Discussion
airway damage, DLTs, cord injury, tracheal injuries, glottis, airway complications, hardness, airway injury, trauma
SARS-COV-2 INFECTION
The present study revealed that thermal softening of DLTs before intubation decreased the incidence and severity of POST in patients with prior SARS-CoV-2 infection following thoracoscopic surgery. The airway resistance during insertion and advancement of DLTs also decreased following their thermal softening, and the resulting airway damage also reduced.The incidence of POST in patients undergoing general anesthesia with DLT is higher than that with SLT; this can reduce postoperative comfort, leading to unpleasantness and irritation in patients after the surgery [Because of a larger outer diameter, harder texture, and deeper insertion into the trachea, DLT intubation may cause greater trauma to the airway; however, fewer methods are available to reduce the incidence of POST due to DLTs [The vocal cords are the most vulnerable area to sustain injury during tracheal intubation; this is because the glottis is the narrowest part of the upper respiratory tract, and it is closer to the DLT. In our present study, the total incidence of vocal cord injury was 55% in the control group. This incidence was higher than that reported in previous studies [Interestingly, compared to previous studies, the laryngoscope used in the present study was a video laryngoscope rather than a direct laryngoscope; the former provides faster and better exposure of the glottis, with a better laryngoscope field of view and less intubation time, which can reduce the incidence of airway complications [The present study has some limitations. First, all tracheal intubations were performed by two anesthesiologists with a rich experience in the intubation of adults with normal airways and were able to intubate quickly. The thermal softening effects may not last long after removal of DLTs from warm saline. Therefore, the findings of this study cannot be generalized to inexperienced physicians and/or patients with difficult airway. Second, although the anesthesiologists were blinded to the study details, they may be able to identify heat-softened DLTs during intubation because of the difference in texture. However, we do not believe that this limitation influenced our results, as we heated only the distal part of the DLT, and the incidence of vocal cord and tracheal injuries is an objective and clear assessment. Third, this study used only one type of polyvinyl chloride DLT for tracheal intubation. Different types of DLTs are prepared from different materials and have varying hardness and tube diameters; this may affect the incidence of POST and airway injury. Further studies are required to determine the optimum approach for inserting different types of DLTs by using a video laryngoscope.