DECREASED PATIENT ANALGESIC REQUIREMENTS AFTER LIVER-TRANSPLANTATION AND ASSOCIATED NEUROPEPTIDE LEVELS

Background. Decreased morphine requirements have been reported after l iver transplantation when compared with other types of major abdominal surgery. The aim of this study was to examine plasma concentrations o f three neuropeptides involved in pain modulation-metenkephalin (ME), beta-endorphin (BE), and substance P (SP)-in patients undergoing ortho topic liver transplantation (OLT) and in control patients undergoing o ther liver operations. We then compared the postoperative analgesic re quirements in these two groups of patients. Methods. Plasma levels of ME, BE, and SP were measured by radioimmunoassay at preincision, preem ergence, and for 3 days after operation in 13 patients undergoing OLT and in 10 control patients. Patient-controlled analgesia morphine deli very was recorded for all patients postoperatively, and plasma morphin e, its metabolites, and patient pain and sedation scores were also mea sured. Results. ME levels were elevated in all OLT patient samples whe n compared with control patient samples, BE levels were not significan tly different at any time. SP levels were significantly decreased only in preincision and preemergence OLT patient samples. Total patient-co ntrolled analgesia morphine delivered during the first 3 postoperative days was significantly less in OLT patients (70 +/- 8 mg) than in con trol patients (101 +/- 12 mg). Plasma morphine, morphine-3-glucuronide , and morphine-6-glucuronide levels were decreased in OLT patients, ho wever, statistical significance was seen only in the morphine-6-glucur onide results. Conclusions. We have shown that postoperative analgesic requirements are decreased in OLT patients, and we suggest that assoc iated increased peripheral ME levels may be contributing to this decre ased requirement. Based on our results, circulating BE and SP are less significant factors affecting postoperative analgesic requirements.