Emergency airway management outside the operating room (OR) is often associated with an increased risk of airway related, as well as cardiopulmonary, complications which can impact morbidity and mortality. These emergent airways may take place in the intensive care unit (ICU), where patients are critically ill with minimal physiological reserve, or other areas of the hospital where advanced equipment and personnel are often unavailable. As such, emergency airway management outside the OR requires expertise at manipulation of not only the anatomically difficult airway but also the physiologically and situationally difficult airway. Adequate preparation and appropriate use of airway management techniques are important to prevent complications. Judicious utilization of pre- and apneic oxygenation is important as is the choice of medications to facilitate intubation in this at-risk population. Recent study in critically ill patients has shown that postintubation hemodynamic and respiratory compromise is common, independently associated with poor outcomes and can be impacted by the choice of drugs and techniques used. In addition to adequately preparing for a physiologically difficult airway, enhancing the ability to predict an anatomically difficult airway is essential in reducing complication rates. The use of artificial intelligence in the identification of difficult airways has shown promising results and could be of significant advantage in uncooperative patients as well as those with a questionable airway examination. Incorporating this technology and understanding the physiological, anatomical, and logistical challenges may help providers better prepare for managing such precarious airways and lead to successful outcomes. This review discusses the various challenges associated with airway management outside the OR, provides guidance on appropriate preparation, airway management skills, medication use, and highlights the role of a coordinated multidisciplinary approach to out-of-OR airway management.
Anesthesia providers are often involved with emergency airway management outside the operating room (OR). These locations include the intensive care unit (ICU), emergency department (ED), radiology suite, regular nursing floor, and other locations within the hospital. Such patients are often critically ill with minimal physiological reserves thus predisposing them to an increased risk of complications compared to elective surgical patients in the OR.1–4 In a recent prospective observational study including 2964 critically ill patients across 29 countries, adverse event occurred after intubation in 45.2% of patients, including cardiovascular instability in 42.6%, severe hypoxemia in 9.3%, and cardiac arrest in 3.1%.5 This “physiologically difficult airway” places the patient at higher risk of cardiovascular collapse with intubation and conversion to positive-pressure ventilation.6 A proportion of these patients also have “anatomically” difficult airways, further increasing the risk for adverse airway-related outcomes. In some cases, although the physiological perturbations may be mild to begin with, they may accentuate with time as the providers struggle with anatomical challenges. Thus, an anatomically difficult airway may also become a physiologically difficult airway. Furthermore, unfamiliar locations add logistical challenges for providers and thus securing an airway in these non-OR locations pose unique challenges and is associated with increased morbidity and mortality.2,7,8 Hence, emergency airway management outside the OR often requires mastery of not only the anatomically difficult airway but also the physiologically and situationally difficult airway.
Postintubation hemodynamic and respiratory compromise is common in critically ill patients, is impacted by the choice of drugs and techniques used, and is independently associated with poor outcomes.9–16 In this narrative review, we will discuss the challenges associated with emergent airway management outside the OR and provide evidence-based guidance on preparation, airway assessment, use of peri-intubation oxygenation techniques, airway management techniques, medication options, human factor considerations, and airway rescue techniques that can help decrease the associated morbidity. In addition, we will also examine important future research considerations for emergency airway management outside the OR.
