Intubation

Intubation being practiced on a dummy (conventional technique using a laryngoscope).

Intubation Main Page
Overview
Types: Endotracheal intubation Nasotracheal intubation Orotracheal intubation Nasogastric intubation Orogastric intubation Fiberoptic intubation Surgical Airway Tracheostomy Cricothyroidotomy
Historical Perspective
Indication
Contraindications
Equipment
Predicting Ease of Intubation
Preprocedure
Procedure
Postprocedure
Tracheal Tube Maintenance
Special Situations
Complications

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List of terms related to Intubation

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Umar Ahmad, M.D.[2]

Synonyms and keywords: Intubate, Endotracheal intubation, Tracheal intubation

Overview

Intubation (sometimes entubation) is a medical procedure involving the insertion of a tube into the body. Patients are generally anesthetized beforehand. Examples include tracheal intubation, and the balloon tamponade with a Sengstaken-Blakemore tube (a tube into the gastrointestinal tract).

The most common intubation is tracheal intubation. The most common route for tracheal intubation is orotracheal where an endotracheal tube is passed from the oropharynx to the trachea. A bulb is then inflated near the distal tip of the tube to help secure it in place and protect the airway from blood, gastric contents and other secretions. Removal of the tube is referred to as extubation of the trachea.

Types

Intubation can exist in various forms. The following are some types of intubation that can occur:

• Endotracheal intubation- This is broad term that encompasses a tube going from the oropharynx to the trachea. This can be further subdivided into two other categories such as Nasotracheal intubation and Orotracheal intubation.
  • Orotracheal intubation- This is a type of intubation in which the tube goes in through the oral cavity to the trachea.
  • Nasotracheal intubation- This is a type of intubation in which the tube goes in through the nasal cavity to the trachea.
• Orogastric intubation
• Nasogastric intubation
• Fiberoptic intubation
• Surgical Airway
  • Tracheostomy
  • Cricothyroidotomy

Historical Perspective

BC

• 3600 BC- The earliest known depiction of a tracheotomy is found on two Egyptian tablets dating back to around 3600 BC.
• 2000 BC- Tracheotomy was described in the Rigveda, a Sanskrit text of ayurvedic medicine written around 2000 BC in ancient India.
• 1550 BC- The 110-page Ebers Papyrus, an Egyptian medical papyrus which dates to roughly 1550 BC, also makes reference to the tracheotomy.
• 400 BC- The Sushruta Samhita from around 400 BC is another text from the Indian subcontinent on ayurvedic medicine and surgery that mentions tracheotomy.
• 124–40 BC- Asclepiades of Bithynia (c. 124–40 BC) is often credited as being the first physician to perform a non-emergency tracheotomy.

1st Century

• 129–199 AD-  Galen of Pergamon (AD 129–199) clarified the anatomy of the trachea and was the first to demonstrate that the larynx generates the voice. In one of his experiments, Galen used bellows to inflate the lungs of a dead animal.

9th Century

• 1025- Ibn Sīnā (980–1037) described the use of tracheal intubation to facilitate breathing in 1025 in his 14-volume medical encyclopedia, The Canon of Medicine.
• 1092–1162- In the 12th century medical textbook Al-Taisir, Ibn Zuhr (1092–1162)—also known as Avenzoar—of Al-Andalus provided a correct description of the tracheotomy operation.

14th Century

• 1543- The first detailed descriptions of tracheal intubation and subsequent artificial respiration of animals were from Andreas Vesalius (1514–1564) of Brussels. In his landmark book published in 1543, De humani corporis fabrica, he described an experiment in which he passed a reed into the trachea of a dying animal whose thorax had been opened and maintained ventilation by blowing into the reed intermittently. The next known report on tracheal intubation and subsequent artificial respiration of animals is when Andreas Vesalius pointed out that the technique could be life-saving. This report remained unnoticed for more than 250 years.
• 1546- Antonio Musa Brassavola (1490–1554) of Ferrara successfully treated a patient suffering from peritonsillar abscess by tracheotomy. Brassavola published his account in 1546; this operation has been identified as the first recorded successful tracheotomy, despite the many previous references to this operation.

15th Century

• 1620-  In 1620 the French surgeon Nicholas Habicot (1550–1624) published a report of four successful tracheotomies.

16th Century

• 1533–1619- Towards the end of the 16th century, Hieronymus Fabricius described a useful technique for tracheotomy in his writings, although he had never actually performed the operation himself.
• 1714- In 1714, anatomist Georg Detharding (1671–1747) of the University of Rostock performed a tracheotomy on a drowning victim.

19th Century

• In 1805, Philip Bozzini used a device he invented and called the lichtleiter (or light-guiding instrument) to examine the human urinary bladder, rectum and pharynx. The practice of gastric endoscopy in humans was pioneered by U.S. Army surgeon William Beaumont
• in 1822 with the cooperation of his patient Alexis St. Martin, a victim of an accidental gunshot wound to the stomach.
• In 1853, Antoine Jean Desormeaux of France examined the human bladder using a device he invented and called the endoscope (this was the first time this term was applied to this practice).
• In 1868, Adolph Kussmaul of Germany performed the first esophagogastroduodenoscopy on a living human. The subject was a sword-swallower, who swallowed a metal tube with a length of 47 centimeters and a diameter of 13 millimeters.
• In 1869, the German surgeon Friedrich Trendelenburg documented successful human tracheotomy for administration of general anesthesia.
• In 1878, the Scottish surgeon William Macewen performed the first orotracheal intubation.
• In 1878, Maximilian Nitze and Josef Leiter invented the cystourethroscope and
• in 1881, Jan Mikulicz-Radecki created the first rigid gastroscope for practical applications.
• On 23 April 1895, Alfred Kirstein performed the first direct laryngoscopy in Berlin, Germany, using an esophagoscope he had modified for this purpose.

