Airway Management

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Key Concepts

Improper face mask technique can result in continued deflation of the anesthesia reservoir bag when the adjustable pressure-limiting valve is closed, usually indicating a substantial leak around the mask. In contrast, the generation of high breathing-circuit pressures with minimal chest movement and breath sounds implies an obstructed airway.
The laryngeal mask airway partially protects the larynx from pharyngeal secretions (but not gastric regurgitation), and it should remain in place until the patient has regained airway reflexes.
After insertion of a tracheal tube (TT), the cuff is inflated with the least amount of air necessary to create a seal during positive-pressure ventilation to minimize the pressure transmitted to the tracheal mucosa.
Although the persistent detection of CO2 by a capnograph is the best confirmation of tracheal placement of a TT, it cannot exclude bronchial intubation. The earliest manifestation of bronchial intubation is an increase in peak inspiratory pressure.
After intubation the cuff of a TT should not be felt above the level of the cricoid cartilage, because a prolonged intralaryngeal location may result in postoperative hoarseness and increases the risk of accidental extubation.
Preventing unintentional esophageal intubation depends on direct visualization of the tip of the TT passing through the vocal cords, careful auscultation for the presence of bilateral breath sounds and the absence of gastric gurgling, analysis of exhaled gas for the presence of CO2 (the most reliable method), chest radiography, or use of fiberoptic bronchoscopy.
Clues to the diagnosis of bronchial intubation include unilateral breath sounds, unexpected hypoxia with pulse oximetry (unreliable with high inspired oxygen concentrations), inability to palpate the TT cuff in the sternal notch during cuff inflation, and decreased breathing-bag compliance (high peak inspiratory pressures).
The large negative intrathoracic pressures generated by a struggling patient in laryngospasm can result in the development of negative-pressure pulmonary edema even in healthy young adults.

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Airway Management: Introduction

Expert airway management is an essential skill for an anesthesiologist. This chapter reviews the anatomy of the upper respiratory tract, describes the necessary equipment, presents techniques, and discusses complications of laryngoscopy, intubation, and extubation. Patient safety depends on a thorough understanding of each of these topics.

Anatomy

Other than rendering a patient insensible to pain, no characteristic better defines an anesthesiologist than the ability to "manage" an airway and a patient's breathing. Successful intubation, ventilation, cricothyrotomy, and regional anesthesia of the larynx require detailed knowledge of airway anatomy. There are two openings to the human airway: the nose, which leads to the nasopharynx (pars nasalis), and the mouth, which leads to the oropharynx (pars oralis). These passages are separated anteriorly by the palate, but they join posteriorly in the pharynx (Figure 5–1). The pharynx is a U-shaped fibromuscular structure that extends from the base of the skull to the cricoid cartilage at the entrance to the esophagus. It opens anteriorly into the nasal cavity, the mouth, the larynx, and the nasopharynx, oropharynx, and laryngopharynx (pars laryngea), respectively. The nasopharynx is separated from the oropharynx by an imaginary plane that extends posteriorly. At the base of the tongue, the epiglottis functionally separates the oropharynx from the laryngopharynx (or hypopharynx). The epiglottis prevents aspiration by covering the glottis—the opening of the larynx—during swallowing. The larynx is a cartilaginous skeleton held together by ligaments and muscle. The larynx is composed of nine cartilages (Figure 5–2): thyroid, cricoid, epiglottic, and (in pairs) arytenoid, corniculate, and cuneiform.

Figure 5–1.

Anatomy of the airway.

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Figure 5–2.

Cartilaginous structures comprising the larynx(Modified and reproduced, with permission, from Mayo Clinic and Foundation from O'Connell F: Management of the airway and endotracheal intubation. In: Critical Care Medicine: Perioperative Management. Murray MJ, Coursin DB, Pearl RG, Prough DS [editors]. Lippincott-Raven Publishers, 1997.)

