Who is at increased risk of pulmonary aspiration?

E-mail: timcook{at}ukgateway.net

Editor—Dr Asai's thorough Editorial1 explains why aspiration may occur during anaesthesia with the classic laryngeal mask airway (cLMA) and other laryngeal masks. Most would accept that the incidence of regurgitation and aspiration with the cLMA is probably higher than that of 1 in 10 000, reported in the literature. However the absence of a large number of publications reporting morbidity and mortality with such events suggests that the consequences of this may be relatively benign. In reality both the use of a tracheal tube and LMA are usually safe procedures with infrequent major complications. However, I wish to make two points.

First, all LMAs should not be considered to be equivalent in performance, risk of aspiration, or protection from pulmonary aspiration. The ProSealTM LMA (PLMA) because of its drain tube and improved airway seal is likely to be a safer device in preventing pulmonary aspiration than the cLMA. This is supported by bench top2 and cadaver3 studies, case reports and controlled trials.4 5 A definitive answer is unlikely as a controlled trial designed to have 80% power and 5% type I error, to detect a 50% reduction in aspiration risk with the PLMA compared with the cLMA would require over 2.5 million elective patients.

The second point is that Dr Asai, as with many contributors to such debates does not consider adequately the consequences of not using a laryngeal mask or other supraglottic airway. In most cases this will mean use of tracheal intubation under neuromuscular blockade. The complications associated directly with tracheal intubation are well known as are those associated with the use of neuromuscular blocking agents. If the reason for intubation is a perceived increased aspiration risk surely it is logical to use a rapid sequence induction.

The incidence of aspiration in two large studies before the introduction of LMAs is interesting. These studies involving ~400 000 patients reported an incidence of aspiration from 1 in 1100 to 1 in 4000 elective patients.6 7 In Olsson's study of 185 000 patients 67% of cases of aspiration were preceded by airway or intubation difficulty.6 In Warner's study of over 200 000 cases (risk 1 in 900 for emergency cases and 1 in 4000 for elective cases), 67% of cases of aspiration occurred either during laryngoscopy or at the time of extubation.7 In a large Australian report of difficult intubations, regurgitation occurred during 1 in 7 cases of difficult intubation8 while in a recent prospective study of 2800 emergency intubations more than two attempts at laryngoscopy was associated with aspiration in 1 in 8 cases.9 One could therefore argue that it is intubation itself that is the commonest cause of pulmonary aspiration; a recent editorial in the USA asked ‘is routine endotracheal intubation as safe as we think?’.10

It is easy for this discussion to become polarized with one party representing only the disadvantages of intubation and the other the disadvantages of not intubating. My comments in this letter clearly come from the former camp. There are many absolute and relative indications for tracheal intubation and contraindications for laryngeal mask use. However, LMAs are intrinsically less invasive than tracheal intubation and tracheal intubation with neuromuscular blockade is not without its complications. Perhaps a reasonable compromise is: ‘routine airway management with a supraglottic/laryngeal mask airway should not be used where there is a contraindication, while tracheal intubation should be used only when there is a specific indication’. In choosing a supraglottic airway, where the absence of risk of aspiration is not certain, but the risk of aspiration is still considered low, the available evidence supports using one such as the PLMA designed and likely to be safer than the cLMA.

Declaration of interest

Tim Cook has received two honoraria from Intavent Orthofix, the distributors of LMAs, for speaking at company meetings.

