Qnox index for quantification of intraoperative nociception and analgesia: a prospective single-centre validation study

Abstract

Background: The Qnox index is a novel monitor to quantify intraoperative nociception based on an electroencephalographic algorithm. We evaluated the ability of the Qnox index to discriminate noxious from non-noxious stimuli, respond to stimuli, and discriminate different levels of analgesia in patients under propofol anaesthesia with neuromuscular block.

Methods: Qnox was compared with heart rate and mean arterial pressure with five designated stimuli: tetanic stimulations without (tetanic 1) and with sufentanil (tetanic 2), skin incision, tracheal intubation, and a non-noxious period. The response around the skin incision was also evaluated at two target remifentanil concentrations.

Results: In 83 adult patients scheduled for elective surgery, Qnox performed worse than heart rate and mean arterial pressure in discriminating tetanic 2, tetanic 1, skin incision, and tracheal intubation noxious stimuli from the non-noxious period, with an area under curve of 0.52 (95% confidence interval 0.43-0.61), 0.54 (0.45-0.62), 0.67 (0.58-0.75), and 0.65 (0.57-0.73), respectively. The post-stimulus values of Qnox increased significantly after tracheal intubation and skin incision, but not after tetanic 1 or tetanic 2. Qnox values after skin incision were similar between the low- and high-remifentanil-concentration groups.

Conclusions: Qnox had a poor ability to discriminate noxious stimuli from non-noxious stimuli. Although Qnox responded to tracheal intubation and skin incision, it did not respond to tetanic stimulations and failed to discriminate different levels of analgesia. The Qnox index was not superior to heart rate or mean arterial pressure in assessing nociception during general anaesthesia.

Clinical trial registration: Chinese Clinical Trial Registry (ChiCTR2100046063).

Keywords: Qnox index; analgesia; heart rate; intraoperative nociception; mean arterial pressure; noxious stimuli.

Fig 1

Study protocol. BIS, bispectral index; TCI, target-controlled infusion.

Fig 2

Receiver operating characteristic curves of post-skin incision and reaction values of Qnox, heart rate, and mean arterial pressure for discriminating noxious stimuli from the non-noxious period. Noxious stimuli: (intubation > skin incision > tetanic 1 > tetanic 2). AUC, area under the curve; HR, heart rate; MAP, mean arterial pressure; RF, remifentanil; Tetanic 1, tetanic stimulation without sufentanil analgesia; Tetanic 2, tetanic stimulation with sufentanil analgesia.

Fig 3

Graded response to four different intensities of noxious stimuli and non-noxious period by post-skin incision and reaction values. Noxious stimuli: (intubation > skin incision > tetanic 1 > tetanic 2). Tetanic 1, tetanic stimulation without sufentanil analgesia; Tetanic 2, tetanic stimulation with sufentanil analgesia. ∗Significant difference between the two adjacent stimuli, P<0.001. ^▲Statistical significance in the opposite direction.