Risk factors for morphine-associated sedation in intravenous patient-controlled analgesia for postoperative pain

Opioid-related oversedation is associated with respiratory depression and can lead to potentially catastrophic adverse events in hospitalized patients. This study aimed to investigate influential factors for postoperative sedation during morphine-based intravenous patient-controlled analgesia (IV-PCA).

We enrolled patients who received morphine-based IV-PCA for postoperative pain at a medical hospital between January 2020 and November 2022. The primary outcome was unintentional sedation within 72 h after surgery. The Observer Assessment of Alertness/Sedation Scale (OAA/S) was used to assess the sedation depth at 12-hour intervals. Multivariable logistic regression models were used to calculate the adjusted odds ratio (aOR) with 95% confidence interval (CI) for the outcome of interest.

A total of 1,461 patients were included for analyses. The multivariable analysis identified six independent factors for morphine-associated sedation, including age (aOR: 1.019, 95% CI: 1.008-1.030), current alcohol drinking (aOR: 2.14, 95% CI: 1.24-3.68), preoperative hemoglobin level (aOR: 0.41, 95% CI: 0.21-0.81, on base-2 logarithmic scale), intraoperative use of midazolam (aOR: 1.62, 95% CI: 1.07-2.45), basal morphine infusion (aOR: 2.08, 95% CI: 1.16-3.71), and duration of IV-PCA (aOR: 1.97, 95% CI: 1.09-3.57, on base-2 logarithmic scale). Basal morphine infusion was also associated with moderate-to-deep sedation (OAA/S score ≤ 3) (aOR: 2.75, 95% CI: 1.38-5.46). Furthermore, the combination of intraoperative midazolam use and basal morphine infusion was associated with an increased risk of sedation, suggesting a potential synergistic relationship.

The identified risk factors for morphine-associated oversedation can facilitate early identification and prevention of complications in high-risk populations. Our findings suggest that perioperative use of sedative-hypnotics and continuous opioid infusions should be approached cautiously in at-risk patients.