Emergency Management of the Difficult Airway: New Techniques, Devices, and Interventional Approaches
Emergency Management of the Difficult Airway: New Techniques, Devices, and Interventional Approaches
Part I: Initial Approach to the Failed Airway and Laryngeal Mask Airway
Authors: Kenneth H. Butler, DO, Associate Residency Director, University of Maryland Emergency Medicine Residency Program, University of Maryland School of Medicine, Baltimore; Brian Clyne, MD, Chief Resident, Division of Emergency Medicine, Department of Surgery, University of Maryland School of Medicine, Baltimore; and Brian D. Euerle, MD, Residency Director, University of Maryland Emergency Medicine Residency Program, University of Maryland School of Medicine, Baltimore.
Peer Reviewer: William B. Ignatoff, MD, Attending Emergency Physician; Med- ical Director for Adult Critical Care Transport and Transfer Referral Center, University Hospitals of Cleveland, OH; Clinical Instructor in Emergency Medicine, Case Western Reserve University, School of Medicine, Cleveland, OH.
Emergency medicine and critical care physicians who are likely to encounter complicated, life-threatening airway emergencies must be skilled in securing an airway with techniques other than those mandated by the standard methods of oral and nasal intubation. The approach to these situations and the equipment that will produce the best results, to a great degree, depends on the clinician’s abilities and experience with airway management. What is clear, however, is that the best defense is a good offense; commonly, even the experienced, skilled clinician will have to press alternative techniques into service to produce a favorable outcome in a complicated, atypical patient.
As a first step, the emergency physician should attempt to identify clinical clues that suggest the presence of a difficult airway and, when appropriate, select an alternative device. This strategy can help prevent a patient’s deterioration or demise caused by multiple attempts using standard methods. Such alternative techniques and devices for airway management include the use of the laryngeal masks, dual-lumen airway devices, transillumination intubation, flexible standard fiberoptics, rigid fiberoptics, and semi-rigid stylets.
Unfortunately, in emergency medicine, there appears to be no precise or formal definition of a "difficult airway." However, the American Society of Anesthesiologists Task Force on Management of the Difficult Airway (see Figure 1 on page 299) defines a difficult airway as a "clinical situation in which a conventionally trained anesthesiologist experiences difficulty with mask ventilation, difficulty with tracheal intubation, or both."1 This task force further defines difficult mask ventilation as occurring when "it is not possible to maintain the PO2 at greater than 90% using 100% oxygen and positive pressure mask ventilation," and difficult intubation as occurring when more than three attempts are required using conventional laryngoscopy. These guidelines focus on three areas of concern: 1) assessment and nature of the difficult airway; 2) consideration of basic management choices for tracheal intubation; and 3) development and implementation of primary and alternative strategies for airway management.
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In the practice of emergency medicine, despite careful pre-procedure evaluation, airway management difficulties may not be predicted in some instances; therefore, strategies for managing the unanticipated difficult airway should be preformulated and practiced. Accordingly, emergency physicians responsible for airway management should be skilled in the use of at least one alternative device for the difficult airway.
With these important concerns in mind, the purpose of this two-part series is to present current strategies and new techniques for managing the difficult airway. Figures and tables are used to guide the physician in specific, patient-directed techniques that will improve outcomes in challenging, life-threatening emergencies.
— The Editor
Identifying the Difficult Airway: Risk Factors and Evaluation
Airway management in acutely ill patients is one of the most challenging aspects of emergency medicine. Not surprisingly, emergency physicians frequently are called upon to provide expeditious airway interventions for patients in extremis, many of whom will have acute respiratory deterioration and airway compromise under the most difficult of circumstances. Typically, little time is available to prepare the patient and ancillary staff for more aggressive strategies or atypical approaches for securing a difficult airway. Accordingly, the few seconds or minutes that are spent in evaluation, planning, and preparation for such contingencies can make the difference between life and death. In order to provide optimal care during resuscitation under these conditions, the emergency physician must be skilled in a variety of methods of airway management and he or she must have the proper equipment and devices available at all times.2
Preparation. The complication rate associated with emergency intubation is much greater than that for routine airway management in the operating room (the frequency of failed intubations in emergency situations is approximately 1 in 500).3 Emergency intubation also is associated with cardiac arrest in more than 1% of cases.4 The most important factor in dictating success or failure in airway management is the skill level of the airway manager. In this regard, the intubating physician must be familiar with various types of airway equipment and he or she must be able to select and apply the appropriate device or technique for every airway resuscitation.5
Knowledge and skill maintenance using alternative, "plan B" strategies will prepare the intubator for difficult cases and facilitate a successful response if intubation failure occurs. This concept of always being prepared and familiar with an alternative strategy applies to every intubation. The airway manager personally must check all airway equipment prior to each shift in the emergency department (ED). Equipment and devices should be arranged in an easily accessible order at the head of the bed. (See Table 1 on page 300.)
