气管插管 英文

Indications and ContraindicationsAny clinical situation in which a definitive airway is necessary and limited neck motion is permissible is an indication for orotracheal intubation. Many of these situations, including cardiac arrest, airway compromise i Indications and Contraindications Any clinical situation in which a definitive airway is necessary and limited neck motion is permissible is an indication for orotracheal intubation. Many of these situations, including cardiac arrest, airway compromise in infection and trauma, and airway obstruction are discussed in detail in Chapter 1 . Most orotracheal intubations are accomplished using a direct laryngoscope. An unstable cervical spine injury is a relative contraindication to direct laryngoscopy. Equipment Laryngoscope Facility in the use of the direct laryngoscope is a prerequisite for orotracheal intubation. Various adult and pediatric blade sizes are available. There are two basic blade designs-- curved (MacIntosh) and straight (Miller and Wisconsin). Slight variations in laryngoscopic technique follow from one's choice of blade design, which is often a matter of personal preference. The tip of the straight blade goes under the epiglottis and lifts it directly, whereas the curved blade fits into the vallecula and indirectly lifts the epiglottis via the hyoepiglottic ligament to expose the larynx. Special blades designed for the anterior larynx include the Siker and the Belscope (Avulunga Pty Ltd, New South Wales, Australia). Each blade type has advantages and disadvantages. The straight blade is usually a better choice in pediatric patients, in patients with an anterior larynx or a long floppy epiglottis, and in individuals whose larynx is fixed by scar tissue. It is less effective, however, in patients with prominent upper teeth, and it is more likely to break teeth. Use of the straight blade is also more often associated with laryngospasm due to its stimulation of the superior laryngeal nerve, which innervates the undersurface of the epiglottis. A straight blade may inadvertently be advanced into the esophagus and initially present one with unfamiliar anatomy until it is withdrawn. The blade has a light bulb at the tip that may slightly hamper vision. The wider, curved blades are helpful in keeping the tongue retracted from the field of vision, allowing for more room in passing the tube in the oropharynx, and they are generally preferred in uncomplicated adult intubations. Aside from patient considerations, some clinicians prefer the curved blade because they find it requires less forearm strength than the straight blade. Tracheal Tubes The standard endotracheal tube is plastic and measures approximately 30 cm. Tube sizing is based on internal diameter (ID), measured in millimeters, and ranges from a 2.0 to a 20.0 mm tube, increasing in increments of 0.5 mm. The outer tube diameter is 2 and 4 mm larger than the internal diameter. Tube size is printed on the tube. There is also a scale, in centimeters, for determining the distance along the tube from the tip. Adult men will generally accept a 7.5 to 9.0 mm orotracheal tube, whereas women can usually be intubated with a 7.0 to 8.0 mm tube. In most circumstances, tubes smaller than these should not be used, especially in patients with chronic obstructive lung disease who may be difficult to wean from the respirator due to excessive airway resistance from a small tube. However, in emergency intubations, particularly if a difficult intubation is anticipated, many clinicians choose a smaller tube and change to a larger tube later if necessary. One exception is in the burn patient, in whom one places as large a tube as possible on the initial attempt because swelling may prohibit subsequent tube placement. For nasal intubation, a slightly smaller tube (by 0.5 to 1.0 mm) is chosen. The cuff of a standard tracheal tube is high-volume and low-pressure. A clinical test for determining correct cuff inflation is to slowly inject air until no air leak is audible while the patient is receiving bag-tube ventilation. This usually occurs with 5 to 8 mL of air if the proper-sized tracheal tube has been selected. Many clinicians use the tension of the pilot balloon as a guide to cuff inflation; slight compressibility with gentle external pressure indicates adequate inflation for most clinical situations. For long-term use, cuff pressure should be measured and maintained at 20 to 25 mm Hg. Capillary blood flow is compromised in the tracheal mucosa when the cuff pressure exceeds 30 mm Hg. In infants and children, the following formula is a highly accurate method for determining correct tracheal tube size: Tube size = [4 + age (years)]/4 For most clinical situations, however, using the width of the nail of the little finger as a guide is sufficiently accurate and has been shown to be more precise than finger diameter 45911. Correct tube size is especially important in the pediatric population, because most patients