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The sensory supply to the upper airway is derived from the cranial nerves (Figure 5–3). The mucous membranes of the nose are innervated by the ophthalmic division (V1) of the trigeminal nerve anteriorly (anterior ethmoidal nerve) and by the maxillary division (V2) posteriorly (sphenopalatine nerves). The palatine nerves provide sensory fibers from the trigeminal nerve (V) to the superior and inferior surfaces of the hard and soft palate. The lingual nerve (a branch of the mandibular division [V3] of the trigeminal nerve) and the glossopharyngeal nerve (the ninth cranial nerve) provide general sensation to the anterior two-thirds and posterior third of the tongue, respectively. Branches of the facial nerve (VII) and glossopharyngeal nerve provide the sensation of taste to those areas, respectively. The glossopharyngeal nerve also innervates the roof of the pharynx, the tonsils, and the undersurface of the soft palate. The vagus nerve (the tenth cranial nerve) provides sensation to the airway below the epiglottis. The superior laryngeal branch of the vagus divides into an external (motor) nerve and an internal (sensory) laryngeal nerve that provide sensory supply to the larynx between the epiglottis and the vocal cords. Another branch of the vagus, the recurrent laryngeal nerve, innervates the larynx below the vocal cords and the trachea.

Figure 5–3.

Sensory nerve supply of the airway.

The muscles of the larynx are innervated by the recurrent laryngeal nerve with the exception of the cricothyroid muscle, which is innervated by the external (motor) laryngeal nerve, a branch of the superior laryngeal nerve. The posterior cricoarytenoid muscles abduct the vocal cords, whereas the lateral cricoarytenoid muscles are the principal adductors.

Phonation involves complex simultaneous actions by several laryngeal muscles. Damage to the motor nerves innervating the larynx leads to a spectrum of speech disorders (Table 5–1). Unilateral denervation of a cricothyroid muscle causes very subtle clinical findings. Bilateral palsy of the superior laryngeal nerve may result in hoarseness or easy tiring of the voice, but airway control is not jeopardized.

Table 5–1. The Effects of Laryngeal Nerve Injury on the Voice.

Nerve Effect of Nerve Injury Superior laryngeal nerve   Unilateral Minimal effects   Bilateral Hoarseness, tiring of voice Recurrent laryngeal nerve   Unilateral Hoarseness   Bilateral     Acute Stridor, respiratory distress     Chronic Aphonia Vagus nerve   Unilateral Hoarseness   Bilateral Aphonia

Unilateral paralysis of a recurrent laryngeal nerve results in paralysis of the ipsilateral vocal cord, causing a deterioration in voice quality. Assuming intact superior laryngeal nerves, acute bilateral recurrent laryngeal nerve palsy can result in stridor and respiratory distress because of the remaining unopposed tension of the cricothyroid muscles. Airway problems are less frequent in chronic bilateral recurrent laryngeal nerve loss because of the development of various compensatory mechanisms (eg, atrophy of the laryngeal musculature).

Bilateral injury to the vagus nerve affects both the superior and the recurrent laryngeal nerves. Thus, bilateral vagal denervation produces flaccid, midpositioned vocal cords similar to those seen after administration of succinylcholine. Although phonation is severely impaired in these patients, airway control is rarely a problem.

The blood supply of the larynx is derived from branches of the thyroid arteries. The cricothyroid artery arises from the superior thyroid artery itself, the first branch given off from the external carotid artery, and crosses the upper cricothyroid membrane, which extends from the cricoid cartilage to the thyroid cartilage. The superior thyroid artery is found along the lateral edge of the cricothyroid membrane. When planning a cricothyrotomy, the anatomy of the cricothyroid artery and the thyroid artery should be considered but rarely should affect the practice. It is best to stay in the midline, midway between the cricoid and thyroid cartilages.

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Equipment

Oral & Nasal Airways

Loss of upper airway muscle tone (eg, weakness of the genioglossus muscle) in anesthetized patients allows the tongue and epiglottis to fall back against the posterior wall of the pharynx. Repositioning the head or a jaw thrust is the preferred technique for opening the airway. To maintain the opening, though, an artificial airway can be inserted through the mouth or nose to create an air passage between the tongue and the posterior pharyngeal wall (Figure 5–4). Awake or lightly anesthetized patients may cough or even develop laryngospasm during airway insertion if laryngeal reflexes are intact. Placement of an oral airway is sometimes facilitated by suppressing airway reflexes and, in addition, sometimes by depressing the tongue with a tongue blade. Adult oral airways typically come in small (80 mm [Guedel No. 3]), medium (90 mm [Guedel No. 4]), and large (100 mm [Guedel No. 5]) sizes.

Figure 5–4.

A: The oropharyngeal airway in place. The airway follows the curvature of the tongue, pulling it and the epiglottis away from the posterior pharyngeal wall and providing a channel for air passage. B: The nasopharyngeal airway in place. The airway passes through the nose and extends to just above the epiglottis.(Modified and reproduced, with permission, from Face masks and airways. In: Understanding Anesthesia Equipment, 4th ed. Dorsch JA, Dorsch SE (editors). Williams & Wilkins, 1999.)