20th Century

• In 1919's, German otolaryngologist Dr. Franz Kuhn developed a flexometallic tube that resisted kinking and could be shaped to the patient's upper airway anatomy. Like O'Dwyer's tubes, it was inserted using blind digital technique. The patients were intubated awake and the hypopharynx was sealed with oiled gauze packing.
• During World War I, Sir Ivan Magill and Robert Macintosh achieved significant advances in techniques for tracheal intubation. The Magill curve of an endotracheal tube and the Magill forceps for positioning the tube during nasotracheal intubation are named after Magill, while the most widely used curved laryngoscope blade is named after Macintosh.
• In 1937, Leech introduced a "pharyngeal bub gasway" with a noninflatable cuff that fit snug into the hypopharynx.
• In 1932, Rudolph Schindler of Germany introduced the first semi-flexible gastroscope. This device had numerous lenses positioned throughout the tube and a miniature light bulb at the distal tip. The tube of this device was 75 centimeters in length and 11 millimeters in diameter, and the distal portion was capable of a certain degree of flexion.
• In 1939 to 1945, During World War II the shift of mask airways to tracheal intubations occured for most surgical procedures.
• Between 1945 and 1952, optical engineers (notably Karl Storz of Germany, Harold Hopkins of England, and Mutsuo Sugiura of the Japanese Olympus Corporation) built upon this early work, leading to the development of the first gastrocamera.
• In 1951, Succinylcholine helped dominate the area of tracheal intubation as it was faster and muscle relaxation was easier to achieve.
• In 1964, Fernando Alves Martins of Portugal applied optical fiber technology to one of these early gastrocameras to produce the first gastrocamera with a flexible fiberscope. Initially used in esophagogastroduodenoscopy (EGD), newer devices were developed in the early 1970s for use in bronchoscopy, rhinoscopy, and laryngoscopy.
• By the mid-1980s, the flexible fiberoptic bronchoscope had become an indispensable instrument within the pulmonology and anesthesia communities.

21st Century

• The Digital Revolution has brought newer technology to the art and science of tracheal intubation. Several manufacturers have developed video laryngoscopes which employ digital technology such as the CMOS active pixel sensor (CMOS APS) to generate a view of the glottis so that the trachea may be intubated. The Glidescope video laryngoscope is one example of such a device.

Indication

A definitive airway (orotracheal, nasotracheal, cricothyrotomy, or tracheotomy) is indicated under any of the following circumstances:

Failure to maintain airway tone

• Stab wound to neck with expanding hematoma

• Swelling of upper airway as in anaphylaxis or infection
• Facial or neck trauma with oropharyngeal bleeding

Decreased consciousness and loss of airway reflexes

• Comatose or intoxicated patients with a depressed level of consciousness who are unable to protect their airways. This is commonly defined as those subjects with a Glasgow Coma Scale ≤ 8. In such cases, the throat muscles may lose their tone so that the hypopharynx becomes obstructed, impeding the free flow of air into the lungs. Furthermore, protective airway reflexes such as coughing and swallowing, which serve to protect the airways against aspiration of secretions and foreign bodies, may be absent. With tracheal intubation, airway patency is restored and the lower airways can be protected from aspiration

• Cervical spine fracture with concern for edema and loss of airway patency

• Intracranial hemorrhage with altered mental status and need for close blood pressure control

• Failure to protect airway against aspiration - Decreased consciousness that leads to regurgitation of vomit, secretions, or blood

Failure to ventilate

• Requirement for mechanical ventilation, including cardiopulmonary resuscitation and general anesthesia. In such situations, spontaneous ventilation may be decreased or absent due to the effect of injury, disease, anesthetic agents, opioids, or neuromuscular-blocking drugs. To enable mechanical ventilation, an endotracheal tube is often used, although there are alternative devices such as the laryngeal mask airway or the CPAP mask.
• Diagnostic or therapeutic manipulation of the airway (such as bronchoscopy, laser therapy or stenting of the bronchi)

• Persistent or recurrent airway obstruction
• Prolonged respiratory effort that results in fatigue or failure, as in status asthmaticus or severe COPD

Failure to oxygenate (ie, transport oxygen to pulmonary capillary blood)

• Apnea or hypoventilation (e.g., closed head injury, intoxication or poisoning, cervical spine injury, flail chest)

• Septic shock with high minute-ventilation and poor peripheral perfusion

• End result of failure to maintain and protect airway or failure to ventilate
• Diffuse pulmonary edema
• Large pneumonia or air-space disease
• acute respiratory distress syndrome (ARDS),
• Near-drowning
• Pulmonary embolism
• Cyanide toxicity, carbon monoxide toxicity, methemoglobinemia

Contraindications

Absolute

• Total upper airway obstruction, which requires a surgical airway
• Total loss of facial/oropharyngeal landmarks, which requires a surgical airway

Relative

Anticipated "difficult" airway, in which endotracheal intubation may be unsuccessful, resulting in reliance on successful bag-valve-mask (BVM) ventilation to keep an unconscious patient alive

• In this scenario, techniques for awake intubation and difficult airway adjuncts can be used.
• Multiple methods can be used to evaluate the airway and the risk of difficult intubation (eg, LEMON rule, 3-3-2, Mallampati class, McCormack and Lehane grade). Please refer to the Difficult Airway Assessment section below for details.

