In reply to: Comparison of safety and efficacy of Supreme laryngeal mask airway and ProSeal laryngeal mask airway

Abstract

Editor, We wish to thank Xue and colleagues for their interest and astute comments regarding our study. We would like to take the opportunity in this letter to clarify some aspects of our randomized controlled study comparing the safety and efficacy of the Supreme versus the ProSeal laryngeal mask airway. The primary outcome of interest was oropharyngeal leak pressure or airway sealing pressure. Xue et al.1 rightly alluded to the classic paper comparing four methods of airway sealing pressure assessment with the laryngeal mask airway. Keller et al.2 concluded that interobserver reliability of all four tests (audible noise, oral capnography, manometric stability and auscultation) were excellent with low intrinsic variability. For our purposes, we chose the first option – audible noise by listening over the mouth to assess the oropharyngeal leak pressure. Clinically, we found the audible noise test to closely correspond with the manometric stability test. A method similar to ours was performed in a previous published prospective study of 100 patients using the Supreme laryngeal mask airway conducted by Cook et al.3 We do concur that the patients' head and neck position may influence the assessment of oropharyngeal leak pressures for the ProSeal and the Supreme laryngeal mask airways. This was formerly illustrated in two studies for the ProSeal laryngeal mask airway by Xue et al.4 as well as Brimacombe et al.5 Our evaluation of oropharyngeal leak pressures was performed in the neutral position with the patient's occiput resting on a standard single-use foam pillow. This same head and neck posture would be the position in which our patients were placed for the duration of the operation. As yet, no investigator has evaluated the effects of the patients' head and neck position on ventilation and oropharyngeal leak pressures for the Supreme laryngeal mask airway. Certainly, this prompts us to think of it as a viable avenue for further research. Our group chose not to evaluate the anatomical positions of the two supraglottic devices using fibreoptic bronchoscopes, as logistical and ethical concerns proved to be impediments. Advancing this point, Xue et al.4 concluded previously that fibreoptic scoring of the ProSeal cuff position was not an accurate test to assess airway seal and ventilation function. Furthermore, Eschertzhuber et al.6 demonstrated in a cross-over study that there were no differences in fibreoptic position of the ProSeal and the Supreme laryngeal mask airways. The patient population we chose consisted of short duration day-surgery orthopaedic and urology cases at low risk of pulmonary aspiration. We excluded patients with gastrooesophageal reflux, obesity and hiatus hernia. In like fashion with our earlier laryngeal mask airway study,7 it is not our institutional practice to routinely place orogastric tubes with supraglottic airways in this low-aspiration-risk patient population. We had no reported cases of aspiration in both studies.7,8 We agree that intraoperative and postoperative analgesia may affect the assessment of pharyngolaryngeal adverse events such as sore throat, dysphonia and dysphagia. Likewise, so will distracting pain from the operative site. Fentanyl was titrated according to a standardized protocol intraoperatively by the anaesthesiologist and postoperatively by the postanaesthesia care unit nurses. Potential confounders were equally distributed with randomization as seen in Table 1 of our study.8 Assessment of pharyngolaryngeal adverse events was done at multiple time intervals of 1, 2 and 24 h postoperatively to take into account possible time, surgical site and analgesic regime bias. The first attempt success rate for the Supreme was statistically higher than that for the ProSeal laryngeal mask airway in a controlled operating room environment. We admit that extrapolation of our findings to the emergency airway management context with a different spectrum of practitioners in a more hostile location may be inequitable. However, we appeal to the readers of this reply to ponder whether the conduct of a prospective randomized controlled trial to address this specific emergency airway management situation is ethically, numerically and logistically possible.