Michael F. Murphy
Overview of the Issues
Although the training and credentials of those performing airway evaluation, management, and rescue may vary widely around the world, the issues related to prehospital emergency airway management demonstrate consistent themes, such as the following:
· Intubation of patients in the field
· Extraglottic devices versus endotracheal intubation (ETI)
· Use of neuromuscular blocking drugs in prehospital airway management
· Verification of intratracheal placement of the endotracheal tube
Airway management in an emergency situation is stressful and anxiety provoking. Crucial decisions must be made rapidly and often without the benefit of a detailed history or physical examination. The environment of care is therefore “error prone.” Strategies designed to minimize error must do so reproducibly in a time-sensitive fashion. Clear definitions and simple evaluation and management memory tools, including mnemonics and algorithms, represent such strategies. Identifying the difficult airway, managing the failed airway, and performing a cricothyrotomy are no different prehospital than they are in-hospital. Thus, the “thinking” and “doing” in the prehospital environment is identical to that which occurs in an emergency department or operating room. However, the environment of care is much different in the prehospital arena and often presents unique features. At times, alternate and innovative methods must be employed in these unique situations.
Delegated Medical Acts and Standardized Medical Protocols
In most North American systems, prehospital care providers perform delegated medical acts based on pre-established, standardized medical protocols. Although protocols ought to reflect best clinical evidence, they are limited from a practical perspective by cost, training, competency maintenance, and space constraints.
Which equipment is available to medics in the field is driven by the protocols approved by the emergency medical services (EMS) system medical director. The type and range of equipment available for managing the difficult airway in the prehospital setting is limited compared to most emergency departments and operating rooms. Even basic equipment such as the Eschmann introducer (commonly known as the “gum elastic bougie”), laryngoscope blades, and endotracheal tubes in an array of types and sizes may be limited in availability. Alternate intubating devices, such as the intubating laryngeal mask airway (ILMA or LMA Fastrach) or light wands (e.g., Trachlight), are often not available due to cost and skills maintenance issues. Rescue devices such as the Combitube, laryngeal mask airway (LMA), and disposable extraglottic devices, such as the LMA Unique, LMA Supreme, Ambu LMA and the King LT airway, are becoming more popular because they are relatively inexpensive, effective, and easy to use, and they do not require access to sterilization facilities. However, as nontracheal ventilation devices, they may not be appropriate in some clinical situations, particularly if adequate ventilation calls for an increase in peak airway pressure beyond the seal capabilities of the device, if the patient is sufficiently responsive to reject the device or if protection against aspiration is mandatory. Surgical airway management devices must be available in any system considering rapid sequence intubation (RSI).
Controversies in Prehospital Airway Management
Inadequate ventilation and oxygenation have been identified as primary contributors to preventable mortality, both in hospital and out of hospital. It would seem intuitive that successful ETI ought to mitigate these deaths, and because of this thinking, ETI became the gold standard in prehospital airway management. However, there has been considerable controversy as to whether patients requiring ETI should have tracheal intubation performed in the field or deferred until hospital arrival. There is ample evidence that ETI is not a benign intervention in the hands of inexperienced personnel who employ the technique infrequently. Studies have identified that intubation in the field may delay transport to higher echelons of care, injure airways, and lead to poorer outcomes.
The Recommended Guidelines for Uniform Reporting of Data from Out-of-Hospital Airway Management identifies four methods constituting “advanced airway management”: direct oral laryngoscopy and intubation, nasotracheal intubation, oral rescue techniques (bag-mask ventilation [BMV], Combitube), and surgical rescue techniques (transtracheal jet ventilation and cricothyrotomy). These four methods may each be modified by five variables:
1. Oral approach: no facilitating sedative drugs or paralytics
2. Nasal approach: no facilitating sedative drugs or paralytics
3. Sedation-facilitated intubation
4. RSI (i.e., the use of paralytics ± induction agents)
5. Other intubation technique (e.g., digital, lighted stylet)
The actual number of alternatives available in an EMS system is limited by protocols, training, and equipment.
New, simple-to-use devices such as the LMA and the Combitube have been introduced successfully in the prehospital care setting. These devices may be employed as an alternative to ETI in the cardiac arrest (or deeply comatose) patient by basic life support providers or as a rescue device in the setting of failed intubation by advanced life support (ALS) or critical care providers.
