Prehospital Airway Management – the Continued Search for Evidence

This article refers to:

Evidence-Based Guidelines for Prehospital Airway Management: Methods and Resources Document

Evidence-Based Guideline for Prehospital Airway Management

Few topics in emergency medical services (EMS) spur as much controversy as prehospital airway management (1). Four decades ago, the training of paramedics to perform endotracheal intubation (ETI) transformed the field, opening the door for EMS personnel to perform life-saving interventions once performed exclusively by physicians (2–5). Four decades later, while EMS practice has matured to include a range of airway techniques, we remain unsure of the clinical role and benefit of these interventions. The potential benefits of prehospital airway management are weighed against its pitfalls and implementation challenges, and thus it is unclear if we are helping or harming patients.

One of the challenges in shaping prehospital airway management practices has been the absence of high-quality scientific data. The publication of the “Evidence Based Guideline for Prehospital Airway Management (EBG)” (6) with its accompanying methodology paper (7), and the preceding “Prehospital Airway Management: A Systematic Review” (SR) (8) represent important milestones in the science of airway management. The sponsorship of these works by federal partners (the National Highway Traffic and Safety Administration and the Agency for Healthcare Research and Quality) underscores national recognition of the importance of prehospital airway management. The creation of the SR and EBG indicate that there is now a body of evidence of sufficient breadth and depth to justify a broad systematic assessment.

A systematic review is a synthesis of evidence using critical methods to identify, define, and assess research on the topic (9). An evidence-based guideline is a systematically developed statement that assists practitioners in making decisions about appropriate health care for specific clinical circumstances (10). EBGs use current research and data, commonly from systematic reviews, to formulate recommendations. The prehospital airway management SR synthesized information from 99 studies to describe the comparative benefits and harms of three prehospital airway management approaches (bag-valve-mask [BVM], supraglottic airway [SGA], and ETI) in the treatment of patients with trauma, cardiac arrest, or non-arrest medical emergencies. The prehospital airway management EBG critically appraised the research identified in the SR to formulate 22 specific recommendations for clinical practice. The EBG used a structured approach, including the application of the GRADE methodology to rate existing data and the incorporation of input from national experts (11).

While the SR and EBG offer important perspectives on the last 40 years of airway management science, they also highlight essential lessons for future research.

We Must Continue to Build the Body of Airway Science

The first lesson is critical – we are not done generating new airway knowledge. The depth and quality of the studies assessed by the EBG was woefully inadequate; of 22 defined questions, only 17 resulted in recommendations, all qualified as “conditional.” Furthermore, the evidence bases for the questions were all rated as suffering from “very low certainty” or “lack of evidence.” We must continue to generate airway research that not only fills the knowledge voids but also raises the standard of scientific quality.

Clinical Trials are Essential

An important corollary not obvious from the SR or EBG is that we cannot depend on observational data alone to advance the field. Observational studies of prehospital airway management are vulnerable to confounding by indication; they can be used to assess the process but not the outcomes of airway management (12). Randomized clinical trials are necessary to identify true effectiveness of prehospital airway interventions. This point is reinforced by the observation that multiple retrospective analyses identified better outcomes with ETI than SGA, but randomized trials found better or no difference in outcomes with SGA (13–15). One must exercise caution when reading the SR and EBG because much of the evidence synthesis did not exclude observational studies.

To date there have been only a handful of prehospital airway management clinical trials, most prominently the Pragmatic Airway Resuscitation Trial (PART), Airways-2, and Cardiac Arrest Airway Management (CAAM) Trial, and the Los Angeles pediatric airway trial (14–17). Ongoing airway clinical trials include the Prehospital Airway Control in Trauma (PACT) Trial and Pediatric Prehospital Airway Resuscitation Trial (Pedi-PART) (18, 19). These trials are important achievements, offering the best and most rigorous assessments of the effectiveness of prehospital airway interventions. Clinical trials require substantial support and resources. We must capitalize on this momentum, pushing national stakeholders such as the National Institutes of Health to expand prehospital research infrastructure so that we can better study and understand airway and other interventions.

