Efficacy and Safety of Oxycodone Hydrochloride for Long-term Analgesia in ICU Patients

The goal of this clinical trial is to learn if oxycodone hydrochloride works to manage pain in patients requiring mechanical ventilation. It will also assess the safety of oxycodone hydrochloride. The main questions it aims to answer are:

1. Does oxycodone hydrochloride effectively lower the CPOT (Critical Care Pain Observation Tool) score in mechanically ventilated patients? 2. What medical problems do participants have when using oxycodone hydrochloride? Researchers will compare oxycodone hydrochloride to remifentanil to see if oxycodone works better to manage pain in these patients.

Participants will:

* Receive either oxycodone hydrochloride injection at a dose of 0.03-0.2 mg/kg/h or remifentanil injection at a dose of 2-9 μg/kg/h. * Have their pain scores assessed every 15 minutes until the CPOT score is less than 3. After reaching the target pain score, assessments will be done every 4 hours. * Have their vital signs and monitoring data recorded. * Have analgesia and sedation scores recorded from days 1 to 7 after administration, with drug dosages adjusted based on pain scores. * Have the incidence of adverse reactions and changes in gastrointestinal function observed and recorded from days 1 to 7 after administration. * If extubated within 7 days, relevant data will be collected based on the time of extubation. * Be followed up on day 28 through the electronic medical record system to gather data on the extubation success rate and incidence of complications within the 28-day period.