The "crash" airway, in which the patient is in an arrest situation, unconscious and apneic

• In this scenario, the patient is already unconscious and may be flaccid; further, no time is available for preoxygenation, pretreatment, or induction and paralysis.
• BVM ventilation, intubation, or both should be performed immediately without medications.

Equipment

Equipment includes the following:

• Laryngoscope Laryngoscope handle, No. 3 Macintosh (curved) blade, and No. 3 Miller (straight) blade.
  • Confirm that light source is functional prior to intubation.
  • A 2010 study demonstrated that single-use metal laryngoscope blades resulted in a lower failed intubation rate than did reusable metal blades.^{null 13}
• Endotracheal (ET) tube
• Stylet
• Syringe, 10 mL (to inflate ET tube balloon)
• Suction catheter (eg, Yankauer)
• Carbon dioxide detector (eg, Easycap)
• Oral and nasal airways
• Ambu bag and mask attached to oxygen source
• Nasal cannula

Laryngoscopes

The vast majority of "noninvasive" tracheal intubations involve the use of a viewing instrument or "scope" of one type or another. Since its introduction by Kirstein in 1895, the most common device used for this purpose has been the conventional laryngoscope. Today, the typical conventional laryngoscope consists of a handle, usually containing batteries, and a set of interchangeable blades. Two basic styles of laryngoscope blade are commercially available: the straight blade and the curved blade. The Macintosh blade is the most widely used of the curved laryngoscope blades, while the Miller blade is the most popular style of straight blade. There are many other styles of straight and curved blades, with accessories such as mirrors for enlarging the field of view and even ports for the administration of oxygen. These specialty blades are primarily designed for use by anesthetists, most commonly in the operating room.

Besides the conventional laryngoscopes, many devices have been developed as alternatives to direct laryngoscopy. These include a number of indirect fiberoptic viewing laryngoscopes such as the flexible fiberoptic bronchoscope, Bullard scope, UpsherScope, and the WuScope. These devices are widely employed for tracheal intubation, especially in the setting of the difficult intubation (see below). Several types of video laryngoscopes are also currently available (e.g., Glidescope, McGrath laryngoscope, Daiken Medical Coopdech C-scope vlp-100, the Storz C-Mac, Pentax AWS and the Berci DCI). Other noninvasive devices which are commonly employed for tracheal intubation are the laryngeal mask airway (used as a guide for tracheal tube placement), the lighted stylet, and the AirTraq. Due to the widespread availability of such devices, the technique of blind digital intubation of the trachea is rarely practiced today, though it may still be useful in emergency situations under austere conditions such as natural or man-made disasters.

Stylets

A stylet is a malleable metal wire which can be inserted into the endotracheal tube to make the tube conform better to the laryngopharyngeal anatomy of the specific individual, thus facilitating its insertion. It is commonly employed under circumstances of difficult laryngoscopy. The Eschmann stylet or gum elastic bougie is a specialized type of stylet, which can also be used for difficult laryngoscopy or for removal and replacement of tracheal tubes without the need for laryngoscopy.

Tracheal Tubes

Most tracheal tubes today are constructed of polyvinyl chloride, but specialty tubes constructed of silicone rubber, latex rubber, or stainless steel are also widely available. Most tubes have an inflatable cuff to seal the trachea and bronchial tree against air leakage and aspiration of gastric contents, blood, secretions, and other fluids. Uncuffed tubes are also available, though their use is limited mostly to pediatric patients (in small children, the cricoid cartilage, the narrowest portion of the pediatric airway, often provides an adequate seal for mechanical ventilation).

The "armored endotracheal tube" is a cuffed, wire-reinforced, silicone rubber tube which is quite flexible but yet difficult to compress or kink. This can make it useful for situations in which the trachea is anticipated to remain intubated for a prolonged duration, or if the neck is to remain flexed during surgery. Polyvinyl chloride tubes are relatively stiff in comparison. Preformed tubes (such as the oral and nasal RAE tubes, named after the inventors Ring, Adair and Elwyn) are also widely available for special applications. These may also be constructed of polyvinyl chloride or wire-reinforced silicone rubber. Other tubes (such as the Bivona® Fome-Cuf® tube) are designed specifcally for use in laser surgery in and around the airway. Various types of double-lumen endotracheal tubes have been developed (Carlens, Robertshaw, etc.) for ventilating each lung independently—this is useful during pulmonary and other thoracic operations.

