Immediate “crash” intubation
Patients with respiratory arrest, agonal respir- ations or deep unresponsiveness require immedi- ate intubation without the use of supplemental medications. The advantages of this approach are technical ease and immediacy. Disadvantages include the potential for increased intracranial pressure (ICP) from the stress of intubation, as well as possible emesis and aspiration.
Rapid sequence intubation
Rapid sequence intubation (RSI) is a series of defined steps intended to allow for rapid oral intubation of a patient without BVM ventilation.
Given that most patients requiring emergent intubation have not fasted and may have full stomachs, BVM ventilation may inadvertently lead to gastric distention and increase the risk of aspiration. To avoid this complication, the patient is first pre-oxygenated with 100% supple- mental O2to allow for a period of apnea without assisted ventilation. This is followed by the sequential administration of an induction agent and a rapidly-acting neuromuscular blocking agent (NMBA) to induce a state of unconscious- ness and paralysis, respectively. The patient may then be intubated without the need for BVM ventilation.
The steps making up RSI can be thought of as nine “Ps” (Table 2.2).
Possibility of success
The patient should be carefully evaluated for a potentially difficult airway, and assessed for ease of BVM ventilation should the intubation prove difficult or impossible.
Airway management
Anticipating the difficult airway
When evaluating a patient for ease of intubation and ventilation, it is important to use a consistent approach. A logical easily-remembered approach to identifying the difficult airway is the LEMON law (Look externally, Evaluate the 3-3-2 rule, Mallampati, Obstruction, Neck mobility).
Look externally
A brief and targeted exam of the jaw, mouth, neck and internal airway may help identify features that predict a difficult airway. Initial inspection should identify anatomic features such as morbid obesity, abnormal facial shape, facial or neck trauma, large or abnormal teeth, protruding tongue or the presence of facial hair that may pose a challenge to intubation, ventila- tion or both. An abnormal facial shape, extreme cachexia, a “toothless” mouth with sunken cheeks, trauma to the lower face or facial hair may pre- vent an adequate seal for effective BVM ventila- tion. Large buckteeth or central incisors, a receding mandible or short bull-neck may provide anatomic barriers to oral intubation. Obesity generally makes intubation and ventilation more challenging. Some of these features may also be remembered by the mnemonic BONES (Beard, Obese, No teeth, Elderly, Sleep apnea/snoring.) Evaluate the 3-3-2 rule
The 3-3-2 rule describes the ideal dimensions of the airway that facilitate direct visualization of the larynx. It is easily remembered as three (of the patient’s) fingers in the mouth, three fingers
under the chin and two fingers at the top of the neck. The ability to accommodate three fingers in the mouth indicates an adequate mouth opening.
Three fingers from the tip of the chin (mentum) to the floor of the mouth (hyoid bone) indicate the patient’s mandible is large enough to accom- modate a normally-sized tongue. A small man- dible and large tongue may obstruct access to the larynx during intubation. Finally, two finger’s breadth from the floor of the mouth (hyoid bone) to the thyroid cartilage indicates an adequate neck length and laryngeal position. A high or anteriorly-placed larynx may be very difficult to visualize during laryngoscopy.
Mallampati
The Mallampati classification is a scale (I–IV) used to predict the ability of a patient’s mouth to accommodate both the laryngoscope and ETT. To determine a patient’s classification, ask the patient to extend their neck, open their mouth as widely as possible and stick out their tongue without phonating. The degree to which the base of the tongue, faucial pillars, uvula and posterior pharynx are visible determines the Mallampati class (Figure 2.8). Class I and II predict greater oral access for the laryngoscope and superior laryngeal exposure, thereby portending a greater likelihood of successful intubation. In the case of Class III and IV scores, the tongue is large in relation to the oral cavity, signifying limited oral access, a limited view and higher intubation failure rates.
Obstruction of the airway
Upper airway obstruction can make intubation and ventilation difficult if not impossible. When time allows, patients should be screened for the presence of upper airway infections (epiglottitis, peritonsillar abscess, preverterbral abscess), laryn- geal masses or tumors, or any other upper airway conditions that may complicate laryngoscopy and BVM ventilation. Foreign bodies, extrinsic airway compression and direct airway trauma (including the possibility of airway disruption) should be considered strong evidence of an obstruction that could hinder or preclude intub- ation and ventilation.
