Human factors and the ‘next generation’ airway trolley

The impact of human factors on clinical performance during airway emergencies is well recognised 1-5. Although this includes 'teamwork skills' such as leadership, role allocation and communication, the scope of human factors is much broader than this. As the scientific discipline concerned with understanding and optimising the interactions between humans and other elements of a system, human factors involves considering the impact of aspects of the individual, environment, processes and culture on human performance 6. The availability and presentation of airway equipment is a key component of the clinical environment in relation to airway management 7. In an effort to address the individual preferences of multiple clinicians, the difficult airway trolley has traditionally been a repository for a diverse array of equipment, often without standardisation of contents or layout. More recently, there has been increasing recognition of the potential for this 'all-inclusive' philosophy to negatively impact on clinical performance during an airway crisis. This has prompted calls for a more restrained and deliberate approach to the selection and presentation of airway equipment 8. This editorial will discuss key principles for incorporating human factors into airway trolley design and implementation so as to enhance team performance. Both the Australian and New Zealand College of Anaesthetists and the Difficult Airway Society have published recommendations for airway trolley content that emphasise ensuring certain categories of equipment rather than specific devices are available 8, 9. A well designed airway trolley should contain a limited range of strategically chosen equipment. Devices that perform essentially the same function should be eliminated, and equipment that overcomes specific challenges should be prioritised. Selection of the single best device for a particular purpose should be supported by evidence where possible. Limiting devices in the trolley reduces clutter and makes items more readily visible, prompting potential use and facilitating rapid access. In addition, it simplifies decision making, particularly in situations of cognitive overload. Having fewer devices helps prevent choice overload ('analysis paralysis'), whereby an inability to decide between a multitude of options results in no action being taken. It also reduces the risk of choice fatigue, a deterioration in the quality of successive decisions that can result in a clinician desperately attempting every airway management option available during an emergency, however futile or inappropriate. A further benefit of limiting the variety of devices is that this logically reduces the number of techniques that must be learned, making it easier for clinicians to ensure they are proficient with the equipment stocked. This is an increasing challenge as the spectrum of available devices continues to expand. When selecting devices for inclusion it is important to consider the way in which an airway trolley is intended to be used. A dedicated airway rescue trolley 10 can further restrict items to those which might be required in a time-critical fashion during an emergency, with less urgently required equipment being sourced from a nearby storage area. Conversely, a more comprehensive trolley, expected to cater for all difficult airway situations 11, should include equipment for procedures such as awake tracheal intubation, conversion of supraglottic airway to tracheal tube and staged extubation, as well as medications to facilitate 'withdrawal' 12 from airway management (i.e. restoring spontaneous maintenance of airway patency and ventilation, often imprecisely referred to as 'waking') such as sugammadex. Similarly, dedicated adult or paediatric trolleys 11, 13 are able to stock a more limited range of equipment sizes rather than those required for use in all age ranges. Compatible screens for use with included videolaryngoscopes or bronchoscopes, should ideally be incorporated into the trolley. Finally, the skill set and preferences of the users must be acknowledged. A consultative approach is advised as there is no value in including equipment that airway operators are unable to use effectively. Equipment layout has been identified as a key element of the clinical system that may function as either an enabler or barrier to airway management, particularly in critical airway situations 7, 11. The airway trolley should be organised in a manner that supports the needs of clinicians and aligns with how devices are likely to be accessed during airway management. This has led to the concept of 'clinical integration': aligning trolley layout with local airway management pathways, such that the airway trolley effectively becomes an extension of the relevant cognitive aid 9, 10. Using this approach, the airway trolley has the potential to prompt clinical teams to execute their airway management strategy by presenting options to optimise the three upper airway types (facemask ventilation, supraglottic airway and tracheal intubation), encouraging efficient progression between them and ultimately urging clinicians to commit to the rescue of the can't intubate, can't oxygenate (CICO) situation when necessary. At a minimum, airway trolleys adopting this approach typically feature distinct drawers dedicated to each of the three upper airway types as well as for CICO rescue. Non-urgently required items are ideally located in separate drawers. Clear labelling facilitates identification of urgently needed items, enables adult and paediatric equipment to be easily differentiated and can also be used to create links with the respective cognitive aid. The use of icons and colour coding (Figs. 1-4) may result in easier and faster identification of equipment within the airway trolley when clinicians are under stress. Within each drawer, the degree of integration with the cognitive aid and the strategies used to structure the presentation of equipment may vary: The Vortex trolley 10 arranges equipment according to the optimisation categories used by this cognitive tool, including graphic prompts for non-equipment interventions such as airway manipulations and administration of medications (Fig. 3). In contrast, the trolley developed by The Children's Hospital at Westmead 13 uses vacuum sealed bags to group sets of compatible equipment appropriate to a given weight range (Fig. 4). Thus, although a logical sequence in the presentation of equipment is encouraged, the ideal layout is not yet known and further