Portal de Periódicos da CAPES

Editorial I: The classic laryngeal mask airway: a tried and tested airway. What now?

2006; Elsevier BV; Volume: 96; Issue: 2 Linguagem: Inglês

10.1093/bja/aei312

1471-6771

Tim Cook,

Anesthesia and Sedative Agents

Safe, effective airway management is a foundation of quality anaesthetic practice and the classic laryngeal mask airway (cLMA) (LMA-Classic™, Intavent Orthofix, Maidenhead, UK) is one of the keystones of modern anaesthetic practice. The past 2 years have seen the introduction of inexpensive competitors. With this, the decision as to which laryngeal mask to use is being taken out of the hands of anaesthetists by managers and purchasers in many hospitals. This has great implications for anaesthetic practice and this editorial considers the many issues raised by the introduction of single-use laryngeal masks. The cLMA achieves a reliable airway with a low incidence of major complications and pharyngo-laryngeal morbidity. Consequently, since its introduction, the cLMA has transformed routine anaesthesia. There have been an estimated 200 million patient uses, over 2500 academic papers and, some would argue, only one death directly attributable to its use.1Keller C Brimacombe J Bittersohl J Lirk P von Goedecke A Aspiration and the laryngeal mask airway: three cases and a review of the literature.Br J Anaesth. 2004; 93: 579-582Crossref PubMed Scopus (100) Google Scholar Whether this is accepted, or not, even the fiercest of detractors must accept the cLMA has an enviable safety record. It is often regarded that Dr Brain got it pretty much right the first time. However this assumption is worth examining. Brain’s attempts to produce the device that finally became the cLMA began in 1981 and evolved slowly, requiring several materials, more than 200 prototypes and 7000 patient studies before the design was finalized and the product launched in 1988. Since then the cLMA design has remained unaltered. Brain’s original prototype was made from the black rubber cuff of a Goldman nasal mask (mask) and a plastic tracheal tube (shaft). During its development both latex and polyvinylchloride (PVC) were tested as materials for constructing the cLMA before settling on silicone. PVC was rejected as being too rigid.2Scanlon P Carey M Power M Kirby F Patient response to laryngeal mask insertion after induction of anaesthesia with propofol or thiopentone.Can J Anaesth. 1993; 40: 816-818Crossref PubMed Scopus (113) Google Scholar PVC has two advantages over silicone: first it is cheaper and second nitrous oxide diffuses through it less readily, so intracuff pressure alters little during anaesthesia.3Van Zundert AA Fonck K Al-Shaikh B Mortier E Comparison of the LMA-Classic™ with the new disposable Soft Seal laryngeal mask in spontaneously breathing adult patients.Anesthesiology. 2003; 99: 1066-1071Crossref PubMed Scopus (54) Google Scholar During the development of the cLMA, Brain encountered several problems including difficulties with insertion, creating an effective airway seal, and protection against aspiration.4Brain AIJ The development of the laryngeal mask—a brief history of the invention, early clinical studies and experimental work from which the laryngeal mask evolved.Eur J Anaestheiol. 1991; : 5-17Google Scholar Some of these factors interacted with each other: for example, devices with a higher seal pressure were generally harder to insert. As a result the cLMA was in some ways a compromise, allowing relatively easy insertion but achieving only a low airway seal pressure.4Brain AIJ The development of the laryngeal mask—a brief history of the invention, early clinical studies and experimental work from which the laryngeal mask evolved.Eur J Anaestheiol. 1991; : 5-17Google Scholar One design issue that exercised Brain’s inventive skills more than others was the problem of epiglottic downfolding during insertion, leading to airway obstruction (severe enough in 1% of cases to require repositioning of the mask with a laryngoscope).5Brimacombe J Laryngeal Mask Anesthesia, Principles and Practice. 2nd edn. WB Saunders Co., London2004Google Scholar Brain tried several insertion tools and techniques to avoid this problem and made at least four specific mask modifications (incorporating balloons and levers) to correct it. In 1984, he designed a prototype of silicone, and the mask portion was produced as an ellipse without a central orifice, requiring this to be cut away before attaching to the device’s stem. It was simple to modify this orifice to create two parallel bars, which the current cLMA now retains. This resolved the problems of epiglottic downfolding and obstruction. These bars were patented in 1988. The patent on the cLMA expired in 2003. There are currently six companies producing alternatives based on the original cLMA. Given the success of the cLMA it was not surprising that competitors chose to market similar devices. What is perhaps surprising is that all these companies are producing and marketing single-use LMAs, rather than reusable devices. Only one of these companies (Marshall Medical, Bath, UK) markets a reusable silicone laryngeal mask, with all others being single-use PVC devices. While the cLMA itself no longer has a patent, the epiglottic bars remain