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The cricothyroid membrane is located between the thyroid and cricoid cartilages (Figure 30-2A). Both structures are easily palpated but are not directly seen because they are covered with the pretracheal fascia. In men, the thyroid cartilage is prominent and creates the "Adam's apple"; in women and children, the thyroid and cricoid cartilages can be hard to distinguish from each other.
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The cricothyroid membrane is found approximately one-third the distance from the manubrium to the chin in the midline in patients with normal habitus (Figure 30-2B). In a patient with a short, obese neck, the membrane may be hidden at the level of the manubrium. In a patient with a thin, long neck, it may be midway between the chin and the manubrium. The thyroid gland overlies the trachea; both structures are difficult to palpate. One easy way to find the cricoid membrane is to slowly palpate the trachea as you move up toward the head from the sternal notch; when your fingers "fall off" after a firm structure, you have palpated the thyroid cartilage. Next, slowly palpate downward toward the feet, and the first "soft spot" after that thyroid cartilage is the cricoid membrane.
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The vascular structure potentially injured during the course of a properly performed cricothyrotomy is a thyroid artery, a branch of the aorta running up to the thyroid gland in the midline. This vessel infrequently reaches the level of the cricothyroid membrane. A carotid injury is potential when landmarks are not seen or not adhered to or when technique is poor; this can be catastrophic and requires immediate direct pressure to avoid harm.
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The equipment needed to perform a surgical cricothyrotomy is listed in Table 30-2.
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PATIENT PREPARATION AND POSITIONING
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Place the patient supine, with the neck slightly hyperextended if no cervical trauma is present (neutral if there is suspected trauma) so neck structures can be palpated and identified. If time permits, apply antiseptic solution to the skin. Ventilate with a bag-valve mask connected to 100% oxygen while preparing.
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The procedure for performing a surgical cricothyrotomy is summarized in Table 30-3.
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SURGICAL CRICOTHYROTOMY USING SELDINGER TECHNIQUE
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This method uses the Seldinger technique (Figure 30-8). Make a small vertical incision through the skin at the cricothyroid membrane. Insert the needle and aspirate air to make sure the needle is in the trachea. Next, pass the guide wire through the needle, directing the guide wire caudally. Place a tracheostomy tube over the dilator, and make a "nick" in the skin to ease penetration. Then pass the dilator, with the tracheostomy tube, over the guide wire into the trachea. Once the dilator is in the trachea, remove the guide wire, direct the tracheostomy tube into the trachea, and verify correct placement. Indications and complications are similar to the open method, and direct comparisons in real use do not exist. Multiple commercial kits exist, but proper use requires deliberate, repetitive training.
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Acute complications after emergency cricothyrotomy occur in up to 15% of cases.6 Venous bleeding usually occurs from small veins and stops spontaneously. Using a vertical neck incision that is not too long decreases the chance of ongoing bleeding. Arterial bleeding can be from the thyroid artery or from a small artery at the base of the cricothyroid membrane. The first step in controlling ongoing bleeding is to apply gentle pressure. If bleeding persists, topical hemostatic agents or ligation may be necessary. A small amount of bleeding usually creates no hemodynamic concerns, but it can make the procedure more challenging.
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In an obese patient, it is possible to place the tube anterior to the larynx and trachea into the mediastinum, making ventilation impossible. Signs of an incorrectly positioned tube are high airway pressures, absent breath sounds, and massive subcutaneous emphysema. If this complication is suspected, remove the tube and make a second attempt at insertion. Endotracheal tubes passed through the cricoid membrane may curl toward the mouth, making ventilation impossible. A gum elastic bougie can help direct the endotracheal tube.5
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Laceration of the trachea, esophagus, or recurrent laryngeal nerves is rare and is more likely to occur if one is unfamiliar with the neck anatomy. Pneumothorax is usually secondary to barotrauma caused by ventilation initiated immediately after tube placement.
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A tube left in the narrow space between the cricoid and thyroid cartilages can erode both cartilages, and bacterial chondritis may occur. The cartilages will be destroyed and eventually scar, leading to stenosis and loss of the function of the larynx. Because cricothyrotomy has a high incidence of airway stenosis,6 a change to tracheostomy is common after 2 to 3 days.