Neck mobility
Proper mobility and alignment of the head and neck can facilitate laryngoscopy and intubation.
Certain conditions such as cervical spine immo- bilization and degenerative arthritis may limit mobility and complicate intubation.
Airway management
Table 2.2 The nine P’s of Rapid Sequence Intubation
Time Action
0 10 minutes Possibility of success 0 10 minutes Preparation
0 5 minutes Pre-oxygenation 0 3 minutes Pretreatment
Time zero Paralysis (with induction) 0 20–30 seconds Protection and positioning 0 45 seconds Placement
0 45 seconds Proof
0 1 minute Post-intubation management
Preparation
Prior to initiating RSI, careful preparation is essential to achieving success. This point cannot be emphasized enough. The SOAP ME mnemonic is used to summarize the necessary preparatory steps.
SOAP ME Suction
Suction should be tested and available at the bedside.
Oxygen
A high flow O2mask and BVM ventilation device should be ready for use.
Airway equipment
At least two functioning laryngoscope handles and the appropriately-sized and shaped laryngo- scope blades should be available. The anticipated blade of choice should be clicked into position to ensure that the light functions properly. An ETT should be chosen based on the patient’s anatomy, and one smaller size should be prepared as well.
The typical adult male will accept a 7.5- or 8.0-size ETT, the typical adult female a 7.0- or 7.5-size ETT. In children, the ETT size may be estimated by the formula ETT size 4(age in years/4). The ETT cuff should be inflated to test for an air leak.
A stylet should be inserted within the ETT to shape it into a configuration that will facilitate insertion into the airway. This configuration varies between physicians, although most prefer a gentle curve at the distal portion to a near 45-degree angle. Care must be taken to ensure that the tip of the stylet
does not protrude from the end of the ETT or through the small distal side port (Murphy’s eye).
Preparation of the ETT with the stylet inserted is recommended, as it is easier to remove a stylet (if not needed) than to add one during RSI.
Pharmacy
The patient should have at least one IV line, and patency should be ensured. The specific RSI medications, proper dosing and sequence of administration should be determined, and the agents drawn up and labeled.
Monitoring Equipment
Cardiac blood pressure and pulse oximetry mon- itoring are mandatory for all patients. If avail- able, an end-tidal CO2(ETCO2) monitor should be prepared as well.
Respiratory therapy should be at the bedside, as they play a crucial role in assisting with airway management, including securing the ETT and post-intubation care. When dealing with a com- plicated airway, anesthesiology or ear, nose and throat (ENT) specialists should be called in to assist with airway management.
Pre-oxygenation
During RSI, the process of direct laryngoscopy and ETT placement precludes the delivery of O2to the paralyzed apneic patient, which could lead to arterial O2desaturation (90%). Pre-oxygenation establishes an O2 reservoir within the patient’s lungs and body tissues that allows for a period of prolonged apnea without detrimental arterial O2 desaturation. This is accomplished through the
Airway management
Class II Class III Class IV
Class I Figure 2.8
Mallampati classification. The classification of tongue size relative to the size of the oral cavity as described by Mallampati and colleagues. Class I: faucial pillars, soft palate, and uvula visualized. Class II: faucial pillars and soft palate visualized, but the uvula is masked by the base of the tongue. Class III: only the base of the uvula can be visualized. Class IV: none of the three structures can be visualized.
Airway management
administration of 100% O2 to the patient for 5 minutes prior to paralysis, effectively leading to “nitrogen washout.” This replaces room air (80%
nitrogen, 20% O2) in the lung with nearly 100% O2. The time to desaturation following pre- oxygenation is determined by the duration of pre- oxygenation as well as the patient’s age and body habitus. Children and obese adults tend to desat- urate more rapidly than typical adults.
A non-rebreather O2mask delivers O2concen- trations in the range of 70–75%. A ventilation bag and mask placed over the patient’s mouth and nose (without actively bagging) delivers 100% O2 to the patient. In circumstances where time is limited, a patient can be quickly pre-oxygenated by taking eight vital capacity (the largest possi- ble) breaths in rapid succession from a 100% O2 source.