under patent until 2008. Whether these are strictly necessary remains unclear, and there are other solutions to epiglottic downfolding, such as a deeper bowl. So, why have the manufacturers of alternatives to the cLMA chosen to market single-use devices, made of a material rejected by the original manufacturers for the reusable version? The likely answer is that PVC is cheaper than silicone, allowing competitively priced single-use masks. The rationale for choosing single-use devices is more complex. Excluding commercial factors, the main driving factor for the change towards single-use equipment in the late 1990s appeared to be concerns over infection risk, particular prion disease, the causative agent of new variant Creutzfeldt–Jakob disease (vCJD). In the UK this led the Department of Health, the Association of Anaesthetists (AAGBI) and the Royal College of Anaesthetists (RCA) all to recommend use of disposable equipment. In the case of the AAGBI the document ‘Infection Control in Anaesthesia’ states ‘Where appropriate, single-use disposable equipment will remove the difficulties of reuse and decontamination procedures. The use of such equipment is to be encouraged’ and ‘the development of inexpensive disposable laryngeal masks will be of considerable benefit.’6AAGBI Infection control in anaesthesia. AAGBI, London2002Google Scholar However, others are less persuaded. Brimacombe recently described the rush towards single-use laryngeal masks as ‘driven by fears of the unknown … and scientific misinformation’.7Brimacombe J Laupu W Keller C Time to dispose of the nondisposable LMAs.Anesth Analg. 2005; 100: 897Crossref PubMed Scopus (2) Google Scholar vCJD is a particularly awful and emotive disease, but this fact should not deflect from a dispassionate analysis of risk. Polarization of the debate leads to accusations of ‘irresponsibility’ at one extreme and ‘scaremongering’ at the other. Lymphoid tissue has been cited as particularly high risk as, unlike other forms of prion disease, vCJD prion protein is detectable in lymphoid tissue from infected patients. Therefore, tonsillectomy and adenoidectomy were specifically singled out in Government and RCA guidance as surgery after which reusable laryngeal masks must not be reused and single-use laryngeal masks are a realistic alternative.8Smith G Variant CJD What you need to know at present.in: Bulletin of the Royal College of Anaesthetists. May 2001: 302-304Google Scholar Whether current practice reflects this guidance is not known. However, since 2000 the number of deaths from vCJD, rather than rising, has halved (http://www.cjd.ed.ac.uk/figures.htm). Estimates of the extent of the UK epidemic have been reduced dramatically from >100000 deaths, first to ‘between 10 and 7000’9Ghani AC Ferguson NM Donnelly CA Anderson RM Factors determining the pattern of the variant Creutzfeldt–Jakob disease (vCJD) epidemic in the UK.Proc R Soc Lond B Biol Sci. 2003; 270: 689-698Crossref PubMed Scopus (40) Google Scholar and then to 40 over the next 70 yr (95% confidence interval 9–540).10Ghani AC Donnelly CA Ferguson NM Anderson RM Updated projections of future vCJD deaths in the UK.BMC Infect Dis. 2003; 3: 4Crossref PubMed Scopus (77) Google Scholar A histological study in the UK of 2000 surgically removed tonsils, in 2004, found no evidence of prion protein.11Frosh A Smith LC Jackson CJ et al.Analysis of 2000 consecutive UK tonsillectomy specimens for disease-related prion protein.Lancet. 2004; 364: 1260-1262Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar A UK study of 16 703 tonsil and appendix specimens identified prion protein in three appendix specimens.12Hilton DA Ghani AC Edwards P et al.Prevalence of lymphoreticular prion protein accumulation in UK tissue samples.J Pathol. 2004; 203: 733-739Crossref PubMed Scopus (368) Google Scholar One specimen showed prion protein staining typical of vCJD and two showed atypical staining, considered as possible false positives. No prion protein was found in 1739 tonsil specimens.12Hilton DA Ghani AC Edwards P et al.Prevalence of lymphoreticular prion protein accumulation in UK tissue samples.J Pathol. 2004; 203: 733-739Crossref PubMed Scopus (368) Google Scholar In 2003, Blunt and Burchett13Blunt MC Burchett KR Variant Creutzfeldt–Jakob disease and disposable anaesthetic equipment-balancing the risks.Br J Anaesth. 2003; 90: 1-3Crossref PubMed Google Scholar speculatively estimated a ‘worse case scenario’ of the theoretical risk of prion transfer from an anaesthetic airway to be between 1 and 10 in 100000. They noted that even a small deterioration in safety resulting from using a single-use device of poorer quality in place of a reusable device, would increase the overall risk to patients, and go against the recommendation of the Spongiform Encephalopathy Advisory Committee.13Blunt MC Burchett KR Variant Creutzfeldt–Jakob disease and disposable anaesthetic equipment-balancing the risks.Br J Anaesth. 