COMPLICATIONS AND PREVENTION STRATEGIES
|Difficult intubation or multiple attempts (%)||Severe hypoxia (%)||Hypotension (%)||Esophageal intubation (%)||Aspiration (%)||Cardiac arrest (%)|
|Cook et al7||6.7||–||–||13.3||13.3||–|
|De Jong et al8||11||22||–||5||–||2.7|
|Griesdale et al18||13.2||19.1||9.6||7.4||5.9||0|
|Jaber et al19||12||26||25||4.6||2||2|
|Schwartz et al22||8||–||–||8||4||3|
|Smischney et al23||4.8||17.6||41||0.2||1.2||–|
|Park et al21||0.8||6.4||3.0||3.5||–||0.6|
|Yoon et al24||11.9||–||–||3.6||–||0.6|
|Martin et al20||10.3||–||–||2.8||4.2||–|
|Infrastructure||Limited space, poor access to patient’s head, limited monitoring capability, lack of adequate lighting|
|Equipment||Adjunct airway devices such as fiber-optic bronchoscope, supraglottic airways, oral/nasal airways, bougie, videolaryngoscope, and emergency invasive airway access equipment may not be readily available|
|Unavailability of noninvasive ventilation, high-flow nasal cannula, etc, to provide adequate pre- and apneic oxygenation|
|Personnel||Depending on timing and location, availability of trained personnel for assistance and backup may be limited|
|Airway assessment||May be difficult or impossible due to lack of time or patient cooperation|
|Aspiration risk||Full stomach, gastroparesis associated with critical illness|
|Anatomically difficult airway||Difficult anatomy, maxillofacial trauma, cervical spine injury, airway injuries, burns, radiation, retropharyngeal abscess, masses, etc|
|Physiologically difficult airway||Uncooperative patient, presence of shunt or ventilation-perfusion mismatch, reduced functional residual capacity|
|Poor physiologic reserve due to underlying illness|
|Hemodynamic instability secondary to hypovolemia, critical illness, patient’s baseline physiology, or drugs used to facilitate intubation|
|Training||Limited training in emergency airway management|
|Experience||Unavailability of experienced providers depending on the timing and location|
|Human factors||Stress leading to tunnel vision, cognitive overload, and increased likelihood of errors|
|Inadequate communication between teams and team members|
Emergency airway management in out-of-OR locations is associated with significant complications and hence is considered an extremely high-risk procedure.17 Peri-intubation hypoxia and hypotension especially are associated with high morbidity and mortality. It is important to identify risk factors as well as predict which patients are likely to develop these complications13,14 (Table 1).7,8,18–24 Considering the high rates of complications, adequate preparation during the peri-intubation period is essential. One of the initial steps should be an assessment for potential difficulty, which includes evaluating anatomic, physiologic, or situational challenges that may be present (Table 2). This should be followed by preparation and optimization of the patient as well as the team for difficulty—including using a checklist, ensuring availability of necessary equipment and personnel, maximizing preoxygenation, and hemodynamic optimization among others. Time permitting, a thorough discussion with the patient or their surrogate on the acceptance of intubation and mechanical ventilation should be held. In case of a true emergency, a clear documentation of code status should be ascertained.
The prevalence of a difficult airway is reported to range from 11% to 50% for intubations performed outside of the OR.18,19,22 Identifying a potentially difficult airway is crucial; however, current bedside screening tests are limited by their poor sensitivity and specificity.25 A history of difficulty with airway management described by the patient or documented in the patients’ medical record is important. Time permitting, an airway examination should be conducted, including evaluation for gross anatomic alterations or features of syndromic affiliation and previous tracheostomy scars. Among the bedside airway assessment tests, the upper lip bite test has the highest sensitivity,26 and the combination of mallampati (MP) score and thyromental distance (TMD) provides the most accuracy at predicting difficult intubation.25 It is important to recognize that many of these commonly used methods for assessing airway before elective intubation are not feasible in this setting where the patient may be uncooperative, sedated, agitated, unstable, or delirious.27,28
|Mallampati score of III or IV||5|
|Reduced cervical spine mobility||1|
|Limited mouth opening <3 cm||1|
|Coma (Glasgow score <8)||1|
While recognizing the anatomically difficult airway (obtaining a glottic view or passing an endotracheal tube is challenging) is 1 part of the preintubation assessment, the anticipation of physiologic challenges before airway management is equally important. The MACOCHA score (Mallampati score III or IV, sleep Apnea syndrome, decreased Cervical mobility, mouth opening <3 cm, Coma defined by a Glasgow score <8, severe Hypoxemia, and if the practitioner is not an Anesthetist) that combines anatomic, physiologic, and operator characteristics explicitly highlights the increased patient risk when the intubating physician is not an anesthesiologist. The score is very relevant to the out-of-OR setting and was recently validated in a multicenter study29 (Table 3). Although it may not be possible to assess all the components in an uncooperative patient (eg, MP score), assessment of risk using the MACOCHA score should be considered in appropriate patients.
Equipment and Personnel
Considering the unpredictability associated with these situations, we suggest preparing for every urgent or emergent airway in a way that assumes that every step might fail. Appropriate hemodynamic monitored and continuous Etco2 monitoring should be utilized when feasible. The interval for blood pressure management should be changed to 2 to 3 minutes during the procedure to detect hypotension in a timely manner. Similarly, it is advisable to make the monitors, especially pulse oximetry, loud and audible to everyone in the room. Next, it is important to ensure that necessary equipment is on hand and functional. Considering that blood and vomitus in the airway are common in this situation and may predict a difficult airway,30 availability of functioning high-efficiency suction devices should be ensured. The Suction Assisted Laryngoscopy and Airway Decontamination (SALAD) strategy involving oral airway decontamination while simultaneously preserving videolaryngoscopy (VL) views may be useful.31 The technique utilizes the Ducanto suction catheter, a large bore, multiport, “always on,” softer-plastic suction device that is anatomically shaped like a patient’s airway making it easy to position and work with other complementary devices used to clear a patient’s airway. However, this may not always work and VL may be ineffective in the presence of excessive blood/vomitus/secretions, thus necessitating direct laryngoscopy (DL).
