Optimal effect-site concentration of remifentanil to prevent hemodynamic changes during nasotracheal intubation using a video laryngoscope

Abstract

Background: Nasotracheal intubation is the most commonly used method to secure the field of view when performing surgery on the oral cavity or neck. Like orotracheal intubation, nasotracheal intubation uses a laryngoscope. Hemodynamic change occurs due to the stimulation of the sympathetic nervous system. Recently, video laryngoscope with a camera attached to the end of the direct laryngoscope blade has been used to minimize this change. In this study, we investigated the optimal effect-site concentration (Ce) of remifentanil for minimizing hemodynamic responses during nasotracheal intubation with a video laryngoscope.

Methods: Twenty-one patients, aged between 19 and 60 years old, scheduled for elective surgery were included in this study. Anesthesia was induced by slowly injecting propofol. At the same time, remifentanil infusion was initiated at 3.0 ng/ml via target-controlled infusion (TCI). When remifentanil attained the preset Ce, nasotracheal intubation was performed using a video laryngoscope. The patient's blood pressure and heart rate were checked pre-induction, right before and after intubation, and 1 min after intubation. Hemodynamic stability was defined as an increase in systolic blood pressure and heart rate by 20% before and after nasotracheal intubation. The response of each patient determined the Ce of remifentanil for the next patient at an interval of 0.3 ng/ml.

Results: The Ce of remifentanil administered ranged from 2.4 to 3.6 ng/ml for the patients evaluated. The estimated optimal effective effect-site concentrations of remifentanil were 3.22 and 4.25 ng/ml, that were associated with a 50% and 95% probability of maintaining hemodynamic stability, respectively.

Conclusion: Nasotracheal intubation using a video laryngoscope can be successfully performed in a hemodynamically stable state by using the optimal remifentanil effect-site concentration (Ce₅₀ , 3.22 ng/ml; Ce₉₅ , 4.25 ng/ml).

Keywords: Effect-Site Concentration; Nasotracheal Intubation; Remifentanil; Video Laryngoscopes.

Fig. 1. Consecutive patients in hemodynamic stability group (S) and hemodynamic instability group (F). The “S” group was defined as less than a 20% change in heart rate (HR) and systolic blood pressure (SBP) at just after tracheal intubation compared to those of just before tracheal intubation. If a patient's HR or SBP change exceeded 20%, then they were assigned to the “F” group. If the patient belongs to the “S” group, the target concentration of remifentanil for the next patient was decreased by 0.3 ng/ml. When the patient's vital sign meets the “F” group's criteria, the target concentration of remifentanil for the next patient was increased by 0.3 ng/ml.

Fig. 2. Changes in heart rate (HR) and systolic blood pressure (SBP) of each patient in the ‘hemodynamic stability’ group (A) and ‘hemodynamic instability’ group (B). T0: baseline, T1: before nasotracheal intubation, T2: just after nasotracheal intubation, T3: 1 min after nasotracheal intubation.

Fig. 3. Predicted probability of maintaining hemodynamic stability plotted against effect-site concentrations of remifentanil. X: effect-site concentration of remifentanil when hemodynamic instability was observed, O: effect-site concentration of remifentanil when hemodynamic stability was observed. Red solid line indicates population prediction. The estimates of effect-site concentration of remifentanil associated with 50% and 95% probability of maintaining hemodynamic stability were 3.22 and 4.25 ng/ml, respectively.