Quantitative assessment of nociception by qNOX indices during nursing procedures of mechanically ventilated patients in ICU: A prospective observational study

Accurate nociception assessment in nonverbal, mechanically ventilated ICU patients remains a significant clinical challenge. This study evaluated the utility of the qNOX index, an EEG/EMG-derived metric, for detecting nociceptive responses during routine ICU procedures (endotracheal suctioning and turning), compared to traditional measures such as the Bispectral Index (BIS). In this prospective observational study, 102 mechanically ventilated patients were enrolled, with 323 pain assessments performed. Mean (qNOXm) and instantaneous (qNOXi) qNOX indices, alongside BIS and vital signs, were continuously recorded before, during, and after procedures. The Behavioral Pain Scale (BPS) was assessed at predefined time points. Primary outcomes included qNOX's discriminative ability (ROC analysis, AUC), correlation with BPS (Spearman's test), and predictive value (linear mixed-effects model analyses). Optimal thresholds were determined using the Youden index and restricted cubic spline (RCS) analysis. qNOX demonstrated numerically higher discriminatory performance compared to BIS, with higher specificity during suctioning (77.8% vs. 73.3%) and turning (80.6% vs. 64.5%). Area Under the Curve (AUC) values for qNOX were consistently greater across sedation levels (light sedation: 0.735–0.747 vs. BIS 0.610; deep sedation: 0.729–0.753 vs. BIS 0.698). qNOX correlated strongly with BPS (qNOXm: r = 0.53; qNOXi: r = 0.52; both P < 0.0001) and exhibited a nonlinear relationship ( P < 0.001). Linear mixed-effects model analyses confirmed qNOX's predictive value, with each unit increase in qNOXi associated with a 11.2% rise in the odds of pain (OR: 1.112, 95% CI: 1.075–1.152). qNOX exhibits a significant correlation with the BPS during nociceptive procedures in mechanically ventilated ICU patients. These findings position qNOX as a promising, objective complementary tool for real-time nociception monitoring in critically ill patients who are deeply sedated, paralyzed, or neurologically impaired. • This prospective observational study evaluated the utility of the qNOX index for detecting nociception during routine nursing procedures in non-communicative, mechanically ventilated ICU patients. • qNOX showed a stronger correlation with the Behavioral Pain Scale (BPS) than the Bispectral Index (BIS), and demonstrated numerically higher specificity in discriminating procedural pain. • qNOX maintained consistent discriminative performance across both light and deep sedation levels. • These findings support qNOX as a promising objective and continuous complementary tool for nociception monitoring in critically ill patients who are deeply sedated, paralyzed, or neurologically impaired.