Observational Methods to Confirm Tube Placement

• Direct visualization of the tube passing through the vocal cords
• Clear and equal bilateral breath sounds on auscultation of the chest
• Absent sounds on auscultation of the epigastrium
• Equal bilateral chest rise with ventilation
• Fogging of the tube
• An absence of stomach contents in the tube

Instruments to Confirm Tube Placement

No single method for confirming tracheal tube placement has been shown to be 100% reliable. Accordingly, the use of multiple methods to confirm correct tube placement is now widely considered to be the standard of care. At least one of the methods utilized should be an instrument. Waveform capnography has emerged as the gold standard for the confirmation of correct tube placement and maintenance of the tube once it is in place. Other methods include:

• Colorimetric end tidal carbon dioxide detector
• Self-inflating esophageal bulb
• Pulse oximetry (important limitations include a significant delay in the decrease in oxygen saturation, especially if subject has been pre-oxygenated)
• Esophageal Detection Device

Predicting Ease of Intubation

• Look externally (history of craniofacial traumas/previous surgery)
• Evaluate 3,3,2 - three of the subject's fingers should be able to fit into his/her mouth when open, three fingers should comfortably fit between the chin and the throat, and two fingers in the thyromental distance (distance from thyroid cartilage to chin)
• Mallampati score
• Obstructions (stridorous breath sounds, wheezing, etc.)
• Neck mobility (can subject tilt head back and then forward to touch chest)
• Cormack-Lehane grading system (according to the percentage of glottic opening on laryngoscopy)

Preprocedure

Anesthesia

Rapid sequence intubation (RSI) is predicated on the administration of medications in a specific sequence. The two phases of medication administration are induction and paralysis. In general, preoxygenation is carried out while medications are being drawn up.

Preoxygenation

Preoxygenation with high-flow oxygen via a nonrebreather mask for 3-5 minutes leading up to intubation results in supersaturation of oxygen in the alveoli by way of displacement of nitrogen (nitrogen washout). This allows the patient to maintain blood oxygen saturation during the apneic period of paralysis and allows the physician more time to successfully intubate.

In healthy adult volunteers who have been preoxygenated for 3-5 minutes, the average time to desaturation (oxygen saturation <90%) is approximately 8 minutes. This time is significantly shorter in patients who are critically ill and have a much higher metabolic demand for oxygen. ^{null 1}

Use the least assistance necessary to obtain good oxygen saturation and adequate preoxygenation (see Technique section below).

• High-flow oxygen via nonrebreather mask may be appropriate for a patient with good respiratory effort.
• High-flow oxygen via well-fitting bag-valve-mask (BVM) without additional positive pressure (ie, squeezing the bag) may be needed for those with more respiratory compromise.
• High-flow oxygen via BVM with positive pressure assistance (squeezing the bag) is used only when necessary.

Apneic oxygenation

Because pulmonary blood flow is still occurring during the apneic period of ETT placement, oxygen is continually being diffused out of the alveoli epithelium at 250 mL/min and into the capillary endothelium and attaching itself to circulating hemoglobin. Despite no ventilations (RSI dictates this in assuming full stomachs unless oxygen saturations are low) after the patient is paralyzed, there is actual flow and movement of oxygen down these concentration gradients as the alveoli are somewhat subatmospheric and a mass flow of gas (oxygen) flows from the airways into the alveoli. By applying an NC at 15 L/min (noxious and otherwise not tolerable in the awake patient) proximal airways can come close to a FiO₂ of 1.0 and serve to replace the alveoli oxygen. ^{null 14} Taha et al have shown that apneic oxygenation via an NC during RSI in comparison to those without this technique desaturated in 6 minutes compared with 3.65 minutes. ^{null 15}

Pretreatment

Pretreatment agents may be used to mitigate the physiologic response to laryngoscopy and induction and paralysis, which may be undesirable in certain clinical situations.  Note though clinical dogma has supported their use in the past, evidence in the literature is deficient in this area and because of this, these are mentioned from a historical perspective. 

Pretreatment medications are typically administered 2-3 minutes prior to induction and paralysis. These medications can be remembered by using the mnemonic LOAD (ie, Lidocaine, Opioid analgesic, Atropine, Defasciculating agents).

• Lidocaine (1.5 mg/kg IV) may suppress the cough or gag reflex experienced during laryngoscopy and has been considered to play a role in blunting increases in mean arterial pressure (MAP), heart rate (HR), and intracranial pressure (ICP). For this reason, it is commonly administered to patients with suspected intracranial hemorrhage, tumor, or any other process that may result in increased ICP, and it may be considered as part of RSI for patients in whom increased MAP could be harmful (eg, leaking aortic aneurysm). However, studies do not consistently demonstrate the effectiveness of lidocaine for these indications in patients in the emergency department (ED), and, based on this lack of evidence, a statement regarding its absolute indication cannot be made. ^{[[null 16], [null 17], [null 18], [null 19], [null 20], [null 21], [null 22], [null 23], [null 24], [null 8]]}
• Opioid analgesic (fentanyl 3 mcg/kg IV) mitigates the physiologic increase in sympathetic tone associated with direct laryngoscopy (ie, blunts increases in blood pressure, heart rate, and mean arterial pressure). One author recommends this in patients with suspected high ICP, ^{[[null 25], [null 26], [null 27]]} though some data also suggest that these agents may increase ICP. ^{[[null 28], [null 29], [null 30], [null 31], [null 32], [null 33]]} Opioid analgesics may also be useful in patients with an aortic emergency (eg, aortic dissection or leaking aortic aneurysm) in whom blood pressure spikes should be avoided. At this time, no conclusive evidence supports the use of opioids in RSI.
• Atropine (0.02 mg/kg IV) may decrease the incidence of bradydysrhythmia associated with direct laryngoscopy (stimulation of parasympathetic receptors in the laryngopharynx) and administration of succinylcholine (direct stimulation of cardiac muscarinic receptors). Previous recommendations indicated that all children younger than 10 years receive atropine prior to intubation, but this has fallen out of favor because of the lack of supporting data. Even if bradydysrhythmias occur, they are usually self-limited and clinically nonrelevant. However, atropine should be available in case a clinically significant decrease in heart rate occurs. Because of the increase in cardiac vagal tone, atropine can be considered for use in children younger than 1 year and should at least be at the bedside in this age group. ^{[[null 34], [null 35]]}
• Some evidence indicates that bradycardia can occur equally with or without atropine during intubation. ^{[[null 36], [null 34]]} Atropine can also be used in adolescents and adults for symptomatic bradycardia.
• A "defasciculating" dose of a nondepolarizing agent may reduce the duration and intensity of muscle fasciculations observed with the administration of succinylcholine (due to the stimulation of nicotinic acetylcholine receptors). The recommended dose is 10% of the paralyzing dose (eg, 0.01 mg/kg for vecuronium). Equivocal studies suggest such pretreatment may help reduce increases in intracranial pressure related to the procedure.
• The crux of RSI is to take the awake patient, with an assumed full stomach, and very quickly induce a state of unconsciousness and paralysis and securing the airway. This is done without positive pressure ventilation, if possible.

