Airways and Emergency Airway Management

Chapter 30


Airways and Emergency Airway Management image




Airway management is an essential skill for the intensivist. A secure, patent airway facilitates respiratory gas exchange and clearance of orotracheal secretions, limits aspiration of orogastric contents, and can provide a route for the administration of humidified gases and some medications. Although the patient’s own anatomic airway may be sufficient to meet these needs, in the context of critical illness, invasive and non-invasive airway management techniques are often required. This encompasses familiarity with the equipment and standard techniques used for bag-valve mask ventilation, endotracheal (ET) tubes (Figure 30.1), ET intubation, and the pharmacologic agents that may be required to accomplish these maneuvers (Tables 30.1 and 30.2).





Emergency airway management in the intensive care unit (ICU) setting is potentially more technically difficult and hazardous than airway management in the elective setting. The difficult airway has been defined as the clinical situation in which a skilled operator experiences difficulty with mask ventilation, tracheal intubation, or both. When confronted with either an anticipated or unanticipated difficult airway, the intensivist should be familiar with methods of advanced or “rescue” airway management, including fiberoptic bronchoscopic intubation, laryngeal mask airway (LMA) or other blind-insertion devices, and emergent surgical airway access. Generally accepted predictors of difficult mask-ventilation or ET intubation are presented in Box 30.E1. image


Finally, the intensivist must be able to diagnose and resolve common and potentially life-threatening airway complications, including, but not limited to, mainstem or esophageal intubation, ET cuff leak or cuff herniation, ET tube obstruction, tracheostomy bleeding, and inadvertent extubation or decannulation.



Useful Drugs in Emergency Airway Management


Favorable conditions for airway management require judicious use of a variety of medications. Local anesthetics, sedative hypnotics, analgesics, and neuromuscular blockers in standard concentrations or prefilled syringes should be readily available in the ICU.



Local Anesthetics


Topical application or infiltration of local anesthetics can blunt airway reflexes and facilitate awake or semi-awake fiberoptic intubation by the oral or nasopharyngeal route. Lidocaine is used most commonly and is often combined with a vasoconstrictor designed to constrict mucosal blood vessels and minimize bleeding. Local anesthetics may be delivered topically using a standard nebulizer, a curved atomizer, an aerosol spray, or via soaked pledgets. The glossopharyngeal and laryngeal nerves may also be blocked by local infiltration, and the upper airways may be anesthetized using a transtracheal approach. Alternatively, the injection port of the bronchoscope may be used to deliver local anesthetic agents directly to the larynx as the scope is advanced into the airway.


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BOX 30.E1   Risk Factors Associated with a Difficult Airway






Adapted from Lavery GG, McCloskey BV: The difficult airway in adult critical care. Crit Care Med 36:2163-2173, 2008.


Safe use of local anesthetics depends on their proper dosing, appropriate administration, knowledge of maximum allowed dose, and signs of toxicity. Early signs of overdose include a metallic taste in the mouth and tinnitus. Higher doses may precipitate seizures or intractable cardiac arrhythmias.




Hypnotic Agents, Sedatives, and Neuromuscular Blockers


A variety of hypnotic agents, commonly used to induce general anesthesia in the operating room, can also be used to facilitate ET intubation in the ICU. In general these agents are selected for their rapid onset and short duration of action. Key properties and doses are presented in Table 30.1. To varying degrees, all of these agents can worsen hypotension in critically ill patients who are in shock, receiving pressors, or severely hypovolemic. Other agents, such as fentanyl, ketamine, or midazolam, can be used in these clinical circumstances and are favored during conscious sedation for semi-awake intubation or bronchoscopy. In order to produce favorable intubating conditions, hypnotic induction agents are frequently used in conjunction with a neuromuscular blocker. Since its introduction in the 1950s, succinylcholine has been the agent of choice for emergency intubation because of its rapid onset and short duration of action. Rocuronium, which approaches the rapid onset of succinylcholine without its numerous adverse effects, has gained favor. Table 30.2 lists dosing, adverse effects, and clinical considerations for the use of neuromuscular blockers for intubation.



