Newer airway devices: Future promising?

“The greater the difficulty, the more glory in surmounting it. Skillful pilots gain their reputation from storms and tempests”

Airway management is the cornerstone of anaesthesia and resuscitation. Incidence of difficult intubation by direct laryngoscopy is estimated to be between 4.5% and 7.5%.[1] Conventional airway management involves use of the mask, the direct laryngoscope and the endotracheal (ET) tube, whereas fibreoptic bronchoscope has been the gold standard for access and intubation in difficult airways. Over the years, continued incidences of hypoxia during airway management led to efforts to devise effective alternatives.

Much of the innovation has been in the form of supraglottic airway devices (SADs) and video display units. Ideally, such devices should be easier to use technically, allow early and fast insertion, provide adequate cuff seal without distortion of cuff shape, protect against aspiration, allow easy intubation, allow controlled ventilation, maintain airway anatomy, allow easy removal alone or if used for intubation, available for all age groups, should be reusable, easily sterilisable, cheap and most importantly, should be validated for regular use based on effectiveness in large population.

The first major innovation was in the form of laryngeal mask airway (cLMA, LMA Classic™), about 20 years ago. Its advantage was its use as a hands-free replacement for mask and as an airway. Risk of inadequate cuff seal and aspiration led to incorporation of drain tube in LMA Proseal™. The intubating LMA (iLMA/LMA Fast Trach™) was developed to specifically allow for an effective “blind intubation.” The LMA C Trach™ with liquid crystal display (LCD) viewer cum light source enabled ventilation, glottis visualisation, and tracheal intubation via laryngeal mask conduit. It has been used effectively in the presence of conditions with difficult airway.[2] Both iLMA and LMA Proseal™ have, however, been used in varying conditions successfully.

Compared to ET intubation, SADs are easier to use and do not need muscle relaxant for insertion; in addition, haemodynamic responses are less as compared to ET intubation. Effective ventilation and separation from oesophagus with good cuff seal are important. The cuff inflation volume is generally more in the SADs, reaching 85–100 ml in the pharyngeal cuff of the oesophageal tracheal Combitube® compared to just few millilitres in an ET tube. LMA Proseal™ and LMA Classic™ produce better seal compared to i-gel airway™.[3] Pressure exerted by the cuff can traumatise the mucosa. Recommended volumes, if crossed, can cause pressures more than the corresponding mucosal perfusion pressures.[4] Sore throat is a well-known adverse effect of SADs; the incidence is less with i-gel™, which does not have an inflatable cuff.[5] Gastro-oesophageal regurgitation is a risk in devices with cuffs and without any suction/gastric drainage options. LMA Proseal™ and laryngeal tube suction™ (LTS) Sonda laryngeal tube (SLT) are devices which can allow suction/placement of a gastric tube.

The adverse effects discussed above are inherent to inflatable cuffs and they are less likely to be corrected in future models.

Among the SADs, iLMA is specifically designed for intubation and provided with designated low-volume cuff ET tube.

The streamlined pharynx airway™ liner (SLIPA™) has the advantage that the effects of nitrous oxide on sealing pressure seen with other devices with cuffs are not a concern here as it does not have a cuff. The laryngeal tube (LT™) can be used with spontaneous and controlled ventilation. Insertion of LT is reported to be easier compared to LMA classic for inexperienced personnel.[6] The Cobra Perilaryngeal Airway (CobraPLA™) has been used as a rescue device in “cannot ventilate, cannot intubate” (CVCI) situations and for routine airway management with spontaneous as well as controlled ventilation. Risk of aspiration remains with this device, especially with controlled ventilation.[7] The SADs are getting affordable by Indian standards and it is a matter of time before more evidence is collected locally and airway adverse effects are minimised.

Among the devices with video displays, Airtraq® laryngoscope (AL), Glidescope® video laryngoscope (GVL), Pentax-AWS® and McGrath® video laryngoscope have been successfully used in both normal and difficult airways. C-MAC® allows recording of both images and videos and is available with Macintosh #3 and #4 blades, straight blades, and recently, the D-blade (which has an elliptical tapering shape), claimed to be useful in difficult airway. It is used in the same way as a regular laryngoscope; laryngoscopic view and Cormack and Lehane grading have been shown to improve when C-MAC is used.[8] The video laryngoscopes are very costly devices; their wider use is only possible if costs are brought down in the coming years.

Majority of the newer devices have been used and are available for paediatric age group.[9] Time to insertion was longer with i-gel, but both Ambu Aura Once laryngeal mask® and pediatric i-gel™ were used with high success rates in a recent trial in 218 children.[10] Since i-gel tends to slip out, it is advised to tape it securely.

LMAs have been successfully used during magnetic resonance imaging (MRI) procedures. Ambu® Disposable Laryngeal Mask and the i-gel™ airway have been associated with the best image quality and prominent artefacts were seen with LMA Proseal™.[11]

Airway devices in out of hospital cardiac arrest states: Time is a factor when airway is to be secured in cardiac arrest situations as uninterrupted chest compressions are recommended and SADs have a very useful role here (LMAs, Combitube). Widespread and effective use has in fact led to the “upgradation” of LMA as a routine management device instead of an emergency device, both in American and European difficult airway algorithms.[1213]

Airtraq®, LMA C-trach™ and the other videoscopes have the potential to be used as part of algorithms, even in difficult airways.[14] It is also suggested that backup strategies need to be included in algorithms if ‘backup devices’ such as LMAs fail.

There is a need to highlight the possible advantages of customising guidelines to suit local conditions, including optimal usage of available equipment, within the available pool of skilled operators to realise the full potential of the new devices.[15]

Too many devices are being introduced into the market and the practitioners are confused as to their utility, with inadequate scientific evidences regarding their efficacy and safety. Some devices including certain airway guides and invasive devices have not been discussed in the present editorial. The Difficult Airway Society (DAS), United Kingdom, has launched a unique working group, the Airway Device Evaluation Project Team (ADEPT), to establish a process by which the airway management community within the profession could itself lead a process of formal device/equipment evaluation.[16] This is a novel idea since at one extreme we continue to face airway mishaps and at the other, are bombarded with newer devices and gadgets. However, it is imperative that any device tested and validated in large population groups must become part of airway armamentarium in future and efforts must be made to reduce problems of availability, access, training and cost of the devices. After all, airway related mortality is still the major cause of anaesthesia related mortality, and thus the quotation by Epictetus aptly applies to developments of these various devices.[17] We are possibly closer than ever in effectively bridging the gap between conventional direct laryngoscopy and the fibrescope for airway management, and thus reduce airway related hypoxia.