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Tracheal intubation is best accomplished via the rapid sequence intubation (RSI) method with direct visualization using a laryngoscope. Other techniques that have been described are blind nasal tracheal intubation, blind oral intubation via palpation, intubation via fiberoptic or video laryngoscopy visualization and guidance. These techniques have been less well described and hence the experience level among practitioners is not as extensive. Under the stress of an airway emergency, the likelihood of success is greatest with the technique that the practitioner has the greatest skill, expertise, and experience with. In teaching centers, another factor is the requirement that the procedure is supervisable and confirmable by the teaching physician.
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RSI is described in a series of the following steps (a sequence):
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Patient assessment, preparation, resuscitation
Premedications
Hyperoxygenation
Cricoid pressure (Sellick maneuver)
Paralyzing agent
Sedation agent
Intubation
Confirmation of intubation
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Step 1. Assess the patient and perform immediate resuscitation measures such as mask ventilation, if necessary. Patient assessment includes determining the need and priority for intubation. Decompressing the stomach with a nasogastric tube can be helpful to improve ventilation; however, it makes the maintenance of a mask seal more difficult if BMV is necessary, it can be noxious triggering movement, which would be adverse to patients with cervical spine injuries, and it can interfere with gastroesophageal sphincter function increasing the risk of gastric regurgitation. In most instances, it is better to pass a nasogastric tube after intubation.2 Clinical assessment includes the determination of whether a nasogastric tube should be inserted prior to intubation or after intubation is confirmed. Preparation includes procuring the supplies necessary for the procedure (suction, laryngoscope, ventilation devices, ETT, tracheal intubation confirmation devices, etc.) as well as the practice sessions and creating an environment conducive to optimally performing RSI. The latter of which must be in place prior to the presentation of the emergency case requiring RSI. Posting Table 17-2 would be part of basic preparation.3
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Step 2. Premedications depend on the clinical circumstances and practitioner preference. An abbreviated list of these includes atropine and lidocaine. Atropine potentially reduces oral secretions and the risk for laryngoscopy-induced bradycardia. Lidocaine potentially blunts the rise in intracranial pressure (ICP) during laryngoscopy, which is more important for patients with elevated ICP.
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Step 3. RSI includes a brief period of apnea during intubation, which is best tolerated if the patient can maintain oxygenation during this period. This is best accomplished with hyperoxygenation prior to intubation. For patients who are breathing spontaneously, applying 100% FIO2 by high-flow nonrebreathing mask or Rusch bag and mask maximizes oxygen hemoglobin saturation which is measurable via pulse oximetry, and additionally, it saturates the nonhemoglobin (plasma) oxygen content which is not measurable via pulse oximetry but can increase oxygen content by approximately 20%. Hypoxic patients and patients who are not spontaneously breathing sufficiently should be mask ventilated via BMV (PEEP may be necessary in many of these patients) to maximally oxygenate the patient prior to intubation. Patients who are still hypoxic despite rescue measures are at high risk for worsening hypoxia and deterioration during intubation. However, such scenarios are commonly encountered in the emergency department, and they must still be intubated to take resuscitation to the next step.
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Step 4. Cricoid pressure occludes the esophagus. This optional step is known as the Sellick maneuver and it potentially reduces the risk of passive regurgitation. It can also push the larynx more posteriorly to facilitate visualization during laryngoscopy. While cricoid pressure potentially reduces the risk of passive gastric regurgitation, it does not prevent vomiting if the patient is actively retching.
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Step 5. Selecting a paralyzing agent is controversial. The two common choices are succinylcholine and rocuronium. A detailed discussion of the differences between these two is beyond the scope of this chapter. The basic differences are that succinylcholine has a shorter duration, but a higher risk of adverse reactions that include malignant hyperthermia, and hyperkalemia, whereas rocuronium has a longer duration of paralysis but a lower risk of adverse reactions. The onset of paralysis by using agents such as vecuronium and pancuronium is slower than the onset of succinylcholine. The onset time of rocuronium is similar to the onset time of succinylcholine.
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Further reading about RSI will reveal principles known as priming and defasciculation. Many experts recommend these; however, this practice prolongs the time to intubation. While these principles fit best with anesthesia practices for stable patients, the typical emergency department patient requires emergent intubation. “Priming” is the principle of giving a small dose of rocuronium 1 to 2 minutes prior to the full dose of rocuronium. Priming reduces the paralysis onset time of the full dose of rocuronium by a few seconds, but it prolongs the RSI procedure by 1 to 2 minutes. “Defasciculation” is the practice of administering a small dose of rocuronium 1 to 2 minutes before administering succinylcholine. Succinylcholine typically results in brief muscle contractions prior to the onset of paralysis known as fasciculations, which are sometimes associated with muscle pain (in muscular patients), movement, and hyperkalemia. Defasciculation prevents these fasciculations. Both priming and defasciculation have minimal benefit or no benefit while delaying the intubation itself.
