Who is at increased risk of aspiration?

* E-mail: jbrimaco{at}bigpond.net.au

Editor—We read with interest Asai's editorial about the risks of pulmonary aspiration,1 which was precipitated by our report of three cases of pulmonary aspiration occurring with the laryngeal mask airway (LMA®).{dagger}2 Asai commented on the six factors leading to aspiration (predisposing, patient, operation, anaesthesia, device and variability in the material aspirated) and concluded that we lack sufficient data to make evidence-based decisions and need to conduct further research to reduce these uncertainties. While agreeing with Asai's conclusions, we feel that his comments about device factors, which focus negatively on the LMA, warrant closer scrutiny.

Firstly, Asai states that ‘The presence of the LMA decreases the lower oesophageal sphincter tone, and this may, in theory, increase the risk of regurgitation and aspiration’, citing a 1992 manometric study by Rabey and colleagues.3 While accepting that indirect evidence from dye and pH studies supports this statement,4 the other manometric studies, which were uncited by Asai, do not. Bunchungmongkol and colleagues,5 in a study of 20 children aged 1–5 yr breathing spontaneously, found that lower oesophageal sphincter tone was unchanged by classic LMA insertion or cuff inflation. Keller and Brimacombe,6 in a study of 10 awake volunteers with topical anaesthesia, found that the classic and ProSealTM LMA did not interfere with lower oesophageal sphincter tone with the cuff either partially or fully inflated.

Secondly, Asai states that ‘As the incidence of gastric insufflation is greater for the classic LMA than other supraglottic devices or a tracheal tube, the patient receiving the LMA is at higher risk of regurgitation and aspiration’, citing no papers. While accepting that this may be true compared with the tracheal tube, there is little evidence that this is true compared with other supraglottic (extraglottic7) devices. In fact, there is only one patient study (by Asai) hinting that gastric insufflation is more common with the classic LMA than the laryngeal tube airway (P=0.07)8 and three manikin studies, by one group, showing that it is more common than the oesophageal tracheal combitube.9 In addition, there is one study using a rubber model of the pharynx showing that the classic LMA provides less effective protection from regurgitation during positive pressure ventilation than the Streamlined Liner of the Pharynx Airway (SLIPATM).10 There is no evidence that it is more common with the classic LMA compared with the dozen or more other extraglottic airway devices currently available.

In summary, we feel that the uncertainties about the risk of aspiration also encompass the uncertainties about whether the LMA reduces lower oesophageal sphincter tone and increases the risk of gastric insufflation compared with other extraglottic airway devices.

J. Brimacombe1,* and C. Keller2

1 Cairns, Australia
2 Innsbruck, Austria


 
E-mail: asait{at}takii.kmu.ac.jp

Editor—I thank Drs Brimacombe and Keller for their comments on my Editorial.1 First, let me clarify that I did not intentionally focus negatively only on the classic LMA, as I stated ‘the presence of a laryngeal mask airway (and perhaps any other supraglottic airway that is inserted into the oesophageal inlet) decreases...’.1

About the first point, I could equally have said that ‘the presence of a laryngeal mask airway may decrease the lower oesophageal sphincter tone’. Stimulation of the pharynx or the oesophagus, even by a small amount of water, may reduce the lower oesophageal spincter tone.11 12 Scientific inference is that the presence of an airway device in the oesophageal inlet should decrease the lower oesophageal tone. The report by Rabey and colleagues3 supports this inference. In contrast, the cited studies do not support this inference. In the Bunchungmongkol study,5 the finding of no significant difference may have been a false negative (beta error), and in fact, in two of 20 children the tone markedly decreased (by 10 and 14 mm Hg). Keller and Brimacombe6 stated in their study that relaxation of the lower oeosphageal spincter tone by stimulation of the pharynx ‘may occur only when higher brain function is impeded by general anaesthesia’ and thus the results obtained from ten awake volunteers may not be applicable to anaesthetized patients. Therefore, it seems reasonable to conclude, from the best evidence currently available, that in anaesthetized patients, the laryngeal mask (and perhaps any other supraglottic airway that is inserted into the oesophageal inlet) may decrease the lower oesophageal spincter tone.

