Incidence and influential factors of postoperative pruritus in morphine-based intravenous patient-controlled analgesia.

Background: Pruritus is a distressing symptom of systemic opioid analgesia that responds poorly to conventional anti-pruritus treatments. This study aimed to determine the incidence and risk factors for postoperative pruritus using intravenous patient-controlled analgesia (IV-PCA).

Methods: Opioid-naïve patients who underwent morphine-based IV-PCA for postoperative pain at a tertiary center between January 1, 2020 and June 30, 2023, were included retrospectively. The primary outcome was pruritus within 72 hours after surgery. Cumulative morphine consumption and pain numerical rating scores were measured to evaluate the potential impact of pruritus on postoperative pain control.

Results: A total of 1696 patients were enrolled, of whom 119 (7.0%) developed pruritus during the study period. Five independent factors for pruritus were identified, including intraoperative uses of hydroxyethyl starch solutions (adjusted odds ratio [aOR]: 0.13, 95% CI, 0.04-0.43), lockout interval of IV-PCA (aOR: 0.50, 95% CI, 0.27-0.94, on base-2 logarithmic scale), droperidol addition to morphine solutions (aOR: 0.53, 95% CI, 0.35-0.81), cumulative morphine dose (aOR: 1.76, 95% CI, 1.47-2.12, on base-2 logarithmic scale), and postoperative uses of antihistamines (aOR: 2.90, 95% CI, 1.83-4.60) (c-statistic = 0.745). Patients with pruritus had higher postoperative morphine consumption (median: 67.5 mg, interquartile range: 38.3-94.0 vs 38.0 mg, 21.0-65.4, p < 0.001) but similar pain intensity compared to those without pruritus.

Conclusion: Increasing the lockout interval and the droperidol regimen may protect patients from morphine-induced pruritus after IV-PCA. Further studies are warranted to clarify the mechanisms underlying the anti-pruritus effects of hydroxyethyl starch.