R.S.I - Rapid Sequence Intubation - Review

The

rationale behind RSI is to prevent aspiration and its potential problems, including aspiration

pneumonia, and to counteract the increase in systemic arterial blood pressure,

heart rate, plasma catecholamine release, intracranial pressure (ICP), and

intraocular pressure (IOP) that occurs with endotracheal intubation.

RSI generally consists of seven steps: (1) preparation, (2) preoxygenation, (3) pretreatment,

(4) paralysis with induction, (5) protection and positioning, (6) placement of the

tube in the trachea, and (7) postintubation management.

oxygen, suction,

bag-valve mask (BVM), laryngoscope and blades, endotracheal (ET) tubes with a stylet

with one size larger and smaller than the anticipated ET size, resuscitation equipment,

and supplies for rescue maneuvers (eg, laryngeal mask airways [LMA] or cricothyrotomy.

1. Suction, Oxygen, Airway, Pharmacology, Monitoring, Equipment.

2. Preoxygenation should be occurring during the preparation step. The purpose of preoxygenation

is to replace the nitrogen in the patient’s functional residual capacity

(FRC) with oxygen or ‘‘nitrogen wash-out oxygen wash-in.’’ ‘‘Denitrogenation’’ can

be accomplished in 3 to 5 minutes by having the patient breathe 100% oxygen via

a tight-fitting facemask or, if time is an issue, with four vital capacity breaths. positive pressure ventilation should be

avoided during the preoxygenation step because of a risk for gastric insufflation

and possible regurgitation. Because effective ventilation by the patient is not feasible

in many ED patients, BVM ventilation may be necessary in apneic patients or patients

with ineffective spontaneous breathing. In these instances, use of the Sellick procedure

with gentle cricoid pressure should be applied in an attempt to limit gastric distention

and avoid aspiration during BVM ventilation. In the preoxygenation phase, replacing the nitrogen reservoir in the lungs with oxygenallows 3 to 5 minutes of apnea without significant hypoxemia in the normoxic

adult.

3. Ancillary medications are administered during the pretreatment step to mitigate the

negative physiologic responses to intubation. For maximal efficacy, the pretreatment

drugs should precede the induction agent by 3 minutes, although this is not always

possible. The pretreatment phase and preoxygenation phase can (and usually) do occur

simultaneously during most instances of RSI in the ED. Medications and their usual

dosages that may be given during the pretreatment phase are lidocaine 1.5 mg/kg,

fentanyl 2–3 mcg/kg, and atropine 0.02 mg/kg (minimum 0.1 mg, maximum 0.5 mg.

The clinical indications for these drugs are (1) for patients with elevated ICP and impaired

autoregulation: administer lidocaine and fentanyl, (2) patients with major vessel

dissection or rupture or those with significant ischemic heart disease give fentanyl, (3)

adults with significant reactive airway disease, premedicate with lidocaine, and (4) atropine

is indicated for pediatric patients %10 years old and in patients with significant

bradycardia if succinylcholine is given. One caveat to remember is to give fentanyl with

caution to any patient in shock (whether compensated or uncompensated) who is dependent

on sympathetic drive because of a potential decrease in blood pressure with

fentanyl administration.

In patients who are receiving succinylcholine as their induction agent and who are at

risk for increased ICP, one tenth of the normal paralyzing dose of a nondepolarizing

(ND) neuromuscular blocking agent (NMB) can be given 3 minutes before receiving

succinylcholine. The purpose of the defasciculating dose of the ND-NMB is to prevent

the fasciculations (and therefore, the increase in ICP) that occurs with succinylcholine.

For example, the dose would be 10% of the paralyzing dose of rocuronium (10% of 0.6

mg/kg 5 0.06 mg/kg). The mnemonic ‘‘LOAD’’ has been used to indicate the pretreatment

drugs for RSI: L 5 lidocaine, O 5 opioid (specifically, fentanyl), A 5 atropine, and

D 5 defasciculation.

