The recent article of Seet et al.1 comparing the safety and efficacy of Supreme laryngeal mask airway (LMA) and ProSeal LMA in a randomized controlled trial was of great interest to us. The results of this study showed that compared with ProSeal LMA, Supreme LMA had a lower oropharyngeal leak pressure and a higher success rate of the first insertion attempt. However, several design aspects of this study should be clarified.
In this study, the position of the patient's head and neck during assessment of ventilation and oropharyngeal leak pressure is not clearly described. There is no study assessing the effects of position of the patient's head and neck on ventilation and oropharyngeal leak pressure of Supreme LMA. However, previous studies have demonstrated that the position of the patient's head and neck can significantly change airway seal and ventilation quality of ProSeal LMA.2,3
In this study, initial assessment of ventilation was done by observation of the square wave tracing on the capnography and thoracoabdominal movement. It is not clear how the authors assess ventilation quality by the Supreme and ProSeal LMAs. We would like to know whether normal thoracoabdominal movement and capnography with obvious gas leakage are considered an effective airway. In addition, criteria by which the LMA should be repositioned were also not clearly defined. A three-point ventilation score described by Keller et al.4 is a useful method to assess ventilation quality by the LMA.
The anatomical positions of the Supreme and ProSeal LMAs were not evaluated by the fibreoptic bronchoscope, and furthermore the orogastric tube placement through the drainage tube of the Supreme and ProSeal LMAs was also not performed in this study. It is generally believed that passage of a lubricated orogastric tube via the drainage tube and aspiration of gastric juice is an essential test for determining the correct placement of the two LMAs.5,6 It is reported that the orogastric tube placement through the drainage tube is more difficult with Supreme LMA than with ProSeal LMA.7 Also, difficult placement of the orogastric tube often suggests obstruction of the drainage tube, caused for example by its folding over. This does not only eliminate an important function of the Supreme and ProSeal LMAs for gastric access but also puts the patient at increased risk of gastric insufflation and aspiration during airway maintenance with them.
In this study, sore throat was assessed as a side-effect of the two LMAs. When postoperative sore throat between groups is compared, standardization of postoperative analgesia should be a crucial component of study design.8 The type and dose of analgesia and the timing of its administration in relation to the assessment of sore throat should have been described in their methods. In the absence of a comparison of a postoperative analgesic protocol, the secondary outcome findings and their subsequent conclusions should be interpreted with caution, as they may have been determined using incomplete methodology.
Finally, this study was performed in patients undergoing elective ambulatory surgeries, patients' airways were not well defined and all of the LMA insertions were completed by anaesthesiologists with more than 5 years of experience. Therefore, the results of this study should not be extrapolated to the patients who require an airway rescue device, especially for patients with a difficult intubation in emergency situations and in hostile environments outside of the operating room. Under these circumstances, first responders may not have the opportunity to be trained regularly on the use of advanced airway devices and may be faced with the most challenging airways. Also, their results do not show that use of the Supreme LMA in such groups would be appropriate.
All the authors have no any financial arrangement with the makers of the ProSeal laryngeal mask airway and Supreme laryngeal mask airway.
1 Seet E, Rajeev S, Firoz T, Yousaf F, Wong J, Wong DT, Chung F. Safety and efficacy of laryngeal mask airway Supreme versus laryngeal mask airway ProSeal: a randomized controlled trial. Eur J Anaesthesiol
2 Brimacombe J, Keller C. Stability of the LMA-ProSeal and standard laryngeal mask airway in different head and neck positions: a randomized crossover study. Eur J Anaesthesiol 2003; 20:65–69.
3 Xue FS, Luo MP, Liu HP, et al
. The effects of head flexion on airway seal, quality of ventilation and orogastric tube placement using the ProSealTM laryngeal mask airway. Anaesthesia 2008; 63:979–985.
4 Keller C, Brimacombe J, Keller K, Morris R. A comparison of four methods for assessing airway sealing pressure with the laryngeal mask airway in adult patients. Br J Anaesth 1999; 82:286–287.
5 Brain AI, Verghese C, Strube PJ. The LMA ‘ProSeal’: a laryngeal mask with an oesophageal vent. Br J Anaesth 2000; 84:650–654.
6 Verghese C, Ramaswamy B. LMA-Supreme: a new single-use LMA with gastric access: a report on its clinical efficacy. Br J Anaesth 2008; 101:405–410.
7 Hosten T, Gurkan Y, Ozdamar D, et al
. A new supraglottic airway device: LMA-supreme, comparison with LMA-Proseal. Acta Anaesthesiol Scand 2009; 53:852–857.
8 Jaensson M, Olowsson LL, Nilsson U. Endotracheal tube size and sore throat following surgery: a randomized-controlled study. Acta Anaesthesiol Scand 2010; 54:147–153.