MAGNETRON-BASED IN-LINE MICROWAVE FLUID WARMER

Objective. To develop an in-line microwave fluid warming system that e liminates the difficulties of uneven heating that are characteristic o f batch-mode microwave fluid warmers. Methods, Using a commercial micr owave oven, we developed a method for warming fluid as it flowed throu gh tubing along a defined path in the oven's cavity. Algorithms utiliz ing either proportional or adaptive control were used to control micro wave heating cycles by varying the heating pulsewidth during 3-second epochs. Methods of fluid entry and exit were devised to minimize micro wave leakage. Heating performance was tested using icewater at multipl e flow rates from 18 mL/min to 105 mL/min. Results. In all warming tes ts, the system achieved temperature control without exceeding the maxi mum temperature allowable based on American Association of Blood Banks requirements. The adaptive control maintained the set temperature, wi th peak-to-peak oscillations of 2 degrees C or less. Microwave leakage was below the commercially required limit for home microwave applianc es. Conclusions, The combination of proportional and adaptive control is successful in controlling the permanent magnet magnetron microwave energy to heat the icewater tested. The in-line microwave warmer has t he potential to become a successful medical fluid warmer. More study i s needed to determine the stability of the control system under clinic al conditions, and to evaluate its utility for warming blood.