Paralysis with induction is achieved by the rapid intravenous administration in quick

succession of the induction agent and the NMB. The selection of a specific sedative

depends on multiple factors: the clinical scenario, which includes patient factors (includes

cardiorespiratory and neurologic status, allergies, comorbidity) and the clinician’s

experience/training and institutional factors, as well as the characteristics of

the sedative.28 Sedatives commonly used for induction during RSI are barbiturates

(pentobarbitol, thiopental, and methohexitol),29 opioids (fentanyl),1 dissociative anesthetics

(ketamine),30 and nonbarbiturate sedatives (etomidate,31 propofol,32 and the

benzodiazepines).21,33 The dosages and characteristics of these agents and are summarized

in Table 1. One caveat to remember is that the induction dosages of these

sedatives may be different (generally, slightly higher) than the dose used for sedation.

For example, for etomidate the usual dose for procedural sedation is 0.2 mg/kg and for

RSI is 0.3 mg/kg.

5.Several caveats regarding the proper technique need to be considered: location,

timing, and amount of pressure. Cricoid pressure should be applied as soon as the patient

starts to lose consciousness and should be maintained until the correct endotracheal

position is verified. Pressure should be gentle but firm enough to compress the

esophagus between the cricoid cartilage and the anterior surface of the vertebral

body. The cricoid cartilage is opposite the C4–C5 vertebrae in an adult, and C3–C4

in an infant.

Step 6—Placement of the Endotracheal Tube in the Trachea

When the jaw becomes flaccid from the paralytics, it is time to begin intubation by

standard methods. ET tube placement should be confirmed by the usual techniques.

Step 7—Postintubation Management

After ET tube placement and confirmation, the ET tube must be secured. A chest radiograph

is done not only to check for proper ET tube placement but also to evaluate

the pulmonary status and to monitor for any complications of the intubation and RSI.

Continued sedation and analgesia, sometimes with paralysis as well as cardiopulmonary

monitoring, is indicated as long as the patient requires advanced airway support

Etomidate, the most commonly used sedative for RSI in adults, can also be administered

for pediatric RSI.31 The usual dose is 0.3 mg/kg or 20 mg in a 70-kg adult. It often

is used in trauma patients with known or potential bleeding, hypovolemic patients, and

patients with limited cardiac reserve, because it does not have significant cardiovascular

effects. Etomidate also decreases ICP and the cerebral metabolic rate, which

suggests that it may have a neuroprotective effect. These features are why some clinicians

consider it the sedative of choice in a patient who has multiple trauma with

both a head injury and hemorrhage or shock.

Etomidate does inhibit 11-b-hydroxylase, an enzyme necessary for adrenal steroid

production.35 Transient adrenal suppression has been noted after a single dose of etomidate,

although this is probably not clinically significant.36 Some data indicate that

etomidate has a negative impact on patient outcome in critically ill patients with sepsis

and septic shock.37–39 This has led to the suggestion that a corticosteroid be coadministered

when etomidate is given for RSI.38 Although either dexamethasone (0.1 mg/kg)

or hydrocortisone (1–2 mg/kg) may be given, dexamethasone often is chosen because

it does not interfere with the adrenocorticotropin hormone (ACTH) stimulation test,

which may be needed to later test for adrenal insufficiency. In any case, infusions

of etomidate for continued postintubation sedation are contraindicated. Myoclonus is another side effect of etomidate that may interfere with intubation if

a paralytic is not used,40 although this is not the situation with RSI in which a sedative

and paralytic generally are coadministered in quick succession.

Thiopental is the most commonly used barbiturate for pediatric RSI6 and may be the

most commonly used barbiturate for anesthesia induction.41 However, it used is less.

Thiopental decreases both cerebral blood flow and

the metabolic demands of the brain, which makes it an ideal sedative agent in patients

with known increased ICP or patients with head injury who are hemodynamically stable.

Thiopental has negative cardiovascular effects: myocardial depression and peripheral

vasodilatation. Thus, hypotension with associated hypoperfusion can occur

in patients who are hypovolemic or have myocardial depression. Generally, when hypotension

occurs, there is a compensatory baroreceptor mediated reflex tachycardia.

Unfortunately, patients who are hypovolemic or in shock or who are already tachycardic

may not be capable of further compensatory heart rate increases and can experience

a drop in blood pressure with thiopental administration.

Thiopental has some respiratory side effects. It has a dose- and rate-related (eg,

high dose, rapid administration) respiratory depression of the central nervous system

(CNS) that can cause apnea, especially in head injured or hypovolemic patients. With

‘‘light’’ anesthesia, several untoward effects may occur, especially during airway manipulation:

catecholamine release causing systemic or intracranial hypertension, laryngospasm,

cough, and bronchospasm, especially in asthmatic patients.41 To

mitigate or avoid these negative effects, it has been recommended to coadminister

an analgesic (such as fentanyl) especially in head-injured patients.