Pretreatment
During RSI, the use of succinylcholine (SCh), a depolarizing NMBA, and the act of intubation can lead to a number of adverse effects including increased ICP, increased intraocular pressure, increased intragastric pressure, bronchospasm in patients with reactive airway disease, increased sympathetic discharge and bradycardia (especially in children).
Selected pretreatment medications may be given to mitigate these adverse effects; they may be remembered using the mnemonic LOAD (Lido- caine, Opioid, Atropine, Defasciculation). These
medications, their indications, mechanisms of action and doses are summarized in Table 2.3.
Paralysis (with induction)
The next step in RSI is the rapid IV administration of an induction agent followed immediately by an NMBA to induce complete motor paralysis.
Induction agents
All patients with few exceptions (i.e., benzodi- azepine overdose) should receive an induction agent prior to neuromuscular blockade. Induc- tion agents induce complete loss of consciousness prior to NMBA-induced paralysis. Paralysis with- out sedation can lead to detrimental physiologic and undesirable psychologic sequelae. When com- bined with NMBAs, induction agents also enhance muscle relaxation, thereby creating improved intubating conditions.
There is no single induction agent of choice for RSI in the ED. The choice of an induction agent is based on the patient’s clinical circumstance and the agent’s attributes. The most commonly used induction agents are discussed below and sum- marized in Table 2.4.
Etomidate
Etomidate is a non-barbiturate sedative-hypnotic agent. For most ED patients, it is the induction agent of choice for RSI. It has a rapid onset, brief duration of action and causes minimal respira- tory and myocardial depression. Etomidate is the
Drug Indication Mechanism Adult dose Pediatric Notes
(IV) dose (IV) Lidocaine ↑ICP, RAD ↓intracranial response 1.5 mg/kg 1.5 mg/kg
to intubation, mitigates bronchospasm in RAD
Opioid ↑ ICP, ischemic Blunts sympathetic 3–6 mcg/kg 1–3 mcg/kg Use with caution
(fentanyl) heart disease, response to in young children
aortic dissection laryngoscopy
Atropine Children SP10 years Mitigates bradycardic 2.0 mg 0.02 mg/kg
Adults receiving a response to SCh (minimum dose
second dose of SCh 0.1 mg)
Defasciculation ↑ ICP or globe Defasiculates and 0.01 mg/kg 0.01 mg/kg Only for adults
(pancuronium, injury mitigates ICP and children
vecuronium) response to SCh 20 kg
ICP: intracranial pressure; LOAD: lidocaine, opioid, atropine, defasciculation; RAD: reactive airway disease;
SCh: succinylcholine.
Table 2.3 Pretreatment medications: LOAD
Airway management
most hemodynamically stable of the currently available induction agents. Even so, the dose should be reduced by 50% to 0.15 mg/kg in unsta- ble patients. Etomidate reduces cerebral blood flow and cerebral metabolic O2demand without adversely affecting cerebral perfusion pressure.
Due to such cerebroprotective effects and its unique hemodynamic stability, etomidate is con- sidered the induction agent of choice in patients with elevated ICP. Side effects of etomidate include vomiting, pain at the injection site, myoclonic movements and hiccups. Adverse effects from cortisol suppression have not been reported with one-time use in the ED.
Ketamine
Ketamine is a dissociative anesthetic derived from phencyclidine (PCP) that induces a cataleptic state rather than true unconsciousness. It results in analgesia, amnesia and anesthesia. Ketamine stimulates the endogenous release of cat- echolamines causing a rise in heart rate, blood pressure, myocardial consumption and bron- chodilation. For this reason, it is the induction agent of choice for hypotensive, hypovolemic or bronchospastic patients requiring intubation.
Care should be taken in patients with ischemic
heart disease. As ketamine increases ICP, cere- bral blood flow, and cerebral metabolic rate, it is generally avoided in patients with potentially increased ICP. Ketamine is known to enhance laryngeal reflexes, increase airway secretions and precipitate laryngospasm. For this reason, atropine 0.02 mg/kg IV may be given in conjunc- tion with ketamine to promote a drying effect.