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Step 6. Selection of a sedation agent is similarly controversial. A detailed discussion of this is beyond the scope of this chapter. Table 17-2 describes a basic method of selecting a sedation agent.3 Selection criteria may be separated into patients with head trauma (or increased ICP), hypotension, and respiratory failure due to asthma. Considering these three factors permits the selection of a sedative. Thiopental has cerebroprotective properties, but it is a myocardial depressant, can lower blood pressure, and it is no longer available. Ketamine increases blood pressure and bronchodilation, but it also increases ICP. Etomidate is a more intermediate agent, and is purported to be a universal RSI sedative because of less adverse effects and it has some cerebroprotective properties. Benzodiazepines are moderate sedatives, require titration (not feasible in RSI), and most often do not result in sedation deep enough for intubation. However, they have few adverse side effects and are used by some practitioners for RSI. Propofol has also been added to the list of possible sedatives with RSI; however, it does not have substantial advantages over the agents listed in Table 17-2. Another option is to use no sedative at all. This is a serious consideration in hypotensive patients or those at risk for septic shock. Any agent administered to patients under significant cardiovascular stress (including benzodiazepines, ketamine, and etomidate) could result in acute deterioration such as cardiac arrest, and thus the benefit of a sedative must be considered against this risk for severe patients.
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Another issue of controversy is whether to give the sedative before the paralyzing agent or vice versa. Giving the paralyzing agent first reduces the time to intubation. Since the paralyzing agent takes 60 to 90 seconds to achieve sufficient paralysis, the sedation agent can be given during this waiting time. Giving the sedation agent first (as listed in Table 17-2) permits the patient to avoid the sensation of becoming paralyzed. These differences have different priorities in various clinical circumstances. Giving the paralyzing agent first makes more sense in severe patients in need of immediate intubation. Giving the sedation agent first makes more sense if the patient is conscious and the patient is less seriously in need of immediate intubation. Regardless of which is given first, the paralyzing agent and the sedation agent should be given in “rapid sequence.”
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Step 7. ETT size selection is critical in children. The common formula cited is 4 + (age/4). Thus, a 6-year-old would need a 5.5 ETT. Newborns should be intubated with a 3.0 or 3.5 ETT (smaller for premature infants). However, memorizing a formula may risk error. Using a length-based resuscitation system or posting Table 17-2 in the resuscitation room would be more reliable. Posting Table 17-2 has the added advantage of including drug doses, drug selection criteria, and the depth of the ETT. Selection of a laryngoscope blade type is a matter of personal preference. The classic teaching is that straight blades are better for young children, and curved blades are better for older children; however, both blade types are available in all sizes and are really a matter of personal preference. Visualization of the larynx can be facilitated by adjusting the degree of cricoid pressure. Repeating the fact that the narrowest point of the airway is the cricoid (below the cords) is useful because advancing the ETT through the cords will sometimes stop at the cricoid. ETTs can be cuffed or uncuffed. A cuffed ETT provides better airway protection and a tighter seal, which is beneficial when higher ventilation pressure is required. However, with small ETTs, the deflated cuff significantly increases the size of the ETT making it more difficult to advance. A commonly cited cutoff in the past was age 9 (size 6 ETT), below which uncuffed ETTs were recommended. However, current recommendations permit the option of cuffed ETTs to infants and children,2 but not neonates. Cuff inflation pressures should be measured and kept below 20 cm H2O.2
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Step 8. Confirmation of tracheal intubation should be confirmed with more than one method and one of these methods should be a carbon dioxide detection device. Colorimetric ETCO2 indicators that visibly change color during ventilation (Fig. 17-10) reliably confirm that the trachea is intubated in most instances. These colorimetric ETCO2 indicators come in different sizes. Using an adult sized unit for a newborn will not work since the volume of CO2 produced by the newborn will be insufficient to change its color. In addition, many colorimetric ETCO2 indicators will eventually become disabled due to water vapor saturation. An ETCO2 monitor quantifies the ETCO2 (which can be correlated to the patient's venous or arterial PCO2), displays the actual waveform of ETCO2 production, and it can be used continuously and indefinitely. A typical square waveform reliably confirms tracheal intubation, whereas a nonsquare waveform raises concerns that the trachea is not intubated (Fig. 17-11).
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ETCO2 is not produced in the absence of pulmonary perfusion. Inadequate CPR will result in no ETCO2. CPR is a known false-negative (i.e., the trachea is intubated, but ETCO2 is negative). The presence of an ETCO2 square waveform during CPR confirms tracheal intubation and pulmonary perfusion, confirming effective chest compressions.
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Auscultation can confirm equal chest aeration, and the absence of gastric breath sounds. Visualization can confirm chest rise and fall with ventilation, and condensation visible in the ETT. Improvements in oxygenation and resuscitation parameters are consistent with tracheal intubation. None of these definitively confirm tracheal intubation; however, collectively, the presence of all of these highly support successful tracheal intubation. The esophageal detector bulb (also known as the “turkey baster”) method utilizes a rubber bulb attached to an ETT connector (Fig. 17-12). Squeeze the bulb, then apply it to the ETT. If the bulb inflates rapidly, this suggests that the tube is in the trachea or the pharynx. If the bulb inflates slowly or it does not inflate, this suggests that the tube is in a collapsible tube such as the esophagus.
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If tracheal intubation is in doubt, direct visual confirmation with the laryngoscope should be attempted. Once tracheal intubation is confirmed, the ETT depth needs to be optimized based on the clinician's visual intubation depth (during laryngoscopy) and the ETT depth guidelines in Table 17-2. The ETT should be secured. There are several ways to do this using tape, and there are commercial products designed for securing the ETT. A chest x-ray is useful to confirm the placement of the tip of the ETT, which should be within the trachea, above the tracheal bifurcation. The ETT position can be readjusted if needed, being careful not to extubate the patient.