Indications for Intubation
Indications for intubation include airway obstruction, airway protection (any cause of depressed level of consciousness, eg, stroke, trauma, or intoxication), facilitation of mechanical support for respiratory failure (hypoxemic or hypercapnic), and circulatory failure (shock).
All necessary equipment should be available and checked prior to any intubation attempt regardless of predicted difficulty7,8 (Table 97–1). The patient should be monitored with at least pulse oximetry, blood pressure cuff, and continuous electrocardiogram. Intravenous access should be secured.
Table 97-1Equipment for endotracheal intubation. ||Download (.pdf) Table 97-1 Equipment for endotracheal intubation.
High flow oxygen source
Facemask and bag-mask device
Suction catheters and Yankauer
Oropharyngeal and nasopharyngeal airways
Laryngoscope handles and blades (different types and sizes)
Endotracheal tubes (different sizes)
Medications (induction agents, neuromuscular relaxants, vasopressors)
Confirmation placement device
The airway contains three visual axes: (1) mouth, (2) oropharynx, and (3) larynx. In the neutral position, these axes form acute and obtuse angles with one another and the glottic opening is not visualized.11 The traditional teaching is that the “sniffing the morning air” position (Figure 97–2) helps align the oral, pharyngeal, and laryngeal axes.13 This is achieved by flexing the neck and extending the head at the atlantooccipital joint.7,8 Cervical flexion approximates the pharyngeal and laryngeal axes, and extension at the atlantooccipital joint brings the oral axis into better alignment with the other two.11 However, over the past decade, several authors have controversially challenged this issue.14,15,16 Adnet et al studied magnetic resonance imaging (MRI) scans of healthy volunteers in 3 anatomic positions (neutral, simple extension, and in the sniffing position) and concluded that the “sniffing position” does not achieve alignment of the 3 important axes.15 Despite this, we consider that the sniffing position is probably the best starting position for direct laryngoscopy.
Three-axis alignment. (A) Head in neutral position. (B) Elevation of head approximates the laryngeal and pharyngeal axes. (C) Extension at the atlantooccipital joint brings the visual axis of the mouth into better alignment with those of larynx and pharynx. (Reproduced with permission from Hagberg C: Benumof and Hagberg’s Airway Management, 3rd edition. Philadelphia: Elsevier Saunders; 2013.)
In patients at risk of aspiration, compressing the cricoid cartilage posteriorly against the vertebral body (ie, Sellick maneuver) may reduce the diameter of the upper esophageal sphincter and prevent regurgitation of stomach content into the trachea during intubation, but may also interfere with laryngoscopy and endotracheal tube insertion.
Preoxygenation should take place prior to any airway intervention. The two primary goals of preoxygenation are (1) maximization of the arterial PaO2 and (2) denitrogenation of the functional residual capacity. A beneficial secondary goal of the process is hypocarbia.
Preoxygenation can temporarily raise the SpO2 and PaO2, maximizing blood oxygen content. Although dissolved oxygen adds little to the oxygen content of blood as the SpO2 nears 100%, critically ill patients often suffer from anemia, increased oxygen consumption and regional hypoperfusion, so any increase in dissolved oxygen (eg, 1.5 mL O2/100 mL of blood) is desirable. More importantly, preoxygenation replaces the nitrogen in the functional residual capacity with oxygen. The functional residual capacity is approximately 30 mL/kg, oxygen consumption is 3 to 4 mL/kg/min, and in healthy patients this “oxygen reserve” may allow up to 8 minutes of apnea before the SpO2 decreases below 90%. However, efficiency of denitrogenation and the time to critical SpO2 decrease is markedly reduced in critically ill patients and apnea rarely tolerated for more than 60 to 120 seconds; but, any increase in the time to desaturation will decrease morbidity and mortality.
Encouragement of hyperventilation during preoxygenation may result in hypocarbia that is desirable in the soon to be apneic patient. During the first minute of apnea the Pco2 will increase by 6 mm Hg and afterward by 3 mm Hg per minute. Hypercarbia will cause hemodynamic instability, cardiac arrhythmias, and increase the intracranial pressure, even while the SpO2 remains in a safe range.