Tracheal intubation (TI) is considered an aerosol-generating procedure, and can impact the transmission of respiratory virus illnesses such as coronavirus disease 2019 (COVID-19).32–34 In an international multicenter cohort study, around 10% of health care workers involved in TI of patients with suspected or confirmed COVID-19 were found to have a COVID-19–related outcome.35 Hence, as recommended by national organizations, providers involved with TI in such patients should adhere to full contact and airborne personal protective equipment.36–38 In situations where adequate history and testing results are unavailable or in areas where such airborne diseases are endemic, providers should err on the side of caution and adhere to the same precautions in all patients. Also, in such circumstances, intubation should be performed in an airborne infection isolation room by an experienced provider, with additional help available outside the room. More guidance in this matter has also been provided by a joint taskforce of the Society of Critical Care Medicine (SCCM), American Society of Anesthesiologists (ASA), and Society of Critical Care Anesthesiologists (SOCCA).39
It is also important to take into account the situational challenges that accompany airway management outside of the OR, contributing to the “situationally” difficult airway. The time of the day, available infrastructure (including equipment and personnel), as well as patient condition may influence performance. It is important to quickly decide whether to intervene immediately, intervene soon (stabilize, transfer, then intubate), or to not intervene at all. Maintaining astute situational awareness helps maximize the team’s ability to identify cues, synthesize thoughts, and predict the next step. The presence of a dedicated airway team for out-of-OR airway emergencies is ideal, and it is recommended that institutions, no matter their size, should identify airway experts who will comprise an airway response team and be available 24/7.40 The primary training of these experts may vary depending on the available workforce in each institution. Furthermore, it is ideal to have a standardized and universal notification system in place so that all team members can be made aware of an event.40
The airway team may be working at the bedside with other hospital staff that are inexperienced or stressed. Elucidating the skill level of available staff and establishing clear roles and expectations are essential elements of successful intervention. Closed-loop communication is essential in such stressful situations and can help prevent medical errors, as well as increase the speed and efficiency with which tasks are completed.41 Providers involved in these procedures should possess interpersonal and leadership skills needed to successfully coordinate efficient team-based care. These crisis resource management (CRM) skills can impact patient safety in acute health care fields.42 Utilizing the Team Strategies and Tools to Enhance Performance and Patient Safety (TeamSTEPPS) approach,43 and incorporating “high-risk, low-frequency” event simulation curriculum can prepare providers for adverse situations even though their exposure to such events in real life may be limited.44
The advent of checklists has long been regarded by various industries as a method to reduce cognitive load and reduce errors in stressful situations.45 This is no different in medicine.46 Instituting a checklist for non-OR airways may help ensure the necessary preparations and precautions have been taken, while simultaneously reducing cognitive overload to allow better decision-making. Although a recent systematic review and meta-analysis did not find a difference in mortality or most secondary outcomes associated with checklist use, the robustness of the meta-analysis was limited by the predominance of observational studies.47 Perhaps, the key is to keep the checklist simple and succinct, thus improving compliance and acceptance.48 The implementation of an “intubation bundle” can reduce life-threatening complications associated with emergency airway management49 but needs further validation before recommending routine use. The checklist, “PREPARE,” designed for out-of-OR airway management (P: preoxygenate/position; R: reset/resist; E: examine/explicit; P: plan A/B; A: adjust/attention; R: remain/review; E: exit/explore), targets not just the patient but the entire airway team and may be helpful as a cognitive aid.50 Another novel approach, the “Vortex,” is a simple, “lifeline” driven, predominantly visual cognitive aid that can be used in real time during airway emergencies.51 Once a secure airway has been established, utilizing checklists such as IPASS (I: illness/severity; P: patient summary; A: action/to-do list; S: situation/summary; S: synthesis) can help ensure patient safety during crucial hand-offs.52 Establishing similar checklists or intubation bundles at individual institutions can help ensure adequate preparation, provide a uniform structure that encourages a consistent approach, and improve communication and coordination at each airway encounter.