Ketamine, a dissociative anesthetic, exerts its effects by interrupting the connection

between the thalamo-neocortical tracts and the limbic system. Unlike all the other

sedatives, it has an additional advantage in that it also has analgesic properties.  Ketamine also causes an increase in ICP by both an increase in systemic blood

pressure and cerebral vasodilatation and, therefore, is contraindicated in patients

with ICP, an intracerebral hemorrhage, an intracranial mass, or head trauma; although

a recent study has challenged this contraindication.42 This French study compared the

cerebral hemodynamics of ketamine combined with midazolam and found no significant

difference in ICP or cerebral perfusion pressure when compared with midazolamsufentanil.

Ketamine is probably the sedative of choice for asthmatic patients for many reasons.

Ketamine, through the release of endogenous catecholamines, relieves bronchospasm

by dilating bronchial smooth muscle and stimulating the pulmonary

b receptors. Ketamine increases tracheobronchial/oropharyngeal secretions. Fortunately, pretreatment with atropine (preferred for RSI) or glycopyrollate (preferred

for sedation) prevents excess secretions.27,44 The dose of atropine for RSI is

0.01 to 0.02 mg/kg intravenously with a minimum of 0.1 mg and a maximum of 0.5

to 1.0 mg. Glycopyrollate is the antimuscarinic drug of choice for procedural

sedation because it has a greater antisialagogue effect and fewer side effects (less

tachycardia, fewer dysrhythmias, and no CNS side effects).44 In addition, atropine

crosses the blood–brain barrier (glycopyrollate does not so it has no CNS side effects)

and may increase the incidence of emergence reactions.

The main disadvantage of the benzodiazepines

is that they can cause respiratory depression and apnea. Other uncommon

side effects are paradoxical agitation, vomiting, coughing, and hiccups.

Propofol

Propofol is an ultra–short-acting sedative hypnotic agent. It has no analgesic effects,

and its amnestic effects are variable. The advantages of propofol are its very quick. onset and short duration. It also has antiemetic properties, can be used in malignant

hypothermia patients. Propofol also has negative cardiovascular

effects so it should be used with caution in patients with volume depletion, hypotension,

or cardiovascular disease.

Pathophisiology

The nicotinic receptor, a protein particle located on the postsynaptic myocyte membrane

has two parts: a binding component and an ionophore component. The binding

component projects outward from the postsynaptic myocyte membrane into the synaptic

space where it binds the neurotransmitter Ach. The ionosphere component extends

through the postsynaptic neural membrane to the interior of the postsynaptic

membrane. The ionosphere may serve as an ion channel that permits the movement

of ions (in this case primarily sodium ions, as well as other ions) through the membrane.

Acetylcholine (Ach), the neurotransmitter at cholinergic synapses, is released from the

ending of preganglionic and postganglionic parasympathetic nerves and preganglionic

sympathetic nerves.

Ach then diffuses across the synaptic cleft to the motor endplate. Attachment of Ach

to the nicotinic receptors on the skeletal muscle leads to a conformational change in

the nicotinic receptor. This altered protein molecule on the nicotinic skeletal muscle

receptor increases the permeability of the skeletal myocyte cell to various ions (sodium,

potassium, chloride, and calcium) with an influx of sodium into the skeletal myocyte

(see Fig. 4). This produces a large positive potential charge within the skeletal myocyte, referred to as the ‘‘end plate potential.’’ The end plate potential creates an

action potential that travels along the skeletal myocyte membrane causing muscle

contraction. The release of Ach from the nicotinic receptor on the skeletal myocyte ends depolarization.

Ach can either diffuse back into the nerve ending or be broken down by the

acetylcholinesterase enzyme into choline and acetic acid (see Fig. 5). Under normal

circumstances, large amounts of the enzyme acetylcholinesterase are found in the

synaptic space.

Neuromuscular blocking agents (NMBs) are substances that paralyze skeletal

muscles by blocking nerve impulse transmission at the neuromuscular or myoneural

(muscle-nerve) junction.

