FIG. 15-1. A. Oral pharyngeal laryngeal axes. B. Sniffing position.
The patient should be thoroughly preoxygenated prior to intubation if time permits. Begin with the laryngoscope in the left hand and an ET tube or suction apparatus in the right hand. After dentures and any obscuring blood, secretions, or vomitus are removed, the suction is exchanged for the ET tube and inserted during the same laryngoscopy.
The blade is inserted into the right corner of the patient's mouth. If a curved Macintosh blade is used, the flange will push the tongue toward the left side of the oropharynx. If the blade is inserted directly down the middle, the tongue can force the line of sight posteriorly—which is a common reason for the putative "anterior larynx." After visualization of the arytenoids, lift the epiglottis directly with the straight blade or indirectly with the curved blade. The larynx is exposed by pulling the handle in the direction that it points, that is, 90° to the blade. Cocking the handle back, especially with the straight blade, risks fracturing central incisors and is ineffective at revealing the cords.
There are a variety of other straight and curved blades available. To mention a few, the Guedel blade is a straight blade with an acute 72° angle to the handle. The Schapira straight blade has a side concavity that helps cradle the large tongue and push it toward the left side of the mouth. The CLM curved laryngoscope blade has a hinged tip. This permits elevation of the epiglottis with minimal force, since the fulcrum is repositioned down within the pharynx.
One technique to avoid the most common error, overly deep insertion of the blade, is to look for the arytenoid cartilages. If only the posterior commissure is visible, have an assistant apply more pressure on the cricoid (Sellick maneuver) or perform the laryngeal lift. Another option is the "BURP" technique. 1 The larynx is manually displaced posteriorly (backward) against the cervical vertebrae, superiorly (upward), and laterally to the right (rightward pressure). To avoid error, the cuff must be seen passing completely through the cords. Last-ditch attempts at blind passage will only invite anoxia. The intubator should never be reluctant to abort the attempt if visualization of the larynx is not successful. Whenever feasible, have an assistant apply steady cricoid pressure with the thumb and index finger during the intubation to help prevent aspiration.
With proper technique and practice, semirigid, malleable, blunt-tipped metal or plastic stylets are not usually necessary for most patients. Should the patient's anatomy call for them, a selection of proper-sized stylets must be available. The tip of the stylet should not extend beyond the end of the ET tube or exit Murphy's eye.
One aid to intubation with direct vision is the use of a thin, flexible intubation stylet. This type of stylet can be inserted blindly around the epiglottis into the trachea. The ET tube is then threaded over it into the trachea and the stylet is removed. The Eschmann tracheal tube introducer or stylet, also known as the "gum elastic bougie," is a valuable aid for difficult oral intubations. Another option is to use the tip on the laryngeal tracheal anesthesia kit. With either stylet, orient the tube so that Murphy's eye is at 12 o'clock.
The tube should never be forced through the vocal cords. Forced insertion can result in avulsion of the arytenoid cartilages or laceration of the vocal cords. Usually, any difficulty in passing the tube is a result of either the tube being too large or too soft and flexible. Directed transoral or translaryngeal anesthesia with lidocaine can help relax the cords. If this fails, sometimes lining up the bevel with the glottic opening will also be successful.
The tube should be advanced until the cuff disappears below the cords. Correct tube placement is about 2 cm above the carina. From the corner of the mouth, this is approximately 23 cm in men and 21 cm in women. The base of the pilot tube is usually at teeth level. The tube is also positioned by palpating its tip at the suprasternal notch and advancing it 2 to 3 cm. To avoid ischemia of the tracheal mucosa, keep the cuff pressure below 40 cmH 2O. The minimal intracuff pressure to prevent aspiration is 25 cmH2O.2
After cuff inflation, auscultate to verify bilateral lung expansion and if satisfied insert an oropharyngeal airway or bite block. Some advocate first listening over the stomach, since the early detection of errant esophageal intubation is desirable to minimize insufflation of the stomach with subsequent regurgitation. Inadvertent endobronchial intubation is usually on the right side. The operator should secure the tube, being careful not to impede cervical venous return with the umbilical tape or fixator. The use of a modified clove-hitch knot or a commercial fixator is ideal and also helps avoid kinking the pilot tube. Ventilation should be initiated using 100% oxygen with a tidal volume of 10 to 15 mL/kg at a rate of 10 to 15 breaths per minute.
Endobronchial or esophageal intubation will result in hypoxia or hypercarbia. There is no clinically reliable substitute for direct visualization of the tube passing through the vocal cords. Hence the adage, "when in doubt, take it out." Nevertheless, there are a number of options to help confirm intratracheal tube positioning. Clinical assessments—including chest and epigastric auscultation, tube condensation, and symmetrical chest wall expansion—are not infallible in the ED. "Breath sounds" from the stomach can be transmitted through the chest following gastric insufflation.
The two basic categories of adjuncts include end-tidal CO2 detectors or monitors and esophageal detection devices (EDDs). Both have advantages provided that the operator remains cognizant of the sources of interpretation error. Capnometers are the devices that measure CO 2 in the expired air. The most commonly used capnometric devices used in the ED are colorimetric, with a pH-sensitive purple-colored filter paper. When in contact with CO 2, hydrogen ions are formed resulting in color changes depending upon the concentration of CO2. For example, with the Nellcor Easy Cap II, a yellow color develops on exposure to 2 to 5% ETco2, equivalent to 15 to 38 mmHg CO2. There is no color change, that is the filter paper remains purple, with an ET co2 of <0.5%, equivalent to <4 mmHg CO2. An intermediate color results with an ETco2 of 0.5% to 2%, corresponding to 4 to 15 mmHg CO2. Generally these readings are accurate within +/- 3 mmHg. While capnometers are useful for general readings, as in assessing proper ETT placement, they are not accurate enough when precise determinations are necessary. Capnography is the real-time display of characteristic CO2 waveforms.
