Chapter 3
Airway management is the cornerstone of resuscitation and is a defining skill for the specialty of emergency medicine. RSI with direct laryngoscopy is the most commonly used method for emergency intubation, but emergency airway management includes various intubation maneuvers, use of ancillary devices and rescue techniques when intubation fails.
Airway
A decision to intubate should be based on careful assessment of the patient with respect to three essential criteria： 1 failure to maintain or protect the airway, 2 failure of ventilation or oxygenation, and 3 the patients anticipated clinical course and likelihood of deterioration.
In most patients,intubation is technically easy and straightforward.Preintubation assessment should evaluate the patient for difficult intubation, difficult bag-mask ventilation BMV, difficult ventilation with an extraglottic deviceEGD, and difficult cricothyrotomy. Knowledge of all four domains is crucial to successful planning. Neuromuscular paralysis generally should be avoided in patients for whom a high degree of intubation difficulty is predicted, unless the administration of the NMBA is part of a planned approach to the difficult airway.
Difficult Direct Laryngoscopy： LEMONWhen direct laryngoscopy is planned, a standard screening process for difficulty should be undertaken with every patient. One such approach uses the mnemonic LEMON Box 3-1.
Box 3-1.LEMON Approach for Evaluation of Difficult Direct Laryngoscopy
L-Look Externally. The patient first should be examined for external markers of difficult intubation. For example, the severely bruised and bloodied face of a combative trauma patient, immobilized in a cervical collar on a spine board, might correctly invoke an immediate appreciation of anticipated difficult intubation.E-Evaluate 3-3-2. The second step in the evaluation of the difficult airway is to assess the patient''s anatomy to determine his or her suitability for direct laryngoscopy. Direct laryngoscopy requires the ability to visualize the glottis by direct vision through the mouth, using alignment of the oral, pharyngeal, and laryngeal axes.The 3-3-2 rule is an effective summary of these geometric evaluations. The 3-3-2 rule requires that the patient be able to place 3 of his or her own fingers between the open incisors, 3 of his or her own fingers along the floor of the mandible beginning at the mentum, and 2 fingers from the laryngeal prominence to the floor of the mandible Fig. 3-1. A patient with a receding mandible and high-riding larynx can be impossible to intubate using direct laryngoscopy.
M-Mallampati Scale. Oral access is assessed using the Mallampati scale Fig. 3-2. Visibility of the oral pharynx ranges from complete visualization, including the tonsillar pillars class Ⅰ, to no visualization at all, with the tongue pressed against the hard palate class Ⅳ. Class I and class Ⅱ predict adequate oral access, class Ⅲ predicts moderate difficulty, and class IV predicts a high degree of difficulty. A Mallampati score may have to be improvised with the direct laryngoscope blade as a tongue depressor in obtunded or uncooperative patients.O-Obstruction or Obesity. Upper airway supraglottic obstruction may make visualization of the glottis, or intubation itself, mechanically impossible. Conditions such as epiglottitis, laryngeal tumor, Ludwig''s angina, neck hematoma, or glottic polyps can compromise laryngoscopy, passage of ETT, BMV, or all three.Obese patients generally are more difficult to intubate.N-Neck Mobility. Neck mobility is assessed by having the patient flex and extend the head and neck through a full range of motion. Modest limitations of motion do not seriously impair laryngoscopy, but severe loss of motion, as can occur in ankylosing spondylitis or rheumatoid arthritis, may render laryngoscopy impossible. Cervical spine immobilization in trauma artificially reduces cervical spine mobility and predicts a more difficult laryngoscopy, but direct laryngoscopy is still highly successful in this group of patients.
Identification of a difficult intubation does not preclude use of an RSI technique. The crucial determination is whether the clinician judges that the patient has a reasonable likelihood of intubation success, despite the difficulties identified, and that ventilation with a bag and mask or an EGD will be successful in the event that intubation fails.
Difficult Bag-mask Ventilation： MOANSAttributes of difficult BMV have largely been validated and can be summarized with the mnemonic MOANS Box 3-2.Box 3-2.MOANS Mnemonic for Evaluationof Difficult Bag-Mask Ventilation
Mask seal Obstruction or obesity Aged No teeth Stiffness resistance to ventilationMask seal compromise or difficulty; Obstruction particularly supraglottic obstruction, but it can be present anywhere in the airway or Obesity because of redundant upper airway tissues,chest wall weight, and resistance of abdominal mass; advanced Age; edentulousness No teeth, which independently interferes with mask seal; and Stiffness or resistance to ventilation e.g., asthma, COPD, pulmonary edema, restrictive lung disease, term pregnancy may each contribute to increased difficulty with BMV.A new approach involves placing the mask inside the patients lower lip. This may limit air leak in patients without teeth and eliminates the risk of aspiration associated with dental prosthetics or rolled gauze Fig. 3-3.
