To present a randomized trial investigating immediate vs delayed voltage escalation during shock wave lithotripsy (SWL). SWL efficiency is affected by the energy setting of the lithotripter, the consumption level of the electrode, and the rate of shock wave administration. Preliminary data have suggested that delaying voltage escalation for SWL might both improve fragmentation and minimize renal injury.

A total of 160 patients with previously untreated radiopaque renal calculi were randomized to undergo immediate vs delayed voltage escalation SWL. Success was defined as an asymptomatic patient who was stone free or had adequate fragmentation (sand or fragments ≤4 mm) at 3 months after treatment.

Of the 160 patients, 83 were treated with immediate voltage escalation SWL and 77 patients with delayed escalation. The groups were similar in sex, body mass index, stone area, and stone location. The overall success rate at 3 months was 72.5% for immediate vs 54.5% for delayed SWL (P = .021). After adjusting for body mass index, sex, and stone location, the stone area decreased more rapidly in patients treated with immediate voltage escalation (P = .002). A trend was also seen for immediate voltage escalation to be more effective in the treatment of smaller calculi with a cross-sectional area of <100 mm² (P = .089) compared with calculi with a cross-sectional area of ≥100 mm² (P = .248). No differences were seen in the complications or ancillary procedures between the 2 treatments (P = .667 and P = .355, respectively). No perinephric hematomas were observed in either group.

These results suggest that delayed voltage escalation might not provide superior stone fragmentation compared with conventional, immediate voltage escalation.