Rapid Sequence Intubation

Airway management is arguably one of the most important skills for an emergency physician to master because failure to secure an adequate airway can quickly lead to death or disability.[1] Endotracheal intubation using rapid sequence intubation (RSI) is the cornerstone of emergency airway management.[2, 3]

The decision to intubate is sometimes difficult. Clinical experience is required to recognize signs of impending respiratory failure. Patients who require intubation have at least one of the following five indications:

• Inability to maintain airway patency
• Inability to protect the airway against aspiration
• Failure to ventilate
• Failure to oxygenate
• Anticipation of a deteriorating course that will eventually lead to respiratory failure

RSI is the preferred method of endotracheal tube intubation (ETTI) in the emergency department (ED). This is because it results in rapid unconsciousness (induction) and neuromuscular blockade (paralysis). This is important in patients who have not fasted and because of this are at much greater risk for vomiting and aspiration. To this end, the goal of RSI is to intubate the trachea without having to use bag-valve-mask (BVM) ventilation, which is often necessary when attempting to achieve intubating conditions with sedative agents alone (eg, ketamine, etomidate, propofol).

Instead of titrating to effect, RSI involves administration of weight-based doses of an induction agent (eg, ketamine, etomidate) immediately followed by a paralytic agent (eg, rocuronium, succinylcholine) to render the patient unconscious and paralyzed within 1 minute. These medications share commonality in short onset/offset times and potent efficacies. This method has been proven safe and effective in EDs over the past 4 decades, and it is considered the standard of care. When administered by experienced, well-trained emergency physicians, use of neuromuscular blocking agents in patients undergoing emergent tracheal intubation is associated with a significant decrease in procedure-related complications.[4]

RSI is not indicated in a patient who is unconscious and apneic. This situation is considered a "crash" airway, and immediate BVM ventilation and endotracheal intubation without pretreatment, induction, or paralysis is indicated.

RSI should be approached with caution in a patient with a suspected difficult airway. If difficulty is anticipated, then an awake technique or the use of airway adjuncts (eg, fiberoptic intubation) is recommended. Alternatively, anesthesia personnel may be called upon to assist in securing the airway of a difficult-to-intubate patient.

Extrapolating known techniques and procedures that are intuitive and evidence-based from the emergency department to the field often makes sound clinical sense. However, the same standards that govern such modalities should apply wherever they are practiced. Recent literature has questioned the benefit of RSI in the prehospital setting.[5] Contributing factors may be the inducement of hyperventilation and hypoxia, both of which have been shown to increase mortality in trauma patients undergoing prehospital RSI.[6]

Additional studies have shown that the use of prehospital RSI is associated with an increased incidence of transient and prolonged hypoxia (57% of patients with a median hypoxic time of 60 s), often going unnoticed by the paramedic.[7] Lack of initial and ongoing training, national variability in paramedic protocols, and inadequate experience must be studied and monitored. Randomized prospective studies are needed to better delineate and define the use of prehospital RSI. The ubiquitous use of video-assisted laryngoscopes (VALs) in EDs has been shown to decrease complications in RSI, and, as more prehospital personal train in this modality, similar results may be shown. Indeed, the amount of training required in VAL compared with direct laryngoscopy is less and glotic visualization has been proven to be easier.

There is a general lack of clinical evidence in several areas of RSI, including use of atropine as an adjunct agent for children, the role of lidocaine in pretreatment, the role of a "defasciculating" or priming dose of a nondepolarizing paralytic agent, relative contraindications for use of succinylcholine, and even the amount and methods of preoxygenation and the need to use cricoid pressure (Sellick maneuver). Use of the Sellick maneuver in preventing aspiration has never been proven, but it has been confirmed in increasing airway resistance and decreasing tidal volumes. Also, MRI studies have shown that the esophagus more consistently lies to the right of the trachea than posterior. This article highlights some of these controversies, and the interested reader can also review El-Orbany's 2010 article.[8]

This article focuses on direct laryngoscopy using a traditional direct laryngoscope.  VAL is discussed as well.

Failure to maintain airway patency, as follows:

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

Decreased consciousness and loss of airway reflexes, as follows:

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

Failure to ventilate, as follows:

• End result of failure to maintain and protect airway
• 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), as follows:

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

Anticipated clinical course or deterioration (eg, need for situation control, tests, procedures), as follows:

• Uncooperative trauma patient with life-threatening injuries who needs procedures (eg, chest tube) or immediate CT scanning
• Stab wound to neck with expanding hematoma
• Septic shock with high minute-ventilation and poor peripheral perfusion
• Intracranial hemorrhage with altered mental status and need for close blood pressure control
• Cervical spine fracture with concern for edema and loss of airway patency

Absolute contraindications include the following:

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

Relative contraindications include the following:

• 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.

