Prehospital Cardiac Arrest Airway Management: An NAEMSP Position Statement and Resource Document

Abstract

Airway management is a critical component of out-of-hospital cardiac arrest (OHCA) resuscitation. Multiple cardiac arrest airway management techniques are available to EMS clinicians including bag-valve-mask (BVM) ventilation, supraglottic airways (SGAs), and endotracheal intubation (ETI). Important goals include achieving optimal oxygenation and ventilation while minimizing negative effects on physiology and interference with other resuscitation interventions.

NAEMSP recommends:

• Based on the skill of the clinician and available resources, BVM, SGA, or ETI may be considered as airway management strategies in OHCA.

• Airway management should not interfere with other key resuscitation interventions such as high-quality chest compressions, rapid defibrillation, and treatment of reversible causes of the cardiac arrest.

• EMS clinicians should take measures to avoid hyperventilation during cardiac arrest resuscitation.

• Where available for clinician use, capnography should be used to guide ventilation and chest compressions, confirm and monitor advanced airway placement, identify return of spontaneous circulation (ROSC), and assist in the decision to terminate resuscitation.

Key words:

• prehospital
• EMS
• cardiac arrest
• intubation
• airway
• ventilation

Introduction

Airway management is a critical component in the resuscitation of patients with non-traumatic out-of-hospital cardiac arrest (OHCA) (1). While endotracheal intubation (ETI) has long been advocated as the primary means of securing the airway during OHCA, multiple other modalities are available to emergency medical services (EMS) clinicians including supraglottic airways (SGAs) and bag-valve-mask (BVM) ventilation (2). Regardless of the chosen technique, it is important that airway maneuvers not interfere with other aspects of resuscitation, particularly chest compressions. This resource document reviews the rationale and data supporting NAEMSP’s recommendations regarding airway management during OHCA.

Selecting the Airway Management Technique

Based on the skill of the clinician and available resources, BVM, SGA, or ETI may be considered as airway management strategies in OHCA.

The airway management strategy selected in OHCA may be influenced by arrest circumstances, patient factors, resuscitation stage, available equipment, and skill level of the EMS clinician. Timing of various airway techniques may also vary as the importance of oxygenation and ventilation increase as resuscitation efforts extend (3,4). EMS clinicians may use a bag-valve device attached to a face mask (i.e., BVM) or to an advanced airway such as an SGA or endotracheal tube. While there are no randomized controlled trials (RCT) that have directly compared all three methods (BVM, SGA, ETI) in OHCA, three RCTs published in 2018 (5–7) have advanced the science and provide the best current evidence to guide recommendations (8). Although data are limited, patient-centered outcomes are similar between BVM, SGA, and ETI in adult cardiac arrest.

BVM vs. SGA

No RCTs have directly compared BVM and SGA in adult OHCA. A recently published systematic review and network meta-analysis found no difference in survival to hospital discharge, 30-day survival, or neurological function between BVM and SGA (9).

BVM vs. ETI

A single RCT performed in a physician-led EMS system enrolled 2043 adults and failed to demonstrate non-inferiority for 28-day survival with favorable neurological function for BVM vs. ETI (5). The ETI success rate in this study was 98%. Jabre et al. reported more airway complications with BVM than ETI, including difficult airway management (18.1 vs. 13.4%, p = 0.004), airway failure (6.7% vs. 2.1%, p < 0.001), and regurgitation of gastric contents (15.2% vs. 7.5%, p < 0.001). A systematic review and meta-analysis also found no difference in return of spontaneous circulation (ROSC) rates, survival, neurological function measured by cerebral performance category (CPC), or harm for adults with cardiac arrest (9).

