High frequency ventilation has been claimed to improve the efficiency of extracorporeal shock wave lithotripsy (ESWL) by minimizing the movement of urinary stones during the procedure. A ventilatory mode, QRS-activated ventilation, was developed in which the stones remain motionless during the delivery of shock waves. As the shock wave is triggered to occur approximately 20 milliseconds after the R wave of the QRS complex, the mechanical breath was synchronized to occur approximately 150 ms later. QRS-activated ventilation is used in 16 patients undergoing ESWL under general anesthesia. Tidal volume was set at 3 ml/kg (234 ± 36 ml; mean ± SD) at a rate that equaled the heart rate (71 ± 9 beats/min). The time between the R wave and the initiation of mechanical breath (T1) was 124 ± 25 ms, time of mechanical breath itself (T2) was 431 ± 67 ms, and time between end of T2 and next R wave (T3) was 264 ± 84 ms. End-tidal C02 measured by the large breath technique was 28.1 ± 4.8 mmHg. During the clinical use of QRS-activated ventilation and during earlier studies using an EKG simulator and a test lung, the shock wave occurred invariably at end-expiration even at high heart rates.
- Positive pressure ventilation
- extracorporeal shock wave lithotripsy
- kidney calculi