Preoxygenation may be achieved by administration of 100% oxygen with a tight-fitting face mask, application of continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP), or manually assisted bag-mask ventilation. The choice of method is highly dependent on personal preference or unit policy and the emergent nature of the procedure. The authors of this chapter recommend that while setting up for intubation at minimum a tight-fitting Fio2 1.0 face mask should be applied and if time allows BiPAP be initiated.
Face Mask and Bag-Valve Device
Face masks are designed to form a seal around the mouth and nose and connect to a bag-valve device.6 The operator stands at the patient’s head and presses the mask onto the patient’s face with the left hand. The thumb should be on the nasal portion of the mask, the index finger near the oral portion, and the rest of the fingers spread on the left side of the patient’s mandible so as to pull slightly anterior.8 The 2 key elements are to establish a tight fit with the mask, covering the patient’s mouth and nose to prevent air leaks, and an unobstructed airway.6,8 The minimum effective insufflation pressure should be used to decrease the risk of insufflating the stomach and increasing the risk of aspiration.8
If ventilation is not effective, 2 maneuvers can be performed to improve airflow obstruction. Head extension, by stretching the anterior neck structures and moving the hyoid bone and attached structures anteriorly, is probably the most important single maneuver for maintaining space between the pharyngeal soft tissues (caution is advised in patients with unstable cervical spine). Jaw thrust, achieved by exerting anterior pressure behind the angles of the mandible, can also reduce the airway obstruction.6
If ventilation is not adequate despite proper positioning of the patient and proper use of the bag-valve device, several airway adjuncts may be helpful.8
An oropharyngeal airway (Figure 97–3) is semicircular and made of plastic. The 2 types are the Guedel airway, with a hollow tubular design, and the Berman airway, with airway channels along the sides.7 Both are inserted with the curved portion toward the mouth floor with the help of a tongue depressor to lower the tongue if needed. It should be inserted only when the pharyngeal reflexes are depressed, to minimize the risk of coughing and laryngospasm.6
Oropharyngeal airway (Guedel).
The nasopharyngeal airway is a soft tube approximately 15-cm long that is inserted through the nostril into the posterior pharynx. This device may be preferable in patients with limited mouth opening and poor dentition. It is also better tolerated in conscious patients. The airway should be lubricated and a vasoconstrictor should be applied before insertion. Its use is contraindicated in patients with skull base trauma, rhinorrhea, and severe coagulopathy.6,8
Induction Agents/Muscle Relaxants
Endotracheal intubation is safer and the success rate is higher in the sedated paralyzed state. Given the frequency of difficulty encountered, persons who are not experts and not comfortable with the administration of hypnotics and paralytics should defer to experts.
The choice of sedative hypnotic agent should emphasize hemodynamic stability and short duration of action. Hypotension is best avoided if etomidate (2-3 mg/kg) or ketamine (1-5 mg/kg) are used. Etomidate may cause myoclonus, does not promote muscle relaxation, burns on injection, and is associated with decreased endogenous steroid production, but its hemodynamic stability is unmatched. The administration of propofol to critically ill patients, even in low doses (eg, 1-1.5 mg/kg), almost always causes hypotension.
The choice of paralytic should emphasize short onset of action (ie, “rapid-sequence intubation”, ~ 60-75 seconds) and limits the choice to the depolarizing agent succinylcholine, and the nondepolarizing agent rocuronium. Succinylcholine (1-1.5 mg/kg) is the most rapid in onset (30-45 seconds) and shortest in duration (5-10 minutes), but in normal patients may raise the potassium level, and in certain conditions (eg, paralytic stroke, major burns) this rise may be quite profound and result in a hyperkalemic arrest. In these conditions, rocuronium (0.6-1.2 mg/kg) is preferable, although its duration of action is longer than succinylcholine (30-50 minutes).
