Earlier Endotracheal Intubation by Entropy Guidance Versus Neuromuscular Monitoring

Abstract

Background: The entropy electrode is centrally placed on the forehead over the muscles of frontalis, orbicularis oculi, and corrugator supercilii. It determines response entropy (RE), which is the electromyogram component, and state entropy (SE), which is the electroencephalogram component. We hypothesized that due to the central location of entropy, the decreasing value of RE-SE ≤ 2 with SE ≤ 45 could denote an adequate combination of hypnosis, muscle paralysis, and analgesia required for endotracheal intubation. This could result in earlier intubation compared to when guided by train-of-four (TOF) = 0. Objectives: The primary objective of the study was to evaluate if entropy values of RE-SE ≤ 2 with SE ≤ 45 can be used as a measure of adequate condition for endotracheal intubation. We also sought to determine the TOF at this point. Methods: Endotracheal intubation was performed in group E (Entropy; n = 30) at RE-SE ≤ 2 with SE ≤ 45 and in group T (TOF; n = 30) at TOF = 0. A propofol bolus (20 mg) was administered if the patient had a hypertensive response or moved in response to endotracheal intubation. The TOF was noted at the time of intubation in group E. We also measured the time to intubation, jaw and vocal cord relaxation, patient movement or coughing, SE, TOF, and vital parameters. Statistical analysis was performed with two-tailed students’ t test, paired t test, chi-square test, and ANOVA. The difference between groups was considered significant if the p value was < 0.05. Results: The time to intubation was significantly shorter in group E than in group T (92.5 ± 63.5 seconds vs. 209.2 ± 59.6 seconds; P < 0.001) with a mean TOF of 87.3% ± 8.4% in group E. Intubating conditions in terms of jaw relaxation, patient movement, and coughing were not significantly different between the two groups. Vocal cord relaxation was significantly inadequate in six patients in group E (P < 0.01); however, there was no difficulty in introducing the endotracheal tube with no postoperative adverse effects such as sore throat. Conclusions: Adequate conditions for endotracheal intubation were achieved 90 seconds after the administration of fentanyl, propofol, and vecuronium for anesthesia induction when it is guided by RE-SE ≤ 2 with SE ≤ 45, which is earlier than when guided by TOF = 0.