We compared the work needed to retract a non-lubricated and a lubricated stylet from a tracheal tube over 24 h. Stylets were lubricated with sterile water, silicone fluid, lidocaine spray, lidocaine gel, MedPro® lubricating gel or Lacri-Lube®. The mean (SD) work in joules needed to retract the stylet by 5 cm from the tracheal tube was recorded immediately (time 0), at 5 and 30 min and at 1, 3 and 24 h. At time 0 lubrication with sterile water (0.53 (0.09); p = 0.001), silicone fluid (0.43 (0.10); p < 0.001), lidocaine gel (0.60 (0.15); p = 0.01) and MedPro gel (0.57 (0.07); p = 0.005), were better than no lubrication (0.94 (0.28)). Where a tracheal tube is pre-loaded with a stylet for use at an indeterminate time, silicone fluid was the best choice of lubricant as it performed consistently well up to 24 h. At 24 h only silicone fluid (0.49 (0.01)) outperformed no lubrication (0.77 (0.24); p = 0.04).
Anaesthesia personnel frequently participate in airway emergencies throughout the hospital utilising pre-prepared emergency equipment. Such equipment often includes tracheal tubes with pre-loaded stylets. The stylet provides stiffness to the tracheal tube to facilitate tracheal intubation. In an emergency, difficulty in withdrawing the stylet from the tracheal tube may be detrimental to the patient. In particular, tracheal tube dislodgement or inability to remove the stylet at this critical time can result in morbidity or mortality secondary to inadequate oxygenation. Furthermore, difficulty in the removal of the stylet has led to reports of trauma to the upper airway of the patient , as well as equipment failure [2, 3]. These problems are just as relevant in the non-emergency situation.
Lubrication of the stylet is commonly used to decrease friction between the tracheal tube and the stylet, facilitating removal of the stylet following the placement of the tracheal tube into the glottic opening. There are many types of lubricants commonly used to lubricate the stylet. There is, however, no information in the literature comparing the effectiveness of these lubricants, or their effect over time when tracheal tubes are pre-loaded with stylets.
The aim of this study was to compare the work required to remove stylets from non-lubricated and lubricated tracheal tubes, using a number of commonly available lubricants, and to determine the effect of lubrication over time.
This was a quality assurance study approved by our institution. For this experiment, a new stylet (Satin-Slip®; Mallinckrodt Inc., St. Louis, USA) and a new size 7.0 mm internal diameter (ID) tracheal tube (Intermediate Hi-Lo® Tracheal Tube; Mallinckrodt Inc., St. Louis, USA) were used for each test, so that a total of 210 stylets and 210 tracheal tubes were used. A standard 15-mm connector was inserted maximally into the proximal end of each tracheal tube.
Six commonly available lubricating agents were studied: sterile water (water); silicone fluid (Endoscopic Instrument Lubricant, ACMI, Norwalk, USA); lidocaine spray (Xylocaine® Endotracheal Spray; ASTRA, Mississauga, Canada); lidocaine gel (Xylocaine Jelly; ASTRA, Mississauga, Canada), MedPro® gel, a water-based lubricant (AMG MedPro Lubricating Gel; AMG Medical Inc., Montreal, Canada); and Lacri-Lube® (Ophthalmic Ointment, Allergen Ltd., Buckinghamshire, UK). All lubricants, stylets and tracheal tubes were kept at a room temperature of 22 °C during the experiments.
The test sequence was randomised using a computer random number generator (Excel, Microsoft Corporation, Redmond, WA, USA). Except for the non-lubricated group (control), each stylet was lubricated with one of the test lubricants before placing it in the tracheal tube. The differing nature of the lubricating agents meant that they could not be applied in a standardised manner. For lubrication with water, 3 ml sterile water was instilled into the tracheal tube using a syringe and the excess water was allowed to drain off. The stylet was then inserted and retracted into the tracheal tube three times, as is commonly done in clinical practice, to allow distribution of the water on to the stylet. For lubrication with lidocaine spray, the lidocaine spray was dispensed three times into the tracheal tube, and then the stylet was inserted and retracted three times to again allow adequate distribution. For the silicone, lidocaine gel, MedPro gel and Lacri-Lube groups, a 5-cm length of the respective lubricant was applied onto the stylet. The lubricant was then spread evenly over the stylet before inserting and retracting it into the tracheal tube three times.
Following the application of the lubricant, the stylet was introduced into the tracheal tube until the distal tip of the stylet was at the proximal edge of the bevel of the tracheal tube. A 7.0-mm ID tracheal tube was used, as this is commonly one of the smaller tracheal tubes used in adults. The tracheal tube loaded with the stylet was then bent to 90° using a protractor at 7 cm from the distal tip (measured using a ruler), which correlates with the set-up of the Trachlight™ lightwand stylet commonly used in our institution . These parameters were easily reproducible, and a 90° angle was also considered to be the maximum angle practitioners would consider bending the tracheal tube before insertion.
The stylet was then withdrawn at a constant velocity for a distance of 5 cm, and the amount of work required to do so was recorded. The absence of acceleration allowed for a simple work analysis (work = force × distance). A commercial device capable of measuring this was not available and therefore an in-house designed device was used (Fig. 1). It comprised a hanging mass scale (CE Digital Hanging Scale, Model PF-905D25; Orix Enterprise, Taichung, Taiwan), calibrated in newtons, fixed to the moving portion of a syringe infusion pump (Harvard Apparatus Syringe Infusion Pump 22, St. Laurent, Quebec, Canada). A ruler was fixed to the stationary portion of the syringe pump, and a needle attached to the mobile portion of the syringe pump was used to measure the distance of the stylet withdrawal. The tracheal tube was attached to the fixed portion of the syringe pump with two vices via the 15-mm connector, and the stylet was secured to the moving hanging mass scale. During the removal of the stylet, the instantaneous force in newtons was manually recorded every millimetre interval until the stylet was withdrawn from the tracheal tube by 5 cm. The peak withdrawal force had been reached in all cases by 5 cm of stylet withdrawal. Each experiment was video recorded to ensure accurate data collection.