younger than 8 years are intubated with an uncuffed tube; adequate tube size is necessary to provide a good seal between the tube and the upper trachea and to prevent aspiration. A cuffed tube is used in children with decreased lung compliance who may require prolonged mechanical ventilation. In a child, the smallest airway diameter is at the cricoid ring rather than at the vocal cords, as in adults. Hence, a tube may pass the cords but go no farther. Should this occur, the next smaller sized tube should be passed after reoxygenation. Adult endotracheal tubes will accept a standard adaptor on which the ventilator tubing will fit. Pediatric tubes require a special adaptor with a distal end small enough to accommodate the small tube size. Preparing for Intubation Before beginning intubation, a number of issues should be addressed. In chronologic order, they are (1) confirm that the required intubation equipment is available and functioning; (2) position the patient correctly; (3) assess the patient for difficult airway; (4) establish intravenous (IV) access, time permitting; (5) draw up essential drugs, and; (6) attach the necessary monitoring devices. In the haste of the moment, it is a common error to fail to position the patient properly or to proceed with the procedure before the proper equipment is assembled and checked. Simple omissions, such as failing to restrain the patient's hands, removing dentures, or misplacing the suction device, can seriously hamper the performance of the procedure. A suggested pre-intubation checklist is presented in Table 2-2 . In addition to the preparation necessary for optimum patient care, the operator should also minimize exposure to potentially infectious materials . Generally, the operator should be gloved and should wear eye and mouth protection to guard against exposure to patient secretions. The endotracheal tube cuff should be checked for leaks by inflating the balloon before attempting intubation. The tube is prepared for placement by passing a flexible stylet down the tube to increase its stiffness and enhance control of the tip of the tube. The stylet should not extend beyond the end of the tube. The tube is then bent in a gradual curve with a more acute angling in the distal one-third to more easily access the anterior larynx. The tip and cuff of the tube are lubricated with viscous lidocaine or another water-soluble gel. The patient should be positioned to optimally align the oral, pharyngeal, and laryngeal axes . The desired position was aptly described by Magill to make the patient appear to be "sniffing the morning air," with the head extended on the neck and the neck slightly flexed relative to the torso. A small towel under the occiput (to raise it 7 to 10 cm) may facilitate positioning. Positioning of the head and neck is a critical step; nonoptimal head positioning may be the sole reason for some intubation failures. The Difficult Airway The majority of difficult intubations are predictable. Perhaps the most frequently encountered condition associated with a difficult intubation is the agitated or combative patient. Fortunately, this condition can be readily eliminated through pharmacologic intervention. The classic parameters that predict a difficult intubation include a history of previous difficult intubation, prominent upper incisors, limited ability to extend at the atlanto-occipital joint, [5] poor visibility of pharyngeal structures when the patient extends the tongue (Mallampati's classification, or the tongue/pharyngeal ratio), [6] limited ability to open the mouth, [7] a limited direct laryngoscopic view of the laryngeal inlet, [7] and a short distance from the thyroid notch to the chin with the neck in extension . [8] Radiographic indicators of the ease of intubation include the mandibular length-to-height ratio [9] and the distance from the spine of the atlas to the occiput. [10] In emergency airway management, many of these predictors are not obtainable. An extensive history is rarely available, the patients are frequently uncooperative, and the presence of trauma limits movement of the neck. Fortunately, some of the key predictors are apparent simply by observing the external appearance of the patient's head and neck. Patients with neck tumors, thermal or chemical burns, traumatic injuries to the face and anterior neck, angioedema and infection of the pharyngeal and laryngeal soft tissues, or previous operations in or around the airway suggest a difficult intubation because distorted anatomy or secretions may compromise visualization of the vocal cords. Facial or skull fractures may further limit airway options by precluding nasotracheal intubation. Patients with ankylosing arthritis or developmental abnormalities, such as a hypoplastic mandible or the large tongue of Down's syndrome, are difficult to intubate because neck rigidity and problems of tongue displacement can obscure visualization of the glottis. Besides these obvious congenital