Induction

Induction agents provide a rapid loss of consciousness that facilitates ease of intubation and avoids psychic harm to the patient.

• Etomidate (Amidate) (0.3 mg/kg IV) - Rapid onset, short duration, cerebroprotective, and not associated with significant drop in blood pressure; hemodynamically neutral compared with other agents, such as sodium thiopental. Induces a transient decrease in cortisol levels as high as 86% in some studies. However, properly powered prospective studies are needed to validate this more theoretical phenomenon. Note cortisol levels are affected by severe illness independently of the induction agent used. Critical illness‒related corticosteroid insufficiency occurs in 10-20% of critically ill medical patients and as high as 60% in severe sepsis and septic shock. ^{[[null 37], [null 38]]} Most common agent used in the United States.
• Ketamine (Ketalar) (1-2 mg/kg IV) - "Dissociative" state, analgesic properties, bronchodilator, may decrease rather than increase intracranial pressure. Consider for patients with asthma or anaphylactic shock; possibly avoid in patients with suspected or known aortic dissection or abdominal aortic aneurysm and in patients with acute myocardial infarction. The general teaching has also been to avoid use of ketamine in patients in whom increased ICP is a concern; in particular, trauma patients with evidence of head injury. However, a review of recent literature supports its use in this scenario as the hemodynamic stimulation induced by ketamine may, in fact, improve cerebral perfusion and prevent secondary penumbra ischemia. Furthermore, in the laboratory, ketamine seems to have neuroprotective properties. ^{[[null 39], [null 40], [null 41]]}Because of its positive hemodynamic effects and etomidate’s known tendency to transiently decrease cortisol levels, ketamine is being used more frequently as an induction agent.
• Propofol (Diprivan) (2 mg/kg IV) - Rapid onset, short duration, cerebral protective. However, propofol is a myocardial depressant and also decreases systemic vascular resistance.
• Midazolam (Versed) (0.3 mg/kg IV) - Slower onset (2-3 min without opioid pretreatment) and longer duration (up to several hours) than etomidate. A study by Sagarin et al from a national airway registry demonstrated that midazolam is usually underdosed when used for RSI, presumably because of the concern for hypotension. ^{null 3} Note that the induction dose is about 20 mg for a 70-kg person. Use of midazolam as an induction agent is not recommended because of its delayed time to induction, predilection for hypotension at induction doses, and prolonged duration of action.

Paralysis

Paralyzing agents provide neuromuscular blockade and are administered immediately after the induction agent.

Neuromuscular blockade does not provide sedation, analgesia, or amnesia; thus, administering a potent induction agent is important.

• Depolarizing neuromuscular blocker (eg, succinylcholine [Anectine] at 2 mg/kg IV or 4 mg/kg IM): Rapid onset (45-60 sec) and shortest duration of action (8-10 min). Should be used with caution in patients with known or suspectedhyperkalemia and those with chronic neuromuscular disease.
• Zink's 1995 prospective study of 100 patients in the ED undergoing RSI did not find a change in serum potassium level from before to after RSI with succinylcholine. Exclusion criteria were minimal; a limitation was that postintubation potassium level was checked at only 1 time interval (5 min).
• Nondepolarizing neuromuscular blocker (NMB) (eg, rocuronium [Zemuron] at 1-1.2 mg/kg IV): Slightly longer onset of action (60-75 sec) than succinylcholine and longer duration of action (30-60 min). Use with caution in patients in whom difficult intubation is possible. Does not result in muscle depolarization or defasciculation and does not exacerbate hyperkalemia. Sugammadex is a new NMB reversal agent that has been shown to be safe and effective for reversal of neuromuscular blockade induced by nondepolarizing agents. Reversal occurs at 1.5 minutes with a dose of 16 mg/kg and at 3 minutes with a dose of 4 mg/kg. It has been shown to induce full reversal of such agents faster than succinylcholine’s normal metabolic breakdown and for the first time in over 50 years offers a safe alternative and viable option for emergent RSI.

Procedure

In cases of trauma in which cervical spine injury is suspected and not yet ruled out, intubation must be performed without movement of the head. Immobilization is best provided by an experienced assistant. In cases in which cervical injury is not a concern, proper head positioning greatly improves visualization.

