INSTRUMENTATION A PERSONAL SURVEY
Franco Lugnani - Fabrizio Zanconati*
Urology Service, Sanatorio Triestino Hospital, Trieste, Italy
*Department of Anatomic Pathology, Ospedale Maggiore, Trieste University, Italy
What is Possible:
Of course optimal cryoablation needs adequate apparata . The following technologies may be used:
- Heat sink cryoprobes. These are metal blocks of varying mass and shape which are applied on the target organ after a pre-freezing phase.
- Spray-freezing. A tubing, immersed in liquid nitrogen, conveys the compressed gas on the tissue through a narrow hole.
- Gas-phase-probes. These are based on the Joule-Thompson principle (47): a highly compressed gas is ejected from a tiny opening so as to obtain a sharp freezing of the gas. If this operation is carried out through a metal chamber inserted in the tissue, the contact will produce ice all around.
- Boiling-heat-transfer-cryoprobe. An insulated probe conveys liquid nitrogen with the aid of an insulated distributing-duct. The end of the probe is non-insulated, thus the liquid nitrogen (-182°C) can freeze the tissues surrounding the probe.
At present, both Gas-phase-probes and Boiling-heat-transfer-probes systems are available on the market for prostate use. In order to simplify things, we can say that there are gas and liquid nitrogen-based systems.
What I've Tested:
Since I have very recently had the opportunity of trying out the two main technologies, I would like to give my general impression of their present efficacy, without going into technical details, as this is not the aim of my article.
The ice-ball formed around the probe-end grows progressively in time, and as its diameter grows, isotherms shift. This process may be roughly devided into 3 phases:
1st phase: freezing starts and a small ice-ball forms becoming gradually colder. This phase occurs during the first minutes of functioning.
2nd phase: now the system is running steadily and from the 2nd/3rd minute the frozen area grows rapidly and powerfully.
3rd phase: once the ice-ball has reached a considerable dimension it will start loosing coolness through its large superficies, thus growing slowlier speed and relatively "warmer" on the surface.
CMS-AccuProbe System (liquid nitrogen). The best known and, for years, almost the only system available on the market. Nearly all urological researchers (and most hepatic cryosurgeons) have been using it for years. It is relatively slow in the first phase, very powerful in the intermediate phase and with varying freezing capacity in the last phase (depending on the internal set-up of the machine).
Endocare-Cryocare System (gas). Extremely powerful in the 1st phase and the first half of the 2nd, it gradually looses efficacy.
There is one more system, not on sale at present, which I have tested in a version specially devised for laparoscopic hepatic cryosurgery:
Spembly - Medical Cryo-Needle System (liquid nitrogen-based). Very slow in the 1st phase and extremely powerful in the 2nd and 3rd phase.
My Two Cents Worth:
Technology is constantly improving, and this means that what I have personally seen may be subject to radical changes. I have been assured by all makers, that major improvements are being worked-out on each system.
In any case, I do not here wish to go into all the technical details of the cryophysics and the practica yet purely technological, implications of the different systems and their evaluation methods. Nor is it for me to give commercial judgements on the different companies. However, I believe that anyone who is interested in experimenting cryotechnology will find the following suggestions useful when they make their choice.
- Visit personally at least two different places for each apparatus. It will be time-consuming, but you will have the chance of speaking with the operators, comparing their impressions and judging for yourself. Never be satisfied with a single opinion!
- Try out the machine yourself, simulating surgery in lab conditions. You will learn more about its freezing capacity by observing 5 separate probes (not joined into a single ball), in a water basin at 21°C, than by looking at an intrasurgical U.S. Examine and measure the ice-ball after 10 minutes: the temperature is "warm" where the ice is crystal clear and "cold" where it is white .
Of course, the ice-balls will be greater and colder when applied to tissues (you will not have the frozen liquid’s current stream), but at this stage you only need to find out in which way and at which rate the machine works.
Bear in mind that a very powerful machine with many probes may, of course, be the best to use, but it will surely also be the most difficult and hazardous.
- Ask yourself whether you alone will use the apparatus or if your liver-surgeon colleagues will also make use of it (in this case their opinion will be important and will better to justify the purchase and daily-running costs with the hospital administration).
- The operator must be an expert ultrasonographer. If you are not, insert one in the team and co-operate with him in the procedure. (All the best teams work with these super-experts).
- Consider the running and maintenance costs.
- Try to find out the real improvement potentialities for each apparatus and how their up-dating will be carried out. (ask for written guarantees).
- Consider the costs and duration of the training. Four stages are not sufficient: if the operator is already very familiar with prostatic U.S. he will only need 6 to 8 stages before he can try and learn by himself. On the other hand, if he has never personally carried out a U.S. he should take into serious consideration a period of about 12 months’ full-immersion theory and practice (of course, each one has his own learning-speed, but prostate allows very few short-cuts).
- Ask for an adequate tissue temperature control. Do not be content with the numeral display: the machine should also give a temperature-curve print-out . Remember that the temperature gradient is most important!
- You will need an excellent biplanar probe for U.S. (and since, at this stage, you will have an ecographist with you, this very important detail will be easily dealt with). (By the way, the colour Doppler is not absolutely necessary).
- Carefully check the shape and efficiency of the urethral-warning-system. This is very important.