Patient positioning before intubation should optimize both anatomic and physiological parameters and is essential to increase the success of intubation and avoid complications. The “sniffing” position, by aligning the oropharyngeal–laryngeal axes, may make glottic visualization and TI easier. The “ramped position” improves preoxygenation, prevents reduction in the functional residual capacity, and may reduce the risk of pulmonary aspiration. Provider training has a significant impact on the success with TI related to patient positioning. Pulmonary fellows experienced increased intubation difficulty with intubations performed in the ramped position compared with the sniffing position,53 whereas patients intubated by ED residents showed improved first attempt success with ramping compared with supine.54 A large retrospective study of patients intubated by an anesthesia service—dedicated to outside-of-OR intubations—showed that a combination of ramped plus sniffing positions substantially reduced complication rates, including desaturation.55 Similarly, patient characteristics may also help chose the appropriate position. While an obese patient or someone with high aspiration risk would significantly benefit from a ramped position, a frail patient with limited neck range of motion may not. Current guidelines recommend a head-up position, especially in patients at high risk of aspiration or desaturation.15,56,57 Hence, patient positioning should be individually tailored to patient characteristics, as well as the training history of the intubating provider.58
Preoxygenation and Apneic Oxygenation
A majority of patients that require emergent non-OR airway management have low physiologic reserve, and life-threatening hypoxemia during the procedure is a major concern.59 Adequate preoxygenation is essential to better prepare such patients for intubation and should be an integral component of all emergent airway interventions. It increases the safe apnea time (the time from cessation of breathing or ventilation until the oxygen saturation [Spo2] declines to 90% before desaturation) and can help avoid complications related to hypoxemia. Preoxygenation may be achieved using supplemental oxygen via regular nasal cannula, nonrebreather mask, or high-flow nasal oxygen (HFNO) cannula, as well as noninvasive ventilation (NIV).
In patients with hypoxemic respiratory failure with extensive atelectasis and intrapulmonary shunting, supplemental oxygen via nasal cannula or nonrebreather mask may not be effective and high inspiratory flow requirements may not be met with a nonrebreather mask alone. In such patients, HFNO or NIV may be better choices. The FLORALI 2 study (Clinical Effect of the Association of Non-invasive Ventilation and High Flow Nasal Oxygen Therapy in Resuscitation of Patients with Acute Lung Injury)60 compared NIV or HFNO for preoxygenation in 322 hypoxemic, critically adults undergoing TI and observed no difference in the incidence of severe hypoxemia during TI. However, the subgroup analyses suggested a potential benefit for NIV among patients with a P/F ratio <200. Thus, in patients with severe hypoxemia, NIV with bilevel positive airway pressure (BiPAP) ventilation providing pressure support ventilation maybe a safe and likely the most effective preoxygenation technique.61,62 It should be noted that in many circumstances, there may not be enough time to achieve optimal preoxygenation and also, some patients may not have an appropriate response to preoxygenation.63 Nonetheless, it is important that oxygen therapy be initiated immediately on arrival while preparations are underway to maximum the duration of preoxygenation.
The addition of continuous oxygen into the nasopharynx during apnea (termed apneic oxygenation) may also extend the safe apnea time. Oxygen delivery via the nasal route offers an advantage over others that it does not obstruct access to the airway during TI. Apneic oxygenation via nasal cannula can be provided using unwarmed, dry oxygen via the standard nasal cannula or via heated and humidified HFNO.64 OPTINIV (HFNC combined with NIV for decreasing oxygen desaturation during intubation procedures in ICU hypoxaemic patients), a proof of concept study,65 showed that adding HFNO for apneic oxygenation to NIV for preoxygenation was more effective in reducing the severity of desaturation compared to NIV alone during TI. In summary, for out-of-OR emergent TI, NIV or HFNO should be considered over conventional oxygen therapy for preoxygenation and in patients with moderate to severe hypoxemia, NIV is superior to HFNO. Apneic oxygenation should be continued during attempts at TI and gentle mask ventilation should be considered during rapid sequence intubation (RSI) to prevent or treat hypoxemia.59,66,67
Rapid Sequence Intubation
A RSI technique is often used in patients who need TI in these situations. RSI is designed to facilitate rapid TI in patients at high risk of aspiration and the main objective of the technique is to minimize the time interval between loss of protective airway reflexes and TI. Despite the technique’s widespread use, there is still no agreement on how it should best be performed particularly with regard to manual ventilation and application of cricoid pressure (CP) or Sellick’s maneuver. Avoidance of manual ventilation before TI was traditionally recommended to avoid gastric insufflation, but recent evidence suggests that manual ventilation using bag mask between induction and endotracheal tube placement in otherwise critically ill patients may be well tolerated.68 In patients with physiologically difficult airway, mask ventilation may be lifesaving, and providers should balance the perceived risk of aspiration versus life-threatening complications related to desaturation. The Sellick’s maneuver,69 frequently used as a part of RSI, has been shown to have a questionable benefit.70,71 While there is evidence that gastric insufflation can be prevented by this maneuver,72 there are concerns that application of CP can result in an increased risk of aspiration by decreasing the lower esophageal sphincter tone73 and may impair the laryngeal view and thereby delay intubation and increase the potential for aspiration.74 Since the fasting times are either inadequate or unknown in most cases and critical illness causes impaired gastric emptying and a high risk of aspiration,75 we suggest using RSI with or without Sellick’s maneuver in all emergency out-of-OR intubations. bag mask ventilation (BMV) may be used in patients at high risk of desaturation, when the benefits of this technique outweigh the risks.
