Fentanyl blood concentration-analgesic response relationship in the treatment of postoperative pain.

The inter- and intrasubject variability in blood concentration-analgesic response relationship for fentanyl were investigated using the technique of patient-controlled analgesia (PCA) in 30 consenting patients scheduled for surgical procedures involving an abdominal incision (15 upper and 15 lower abdominal incisions). All patients had a thiopental, nitrous oxide/oxygen, pancuronium anesthetic with 200 microgram fentanyl intraoperatively. Postoperative pain relief was provided with fentanyl from a Janssen On-Demand Analgesic Computer (ODAC) set to provide a basal infusion rate of 20 microgram/hr, a bolus "demand" dose of 20 microgram, and a lockout period of 5 minutes. Frequent blood samples were collected immediately before patients demanded doses, and these were taken as an estimate of the minimum effective concentration (MEC). A mean of 22 samples (range 12 to 45) were collected per patient over a mean study duration of 50 hours (range 24 to 72). The patients required larger hourly fentanyl doses in the first 6-hour period (83.9 +/- 30.1 microgram/hr) than in any other 6-hour period (mean values varied from 37.3 to 63 microgram/hr). The mean (+/- SD) hourly fentanyl dose rate and total cumulative dose were 55.8 +/- 22 microgram/hr (range 28.8 to 136 microgram/hr) and 2739 +/- 1191 microgram (range 900 to 6260 microgram), respectively. The mean (+/- SD) MEC was 0.63 +/- 0.25 ng/ml (five-fold range from 0.23 to 1.18) and the mean intrapatient coefficient of variation in MEC was 30.2% (range 16 to 46%). The MEC values remained relatively constant in all patients over the 48-hour study period.(ABSTRACT TRUNCATED AT 250 WORDS)