• In the neutral position, the oral, pharyngeal, and laryngeal axes are not aligned to permit adequate visualization of the glottic opening (see images below). Proper alignment of the axes for tracheal intubation.
• Three-axis theory. OA is oral axis, PA is pharyngeal axis, and LA is laryngeal axis. Used with permission from Springer Publishing Company.
• Place the patient in the sniffing position for adequate visualization; flex the neck and extend the head. This position helps to align the axes and facilitates visualization of the glottic opening.
• Studies have shown that simple head extension alone (without neck flexion) was as effective as the sniffing position in facilitating endotracheal intubation.

Difficult Airway Assessment

Several methods exist to quickly assess the probability of success during tracheal intubation. One tool for rapid assessment is the LEMON law, as described below. A patient in extremis may not be able to cooperate with all the sections of the LEMON assessment.

L: Look externally

Assessing the difficulty of an airway based on external physical features is not sensitive (not all patients who have a difficult airway appear to have a difficult airway prior to intubation) but is quite specific (most patients who appear to have a difficult airway do indeed have a difficult airway). Physical features such as a small mandible, large tongue, and short bull neck are all red flags for a difficult airway.

E: Evaluate the 3-3-2 rule

The chance for success is increased if the patient is able to insert 3 of his or her own fingers between the teeth, can accommodate 3 finger breadths between the hyoid bone and the mentum, and is able to fit 2 finger breadths between the hyoid bone and the thyroid cartilage.

M: Mallampati classification

The Mallampati assessment is ideally performed when the patient is seated with the mouth open and the tongue protruding without phonating. In many patients intubated for emergent indications, this type of assessment is not possible. A crude assessment can be performed with the patient in the supine position to gain an appreciation of the size of the mouth opening and the likelihood that the tongue and oropharynx may be factors in successful intubation.

O: Obstruction

Obstruction of the upper airway is a marker for a difficult airway. Three signs of upper airway obstruction are difficulty swallowing secretions (secondary to pain or obstruction), stridor (an ominous sign which occurs when < 10% of normal caliber of airway circumference is clear), and a muffled (hot-potato) voice.

N: Neck mobility

The inability to move the neck affects optimal visualization of the glottis during direct laryngoscopy. Cervical spine immobilization in trauma (with a C-collar) can compromise normal mobility, as can intrinsic cervical spine immobility due to medical conditions such as ankylosing spondylitis or rheumatoid arthritis.

Preparation

• Confirm that intubation equipment is functional.
• Assess the patient for difficult airway (see Difficult Airway Assessment section below for recommended method). If the patient meets criteria for difficult airway, rapid sequence intubation (RSI) may be inappropriate. Nonparalysis procedures may be an alternative. The assistance of anesthesia personnel may be warranted.
• Establish intravenous access.
• Draw up essential drugs and determine sequence of administration (induction agent immediately followed by paralytic agent).
• Review possible contraindications to medications.
• Attach necessary monitoring equipment.
• Check endotracheal (ET) tube cuff for leak.
• Ensure functioning light bulb on laryngoscope blade.

Preoxygenation

Administer 100% oxygen via a nonrebreather mask for 3 minutes for nitrogen washout. This is done without positive pressure ventilation using a tight seal.

Though rarely possible in the emergent situation, the patient can take 8 vital capacity (as deep as possible) breaths of 100% oxygen. Studies have shown this can prevent apnea-induced desaturation for 3-5 minutes. ^{null 45}

Assist ventilation with bag-valve-mask (BVM) system only if needed to obtain oxygen saturation =90%.

Pretreatment

Consider administration of drugs to mitigate the adverse effects associated with intubation.

See Anesthesia for more information.

Paralysis with induction

Administer a rapidly-acting induction agent to produce loss of consciousness.

Administer a neuromuscular blocking agent immediately after the induction agent.

These medications should be administered as an intravenous push.

Protection and positioning

Though clinical dogma dictates that the Sellick maneuver (firm pressure over the cricoid cartilage to compress the proximal esophagus) be initiated to prevent regurgitation of gastric contents, literature is lacking in support of this technique and in fact may impede laryngeal view.

Initiate this maneuver upon observing the beginning of unconsciousness.

Maintain pressure throughout intubation sequence until the position of the ET tube is verified. Note that proper laryngeal view has been shown to be best accomplished by the bimanual method and should be used if the Sellick maneuver fails to show the vocal cords.

Classical teaching dictates that cricoid pressure decreases the risk of gastric regurgitation into the lungs. However, in a study by Smith et al, the esophagus was partially lateral to the trachea in more than 50% of the subjects. ^{null 46} Also, in an ultrasound study, 29 of 33 esophagi were partially displaced to the left of the trachea. ^{null 47} In a meta-analysis, Butler and Sen showed that little evidence supports the notion that cricoid pressure decreases the risk of aspiration in RSI. ^{null 9}

Placement with proof

Visualize the ET tube passing through the vocal cords.

Confirm tube placement.

• Observe color change on a qualitative end-tidal carbon dioxide device or utilize a continuous end-tidal carbon dioxide (ET-CO2) monitor.
• Use the 5-point auscultation method: Listen over each lateral lung field, the left axilla, and the left supraclavicular region for good breath sounds. No air movement should occur over the stomach.
• Two pilot studies have shown that ultrasonography can reliably detect passage of a tracheal tube into either the trachea or esophagus without inadvertent ventilation of the stomach. ^{[[null 47], [null 48]]}

See the image panel below.