The use of end-tidal CO2 pressure (Petco2) monitoring can help confirm endotracheal intubation.3 A color change to yellow indicates endotracheal placement. Colorimetric or infrared detection of Petco2, however, may not occur even with proper ETT placement, during states of low pulmonary perfusion such as during cardiac arrest, inadequate chest compressions during CPR, or massive pulmonary embolism. Other causes of false-negative interpretations include massive obesity. Severe pulmonary edema may obstruct the ETco2 monitor with secretions. On the other hand, there may be an initial false-positive detection of CO 2 following esophageal intubation if carbonated beverages have been ingested by the patient, or for a few minutes after bolus sodium bicarbonate administration. Another cause is gastric distention resulting from bag-valve-mask ventilation. A heated humidifier or nebulizer or epinephrine instilled via the ET tube can also cause false-positive interpretations.
Correct technique is essential for accurate interpretation. After intubation and cuff inflation, attach the capnometer to the ET tube. Then attach a bag-valve-mask unit to the detector and ventilate the patient with about six ventilations to wash out residual CO 2. Then check for the Petco2-induced color changes. If capnography is also available, a persistent positive capnograph formation after clear and direct visualization of tube placement approaches certainty. On rare occasion, misplacement of the hypopharyngeal glottic tube tip may result in misleadingly normal oximetry and capnography. This error can be recognized by the inadequate depth of tube insertion, ventilatory volumes, or on chest x-ray.
Esophageal detection devices also offer the potential to accurately determine tube location. The various designs all depend on their proper function as in-line aspirators of the ET tube. The device adaptors fit over the 15-mm ET tube connector. One of the advantages of the EDD is that accuracy does not depend on adequate cardiac output and pulmonary perfusion. Instead, proper functioning is predicated on the anatomic differences between the esophagus and the trachea. When the ET tube is in the esophagus, the soft, noncartilagenous walls will collapse and air cannot be aspirated easily. 4
To perform the syringe aspiration technique, attach the device after intubation but before ventilation. Then attempt to retract the syringe plunger. Resistance to aspiration reflects occlusion from esophageal collapse. If there is no resistance during aspiration, one assumes that the tube is in the trachea. If a self-inflating bulb is used, first compress the bulb and then attach it to the ET tube. One advantage of the bulb is that it requires only a single hand.
As expected, these devices are also not infallible. When the seal with the device leaks, there may be an erroneous assumption of intratracheal tube placement. In the prehospital setting, some studies report that the EDDs demonstrate poor sensitivity for esophageal intubations. On the other hand, the EDDs have a potential advantage over PetCO2 in cardiac arrest patients.4
The emergency physician should never assume that continued airway patency is assured after ET tube insertion. Repeated suctioning is necessary to prevent thrombotic or inspissated secretions from obstructing the tube. Endobronchial ball-valve obstruction can also occur with a clot. This will impair ventilation and produce hyperinflation of individual lobes.
Cuff displacement or overinflation can result in ball-valve obstruction of the airway. Cuffs inflated in the field during frigid conditions will expand with warming. Deflate the cuff when tracheal ball-valve obstruction is suspected. If the tube is blocked, deflation will allow exhalation.
There are a variety of other correctable intubation complications that should be kept in mind. If the ET tube cuff leaks after the intubation, first check for a defective inflation valve. One simple fix is to attach a three-way stopcock to the valve and reinflate the cuff. Then turn the stopcock off. If the cuff itself seems to be leaking slowly, it may be sealable. An option is to instill an aspirable mixture of normal saline and 2% lidocaine jelly into the cuff in a 3:1 ratio.
If the ET tube needs to be replaced, consider the use of a tube changer. A classic technique is to use nasogastric tubing at least three times longer than the ET tube. Standard room-temperature tubing, however, may not be a sufficiently rigid guide. There are a number of commercially available semirigid catheters that include 15-mm adaptors or connectors to permit ventilation during the tube exchange. These devices have quick-connect adapters that incorporate through-lumen designs to ensure adequate airflow during the procedure.
If the ET tube is inserted too deeply, carinal stimulation can cause bronchospasm. Unilateral pulmonary edema is also reported. The ET tube may be obstructed by a bulging cuff, secretions, kinking, or biting. The cuff may simply be overinflated. If the cuff was inflated with frigid air in the field, it may expand and compress the tube after warming.
Although uncommon, morbidity related to emergent endotracheal intubation does occur and may be quite debilitating. Arytenoid cartilage avulsion or displacement, usually on the right, prevents the patient from phonating properly. Intubation of the pyriform sinus and pharyngeal-esophageal perforation has been reported. Chordal synechiae may develop anteriorly or commissural stenosis posteriorly.
Subglottic stenosis is the most disastrous sequela. The physician should avoid cuff overinflation and attempt to minimize tube motion in the larynx and trachea. This usually occurs in patients with poorly secured tubes who are combative or on ventilators. Gastric rupture with tension pneumoperitoneum can occur after a difficult intubation.
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