Difficult Extraglottic Device Placement： RODSPlacement of an EGD, such as a laryngeal mask airway LMA, often can convert a cant intubate, cant oxygenate situation to a cant intubate, can oxygenate situation, which allows time for rescue of a failed airway.Difficulty achieving placement or ventilation with an EGD is predicted by the mnemonic RODS. Fortunately, if the clinician has already performed the LEMON and MOANS assessments, only the D for distorted anatomy remains to be evaluated Box 3-3. EGD are placed blindly and have either a mask or a balloon structure that, when inflated, obstructs the oropharynx proximally and the esophageal inlet distally, permitting indirect ventilation. Distorted upper airway anatomy can result in a poor seal and ineffective ventilation.Box 3-3.RODS Mnemonic for Evaluation of Difficult Extraglottic Device PlacementRestricted mouth opening Obstruction or obesity Distorted anatomy Stiffness resistance to ventilation
Difficult Cricothyrotomy： SMARTDifficult cricothyrotomy can be anticipated
whenever there is disturbance of the ability to locate and access the landmarks of the anterior airway via the neck and is remembered by the SMART mnemonic Box 3-4. Prior surgery; hematoma, tumor, or abscess; scarring; local trauma; obesity; edema; or subcutaneous air each has the potential to make cricothyrotomy more difficult. Perform an examination for the landmarks needed to perform cricothyrotomy as part of the preintubation difficult airway assessment of the patient.Box 3-4.SMART Mnemonic for Evaluation of Difficult Cricothyrotomy
Measurement and Incidence of Intubation DifficultyThe most widely used system for grading laryngoscopic view of the glottis is that of Cormack and Lehane CL, which grades laryngoscopy according to the extent to which laryngeal and glottic structures can be seen. In grade 1 laryngoscopy, all or nearly all of the glottic aperture is seen. Grade 2 laryngoscopy visualizes only a portion of the glottis arytenoid cartilages alone or arytenoid cartilages plus part of the vocal cords. Grade 3 laryngoscopy visualizes only the epiglottis. In grade 4 laryngoscopy, not even the epiglottis is visible.Emergency adult inpatient intubations, as many as 10% were considered difficult.The incidence of difficult ED intubations is likely much higher, with some estimates between 4% and 26%.A grade 1 view is associated with virtually 100% intubation success.
Confirmation of Endotracheal Tube PlacementThe most serious complication of endotracheal intubation is unrecognized esophageal intubation with resultant hypoxic brain injury. Although direct visualization of the ETT passing through the vocal cords generally is a reliable indicator of tracheal intubation, such clinical anatomic observations are fallible, and additional means are required to ensure correct placement of the tube within the trachea.Traditional methods, such as chest auscultation, gastric auscultation, bag resistance, exhaled volume, visualization of condensation within the ETT, and chest radiography, all are prone to failure as means of confirming tracheal intubation.Other clinical techniques are readily available for detecting tracheal or esophageal intubation.Immediately after intubation, the intubator should apply ETco2 detection device to the ETT and assess it through six manual ventilations. Disposable, colorimetric ETco2 detectors are highly reliable, convenient, and easy to interpret, indicating adequate CO2 detection by color change Fig. 3-4 and Fig. 3-5, see color illustrations. ETco2 detection is highly reliable in determining tracheal and esophageal intubation in patients with spontaneous circulaton.
ETco2 detection should be considered the primary means of ETT placement confirmation. Secondary means include physical examination findings, oximetry, and radiography. The examiner should auscultate both lung fields and the epigastric area. Pulse oximetry is useful in detecting esophageal intubation but may not show a decreasing SaO2 for several minutes after a failed intubation.The primary purpose of chest radiography is to ensure that the tube is well positioned below the cords and above the carina.In cases in which doubt persists, a fiberoptic scope can be passed through the ETT to identify tracheal rings.
Approach to IntubationAfter it is determined that the patient requires intubation, an approach must be planned.The approach is predicated on two key determinations that must be made before active airway management is begun Fig. 3-6. The first determination is whether the patient is in cardiopulmonary arrest or a state of near arrest and is predicted to be unresponsive to direct laryngoscopy. Such a patient is treated with the crash airway algorithm by an immediate intubation attempt without use of drugs, supplemented by a single, large dose of succinylcholine if the attempt to intubate fails and the patient is thought not to be sufficiently relaxed Fig. 3-7. Next, it must be determined whether the patient represents a difficult intubation as determined by the LEMON, MOANS, RODS, and SMART evaluations, and if so, the difficult airway algorithm is used Fig. 3-8.
