Successful intubation is a critical and central intervention in the emergency department (ED). In particular, the concept of first pass success is frequently promoted as the goal of emergency airway management [1-4]. However, first intubation attempts in EDs are often unsuccessful; the literature documents that 17% to 29% of all ED intubations require two or more intubation attempts [4-8].

Given the emerging evidence that repetitive intubation attempts are associated with an increased risk of adverse events in the ED [3,4], early and successful rescue intubation approaches – e.g., use of alternative methods, devices, and intubators – become important. The international anaesthesia consensus statement emphasizes early use of rescue intubation approaches in the airway management [9-12], and several studies from the anaesthesia and pre-hospital literature support this approach [13-16]. However, to the best of our knowledge, there is no evidence to support or refute the early use of rescue intubation in the ED.

To address this knowledge gap in the literature, by using large prospective multicentre registry data of emergency airway management, we aimed to examine whether preceding multiple failed intubation attempts are associated with a decreased success rate on the first rescue intubation in the ED.

Using the data from two large prospective multicentre observational registries of patients undergoing airway management in the EDs, we demonstrated that the success rate on the first rescue intubation attempt declined as the number of preceding failed intubation attempts increased. To the best of our knowledge, this is the first demonstration of an association between multiple failed intubation attempts and success rates at the rescue intubations in ED airway management.

Airway management has been advocated as the first step for critically ill patients in the ED. However, most of scientific knowledge of airway management originates from out-of-hospital or anaesthesia settings [10,22-28]. Generalizability of these data to the ED setting might be limited because of the difference in patient population (e.g., most of ED patients undergoing airway management are critically ill and have a limited physiologic reserve), setting (i.e., EDs are less controlled setting), individual training level of intubators, and resources. Many vital questions about ED-based airway management to avoid ineffective or potentially harmful interventions remains to be elucidated [29]. Although high-quality prospective clinical trials will provide more rigorous evidence to advance the science of ED airway management, it is often difficult to study airway management in critically ill patients in the ED setting. In the last decade, large prospective registries represented by the National Emergency Airway Registry, Korean Emergency Airway Management Registry, and JEAN registries have provided scientific evidence of emergency airway management [5-7,20]. These registries allow insights into not only individual and group performance but also infrequent outcomes such as failed intubations and rescue intubations. Although rescue intubation is deemed to be important [3,30-32], previous studies in the ED setting only examined the characteristics of rescue intubations and the predictors for successful rescue attempts after one failed attempt (i.e., not after multiple failed intubation attempts) [8,19].

The American Society of Anesthesiologists guidelines recommend the early use of alternative approaches after multiple failed intubations [10]. Several studies in the non-ED setting support this approach [13-15,33-35]. For example, two small single-centre studies reported successful implementations of the predefined algorisms that use alternative devices (e.g., gum elastic bougie and supraglottic airways) after two failed laryngoscopic attempts, both in the operating room (n = 100) [34] and prehospital settings (n = 160) [35]. Another single-centre observational study reported that the use of video laryngoscope was effective as a primary rescue device in failed intubation attempts in the ED setting [36]. These studies collectively suggest the importance of early and systematic approaches in rescue intubations after failed intubation attempts. Our data from the large multicentre registries extend these prior investigations by demonstrating the independent association between the number of preceding failed intubation attempts and lower success rates on the first rescue intubation. Our inference supports the recommendation to minimizing the number of initial intubation attempts and focus on changing or optimizing the next attempt to maximize chances of success.

If not directly causative, multiple failed attempts before the rescue attempt have a plausible relationship with the observed lower success rates on the first rescue intubation. Potential reasons for the observed association include the difference in patient characteristics, rescue methods, devices, and providers among the groups according the number of failed attempts. However, the observed association persisted after conditioning on these factors. Alternatively, multiple intubation attempts are known to result in direct airway trauma [3,4], thereby interfering with airway visualization. Additionally, multiple failed attempts may be an identifiable surrogate marker for a number of factors – e.g., unanticipated difficult airway, limited provider awareness of difficult airways, lack of resource or education for emergency airway management – that affect success rates but are difficult to quantify individually.