and pathologic conditions, the short, thick neck poses the greatest difficulty for performing orotracheal intubation. In such individuals, the larynx is anatomically higher and more anterior, which makes it harder to visualize the vocal cords. These individuals are easily identified by observing the head and neck in profile. In such patients, apply laryngeal pressure and consider using the straight blade. Use of other options, including nasotracheal intubation, may be required. It should be emphasized that some patients, despite normal-appearing anatomy and the absence of a complicating history, are unexpectedly difficult to intubate. One must be prepared for this rare but inevitable occurrence. Procedure Adults Direct laryngoscopy. The operator is stationed at the patient's head . The patient is generally supine with the head at the level of the operator's lower sternum. To maintain the best mechanical advantage, the operator keeps his or her back straight and does not hunch over the patient; any bending should occur in the knees. The left elbow is kept relatively close to the body and flexed to provide better support. In the severely dyspneic patient who cannot tolerate lying down, direct laryngoscopy can be performed with the patient seated semi-erect and the laryngoscopist on a stepstool behind the patient. [11] The laryngoscope is grasped in the left hand with the blade directed toward the patient from the hypothenar aspect of the operator's hand. The patient's lower lip is drawn down with the right thumb, and the tip of the laryngoscope is introduced into the right side of the mouth. The blade is slid along the right side of the tongue, gradually displacing the tongue toward the left as the blade is moved to the center of the mouth. If the blade is initially placed in the middle of the tongue, the tongue will fold over the lateral edge of the blade and obscure the airway. Placing the blade in the middle of the tongue and failure to move the tongue to the left are two common errors preventing visualization of the vocal cords. As the blade tip approaches the base of the tongue, the operator exerts a force along the axis of the laryngoscope handle, lifting upward and forward at a 45° angle. The epiglottis should come into view with this maneuver. It may help to have an assistant retract the cheek laterally to further expose the laryngeal structures. Do not bend the wrist; bending the wrist can result in dental injury because the teeth may be used as a fulcrum for the blade. The step following visualization of the epiglottis depends on which laryngoscope blade is used. With the curved blade, the tip is placed into the vallecula, the space between the base of the tongue and the epiglottis. Continued anterior elevation of the base of the tongue and the epiglottis will expose the vocal cords. If the blade tip is inserted too deeply into the vallecula, the epiglottis may be pushed down to obscure the glottis. [6] When using the straight blade, the tip is inserted under and slightly beyond the epiglottis, directly lifting this structure. The jaw and larynx are literally suspended by the blade. If the straight blade is placed too deeply, the entire larynx may be elevated anteriorly and out of the field of vision. Gradual withdrawal of the blade should allow the laryngeal inlet to drop down into view. If the blade is deep and posterior, the lack of recognizable structures indicates esophageal passage; gradual withdrawal should permit the laryngeal inlet to come into view. Proper neck positioning and pressure (cephalad, dorsally, and rightward) on the larynx by an assistant will facilitate visualization and intubation of an anterior larynx. If needed, suctioning is performed at this point. If the vocal cords are still not seen, consider using a tracheal tube introducer (Smiths Industries Medical Systems, Keene, NH). This device, also known as the "elastic gum bougie," is a long, semirigid introducer that is placed, using the laryngoscope, through the laryngeal inlet and into the trachea. [12A] The tracheal tube is then passed over the introducer and the introducer is withdrawn. If resistance is met in passing the tracheal tube, rotate the tube 90° counterclockwise and advance the tube. Tube passage. Once the vocal cords have been visualized, the final and most important step, tube passage under direct vision through the vocal cords and into the trachea, is performed. The tube is held in the operator's right hand and introduced from the right side of the patient's mouth. The tube is advanced toward the patient's larynx at an angle, not parallel with or down the slot of the laryngoscope blade. This way, the operator's view of the larynx is not obstructed by the hand or the tube until the last possible moment before the tube enters the larynx. The tube should be passed during inspiration, when the vocal cords are maximally open. It enters the trachea when the cuff disappears through the vocal cords. The tube is advanced 