T Cook

Bath, UK


 
E-mail: asait{at}takii.kmu.ac.jp

Editor—I agree, in principle, with Dr Cook's claims. Regarding the first point, I stated in my editorial that ‘[n]either do we know whether the ProSeal laryngeal mask, which in theory reduces pulmonary aspiration, truly reduces the incidence and, if any, the degree of aspiration with this device’.1 I believe that I was careful not to overestimate or underestimate the theoretical advantages of the ProSeal over the classic laryngeal mask airway, in reducing pulmonary aspiration. My point was that pulmonary aspiration can occur even when a ProSeal is used and ‘the incidence of aspiration can be reduced by adhering to the guidelines that laryngeal mask airways (classic, intubating, ProSeal) and other supraglottic airways should not be used in anaesthetized patients who are at increased risk of pulmonary aspiration’.1

Regarding the second point, I stated that ‘... to decide whether or not a supraglottic airway is indicated, by weighing its advantages over tracheal intubation against the risk of pulmonary aspiration’.1 I believe that we now know that both the laryngeal mask airway and tracheal intubation are indispensable in clinical practice. I felt that it was unnecessary in my editorial1 to discuss in detail advantages and disadvantages of tracheal intubation over the use of a supraglottic airway, as we all are well aware of these.

I think that Dr Cook's following statement is reasonable: ‘routine airway management with a supraglottic/laryngeal mask airway should not be used where there is a contraindication, while tracheal intubation should be used only when there is a specific indication’. Nevertheless, as I pointed out in my editorial,1 we often face difficult choices in daily clinical practice as to which cases or which circumstances should be regarded as contraindicated, mainly because there are so many uncertainties in estimating the risk of aspiration. For example, some consider that patients undergoing laparoscopic cholecystectomy are at risk of aspiration, whereas others do not. Similarly, should all obese patients, all patients in lithotomy position or all those undergoing laparoscopic surgery, or a prolonged anaesthesia be regarded as at risk? In view of the uncertainties about the risk of pulmonary aspiration, it is inevitable that there are disagreements among anaesthetists on the use of a supraglottic airway in many circumstances.

I had no intention of representing only the disadvantages of tracheal intubation and the other disadvantages of not intubating. As Dr Cook correctly points out, pulmonary aspiration may occur even when tracheal intubation is chosen: aspiration may occur not only before or after tracheal intubation, but also while a cuffed tracheal tube is being placed.1 Therefore, I believe that our primary task (regardless of the choice of an airway device) is to minimize further the occurrence of pulmonary aspiration, by carrying out reliable research to reduce uncertainties about the risk of aspiration.

T. Asai

Osaka, Japan

References

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

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

3 Keller C, Brimacombe J, Kleinsasser A, Loekinger A. Does the Pro-Seal laryngeal mask airway prevent aspiration of regurgitated fluid? Anesth Analg 2000; 91: 1017–20[Abstract/Free Full Text]

4 Evans NR, Gardner SV, James MFM. ProSeal LMA protects against aspiration of fluid in the pharynx. Br J Anaesth 2002; 88: 584–7[Abstract/Free Full Text]

5 Cook TM, Nolan JP, Verghese C, et al. RCT of the ProSeal with the classic LMA in unparalysed patients. Br J Anaesth 2002; 88: 527–33[Abstract/Free Full Text]

6 Olsson GL, Hallen B, Hambraeus-Jonzon K. Aspiration during anaesthesia: a computer aided study of 185 358 anaesthetics. Acta Anaesth Scand 1986; 30: 84–92[ISI][Medline]

7 Warner MA, Warner ME, Weber JG. Clinical significance of pulmonary aspiration during the peri-operative period. Anesthesiology 1993; 78: 56–62[ISI][Medline]

8 Williamson JA, Webb RK, Szekely S, Gillies ER, Dreosti AV. The Australian incident monitoring study. Difficult intubation: an analysis of 2000 incident reports. Anaesth Intensive Care 1993; 21: 602–7[ISI][Medline]

9 Mort TC. Emergency tracheal intubation: complications associated with repeated laryngoscopic attempts. Anesth Analg 2004; 99: 607–13[Abstract/Free Full Text]

10 Maktabi MA, Smith RB, Todd MM. Is routine endotracheal intubation as safe as we think or wish? Anesthesiology 2003; 99: 247–8[CrossRef][ISI][Medline]





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