Which supraglottic airway will serve my patient ... - Wiley Online Library

Editorial 27. Fraisl P, Mazzone M, Schmidt T, Carmeliet P. Regulation of angiogenesis by oxygen and metabolism. Developmental Cell 2009; 16: 167–79. 28. Centre for Maternal and Child Enquiries (CMACE)/Royal College of Obstetricians and Gynaecologists (RCOG) 2010. Joint

Anaesthesia 2014, 69, 1183–1196 Guideline: Management of women with obesity in pregnancy. http://www. rcog.org.uk/files/rcog-corp/CMACERCOG JointGuidelineManagementWomenObesity Pregnancya.pdf (accessed 16/06/2014). doi:10.1111/anae.12832

Supporting Information Additional Supporting Information may be found in the online version of this article: S1. Additional references.

Editorial Which supraglottic airway will serve my patient best? How can we choose the ‘right’ device? There are now so many supraglottic airways (SADs) available, and we need to decide which one to use. The laryngeal mask airway (LMA), introduced into clinical practice in 1988, has stood the test of time, and is now routinely used during general anaesthesia. Nevertheless, the original LMA has its limitations, and modified forms have been developed to address specific requirements, such as a more effective seal permitting positive pressure ventilation, and access to the gastrointestinal tract. In addition, the worldwide acceptance of the LMA has encouraged development of a large number of competitor SADs. Faced with such a choice, we need to match the right device with the right patient, in the hands of a practitioner with the right skills [1], instead of perpetuating the search for the holy grail (the ideal airway device) that will help all our patients. To do this, we should focus on becoming better at predicting which device will suit our

specific patient’s needs as we evolve towards an individualised treatment approach. In the era of evidencebased medicine, introduction of a new device into clinical practice must be justified first with scientific reasoning. In this and recent issues of Anaesthesia, such evidence is provided by way of three metaanalyses on the i-gelâ [2–4] and one on the Ambuâ AuraOnceTM [5].

When can a new device be introduced into clinical practice? To choose the ‘right’ device from new products, we should first judge whether or not a new airway device is ready to be introduced into clinical practice. Cook [6], in his editorial of over a decade ago, has pointed out that many new devices have become commercially available with little or no prior evidence of their clinical efficacy and safety, and some of these untested devices do not perform to an acceptable standard. For example, some single-use laryngoscope blades [7] and singleuse tube exchangers (bougies) [8]

© 2014 The Association of Anaesthetists of Great Britain and Ireland

have been found to be inferior to conventional devices, and we should avoid using such devices. Cook has proposed a more formal, three-stage evaluation process for new devices [6], akin to development of drugs. In stage 1, devices are evaluated ‘on the bench’ and in specifically designed manikins; in stage 2, a rigorous pilot study takes place to determine whether the device is effective and safe; and in stage 3, the device is compared in a randomised controlled trial against the current gold standard device. The ‘ADEPT’ guidance, formulated by the Difficult Airway Society, recommends a minimum level of 3b evidence (a single case-control or historical-control study) to guide selection (or purchase) of airway devices [9]. We may be tempted to rely on manufacturers’ preliminary trial results (industry reports) of device efficacy, but we need to await formal publications in scientific literature where there is some assurance of peer review, appropriate ethical conduct, statistical analysis and an opportunity for reader rebuttal [10]. 1189

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When published level-3b evidence or higher has become available for a new device, we should then check whether or not reported superiority of a new device over the conventional device is clinically meaningful. For example, if an observational study reports that no airway complications occurred during the use of a new SAD in 30 patients, this does not necessarily mean that the incidence of complications is low enough; statistically, a 0% incidence in 30 patients indicates that the upper 95% CI for incidence can be as high as 10% [11, 12]. A minimum sample size of 250 cases would be required to show (with 99% CI) one failure of the device before it constitutes useful evidence in favour of the new device’s clinical acceptability, if the conventional device has a failure rate of 2.5% [11, 12]. Similarly, when insertion time for a new SAD is reported to be significantly shorter than for the conventional device, this significant difference may not be clinically meaningful if the mean difference between the groups is, for example, merely 3 s. One of the recent meta-analyses referred to above concludes that the mean oropharyngeal leak pressure was 3.3 cmH2O higher with the i-gel than with the LMA in children, and the incidence of bleeding associated with insertion of the i-gel was significantly lower than the incidence for the LMA (with a relative rate of 0.46). The former difference may not be clinically meaningful (in particular, in children breathing spontaneously), whereas the latter difference appears more meaningful. Until significantly better features of a new airway device relating to clini1190

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cally important outcome measures have been shown, we should be cautious about replacing the conventional device with a new one.

What else do we need to choose the ‘right’ device? We can judge whether or not a new device has a clinically meaningful difference (superiority) to the conventional device, mainly by assessing the results of randomised controlled studies and meta-analyses. Nevertheless, if randomised controlled studies only show statistically significant differences that are not clinically meaningful, the reports of meta-analyses will not provide clinically meaningful information for our decision making. For example, the metaanalysis by Montblanc et al. [3], of 31 studies comparing the efficacy of the i-gel and the LMA, does not provide clinically meaningful information such as the incidence of suboptimal positioning or pulmonary aspiration, and the ease of insertion, in patients with difficult airways, although it does usefully conclude that postoperative sore throat is less frequent with the i-gel. So what clinically meaningful information do we need about new devices? First, the LMA is generally effective in providing a clear airway during anaesthesia, but there exists a 1% incidence of failure/removal and a subsequent need for tracheal intubation [13]. This reflects the finding that serious airway complications (such as dislodgement of the device or airway obstruction) may occur during the use of a LMA once in every 20 patients [14, 15]; thus we might hope that a new SAD would reduce this incidence. It

