Richard D. Zane
Michael F Murphy
The Clinical Challenge
Many of the principles of prehospital airway management are similar to those in the emergency department (ED), with the obvious exception that the prehospital environment is necessarily austere. Patient management in the prehospital setting is done without many of the resources and backup assistance that are readily available in the ED. In addition, patient care must often be provided in awkward circumstances such as in private homes, in stairwells, in the seat of a damaged automobile, or on the street, where lighting and position are often not ideal. Local protocols, regional and topographic differences in transport time, the availability or unavailability of neuromuscular blocking agents, limited and varied equipment, limited backup, and mandatory transport of the patient all introduce considerations and issues that are not only different from those in the ED, but also different from one prehospital system to another.
Approach to the Airway
The following factors have motivated the most striking changes in the approach to airway management in emergency medical services (EMS) since the last edition of this manual:
· The emergence of extraglottic devices (EGDs) as first-choice alternatives to bag-mask ventilation (BMV) in unresponsive patients for basic life support (BLS) providers
· The use of EGDs instead of endotracheal intubation (ETI) by advanced life support (ALS) urban ground ambulance services in unresponsive patients
· The emergence of “nonparalytic rapid sequence intubation (RSI)” as an alternative to “paralytic RSI” in which a full or tailored dose of an induction agent, but no neuromuscular blocking agent is administered
· Confusion in the literature as to whether ETI is of benefit in ground ambulance ALS EMS services
· A distinct pattern of improved outcomes with RSI where helicopter EMS (HEMS) (also known as air medical transport) had been used.
· The use of high-fidelity human patient simulation training to improve performance
Factors contributing to improved RSI success rates for prehospital providers have also been identified:
· High-quality initial and ongoing airway management training
· Intense medical oversight and quality management programs
· Frequent exposure to patients in need of active airway management
Improved outcomes for services embracing RSI is contingent on three factors:
1. Knowing how to correctly perform RSI
2. Being able to identify those patients where RSI should not be preformed (i.e., identifying the Difficult Airway [see Chapter 7])
3. Being able to rescue the airway in the event that intubation is unsuccessful and BMV fails
The decision to intubate the patient in the prehospital setting is based on the same principles as those applied in the ED (see Chapter 1). A prehospital algorithm for the decision to intubate is shown in Figure 23-1. The initial step is a quick evaluation of the patient, with a particular focus on assessment of the airway and ventilation. If the patient is maintaining the airway, protecting the airway, and ventilating and oxygenating adequately, then intubation is rarely indicated in the prehospital setting. However, failure to maintain or protect the airway or to exchange gases adequately mandates intubation unless the problem can be corrected by other means or transport is very short.
|
|
|
Figure 23-1 • Decision to Intubate. *Caution in trauma; +naloxone, glucose; #BMV, bag-mask ventilation. |
Technique
If the patient is not maintaining his or her own airway, as evidenced by obstructed or noisy breathing, deep coma with unresponsiveness, or apnea, then the jaw-thrust maneuver should be immediately applied to attempt to establish a patent upper airway. Unless the patient has a contraindication to manipulation of the head and neck (e.g., blunt trauma with possible cervical spine injury), the head should be extended on the neck, and the mandible should be thrust forward by pressure applied bilaterally at the angles of the mandible. This is best done using the ring or small fingers of the rescuer's hands so that the remaining fingers can be free to apply and properly seal a mask for ventilation.
If the patient does not begin breathing spontaneously when the jaw-thrust maneuver is applied, then BMV should be initiated, with placement of nasal and oral airways (see Chapter 5). In most circumstances, BMV in this setting should be followed by ETI as soon as adequate preparations have been made, and providing the EMT is trained and credentialled to intubate. If BMV is unsuccessful, despite careful attention to proper technique, then immediate intubation or placement of an alternate airway device, such as a Combitube or laryngeal mask airway (LMA), is indicated (see Chapter 10). As mentioned previously, there is a school of thought emerging that the use of an EGD may leapfrog ahead of BMV as the first-line technique. This is based on the relative ease of use and high ventilation success rates seen with EGDs relative to the more difficult technique of BMV.