Our findings have several implications for airway management in the ED. For clinicians, our data support the strategy limiting the number of intubation attempts and the conventional wisdom emphasizing the early and systematic use of rescue interventions during ED intubation efforts. However, the use of patient characteristics to assess difficult airways and the evidence to guide the provision of optimal airway management in the ED remain limited. For emergency researchers, our findings should underscore the importance of high-quality research into risk stratification and integrated rescue intubation approach, coupled with dissemination of these findings to improve care for patients in the ED.

Our data consist predominantly of academic and urban EDs in Japan where emergency airway management is highly variable across the EDs [7]. Thus, similar studies with data from other countries with different training systems may result in different findings. Although one may surmise a limited generalizability of our inferences, the observed association between the number of preceding failed intubation attempts and decreased rescue success rates was large and persisted across various statistical assumptions. In addition, there are plausible mechanisms to support this conclusion. While we acknowledge that validations of our study findings in systems with established emergency medicine education and training are warranted, we believe that our inferences are clinically plausible and likely applicable to different practice settings.

In sum, based on data from two prospective multicentre observational studies of patients undergoing airway management in the ED, we demonstrated that an increased number of failed attempts was independently associated with a decreased success rate of the first rescue intubation attempt. Our results support the early and systematic use of rescue intubation techniques for emergency airway management, including the use of an experience intubator [5], RSI [37], and video laryngoscope [36,38] supported by the literature.

The current study has several limitations. There are inherent limitations related to the use of surveillance data. The surveillance system used in these registries is subject to self-reporting bias, thereby resulting in an overestimation of intubation success rates. Although independent real-time monitoring of airway management is difficult to perform in the ED, we used the previously applied self-reporting systems with standardized data forms and high capture rates [6,7]. Therefore, we believe that our data represent the best available data.

Second, the JEAN registries were not designed to measure intubation-associated adverse events according to each intubation attempt; therefore, we were unable to examine associations between delayed rescue intubations and adverse events.

Third, as with any observational study, the observed association between the multiple failed intubation attempts and lower rescue success rates does not necessarily prove causality and might be confounded by unmeasured factors. Potential confounding factors include underlying comorbidities, difficulty in intubation (e.g., anatomical deformities and obesity), individual intubator training levels and skill sets, and institution-level characteristics. However, the adjustment for the specialty as a proxy of individual training levels might have partially addressed this potential confounding.

Fourth, a smaller proportion of patients in our registries underwent intubation attempts using RSI and video laryngoscope compared to the previous studies in different practice settings [4-6,8,16,20], owing to, at least in part, a high degree of variation in airway management practices [7]. To address this concern, we fitted mixed model accounting for the potential clustering of patients at the ED level. Interestingly, we found that neither the use of RSI nor video laryngoscope had a higher odds of first rescue success, both of which were not consistent with the literature [8,28,36]. The potential explanation of these findings includes the presence of residual confounders between these factors and rescue success rates, the limited statistical power owing to the small number of RSI and video laryngoscope use, the use of video laryngoscope by novices, and random errors.

Fifth, because our sample consisted predominantly of EDs affiliated with emergency medicine residency programs in Japan, our inferences may not be generalizable to the other healthcare settings (e.g., emergency airway management performed by experienced anaesthesiologists, with a higher use of RSI and video laryngoscope). However, the observed association has plausible mechanisms and persisted across different analytic assumptions. Although formal validation of the study in other healthcare settings is warranted, our inference is likely present in different practice settings.

Finally, our objective was not to examine predictors of the success rates by multiple rescue attempts but those on first rescue attempts. However, as the literature documented that intubation-associated adverse event rates accelerate with the increased number of intubation attempts [3,4], our observations are of direct relevance to the development of more effective emergency airway management for critically ill patients.