Personnel and Device Selection
As discussed, TI in an out-of-OR setting poses significant challenges and appropriate preparation is essential to prevent complications. The key questions related to the actual process of securing the airway revolve around ensuring that a skilled provider perform the procedure and that appropriate tools are used to facilitate timely and uneventful intubation. Since the rates of complications increase with the number of attempts,76,77 it is important that providers proficient in airway management form an integral part of the team. Provider experience can have a significant impact on the number of attempts. Schulte et al78 reported that higher level anesthesia residents used fewer intubations attempts during emergent, nonoperating room intubations as compared to junior residents. Similarly, a recent study evaluating emergent TI by first-year anesthesiology residents showed an increasing rate of relative success and decreasing rate of necessary attempts with the number of TIs.79 It was observed that first time and overall success rate did not plateau until at least 100 intubations were performed and, even at that time, the first-time success rate remained below 85%. Based on the results of the study, the authors recommend supervision by a specialist or senior physician during the first 200 procedures performed by anesthesia trainees. These findings have significant implications for skill acquisition for emergency TIs and should be confirmed for other specialties.
After achieving initial proficiency, it is vital that the skill set and expertise is maintained. The required frequency and intensity of practice needed to maintain this skillset needs further evaluation and validation in real world clinical scenarios. Institution-specific programs targeting proactive maintenance and enhancement of out-of-OR airway management skills, particularly for those who infrequently perform this procedure, are recommended. Tracking of procedures (eg, with procedure logs) or cumulative sum (CUSUM) analysis could also be included as part of individual continuous quality improvement endeavors.
While it is important that attempts at intubation are minimized, it is also important that appropriate training during real world scenarios of emergency airway management is imparted to trainees. Whether the most experienced provider performs the intubation or is there to supervise and take over if the trainee fails should be determined on a case-by-case basis and on the individual competence and experience of the trainee. In most circumstances, having the trainee take the first attempt and defining prespecified criteria (such as the patients’ hemodynamic and respiratory parameters) of when the most experienced provider takes over may be a viable compromise plan. The presence of 2 operators during these procedures has been included as part of the intubation bundle,49 and having an extra pair of trained hands, may help overcome some of the limitations of unfamiliar circumstances and locations. Further, the presence of a second operator can not only help improve patient outcomes (improved times to securing the airway, faster time of recognition of complications, improved speed to next attempts), but also may help provide comfort/reassurance to the primary operator.80
Historically, TI success has been associated with an individual’s skill using a direct laryngoscope and this has spurred debate over who should perform intubations—and how intubations should be performed—outside of the OR.81,82 While anesthesiologists are considered experts in airway management, the availability of an anesthesia service for all out-of-OR airway intubations is not always possible. One common approach wherein, the most trained person on site intubates, and the anesthesiologist acts as a backup, has been utilized in the ED and trauma bay.83 However, there are clinical scenarios of extremis when first-pass success (FPS) is more critical than others and there are times where the skillset of the operator precludes anyone else taking the first attempt, for example, a “bloody airway” mandating an accomplished provider skilled in DL. In such scenarios, time permitting, having the most experienced and proficient provider making the first attempt at intubation, while calling for help is ideal.