The length of a nasal airway can be estimated as the distance from the nares to the meatus of the ear, and should be approximately 2–4 cm longer than oral airways. Because of the risk of epistaxis, nasal airways should not be used in anticoagulated patients or in children with prominent adenoids. Also, nasal airways should not be used in any patient who has a basilar skull fracture. Any tube inserted through the nose (eg, nasal airways, nasogastric catheters, nasotracheal tubes) should be lubricated and advanced along the floor of the nasal passage, not as novices attempt to do—toward the apex of the nasal passage to avoid traumatizing the turbinates or the roof of the nose. Nasal airways are usually better tolerated than oral airways in lightly anesthetized patients.

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Face Mask Design & Technique

The use of a face mask can facilitate delivery of oxygen or of an anesthetic gas from a breathing system to a patient by creating an airtight seal with the patient's face (Figure 5–5). The rim of the mask is contoured and conforms to a variety of facial features. The mask's 22-mm orifice attaches to the breathing circuit of the anesthesia machine through a right-angle connector. Several mask designs are available. Transparent masks allow observation of exhaled humidified gas and immediate recognition of vomiting. Black rubber masks are pliable enough to adapt to uncommon facial structures. Retaining hooks surrounding the orifice can be attached to a head strap so that the mask does not have to be continually held in place. Some pediatric masks are specially designed to minimize apparatus dead space (Figure 5–6).

Figure 5–5.

Clear adult face mask.

Figure 5–6.

The Rendell–Baker–Soucek pediatric face mask has a shallow body and minimal dead space.

Effective ventilation requires both a gas-tight mask fit and a patent airway. Improper face mask technique can result in continued deflation of the anesthesia reservoir bag when the adjustable pressure-limiting valve is closed, usually indicating a substantial leak around the mask. In contrast, the generation of high breathing-circuit pressures with minimal chest movement and breath sounds implies an obstructed airway. Both these problems are usually resolved by proper technique.

If the mask is held with the left hand, the right hand can be used to generate positive-pressure ventilation by squeezing the breathing bag. The mask is held against the face by downward pressure on the mask body exerted by the left thumb and index finger (Figure 5–7). The middle and ring finger grasp the mandible to facilitate extension of the atlantooccipital joint. Finger pressure should be placed on the bony mandible and not on the soft tissues supporting the base of the tongue, which may obstruct the airway. The little finger is placed under the angle of the jaw and used to thrust the jaw anteriorly, the most important maneuver to allow ventilation to the patient.

Figure 5–7.

One-handed face mask technique.

In difficult situations, two hands may be needed to provide adequate jaw thrust and create a mask seal. Therefore, an assistant may be needed to squeeze the anesthesia bag. In such cases, the thumbs hold the mask down and the fingertips or knuckles displace the jaw forward (Figure 5–8). Obstruction during expiration may be due to excessive downward pressure from the mask or from a ball-valve effect of the jaw thrust. The former can be relieved by decreasing the pressure on the mask and the latter by releasing the jaw thrust during this phase of the respiratory cycle. It is often difficult to form an adequate mask fit with the cheeks of edentulous patients. Leaving dentures in place (not recommended) or packing the buccal cavities with gauze may help. Positive-pressure ventilation should normally be limited to 20 cm H2O to avoid stomach inflation.

Figure 5–8.

A difficult airway can often be managed with a two-handed technique.

Most patients' airways can be maintained with a face mask, and an oral or nasal airway. Mask ventilation for long periods may result in pressure injury to branches of the trigeminal or facial nerves. Because of the absence of positive airway pressures during spontaneous ventilation, only minimal downward force on the face mask is required to create an adequate seal. If the face mask and mask straps are used for extended periods, the position should be regularly changed to prevent injury. Care should be used to avoid pressure on the eye, and the eyes should be taped shut to minimize the risk of corneal abrasions.