is well known that a SAD that is placed in a suboptimal position may initially provide a clear airway, but may dislodge or cause laryngospasm (when the tip of the device migrates to the glottis [15]). Therefore, we need studies that assess the incidence of suboptimal positioning of a new and conventional device and show that a new device is less likely to be misplaced. The incidence of pulmonary aspiration with SADs is currently still not low enough, as pulmonary aspiration has been reported during the use of a SAD as frequently as – and even more frequently than – when patient’s tracheas were intubated [16, 17]. This is worrisome, since the use of SADs is generally indicated only in patients at low risk of aspiration. To circumvent this, the use of second generation SADs (with a gastric drain) has been advocated, yet there have still been reports of pulmonary aspiration [18]. Therefore, larger prospective studies are needed to confirm this theoretical advantage of second generation SADs before we can judge if all conventional SADs should be replaced by second generation ones. The efficacy of different SADs may differ considerably in patients with difficult airways. Despite numerous reports of successful use of a SAD in patients in whom both tracheal intubation and facemask ventilation were difficult, insertion of a SAD can be difficult, when there is limited mouth opening, restricted head and neck movement or cricoid pressure applied [19]. One study has shown a higher success rate of insertion and ventilation with the i-gel compared with the LMA when


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cricoid pressure was being applied [20]. Another study, in patients subjected to manual-in-line stabilisation of the cervical spine, has shown that the success rate of insertion of the intubating LMA (FastrachTM) is higher than that of the classic LMA [21]. Only through these kind of studies can we be prepared to rely on the right SAD as a ‘rescue’ in patients with difficult airways.

Role of manikin studies Rai and Popat expressed their concerns that researchers tend to take the easy option of carrying out manikin studies, thus circumventing research in patients, and have called a halt to these proliferating manikin-based studies [22]. We believe that we should assess the efficacy and safety of each new airway device ‘on the bench’, for example in manikins (Cook’s suggested stage-1 study), before using it in patients, but manikin-based studies should be regarded as preliminary. Manikins are generally not good models of real patients (for example, hard plastic and lack of secretions), and thus caution is required to extrapolate results from manikins to patients. For example, time to insert an airway device in manikins will not generally provide any useful information to clinical practice. We suggest that researchers should submit this preliminary part of a manikin-based study as a correspondence letter to a clinical journal, or a medical technology journal. Alternatively, researchers should report the results of the preliminary part of a manikinbased study, together with the formal study in patients.

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Nevertheless, if one has found through a manikin study that a new airway device might be inferior to the conventional device, one has a moral obligation to report to other clinicians about the possible problem, and publication in a clinical journal is the most effective and rational method to disseminate such clinically useful information. In addition, Rai and Popat have pointed out that in some studies, patients are not essential and manikins will suffice; others may require conditions that cannot be recreated easily in patients and manikins can offer excellent alternatives [22].

Manufacturer’s responsibilities As with clinicians, manufacturers and distributers should take responsibility for their products, and should feel incentivised to work more closely with airway specialists, to promote early publication of at least one clinical trial that supports the requisite standard of evidence. Trials with negative outcomes will be as important to both clinicians and manufacturers, and the latter will want to cut their losses and desist further investments in a product that is performing poorly. Manufacturers should also have a moral obligation to notify clinicians when they have made modifications to devices that are already on the market. Many airway devices have been modified, mainly to improve the efficacy and safety, but clinicians sometimes feel that modified devices are inferior to the devices before modifications. There-


fore, we should be careful in using a newly modified airway device, and should be ready to redo studies on the modified devices, as proposed by Cook [6].

Conclusions There is little doubt that new airway devices have increased the efficacy and safety of airway management, but there is still much space for improvement. Both clinicians and manufacturers have a moral obligation to carry out studies on clinically meaningful outcome measures for a new airway device to choose the right device for the right kind of patient. Further studies in manikins, comparing one SAD with another, are unlikely to help the clinician make this choice; reviews such as those of Choi et al. [2], Montblanc et al. [3], Smith & Bailey [4], and Baidya et al. [5], may help distill what clinical evidence we do have and identify outcomes for which there is still insufficient evidence.

Competing interests None of the authors have a financial interest in any equipment manufacturing or distributing company. MSK has received equipment or financial support for education and/ or research from the distributors of Olympus, Pentax, AMBU, Storz and McGrath laryngoscopes. WHT has received equipment/logistics support for research or education and to conduct airway workshops in the Asia-Pacific region from Verathon, Karl Storz, Aircraft Medical, AMBU, Intersurgical, Pentax, Airtraq, King Systems, LMA, Teleflex, 1191

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Smiths Medical, VBM, Laerdal, Cook and I:E Medics. TA has received honoraria from the distributor of the LMA and of the i-gel for giving lectures.

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M. S. Kristensen Consultant and Head of Section for Anaesthesia for Ear, Nose, Throat and Maxillofacial Surgery Department of Anaesthesia Rigshospitalet University Hospital of Copenhagen Copenhagen, Denmark Email: [email protected] W. H. Teoh Senior Consultant Department of Women’s Anaesthesia KK Women’s and Children’s Hospital Singapore T. Asai Professor Department of Anaesthesiology Dokkyo Medical University Koshigaya Hospital Koshigaya Saitama, Japan

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