LAUSR

We read with great interest the article by Cho et al. [1] reporting the effect of tracheal tube size on postoperative sore throat after laparoscopic surgery. They found smaller tracheal tubes reduced postoperative sore throat without affecting ventilation parameters. However, we believe the authors have overlooked some details and limitations that may have affect the results. First, the authors allocated participants to tracheal intubation with larger vs. smaller tubes, including 7.5 mm vs. 6.5 mm internal diameter tubes for males. In their Table 1, some patients in both groups were smokers, and management of patient secretions is necessary during elective surgery, particularly for smokers. Smaller tubes (6.0–6.5 mm) may become critically obstructed from even modest patient secretions. In addition, a 4.0-mm suction catheter (to treat viscid secretions) will occlude a significant proportion of a 6.5-mm tracheal tube, which can result in the transmission of significant negative intra-thoracic pressure, causing lung collapse and haemodynamic instability [2]. We therefore feel that 6.5-mm internal diameter tubes may be inadvisable formale smokers. Second, it is mentioned in the Methods that tracheal tube cuff pressure was set at 15–25 mmHg every 30 min [1]. Trendelenburg was the position most often chosen for colorectal and gynaecological laparoscopic surgery in this study and it has been reported that tracheal tube cuff pressure can increase significantly following changes in the position of patients whose lungs are being ventilated [3]. Therefore, cuff pressure may not have been adjusted straight after a change in surgical position if it was only measured every 30 min, and we do not believe this study ruled out the effect of cuff pressure on sore throat. Indeed, Liu et al. suggested using a sensitive and accurate manometer to adjust tracheal tube cuff pressure in order to avoid the cuff pressure changing significantly intraoperatively [4]. Finally, the authors did not appear to standardise the extubation protocol. Sakkanan and Elakkumanan have shown that the timing of extubation, coughing during extubation and suctioning before extubation can all influence the incidence of postoperative sore throat [5]. In addition, analgesic consumption was not recorded and this may have affected the results. In conclusion, while we acknowledge the contributions of Cho et al. [1], we believe that confounding factors need to be eliminated and that further research is required.