NoL, HR and MABP Responses to Tracheal Intubation Performed With MAC Blade Versus Glidescope

The purpose of this prospective pragmatic study is to evaluate the changes in NoL index, Heart Rate (HR) and Mean Arterial Blood Pressure (MABP) following the painful stimulus that represents laryngoscopy and intubation performed using either the single use blade of the Glidescope (group GVL) or the classically used MAC blade (group MAC). Calculation will be using the variations of NoL, HR and MABP, the peak values of these 3 parameters, and also the area above the curve of each parameter for 3 minutes (above the mean pre-stimulus values) and the amount of time (out of 3 minutes post-stimulus) those 3 parameters will be significantly higher than their respective pre-intubation mean thresholds.

In this prospective, randomized and controlled study, each patient will normally enter the operating room on the day of his surgery. All the normal monitors are installed, along with the NoL monitor. Pre-oxygenation (with 100% 02) is then started. While the patient is doing the pre-oxygenation, MABP, HR and NoL index measures are gathered to establish a baseline for each patient.

Once pre-oxygenation is over, induction with xylocaïne, propofol, remifentanil and rocuronium is given (according to patients' ideal weight). The end of the remifentanil bolus will correspond to the time 0 of our study. To be sure our patients are sleeping and on the same level of anesthetic medication during our study, perfusions of propofol and remifentanil will be administred until tracheal intubation and inhaled anesthetic gaz given. When the patient is asleep and apneic, a Guedel device (chosen according to patient weight and height) is inserted in the mouth, as in usual practice, to ease the manual ventilation until the laryngoscopy. The patient is then ventilated with a face mask. After 5 minutes, the first laryngoscopy is performed (either with GlideScope blade or MAC blade according to randomization). Once a Cormack-Lehane grade I or II is obtained, the movement is ended, and the patient is ventilated again for 4 minutes with the Guedel. If the procedure takes more than 30 seconds to perform (if no view of grade I or II is seen before 30 seconds), the laryngoscopy is considered difficult and the patient will be excluded from the study. At T9 (9 minutes after T0), the second laryngoscopy is done (either with the MacIntosh blade or the GVL blade - the tool used for the second laryngoscopy will always be the one that wasn't used at the first laryngoscopy). The size of the MacIntosh blade (MAC 3 or 4) or the disposable blade for GVL is decided according to the patient size (height and weight). At the second laryngoscopy, the endotracheal tube is still not inserted, only the procedure of laryngoscopy is done, so that we can evaluate the hemodynamic and the NoL index responses related only to the type of device used for laryngoscopy. Then, the operator replaces the Guedel and ventilates the patient with a facemask (100% O2) for 4 more minutes, without stimulating the patient otherwise. At T13 (13 minutes after T0), the third laryngoscopy will be performed (either with the single-use blade for GlideScope or the MacIntosh blade - according to randomization). This time, the ETT is inserted (size 7 or 8, depending on the size and sex of the patient). After ETT insertion, the patient is then ventilated with the anesthesia machine and the perfusions of propofol/remifentanil is discontinued.

Monitors will record HR, MABP and NoL index until 3 minutes after the ETT insertion (end of the study). All the data will be electronically registered every 5 seconds and exported in an anonymous manner for each patient into an excel file at the end of the study.

In this study, each patient is exposed to three laryngoscopies; one with the single use blade for the GlideScope, one with the Macintosh laryngoscopy and one with the ETT insertion (laryngoscopy done with either GlideScope or Macintosh according to randomization). Hence, each patient will be its own control. It will then be more reliable to compare the differences in nociceptive response according to the tool used for laryngoscopy.

Inclusion criteria

• ASA status I or II
• Mallampati class I or II
• Patients > 18 years old
• Elective general, gynecological, neurological, orthopedic, plastic or urological surgery under general anesthesia
• Type of surgery that usually necessitate endotracheal intubation and controlled ventilation

Non-inlusion Criteria:

• Patient refusal
• History of psychiatric diseases or psychological problems (including mental retardation); inability to give consent; language barrier.
• Anticipated difficult airway (Mallampati class III and IV, thyromental distance < 6 cm, mouth opening < 3 cm, neck extension <80° and neck flexion <35°, inability to prognath, meaning bringing lower mandibular before the upper maxilla)
• Patient with history of neck rigidity or instability
• BMI > 30
• Patient with beard (because of recognized risk for difficult ventilation)
• Patient with history of oropharyngeal or tracheal surgery (excluding adenoidectomy, amygdalectomy and teeth removal)
• Severe coronary artery disease
• Serious cardiac arrhythmias (including atrial fibrillation)
• Use of β-blockers (all types)
• History of opioid or illicit drug substance abuse
• Chronic use of psychotropic and/or opioid drugs
• Allergy to remifentanil or propofol
• Pregnancy
• Contraindications to mask ventilation (GI tract obstruction, pregnancy, active GERD, non-fasting patients)
• Difficult mask ventilation (before randomization at the first laryngoscopy)

Exclusion criteria

• Unexpected difficult airway requesting excessive, possibly painful airway manipulations
• Requiring hemodynamic support with vasopressors or inotropes 5 minutes before first laryngoscopy to 3 minutes after insertion of ETT