RSI provides the safest and quickest method of achieving intubation for patients who require emergency intubation but who have neither a crash airway nor a difficult airway. After administration of the RSI drugs, intubation attempts are repeated until the patient is intubated or a failed intubation is identified. If more than one intubation attempt is required, SaO2 is monitored continuously, and if SaO2 falls to 90% or less, BMV is performed until SaO2 is recovered for another attempt. If the clinician cannot maintain SaO2 despite optimal use of BMV or an EGD, a failed airway exists. This is referred to as a cant intubate, cant oxygenate situation. In addition, if three attempts at laryngoscopy have been unsuccessful, a failed airway exists. The three failed laryngoscopy attempts are defined as attempts by an experienced clinician using the best possible patient positioning and technique. If available, video laryngoscopes should be used for one or all of these attempts. Also, if the clinician ascertains after even a single attempt that intubation will be impossible , and no alternative laryngoscope e.g., video laryngoscope is available, a failed airway is present. The failed airway is managed according to the failed airway algorithm Fig. 3-9.
The LEMON, MOANS, RODS, and SMART assessments provide a systematic framework to assist in identifying the potentially difficult airway.When preintubation evaluation has identified a potentially difficult airway, a different approach is used Fig. 3-8, NMBA should not be administered to a patient for intubation unless the clinician believes that 1 intubation is likely to be successful and 2 oxygenation via BMV or EGD is likely to be successful if a first intubation attempt does not succeed and oxygenation is required.In the difficult airway algorithm, the first determination is whether the operator is forced to act. If so, RSI drugs are given and, if intubation is not successful, the airway is considered failed and the operator moves immediately to the failed airway algorithm. In the vast majority of difficult airway situations, however, the operator is not forced to act, and the first step is to ensure that oxygenation is sufficient to permit a planned, orderly approach Fig. 3-8. If oxygenation is inadequate and cannot be made adequate by supplementation with bag and mask, the airway should be considered a failed airway. Whereas inadequate oxygenation should be defined on a case-by-case basis, SaO2 at or below 90% is the accepted threshold. Oxyhemoglobin saturations in the 80s might be considered adequate in some circumstances, particularly if the patient is chronically hypoxemic. When oxygenation is inadequate, the failed airway algorithm should be used because the predicted high degree of intubation difficulty, combined with failure to maintain SaO2, is analogous to the cant intubate, cant SaO2. When oxygenation is adequate, the next consideration is whether RSI is appropriate, on the basis of the operators assessment of the likelihood of 1 successful ventilation with a bag and mask or an EGD in the event intubation is unsuccessful, and 2 the likelihood of successful intubation by laryngoscopy. If the operator judges laryngoscopy likely to succeed and is confident of the ability to oxygenate even if intubation fails, then RSI is performed. In such cases a double setup can be used in which RSI is performed and preparations simultaneously are undertaken for rescue cricothyrotomy or another rescue technique. If RSI is not advisable and time allows, an awake technique can be used.Usually the technique involves sedation and topical anesthesia. The awake technique often is direct or flexible or rigid videolaryngoscopy, assisted by topical anesthesia and sedation comparable to that for a painful procedure. If the glottis is adequately visualized, the patient can be intubated at that time, or, in a stable difficult airway situation, the clinician may proceed with planned RSI, now assured of intubation success. If the awake laryngoscopy is unsuccessful, the patient is intubated with any of numerous techniques shown in the last box in Fig. 3-8. For each of these methods, the patient is kept breathing but variably sedated and anesthetized, and each of the methods results in placement of a cuffed ETT in the
trachea.
Failed AirwayManagement of the failed airway is dictated by an assessment of whether the patient can be oxygenated. If adequate oxygenation cannot be maintained, the rescue technique of first resort is cricothyrotomy Fig. 3-9. If an alternative device i.e., an EGD such as a LMA or Combitube is readily at hand, however, an attempt can be made to use it simultaneously with preparations for immediate cricothyrotomy, as long as initiation of cricothyrotomy is not delayed.Only a single attempt with the EGD is recommended in this circumstance.If adequate oxygenation is possible, several options are available for the failed airway. The fundamental difference in philosophy between the difficult airway and the failed airway is that the difficult airway is planned for, and the standard is to place a cuffed ETT in the trachea. The failed airway is not planned for, and the standard is to achieve an airway that provides adequate oxygenation to avert the immediate problem of hypoxic brain injury. Some of the devices used in the failed airway are temporary and do not provide airway protection.
Methods of IntubationFour methods are most common for intubationof the emergency patient, with RSI being the most frequently used in nonarrested patients.