Given the frequency of hemodynamic instability accompanying intubation in the ICU, preparation and administration of vasoactive medications should occur simultaneously with preparation and probably should precede administration of sedative hypnotics and paralytics. Patients who are already hypotensive prior to endotracheal intubation need reliable venous access through which a vasopressor can be infused. If the mean arterial pressure (MAP) is less than 60 mm Hg the vasopressor infusion should be increased, or alternatively a bolus of vasopressor can be administered. Ephedrine (5-10 mg), phenylephrine (100 μg), and vasopressin (0.5-1 units) have all been frequently used by the authors, usually determined by availability and heart rate. Bradycardic patients should all have at minimum atropine 0.4 mg or glycopyrolate 0.2 mg administered. Hypertensive patients, especially those with intracranial lesions, may benefit from titrated doses of short-acting hypotensive agents such as nitroglycerin (40-100 μg) and esmolol (0.5 mg/kg).
Direct Laryngoscopy and Endotracheal Tubes
Direct laryngoscopy is performed to visualize the laryngeal opening (Figure 97–4). To see through the airway, light must travel from the glottic opening to the laryngoscopist’s eye. Since light travels in a straight line, the technique requires an uninterrupted linear path between the larynx and the observer.11 The tongue and the epiglottis are the anatomic structures that intrude into this line of sight.6 One of the main objectives of direct laryngoscopy is to move the tongue anteriorly into the mandibular space, allowing direct view of the glottic opening.
Glottic opening view. (Reproduced with permission from Calder I, Pearce A: Core Topics in Airway Management, 2nd edition. New York: Cambridge University Press; 2011.)
The laryngoscope has a handle and a blade that snaps securely into the top of the handle. Many blades’ shapes and sizes are available, however, 2 types are commonly used (Figure 97–5). The Macintosh blade is curved along its long axis, has a broad, flat surface, and has a right-angled Z-shaped cross-section. The straight blades (Cranwall, Miller, Phillips, Wisconsin) tend to be narrower than the curve blades and have a D-shaped flange.6,7,8 Which blade to use is in many cases a matter of personal preference, but the straight blade could be of special use in patients with a larger than normal epiglottis, or with a larynx that is positioned more anterior.
Macintosh (curved) and Miller (straight) blades.
The laryngoscope is held in the left hand and introduced into the right side of the mouth. While advancing the blade to the base of the tongue, the blade is simultaneously moved to the midline sweeping the tongue to the left. The tip is advanced and the epiglottis is lifted away from the glottic opening.7 With a curved blade the tip rests and applies upward traction to the base of the tongue at the vallecula; the straight blade tip rests in the posterior surface of the epiglottis and lifts it directly.7,8 Elevating the epiglottis through a lifting motion at 45° from the horizontal using the arm and shoulder exposes the vocal cords. Keeping the wrist stiff to avoid a prying motion that uses the teeth as fulcrum will prevent dental injury.7,8 Once the vocal cords are visualized, the endotracheal tube is advanced from the right corner of the mouth and into the trachea. The cuff is inflated with enough air to prevent a leak with positive pressure ventilation.
Correct placement is confirmed with visualization of symmetric chest expansion, auscultation over epigastrium and lung fields, and an end-tidal CO2 detection device (capnography or calorimetric chemical detection of CO2). After confirmation, the tube is secured in place. A chest radiograph should be ordered in order to confirm correct placement and position of endotracheal tube tip above carina.
Endotracheal tubes are designed to provide a secure channel through the upper airway. The size of the endotracheal tubes is described as the internal diameter in millimeters.6 Tubes are available in 0.5 mm increments, starting at 2.5 mm. Selection of the proper diameter is important because small-diameter tubes increase airway resistance and work of breathing; moreover, certain procedures like bronchoscopy require large tubes. Common sized tracheal tubes are 8 mm for males and 7.5 mm for females. In general, the larger the patient, the larger the endotracheal tube that should be used.6,8 For oral intubation, an endotracheal tube insertion depth of 21 cm from the incisors in females and 23 cm from the incisors in males results in proper positioning about 4 cm above the carina in the majority of patients. The endotracheal tubes have a cuff near the distal end that is inflated to provide a seal to protect from aspiration and to allow positive pressure ventilation. Prevention of excessive cuff pressure may reduce the incidence of tracheal damage. Cuff pressure monitoring should be used whenever possible to maintain a pressure in the range of 25 to 30 cm H2O.6