SGA vs. ETI

The Pragmatic Airway Resuscitation Trial (PART) by Wang et al. compared an initial strategy of King Laryngeal Tube (King LT; Ambu, Copenhagen, Denmark) vs. ETI in 3000 adult OHCA patients (6). Rates of initial airway success were 90.3% with the King-LT and 51.6% with ETI. Seventy-two hour survival was higher in the King LT group than in the ETI group (18.3% vs 15.4%, p = 0.04). Secondary outcomes including ROSC, hospital survival, and survival with favorable neurological status were also all higher in the King LT group. The Airways-2 study by Benger et al. compared an initial strategy of i-gel (Intersurgical, Wokingham, Berkshire, United Kingdom) vs. ETI in 9289 patients (7). Good outcomes (modified Rankin Scale [mRS] 0-3 at discharge or 30 days) were similar between the two groups (6.4% vs. 6.8%, p = 0.33); however, initial ventilation was more successful with i-gel vs. ETI (87.4% vs 79.0%, p < 0.001). The initial ETI success rate was 70% and complications of regurgitation and aspiration were similar between groups (7). A recent systematic review and meta-analysis also found no difference between ETI or SGA in survival to hospital discharge or at 1 month following adult OHCA (20 studies; 180,692 patients) (9). Neurological function at discharge favored ETI over SGA when measured using CPC but not when using the mRS (16 studies; 203,246 patients) (9).

Future Research

More robust and controlled designs are necessary to delineate whether a survival advantage can be attributed to a particular airway device. Most published studies in this area have been retrospective, observational, and prone to multiple forms of bias including indication, survival, and resuscitation time bias (9,10). Further, studies provide limited detail on the process of airway management, and multiple techniques are often used during resuscitations (4, 9). For example, EMS clinicians may start with BVM, and then may move to SGA or ETI (4). Future studies should account for the sequence or timing of interventions when multiple airway techniques are used. Success rates for ETI in cardiac arrest vary across studies from 52 to 98% (5–7). Current guidelines recommend that ETI success rates be considered when selecting the airway management technique; however, the minimally acceptable thresholds for ETI success, both at the clinician and agency level, are unknown (8). While ETI first-attempt success has been associated with reduced adverse events in the emergency department and first-pass success favors SGA (9), the role of first-attempt success in OHCA remains unclear (11,12). Additional airway equipment such as video laryngoscopy (VL) (13,14) and the gum elastic bougie (15–17) may facilitate ETI in OHCA and deserve further study.

Minimizing Interference with Other Resuscitation Priorities

Airway management should not interfere with other key OHCA resuscitation interventions such as high-quality chest compressions, rapid defibrillation, and treatment of reversible causes of the cardiac arrest.

Airway management is a critical component of cardiac arrest resuscitation; however, it has the potential to interfere with other interventions that are essential for good outcomes (18–21). Regardless of the airway management strategy selected, EMS clinicians should focus on prioritizing interventions that are shown to improve patient outcomes during cardiac arrest resuscitation including high-quality chest compressions (optimizing rate and depth, recoil, chest compression fraction), rapid defibrillation for shockable rhythms, and addressing reversible causes of the arrest. High-quality cardiopulmonary resuscitation (CPR) can be maintained during airway management by considering the timing of airway interventions, avoiding pauses in chest compressions for advanced airway placement, and minimizing harms of ventilation after advanced airway insertion.

Timing of Airway Interventions

Airway interventions may be delayed early in the resuscitation to focus on other efforts such as high-quality chest compressions. Equipoise exists around the role of ventilation early in resuscitation, as compression-only CPR by bystanders has been associated with better outcomes compared to CPR interrupted by rescue breaths in some studies (22,23) but not in others (24,25). Delaying ETI until after three cycles of 200 compressions and rhythm analysis as a part of a minimally interrupted cardiac resuscitation protocol may improve outcomes (26). Similarly, an initial strategy of passive oxygen insufflation (providing high-flow oxygen via nasal cannula or facemask without ventilation) may result in more patients with neurologically intact survival at hospital discharge compared to an initial BVM ventilation strategy in witnessed ventricular tachycardia and ventricular fibrillation OHCA (27). It is unknown whether this benefit is due to differences in CPR quality or avoiding positive pressure ventilations, which may be associated with harm (27–29). Nevertheless, airway management and ventilation are likely less critical early in the resuscitation, especially in witnessed ventricular fibrillation/tachycardia OHCA. In these cases, the focus should be on early defibrillation and good quality chest compressions.