| Table 1. Suggested Contents of Bedside Storage Unit for the Difficult Airway | |
| 1. | Rigid laryngoscope blades of varied design and size, laryngo- scope handles |
| 2. | Endotracheal tubes of assorted sizes with preinserted stylets and attached syringes for cuff inflation |
| 3. | Fiberoptic intubation equipment |
| 4. | Devices for nonsurgical airway |
| 5. | Equipment for emergency surgical airway (scalpel, tracheal dilator, tracheal hooks, and tracheostomy tubes) |
| 6. | An exhaled CO2 detector |
| 7. | Magill forceps |
| 8. | Oropharyngeal and nasopharyngeal airways |
| 9 | Water soluble lubricant, anesthetic topicals, vasoconstrictive topicals |
The difficult airway—or patient—may first declare itself in the field when emergency medical services (EMS) personnel report that they are unable to establish intravenous (IV) access or when an established line is lost or infiltrated. Before arrival to the ED, EMS personnel may have made multiple attempts to establish an airway using standard laryngoscopic techniques. The efforts can be complicated by a patient’s combativeness and agitation due to cerebral hypoxia, an immobilized cervical spine, or oral or facial trauma. A detailed mental picture of the patient’s condition and stability of the airway, conveyed by radio transmission, should help ED personnel prepare the resuscitation room prior to the patient’s arrival.
It should be stressed that the risk of intubation failure increases if the resuscitation room equipment is not inventoried properly and checked routinely for proper functioning. The mnemonic S-O-A-P-ME can be used in the anticipatory phase:
S = Suction
O = Oxygen
A = Airway equipment
P = Pharmacology (anticipated drugs needed to facilitate intubation)
ME = Monitoring Equipment (cardiac monitor, pulse oximeter)
Initial Evaluation and Assessment. After arrival to the ED, all patient moorings should be checked, secured, and transferred to a permanent source. A second IV line should be established, because a line inserted in the field may become infiltrated or lose patency due to position or transfer.
The patient’s airway should then be evaluated. An essential step in the assessment of a patient for rapid-sequence intubation is determining whether the patient has attributes that will make bag-mask ventilation, oral intubation, or a surgical airway difficult to achieve. The airway manager must be able to assess and anticipate the degree of difficulty and then select the method of airway management most likely to succeed for that individual case. Despite careful evaluation, however, difficulties will not be predicted in some instances. As a result, strategies for managing the unanticipated, difficult airway should be preformulated and practiced.
External Anatomic Features. Unfortunately, in many cases, there is no time to assess the patient’s internal airway; therefore, most airway management decisions are based on external inspection only. Difficulty should be anticipated in a patient with: 1) a short, muscular neck; 2) a receding mandible; 3) a protruding tongue or upper incisors; 4) mandibular instability; 5) facial trauma; 6) restricted head and neck movement; 7) facial hair; or 8) obesity. Any of these circumstances may cause difficulty in bag-mask ventilation, intubation, or both. It should be stressed, however, that individuals who appear to be perfectly normal and without any medical history or physical findings that would predict a complicated intubation also may present difficulties in intubation.
For endotracheal intubation to proceed effortlessly during direct laryngoscopy, there must be an unobstructed line of view between the mouth and larynx. The space anterior to the larynx determines the ease with which the laryngeal axis can be brought in line with the pharyngeal axis during laryngoscopy and extension of the alantooccipital joint. Placement of a pillow or folded towel under the head of an adult (see Figure 2) or under the shoulders of a child (see Figure 3) may facilitate this alignment. In patients with an anterior larynx, the larynx is anterior to the direct line of sight and the tongue or epiglottis obstructs the view (the tongue is "the enemy"). Difficulty can be anticipated if the patient has restricted ability to open the mouth, prominent maxillary incisors, a large tongue and small pharynx, a short mandible, or limited cervical flexion.
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The thyromental distance should be measured.6-9 A large mandibular space allows more room for compression of the tongue by the laryngoscope blade. A difficult intubation may be expected if the distance from the mentum of the chin to the hyoid bone in an adult is less than three finger breadths when the head is extended. (See Figure 4.) Patients with a shortened distance because of a poorly developed mandible or a short, fat neck will have an anterior larynx.