After a patent airway has been established, the next evaluation should determine whether the patient is protecting the airway from aspiration. Aspiration of gastric contents is a serious adverse event and must be prevented. Failure to maintain a patent airway usually also indicates loss of protective airway reflexes. It is appropriate to administer a “coma cocktail,” which typically includes naloxone in doses of 0.4 to 2 mg as a specific reversal agent for opioid-induced respiratory depression, and glucose, 25 g intravenously, for possible hypoglycemia. In some systems, point-of-care glucose testing is performed rather than empiric glucose administration. If the coma cocktail is unsuccessful in reversing the patient's coma sufficient to permit self-protection of the airway, then BMV and intubation are indicated.
If the patient is maintaining and protecting the airway, the next assessment is of the adequacy of ventilation and oxygenation. If the patient is hypoventilating and a coma cocktail has not already been administered, this should now be done. Oxygenation failure, such as in pulmonary edema, may respond simply to supplemental oxygen via a nonrebreather mask or via bag and mask with assisted respirations. If neither supplemental oxygen nor administration of reversal agents can establish adequate oxygenation, then BMV is indicated, followed by intubation.
Finally, there is a population of patients for whom intubation may be indicated despite adequate airway maintenance and protection and acceptable levels of oxygenation and ventilation. An example is a pulmonary edema patient who is rapidly tiring but is maintaining oxygen saturations at 90%. If long transport time to the hospital is anticipated and the patient is not responding to other interventions, such that it is anticipated that the patient likely will deteriorate and require intubation before arrival at hospital, then early, anticipatory intubation may be appropriate before development of frank hypoxemia with worsening metabolic and respiratory acidosis. Other examples include a patient with drug overdose and rapidly decreasing level of consciousness, the cyclic antidepressant overdose patient who has had a generalized seizure, or certain cases of upper airway trauma in which ongoing airway bleeding or expansion of a hematoma might threaten the patient. In such cases, careful evaluation and consultation with medical control is essential. In most circumstances, expeditious transport of the patient with supplemental oxygen via a nonrebreather mask is the appropriate course of action. Nevertheless, in certain circumstances, intubation may be both prudent and indicated (Fig. 23-1).
Once a decision to intubate is made, the next step is to choose the best method for intubation, based on individual patient circumstances and the attributes of the EMS system and the intubator. The choice will depend on whether neuromuscular blockade is permitted, the availability of airway adjuncts and rescue devices, and whether prehospital cricothyrotomy is possible and permitted, along with a number of individual operator attributes.
If the patient is unresponsive and exhibits agonal cardiac or respiratory activity, the situation is analogous to the crash airway scenario depicted in Chapter 2. The choice here is between BMV, insertion of an alternate airway device (Combitube or LMA), oral tracheal intubation, and blind nasotracheal intubation. Regardless, the patient should have an airway established and oxygenation maintained using a bag and mask until intubation is attempted.
If the patient has a relatively clear upper airway (no trauma, no foreign body, and no obstruction) and is breathing spontaneously, then blind nasotracheal intubation may be reasonable (see Chapter 9). However, apnea is a relative contraindication to blind nasotracheal intubation because the patient's breath sounds are used to guide the tube into place. Similarly, abnormal anatomy or a foreign body in the upper airway also constitutes relative contraindications to this technique. In addition, blind nasotracheal intubation has a lower success rate and higher complication rate than oral intubation. Nevertheless, in some systems and in certain patients, blind nasotracheal intubation may be the preferable method. This may be especially true if the patient's jaw is clenched and the use of neuromuscular blockade is not an option. Also, blind nasotracheal intubation may be a better choice if the patient is relatively inaccessible (e.g., trapped in an automobile) and neither LMA nor Combitube are available.