Avoiding Chest Compression Interruptions

Airway management techniques, especially ETI, are associated with multiple and prolonged interruptions in the delivery of high-quality chest compressions (19, 30,31). ETI with direct laryngoscopy (DL) results in more chest compression pauses compared to VL (26.1% vs 0%) for longer time (4 vs 0 seconds) (32). Repeated attempts with DL result in more pauses compared to additional attempts with VL or SGA (31,32). Chest compression fraction, a critical component of high-quality CPR, is lower for ETI compared with SGA (33–35). SGA placement is also associated with less interruptions in chest compressions and for shorter durations (36). An experienced clinician should perform the initial ETI attempt during ongoing chest compressions, and if needed, any pauses be limited to <10 seconds (35). In situations where clinicians infrequently perform ETI, consideration should be given to the skill of the clinician performing the intubation and the risks and benefits of performing ETI relative to SGA placement or BVM. VL can reduce the duration of pauses and the frequency of long pauses compared to DL (32). Bougie-assisted ETI may be considered and has been used predominantly with DL (16,17).

Since OHCA outcomes are similar across advanced airway techniques (BVM, SGA, ETI), EMS clinicians may elect to forgo ETI and use a BVM alone or BVM followed by insertion of an SGA if ETI may interfere with chest compression quality (6,7, 37,38). Given the importance of high-quality chest compressions in improving resuscitation outcomes, team leaders should monitor for interruptions due to airway management and minimize these interruptions during OHCA resuscitation (35).

In addition to the risk of chest compression interruptions, advanced airways, including SGA and ETI, are associated with hyperventilation, misplacement, dislodgement, and airway injury (20, 39). These risks may counter the benefits of high-quality CPR; therefore, the risks and benefits of placing an advanced airway during CPR should be considered compared to airway management using a BVM alone.

Future Research

Adverse events associated with medical interventions are not consistently reported in the literature (40). As such, the harms of airway management techniques in OHCA may be under-represented. Advanced airways are associated with worse outcomes compared to BVM (41). This may be due to confounding by indication, and high-quality RCTs are needed to better delineate the potential harms of various airway interventions (37,38). The optimal timing for placement of a definitive airway device during resuscitation remains unclear, although a recent analysis of data from the PART study did not show an association between airway timing and survival to hospital discharge (42).

Ventilation Strategies

EMS clinicians should take measures to avoid hyperventilation during OHCA resuscitation.

Current adult American Heart Association guidelines recommend delivery of supplemental oxygen and ventilations with a tidal volume of 500-600 ml per breath over 1 second either via synchronous breaths at a rate of 2 breaths every 30 compressions without an advanced airway, or asynchronous breaths at a rate of 10 breaths per minute or 1 breath every 6 seconds with an advanced airway (43). Limited data are available to support these recommendations, and questions still exist regarding ideal ventilation rate, tidal volume, delivery time, and airway pressure (1, 43,44). However, excessive ventilation rates and volumes are harmful and occur frequently (up to 85.2% of OHCA) (28,29, 43, 45,46). Interventions such as timing lights, compression-adjusted ventilations, and use of volume-limited BVMs can improve compliance with target ventilation rates and tidal volumes during adult CPR (47–58).

Harm of Hyperventilation

The detrimental effects of hyperventilation during CPR are thought to be secondary to elevated intrathoracic pressure caused by air trapping or incomplete exhalation, which decreases venous return and reduces cardiac output (28,29, 56, 59). While human data are limited, experimental animal models suggest a risk of harm with excessive hyperventilation during cardiac arrest (28,29, 44, 56).

Since the initial reports suggesting an association between hyperventilation and poor outcomes, a number of observational studies and case series have been published (28,29). In a retrospective cohort study of 337 OHCA patients, the mean ventilation rate was 15.3 breaths per minute and 85.2% of patients received ventilation rates > 10 breaths per minute, but there was no difference between groups above and below 10 breaths per minute in ROSC, survival to hospital discharge, or 1-year neurologically intact survival (45). Similar results have been seen in other cohorts (57,58). In a prospective observational trial of 285 adult OHCA patients, the mean ventilation rate among those with good neurological outcomes was greater than those with poor neurological outcomes, with mean breaths per minute of 12.7 (SD 6.1) and 7.3 (3.5) (p = 0.003), respectively (60). However, few patients in these observational studies and larger case series were exposed to excessive ventilation rates (>30 breaths per minute), which were reported in the initial case series describing poor outcomes (28,29).