There are several critical factors to remember with RSI. First, a sedative is coadministered

with the NMB. Patients given an NMB may be aware of their environment, including

painful stimuli, even though they are unable to respond. Failure to sedate the

patient allows the possibility of negative physiologic responses to airway manipulation

such as increased ICP, hypertension, and tachycardia. In addition, the patient may be

aware of and remember the intubation, which is considered inhumane. Concomitant

sedative use limits or helps avoid these adverse physiologic responses to airway manipulation

and may even result in a better view of the airway during laryngoscopy.

However, whenever an NMB is used, the physician must be prepared for a difficult

or failed airway with the possibility that a surgical airway may be necessary if the patient

cannot be oxygenated or ventilated adequately with a bag-valve mask or extraglottic

device. Assessment of the airway, especially if there is the potential for

a difficult or failed airway, should be done before administering an NMB.

NMBs are depolarizing or nondepolarizing. Depolarizing agents mimic the action of

Ach. They case a sustained depolarization of the neuromuscular junction, which prevents

muscle contraction. Nondepolarizing agents work by competitive inhibition to

block Ach’s action at the neuromuscular junction to prevent depolarization.

This nonspecific action at sites throughout the body, eg, nicotinic (ganglionic)

and muscarinic autonomic sites, not just at the neuromuscular junction, helps explain

some of their side effects.

Sch is the prototype of the depolarizing agents. Because its chemical structure (eg,

quaternary ammonium compound) is similar to that of Ach, it binds to the acetylcholine

receptor (AchR) on the motor end plate and depolarizes the postjunctional neuromuscular

membrane, resulting in continuous stimulation of the motor end plate AchRs. The

neuromuscular block/motor paralysis is terminated when the NMB (eg, Sch) unbinds

from the AchR and diffuses back into the circulation where it is hydrolyzed by plasma

cholinesterase. Plasma cholinesterase (also referred to as ‘‘pseudocholinesterase’’ or

‘‘butylcholinesterase’’) rapidly hydrolyses Sch to succinylmonocholine (a very weak

NMB) and choline. Sch’s short duration of action is caused by the rapid hydrolysis

by plasma cholinesterase both before Sch reaches and after Sch leaves the neuromuscular

junction, because there is minimal if any pseudocholinesterase at the neuromuscular

junction. Some Ach may diffuse back into the nerve terminal, although the

majority of Ach is hydrolyzed by plasma cholinesterase. Muscle contraction will not reoccur

until the neuromuscular junction returns to the resting state and then is depolarized

again. Transient fasciculations (caused by initial depolarization) are followed by

blockade of neuromuscular transmission with motor paralysis when Sch is given.

The major advantages of Sch are its rapid onset with complete motor paralysis occurring

within 45 to 60 seconds and short duration of action lasting only 6 to 10 minutes

when given in the recommended 1.5-mg/kg intravenous dose. Do not underdose the drug. It

is preferable to overestimate rather than underestimate the dose because an insufficient

dose may make it difficult to intubate if the patient is not adequately paralyzed. The recommended Sch dose in infants (including neonates) is 2 mg/kg

based on their higher volume of distribution,21,47 and some even recommend up to

3 mg/kg in newborns.47 Administer Sch as a rapid bolus followed by a 20 to 30 cc saline

flush to avoid incomplete paralysis. Sch has been given intramuscularly in a 3- to

4-mg/kg dose in a rare life-threatening situation in which there is inability to obtain venous

access. The absolute contraindications to Sch are (1) a history of malignant hyperthermia in the

patient or family and (2) patients at high risk of severe hyperkalemia.

Repeat

dosing or prolonged use of Sch potentiates its effects at the sympathetic ganglia and

vagal effects. The negative muscarinic effects from vagal stimulation may lead to bradycardia

and hypotension even at recommended doses. This is one reason some experts

recommend atropine pretreatment in infants/small children, anyone with

significant bradycardia, and those receiving multiple doses of Sch.

Malignant hyperthermia is a rare genetic myopathetic disorder precipitated by multiple

drugs, especially certain inhalational anesthetics (such as halothane, sevoflurane, desiflurane,

isoflurane) and Sch. It is thought to be caused by an abnormal ryanodine receptor

causing marked leakage of calcium from the sarcoplasmic reticulum of skeletal

muscle cells resulting in extremely high intracellular calcium levels.

