Variation in opioid use during PCA in adolescents

The objective of this investigation was to determine if the variability in the use of opioids for pain following surgery is related to variability in blood concentration of opioids used for pain relief. We measured morphine use and morphine blood concentration in a group of otherwise healthy adolescent girls following spinal surgery. There was considerable variability in morphine use and morphine blood levels as indicated by a large range of values and a moderately large standard deviation. Morphine blood concentration correlated with morphine use. Neither morphine use nor morphine concentration correlated with pain scores. The data indicate that there is considerable variability among patients in the amount of opioid needed to achieve comfort and in the blood concentration associated with comfort. The cause of this variability does not appear to be related to metabolism of opioid, but may be related to psychological differences, differences in pain tolerance and threshold, or differences in the way patients use PCA.