Intubation in critically ill patients is technically more challenging than elective intubation performed in the OR, regardless of who performs the procedure. Patients who might have been intubated with ease in the ORs tend to be harder to intubate in the ICU with antecedent complications.84 The advent of VL has made visualization of the glottic opening easier; however, difficulty with navigating the endotracheal tube to and beyond the larynx is a concern. VL may be beneficial in patients with cervical spine injury or those with suspicion for cervical spine injury as it causes minimal movements of the cervical spine during intubation.85 Studies comparing DL and VL paint a complex and convoluted picture. Systematic reviews and meta-analysis show no overall difference between the 2, and while some suggest that while VL might improve the chances of first attempt success, it may be associated with a higher risk of complications.86–90 It is possible that VL may have been evaluated more positively due to subject bias. De Jong et al88 reported in a meta-analysis of 2133 participants that VL significantly reduced the risk of difficult oro-TI, esophageal intubation, and increased FPS. However, a large majority of the participants were nonanesthesiology trainees, or junior anesthesiology providers and were likely to evaluate VL positively and experience better outcomes with this tool. Interestingly, the same results were not observed in a prehospital setting and when all operators were experienced.91
Part of the challenge is the lack of adequate learning opportunity for nonanesthesiology trainees with DL. While VL is easier to learn and easier to be educated upon, DL has a steeper learning curve and difficult to supervise. Further, emergent airways are the usual teaching scene for these providers where learning DL may be much harder.78 On the other hand, every anesthesiology trainee trains on numerous DL situations and uses VL as an incremental step-up tool for a potential DL failure and or when the airway history mandates better FPS with a videolaryngoscope. It is important to realize that preference of one over the other may also be related to a provider’s comfort and experience with the device. Even though DL can be faster and associated with equal/higher success in the hands of experienced providers, a videolaryngoscope should always be available as a backup tool to rescue difficult intubation and/or unsuccessful first attempt at DL in all out-of-OR emergency airway management scenarios.
Awake intubation may have to be considered in certain situations where anatomic airway difficulty is anticipated and/or the loss of spontaneous respiratory effort by the patient may be detrimental (patient with an anterior mediastinal mass). It is not only important to prepare the patient both psychologically and pharmacologically for the procedure, but also the team of the steps involved. Discussions regarding roles and responsibilities should be held before the procedure and when time permits, one should call for the difficult airway cart as well as additional help from colleagues who have expertise in awake TI. Awake TI involves 2 major components, adequate anesthesia of the airway, and judicious sedation. Rapid onset and readily reversible sedative/analgesics should be titrated to achieve patient comfort without compromising airway patency. Additional preparation includes anesthetizing the airway through topical application of local anesthetics and appropriate nerve blocks. It is vital that a decision regarding awake TI be made as early as possible, and a backup plan established early in the process if the awake approach proves difficult. Awake TI using VL has a comparable success rate and safety profile to flexible bronchoscopy92 and the choice is based on patient factors, operator skills, and availability of equipment.93 Detailed recommendations on performing awake TI have been provided elsewhere.93
Supraglottic airways (SGAs) can be utilized for establishing an airway in out-of-OR intubations and while such devices are often used as the primary airway in the OR, they are usually used after failed intubation as a rescue device in non-OR scenarios.94 Various types of SGA devices (with the ability to accommodate an endotracheal tube) can be used in these circumstances and can act as a bridge for going to the OR for a definitive airway or as a temporary airway before a tracheostomy at the bedside. SGAs are an integral part of difficult airway algorithms and all providers involved with TI should be familiar with their use, and be comfortable at troubleshooting them. The endotracheal tube introducer (Bougie) is also a useful tool when the epiglottis is visible but vocal cords cannot be seen with a significantly higher first attempt intubation success reported in emergency situations.95 Hence, a bougie may be used for TI in the ICU by providers who have experience with its use. However, caution needs to be exercised in patients with possible laryngeal or tracheal injury as the endotracheal tube introducer can exacerbate the injury.96
Airway Rescue Techniques
The discussion on airway management would be incomplete without discussing what to do when things do not go according to plan. There are several well-known cognitive aids that have been developed for when a difficult airway is encountered in the OR97,98; however, limited resources exist for out-of-OR scenarios.17,56 The Figure proposes a comprehensive algorithm for management of emergent out-of-OR airway management, including plans for when an initial attempt at TI is unsuccessful. Acute patient decompensation along with unfavorable situational and logistical factors makes this scenario overtly challenging for even the most experienced providers. It is important that providers involved with managing emergency out-of-OR airways are prepared for the challenges, have practiced the procedural steps, and trained to provide leadership during these stressful circumstances. Keeping calm, calling for help, and rapidly transitioning between different backup plans are the keys to success in these circumstances.
Hypotension or cardiovascular collapse is common during and following TI in critically ill patients, with the incidence varying between 25% and 46%.5,8,18,19,23,99,100 This results from a combination of pharmacologically induced sympatholytic action, conversion from negative-pressure to positive-pressure ventilation as well as the amelioration of the hypoxia- and hypercarbia-associated sympathetic drive. Both peri-intubation hypotension as well as hemodynamic instability after intubation are associated with significant morbidity and mortality.101–105 The patients’ blood pressure during this time may not be a reliable indicator of their hemodynamic status as the sympathetic stimulation from a combination of hypoxia, hypercarbia, and anxiety may be falsely elevating the blood pressure. There is limited prospective data on optimal strategies for hemodynamic support during emergency airway management. Administration of a fluid bolus before intubation has been shown to be of minimal benefit,13 and may actually cause harm and lead to postintubation hypoxemia in nonvolume responsive patients.106 If time and situation permit, assessment of fluid responsiveness by a quick passive leg raising test or bedside point-of-care ultrasound (POCUS) examination may help identify the suitable candidates for a fluid bolus. Another widely used intervention to avoid peri-intubation hypotension is the use of bolus or push-dose vasopressors and/or continuous infusion of vasopressor agents either during or immediately after intubation.49,107 This prophylactic use of vasopressors may be an alternative and needs further investigation.