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Laryngeal Mask Design & Technique

The laryngeal mask airway (LMA) is being increasingly used in place of a face mask or TT during administration of an anesthetic, to facilitate ventilation and passage of a TT in a patient with a difficult airway, and to aid in ventilation during fiberoptic bronchoscopy as well as placement of the bronchoscope. The LMA has surpassed the Combitube as a preferred device to manage a difficult airway. Four types of LMAs are commonly used: the reusable LMA, an improved disposable LMA, the ProSeal LMA that has an orifice through which a nasogastric tube can be inserted and that facilitates positive-pressure ventilation, and a Fastrach LMA that facilitates intubating patients with difficult airways.
An LMA consists of a wide-bore tube whose proximal end connects to a breathing circuit with a standard 15-mm connector, and whose distal end is attached to an elliptical cuff that can be inflated through a pilot tube. The deflated cuff is lubricated and inserted blindly into the hypopharynx so that, once inflated, the cuff forms a low-pressure seal around the entrance to the larynx. This requires an anesthetic depth slightly greater than required for the insertion of an oral airway. Although insertion is relatively simple (Figure 5–9), proper attention to detail will improve the success rate (Table 5–2). An ideally positioned cuff is bordered by the base of the tongue superiorly, the pyriform sinuses laterally, and the upper esophageal sphincter inferiorly. If the esophagus lies within the rim of the cuff, gastric distention and regurgitation become a distinct possibility. Anatomic variations prevent adequate functioning in some patients. However, if an LMA is not functioning properly after attempts to improve the "fit" of the LMA have failed, most practitioners will try another LMA one size larger or smaller. Because down-folding of the epiglottis or distal cuff accounts for many failures, LMA insertion under direct visualization with a laryngoscope or fiberoptic bronchoscope (FOB) may prove beneficial in difficult cases. Likewise, partial cuff inflation prior to insertion may be helpful. The shaft can be secured with tape, as a TT would be. The LMA partially protects the larynx from pharyngeal secretions (but not gastric regurgitation), and it should remain in place until the patient has regained airway reflexes. This is usually signaled by coughing and mouth opening on command. The reusable LMA, which is autoclavable, is made of silicone rubber (ie, it is latex free) and is available in many sizes (Table 5–3).

Table 5–2. Successful Insertion of a Laryngeal Mask Airway Depends Upon Attention to Several Details.

1. Choose the appropriate size (Table 5–3) and check for leaks before insertion. 2. The leading edge of the deflated cuff should be wrinkle-free and facing away from the aperture (Figure 5–9A). 3. Lubricate only the back side of the cuff. 4. Ensure adequate anesthesia (regional nerve block or general) before attempting insertion. Propofol with opioids provide superior conditions compared with thiopental. 5. Place patient's head in sniffing position (Figure 5–9B and Figure 5–16). 6. Use your index finger to guide the cuff along the hard palate and down into the hypopharynx until an increased resistance is felt (Figure 5–9C). The longitudinal black line should always be pointing directly cephalad (ie, facing the patient's upper lip). 7. Inflate with the correct amount of air (Table 5–3). 8. Ensure adequate anesthetic depth during patient positioning. 9. Obstruction after insertion is usually due to a down-folded epiglottis or transient laryngospasm. 10. Avoid pharyngeal suction, cuff deflation, or laryngeal mask removal until the patient is awake (eg, opening mouth on command).

Table 5–3. A Variety of Laryngeal Masks with Different Cuff Volumes Are Available for Different Sized Patients.

Mask Size Patient Size Weight (kg) Cuff Volume (mL) 1 Infant <6.5 2–4 2 Child 6.5–20 Up to 10 21/2 Child 20–30 Up to 15 3 Small adult >30 Up to 20 4 Normal adult <70 Up to 30 5 Larger adult >70 Up to 30

Figure 5–9.

A: The laryngeal mask ready for insertion. The cuff should be deflated tightly with the rim facing away from the mask aperture. There should be no folds near the tip. B: Initial insertion of the laryngeal mask. Under direct vision, the mask tip is pressed upward against the hard palate. The middle finger may be used to push the lower jaw downward. The mask is pressed forward as it is advanced into the pharynx to ensure that the tip remains flattened and avoids the tongue. The jaw should not be held open once the mask is inside the mouth. The nonintubating hand can be used to stabilize the occiput. C: By withdrawing the other fingers and with a slight pronation of the forearm, it is usually possible to push the mask fully into position in one fluid movement. Note that the neck is kept flexed and the head extended. D: The laryngeal mask is grasped with the other hand and the index finger withdrawn. The hand holding the tube presses gently downward until resistance is encountered (Reproduced, with permission, from LMA North America.)

