Intermittent subcutaneous morphine regimen for postoperative pain management following abdominal hysterectomy regarding morphine- and beta-endorphin systemic concentrations.

OBJECTIVES Systemic β-endorphin, an endogenous opioid and stress hormone, has been demonstrated to correlate with the postoperative pain intensity, however its putative role as a postoperative pain biomarker has not been cleared. METHODS Thirty patients scheduled for elective hysterectomy were included into the study. Postoperative pain was assessed by a numeric rating scale from 0 to 10. Plasma morphine concentrations were determined using high performance liquid chromatography with UV detection. Plasma β-endorphin concentrations were measured by a radioimmunoassay. RESULTS Administration of morphine in intravenous infusion turned out to be a markedly better method of morphine administration up to 4th hour postoperatively regarding both drug concentration and pain rating. A significant correlation between systemic β-endorphin concentration and pain rating at the 4th postoperative hour was found. No association between morphine and β-endorphin concentrations was detected. CONCLUSION Systemic β-endorphin is not an appropriate pain marker in postoperative gynaecologic patients.