An emerging alternative to ETI in the respiratory failure patient is prehospital noninvasive ventilation. Several case series have shown continuous positive airway pressure or bilevel ventilation to be feasible and potentially beneficial in the prehospital setting, although further study is necessary to validate its effectiveness and safety.
Evidence
1. Should tracheal intubation be performed in the field at all? There are several dimensions to this controversy:
· Trauma victims: There continues to be skepticism as to whether the intubation of trauma victims in the prehospital care environment improves survival. During the 1980s, it was generally believed that ETI by EMS personnel had the potential to delay transport and was ineffective in improving survival in urban environments, but might be effective in longer transport environments (1). Many studies with conflicting results populated the literature during the 1990s (2,3,4,5,6,7). The lack of clarity led some to speculate that for selected subsets of the trauma patient population, ETI might be of benefit. It seemed logical to analyze patients with acute, severe head injury. Early studies provided no clear direction (8,9,10,11,12,13,14), and a recent large trauma registry study found that prehospital intubation was associated with adverse outcomes after severe head trauma (8). There was a subset of air medical transport patients in this study that may have benefited from ETI in the field, although an accompanying editorial maintained that this factor reflected a retrospective association rather than causation (15). In summary, the question as to whether ETI in trauma victims improves outcome is unresolved, although serious questions as to its benefits have been raised.
· Cardiac arrest: In cardiac arrest patients, the issue of efficacy remains unresolved (16,17,18,19,20). In fact, one study of hospital cardiac arrest victims showed that patients who received only cardiopulmonary resuscitation with chest compressions had comparable survival outcome to those who received chest compression and mouth-to-mouth ventilation (21). Furthermore, a large prospective before/after study to determine the incremented benefit to introducing ALS (including intubation) to a previously optimized system did not show a mortality benefit in cardiac arrest patients (22). The issue as to the effect of oxygenation and ventilation on mortality in cardiac arrest victims in the prehospital arena remains unresolved.
· Children: Early studies showed that tracheal intubation in children by paramedics was associated with higher failure and complication rates than in adults (23). Subsequent studies have tended to confirm this early finding (5,24,25,26,27,28). The only prospective, pseudorandomized trial to investigate the effectiveness of ground paramedics in performing tracheal intubation in children showed that there was no demonstrable advantage in survival outcome following ETI compared to groups with BMV (24). This same study revealed concerns about ETI displacement and lack of recognition thereof. Finally, for a subpopulation of patients where ETI might be expected to show a benefit, children with acute severe head injuries, the issue remains unresolved (29,30). A pervasive critique of these studies is that the results reflect a deficiency in pediatric ETI training for the EMS personnel. In the final analysis, the emergency intubation of children is an uncommon and anxiety-provoking event for most ALS providers. Both factors are likely to increase performance stress and failure rates, compared to the intubation of adults.
2. Is there evidence to support RSI by ALS prehospital providers? The evidence in the EMS literature supporting the use of RSI is, until most recently, nonsupportive except in specific circumstances. For ground EMS systems, several recent well-designed studies have consistently shown suboptimal outcomes, or no difference in outcome, in patients suffering acute severe head injury where RSI was used to facilitate ETI (8,9,31,32). Head injury was deliberately chosen in these studies because prior studies have suggested that optimal oxygenation and ventilation of these patients improve outcomes. Therefore, it was assumed that successful ETI would demonstrate benefit (33).
There have been attempts to determine the reasons for the poor outcomes associated with RSI in ground EMS services. These explanations have included
· Increased on-scene time (average 15 minutes in one study) (34)
· Lack of adequate training of the paramedics (8,13,32)
· Inappropriate hyperventilation and nonrecognition of hypoxia during induction (35)
· Patient paralysis and multiple attempts at intubation (35)
Despite recent studies showing the lack of efficacy of RSI in the ground EMS systems, a distinct pattern of improved outcomes has emerged in the subpopulation of those patients where air medical transport had been used (8,36,37,38,39).
Summary
It is unclear at present whether ETI by prehospital care providers improves outcome for specific populations. What is clear is that active medical direction, intense quality oversight and maintenance of competency programs, and high-quality airway management training are features of EMS systems that have high advanced airway management success rates and improved outcomes. Other issues such as equipment availability, the air versus ground environment, and the logistics associated with rural versus urban critical care transport/EMS suggest that a single, rigid approach to EMS airway management is inappropriate and cannot be supported.
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