The LMA provides an alternative to ventilation through a face mask or TT (Table 5–4). Contraindications for the LMA include patients with pharyngeal pathology (eg, abscess), pharyngeal obstruction, full stomachs (eg, pregnancy, hiatal hernia), or low pulmonary compliance (eg, restrictive airways disease) requiring peak inspiratory pressures greater than 30 cm H2O. Traditionally, the LMA has been avoided in patients with bronchospasm or high airway resistance, but new evidence suggests that because it is not placed in the trachea, use of an LMA is associated with less bronchospasm than a TT. Although it is clearly not a substitute for tracheal intubation, the LMA has proven particularly helpful as a temporizing measure in patients with difficult airways (those who cannot be ventilated or intubated) because of its ease of insertion and relatively high success rate (95–99%). It has been used as a conduit for an intubating stylet (eg, gum-elastic bougie), ventilating jet stylet, flexible FOB, or small-diameter (6.0-mm) TT. Several LMAs are available that have been modified to facilitate placement of a larger TT with or without the use of an FOB. Insertion can be performed under topical anesthesia and bilateral superior laryngeal nerve blocks if the airway must be secured while the patient is awake.

Table 5–4. Advantages and Disadvantages of the Laryngeal Mask Airway Compared with Face Mask Ventilation or Tracheal Intubation.1

Advantages Disadvantages Compared with face mask Hands-free operation More invasive Better seal in bearded patients More risk of airway trauma Less cumbersome in ENT surgery Requires new skill Often easier to maintain airway Deeper anesthesia required Protects against airway secretions Requires some TMJ mobility Less facial nerve and eye trauma N2O diffusion into cuff Less operating room pollution Multiple contraindications Compared with tracheal intubation Less invasive Increased risk of gastrointestinal aspiration Very useful in difficult intubations Less safe in prone or jackknife positions Less tooth and laryngeal trauma Limits maximum PPV Less laryngospasm and bronchospasm Less secure airway Does not require muscle relaxation Greater risk of gas leak and pollution Does not require neck mobility Can cause gastric distention No risk of esophageal or endobronchial intubation

1ENT, ear, nose, and throat; TMJ, temporomandibular joint; PPV, positive pressure ventilation.

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Esophageal–Tracheal Combitube Design & Technique

The esophageal–tracheal Combitube consists of two fused tubes, each with a 15-mm connector on its proximal end. The longer blue tube has an occluded distal tip that forces gas to exit through a series of side perforations. The shorter clear tube has an open tip and no side perforations. The Combitube is usually inserted blindly through the mouth and advanced until the two black rings on the shaft lie between the upper and lower teeth. The Combitube has two inflatable cuffs, a 100-mL proximal cuff and a 15-mL distal cuff, both of which should be fully inflated after placement. The distal lumen of the Combitube usually comes to lie in the esophagus approximately 95% of the time so that ventilation through the longer blue tube will force gas out of the side perforations and into the larynx. The shorter, clear tube can be used for gastric decompression. Alternatively, if the Combitube enters the trachea, ventilation through the clear tube will direct gas into the trachea. Although the Combitube is still listed as an option for managing a difficult airway in the Advanced Cardiac Life Support algorithm, it is rarely used by anesthesiologists who prefer an LMA or other devices for managing patients with difficult airways.

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Tracheal Tubes

TTs can be used to deliver anesthetic gases directly into the trachea and allow the most control of ventilation and oxygenation. Standards govern TT manufacturing (American National Standard for Anesthetic Equipment; ANSI Z–79). TTs are most commonly made from polyvinyl chloride. In the past, TTs were marked "I.T." or "Z–79" to indicate that they had been implant tested to ensure nontoxicity. The shape and rigidity of TTs can be altered by inserting a stylet. The patient end of the tube is beveled to aid visualization and insertion through the vocal cords. Murphy tubes have a hole (the Murphy eye) to decrease the risk of occlusion should the distal tube opening abut the carina or trachea (Figure 5–10).

Figure 5–10.

Murphy tracheal tube.

Resistance to airflow depends primarily on tube diameter, but is also affected by tube length and curvature. TT size is usually designated in millimeters of internal diameter or, less commonly, in the French scale (external diameter in millimeters multiplied by 3). The choice of tube diameter is always a compromise between maximizing flow with a large size and minimizing airway trauma with a small size (Table 5–5).

Table 5–5. Oral Tracheal Tube Size Guidelines.