About the second point, I accept that there is little evidence that gastric insufflation is more likely to occur with the laryngeal mask than with other supraglottic airways. In fact, in a recent study comparing the efficacy of the laryngeal mask and CobraPLA supraglottic airway, gastric insufflation occurred in 4 of 41 patients with the laryngeal mask and in 6 of 39 patients with the Cobra airway.13 At the time of writing, the reported incidence of gastric insufflation during the use of the laryngeal mask was higher than the reported incidence for several other supraglottic airways.

As I stated in the Editorial, pulmonary aspiration is the key factor that will determine the future of supraglottic airways. I agree with Brimacombe and Keller that, in the era of evidence-based medicine, we should analyse the reported results carefully and should clarify what we really know and what we do not. Only by doing so, we can make the use of supraglottic airways safer.

T. Asai

Osaka, Japan

References

1 Asai T. Editorial II. Who is at increased risk of pulmonary aspiration? Br J Anaesth 2004; 93: 497–500[Free Full Text]

2 Keller C, Brimacombe J, Bittersohl J, et al. Aspiration and the laryngeal mask airway: three cases and a review of the literature. Br J Anaesth 2004; 93: 579–82[Abstract/Free Full Text]

3 Rabey PG, Murphy PJ, Langton JA, et al. Effect of the laryngeal mask airway on lower oesophageal sphincter pressure in patients during general anaesthesia. Br J Anaesth 1992; 69: 346–8[Abstract]

4 Barker P, Langton JA, Murphy PJ, Rowbotham DJ. Regurgitation of gastric contents during general anaesthesia using the laryngeal mask airway. Br J Anaesth 1992; 69: 314–15[Abstract]

5 Bunchungmongkol N, Chumpathong S, Catto-Smith AG, et al. Effects of the laryngeal mask airway on the lower oesophageal barrier pressure in children. Anaesth Intensive Care 2000; 28: 543–6[ISI][Medline]

6 Keller C, Brimacombe J. Resting esophageal sphincter pressures and deglutition frequency in awake subjects after oropharyngeal topical anesthesia and laryngeal mask device insertion. Anesth Analg 2001; 93: 226–9[Abstract/Free Full Text]

7 Brimacombe J. A proposed classification system for extraglottic airway devices. Anesthesiology 2004; 101: 559[CrossRef][ISI][Medline]

8 Asai T, Hidaka I, Kawachi S. Efficacy of the laryngeal tube by inexperienced personnel. Resuscitation 2002; 55: 171–5[CrossRef][ISI][Medline]

9 Ocker H, Wenzel V, Schmucker P, Doerges V. Effectiveness of various airway management techniques in a bench model simulating a cardiac arrest patient. J Emerg Med 2001; 20: 7–12[CrossRef][ISI][Medline]

10 Miller DM, Light D. Laboratory and clinical comparisons of the Streamlined Liner of the Pharynx Airway (SLIPATM) with the laryngeal mask airway. Anaesthesia 2003; 58: 136–42[CrossRef][ISI][Medline]

11 Mittal RK, Chiareli C, Liu J, Shaker R. Characteristics of lower esophageal sphincter relaxation induced by pharyngeal stimulation with minute amounts of water. Gastroenterology 1996; 111: 378–84[ISI][Medline]

12 Pouderoux P, Verdier E, Kahrilas PJ. Patterns of esophageal inhibition during swallowing, pharyngeal stimulation, and transient LES relaxation. Am J Physiol 2003; 284: G242–7[ISI]

13 Akca O, Wadhwa A, Sengupta P, et al. The new peripheral airway (CobraPLATM) is as efficient as the laryngeal mask airway (LMATM) but provides better airway sealing pressures. Anesth Analg 2004; 99: 272–8[Abstract/Free Full Text]





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