Mitigating Hyperventilation

Several strategies and devices can either prevent or detect hyperventilation during CPR. However, few interventions address both primary mechanisms, excessive ventilation rates and tidal volumes (Table 1).

Table 1. Summary of hyperventilation interventions and target effects.

Intervention	Rate	Volume
Strategy
Retraining	X	X
Compression-to-ventilation ratio	X
Compression-adjusted ventilation	X
Devices
Auditory and visual prompt devices (e.g., timing lights)	X
Volume-limited bag-valve-mask devices		X
Capnography	X
Thoracic impedance waveforms	X
Novel ventilation feedback flowmeters	X	X
Mechanical ventilators	X	X

Strategies

Strategies that may prevent hyperventilation include retraining, compression-to-ventilation ratios, and compression-adjusted ventilation. Retraining clinicians can help reduce excessive ventilation but may not be effective in achieving recommended rates (28,29, 61). Using a synchronous compression-to-ventilation ratio (e.g., 30:2) strategy, compared to continuous compressions with asynchronous ventilations, can control ventilation rates while maintaining recommended compression rate and fraction (43, 60, 62,63). Similarly, compression-adjusted ventilation is a strategy of guiding ventilations based off the compression count since the last breath; however, unlike a compression-to-ventilation ratio, compressions are not interrupted. Compression-adjusted ventilation has been shown to prevent hyperventilation and improve ventilation rate accuracy in several simulation studies (47–50).

Devices

Devices that may prevent or detect and alert clinicians to hyperventilation include auditory and visual prompt devices (e.g., timing lights and metronomes), volume-limited BVMs, capnography waveforms, thoracic impedance waveforms, novel ventilation feedback devices, and mechanical ventilators. Similar to CPR metronomes that guide chest compression rate, auditory and visual prompt devices have been shown to improve the accuracy of ventilation rates (54, 61, 64,65). In simulation scenarios, EMS clinicians using volume-limited BVMs, including volume-marked and pediatric-size BVMs, more consistently deliver tidal volumes within target range compared with the use of adult BVMs, which can facilitate excessive tidal volumes (51–55). Capnography and thoracic impedance waveforms can be used to monitor ventilation rates during chest compressions, but accuracy may be limited by chest compression artifact (58, 60, 66–70). Novel ventilation feedback devices using flowmeters attached to the BVM allow for real-time monitoring of both ventilation rates and tidal volumes, but further clinical studies are needed (71–74). Lastly, use of a mechanical ventilator during CPR is feasible but requires equipment and skills that may not be available in all EMS settings (75–77).

Future Research

The optimal ventilation rate and tidal volume during CPR for adult OHCA are unknown. It is also unclear what strategy or device may be best to monitor ventilation parameters and prevent hyperventilation. Novel ventilation feedback flowmeters hold promise as a tool to more accurately measure ventilation parameters during CPR and elucidate ventilation targets. How ventilation parameters should be adjusted to account for compression devices is unknown (78–80).

The Role of Capnography

Where available for clinician use, capnography should be used to guide ventilation and chest compressions, confirm and monitor advanced airway placement, identify ROSC, and assist in the decision to terminate resuscitation.

The monitoring of the flow of carbon dioxide through the airway has many potential applications in cardiac arrest patients. More than just a measure of ventilatory status or alveolar gas-exchange at the lungs, end-tidal carbon dioxide (ETCO₂) correlates with cardiac output and provides an indication of tissue perfusion, including both pulmonary and cerebral perfusion (81). In addition to ETCO₂ level (capnometry), continuous wave-form capnography may guide resuscitation, specifically for the continuous assessment of advanced airway placement, ventilation and compressions quality, and for the detection of ROSC or re-arrest. EMS clinicians should be aware that ETCO₂ can be influenced by many factors, such as compressions (82), ventilations (83), etiology of arrest, medications administered (84), and acid contaminants in the airway (e.g., gastric contents) (85), making it challenging to interpret isolated values without incorporating other information and trends. Colorimetric devices are inferior given that they are limited in use to initial confirmation of advanced airway placement and cannot provide continuous monitoring required to guide resuscitation and ventilations.

