The Pro‐Seal laryngeal mask airway

We were interested in recent correspondence relating to reflux of gastric contents into the drain tube of the Pro‐Seal laryngeal mask airway (Dalgleish & Dolgner. Anaesthesia 2001; 56 : 1010). As part of a trial comparing performance of the Pro‐Seal with the classic laryngeal mask airway we inserted a gastric tube into the drain tube of 30 Pro‐Seal laryngeal mask airways in elective surgery patients. All patients were starved for 6 h for solids and 3 h for fluids. In all cases, fibre‐optic examination of the drain tube and the oesophagus below was undertaken before passage of the gastric tube. On no occasion was gastric content seen in the drain tube or in the upper oesophagus. Gastric fluid was aspirated in 29 of 30 cases with a median volume of 22 ml and a range of 0–85 ml. In none of the cases was there any suggestion of clinical regurgitation or aspiration. In a recent case in our intensive care unit, a Pro‐Seal was being used to allow endoscopic guidance during a percutaneous tracheostomy. The patient had been nasogastrically fed and the stomach was aspirated before the procedure. During dilation of the trachea, some nasogastric feed was vented a considerable distance out of the drain tube. Since the endoscope was at the glottic opening during this episode of regurgitation, it was possible to confirm, under direct vision, that there was no laryngeal or tracheal soiling. Large studies and meta‐analysis has suggested that the incidence of aspiration of gastric contents when using a classic laryngeal mask airway is approximately 0.05–0.009% [1, 2]. A recent editorial on mechanical ventilation via the laryngeal mask airway rather speculatively suggested that aspiration of gastric contents might occur in up to 360 patients per year in the UK [3] and implied that such practice could not be considered entirely safe. The choice of whether to use a laryngeal mask airway when artificially ventilating a patient varies considerably in UK practice [4]. If elective cases may have significant volumes of gastric fluid, and there is some doubt as to whether ventilation via the classic laryngeal mask airway is safe, then the Pro‐Seal is likely to be a valuable addition to the airway armamentarium. Laryngeal seal pressure is increased by approximately 50% [5] and the drain tube allows easy and reliable access to the stomach [5]. In addition, the drain tube might be expected to vent gas leaking into the oesophagus reducing gastric dilation, although this is untested. Should regurgitation occur, the drain tube may allow venting of regurgitated material and its appearance in the drain tube may act as an early warning. However, these potential advantages have not been rigorously examined and it is therefore too early to be sure of the role of the Pro‐Seal in anaesthetic practice. What evidence is there that the Pro‐Seal allows a greater margin of safety in the event of regurgitation? At present there is little; we are aware of three cases in which regurgitated matter has appeared in the drain tube without laryngeal or tracheal soiling (A. Brain, Personal communication). Drs Dalgleish and Dolgner's report brings the total to four, but is the first to be published. In addition, a study in cadavers [6] supports the contention. A study, at present only presented at a meeting, of the use of the Pro‐Seal for laparoscopic cholecystectomy showed no more gastric distension than with a tracheal tube (Maltby JR, Beriault MT, Watson NC, Liepert DJ, Fick GH. Laparoscopic cholecystectomy: LMA‐Proseal vs. tracheal intubation. Poster presentation. Canadian Anaesthesiologist's Congress 2001, Halifax, Canada). If we wait for a controlled study between the two devices to give us the answer, it will be a long wait. If the incidence of aspiration during anaesthesia while ventilating through the classic laryngeal mask is 1 in 11 000 cases, as has recently been suggested [3] and this␣number can be halved by using the Pro‐Seal, this would reduce the number of such cases in the UK by 180 per year. Conducting a trial to detect such a reduction, however, would require approximately 1.3 million patients in each group.