The Cavaterm plus system consists of two major components – a balloon catheter (Figure 19.1) and a central unit (Figure 19.2). The length of the preformed highly flexible, antiallergenic, silicone balloon is adjustable to fit the cavity. Thus, it complies with the uterine cavity, ensuring good balloon/cavity surface contact and protecting the cervical canal and vagina from heat effects. Also, the catheter is insulated below the balloon to protect the cervical canal and vagina. The diameter of the catheter is 6 mm and the balloon length can be adjusted between 4 and 8 cm. A device in the central unit generates pulses through the liquid in the catheter that promotes vigorous circulation in the balloon. This ensures an even temperature on the balloon surface and uniform heat treatment. Therefore, a uniform degree of thermal damage will be reached. If there is no circulation, temperature differences of up to 18°C within the balloon have been noted. 1 The heat is generated from self-regulating Soft Heat elements. These
are thin lamellae of a semiconductive ceramic/metal material. Above the working temperature, the electric conductivity decreases rapidly, limiting the heating power, and thus automatically maintaining the desired temperature during the treatment phase. The large surface area, of the Soft Heat elements, combined with the circulation of the liquid, enables them to act as high-performance heat exchangers. The elements heat the circulating fluid to working temperature quickly, while the elements themselves only reach a temperature of a few degrees higher than the target temperature of 78°C. The fluid used is 5% glucose. The catheter is equipped with a pressure-regulating syringe, which allows continuous and precise pressure adjustment to maintain the optimal balloon pressure, 230-240 mmHg, which ensures optimal heat penetration through the tissues. An overpressure safety valve is automatically and quickly activated if an overpressure is sensed, thus maintaining a safe working pressure at all times during the treatment.