Left panel: Bedside ultrasound of anterior neck for proper detection of the endotracheal tube before positive-pressure ventilation is applied. Middle panel: Proper placement of the endotracheal tube in the trachea as the esophagus is normally not visualized. Right panel: Misplacement of the endotracheal tube in the left-sided esophagus. Used with permission from Springer Publishing Company.

Postprocedure

Postintubation management

Secure the ET tube into place.

Initiate mechanical ventilation.

Obtain a chest radiograph.

• Assess pulmonary status.
• Note this modality does not confirm placement; rather, it assesses the height above the carina.
• Ensure that mainstem intubation has not occurred.

Administer appropriate analgesic and sedative agents for patient comfort, to decrease O₂ demand, and to decrease ICP.

Video-assisted laryngoscopy (VAL)

VAL offers the advantage of abandoning the need for alignment of the optical axes in the mouth, pharynx, and larynx in order to visualize the entrance of the glottis and therefore is more effective. Unfortunately, standard ETTI via DL, performed by untrained medical personnel and those who perform it only occasionally, carries a high risk of failure. In several studies looking at the success rate of ETTI via DL performed by medical support staff, medical students, and novice anesthesia residents, the initial success rate varied between 35% and 65%. It has been shown that in order to improve the success rate of DL to over 90%, one would require about 47-56 intubations. ^{null 49} In stark contrast, VAL has been shown to be easily learned and highly successful with minimal training necessary. A prospective trial compared 37 novice residents in VAL versus DL and found that the former yielded a 14% higher success rate and 14% fewer esophageal intubations. ^{null 50} Nouruzi-Sedeh et al evaluated medical personnel with no prior experience in ETTI (paramedic students, nurses, and medical students) and after a brief didactic/manikin session compared their laryngoscopy skills in the operating room between VAL and DL. As in many other similar studies, they showed that VAL led to a significantly higher success rate (93%) compared with DL (51%) in nonphysicians with no prior laryngoscopy experience. Subjects were also noted to have a dramatic improvement after only five ETTIs; they neared a 100% success rate using VAL. ^{null 51} A meta-analysis looked at VAL compared with DL in 17 trials with 1,998 patients. The pooled relative risk for nondifficult intubations was 1.5 and for difficult intubations was 3.5; the authors concluded that VAL improves glottic visualization, particularly in patients with potentially difficult airways. ^{null 52}

Set up for video-assisted laryngoscopy. Used with permission from Springer Publishing Company. Video demonstration of the ease of video-assisted laryngoscopy in aligning the oral, pharyngeal, and laryngeal airway axis and glottic view. Used with permission from Springer Publishing Company. Glottic view via video-assisted laryngoscopy. Used with permission from Springer Publishing Company.

Tracheal Tube Maintenance

The tube is secured in place with tape or an endotracheal tube holder. A cervical collar is sometimes used to prevent motion of the airway. Tube placement should be confirmed after each physical move of the patient and after any unexplained change in his/her clinical status. Continuous pulse oximetry and continuous waveform capnography are often used to monitor the tube's correct placement.

The cuff pressure must be monitored carefully in order to avoid complications from over-inflation, which can include tracheomalacia, tracheoesophageal fistula, or even frank rupture of the trachea. Many of the complications of over-inflated cuffs can be traced to excessive cuff pressure causing ischemia of the tracheal mucosa.

An excessive leak can sometimes be corrected through the placement of a larger (0.5 mm larger in internal diameter) endotracheal tube, and in difficult-to-ventilate pediatric patients children it is often necessary to use cuffed tubes to allow for high pressure ventilation if the leak is too great to overcome with the ventilator.

Special Situations

Nasal intubation

Emergency Intubation

Personnel experienced in direct laryngoscopy are not always immediately available in certain settings that require emergency tracheal intubation. For this reason, specialized devices have been designed to act as bridges to a definitive airway. Such devices include the laryngeal mask airway, cuffed oropharyngeal airway, and the Combitube. Other devices such as rigid stylets, the lightwand (a blind technique) and indirect fiberoptic rigid stylets, such as the Bullard scope, Upsher scope, and the WuScope can also be used as alternatives to direct laryngoscopy. Each of these devices have its own unique set of benefits and drawbacks, and none of them is effective under all circumstances.

Difficult Intubation

Many individuals have unusual airway anatomy, such as those who have limited range of motion of the cervical spine or temporomandibular joint, or who have oropharyngeal tumors, hematomas, angioedema, micrognathia, retrognathia, or excess adipose tissue of the face and neck. Using conventional laryngoscopic techniques, intubation of the trachea can be difficult in such people. Use of the flexible fiberoptic bronchoscope and similar devices has become among the preferred techniques in the management of such cases. Among the drawbacks of these devices are their high cost of purchase, maintenance and repair. Another drawback is that intubation with one of these devices can take considerably longer than that achieved using conventional laryngoscopy; this limits their use somewhat in urgent and emergent situations.

Rapid Sequence Intubation

Rapid-sequence intubation (RSI) refers to the method of sedation and paralysis prior to tracheal intubation. This technique is quicker than the process normally used to induce a state of general anesthesia. One important difference between RSI and routine tracheal intubation is that the practitoner does not ventilate the lungs after administration of a rapid-acting neuromuscular blocking agent. Another key feature of RSI is the application of manual pressure to the cricoid cartilage (this is referred to as the Sellick maneuver) prior to instrumentation of the airway and intubation of the trachea.