Ketamine may produce an unpleasant emergence phenomenon, including hallucinations or fright- ening dreams in the first 3 hours after awaken- ing. Such reactions are more common in adults than children and can be reduced through the concomitant administration of a benzodiazepine such as lorezepam (0.05 mg/kg) or diazepam (0.2 mg/kg) after intubation.
Thiopental and methohexital
The barbiturates thiopental and methohexital are short-acting sedative-hypnotic agents that pro- vide no analgesia. The benefits of these agents are their short onset of action and rapid depres- sion of central nervous system (CNS) activity.
These agents also reduce ICP by reducing cere- bral blood flow, and provide cerebroprotective effects through reductions in cerebral metabolic O2consumption (while still maintaining cerebral Induction Induction Onset of Duration of Benefits Precautions
agents dose (IV) action action
Barbiturates
Thiopental 3–6 mg/kg (adult) 30 sec 5–10 min ↓ICP ↓BP
1–3 mg/kg (elderly) Laryngospasm
Methohexital 1–3 mg/kg 30 sec 5–10 min ↓ICP ↓BP
Short duration Laryngospasm Seizures Benzodiazepines
Midazolam 0.2–0.3 mg/kg 30–60 sec 15–30 min Reversible Apnea
Amnestic No analgesia Anticonvulsant Variable dosing
Etomidate 0.3 mg/kg 15–45 sec 3–12 min ↓ICP Myoclonic jerks
Rarely ↓BP Vomiting No analgesia
Ketamine 1–2 mg/kg 45–60 sec 10–20 min ↑ BP ↑ Secretions
Bronchodilator ↑ ICP
Dissociative Emergence
amnesia phenomenon
Propofol 1.5–3 mg/kg 15–45 sec 5–10 min
BP: blood pressure; ICP: intracranial pressure; IOP: intraocular pressure.
Table 2.4 Induction agents
Airway management
perfusion pressure). Their major disadvantage is their propensity to induce significant hypoten- sion from myocardial depression and venodila- tion. For this reason, these agents are best avoided in hypotensive patients. Other side effects of thiopental include central respiratory depres- sion, histamine release (avoid use in asthmatic patients), tissue injury and necrosis with extra- vasation. It is contraindicated in patients with porphyria. Methohexital is shorter-acting and more potent than thiopental, and not surprisingly associated with more profound hypotension and respiratory depression.
Propofol
Propofol is an alkylphenol derivative with hyp- notic properties. It is rapid acting and has a short duration of action. Although it blunts the potential rise in ICP associated with intubation, it adversely reduces cerebral perfusion pressure as well as systemic blood pressure. As a result, propofol is uncommonly used for induction in the ED.
Midazolam
Midazolam and other benzodiazepines cause amnesia, anxiolysis, central muscle relaxation, sedation, and hypnosis. They also have anticon- vulsant effects. As induction agents, their pri- mary indications are to promote sedation and amnesia, their greatest asset. A drawback to their use is their great dosing variability, depending on the patient’s gender and age. Midazolam is a myocardial depressant and reduces systemic vascular resistance. It should be used with cau- tion in elderly patients and those with hemody- namic compromise. Though midazolam may be used as the primary induction or adjunctive agent during RSI, it is more commonly utilized for sedation in combination with an analgesic agent in patients who are intubated.
Neuromuscular blockade
NMBAs do not provide analgesia, sedation or amnesia; they are used to paralyze the patient, facilitating rapid endotracheal intubation. The ideal NMBA would have a rapid onset, a short duration of action and few adverse side-effects.
SCh, a depolarizing NMBA, comes closest to meeting all of these traits and is the most com- monly used NMBA in the ED. At the neuromus- cular junction, SCh binds tightly to acetylcholine receptors, causing depolarization of the motor endplate and muscle contraction. Clinically, this initially manifests as muscle fasciculations followed by paralysis. IV administration of SCh
results in muscle fasciculations within 10–15 seconds followed by complete paralysis after 45–60 seconds. Because of its short duration of action, patients may begin spontaneously breath- ing within 3–5 minutes.