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Internal Airway Assessment. If time permits, the internal airway should be examined to detect impediments to intubation. In an adult with adequate temporomandibular joint function, an adequate mouth opening measured from the upper to the lower incisors is three finger breadths. (See Figure 5.) For this measurement, an alert patient can be asked to open his or her mouth as widely as possible and protrude the tongue anteriorly. The ease of laryngoscopy also correlates with the ability of the physician to visualize the soft palate, uvula, and faucial pillars.
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The grade of laryngeal view is expressed as a Mallampati score of I through IV (see Table 2).10 High success rates are associated with Classes I and II, and difficult intubation with Classes III and IV. Mallampati classification alone is an imprecise mechanism for preoperative prediction of a difficult intubation. Combining the Mallampati classification with evaluation of the aforementioned risk factors will improve the sensitivity and specificity of the preoperative assessment.11-13
| Table 2. Mallampati Airway Classification System | |
| Class I | Soft palate, fauces, uvula, anterior and posterior tonsillar pillars |
| Class II | Soft palate, fauces, uvula |
| Class III | Soft palate, base of uvula |
| Class IV | Soft palate not visible at all |
| Reproduced with permission from: Deem S, Bishop MJ. Evaluation and management of the difficult airway. Crit Care Clin 1995;11:1-27. | |
Obstructed Airway. Clear, appropriate speech is an indication of upper airway function. Having a patient state his or her name will reflect airway patency as well as cerebral orientation. Hoarseness and stridor are clinical signs of edema or obstruction. All dentures and foreign material must be removed. Obstruction caused by a foreign body, direct airway trauma, an expanding hematoma, an internal mass, epiglottitis, or any process that alters airway integrity will lead to difficulties with bag-mask ventilation and intubation.
Optimizing Success: An Algorithmic Approach to Airway Management
Nonsurgical Vs. Surgical Techniques. In general, nonsurgical techniques are the preferred, first approach for airway management because of their high success rates, low risk, and expediency.14 Under some circumstances, surgical access to the airway should be considered the primary approach. Cricothyrotomy and tracheotomy should be undertaken when a patient has significant oropharyngeal or laryngeal abnormalities. However, because of a high complication rate associated with these procedures, alternative approaches should be considered carefully.
Awake Intubation. Awake intubation should be the initial approach in a patient in whom a difficult intubation is anticipated, but who has adequate ventilation and is able to maintain oxygen saturation at greater than 90%. In this situation, rapid ablation of the patient’s own respiratory drive by paralytics or general anesthesia may complicate airway management.
Awake intubation offers several advantages: 1) spontaneous ventilation is maintained, allowing gas exchange; 2) airway reflexes are preserved, decreasing the risk of aspiration; 3) muscle tone, and thus airway anatomy, are preserved; and 4) the significant adverse effects of pharmacological agents used in intubation are avoided.15,16 The awake approach can be used with virtually any intubation technique (surgical, direct laryngoscopy, blind nasal, fiberoptic, or an alternative device) and it is facilitated with topical or local anesthesia.
Difficult Direct Laryngoscopy and Intubation. The best laryngoscopic view is achieved by optimal positioning of the patient using techniques designed to maximize visualization of the vocal cords. For direct laryngoscopy, the patient is positioned to align the oral, pharyngeal, and laryngeal axes. If the glottic opening is not in view, it may be augmented by external laryngeal manipulation or by the backward, upward, rightward pressure-laryngeal displacement (BURP) maneuver.17,18 This maneuver can improve the laryngoscope view by at least one grade and should be the initial response to every laryngoscopic intubation. If intubation is unsuccessful after three attempts by the most experienced physician, the airway is considered failed.
The Failed Airway. Patients with failed airways have been anesthetized, and intubation attempts were unsuccessful. These patients are then placed into one of two subtypes: 1) mask ventilation is adequate or 2) mask ventilation is inadequate (the "cannot intubate/cannot ventilate" patient). If securing a surgical airway may be difficult or not immediately available, the esophageal-tracheal Combitube or laryngeal mask airway (LMA) may be used.19 (See Figure 6.) There are no strict criteria for the use of a specific nonsurgical device in a specific situation, nor has one proven better than another.3 The choice depends on the individual case and on the experience of the airway manager.