2003; 90: 1-3Crossref PubMed Google Scholar This statement must be even more pertinent as the estimated risk of prion disease tumbles. It is perfectly legitimate to ask if we need single-use laryngeal masks at all? There have, to date, been no reported instances of prion (or viral) cross infection after reuse of reusable airway equipment. Other reasons cited to change to single-use devices include cost and convenience. In the UK, a cLMA costs approximately £90 and sterilization £1–3. Single-use laryngeal masks cost £3.50–7.00 with the price decreasing as a result of competition. Some reports suggest the average cLMA is used less than 20 times.14Goodman EJ Haas AJ The natural half life of a large stock of reusable laryngeal mask airways at a teaching hospital.Anesth Analg. 2004; 99: 626-627Crossref PubMed Scopus (3) Google Scholar Even if this waste is widespread, cost savings by changing to single-use laryngeal masks are either negligible or non-existent. Greater cost-saving is achievable by reducing loss through accidental disposal or theft. Alternatively cost savings would result from using reusable devices until performance deteriorates rather than disposing of them, often in servicable condition, after 40 uses. Recent in vitro work suggests the cLMA and ProSeal LMA may be reused 130 and 80 times, respectively, before failing pre-use tests recommended by the manufacturer.15Doneley S Brimacombe J Keller C von Goedecke A The Proseal™ has a shorter life-span than the Classic™ laryngeal mask airway.Anesth Analg. 2005; 100: 590-593Crossref PubMed Scopus (16) Google Scholar In vivo work supports 60 reuses.16Berry AM Brimacombe J McManus KF Goldblatt M An evaluation of the factors influencing selection of the optimal size of laryngeal mask airway in normal adults.Anaesthesia. 1998; 53: 565-570Crossref PubMed Scopus (89) Google Scholar The use of single-use products raises other practical questions relating to storage and availability. Most hospitals use thousands of cLMAs each year and changing to single-use masks will require all sizes of masks to be available when required. This raises issues of storage capacity, supply line reliability and shelf life. To this one can add environmental issues. The government recently required hospitals to become environmentally responsible purchasers.17Jochelson K Delap C Norwood S Good corporate citizenship and the NHS—a regional mapping. King’s Fund/Health Development Agency, London2004www.hda.nhs.uk/Documents/corp-citizenship.pdfGoogle Scholar PVC, a chlorinated plastic, contributes to the production of the carcinogen dioxin if burnt, and is not biodegradable. The likely route of disposal is therefore landfill sites. Changing to single-use laryngeal masks requires a 40-fold increase in the number manufactured, packaged, transported, stored and disposed of. Is this environmentally responsible? In this risk-averse climate, the possibility exists of changing practice to eliminate one poorly-defined small risk, and introducing a different poorly-defined small risk. In the case of single-use laryngeal masks a new, small risk may arise from the use of PVC. PVC contains chemicals called phthalates, such as di-2-ethylhexyl phthalate, which are used to increase the plastic’s flexibility: an important performance feature for laryngeal masks. These chemicals are not linked to the plastic matrix and slowly leach out during use. Phthalates are potentially ‘carcinogenic, mutagenic and reprotoxic’.18Available at www2.europarl.eu.int/omk/sipade2?PUBREF=-//EP//TEXT+PRESS+DN-2005Google Scholar There is particular concern over phthalates in products that may be placed in the mouth (e.g. children’s toys), a concern highly relevant to airway devices. The issue has been considered important enough for bills banning PVC in some products to be brought before the parliaments of some American states and the European Parliament. Phthalates are banned from use in cosmetics in Europe and, in May 2005, the European Parliament made permanent, a temporary ban on six phthalates in PVC in children’s toys, and called for investigation into healthcare equipment.18Available at www2.europarl.eu.int/omk/sipade2?PUBREF=-//EP//TEXT+PRESS+DN-2005Google Scholar PVC made with more inert plasticizers such as ‘no DOP’ and ‘DINCH’ is available but at a considerably increased cost. Will the issue of phthalates in airway equipment become an important risk issue? Certainly there are factions for and against phthalates, with both lobbies claiming to be supported by good science. Like the risk of vCJD, it is difficult to quantify the risk, if any, posed by phthalates. Life is never risk-free: it is simply a matter of deciding which risks are unavoidable or acceptable. The medical plastics industry however recognizes this issue as important and PVC use in medical disposables has reduced from 58 to 47% in the last 10 yr. At present all PVC single-use laryngeal masks are made of phthalate-containing PVC. Future changes in the organization of sterilization services are also relevant, particularly in the UK. The British government has undertaken several initiatives to improve the standards and consistency of decontamination of surgical instruments since 1991 and several changes are imminent. These include an audit trail for reusable surgical equipment and considerably more stringent standards for sterilization.19The decontamination of surgical instruments in the NHS in England. Update report. ‘A Step Change’ Department of Health. Gateway number 4625, 2005Google Scholar New legislation raises two potential problems. First, some