsy equipment, all of the factors described above should be taken into consideration with no exception. Some factors have bigger influence than others, but all of them together could lead to a dramatic efficiency fall. There are many cases in which, due to efficiency problems, some doctors end up buying a new machine, which proves to be an unnecessary action once the original characteristics of the equipment can be perfectly preserved.  For more information, get in contact with Engemed.