research is needed in this area. The presentation of equipment required for CICO rescue warrants particular attention. It is no longer acceptable to source and assemble equipment for this emergency procedure on an ad hoc basis, as this has the potential to lead to delays and errors. Pre-packaged CICO rescue kits containing standardised and dedicated equipment are advocated. In addition to ensuring that appropriate equipment is readily available, kits such as these may decrease the cognitive load associated with accessing equipment. Clinicians need only request the 'CICO kit' rather than having to recall and articulate individual items during the stress of a time-critical emergency. Similarly, by presenting all necessary equipment, the kit can prompt key actions for performance of this confronting task. Can't intubate, can't oxygenate rescue kits should be readily identifiable and ideally packaged such that the contents are clearly visible even before they are opened (Fig. 5). In this way, the contents can be examined as an airway emergency evolves, providing the opportunity for the proceduralist to mentally rehearse the required actions even before the declaration of a CICO event, as part of the earliest stages of priming for CICO rescue 4, 14. This promotes the concept of transition to CICO rescue, which emphasises simultaneous priming for the procedure in parallel with ongoing attempts to establish alveolar oxygen delivery via the upper airway 2. By linking equipment presentation to the process of airway management, this integrated approach seeks to facilitate clinical decision making and reduce the time to restoration of alveolar oxygen delivery and correction of hypoxaemia. Research is needed to determine whether these theoretical benefits translate into more effective airway management. Standardisation of the content and layout of difficult airway trolleys should ideally occur across all areas in which advanced airway management is practiced 1. This includes the intensive care unit (ICU), emergency department (ED), operating theatre and other anaesthetising locations within an institution. It is during some of the most challenging airway cases that staff from these different areas are brought together at short notice. A consistent template for trolley layout provides familiarity for those clinicians finding themselves in a foreign environment, especially when integrated with local airway guidelines and education. However, although some core categories of equipment might be essential, universally mandating particular devices, specialised equipment or a rigidly prescribed layout is likely to be counterproductive. Such an approach could not only be expected to be met with strong cultural resistance but, in failing to acknowledge the diverse requirements and skill sets of different areas, it would violate a number of the principles being advocated in this editorial. As such, although uniformity is advocated at a broader level, some degree of flexibility must be retained within the standardised template, to ensure the trolley meets local needs. As many clinicians work across multiple institutions, achieving national 1 or even international standardisation of such a template represents something to aspire to, but would present significant challenges, particularly in the face of trying to integrate this with the current diversity of airway guidelines. Resources for managing difficult airways must be easily accessible in a timely manner, ideally in under a minute 8, 15. Although the majority of airway operators would probably agree waiting for over 10 min during the process of difficult airway management to get access to required equipment 16 reflects substandard care, it is easy for such delays to occur. This is particularly true when anaesthetising sites are remote from the operating theatre (e.g. obstetric units, radiology, etc) but still rely on difficult airway equipment stored there 16. Dedicated local difficult airway trolleys are therefore advised for each geographically separate airway management location. Historically, local provision of difficult airway trolleys has not been universal. Surveys in 2012 showed that 30% of Australian and New Zealand ICUs were dependent on a remote difficult airway trolley kept in the operating theatre 17, and only 53% of rural Australian general practitioner anaesthetists had access to a difficult airway trolley 18. In 2010, just over 50% of ICUs in the UK had a dedicated local trolley 19. This rose to 90% in the wake of the 4th National Audit Project (NAP4) 1, representing NAP4's greatest closure of the safety gap in ICU practice 20. Conversely, although NAP4 also had a significant impact on the local availability of difficult airway equipment in UK EDs, in spite of this, nearly half still lacked immediate access to a difficult airway trolley in 2016 20. A 2018 survey of paediatric and neonatal ICUs in the UK revealed that nearly all paediatric units had immediate access to difficult airway equipment but that this was true of only half of the neonatal units 21. In Australia, most EDs and ICUs in a 2015 audit lacked a difficult airway trolley 22 and a number of the authors of this editorial work in large hospitals where 'off the floor' elective airway management locations remain reliant on remotely stored difficult airway equipment. In 2016, over 50% of Japanese EDs still did not have a dedicated local trolley 23. Thus, although substantial gains have been made, serious deficits persist regarding availability of dedicated local difficult airway trolleys in some areas. Within a given airway management location, timely access to difficult airway equipment is also influenced by the local distribution of trolleys and the ratio of trolleys and devices to the number of simultaneous airway interventions occurring there. The number of airway devices available is in turn influenced by cleaning times and use of disposable equipment. The minimum number of trolleys required in each location depends on its physical layout, how many airway interventions are potentially occurring simultaneously and the likelihood of difficulty being encountered. In operating theatres, mathematical modelling suggests that any site with greater than 16 adjoining simultaneous airway management locations, requires at least two difficult airway trolleys 24. This calculation is based on a 10% incidence of difficult airway and accepting up to a 50% risk of two difficult airways occurring simultaneously. We suggest this risk tolerance may be excessive. In addition, the incidence of