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October 22, 2008
9:00 AM - 11:00 AM
Room Hall E2-Area E,
Early Morphine Administration Does Not Prevent Remifentanil-Induced Opioid Tolerance in Children
Conor Mc Donnell, M.B., Rebecca Hull, M.B., Priya Thalayasingam, M.B., Christian Zaarour, M.D., Mark Crawford, M.B.
Anesthesia, Hospital for Sick Children, Toronto, Ontario, Canada
Introduction: Acute tolerance to opioids develops when potent opioid agents like remifentanil are delivered by infusion. Administration of morphine early in the surgical procedure may decrease the incidence/severity of remifentanil-induced opioid tolerance. We hypothesise that acute opioid tolerance experienced in pediatric patients receiving remifentanil by infusion for scoliosis surgery may be decreased by the administration of morphine prior to initiation of the remifentanil infusion.

Methodology: We conducted a randomized, prospective, double-blinded clinical, controlled trial to investigate postoperative morphine consumption and pain scores in adolescents undergoing scoliosis surgery by administering morphine bolus before initiating remifentanil infusion to one group of patients and administering saline to the other group. Twenty-four hour morphine consumption was the primary end point.Sample size estimation was based on 24-hour morphine consumption of 1.65 mg / kg (± 0.41 mg / kg)in this patient population. To demonstrate 25% difference (∼ 0.41 mg / kg),18 patients per group were required for a two – tailed α of 0.05 and a ß of 0.2 (power = 80%). Two –way repeated measures analysis of variance were used for comparisons of 24-hour morphine consumption. Friedman statistic was used for between group comparison of NRS scores and the Mann Whitney rank sum test was used for comparison of ordinal data where appropriate. All comparison tests were two tailed and significance level of 0.05 was used.

Results: Both groups were similar demographically - [table1]Cumulative morphine consumption is demonstrated in -.[figure1]There was no statistical difference at any time point between the two groups. At 24 h after surgery, cumulative morphine consumption in the saline group was 1.24 mg / kg (SD = 0.54) compared to 1.36 mg / kg (SD 0.47) in the morphine group. Differences in pain, sedation and nausea & vomiting scores were not statistically significant.

Conclusions: The administration of morphine prior to initiating remifentanil infusion does not decrease post-operative 24-hour morphine consumption post pediatric scoliosis repair.Mean 24-hour morphine consumption observed in the saline group is less than that observed in previous studies. Duration of anaesthesia was shorter (391 ± 97 minutes in morphine group) compared to previous studies (456 ± 95 minutes).Time may be an important factor in the development of remifentanil induced acute opioid tolerance.

Anesthesiology 2008; 109 A1705
Table 1: Patient Characteristics and Intraoperative Outcomes
Morphine (n =18 )Saline (n =19 )
Age (yr)14.8 ± 1.714.5 ± 1.9
Weight (kg)54.2 ± 8.851.3 ± 8.4
Male: Female4:143:16
Thoracic Cobb angle (degrees)63 (45-74)62 (41-81)
Length of Instrumentation (vertebral levels)10 (8-14)10 (7-12)
Anesthesia Duration (min)415 ± 83391 ± 97
Remifentanil infusion rate (μ ± 0.100.30 ± 0.06
Values are mean ± SD, ratio, or median (range). Patient demographics and extent of surgery were comparable in the two groups
Figure 1