To simplify rapid sequence intubation (RSI), one can think of administering essentially two drugs: an induction agent (etomidate) and a paralytic agent (succinylcholine). These fulfill the criteria of possessing a short onset/duration and high potency.

To intubate a trauma patient with C-spine precautions, the cervical collar may be removed with a dedicated assistant providing inline immobilization. Removing the anterior part of the cervical collar while maintaining inline cervical spine immobilization is acceptable and may cause less cervical spine movement than cervical collar immobilization during laryngoscopy for endotracheal intubation.

Position the head and neck in the sniffing position by flexing the neck and extending the atlanto-occipital joint. Reposition the head if an adequate view of the glottic opening is not achieved.

The patient must be adequately preoxygenated to prevent desaturation during the period of apnea after the paralytic agent has been administered (to minimize the risk of gastric content aspiration). The least amount of ventilation support required to obtain good oxygen saturation should be used during this period. Blow-by high-flow oxygen via a nonrebreather mask is usually used, but for patients who are noted to desaturate (eg, beyond 90%), breaths delivered via 100% oxygen bag-valve-mask (BVM) may be required.

To minimize the risk of gastric aspiration, the Sellick maneuver (firm pressure over the thyroid cartilage) may be initiated as soon as positive-pressure ventilation is started (eg, during pretreatment if the patient is not able to maintain airway reflexes) and should be continued until inflation of the tracheal cuff of the endotracheal tube in the trachea. Note, however, that recent evidence questions the benefit of this modality.[9, 10]

Firm backward, upward, and rightward pressure (BURP) on the patient's thyroid cartilage can improve the Cormack/Lehane view up to one full grade. Typically, the assistant performing the Sellick maneuver can assist, resulting in a combined Sellick-BURP maneuver.

A No. 3 Macintosh or No. 3 Miller blade is generally sufficient for most patients, but a No. 4 blade (ie, next larger size) may be required in some adults. Note, some clinicians routinely use a No. 4 Macintosh blade, as it can be used in substitution of a Miller without switching blades.

A recent study by Brown III et al shows an overall improvement in glottic exposure with video compared to direct laryngoscopy.[11] More importantly, 25% of patients undergoing direct laryngoscopy displayed a poor glottic view; the use of video laryngoscopy improved this to a good view in nearly 80% of these patients.

Provide appropriate analgesia and sedation for patient comfort after RSI is successfully completed, especially if the patient is chemically paralyzed with a longer-acting paralytic agent (eg, vecuronium).

RSI is a procedure for patients with a critical disease or traumatic process. The selection of technique and specific agents is determined individually for each patient and situation. This article focuses on straightforward RSI for adults. Different techniques, equipment, and agents may be used for complex or rescue situations.

Accurate confirmation of correct placement of the tube in the trachea is essential. Direct visualization of the tube was previously the criterion standard for confirming placement; however, this method can be fraught with human error. The current criterion standard is end-tidal carbon dioxide detection, using either a calorimetric capnometer that changes color from purple to yellow with CO2 exposure or a quantitative capnometer that measures CO2 levels and can display a waveform. The yellow color change should occur rapidly within 1-2 breaths, and esophageal or supraglottic placement should be assumed if the color change is less rapid or does not occur at all. Important to note is that color change with a calorimetric capnometer can occur with esophageal placement and can be misleading. For this reason, a capnography with continuous waveforms is the preferred modality. Color change may not be reliable in cases of prolonged cardiac arrest. Clinical parameters such as pulse oximetry readings or tube condensation may be nonspecific and misleading. A canine study by Kelly and colleagues demonstrated tube condensation in up to 83% of esophageal intubations.[12]

The step of preoxygenation maximizes hemoglobin and plasma oxygen saturation and creates an oxygen reservoir in the lungs by replacing nitrogen at the alveolar level and supersaturating the blood with oxygen (nitrogen washout). This oxygen reservoir in the lungs can eliminate the need for BVM ventilation for most patients undergoing RSI during the iatrogenically created period of apnea. Preoxygenation is accomplished by delivering 100% oxygen at high flow given to a spontaneously breathing patient through a nonrebreather mask for 3 minutes without "bagging" the patient.

Studies such as the one by Barker and colleagues have shown that 8 vital capacity breaths over 60 seconds results in the same degree of preoxygenation as the standard 3 minutes of tidal volume breathing of 100% oxygen by mask. This technique may be used as an alternate to the traditional 3-minute tidal volume technique. Comorbidities such as the presence of a hypermetabolic state, obesity, or a primary respiratory problem (eg, congestive heart failure, acute respiratory distress syndrome, pneumonia) cause patients to desaturate rapidly despite attempts at adequate preoxygenation.