Oral intubation via direct laryngoscopy is also an acceptable method for the unresponsive patient and is the method of choice if the patient's jaw is not clenched. In the case of the unresponsive patient, intubation proceeds exactly as described previously in discussions of the crash airway scenario. Direct laryngoscopy is performed, and the tracheal tube is placed under direct vision. If direct laryngoscopy is unsuccessful in visualizing the vocal cords, then a drug-assisted intubation is required. In some settings, drug-assisted intubation will include both induction (sedative) agent and neuromuscular blockade. In other settings, where neuromuscular blockade is not permitted, drug-assisted intubation will be done with sedation (at times to the point of induction of general anesthesia) alone. In either case, drug-assisted intubation may be preferable to blind nasotracheal intubation, even in the clenched jaw patient.
If the patient is conscious and combative and requires intubation, then drug-assisted intubation is indicated. At the outset, though, the benefits and risks of intubation should be weighed against the benefits, and risks of rapid transport without intubation. Combative or uncooperative behavior is a strong relative contraindication to blind nasotracheal intubation (NTI) because of the increased risk of complications in attempting to insert the tube in a patient who is resisting. If the patient is not frankly comatose and is not uncooperative or combative, then assessment must be made as to whether the patient would tolerate laryngoscopy. If the patient is sufficiently cooperative or sufficiently obtunded to permit oral laryngoscopy without medications, then NTI may be attempted. Again, preference is expressed for oral intubation over nasal intubation except in circumstances in which the jaw is clenched preventing oral access. Even in such cases, oral intubation with medication may be preferable to blind nasotracheal intubation.
Blind nasotracheal intubation is discussed in detail in Chapter 9. In general, although blind nasotracheal intubation has been widely used in prehospital care, it has declined in popularity as medications are being introduced to facilitate intubation in the prehospital setting. Blind nasotracheal intubation has two main indications. First, in circumstances in which direct laryngoscopy and visualization of the glottis are impossible, blind nasotracheal intubation may be the method of choice. An example is the patient who is trapped in the automobile after a motor vehicle crash and requires intubation before extrication can be accomplished. In such cases, blind nasotracheal intubation may be the only method that can be used by an operator either from inside or outside the vehicle. The second circumstance is the patient with a clenched jaw. A small number of patients will have increased masseter tone and hence a clenched mandible, even when they are deeply unconscious and breathing inadequately. In such cases, the choice is between administering medications for oral intubation or performing blind nasotracheal intubation. Even though RSI is clearly the method of choice under these circumstances, many prehospital care providers do not have this option, and blind nasotracheal intubation may be preferable or may be the procedure of choice for the individual operator.
In general, blind nasotracheal intubation should not be performed in patients with asthma, chronic obstructive pulmonary disease, or pulmonary edema unless drug-assisted intubation is impossible. In such patients, prolonged attempts at nasotracheal intubation impair oxygenation and can worsen existing hypoxemia and lead to respiratory arrest. Again, this is a judgment call, and an individual provider might choose to attempt nasotracheal intubation on the patient with status asthmaticus; however, great caution must be exercised because prolonged or traumatic attempts may significantly worsen the patient's condition.
The prehospital environment is unique in that a provider may be far from assistance and rescue airway techniques, and devices have an important role. Although several new devices have been developed that may be useful for airway management in the prehospital setting, providers should become very facile with one or perhaps two rescue techniques and devices:
1. LMA. The LMA is described in detail in Chapter 10. The LMA is rapidly becoming the rescue device of choice for many prehospital systems and has gained some traction as a primary airway device in lieu of BMV for BLS providers and ETI for ALS providers. The LMA is inserted blindly through the oropharynx, and the skill is fairly easy to acquire. Although the LMA does not protect the airway against aspiration, it does provide effective ventilation in virtually every patient into whom it is placed properly. In certain circumstances, the patient can be intubated through the LMA. The standard LMA is available in both reusable and disposable models for prehospital systems. The disposable model is preferable because the LMA will likely stay with the patient once the patient arrives in the receiving hospital. Although the disposable LMA (LMA Unique) is available only in adult sizes, the reusable LMA (LMA Classic) has sizes ranging from neonate to large adult.
