The New GlideRite DLT Stylet®: An Observational Study

INTRODUCTION Anesthesia in thoracic surgery (non cardiac) often requires pulmonary isolation techniques in order to facilitate the surgery, to protect a healthy lung, and to control the ventilation. The double lumen tube (DLT), in right and left version, is the technique of choice to obtain lung isolation, whereas the bronchial blocker can also be used.

Double-lumen tube One-lung ventilation is required in most of thoracic surgeries. Many strategies can be used to achieve lung isolation: 1) use of endobronchial tube, 2) use of a single-lumen tube (SLT) and a bronchial blocker (BB),or 3) use of a double-lumen tube (DLT). There is many advantages of using a DLT: easier to position, shorter time of lung collapsing and re-expansion than BB, each lung can be suctioned/ventilated separately, and less subject to displacement than BB. Since no medical instrument is perfect, DLT has also some inconvenient: DLT are larger, and less compliant than a SLT. They also have two cuffs, one bronchial and another one tracheal. The latter is causing problem when intubating patients with teeth at the superior jaw. Precautions have to be taken to avoid rupturing the tracheal cuff. These characteristics are exaggerated when anesthesiologist faces a patient with a difficult airway. These cases are usually managed by first proceeding to a standard intubation with a SLT, second, use an airway exchange catheter (AEC) to withdraw the SLT, and then, advance the DLT into the proper position. Thereafter, the gold standard is to confirm the DLT position with a fiberoptic bronchoscope (FOB). If direct laryngoscopy provides poor glottis visualization, another option is to proceed to a FOB-assisted DLT intubation.

Video laryngoscopes Over the last decade, video laryngoscopes have been developed to handle difficult airway management. They have the advantage of improving Cormack-Lehane (CL) grade over direct laryncoscopy. Many manufacturers distribute video laryngoscopes: the Storz® C-MAC™, the McGrath® Series-5™, and the GlideScope® Video Laryngoscope™ (GVL) are few examples. This latter is frequently used in our centre to allow tracheal intubation with a SLT in numerous situations where conventional laryngoscopy is not possible. The GVL requires the same technique than a direct laryngoscopy without a line of sight, turning CL Grade III or IV into CL Grade I or II.

Stylet To facilitate the endotracheal tube (ETT) insertion using the GVL, either a semi-rigid or a malleable stylet must be used. There is also a lot of discussion about the best stylet configuration allowing the tip of the ETT to be positioned at the glottis opening and advancing the tube into the trachea, but no consensus has been obtained yet. Difficult airway management may be optimized by shaping the SLT using a malleable stylet, directing the ETT through vocal cords. The main problem of malleable stylet is that it loses its initial shape when the ETT goes through narrow airways. It is why many clinicians prefer the semi-rigid stylet when using the GlideScope®. Double-lumen tubes are already supplied with a malleable aluminum stylet in order for them to maintain their initial shape, and some authors found that accuracy of placement have improved when it is retained into a left-DLT for the entire intubation procedure.

New semi-rigid stylet Video laryngoscopes have been designed to be mostly used with SLT, but recent publications have suggested using a GlideScope® for primary DLT placement in difficult airways, as described by Hernandez, A et al. in 2005 and Chen, A et al. in 2008. Even if DLT are provided with a stylet, the technique of intubation with the GVL remains difficult, mainly because the aluminum stylet is too malleable. Verathon Inc. has marketed the GlideRite® rigid stylet, especially design to use with the GlideScope®. Its length fits most of SLT, its shape is adapted to the GVL's curvature, and the curvature can be modified to accommodate a difficult airway only with intentional movement. In collaboration with Verathon Inc., we have designed a new semi-rigid intubating stylet that can be use for primary DLT intubation with the Glidescope® Videolaryngoscope, the GlideRite DLT Stylet®. This improved intubating tool is sharing the same curve but is longer than the GlideRite® rigid stylet. It present a specific handle to fit with the DLT and to orient the distal extremity into the right or left bronchus. The new stylet fits 35 to 41 French, left of right-sided DLTs. Anticipated benefits of this new design are a shorter time required to position the DLT, less intubating attempt, lower risk of trauma to the airway, lower risk of desaturation and, lower risk of tracheal cuff' rupture, resulting in a one-step lung isolation.

HYPOTHESIS We believe that, under video laryngoscopy, the use of the semi-rigid GlideRite DLT Stylet® for primary insertion of DLT is possible.

The gain of rigidity that we have developed for the GlideRite DLT Stylet® imposes its shape to the DLT, and conserves it while the tube is guided through the superior airway. We hope that the combination of both the GlideScope® and the new semi-rigid stylet will increase the number of successful primary intubation with a double lumen tube. Furthermore, its utilization could drastically decrease associated risks of blind DLT intubation with an AEC. These risks are oxygen desaturation, pulmonary aspiration, and superior airway trauma.

OBJECTIVES The primary objective of this observational study is to determine the GlideRite DLT Stylet® efficiency during endotracheal intubation with a double lumen tube under video laryngoscopy (GlideScope®).

The secondary objectives are:

1. To time the intubating process.
2. To count the number of attempt to obtain a successful intubation.
3. To verify the correlation between the difficult intubation score and a successful intubation.
4. To note all complications associated to the GlideRite DLT Stylet® utilization.

METHODS After obtaining local REB approval, 50 patients having a thoracic surgery (non cardiac) via either thoracoscopy or thoracostomy, were enrolled to this observational study between May 14th 2010 and January 17th 2011.

Intraoperative proceeding Before anesthesia was induced, patients were pre-oxygenated in order to obtain an inspired-expired O2 gradient ≤10%. Anesthesia was performed in conformity with local practice standards. Curarization was achieved by injecting a dose of ≥1.0 mg/kg (ideal body weight) of rocuronium (Zémuron®, Merck \& Co., Whitehouse Station, NJ, USA). If mask ventilation was proven to be difficult, the patient was excluded from the study. The malleable stylet was removed from the DLT (Broncho-Cath R- or L-DLT, 35 to 41Fr, Mallinckrodt Inc, St-Louis, MO, USA) and replaced with a GlideRite DLT Stylet® (Verathon Medical ULC, Burnaby, BC, Canada). Before proceeding to the intubation, curarization level was verified with a neuromuscular stimulator, absence of thumb movement when a train-of-four was applied allowed us to begin the protocol.

The timer was started when either the GlideScope® blade (Verathon Medical ULC, Burnaby, BC, Canada) was inserted between the lips and stopped when the tracheal cuff was passed through the vocal cords. In case of patients presenting with upper teeth, the timer was started when the DLT was inserted between the lips. Immediately after intubation, intratracheal position was confirmed with FOB. When a patient had teeth at the superior jaw, the DLT was inserted first into the mouth in order to avoid rupturing the tracheal cuff. External larynx manipulations were allowed at all time. If after one (1) minute, the intubation was not successful, the anesthesiologist could then modify the stylet shape. If after two (2) minutes, the intubation was still not achieved, the DLT and GVL blade were withdrawn, and mask ventilation was started again. At that time, the anesthesiologist could use the intubation technique of his choice. The position of the DLT was confirmed by the visualization of the trachea through the FOB. Throughout this process, if oxygen saturation dropped below 94%, mask ventilation was started to increase saturation up to 98% or more before another intubation could be attempted. If oxygen saturation dropped below 90%, mask ventilation was started to increase saturation up to 98% or more, the patient was then excluded from the study, and the anesthesiologist could use the intubation technique of his choice.

Statistical analysis Data obtained during the preoperative period will be correlated with the success rate, the time to achieve a successful intubation and, the number of attempt.