Intrathecal Hydromorphone Dosing for Adolescent Spinal Fusion: A Prospective Dose-Escalation Study

Intrathecal opioids are widely used for postoperative analgesia in pediatric spine surgery, but optimal dosing remains undefined. We evaluated the relationship between intrathecal hydromorphone (ITH) dose, analgesia, and adverse effects in adolescents undergoing posterior spinal fusion (PSF).

In this single-center, prospective, blinded dose-escalation study using a biased-coin up-down sequential allocation design, patients aged 10-17 years undergoing PSF received ITH starting at 3.5 mcg kg^-1, with dose adjustments based on analgesic response (range 2.0 to 7 mcg kg^-1 with a maximum of 400 mcg). The primary outcome was maximum postoperative pain within 18 h. Secondary outcomes included pain burden (area under the curve), 24-h systemic opioid consumption (oral morphine equivalents [OME], excluding ITH), adverse effects, supplemental diazepam use, and rescue opioid use. Associations between dose and outcomes were assessed using Spearman correlation and logistic regression.

Twenty-seven patients completed the study. The median ITH dose received was 5.5 mcg kg^-1 (IQR, 3.5-7.0), with a median absolute dose of 370 mcg (IQR, 180-400). No significant association was observed between ITH dose and maximum pain (r = 0.16, p = 0.41), pain burden (r = 0.32, p = 0.10), or 24-h OME (r = 0.13, p = 0.52). ITH dose was not significantly associated with the time to rescue opioid (HR = 1.24; 95% CI 0.68-2.25; p = 0.485) or diazepam (HR = 1.10; 95% CI 0.72-1.71; p = 0.655). Adverse respiratory events occurred at doses > 5 mcg kg^-1 without improved analgesia.

Increasing ITH dose was not associated with improved analgesia or change in supplemental opioid or diazepam use. Doses > 5 mcg kg^-1 were associated with adverse respiratory effects. These findings support conservative dosing strategies and underscore the need to define the minimum effective dose in pediatric populations.