Critique of the Dornier HM3 lithotripter as a clinical algesimeter

The power and nociceptive intensity of shock waves generated by the Dornier HM3 extracorporeal shock wave lithotripter (ESWL) are voltage dependent and suited to algesimetry in a controllable voltage range of 8-30 kV. Fidelity of the HM3 as an algesimeter was tested by: (1) In vitro measurements of shock pressure at voltages between 14 and 30 kV were recorded by a force transducer at the point of clinical focus. (2) Unanaesthetized volunteer (n = 5) assessment and VAS pain scores of shocks in the range of 10-24 kV, yielding highly significant correlations between blinded randomized shock voltage (r = 0.88), and VAS scores (r = 0.84). (3) Voltage-tolerance curves generated from 33 ASA class 1 or 2 patients undergoing ESWL treatment under epidural analgesia with 0.125% bupivacaine, fortified with a bolus epidural dose of 100 micrograms fentanyl if pain arose during treatment. Voltage tolerance was increased by 50% after an epidural bolus of 100 micrograms fentanyl (P less than 0.001). The respiratory consequences of epidural fentanyl were assessed by changes of respiratory rate and rhythm recorded from capnographic tracings of expired carbon dioxide. This study indicates that the Dornier HM3 system provides a valuable opportunity to conduct precise, quantitative measurements of induced deep truncal pain, as well as the effectiveness and respiratory cost of analgesic interventions directly applicable to the safe management of acute pain.