A patient who is hypoxemic during attempts at intubation should undergo positive pressure ventilation with a BVM to raise PaO2 levels. Consider applying cricoid pressure.

In the setting of the COVID-19 pandemic, it is important that tracheal intubation be performed in accordance with recommendations from national and international organizations.[13] Because tracheal intubation can be an aerosol-generating procedure, emergency medicine clinicians should exercise caution when performing endotracheal intubation or resuscitation involving emergency intubation or cardiopulmonary resuscitation. All reusable patient-care equipment must be cleaned and disinfected before use on another patient, according to the manufacturer’s instructions.

Guidelines on intubation and extubation in the ICU were released in January 2019 by the French Society of Anaesthesia and Intensive Care Medicine (SFAR) and the French-Speaking Intensive Care Society (SRLF).[14]

Complicated ICU intubation

Consider all patients admitted to ICUs at risk of complicated intubation.

In order to reduce the risk of a complicated intubation, use careful preparation and take steps to maintain oxygenation and cardiovascular stability, which will help anticipate and prevent respiratory and hemodynamic complications.

Differentiate risk factors for a complicated intubation from predictive factors of a difficult intubation.

An additional recommendation for pediatric patients is to consider all patients to be at risk for complicated intubation.

Equipment for difficult intubation

To confirm the correct position of the endotracheal tube, supraglottic device, or direct approach through the trachea, capnographic control is necessary.

A difficult airway trolley and a bronchoscope (conventional or single use) are needed for emergent management of a difficult intubation.

To improve the success rate of endotracheal intubation, use metal blades for direct laryngoscopy.

Videolaryngoscopes should be used initially or after failure of direct laryngoscopy in order to limit intubation failures.

For oxygenation and to facilitate intubation under bronchoscopic control, use supraglottic devices.

For pediatric patients, laryngoscopic blades used should be suited to the habits of the practitioners (eg, Miller straight blade, Macintosh curved blade). Exposition failure warrants a change in the type of blade used. Additionally, oral intubation is preferred, as are cuffed tubes to limit reintubations due to leakage.

Drugs in difficult intubation

Hypnotic agents (eg, etomidate, ketamine, propofol) facilitate rapid sequence induction. The choice of agent depends on patient history and clinical situation.

Succinylcholine can be used in critically ill patients to facilitate tracheal intubation during rapid sequence induction. If succinylcholine is contraindicated, rocuronium dosed above 0.9 mg/kg (1-1.2 mg/kg) is an alternative. Note that sugammadex should be available for possible emergent use if rocuronium is used.

An additional recommendation for pediatric patients is the use of atropine before intubation and during induction for those older than 28 days up to age 8 years, particularly in children with septic shock or hypovolemia or if suxamethonium is used.

Protocols and algorithms in difficult intubation

Noninvasive ventilation should be used for preoxygenation of hypoxemic patients. For patients who are not severely hypoxemic, high-flow nasal oxygen can be used.

Include a respiratory component in the intubation protocol in order to decrease respiratory complications. Integrate a postintubation recruitment maneuver into the respiratory component for hypoxemic patients.

After intubation of hypoxemic patients, a positive end-expiratory pressure of at least 5 cm water is recommended.

A cardiovascular component to the protocol to address fluid challenges and early administration of amines to decrease cardiovascular complications is recommended.

Extubation prerequisites

To decrease the risk of extubation failure, a spontaneous breathing trial is recommended before any extubation in ICU patients ventilated for greater than 48 hours.

However, the spontaneous breathing trial is not adequate as a lone method for detecting extubation failure risk. As such, it is suggested that screening be conducted for other risk factors, such as excessive tracheobronchial secretions, swallowing disorders, ineffective cough, and altered consciousness.

Extubation failure

To predict the occurrence of laryngeal edema, perform a cuff leak test before extubation. If the patient has at least one risk factor for inspiratory stridor, the cuff leak test is recommended before extubation to reduce the risk of failure related to laryngeal edema.

During mechanical ventilation, it is recommended to institute measures to prevent and treat laryngeal pathology.

In the event the leak volume is low or zero, corticosteroids can be prescribed to help prevent extubation failure related to laryngeal edema. If corticosteroid therapy is selected, the recommendation is to start it at least 6 hours before extubation.

For pediatric patients, corticosteroid therapy should be started 24 hours pre-extubation in order to be effective.