Age Internal Diameter (mm) Cut Length (cm) Full-term infant 3.5 12 Child Adult   Female 7.0–7.5 24   Male 7.5–9.0 24

Most adult TTs have a cuff inflation system consisting of a valve, pilot balloon, inflating tube, and cuff (Figure 5–10). The valve prevents air loss after cuff inflation. The pilot balloon provides a gross indication of cuff inflation. The inflating tube connects the valve to the cuff and is incorporated into the tube's wall. By creating a tracheal seal, TT cuffs permit positive-pressure ventilation and reduce the likelihood of aspiration. Uncuffed tubes are usually used in children to minimize the risk of pressure injury and postintubation croup (see Chapter 44).

There are two major types of cuffs: high pressure (low volume) and low pressure (high volume). High-pressure cuffs are associated with more ischemic damage to the tracheal mucosa and are less suitable for intubations of long duration. Low-pressure cuffs may increase the likelihood of sore throat (larger mucosal contact area), aspiration, spontaneous extubation, and difficult insertion (because of the floppy cuff). Nonetheless, because of their lower incidence of mucosal damage, low-pressure cuffs are more commonly recommended.

Cuff pressure depends on several factors: inflation volume, the diameter of the cuff in relation to the trachea, tracheal and cuff compliance, and intrathoracic pressure (cuff pressures increase with coughing). Cuff pressure may rise during general anesthesia as a result of the diffusion of nitrous oxide from the tracheal mucosa into the TT cuff.

TTs have been modified for a variety of specialized applications. Flexible, spiral-wound, wire-reinforced TTs (armored tubes) resist kinking and may prove valuable in some head and neck surgical procedures or in the prone patient. If an armored tube becomes kinked from extreme pressure (eg, an awake patient biting it), however, the lumen will tend to remain occluded and the tube will need replacement. Other specialized tubes include microlaryngeal tubes (see Chapter 39), RAE preformed tubes (see Figures 39–1 and 39–3), and double-lumen TTs (see Figure 24–8). There is now a Parker FlexTip TT that has a tapered distal opening that is more elastic. All TTs have an embedded line that is opaque on radiographs to allow visualization in situ.

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Rigid Laryngoscopes

A laryngoscope is an instrument used to examine the larynx and to facilitate intubation of the trachea. The handle usually contains batteries to light a bulb on the blade tip (Figure 5–11), or alternately to power a fiberoptic bundle that terminates at the tip of the blade. Light from a fiberoptic bundle tends to be more direct and less diffuse. Also, laryngoscopes with fiberoptic light bundles in their blades can be made magnetic resonance imaging (MRI) compatible. The Macintosh and Miller blades are the most popular curved and straight designs, respectively, in the United States. The choice of blade depends on personal preference and patient anatomy. Because no blade is perfect for all situations, the clinician should become familiar and proficient with a variety of blade designs (Figure 5–12).

Figure 5–11.

A rigid laryngoscope.

Figure 5–12.

An assortment of laryngoscope blades.

Specialized Laryngoscopes

In the past 15 years, two new laryngoscopes have been developed that help the anesthesiologist secure the airway in a difficult-airway patient—the Bullard laryngoscope and the Wu laryngoscope (Figure 5–13). Both have fiberoptic light sources and curved blades with elongated tips and were designed to help see the glottic opening in patients with large tongues or whose glottic opening is very anterior. Many anesthesiologists believe that these devices are preferred in patients in whom a difficult airway is anticipated. However, as with other devices used to manage patients' airways, expertise in their use should be gained in normal patients before using it urgently or emergently in a patient with a difficult airway.

Figure 5–13.

Specialized laryngoscopic blades for managing a difficult airway. A: Fully assembled Wu laryngoscope with a tracheal tube in the tracheal tube passage, a suction catheter in the tracheal tube lumen, and oxygen tubing connected to the oxygen port. B: Newer version (Elite) of the Bullard laryngoscope. The handle has been reshaped. There is a built-in focus adjustment in the eyepiece. On the viewing arm adjacent to the handle is a spring-loaded mechanism to hold the multifunctional stylet (Courtesy of Circon Acmi, a division of Circon Corp.)

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原帖由 BRUCE999 于 2008-10-6 14:22 发表

                               
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Key ConceptsImproper face mask technique can result in continued deflation of the anesthesia reservoir bag when the adjustable pressure-limiting valve is closed, usually indicating a substantial leak  ...

摩根第四版英文原版本论坛提供下载，欢迎大家同时对照学习。
但像楼上的这样贴出来起不到一点学习和讨论的作用。建议删除。

1001

有几个帖都这样，我也觉得这样挺累人的，不过可能对没金币的新人可能有点用，不如看看大家的意见再处理。

[ 本帖最后由 1001 于 2008-10-7 22:16 编辑 ]