Purpose: To explore the effect of analgesic management under the guidance of qNOX monitoring on the comfort level and prognosis of patients with mechanical ventilation in ICU.

Method:After admission to ICU, the patients were randomly divided into the analgesia group guided by BPS（Behavioral Pain Scale） and physiological indicators monitoring and qNOX-guided analgesia group (qNOX group). Sedation and analgesia program after admission to ICU (continuous injection pump) : propofol 1.5-4.5mg/kg.h, remifentanil 5-8ug/kg.h, maintain sedation goals RASS（Richmond Agitation-Sedation Scale）-3 to -4 scores, BPS（Behavioral Pain Scale）3 to 4 scores. The researchers worked with the bedside nurse to plan different care procedures, including :1) central venous catheter or arterial catheter puncture; 2) The patient is turned over completely so that the back can be washed and the sheets changed; 3) Endotracheal sputum aspiration (patients with intubation or in tracheotomy state ); 4) Dressing the wound.

Primary outcome:Value of qNOX at BPS（Behavioral Pain Scale）≥5 (qNOX sensitivity, specificity, positive predictive value and negative predictive value) Secondary outcome:To investigate the patient baseline variables that may affect qNOX; Variables that may influence qNOX in relation to critical illness.

Inclusion Criteria:

1. Patients aged 18 years or older who are undergoing abdominal, orthopedic, ENT（ear-nose-throat）, urological, neurosurgical or cardiothoracic surgery and require ICU treatment with mechanical ventilation while having an RASS（Richmond Agitation-Sedation Scale）-3 or -4 score;
2. Patients unable to self-assess pain intensity using NRS（Numerical Pain Rating Scale）;
3. Patients who have provided informed consent.

Exclusion Criteria:

1. < 18 years of age;
2. Pregnant individuals;
3. Patients with communication impairments, such as those who have experienced cerebrovascular accidents;
4. A decision to withdraw life-sustaining treatment or an unstable medical condition that disrupts planned routine care.

ICU patients receiving mechanical ventilation.