2. Combitube. The Combitube is widely used both as a rescue device and for elective anesthesia. The insertion technique is described in Chapter 10. The Combitube is also relatively easily learned, has a high ventilation success rate, and can be inserted into a patient in difficult circumstances, such as from the outside of a vehicle. The Combitube should not be confused with the esophageal obturator airway, which is a dangerous device that has no place in modern airway management.
3. Continuous positive airway pressure. Noninvasive ventilatory support (NVS) is addressed in detail in Chapter 38. NVS, specifically continuous positive airway pressure (CPAP), is slowly becoming more common in the out-of-hospital setting, especially in ground or air critical care transport. CPAP is most useful in treating patients who require minimal to moderate additional ventilatory support, such as those with congestive heart failure or an exacerbation of chronic obstructive pulmonary disease.
Failed Intubation
Occasionally, the prehospital provider will be faced with a failed intubation. The potential for a failed intubation in the field should be heralded by the evaluation of the patient for difficult airway attributes, as discussed in Chapter 7. If a difficult airway is anticipated, it may be most prudent to transport the patient rapidly to the ED for definitive care rather than attempting to intubate in the field, consuming valuable time and perhaps ending in a failed intubation and further damaging the airway, making intubation ultimately more difficult. Transport time should also be considered when determining whether it is appropriate to perform drug-assisted intubation. Again, in many settings, especially urban systems with short transport times, transport to the ED may be preferable to struggling with a difficult airway in the prehospital setting.
Traditionally, the primary rescue device for failed intubation has been BMV, although the thinking on this is evolving as described previously. Nonetheless, prehospital providers must be expert at BMV using both one-handed and two-handed techniques, supplemented by oral and nasal pharyngeal airways. If BMV is inadequate at providing effective oxygenation, the patient should be repositioned, the jaw thrust should be applied vigorously, oral and nasal airways should be placed (if not already), a two-handed technique should be used to seal the mask to the patient, and any other steps should be taken that the operator determines might be helpful (see Chapter 5). A subjective sense that BMV is inadequate or failing should motivate the immediate placement of an EGD. Again, meticulous BMV and rapid transport might be the appropriate action if oxygenation is adequate and intubation appears difficult or impossible.
If intubation is unsuccessful, it is important to try to determine why. Chapter 6 describes the sequence of steps involved in successful direct laryngoscopy. Repositioning of the patient, a change in equipment, or even a change in operator may help. In addition, prehospital providers should be familiar with techniques such as the Backward, Upward, Rightward Pressure (BURP) maneuver that may facilitate direct laryngoscopy and intubation, and with the use of routine intubation aids such as the Eschmann introducer, also known as the “gum elastic bougie.”
When laryngoscopy fails, digital or tactile intubation may be an option (Chapter 9). This is a blind technique that uses anatomical landmarks to guide the placement of one's fingers and maneuver an endotracheal tube into the glottis by sliding the tube along the tongue to the undersurface of the epiglottis and then through the glottic opening. By palpating the epiglottis with the index and long fingers, the epiglottis can be picked up by the long finger and directed anteriorly. The tube is then guided by the index finger under the epiglottis and into the trachea. A stylet bent at a 90-degree angle 4 to 6 cm from the tip of the tube should be used to assist in placement. Although exceedingly rare, some advantages of digital intubation include relatively rapid placement even with experienced providers, no need for special equipment, no requirement to visualize the glottis, and no movement of the head and neck. The major significant limitations are the size of the operator's hands relative to the patient's oral cavity and that the patient must be unconscious.
Some systems allow cricothyrotomy to be performed in the prehospital setting. If this is the case, adequate training and skill maintenance are important. Cricothyrotomy in the field should be an exceedingly rare event. Cricothyrotomy accounts for only approximately 1% of all ED intubations, and although use has varied in reports among various systems, one might anticipate a similar or lower percentage in the field.
