What are the parameters for predictive selection of patients requiring anesthesia for extracorporeal shockwave lithotripsy?

Objective: Additional anesthesia is required to minimize the tolerable pain level in efficiently performed extracorporeal shockwave lithotripsy (ESWL) with electrohydraulic and electromagnetic sources. In order to assess optimum anesthesia for each patient undergoing a standardized ESWL protocol, pain measurement and scoring were carried out. We attempted to determine the individual type and amount of analgesia prior to treatment.
Methods: Patients (n = 95) with urolithiasis underwent pain measurement and scoring prior to ESWL. 'Threshold of pain' (TP) and 'maximal tolerable pain (MTP) were assessed by inducing ischemia pain with the submaximum effort tourniquet technique. Pain intensity was assessed by a verbal rating scale (VRS). The results of pain measurement and amount of analgosedation were correlated in two phases. Patients were administered an oral premedication of 0.1 mg/kg midazolam. Phase 1: 60 patients were randomized into three groups: (1) piritramide (0.1-0.3 mg/kg) and midazolam (1-3 mg) i.v. (2) Lidocaine/prilocaine cream topically (30 g) to skin and diclofenac supp. 100 mg. (3) No analgesia. Phase 2: Based on the data of phase 1, cut-off points for TP and MTP were set for female and male patients. In accordance with these results, 35 patients comprised group 1 for anesthesia with piritramide/midazolam, group 2 with lidocaine/prilocaine cream and diclofenac supp. and group 3 for no analgesia at all. The electromagnetic shockwave sources Modulith SLX and Lithostar Plus were utilized.
Results: Phase 1: All patients randomized for group 1 (intravenous analgosedation) were treated in accordance with the protocol. 65% of group 2 (cream/suppository) tolerated treatment as planned. 35% of patients selected for ESWL without analgesia (group 3) remained within this group. Patients requiring additional analgosedation displayed lower TP and MTP. The cut-off points for females and males were TP >/=25/35 s and MTP >/=45/60 s, respectively. Phase 2: 20/35 patients were preselected for a nonintravenous protocol. Five out of these 20 violated the protocol. The rate of additionally administered analgesia was lower than in phase 1: 35:10% in group 2 (cream/supp.), 65:40% in group 3 (no analgesia).
Conclusions: The TP and MTP levels are lower in patients requiring stronger analgesia. The determined parameters are suitable for patient preselection and individual assessment of anesthesia prior to ESWL. It may be assumed that 50% of patients administered intravenous opioids are overtreated. Routine pain measurement for patient depends on the individual pain tolerance level. A third phase of this study recruiting a large number of patients will contribute to the confirmation of these results.