challenging, time-critical intubations in EDs and ICUs may be greater than this. Thus, this ratio may underestimate the need for multiple trolleys in many environments. Further impacting this ratio is the time required to dispatch local airway trolleys to the point of care. To ensure deployment within the advocated 1 min time-frame 8, 15, local airway trolleys would need to be located within around 30 m of each airway point of care. In fact, we contend that any equipment that might be required in a time-critical fashion should already be present at the bed-side whenever planned airway management takes place (i.e. a 1:1 ratio). This may currently be achievable in some ICU and ED settings where the difficult airway trolley is often routinely brought to the bed-side. In contrast, in high volume airway management environments such as operating theatres, providing 1:1 availability of expensive items such as videolaryngoscopes largely remains an aspirational target, although exceptions exist 25. As the cost of these devices declines over the next few years, however, it is likely that a price point will be reached that makes widespread universal point-of-care availability feasible. In the meantime, it is realistic that, even in operating theatres, the majority of other airway rescue equipment should be routinely available at the bed-side. Preferably, this equipment would be presented in dedicated point-of-care airway rescue trolleys that are immediately accessible to the airway assistant and employ the same principles we have outlined for design of the main difficult airway trolley. This contrasts with the current presentation of airway equipment in operating theatres, which is often dispersed across a range of locations including storage in a generalised 'anaesthetic trolley'. These trolleys, which may not be readily accessible to the airway assistant during induction, tend to unite a diverse array of anaesthesia-related equipment including drugs, fluids, intravenous cannulae, monitoring and airway equipment rather than being directed towards any specific functional purpose. Thus, not all emergency airway equipment should be confined to the main difficult airway trolley. Based on the work of A. Heard 26, clearly labelled point-of-care CICO rescue kits, typically with nationally consistent content for both cannula and scalpel techniques (Fig. 5), are now commonplace in Australian operating theatres (http://vortexapproach.org/cico/#cicokits). Contrary to their traditional placement in the bottom drawer of the difficult airway trolley, these are located prominently on the walls or anaesthetic machines in every theatre as well as on trolleys. This increases not only the proximity of the kits but also their visibility, which facilitates routine checking of their availability, encourages clinicians to become familiar with their contents and provides a persistent daily reminder of CICO rescue as a potential option for airway management. Anecdotally, the prominence of the kits also provides a stimulus for discussion between airway operators and their assistants regarding CICO rescue equipment and techniques, as well as the indications for use of the kits and the triggers for accessing them. This raises awareness of techniques which might otherwise rarely be discussed. During an evolving airway emergency, having the CICO kits visible also enables them to act as a prompt to either prime for or perform CICO rescue. The same benefits could be realised in EDs and ICUs if the use of point-of-care kits was expanded to include locating them in each resuscitation or ICU bay. Universal point-of-care availability of standardised CICO rescue kits across the operating theatre, ED and ICU is an approach that is being implemented in some Australian hospitals. Although planned airway management typically occurs in critical care areas, the need for emergency airway management can also arise unpredictably in any area of a hospital. Although basic airway equipment is usually available in local resuscitation ('crash') trolleys, more specialised equipment can be transported to these peripheral areas using 'grab bags' or dedicated mobile emergency trolleys that are delivered by the team responding to an emergency call. Ideally, such a system is coupled with access to a difficult airway response team to provide the requisite technical expertise 27. Maximising the impact of the interventions outlined above requires that all clinicians involved in airway management are familiar with the location of the trolley, its contents, layout and any associated airway resources. Orientation to these aspects and regular ongoing training should be provided by way of a formal education programme 28. Such an education programme would ideally involve scenario-based simulation training, using equipment identical to that in the clinical environment and incorporating instruction in both technical and non-technical skills. Such training is especially important in high-risk areas such as obstetrics, ICU and EDs 29. In this way, the difficult airway trolley is able to be further integrated with the clinical environment and the needs of the clinicians working there. Evidence suggests that such training is not commonplace, however, and that Australia and New Zealand may be lagging behind the UK and North America in this regard 29. Several 'next generation' airway trolleys exemplifying implementation of the above principles are currently in clinical use. These include the Vortex Airway Rescue Cart 10, Epworth Difficult Airway Trolley 11 Royal North Shore Hospital Trolley 30 and The Children's Hospital at Westmead Difficult Airway Trolley 13. Ongoing audits of users and clinical events will be important to determine the impact of these human factors oriented trolleys and identify ideal design features. In the meantime, however, the era of the difficult airway trolley as an isolated, central and exhaustive repository of difficult airway equipment should come to an end. NC is the creator of the 'Vortex Approach' but has no financial interest in this material which is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. WB has received an honorarium from MSD for organising a conference, has received loan airway equipment for airway courses he teaches on and is an executive board member of the Airway Management Special Interest Group (ANZCA/ASA/NZSA). JG runs the Confidence and Competency Assessment Modelling (CCAM) course which is a not-for-profit course administered by a charitable foundation, in which he has no financial interest. No other conflicts of interest declared.