Even in ‘‘normal’’ patients, Sch may increase the serum potassium up to 0.5 mEq/L

because of depolarization of the myocytes (skeletal muscle cells). Generally, the rise

has no clinical significance except in patients with a predisposition to hyperkalemia,

such as a patient with rhabdomyolysis or patients with chronic skeletal muscle disease

in whom there is ‘‘up-regulation’’ from increased sensitization of extrajunctional AchR.

so the risk of life-threatening hyperkalemia

does not start until days (usually 3–5 days) after the injury or illness onset.

Although the longstanding tenet has been to avoid Sch in patients in chronic renal

failure who have normokalemia, there is no supportive evidence for this.

Its safe in patients with Increased intracranial pressure and intraocular pressure. Fasciculations are involuntary, unsynchronized muscle contractions. They are caused

by the depolarization of Ach receptors.

Nondepolarizing (ND) NMBs competitively block Ach transmission at the postjunctional

cholinergic nicotinic receptors. Unlike Sch, which causes a conformational change

in the AchR receptor resulting in depolarizination of the neuromuscular junction, the

nondepolarizing NMB prevents Ach from access to the nicotinic receptor, thereby preventing

muscle contraction. Fasciculations do not occur with the ND-NMBs.

Currently, the only ultra short NMB available in the United States is the depolarizing

NMB, Sch. However, doubling the dose of rocuronium from 0.6 mg/kg to 1.2

mg/kg shortens the onset of complete neuromuscular blockade from about 1.5 minutes

(mean, 89 seconds) to 1 minute (mean, 55 seconds).50 If Sch cannot be used

and intubation in less than 90 seconds is needed, then the higher doses of the NDNMB

can be used.

The ND-NMBs are used: 1) for muscle relaxation if Sch is contraindicated or unavailable,

2) to maintain postintubation paralysis (remember that repeated doses of Sch

should be avoided, if possible), and 3) as a pretreatment agent to lessen or eliminate

the fasciculations and their side effects (eg, myalgias and increased IOP, ICP, intragastric

pressure [IGP]) associated with Sch use.

Short-acting ND-NMBs include rapacuronium

and mivacurium; intermediate acting include vecuronium, rocuronium,

atracurium, and cisatracurium; and long-acting include pancuronium, pipecuronium,

d-tubocurarine, metacurine, doxacurium, alcuronium, and gallamine.

A Cochrane meta-analysis concluded ‘‘succinylcholine

created superior intubation conditions to rocuronium when comparing

both excellent and clinically acceptable intubating conditions.

In clinical practice, the ND-NMB is generally administered 2 minutes before giving

the intubating dose of Sch. Giving ND-NMB increases the muscle’s resistance

to Sch’s action such that increasing the Sch dose by 50% is recommended. for the emergent intubation in the ED

is the extra time (about 2 or more minutes) added to the procedure before intubation

occurs. Some clinicians also use fasciculations as a clue to when neuromuscular

blockade has occurred, and conditions are ready for ET tube placement.

A drug familiar to emergency medicine, lidocaine, can be used as an alternative to

ND-NMB for priming before Sch administration. Lidocaine is effective in minimizing or

preventing the fasciculations with their side effects that occur after Sch administration.

The dose is 1.5 mg/kg of lidocaine.

‘‘Facilitated intubation’’ refers to the use of a sedative only (without a paralytic) to pharmacologically

assist with intubation. Facilitated intubation, also referred to as ‘‘pharmacologically

assisted intubation,’’ has been recommended by some clinicians in

specific circumstances because it does not involve neuromuscular blockade. Some

advocate the avoidance of a neuromuscular paralysis and the use of sedation alone

(‘‘facilitated intubation’’) in clinical scenarios in which a difficult airway is anticipated.

For facilitated intubation, the most common sedative used has been etomidate, although

midazolam has also bee used.

For ED intubations, the results of the NEAR studies confirm the superiority of RSI

over facilitated intubation.6,34 The successful intubation rate for first attempt was

RSI 5 85%, and sedative only (no NMB) 5 76%. The successful rate for first intubation

was RSI 5 91%, and sedative only (no NMB) 5 88%.34 For pediatric patients, the

first attempt intubation success rates were RSI, 78%; sedative only, 44%; and no

medication. 47%