Effect-site Concentration Of Remifentanil For Inhibiting Cardiovascular Responses To Double-lumen Tube Intubation With Airtraq Videolaryngoscopy: A Comparison With Macintosh Laryngoscopy

Background: Double-lumen tube（DLT）is a common method to achieve single lung ventilation in thoracic surgery.DLT intubation may cause a strong cardiovascular stress response,increasing the risk of myocardial ischemia and cerebral hemorrhage.Remifentanil is one of the widely used opioids in clinic,which can effectively inhibit the hemodynamic fluctuation caused by endotracheal intubation.It is known that video laryngoscope plays important roles in airway management.Compared with the Macintosh laryngoscope,video laryngoscope does not rely on the alignment of the oral,pharyngeal,and laryngeal axes,so it can improve the glottis exposure with less force and improve the success rate of intubation.However,it is still controversial whether video laryngoscopy can cause lower hemodynamic response and it is not clear whether the required dose of remifentanil is lower during DLT intubation.Therefore,Dixon’s up and down method was used to determine the median effective effect-site concentration(EC₅₀)of remifentanil for inhibiting cardiovascular responses to DLT intubation with Airtraq video laryngoscope or with Macintosh laryngoscope.Methods: Patients who were scheduled for thoracic surgery requiring DLT intubation were randomly assigned to Airtraq group or Macintosh group.The Narcotrend index was used to monitor depth of anesthesia and radial artery cannulation was performed to monitor continuous arterial pressure.Anesthesia was induced with target controlled infusion（TCI）of propofol at a target plasma concentration of 4 μg/ml.After the patients lost consciousness,rocuronium（1mg/kg）was administered intravenously and TCI of remifentanil was initiated.Patients received DLT intubation with Airtraq videolaryngoscope in Airtraq group or Macintosh laryngoscope in Macintosh group.The EC₅₀ of remifentanil in the two groups was determined using Dixon’s up and down method,starting at 3.6 ng/ml with a step size of 0.3 ng/ml of effect-site concentration of remifentanil.The positive cardiovascular responses was defined by an increase of either HR or MAP>20% within 3 minutes after DLT intubation,compared with the values immediately before intubation.The Probit regression analysis was used to calculate the EC₅₀ and 95% confidence interval（95% CI）of each group.Results: A total of 62 patients were enrolled in the study.There was no significant difference in the baseline characteristics and Narcotrend index at each time point between the two groups.The EC₅₀ of remifentanil for inhibiting cardiovascular response to DLT intubation is higher in Airtraq group than in Macintosh group（5.38 ng/ml [95%confidence interval（CI）5.11–5.72 ng/ml] versus 4.82 ng/ml [95% CI 4.59–5.12 ng/ml],respectively）.The estimated EC95 of remifentanil for inhibiting cardiovascular response to DLT intubation in Airtraq group 6.23 ng/ml（95% CI 5.82–7.67 ng/ml）was higher than that in Macintosh group 5.59 ng/ml（95%CI 5.23–6.85 ng/ml）.Conclusions: This study demonstrated that the EC₅₀ of remifentanil for inhibiting cardiovascular response to DLT intubation was increased with Airtraq videolaryngoscope,by comparison with Macintosh laryngoscope.