Extubation and respiratory therapy

Suggested prophylactic measures include high-flow oxygen therapy via a nasal cannula (1) after cardiothoracic surgery, (2) after extubation in hypoxemic patients, and (3) in patients at low risk of reintubation. Additionally, noninvasive ventilation is suggested as a prophylactic measure in patients at high-risk of reintubation, especially hypercapnic patients.

Noninvasive ventilation is suggested as a therapeutic measure to treat acute postoperative respiratory failure, especially after lung resection or abdominal surgery.

Noninvasive ventilation is not suggested as treatment for acute respiratory failure after extubation in the ICU unless the patient has underlying COPD or if blatant cardiogenic pulmonary edema is present.

For pediatric patients, noninvasive ventilation is not recommended in low-risk patients.

Physiotherapist treatment is likely required before and after endotracheal extubation following mechanical ventilation for more than 48 hours to reduce weaning duration and risk of extubation failure. A physiotherapist also should probably attend endotracheal extubation; this may help limit immediate complications (eg, bronchial obstruction in patients at high risk for extubation failure).

Equipment includes the following:

• Laryngoscope (see image below): 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. ^[15]
• Laryngoscope handle, No. 3 Macintosh (curved) blade, and No. 3 Miller (straight) blade.
• 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

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.[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.

Preoxygenation can also be accomplished with high-flow nasal cannula oxygen, which is very different from using a nonrebreather mask or increased nasal cannula oxygen. This is a modality of oxygen delivery that has had an increase in use, as both flow and oxygen levels can be adjusted. High flows translate to some positive airway pressures (much like CPAP), which can also help with airway patency.

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.[16] 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.[17]

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.[8, 18, 19, 20, 21, 22, 23, 24, 25, 26]

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,[27, 28, 29] though some data also suggest that these agents may increase ICP.[30, 31, 32, 33, 34, 35] 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.[36, 37] Some evidence indicates that bradycardia can occur equally with or without atropine during intubation.[36, 38] 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.

Some practitioners bypass the pretreatment phase and go straight to induction agents. The exception is that some still administer opioids, but in conjunction with the induction agent and not as pretreatment.

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) has a rapid onset, a short duration, is cerebroprotective, and is not associated with a significant drop in blood pressure. It is hemodynamically neutral compared with other agents, such as sodium thiopental. It 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.[39, 40] It is the most common agent used in the United States.

Ketamine (Ketalar) (1-2 mg/kg IV) produces a "dissociative" state, has analgesic properties, is a bronchodilator, and may decrease rather than increase intracranial pressure. Consider it for patients with asthma or anaphylactic shock; possibly avoid it 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 the 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.[41, 42, 43] 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) has a rapid onset, a short duration, and is cerebral protective. However, propofol is a myocardial depressant and it decreases systemic vascular resistance.

Midazolam (Versed) (0.3 mg/kg IV) has a 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.[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.

A depolarizing neuromuscular blocker (eg, succinylcholine [Anectine] at 2 mg/kg IV or 4 mg/kg IM) has a rapid onset (45-60 sec) and the shortest duration of action (8-10 min). It should be used with caution in patients with known or suspected hyperkalemia and those with chronic neuromuscular disease. Also use caution in patients with chronic renal failure or dialysis-dependent patients as they are prone to be hyperkalemic and this may be unsuspected. 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).[44]

A nondepolarizing neuromuscular blocker (NMB) (eg, rocuronium [Zemuron] at 1-1.2 mg/kg IV) has a 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.[45]

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).

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.[46]

Complications include the following:

• Esophageal intubation

• Iatrogenic induction of an obstructive airway

• Right mainstem intubation

• Pneumothorax

• Dental trauma

• Postintubation pneumonia

• Vocal cord avulsion

• Failure to intubate

• Hypotension

• Aspiration

Several methods exist to quickly assess the probability of success during tracheal intubation.[1] 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 (see hyomental distance in the first image below), and is able to fit 2 finger breadths between the hyoid bone and the thyroid cartilage (see thyrohyoid distance in the second image below).

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 (see image below).

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.[47]

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.[48] Also, in an ultrasound study, 29 of 33 esophagi were partially displaced to the left of the trachea.[49] In a meta-analysis, Butler and Sen showed that little evidence supports the notion that cricoid pressure decreases the risk of aspiration in RSI.[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.[49, 50]

See the image panel below.

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.[51] 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.[52] 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.[53] 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.[54]

VAL is now available as both a portable unit that is attached to a laryngoscope and as a stand-alone unit that is wheeled to the bedside. Utilization is often one of personal preference or institutional availability.

See the images and video below.