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Laryngeal Mask Airway (LMA)
The LMA (Laryngeal Mask Company, Ltd.) is an airway management device intended as an alternative to the face mask. It was introduced in 1988 in the United Kingdom and became available in the United States in 1992. It is most commonly used for airway control during routine anesthesia delivery in the operating room. More recently, it has been applied in prehospital and emergency settings. Properly trained health care professionals (paramedics, emergency medicine physicians) can place the LMA rapidly and reliably (approximately 20 seconds). This can be accomplished faster than placement of endotracheal tube (ETT) during direct laryngoscopy. Studies have estimated that as few as 1 in 880,000 patients without a gross anatomic anomaly cannot be ventilated with an LMA.20
The LMA is made primarily of medical-grade, latex-free silicone rubber. It can be used a maximum of 40 times before being discarded. It has three main components: 1) an airway tube; 2) a mask; and 3) a mask inflation line. (See Figure 7.) The large-bore airway tube has a 15 mm standard male adapter. The other end is fitted with a specially shaped cuff that is inflated and deflated via a valve on the end of the inflation line. The mask is designed to conform to the contours of the hypopharynx, with its lumen facing the laryngeal opening. The LMA is a minimally stimulating and invasive device. When inserted fully and correctly, the LMA tip occupies the entire hypopharynx and rests against the upper esophageal sphincter behind the cricoid cartilage at the approximate level of the sixth to seventh cervical vertebrae. The sides of the device face into the pyriform fossae, and the upper border rests against the base of the tongue. (See Figure 8.)
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There have been no reports of death directly attributable to the LMA. The incidence of aspiration is low (~2:10,000),21 which is comparable to the incidence of aspiration associated with standard endotracheal intubation.
Indications. The LMA is a method of establishing a clear airway during resuscitation of an unconscious patient whose glossopharyngeal and laryngeal reflexes are absent and who requires ventilation. The LMA should be used when tracheal intubation is precluded by lack of available expertise or equipment and when tracheal intubation attempts have failed. Placement of the LMA appears to be unrelated to the Mallamapti score and is unaffected by manual inline traction or the presence of a hard cervical collar. Since the distal end of the LMA faces the opening of the larynx, it can be used as a guide to fiberoptic visualization of the larynx and trachea while ventilation of the patient is maintained. Computed axial tomography (CAT) scans and magnetic resonance imaging (MRI) have been performed successfully while LMAs were in place.
The LMA comes in seven sizes. (See Table 3.) The standard device, for multiple (up to 40) uses, is cleaned with mild soap, water, and standard steam autoclaving. The cost of the standard LMA is approximately $240. Single-use LMAs also are available at a cost of about $36.
| Table 3. LMA Sizes and Patient Sizes | |
| LMA size | Patient |
| 1 | Neonates/infants up to 5 kg |
| 1 1/2 | Infants between 5 and 10 kg |
| 2 | Infants/children between 10 and 20 kg |
| 2 1/2 | Children between 20 and 30 kg |
| 3 | Children heavier than 30 kg and small adults |
| 4 | Normal and large adults |
| 5 | Large adults |
Contraindications. The LMA is ineffective for prolonged positive-pressure ventilation in the presence of high pulmonary pressures. The laryngeal seal may not be sufficient to allow prolonged positive pressure in patients with abnormal lungs, and gastric distention will ensue. Although the LMA does not protect against aspiration of gastric contents, this was not a complication in several studies of prehospital emergency personnel treating patients with full stomachs.21
LMA-Fastrach. The LMA-Fastrach is an advanced type of LMA designed to facilitate tracheal intubation with an endotracheal tube (ETT). It permits single-handed insertion from any position without moving the patient’s head and neck from a neutral position. Its rigid, anatomically curved airway tube (made of steel) is wide enough to accept a cuffed 8 mm ETT and short enough to ensure passage of the ETT cuff beyond the vocal cords. The tube is fitted with a rigid handle to facilitate one-handed insertion, removal, and adjustment of the device’s position. An epiglottic elevating bar in the mask lifts the epiglottis anteriorly and allows the ETT to pass into the trachea. (See Figure 9.)
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The manufacturer recommends use of a dedicated straight 8 mm cuffed silicone tube for intubation through the device for the best results. (See Figure 10.) The success rate as a ventilatory device is comparable to that of the standard LMA (> 98%). The success rate as a blind intubation guide can be as high as 99%, and intubation usually is successful on the first attempt.22,23
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The intubation LMA (ILMA) allows ventilation to continue during intubation attempts, thereby preventing hypoxemia. A high anterior larynx may facilitate alignment of the ILMA tube and glottic aperture. No movement of the cervical spine is required for intubation. Placement of the ILMA and intubation are blind techniques (although a fiberoptic scope can be used for placement of the ETT); therefore, accessory equipment is not required and placement is not affected by heavy secretions or blood, which may impair fiberoptic techniques. Once intubation has been accomplished and the ETT cuff is inflated, the LMA-Fastrach can be removed while the ETT is kept in place using the flexible stabilizing rod as a guide.