reusable equipment may not be robust enough to withstand the new disinfection processes. Second, many non-compliant sterilizing machines will need to be replaced, or the work sent elsewhere. Government plans include a reduction in the number of Central Sterile Service Departments (CSSD) and commission of ‘Super CSSD’ with much decontamination/sterilization being contracted out. These CSSD may not be able, or willing, to sterilize airway equipment and if they do costs are likely to increase. Solutions to these problems must be found well before the implementation date of 2007. Having considered the principles of single-use laryngeal masks, what are the practicalities? Is there clinical evidence to guide the clinician in deciding whether to change to single-use laryngeal masks, and if so which to choose? Sadly, no. It is important to note that efficacy and safety of ‘me-too’ devices cannot be assumed: consider the introduction of single-use surgical equipment for tonsillectomy: rapidly withdrawn after reports of poor performance, an increase in post-tonsillectomy bleeding and at least one death.20Department of Health. Re-Introduction of re-usable instruments for tonsil surgery (press release 14 December 2001). London: Department of HealthGoogle Scholar Minor changes in medical equipment can have important unforeseen consequences. Recent examples include the poor performance of single-use bougies21Marfin A Pandit JJ Hames KC Popat MT Yentis SM Use of the bougie in simulated difficult intubation. 2. Comparison with multiple-use bougie.Anaesthesia. 2003; 58: 852-855Crossref PubMed Scopus (53) Google Scholar and laryngoscope blades.22Twigg S McCormick B Cook TM A randomised evaluation of the performance of single-use laryngoscopes in simulated easy and difficult intubation.Br J Anaesth. 2003; 90: 8-13Crossref PubMed Scopus (52) Google Scholar Precedents exist, and it would be wrong to assume that single-use laryngeal masks (of varying designs and materials) behave identically to the reusable cLMA. At the time of writing, there are no peer-reviewed publications relating to any of these new laryngeal masks except the Softseal (Portex, Hythe, Kent, UK) and the LMA-Unique (Intavent Orthofix) which tend to favour the traditionally designed devices. The point is not to criticize a particular device, as there are no publications at all on which to judge the other devices! However, the reusable cLMA has a considerable pedigree with many millions of uses and thousands of publications. The single-use laryngeal masks are supported either by no evidence, or by limited, mostly negative evidence. To further confuse matters at least three of the six single-use devices have been modified since their introduction, either in the materials used or in their design. This poses further problems: when publications do appear it is likely to be impossible to determine which version of a device was studied.23Cook TM Spoilt for choice? New supraglottic airways.Anaesthesia. 2003; 58: 107-110Crossref PubMed Scopus (81) Google Scholar It may be that the performance and safety of single-use devices exceeds that of the original cLMA, but this is conjecture. What is open to criticism is the ease with which devices, with limited evidence of efficacy or safety, enter the marketplace. When the cLMA was first launched there were only two publications, both authored by the inventor. In short, notwithstanding extensive clinical study by the inventor over 7 yr, the cLMA was introduced before publication of peer-reviewed evaluation of the efficacy or safety. Twenty-two years on the introduction of new anaesthetic equipment has barely progressed.23Cook TM Spoilt for choice? New supraglottic airways.Anaesthesia. 2003; 58: 107-110Crossref PubMed Scopus (81) Google Scholar There appears to be too little statutory control, too much marketing and generally a paucity of robust data on either efficacy or safety before products are marketed. As an example there is no British or European standard for a laryngeal mask. New devices therefore need only to pass the criteria necessary for CE marking before being able to be distributed throughout Europe. These criteria focus on the manufacturing process and the quality of materials used. It is far from clear whether any of the statutory requirements actually examine whether devices are ‘fit for purpose’. In the USA the Food and Drug Administration is in the process of creating standards for supraglottic airways. It is hoped that this will take this field forward. The cLMA has performed well over the last two decades and is, in many countries, the standard supraglottic airway. The specialty now has the opportunity to reflect on this device’s performance and decide whether changes in design, materials and performance, consequent on single-use alternatives, are desirable, acceptable or neither. Dr Cook has received honoraria from Intavent Orthofix and the LMA company, both distributors of the LMA-Unique™ and the Classic LMA™. He has also received free samples of single-use laryngeal masks from Mallincrodt-Tyco, Ambu, Intersurgical and Marshall Medical and cost price devices from Smiths Portex. All devices were used for research. No company influenced the content of this article or saw it before submission.