The dose of SCh is 1.5 mg/kg rapid IV push in adults. In children 10 years of age, the recom- mended dose is 2 mg/kg rapid IV push. In new- borns, use 3 mg/kg rapid IV push. There is little harm to giving too much SCh; however, giving too little SCh can result in an inadequately para- lyzed patient and affect one’s ability to success- fully intubate.
The main drawback to SCh are its side effects, including muscle fasciculations, bradycardia, hyperkalemia, prolonged neuromuscular block- ade, trismus (masseter spasm) and malignant hyperthermia. The muscle fasciculations are asso- ciated with rises in ICP, intragastric and intra- ocular pressure, and can be inhibited through the use of a defasciculating dose of a non-depolarizing NMBA. The bradycardia that follows the admin- istration of SCh most commonly occurs in children and can be avoided by pretreatment with atropine (0.02 mg/kg). Under usual circumstances, SCh induces a small but clinically insignificant rise in serum potassium of 0.5 mEq/L. However, in large burns, crush injuries, denervation or neuro- muscular disorders, the administration of SCh may lead to an exaggerated rise in potassium levels of 5–10 mEq/L and result in hyperkalemic dysrhythmias or cardiac arrest. Fortunately, the hyperkalemia risk is not immediate in these patients but occurs typically 2–7 days post-event, depending on the injury or underlying process.
Non-depolarizing NMBAs such as rocuronium compete with acetylcholine for receptors at the neuromuscular junction, thereby causing paraly- sis. Although these agents are commonly used as defasciculating agents or for post-intubation patient management, they may also be used as the primary RSI paralytic agent in specific patient populations or in patients who have a con- traindication to SCh. They have much fewer side effects than SCh but are generally less effective for intubation because of their delayed time to paralysis, prolonged duration of action, or both.
Specific attributes of the depolarizing and non- depolarizing NMBAs are listed in the Table 2.5.
Protection
Following the administration of induction and paralytic agents, the patient will predictably lose consciousness and become apneic. Sellick’s
Neuromuscular Intubating Onset Duration blocking agent dose (IV)
Depolarizing agent
Succinylcholine 1.5 mg/kg (adult) 45–60 sec 6–12 min 2 mg/kg (child)
3 mg/kg (infant) Non-depolarizing
Rocuronium 1.0 mg/kg 50–70 sec 30–60 min
Vecuronium 0.15 mg/kg 90–120 sec 60–75 min
Pancuronium 0.1 mg/kg 100–150 sec 120–150 min
Airway management
maneuver (cricoid pressure) should be applied by an assistant just as the patient is noted to lose consciousness. This application of firm pressure (10 lb) to the cricoid cartilage compresses the esophagus and prevents passive regurgitation of gastric contents (Figure 2.9). Sellick’s maneuver should be maintained until the ETT has been placed, its position verified, and the cuff inflated.
If Sellick’s maneuver is applied too early, the patient may find it uncomfortable or vomit. This maneuver should be discontinued if the patient is actively vomiting because of the risk of esophageal rupture.
Positioning
Based on the patient’s age, anatomy and other conditions (cervical arthritis, cervical spine pre- cautions), the patient should be carefully pos- itioned in the manner that increases the odds of successful intubation.
The airway can be thought of as having three separate axes: the oral, pharyngeal and laryn- geal. Proper positioning prior to laryngoscopy helps align these axes and improve visualization of the glottis. In the neutral position, these axes are misaligned (Figure 2.10).
Placing a small pillow under the patient’s occiput flexes the lower cervical spine relative to the torso and aligns the pharyngeal and laryn- geal axes (Figure 2.11). Positioning the patient in the “sniffing” position with extension of the head on the neck aligns all the three axes (Figure 2.12).
Patients with possible cervical spine injury should be maintained in the neutral position.
Placement
After the administration of SCh, the patient will predictably have muscle fasciculations followed
OA PA
LA
Figure 2.10
Head on bed, neutral position. PA: pharyngeal axis; OA:
oral axis; LA: laryngeal axis. Reproduced with permission from Walls RM et al, Manual of Emergency Airway Management, 2nd ed. and Companion Manual to the Airway Course (www.theairwaysite.com), Lippincott Williams & Wilkins, 2004.
Figure 2.9
Cricoid pressure (Sellick’s maneuver).
Table 2.5 Neuromuscular blocking agents