The LMA-Fastrach is available in three sizes. (See Table 4.) The cost is $500 for each device or $1,300 for the complete set. Like the standard LMA, the LMA-Fastrach can be used as many as 40 times and is cleaned with mild soap, water, and steam autoclaving.
| Table 4. LMA-Fastrach Sizes and Patient Sizes | |
| Size | Patient |
| 3 | Small adults |
| 4 | Normal adults |
| 5 | Large adults |
References
1. Caplan RA, Benumof JL, Berry FA, et al. Practice guidelines for management of the difficult airway: A report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology 1993;78:597-602.
2. Crosby ET, Cooper MR, Douglas MJ, et al. The unanticipated difficult airway with recommendations for management. Can J Anesth 1998;45:757-776.
3. Mascia MF, Mattasko MT. Emergency airway management by anesthesiologists. Anesthesiology 1993;79:A1054.
4. Mort TC. Incidence and risks leading to cardiac arrest following emergency intubation. Crit Care Med 1994;22:A137.
5. Murphy M, Walls RM. The difficult or failed airway. In: Walls RM, ed. Manual of Emergency Airway Management. 3rd edition. Wellesley, MA: Airway Management Education Center; 1999:51-64.
6. Clinton JE, Ruiz E. Emergency airway management procedures. In: Roberts JR, Hedges JR, eds. Clinical Procedures in Emergency Medicine. 2nd edition. Philadelphia: WB Saunders; 1991:chapter 1.
7. Wilson ME, Spiegelhalter D, Robertson JA, et al. Predicting difficult intubation. Br J Anaesth 1998;61:211-216.
8. Lewis M, Keramati S, Benumof JL, et al. What is the best way to determine oropharyngeal classification and mandibular space length to predict difficult laryngoscopy? Anesthesiology 1994;81: 69-75.
9. Matthew M, Hanna LS, Aldrete JA. Preoperative indices to anticipate difficult trachea intubation. Anesth Analg 1989;68:S187.
10. Mallampati SR, Gatt SP, Gugino LD, et al. A clinical sign to predict difficult tracheal intubation: A prospective study. Can Anaesth Soc J 1985;32:429-434.
11. Rocke DA, Murray WB, Rout CC, et al. Relative risk analysis of factors associated with difficult intubation in obstetric anesthesia. Anesthesiology 1992;77:67-73.
12. el-Ganzouri AR, McCarthy RT, Tuman KJ, et al. Preoperative airway assessment: Predictive value of a multivariate risk index. Anesth Analg 1996;82:1197-1204.
13. Tse JC, Rimm EB, Hussain A. Predicting difficult endotracheal intubation in surgical patients scheduled for general anesthesia: A prospective blind study. Anesth Analg 1995;81:254-258.
14. Burtner DD, Goodman M. Anesthetic and operative management of potential upper airway obstruction. Arch Otolaryngol 1978;104: 657-661.
15. Deem S, Bishop MJ. Evaluation and management of the difficult airway. Crit Care Clin 1995;11:1-27.
16. Benumof JL. Management of the difficult adult airway: With special emphasis on awake tracheal intubation. Anesthesiology 1991;75: 1087-1110.
17. Benumof JL, Cooper SD. Quantitative improvement in laryngoscopic view by optimal external laryngeal manipulation. J Clin Anesth 1996;8:136-140.
18. Takahata O, Kubota M, Mamiya K, et al. The efficacy of the "BURP" maneuver during a difficult laryngoscopy. Anesth Analg 1997;84:419-421.
19. Benumof J. Laryngeal mask airway and the ASA difficult airway algorithm. Anesthesiology 1996;84:686-699.
20. Parmet JL, Colonna-Romano P, Miller P. The role of the laryngeal mask airway (LMA) in the cannot intubate/cannot ventilate scenario. Anesthesiology 1997;87:A1026.
21. Brimacombe JR, Berry A. The incidence of aspiration associated with the laryngeal mask airway: A meta-analysis of published literature. J Clin Anesth 1993;7:297-305.
22. Rosenblatt WH, Murphy M. The intubating laryngeal mask: Use of a new ventilating-intubating device in the emergency department. Ann Emerg Med 1999;33:234-238.
23. Brain AI, Verghele C, Addy EY, et al. The intubating laryngeal mask. II: A preliminary clinical report of a new means of intubating the trachea. Br J Anesth 1997;79:704-709.
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