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PCA-derived factors that may be predictive of postoperative pain in pediatric patients: a possible role for the PCA ratio.

OBJECTIVE
No method exists to reliably predict which patients will develop severe postoperative pain. The authors hypothesized that data derived from patient-controlled analgesia (PCA) pumps (specifically the ratio of patient demands to pump deliveries) may predict which patients would develop severe pain after scoliosis repair.


SETTING
Quaternary, university-affiliated, pediatric hospital.


PATIENTS AND PARTICIPANTS
Forty American Society of Anesthesiologists I-Il pediatric patients who had undergone elective scoliosis repair and had consented to recruitment to a randomized clinical trial investigating the effects of early morphine administration on remifentanil-induced hyperalgesia.


INTERVENTIONS
To test the hypothesis of the current study, the authors calculated the PCA ratio of demand to delivery at every 4 hours throughout the first 24 hours after surgery for all the patients recruited to the original study.


MAIN OUTCOME MEASURES
The authors compared calculated PCA ratios, numeric rating scale pain scores, and cumulative morphine consumption for those patients who developed severe postoperative pain and met the criteria for opioid rotation versus those patients who did not.


RESULTS
Seven patients required opioid rotation from PCA morphine to PCA hydromorphone. Eight hours after surgery, the median PCA ratio for those seven patients (2.5[range, 1.8-4.3]) was significantly greater than that for all other recruited patients (1.3 [range, 0-2.7]; p < 0.001).


CONCLUSIONS
Patients who developed severe postoperative pain and met the criteria for opioid rotation demonstrated significantly increased PCA ratios of demand to delivery as early as 8 hours after surgery.