Gastric Aspiration Precautions


Patients requiring urgent or emergent intubation in the ICU may have a full stomach, and in the setting of trauma or critical illness nearly all patients will have delayed gastric emptying, impaired protective physiologic mechanisms, and diminished airway reflexes. Accordingly, precautions should be taken against the aspiration of orogastric contents. In patients considered to be at high risk for urgent intubation, enteric feeding should be postponed, and gastric tubes, if present, should be suctioned. To decrease gastric pH, some clinicians advocate prophylactic premedication with nonparticulate antacids or histamine-receptor antagonists. Metoclopramide, a dopaminergic antagonist that increases lower esophageal sphincter tone and stimulates upper gastrointestinal motility, may also be used to promote gastric emptying. First described by Sellick in 1961 and widely accepted despite limited data supporting its efficacy, the application of cricoid pressure has been advocated as a means of preventing passive regurgitation of gastric contents. Although randomized controlled trials are lacking, rapid sequence induction (RSI) has also gained widespread acceptance among U.S. anesthesiologists and emergency department (ED) physicians. The principal aim of RSI is to reduce the time interval between loss of consciousness and intubation of the trachea while avoiding positive pressure ventilation of the unprotected airway. Standard RSI includes preoxygenation with 100% oxygen, administration of a rapid-onset and preferably short-acting induction agent and neuromuscular blocker, application of cricoid pressure, and avoidance of positive pressure ventilation until inflation of the ET cuff. Many providers favor the use of a “modified RSI” in which a gentle postinduction positive pressure breath is provided prior to administration of neuromuscular blockade to demonstrate that mask ventilation will be possible.



Equipment for Emergency Airway Management


An ever-expanding arsenal of rescue devices and airway adjuncts are available for emergency airway management. The devices and equipment reviewed here should be familiar to every intensivist, and most should be immediately available in the ICU. It bears repeating, however, that effective use of these tools requires practical, supervised experience in the ICU, ED, trauma bay, or operating room.



Tools for Mask Ventilation


Effective ventilation by face mask is a fundamental skill that every intensivist should master. Face mask ventilation may be lifesaving, but is sometimes underemphasized or taken for granted. Every patient room in the ICU should be stocked with a face mask and self-inflating (bag-valve mask) manual resuscitation bag that can be readily connected to wall oxygen.


Difficulty in achieving satisfactory mask ventilation, as evidenced by cyanosis, failure of chest rise, decreasing oxygen saturation, or the absence of end tidal CO2, may be related to inadequate mask seal, obstruction of the patient’s airway, or both. Repositioning the patient’s head to achieve a sniffing position, applying a jaw thrust maneuver, or using a two-handed mask grip may improve conditions. Additionally, oral or nasopharyngeal airways may be inserted to maintain upper airway patency. Oral airways are particularly useful in relieving airway obstruction in obese or edentulous patients. These airways are made of hard plastic and should not be used as bite blocks, as their long-term use may cause lingual nerve injury. Nasopharyngeal airways are generally soft, flexible rubber and should be lubricated before insertion to prevent excessive nasopharyngeal trauma or bleeding. They are contraindicated in patients with coagulopathy or significant facial or skull-base trauma.



Tools for Laryngoscopy


The modern laryngoscope consists of a standardized handle, a light source, and a curved or straight blade designed to displace the tongue, illuminate the larynx, and guide an ET tube through the vocal cords and into the trachea. Numerous blade designs have been introduced over the years. In adult patients, however, the Miller and MacIntosh blades remain the most commonly used. The long, straight, and relatively narrow Miller blade has a gently curved tip and is designed to elevate the epiglottis directly. Many operators prefer this blade in cases of limited mouth opening as it allows greater anterior displacement of the mandible. The MacIntosh blade is curved, wider, and has a perpendicular flange along the underside of the blade’s left side, designed to sweep the tongue to the left and out of the operator’s field of view. The tip of the MacIntosh blade is designed to rest in the vallecula, thereby elevating the epiglottis indirectly. Both blades are available in multiple sizes. Most adults can be intubated using a Miller 2 or MacIntosh 3.


Several rigid indirect laryngoscopes are also available. These devices transmit a close-up view of the glottis from the blade tip to an eyepiece or liquid crystal display (LCD) screen using fiberoptic technology. The principal advantage of these scopes is that they eliminate several of the variables that may result in difficult direct laryngoscopy. In particular, they allow indirect visualization of the vocal cords with minimal need to sublux the jaw or extend the neck. This may be particularly important in patients with limited mobility of the mandible or cervical spine.


In the case of a known or anticipated difficult airway, semi-awake flexible fiberoptic bronchoscopy is the technique of choice for many practitioners. Sedation is minimized to preserve spontaneous respiratory drive and airway reflexes are blunted by topical or local anesthetics. An ET tube is then loaded over a flexible fiberoptic bronchoscope, inserted into the oropharynx via oral airway or bite block, and advanced through the vocal cords using optical guidance. A combination of tip flexion and scope rotation allows three-dimensional navigation.

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Jul 7, 2016 | Posted by in CRITICAL CARE | Comments Off on Airways and Emergency Airway Management

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