Patient controlled analgesia for shock wave lithotripsy: the effect of self-administered alfentanil on pain intensity and drug requirement

Abstract

Purpose: Second generation lithotriptors offer immersion-free treatment and a decrease in shock wave induced pain. Pain sensations caused by advanced lithotriptors vary widely and have a significant impact on clinical management. We tested patient controlled analgesia during extracorporeal shock wave lithotripsy (ESWL) and quantified analgesic requirements by means of patient controlled analgesia during ESWL of renal stones.

Materials and methods: Patients with renal stone disease undergoing ESWL were randomized prospectively to receive an alfentanil infusion titrated by 4 different anesthesiologists not otherwise involved in the study (22 controls) or to self-administer alfentanil via a patient controlled infusion pump (22 patients). As a measure of individual pain sensitivity the detection, pain and tolerance thresholds of electrocutaneous sensitivity were determined in all patients.

Results: Alfentanil was used more often in the patient controlled analgesia group than in the control patients (12 versus 8 required the narcotic, respectively, p = 0.226). Patients using patient controlled analgesia needed less drug (0.5 versus 2.15 mg., p = 0.005, median values), tolerated higher discharge voltages and pain intensities, needed significantly fewer shock waves to complete stone fragmentation (1,612 versus 2,105, p = 0.014) and had shorter treatment times (36.9 versus 46.2 minutes, p = 0.069). There was a significant correlation between the duration of shock wave exposure tolerated without analgesia, and pain (p = 0.0009) and tolerance (p = 0.0020) thresholds but not with regard to detection thresholds (p = 0.1400). Male patients showed significantly higher tolerance thresholds to electrocutaneous stimulation (10.2 versus 6.9 mA., p = 0.0238), which corresponded to longer analgesia-free treatment times in male versus female patients (31.7 versus 19.4 minutes, p = 0.0510).

Conclusions: Patient controlled analgesia increases pain tolerance, decreases narcotic requirements, simplifies ESWL as an outpatient procedure and can be used to quantify analgesic requirements during lithotripsy. Pain and tolerance thresholds of electrocutaneous sensitivity are sensitive markers of pain tolerance during lithotripsy, which may be more pronounced in male patients.