Plasma opioid levels during extracorporeal gallstone lithotripsy

Plasma levels of beta-endorphin (beta-EP), met-enkephalin (met-ENK), ACTH, cortisol, and prolactin were measured in 20 patients who underwent extracorporeal gallstone lithotripsy (ESWL) before the treatment, at 500 shock waves (SW) (15-20 min), at 1000 SW (40-50 min), and 10 min after the end of ESWL. According to the Visual Analog Scale, nine patients had no pain, seven patients had pain from level 1 to 5, and four patients had pain from 5 to 10. No complications were observed. Plasma beta-EP values increased during the treatment, both in patients without pain and in those with pain. Only in the former group was the increase significant (baseline values (pmol/L): no pain = 4.04 +/- 1.3; pain 1-5 = 3.6 +/- 1.06; pain 5-10 = 2.9 +/- 0.5. Peak values: no pain = 6.6 +/- 1.2 (p < 0.005); pain 1-5 = 4.6 +/- 2.5; pain 5-10 = 4.5 +/- 2.2). Moreover, a negative correlation between beta-EP levels and individual pain scores during ESWL has been observed (CC = -0.64, p < 0.003). Plasma met-ENK levels reached the peak at 1000 SW and declined 10 min after the end of the treatment, although they were always higher than basal values (baseline values (pg/ml): no pain = 45 +/- 12; pain 1-5 = 38 +/- 10; pain 5-10 = 48 +/- 8. Peak values: no pain = 112 +/- 42 (p < 0.005), pain 1-5 = 114 +/- 48 (p < 0.005), pain 5-10 = 85 +/- 10 (p < 0.005). This behavior has been the same, regardless of the presence or absence of pain. We conclude that during ESWL, a rise of beta-EP and met-ENK occurs, and the increase of the former can be responsible for induction of analgesia because of its inverse correlation with pain intensity.