3 to 4 cm beyond this point. It is not enough to see the tube and the cords; the tube must be seen passing through the vocal cords to ensure tracheal placement. When the vocal cords are stimulated, laryngospasm-- the persistent contraction of the adductor muscles of the vocal cords--may prevent passage of the tube. Inadequate anesthesia is often the cause. Pretreatment with topical lidocaine decreases the likelihood of this occurring. Two percent or 4lidocaine is sprayed directly on the cords. An infrequent but effective route for achieving tracheal anesthesia is via transtracheal puncture, injecting a bolus of 3 to 4 mL of lidocaine through the cricothyroid membrane. Laryngospasm is usually brief and is often followed by a gasp. The operator should be ready to pass the tube at this moment. Occasionally, the spasm is prolonged and needs to be broken with sustained anterior traction applied at the angles of the mandible--the jaw lift. At no time should the tube be forced, because permanent damage to the vocal cords may result. Consideration should be given to using a smaller tube. Prolonged, intense spasm may ultimately require muscle relaxation with a paralyzing drug . The pediatric patient is far more prone to laryngospasm than is an adult. [12] In a child, if vocal cord spasm prevents tube passage, a chest thrust maneuver may momentarily open the passage and permit intubation. Positioning and securing the tube. The endotracheal tube should be secured in a position that minimizes both the chance of inadvertent endobronchial intubation and the risk of extubation. The tip should lie in the midtrachea with room to accommodate neck movement. Because tube movement with both neck flexion and extension averages 2 cm, the desired range of tip location is between 3 and 7 cm above the carina. [14] On a radiograph, the tip of the tube should ideally be 5 ± 2 cm above the carina when the head and neck are in a neutral position. On a portable radiograph, the adult carina overlies the fifth, sixth, or seventh thoracic vertebral body. If the carina is not visible, it can be assumed that the tip of the tube is properly positioned if it is aligned with the T3 or T4 vertebra. In children, the carina is more cephalad than in the adult, but it is consistently situated between T3 and T5. In children, T1 is used as the reference point for the tip of the endotracheal tube. [15] An estimate of the proper depth of tube placement can be derived from the following formulas, the lengths representing the distance from the tube tip to the upper incisors in children and from the upper incisors [18] or the corner of the mouth [19] in adults: Adults: Tracheal tube depth (cm) = 21 cm (women) Tracheal tube depth (cm) = 23 cm (men) In adults, this method has been shown to be more reliable than auscultation in determining the correct depth of placement. [18] The cuff is inflated to the point of minimal air leak with positive-pressure ventilation. In an emergency intubation, 10 mL of air is placed in the cuff, and inflation volume is adjusted after the patient's condition is stabilized. After tracheal tube placement, both lungs are auscultated under positive-pressure ventilation. Care is taken to auscultate laterally because midline auscultation may lead to an erroneous impression of tracheal placement when the tube is actually in the esophagus. With the tube in position and the cuff inflated, the tube is secured in place. Commercial endotracheal tube holders, adhesive tape, or umbilical (nonadhesive cloth) tape can be attached securely to the tube and around the patient's head . The tube should be positioned in the corner of the mouth, where the tongue cannot expel it. This position is also more comfortable for the patient and allows for suctioning. A bite-block or oral airway to prevent endotracheal tube crimping or damage from biting is commonly incorporated into the system used to secure the tube. Infants and Children Appreciation of the anatomic differences between children and adults is helpful when intubating the pediatric patient . Infants' proportionately larger head naturally places them in the "sniffing position," so a towel under the occiput is rarely necessary. The large head can even result in a posterior positioning of the larynx that prevents visualization of the vocal cords; a small towel under the child's shoulders should correct this problem. The head also may be floppy, and it can be stabilized by an assistant during intubation. The child's increased tongue-to-oropharynx ratio and shorter neck hinder forward displacement of the tongue and, coupled with a long U-shaped epiglottis, can make visualization of the glottis difficult. Consequently, direct laryngoscopy in the infant and young child is generally best performed with a straight blade: Miller size 0 for premature infants, size 1 for normal-sized infants, and size 2 for older children. The infant's larynx lies higher and relatively more anterior. One can have an assista