We Must Apply Innovative Research Strategies

Innovative approaches are needed to tackle the myriad of airway management questions. For example, the EBG was organized around 22 distinct scientific questions reflecting distinct patient and procedural subsets. These common subsets include airway technique (BVM vs. SGA vs. ETI), medical condition (cardiac arrest vs. trauma vs. non-arrest medical), method of drug assistance (rapid sequence intubation vs. sedation-assisted intubation vs. conventional intubation), and age group (adults vs. children) (20). The conundrum is that it is impossible to host a comprehensive series of clinical trials for such a wide range of subgroups.

Pedi-PART is a good example of an innovative trial that overcomes many design and logistical challenges. Pedi-PART will use a Bayesian adaptive sequential comparison platform trial design to determine the best prehospital airway management strategy (BVM, ETI, or SGA) in critically ill children (18). Because it is difficult to randomize three different airway interventions in the prehospital setting, the trial will be organized in two stages, each randomizing only two interventions: Stage I = BVM vs. SGA, and Stage II = [winner of Stage I] vs. ETI. The transition from Stage I to Stage II will be determined by frequent Bayesian interim analyses, which allows coordination of two separate trials and enables the total pool of 3000 subjects to be shared across the two stages. The primary analyses will use Bayesian hierarchical models to account for the heterogeneity of effect between key subsets, including medical conditions (cardiac arrest, trauma, non-arrest medical) and age groups (adults, teens, child, toddler, infant).

The Most Valuable Pearls of Evidence May Be Hidden from Systematic View

While the systematic rigor of the SR and EBG are appealing, they may miss key morsels of knowledge from “Easter eggs” hidden in secondary study findings. For example, in the PART trial, successful airway insertion was 2.8 min faster with the laryngeal tube than ETI, highlighting the faster speed of SGA insertion (15). Also, the intubation success rate was only 53.1%, highlighting the potential influence of airway management proficiency. The primary result of the CAAM Trial was uninterpretable, but the trial identified higher airway management difficulty and rates of regurgitation with BVM than ETI (16).

Nonsystematic approaches may have a role in shaping airway practices. The National Association of EMS Physicians’ compendium of recommended practices for prehospital airway management is based upon consensus by national experts (21). While not using the rigorous review methods applied by the NHTSA EBG, few would argue with the soundness of the practical NAEMSP recommendations. The tension between systematic and nonsystematic approaches is evident in the appendix of the NHTSA EBG, which contains a series of good practice statements from the expert panel. These compelling recommendations were necessarily excluded from the EBG because they fell outside the formal scope of the review.

To Better Understand Airway Management, We Need to Look Beyond the Airway

By better understanding ventilation delivery, physiology, and outcomes, we may be able to better understand the merits of different prehospital airway management techniques. The Resuscitation Outcomes Consortium amassed a repository of over 25,000 CPR process files recorded during out-of-hospital cardiac arrests (22). We must build similar infrastructure linking prehospital cardiac monitor and capnography measurements with clinical data. We must also evolve methods for ventilation detection and measurement. While waveform capnography is the current standard method, novel technology based on lung spirometry and changes in thoracic impedance offer additional methods for characterizing ventilations (23–25).

We must also deepen our understanding of ventilation patterns. Calculation of respiratory rate alone is unlikely to yield meaningful insights. Recent studies highlight that prehospital ventilation encompasses periods of normo-, hypo-, and hyperventilation, and that estimates of these events depend upon the methods of measurement (26, 27). Longitudinal trends in ventilation are also likely important, as are novel capnography measures such as the airway opening index (24, 28). State-of-the-art approaches such as machine learning will undoubtedly help us to identify novel dimensions of ventilation and to link these patterns with the preceding airway management approaches and events (29).

It is an exciting time for prehospital airway science. After four decades, we finally have a basic scientific understanding of prehospital airway techniques and their clinical outcomes and consequences. The lessons learned from this first chapter are inspirational and should bolster our resolve as we move into the future. With this determination we will find the best possible prehospital airway strategies to serve our patients.

Henry E. Wang
Department Emergency Medicine, The Ohio State University, Columbus, Ohio
[email protected]

Disclosure statement

Dr. Wang receives research grant support from the National Institutes of Health, the Department of Defense, Marinus, Inc, Quidel, Inc, and Vasomune, Inc. Dr. Wang also receives consulting fees from the American College of Emergency Physicians as editor-in-chief of the Journal of the American College of Emergency Physicians Open. Dr. Wang is Principal Investigator of the Pedi-PART Trial (UG3-HL165019).