Rapid Sequence IntubationRSI is the cornerstone of modern emergency airway management and is defined as the virtually simultaneous administration of a potent sedative induction agent and an NMBA, usually succinylcholine, for the purpose of endotracheal intubation. The central concept of RSI is to take the patient from the starting point e.g., conscious, breathing spontaneously to a state of unconsciousness with complete neuromuscular paralysis, then to achieve intubation without interposed assisted ventilation. The purpose of RSI is to avoid PPV until the ETT is placed correctly in the trachea with the cuff inflated. This requires a preoxygenation phase, during which the nitrogen reservoir in the functional residual capacity in the lungs is replaced with oxygen, permitting at least several minutes of apnea in the normal adult before oxygen desaturation to 90% ensues Fig. 3-10, see color illustration.Use of RSI also facilitates successful endotracheal intubation by causing complete relaxation of the patients musculature, allowing better access to the airway. Finally, RSI permits pharmacologic control of
Fig. 3-10 Desaturation time for apneic, fully preoxygenated patients. Children, patients with comorbidity, and obese patients desaturate much more rapidly than healthy, normal adults. The box on the lower right side of the graph depicts time to recovery from succinylcholine, which in almost all cases exceeds safe apnea time. Note also the precipitous decline of oxygen saturation from 90% to 0% for all groups.
the physiologic responses to laryngoscopy and intubation, mitigating potential adverse effects. These effects include further ICP increase in response to the procedure and to the sympathetic discharge resulting from laryngoscopy Box 3-5. RSI is a series of discrete steps, and every step should be planned Box 3-6.
Box 3-5.Pretreatment Agents for RSI
Box 3-6.The Seven Ps of RSI
Preparation. In the initial phase, the patient is assessed for intubation difficulty, and the intubation is planned, including determining dosages and sequence of drugs, tube size, and laryngoscope type, blade and size. Drugs are drawn up and labeled. All necessary equipment is assembled.At least one and preferably two good-quality intravenous lines should be established. Redundancy is always desirable in case of equipment or intravenous access failure.Preoxygenation. Administration of 100% oxygen for 3 min of normal, tidal volume breathing in a normal, healthy adult establishes an adequate oxygen reservoir to permit 8 min of apnea before oxygen desaturation to less than 90% occurs Fig. 3-10. Oxygen saturation monitors permit earlier detection of desaturation during laryngoscopy, but preoxygenation remains an essential step in RSI.Pretreatment. During this phase, drugs are admin istered 3 min before administration of the succinylcholine and induction agent to mitigate the effects of laryngoscopy and intubation on the patients presenting or comorbid conditions. Pretreatment focuses on three main objectives, in certain at-risk patients. The three groups of patients at risk are those with reactive airways disease, elevated ICP, or a cardiovascular or neurovascular condition for which an acute elevation in BP and HR might be hazardous Box 3-5.Paralysis with Induction. In this phase, a potent sedative agent is administered by rapid intravenous push in a dose capable of rapidly producing unconsciousness. This is immediately followed by rapid administration of an intubating dose of an NMBA, usually succinylcholine. It is usual to wait 45 s from the time the succinylcholine is given to allow sufficient paralysis to occur.Positioning. The patient should be positioned for intubation as consciousness is lost. Usually, positioning involves head extension, often with flexion of the neck on the body.Accordingly, Sellick''s maneuverapplication of firm backward-directed pressure over the cricoid cartilageshould be considered optional, applied selectively, and released or modified to improve laryngeal view or tube passage, as indicated. During this phase after administration of the induction agent and NMBA, although the patient becomes unconscious and apneic, BMV should not be initiated unless the oxygen saturation falls to 90%.Placement of Tube. Approximately 45 s after the administration of succinylcholine, the patient is relaxed sufficiently to permit laryngoscopy. The ETT is placed under direct visualization of the glottis. If the first attempt is unsuccessful, but oxygen saturation remains high, it is not necessary to ventilate the patient with a bag and mask between intubation attempts. If the oxygen saturation is approaching 90%, the patient may be ventilated briefly with a bag and mask between attempts to reestablish the oxygen reservoir. When BMV is performed, Sellicks maneuver is advisable to minimize passage of air into the stomach.Postintubation Management. Obtain a chest radiograph to confirm that mainstem intubation has not occurred and to assess the lungs. In general, long-acting NMBAe.g., pancuronium, vecuronium are avoided and the focus is on optimal management using opioid analgesics and sedative agents to facilitate mechanical ventilation. An adequate dose of a benzodiazepine e.g., midazolam 0.1-0.2 mgkg intravenous and an opioid analgesic e.g., fentanyl 3-5 gkg intravenous, or morphine 0.2-0.3 mg kg intravenous is given to improve patient comfort and decrease sympathetic response to the ETT. Propofol infusion 5-50 gkgmin intravenous with supplemental analgesia is an effective method for managing intubated patients without hypotension or ongoing bleeding and is especially helpful for management of neurologic emergencies, as its clinical duration of action is very short
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