Information regarding optimal use and indications for induction agents, neuromuscular blocking (NMB) agents, and vasopressors in the pharmacologic management of the out-of-OR airways continues to evolve. Decision-making around the optimal use and choice of pharmacologic agents to facilitate intubation must be individualized with careful consideration of each patient’s situation and comorbidity profile. Commonly used drugs during airway management are presented in Table 4.
|Drug||Dose (intravenous)||Onset of action||Duration of effect||Indications||Precautions|
|Fentanyl||0.5–2 µg/kg||2–3 min||30–60 min||Blunt intubation response||Respiratory depression, hypotension, rare chest wall rigidity at high doses|
|Etomidate||0.2–0.3 mg/kg||30–60 s||3–5 min||Induction agent, hemodynamic stability||Decreases seizure threshold, inhibits cortisol synthesis|
|Propofol||1–2 mg/kg||10–50 s||3–10 min||Induction agent, anticonvulsive effects||Hypotension, myocardial depression|
|Ketamine||1.5–2 mg/kg||1–2 min||5–15 min||Induction agent, analgesia, bronchodilation, hemodynamic stability||Catecholamine surge and its antecedent effects.
Respiratory depression and apnea at high doses
Direct myocardial depression in catecholamine depleted states
|Succinylcholine||0.5–2 mg/kg||30–60 s||5–15 min||Muscle relaxation, rapid onset and offset||Hyperkalemia in susceptible patients, prolonged effect in patients with atypical pseudocholinesterase, precipitate MH in susceptible patients|
|Rocuronium||1.2 mg/kg||45–60 s||45–70 min||Muscle relaxation||Long duration of action|
Among the induction agents, ketamine, a NMDA (N-methyl-D-aspartate) antagonist, preserves the patient’s internal respiratory drive at subinduction doses, while providing hypnosis. Hence, it is unique in its ability to be used for “delayed sequence intubation,” wherein airway preparation and preoxygenation may be optimized in an otherwise uncooperative or agitated patient.108 However, increased airway secretions may become a concern, and pretreatment with glycopyrrolate may be beneficial. It usually does not cause hypotension due to its sympathomimetic properties from enhanced catecholamine activity,109 but can lead to hemodynamic collapse in patients with depleted catecholamine stores. Caution should be exercised with its use in patients in whom excessive sympathetic stimulation could be detrimental.110 Further, ketamine can cause respiratory depression and apnea at higher doses111 and hence the dose should be chosen judiciously. The combination of ketamine and propofol (ketofol) is often used for procedural sedation and based on a recent study, may offer an acceptable hemodynamic profile when used for intubation in critically ill patients.15 Etomidate is frequently used in emergent intubations in critically ill patients, as it tends not to cause hypotension on induction. However, since it is unable to blunt the sympathetic response to intubation, hypertension and increased myocardial oxygen demand are a concern with its use. It is a selective adrenocortical 11 beta-hydroxylase inhibitor and causes transient adrenal insufficiency, the clinical implications of which are debatable.112 In a large meta-analysis, single-dose etomidate did not increase mortality in patients with sepsis and similar findings were also observed in an analysis conducted by the Cochrane Group.113,114 Corticosteroid supplementation, especially in patients with septic shock, may mitigate the risk of adrenal insufficiency and should be considered.115 Propofol has vasodilatory and mild cardiac depressant properties, and can have a profound effect on hemodynamics, especially in patients with hypovolemia and/or impaired cardiac function. Titrating the dose, limiting the initial bolus of the drug sometimes to much <0.5/kg (particularly in the critically ill or neurologically altered, or the elderly), preemptive or concomitant administration of vasopressor agents and judicious fluid administration may avoid significant hemodynamic perturbations.116 With a lack of consensus on an ideal induction agent, we recommend the use of etomidate or ketamine as the first choice induction agent based on specific scenarios and suggest that the use of propofol be limited to situations where TI is required for airway protection in the absence of cardiopulmonary compromise.