The force was determined immediately after the tracheal tube was loaded with the stylet (time 0), at 5 and 30 min, and 1, 3 and 24 h. Each experiment was repeated five times for each lubricant and the control at each time point, giving a total of 210 experiments. The work in joules required to withdraw the stylet by 5 cm was determined by the area under the curve of the force:distance plot. Data were analysed using ANOVA with repeated measures and post hoc Tukey’s test for multiple comparisons (SPSS Inc., Chicago, USA), with p < 0.05 indicating statistical significance.
Figure 2 summarises the work required to remove the stylet from the tracheal tube for the control and the lubricant groups up to 24 h, and compares the results both within and between the groups. Lubrication with silicone gave the best results overall (Fig. 2). At times 0, 30 min, 1, 3 and 24 h, significantly less work was required to retract the stylet compared with the control (p < 0.001, p = 0.004, p < 0.001, p = 0.04, p = 0.04, respectively). It behaved more consistently at each time point, and over the 24 h, with less variability both within and between time points compared to the control. Silicone also significantly outperformed lidocaine spray at 30 min, 1, 3 and 24 h (p < 0.001, p < 0.001, p = 0.008, p = 0.001, respectively), and lidocaine gel at 30 min, 1 and 24 h (p = 0.001, p < 0.001, p < 0.001, respectively).
The control showed no statistically significant difference in work needed to retract the stylet over time. It behaved inconsistently with more variability both within and between most time points compared to other groups (Fig. 2).
At time 0, there was no difference between the water, silicone, lidocaine gel and MedPro gel groups, and they all outperformed the control (p = 0.001, p < 0.001, p = 0.01, p = 0.005, respectively). There was, however, no difference between lubrication with lidocaine spray and Lacri-Lube compared to the control at time 0. Lubrication with water and lidocaine gel required significantly more work to retract the stylet at 24 h compared to time 0 (p = 0.028, p = 0.007, respectively).
Easy and atraumatic removal of a stylet from a tracheal tube is vital to ensure that the airway of a patient is quickly secured in both emergency and routine tracheal intubations. Lubrication of the stylet facilitates this objective. In assessing the force required to remove different bougies from different tracheal tubes, a recent paper found that some tracheal tube and bougie combinations are very difficult to separate without excessive force where lubrication is not used . We have demonstrated that for removal of stylets from tracheal tubes, some lubricants perform better than others compared to no lubrication, and that over time some lubricants lose their lubricating properties.
Overall, at time 0, less work was required to retract the stylet from a tracheal tube in the water, silicone, lidocaine gel and MedPro gel groups, compared with the control. Over 24 h, however, only silicone performed better than the control at all points in time, apart from at 5 min. Although it is not clear why silicone did not outperform the control at this time point, we speculate that it is possibly the result of a small sample size together with a large variability in the control.
The water and lidocaine gel groups needed significantly more work to retract the stylet at 24 h, when compared to time 0. We postulate that for water, this may have been due to evaporation, while for lidocaine gel, it may have been due to a solidification of the lidocaine gel in the tracheal tube as the lubricant dried.
Some of the results showed large variability in the amount of work required to retract the stylet. It is possible that the amount of lubricant used to lubricate the stylets was inadequate or inconsistent, or that the precision of the measuring device was less than expected. We were unable to apply the different lubricants to the stylets in a standardised manner due to their differing physical properties. To minimise inconsistencies, the same investigator (ORH) applied the lubricants and prepared the stylets. The measuring device used in this study was not validated. It was designed in-house as there was no similar, validated, commercial device available to us.
It is possible that inadequate study power contributed to the variability seen in the results in some groups. We are unaware of any previously reported similar investigations and, therefore, were unable to anticipate both the work required to withdraw the stylet and any differences between or within the groups, making a prospective power analysis not possible. Given the significance of our results we did not perform a retrospective power analysis.
The safety profile of the various lubricants is a potential factor that may affect the choice of lubricant, and whether tracheal tubes should be pre-loaded with lubricated stylets. This was not assessed in this study, but there is some evidence in the literature that various lubricants may have a detrimental effect on the tracheal tube and the stylet. Silicone fluid has not been tested for use as described in our experiment. However, silicone fluid has been used clinically for many decades for flexible bronchoscopy, as well as many other fibreoptic instruments. Lidocaine-based products have been associated with postoperative sore throat, as well as damage to the tracheal tube cuff [6, 7]. There are reports of various water-based gels causing blockages in tracheal tubes, both at the time of initial application, and also after time when the gel has dried [8–10].
Our data suggest that where tracheal tubes are being pre-loaded with stylets for use at an indeterminate time, silicone fluid is the best choice of lubricant as it performs consistently well over time up to 24 h. Where a stylet-loaded tracheal tube is being used immediately, lubrication with sterile water, silicone fluid, lidocaine gel or MedPro gel is better than no lubrication.
We thank Colleen O’Connell, Research Associate, for her help with the statistics.
No external funding and no competing interests declared.