Role in Guiding Ventilation and Confirming Advanced Airway Placement

In properly placed endotracheal tubes and SGAs, capnography provides breath by breath status of the airway placement. If the advanced airway is displaced, the capnography waveform will abruptly disappear and the ETCO₂ reading will drop toward zero. This is the preferred choice to confirm airway placement and, subsequently, to detect dislodgment (85). Therefore, capnography should be used for airway management during OHCA resuscitation with ETI and SGAs. Even in low-flow states such as cardiac arrest, capnography has been shown to be 100% sensitive and specific for correct ETT placement (86).

Capnography can also be used to monitor ventilation via ETT, SGA, or BVM (87–89). The waveform and numerical data provide an accurate respiratory rate, thereby mitigating hyperventilation. Ventilation failure can be identified by change in height, frequency, rhythm, baseline, or shape of the ETCO₂ curve.

Role in Guiding CPR

ETCO₂ levels are directly related to cardiac output even in low-flow states such as cardiac arrest (90). Limited evidence shows modest increases in ETCO₂ with increased compression depth, rate, and release velocity (91). More recent data reveal that greater ventricle compression is directly related to ETCO₂ as measured by transthoracic echocardiography (92). Hence, capnography can be used to optimize effectiveness of compressions. The 2020 American Heart Association guidelines suggest that targeting compressions to a minimum ETCO₂ goal of 10 mmHg during chest compressions, and ideally 20 mmHg or higher, may improve CPR efficacy (93). There are also exploratory data suggesting capnography may have a role in predicting successful defibrillation (94–96). Thus, capnography may be used to optimize chest compressions and guide timing of defibrillations, though further data are need to operationalize the latter.

Role in Identifying ROSC

There are compelling data demonstrating the value of capnography to identify ROSC. The sudden increase in cardiac output with ROSC results in increased pulmonary circulation, and thus more CO₂ offload from the lungs. An abrupt rise in ETCO₂ has high specificity, albeit low sensitivity, for diagnosing ROSC (97,98). Studies have suggested that a sudden rise of approximately 10 mmHg or more is suggestive of ROSC (99,100). However, precise increments or absolute thresholds to determine ROSC are not feasible due to variability in resuscitation factors including the etiology of arrest, rate of ventilation, and effectiveness of preceding chest compressions, as well as the cardiac output once ROSC is obtained (81–83, 101,102).

Role in Determining Prognosis

The prognostic capability of waveform capnography is promising. Several observational analyses have aimed to predict the likelihood of achieving ROSC and hospital survival using ETCO₂ at various timepoints during the arrest and following ROSC (103–107). No change in ETCO₂ levels or absolute thresholds can definitively predict ROSC or neurologically intact survival.

Capnography may help to signal re-arrest. If the ETCO₂ precipitously drops, this may indicate a drop in cardiac output, or complete failure of the ventricles to contract; however, other causes of a sudden drop in ETCO₂ (e.g., airway dislodgement) must also be considered (84, 108,109).

Finally, ETCO₂ may be one tool to help inform the decision for termination of resuscitation (TOR) due to futility, although the exact threshold and timing of measurement are unclear. A 2018 systematic review with significant heterogeneity between studies revealed that in 215 patients there was a 0.5% chance of ROSC if the ETCO₂ was less than 10 mmHg following 20 minutes of CPR (110). Other investigators have identified that in the absence of endotracheal tube dislodgement or obstruction, an ETCO₂ less than 10 mmHg, 3 minutes following ETI, is associated with low rates of ROSC (111,112). For ETCO₂ to be used alone in TOR decisions, it must have a sensitivity approaching 100% for predicting ROSC. Given the numerous factors that can influence ETCO₂, the prognostic capability of ETCO₂ for determining futility of ongoing resuscitation remains controversial and should not be the sole deciding factor for TOR.

Future Research

There is a need for future research to define the full potential of capnography in the management of adult OHCA, including accurately measuring ETCO₂ via BVM, identifying the optimal ETCO₂ threshold to determine futility of ongoing resuscitation, managing persistent arrest when ETCO₂ values are elevated (>20 mmHg), and optimizing response to defibrillation by timing shocks based on end-tidal waveform (94–96).