A randomized controlled trial comparing nociception level (NOL) index, blood pressure, and heart rate responses to direct laryngoscopy versus videolaryngoscopy for intubation: the NOLint project

Purpose: The effect of direct laryngoscopy using a Macintosh blade (MAC) vsGlideScope™ videolaryngoscopy using a Spectrum LoPro blade (GVL) on nociceptive stimulation has not been quantitatively studied. This study used the new nociception level (NOL) index to compare the nociceptive response induced by GVL or MAC during laryngoscopy with or without intubation. Methods: Patients underwent two laryngoscopies at four-minute intervals (L1, L2), one with GVL and the other with MAC (first randomization). A third laryngoscopy (L3) followed by tracheal intubation was performed four minutes after L2 (GVL or MAC, second randomization). Nociception was quantitatively assessed by NOL and standard hemodynamic parameters (heart rate [HR] and mean arterial pressure). For the crossover design, blade comparisons accounted for sequence and blade type. A possible carryover effect between laryngoscopies was assessed. Results: In the 50 patients randomized, there was no carryover effect from one laryngoscopy to the next for all analyzed parameters. Nociception level index peak values were higher with MAC than GVL. Analysis of ΔNOL showed a lower nociceptive response with GVL for L1+L2 combined. Mean peak NOL values were significantly higher after L3+intubation than after L1+L2, for both GVL and MAC groups. Analysis of ΔHR values did not show a significant difference between GVL and MAC for any laryngoscopy. Conclusion: Laryngoscopy alone with GVL induces less nociception than with MAC. The NOL was more sensitive than HR at detecting nociceptive responses to MAC vsGVL. Additionally, and irrespective of which technique/blade was used, the combination of laryngoscopy + tracheal intubation produced a much greater nociceptive response than the laryngoscopy alone. Trial registration: www.clinicaltrials.gov (NCT03277872); registered 29 August 2017.