Drug Dosage and Administration
The evidence addressing the use of RSI by EMS personnel is discussed in detail in Chapter 25. The use of RSI, neuromuscular blockade, and sedatives is highly variable from one EMS system to another. Even though an ever-growing number of prehospital systems are using neuromuscular blockade to facilitate intubation in the field, many EMS systems have not instituted RSI for myriad reasons, including training and skill retention issues, short transport times, medical oversight and adequacy of quality management systems, and the failure of the literature to consistently identify clear benefits.
Medication administration for prehospital airway management can occur in two forms: (a) sedation alone (e.g., nonparalytic RSI), and (b) sedation with neuromuscular blockade (e.g., paralytic RSI).
HEMS services and critical care and specialized transport teams are usually trained and experienced in the use of neuromuscular blockade for intubation and encounter sufficient numbers of cases to maintain skills and knowledge (see Chapter 25). Field protocols for sedation or sedation with neuromuscular blockade vary from system to system. In general, sedation is used when the patient is not sufficiently cooperative for intubation, when mandibular relaxation is believed to be inadequate, or when the jaw is clenched. In such cases, sedative agents such as midazolam, diazepam, lorazepam, or others are administered and titrated until the patient can be intubated. Some systems permit induction doses of medications to be used, particularly etomidate. In systems using neuromuscular blockade, a protocol typically dictates both the indications for and the manner of administration of neuromuscular blockade. In such cases, it is almost always mandatory to administer a sedative agent along with the neuromuscular blocking agent to ensure that the patient is optimized for intubation and that there is no undue physiological or psychological stress from the intubation attempts. Prehospital sequences are typically much simpler than those used in the ED in that pretreatment agents are rarely used. A typical prehospital, drug-assisted intubation protocol using neuromuscular blockade is shown in Box 23-1.
BOX 23-1 Simplified Rapid Sequence Intubation for Prehospital Care
1. Prepare equipment, and ensure that the patient is in an appropriate area for intubation.
2. Preoxygenate the patient with nonrebreather mask or BMV for at least 3 minutes, if possible.
3. Pretreatment drugs—infrequently used. Suggestion: lidocaine 1.5 mg/kg intravenously for head injury, reactive airways disease.
4. Paralysis with sedation—administer sedative drug in adequate dose (e.g., midazolam 0.2 mg/kg) and neuromuscular blocking agent (e.g., succinylcholine 1.5 mg/kg).
5. Protection—wait 20 seconds. Apply Sellick's maneuver.
6. Placement—45 seconds after drugs are given, intubate. Confirm endotracheal tube placement, secure tube, transport patient.
The sequence is simplified in the prehospital setting because the medication options are fewer. Prehospital providers rarely carry a wide array of induction agents, and the circumstances are less controlled.
Postintubation Management
Most commonly in the prehospital environment, after securing an airway, the patient is bag ventilated rather than placed on a mechanical ventilator, although the latter is preferable if available. Because airway management is often a high-intensity situation, it is important to attempt to control respiratory rate and tidal volume, which are often inappropriately elevated because of the provider's excitement. As interfacility critical care and specialized care transport become more common, transport ventilators permitting postintubation ventilation will become more prevalent in the pre- or interhospital environment.
Tips and Pearls
· Always weigh the risks and benefits of intubation in the prehospital setting against transport to the ED. In many circumstances, rapid transport might be the best way of managing the airway.
· Master BMV. There are few airway emergencies in the prehospital setting that will not be temporized or managed adequately with proper BMV until the patient can be transported to the hospital, particularly when transport times are short.
· If transport times are long, especially in systems with high rates of trauma, consider introducing neuromuscular blockade into the prehospital setting. This approach requires a comprehensive program, including quality oversight.
· Newer devices, such as the LMA and Combitube, have a vitally important role in prehospital care.
· All prehospital intubations should have their airway reassessed on arrival at the ED. Even though prehospital providers are extensively trained in acute airway management and are comfortable caring for patients in respiratory distress, up to 25% of prehospital intubations are found to be esophageal on arrival at the ED. Confirmation of endotracheal tube placement with an end-tidal carbon dioxide detector should be a first priority both in the field and on arrival.