RSI involves pre-oxygenating the patient with a tightly-fitting oxygen mask, followed by the sequential administration of pre-determined doses of a hypnotic drug and a rapid-acting neuromuscular blocker. Hypnotics used include thiopental, propofol and etomidate. Neuromuscular-blocking drugs used include suxamethonium (sometimes with a defasciculating dose of vecuronium) and rocuronium.[1] Other drugs may be used in a "modified" RSI. When performing endotracheal intubation, there are several adjunct medications available. No adjunctive medications, when given for their respective indications, have been proven to improve outcomes.[2] Opioids such as alfentanil or fentanyl may be given to attenuate the responses to the intubation process (tachycardia and raised intracranial pressure). This is supposed to have advantages in patients with ischemic heart disease and those with intra-cerebral hemorrhage (e.g. after traumatic head injury or stroke). Lidocaine is also theorized to blunt a rise in intracranial pressure during laryngoscopy, although this remains controversial and its use varies greatly. Atropine may be used to prevent a reflex bradycardia from vagal stimulation during laryngoscopy, especially in young children and infants.

This procedure is usually performed by an anesthesiologist or CRNAs (certified registered nurse anesthetists) in surgery, by respiratory therapists in multiple settings, and by medical personnel in the emergency department. It may also be performed in the prehospital setting[1] by persons trained to the EMT-Intermediate or paramedic level, including flight medics and flight nurses.

Another alternative is intubation of the awake patient under local anesthesia using a flexible endoscope or by other means (e.g., using a video laryngoscope). This technique is preferred if difficulties are anticipated, as it allows the patient to breathe spontaneously throughout the procedure, thus ensuring ventilation and oxygenation even in the event of a failed intubation.

Some alternatives to intubation are

• Tracheotomy - a surgical technique, typically for patients who require long-term respiratory support
• Cricothyrotomy - an emergency technique used when intubation is unsuccessful and tracheotomy is not an option.

Because the life of a patient can depend on the success of an intubation, it is important to assess possible obstacles beforehand. The ease of intubation is difficult to predict. One score to assess anatomical difficulties is the Mallampati score, which is determined by looking at the anatomy of the mouth and based on the visibility of the base of uvula, faucial pillars and the soft palate. It should however be noted that no single score or combination of scores can be trusted to detect all patients who are difficult to intubate. Therefore, persons performing intubation must be familiar with alternative techniques of securing the airways.

Pediatric Patients

Most of the general principles of anesthesia can be applied to children, but there are some significant anatomical and physiological differences between children and adults that can cause problems, especially in neonates and children weighing less than 15 kg. For infants and young children, oral intubation is easier than nasal. Nasal route carries risk of dislodgement of adenoid tissue and epistaxis, but advantages include good fixation of tube. Because of good fixation, nasal route is preferable to oral route in children undergoing intensive care and requiring prolonged intubation. The position of the tube is checked by auscultation (equal air entry on each side and, in long-term intubation, by chest X-ray). Because the airway of a child is narrow, a small amount of oedema can produce severe obstruction. Edema can easily be caused by forcing in a tracheal tube that is too tight. (If length of the tube is suspected to be large, immediate changing it to the smaller size is suggestible.)

The appropriate length for the endotracheal tube can be estimated by doubling the distance from the corner of the child's mouth to the ear canal. The tip of the tube should be at midtrachea, between the clavicles on an AP chest X-ray. The correct diameter of the tube is that which results in a small leak at a pressure of about 25 cm of water. The appropriate inner diameter for the endotracheal tube is roughly the same diameter as the child's little finger. For normally nourished children 2 years of age and older, the internal diameter of the tube can be calculated using the following formula:

• Internal diameter of tube (mm) = (patient's age in years + 16) / 4

For neonates, 3 mm internal diameter is accepted while for premature infants 2.5 mm internal diameter is more appropriate.

Complications

• Esophageal intubation
• Iatrogenic induction of an obstructive airway
• Right mainstem intubation
• Pneumothorax
• Dental trauma
• Postintubation pneumonia
• Vocal cord avulsion
• Failure to intubate
• Hypotension
• Aspiration

Tracheal intubation is potentially a very dangerous invasive procedure that requires a great deal of clinical experience to master. When performed improperly (e.g., unrecognized esophageal intubation), the associated complications may rapidly lead to the patient's death. Consequently, in recent editions of its Guidelines for Cardiopulmonary Resuscitation the American Heart Association has de-emphasized the role of tracheal intubation in advanced airway maintenance, in favor of more basic techniques like bag-valve-mask ventilation. Despite these concerns, tracheal intubation is still considered the definitive technique for airway management, as it allows the most reliable means of oxygenation and ventilation, while providing the highest level of protection against vomitus and regurgitation.

Although the conventional laryngoscope has proven effective across a wide variety of settings and patients, its use and misuse can result in serious complications (e.g., trauma to oropharyngeal and dental structures). Newer technologies such as flexible fiberoptic laryngoscopy have fared better in reducing the incidence of such complications, though the most common cause of intubation trauma remains a lack of skill on the part of the laryngoscopist.

Related Chapters

• Bronchoscopy
• Cricothyrotomy
• Jet ventilation
• Mechanical ventilation
• Positive end-expiratory pressure
• Positive pressure ventilation
• Tracheobronchial injury
• Tracheotomy

External Links

• Videos of direct laryngoscopy recorded with the Airway Cam (TM) imaging system, a head mounted camera system that captures the perspective of the operator.
• Airway devices for intubation