The choice of paralytic is multifaceted. Succinylcholine, which is a depolarizing neuromuscular blocker, provides a rapid onset and short duration of action. Its use has been associated with malignant hyperthermia, a rare yet life-threatening condition.117 Also, succinylcholine can cause acute hyperkalemia in susceptible patients, due to depolarization of the upregulated muscle nicotinic acetylcholine receptors (AChRs), which leads to efflux of intracellular potassium into the plasma.118 The administration of succinylcholine is contraindicated in patients with known decreased plasma cholinesterase activity, recent burns or trauma within 24 to 72 hours, and muscle myopathies. It should be used with caution in patients with disuse atrophy, those who have been bedridden and in those with intraabdominal sepsis lasting longer than 1 week, for the risk of succinylcholine-induced hyperkalemia.119 Nondepolarizing neuromuscular blockade via rocuronium and vecuronium does not carry the same risk of malignant hyperthermia or acute hyperkalemia, but the onset and duration of action is highly dependent on the doses used for intubation. Benzylisoquinolinium group of muscle relaxants such as atracurium and cis-atracurium, despite having a predictable metabolism profile, have no role in out-of-OR emergent airway management.
Sugammadex, a modified γ-cyclodextrin, can bind to and encapsulate steroidal NMB drugs such as rocuronium and vecuronium in the plasma, thus reducing their concentration at the neuromuscular junction and rapidly terminating the block.120 Sugammadex at a dose of 16 mg/kg has been found to reverse neuromuscular block 3 minutes after administration of RSI doses of rocuronium.121–123 Nevertheless, It is important to note that waking up the patient may not be an option in most out-of-OR intubations, especially in the critically ill patients. Waking up the patient should only be considered in stable patients in whom rescue ventilation using a facemask or supraglottic airway device is feasible. While meta-analyses have reported that the intubating conditions are better with succinylcholine,124,125 a recent study showed that clinician grading of intubating conditions was similar with both these drugs, and intubation-related complications occurred more often in the succinylcholine group.126 The evidence comparing rocuronium with succinylcholine should be interpreted while accounting for the dose of rocuronium used, since higher doses of rocuronium may have significantly different onset of action as well as intubating conditions.127–130 Further, the use of rocuronium can be “optimized” to match the speed of onset of succinylcholine, not only by using higher doses but also by generous bolus injections of saline flushes after intravenous administration.131–133 There is also a theoretic benefit of using a nondepolarizing agent for such intubations as the fasciculations associated with succinylcholine may increase oxygen consumption and decrease apnea time or result in frank desaturation.134 Further studies are needed to assess the differences in outcomes with the use of these drugs for out-of-OR intubations before recommending one versus the other.
AREAS OF FUTURE RESEARCH
Facial appearance may enhance the ability to predict a difficult airway. The use of AI enabled automatic face-analysis approach to detect morphological traits related to difficult intubation can be very helpful, especially in uncooperative patients and needs evaluation.135 Considering that personalized approach may be necessary for the unique experiences seen in out-of-OR intubations, further classification of such scenarios based on organ system involvement and simulation-based research on optimizing each scenario may be necessary. Also, simulation-based teaching of leadership skills, teamwork and communication, procedural efficiency, and speed needs further exploration. The role of POCUS in such scenarios could be lifesaving and addition of POCUS to assess patient’s cardiopulmonary status as well as gastric contents before each TI akin to an anatomic airway assessment needs evaluation. Simulation-based training modules can help prepare providers for the various challenges associated with out-of-OR emergent airways and integration of such modules into the training curriculum needs methodical examination. Studies investigating patient positioning, techniques for preoxygenation as well as apneic oxygenation, and the role of RSI/Sellick’s maneuver based on patients’ physiologic derangements rather than location would be beneficial. The controversy surrounding the use of VL or DL as the first choice continues and should be reexplored within the context of training specific to each group of providers. Future study should also address device development, including different blade shapes, angles, lengths, and cameras as well as stylet modifications including flexibility allowing for dynamic navigation. Last but not least, the optimum choice of drugs for induction of anesthesia as well as muscle relaxation based on patient’ physiological perturbations should be evaluated.
As airway experts, anesthesia providers must be prepared to take their skills from the OR to less controlled environments in various other areas of the hospital for emergent airway management. Considering the high rates of complications associated with emergency airway management out of the OR, it is prudent that a well-thought out, patient and situation-specific plan is established before the procedure. A thorough airway examination including assessment of physiological challenges, availability of appropriate personnel and equipment, hemodynamic goal setting, and multidisciplinary collaboration are essential to improve patient outcomes. Pre- and apneic oxygenation should be considered in patients with precarious respiratory status and optimization of hemodynamics with pressors or fluid administration should be tailored to individual patient needs.