· Air medical, critical care, and specialized transport programs are frequently asked to transport patients from a community hospital ED or intensive care unit to a tertiary care facility. These teams are occasionally confronted with the situation in which a patient has not had his or her airway definitively managed, but it is needed for safety in transport. It is always preferable to manage these airways while still in the sending health care facility as opposed to en route in an ambulance or helicopter.
Evidence
The evidence base on which important decisions relating to airway management in prehospital care are based is growing and is presented in Chapters 7 and 25. However, several important issues need to be resolved:
· Are EGDs more effective than BMV in unresponsive patients in the hands of BLS personnel, and do the outcomes reflect that fact?
· Are the outcomes of unresponsive patients managed with EGDs rather than ETI by ALS personnel improved?
· How should ALS providers manage the airway in responsive patients that require airway management?
· Does ETI by ALS personnel improve outcomes generally and in specific subpopulations of patients?
· What factors are critical to ensuring that RSI is performed safely in EMS?
· Is there evidence that airway intervention improves outcome (e.g., cardiac arrest)?
1. Is there evidence in the EMS literature to suggest that intubation success rates employing “nonparalytic RSI” are as high as with “paralytic RSI”? It is well established in the anesthesia literature that the use of an induction agent alone provides poorer intubating conditions than when a neuromuscular blocking agent is coupled with the induction agent. Bozeman, Kleiner, and Huggett (1) compared two groups in a HEMS system, one using etomidate alone and the other employing neuromuscular blockade (RSI group). The view of the larynx (laryngeal view grade) was significantly better in the RSI group, as was the intubation success rate (92% success with paralytic RSI vs. 25% in the nonparalytic RSI group). Sonday et al. (2), in contrast, found little difference, whereas Kociszewski et al. (3) found that the neuromuscular agent significantly improved the ease and success of intubation over induction alone.
2. Is there any evidence that intubation training of paramedics on high-fidelity patient simulators is as good as training on live patients in the operating room (OR)? Hall et al. (4) studied 36 paramedic students that had never intubated before. He randomized them into two groups. Both groups received didactic instruction and manikin training. Then half went to the OR to intubate 15 patients, while the other group received 10 hours of training on a high-fidelity simulator. The entire group was then tested on 15 live intubations. Overall success rates, success on first attempt, and complication rates were similar in both groups.
Interestingly, simulation has also been shown to be a valid evaluation tool for emergency airway management skills. Overly, Sudikoff, and Shapiro (5) evaluated the acute airway management skills of 16 pediatric residents and found that high-fidelity patient simulation was useful in evaluating not only the individual's skill set, but also the quality of the training program that produced the resident. Rosenthal et al. (6) had similar findings in the training and evaluation of interns.
References
1. Bozeman WP, Kleiner DM, Huggett V. A comparison of rapid-sequence intubation and etomidate-only intubation in the prehospital air medical setting. Prehosp Emerg Care 2006;10:8–13.
2. Sonday CJ, Axelband J, Jacoby J, et al. Thiopental vs. etomidate for rapid sequence intubation in aeromedicine. Prehospital Disaster Med 2005;20:324–326.
3. Kociszewski C, Thomas SH, Harrison T, et al. Etomidate versus succinylcholine for intubation in an air medical setting. Am J Emerg Med 2000;18:757–763.
4. Hall RE, Plant JR, Bands CJ, et al. Human patient simulation is effective for teaching paramedic students endotracheal intubation. Acad Emerg Med 2005;12:850–855.
5. Overly FL, Sudikoff SN, Shapiro MJ. High-fidelity medical simulation as an assessment tool for pediatric residents' airway management skills. Pediatr Emerg Care 2007;23:11–15.
6. Rosenthal ME, Adachi M, Ribaudo V, et al. Achieving housestaff competence in emergency airway management using scenario based simulation training: comparison of attending vs. housestaff trainers. Chest 2006;129:1453–1458.
