Rapid sequence induction


In advanced airway management, rapid sequence induction – also referred to as rapid sequence intubation or as rapid sequence induction and intubation – is a special process for endotracheal intubation that is used where the patient is at a high risk of pulmonary aspiration or impending airway compromise. It differs from other forms of general anesthesia induction in that artificial ventilation is generally not provided from the time the patient stops breathing until after intubation has been achieved. This minimizes insufflation of air into the patient's stomach, which might otherwise provoke regurgitation.
"Classic" RSI involves pre-filling the patient's lungs with a high concentration of oxygen gas, followed by applying cricoid pressure, administering rapid-onset sedative or hypnotic and neuromuscular-blocking drugs that induce prompt unconsciousness and paralysis, inserting an endotracheal tube with minimal delay, and then releasing the cricoid pressure. "Modified" RSI refers to changes that deviate from the classic pattern, usually to reduce acidosis or improve oxygenation in case of cardiac, neurological and asthmatic patients, but at the expense of increased regurgitation risk; examples of modifications include giving ventilations before the tube has been placed, or not using cricoid pressure. The induction agents and muscle relaxants may differ in each cases.
The procedure is used where general anesthesia must be induced before the patient has had time to fast long enough to empty the stomach; where the patient has a condition that makes aspiration more likely during induction of anesthesia, regardless of how long they have fasted ; or where the patient has become unable to protect their own airway even before anesthesia.
The induction drugs traditionally used for RSI have short durations of action, wearing off after only minutes. This confers a degree of fault tolerance on the procedure when it is used in elective or semi-elective settings: if intubation is unsuccessful, and if the clinical condition allows it, the procedure may be abandoned and the patient should regain the ability to protect their own airway sooner than would be the case under routine methods of induction. Conversely, in emergency settings where the patient's condition does not allow for them to be woken up immediately, a failed intubation under RSI places them at very high risk for respiratory compromise.

Common medications

Premedication

Premedication is used to reduce anxiety of those who are going to be intubated and to reduce the anticipated physiological response of the patient during intubation.
Administration of induction agents followed by neuromuscular blockade agents helps to achieve optimal conditions for intubation.
Paralytics are also known as neuromuscular-blocking drugs. NMB can reduce the complication rates of rapid sequence induction such as inadequate oxygenation of the blood, airway complications, and instability of the cardiovascular system. NMB can be divided into two types: depolarising and non-depolarising blockers. Depolarising blockers resembles the acetylcholine and activates the motor end-pate of the neuromuscular junction. Meamwhile, non-depolarising blockers competitively blocks the NMJ without activating the motor end plate.

Depolarising blockers

In myasthenia gravis, the number of acetylcholine receptors is reduced due to antibodies attack. Therefore, dosages greater than 2 mg/kg is required for these people. In Lambert Eaton syndrome, the number of acetylcholine receptors is upregulated. Although this condition has increased response to the non-dopolarsing NMB, it does not shows increased response to depolarsing blockers. Therefore, acetylcholine dose reduction is not needed for Lambert Eaton syndrome. For those with pseudocholinesterase enzyme deficiency, the person can remain paralysed up to 6 to 8 hours because there is not enough enzymes to break down acetylcholine. Therefore, acetylcholine should be avoided in these people. On the other hand, although there is also a relative decrease in pseudocholinesterase enzymes in those with liver disease, kidney disease, anemia, pregnancy, chronic cocaine use, amphetamine abuse, increased age, and connective tissue disease, the acetylcholine effect is minimal and dose reduction is not needed.
The most significant side effect of acetylcholine is malignant hyperthermia and hyperkalemia. In malignant hyperthermia, mutation of ryanodine receptor at chromosome 19 is responsible for the increased release of calcium from the calcium channels, thus triggering increase in muscle contraction and temperature rise. This only happens when acetylcholine is administered. For those who had history of receiving succinylcholine and developed fever, tachycardia, and muscle rigidity. Muscle rigidity in the masseter muscle causes intubation to be impossible. Rhabdomyolysis of the muscles also occurs which lead to increase in calcium, potassium, and creatine kinase concentrations. Blood gas analysis which cause mixed respiratory and metabolic acidosis. Dantrolene is the treatment of choice that binds to ryanodine receptors that inhibits calcium release from the sarcoplasmic reticulum. However, such drug is labour-intensive for pharmacy to prepare. Other physiological derangements should be treated supportively. The serum potassium levels typically increase by 0.5 to 1 mEq/L and is not contraindicated in those with diabetic ketoacidosis and acute kidney failure. Only if the person has symptomatic hyperkalemia, then rocuronium should be considered. In those with prolonged immobilisation, crush injuries, burns, and myopathies, there is increase in extrajunctional cholinergic receptors, thus potential potassium rise is higher in these people. For those with acute nerve injuries or stroke, the increase in acetylcholine receptors will only occurs after five to fifteen days after injury. Therefore, succinylcholine can be given within the first 24 hours of injury. The increase in succinylcholine sensitivity remains elevated after 2 to 6 months after the injury. Other side effects of succinylcholine includes increase in intraocular pressure and increase in intracranial pressure.

Non-depolarising blockers

Rapid sequence intubation refers to the pharmacologically induced sedation and neuromuscular paralysis prior to intubation of the trachea. The technique is a quicker form of the process normally used to induce general anesthesia. A useful framework for describing the technique of RSI is the "seven Ps".

Preparation

The patient is assessed to predict the difficulty of intubation. Continuous physiological monitoring such as ECG and pulse oximetry is put on the patient. The equipment and drugs for the intubation are planned, including the endotracheal tube size, the laryngoscope size, and drug dosage. Drugs are prepared in syringes. Intravenous access is obtained to deliver the drugs, usually by placing one or two IV cannulae.

Preoxygenation

The aim of preoxygenation is to replace the nitrogen that forms the majority of the functional residual capacity with oxygen. This provides an oxygen reservoir in the lungs that will delay the depletion of oxygen in the absence of ventilation. For a healthy adult, this can lead to maintaining a blood oxygen saturation of at least 90% for up to 8 minutes. This time will be significantly reduced in obese patients, ill patients and children. Preoxygenation is usually performed by giving 100% oxygen via a tightly fitting face mask. Preoxygenation or a maximum of eight deep breaths over 60 seconds results in blood oxygenation is not different from that of quiet breathing volume for 3 minutes.
Newer methods of pre oxygenation include the use of a nasal cannula placed on the patient at 15 LPM at least 5 minutes prior to the administration of the sedation and paralytic drugs. High flow nasal oxygen has been shown to flush the nasopharynx with oxygen, and then when patients inspire they inhale a higher percentage of inspired oxygen. Small changes in FiO2 create dramatic changes in the availability of oxygen at the alveolus, and these increases result in marked expansion of the oxygen reservoir in the lungs prior to the induction of apnea. After apnea created by RSI the same high flow nasal cannula will help maintain oxygen saturation during efforts securing the tube. The use of nasal oxygen during pre-oxygenation and continued during apnea can prevent hypoxia before and during intubation, even in extreme clinical cases.

Pretreatment

Pretreatment consists of the medications given to specific groups of high-risk patients 3 minutes before the paralysis stage with the aim of protecting the patient from the adverse effects of introducing the laryngoscope and endotracheal tube. Intubation causes increased sympathetic activity, an increase in intracranial pressure and bronchospasm. Patients with reactive airway disease, increased intracranial pressure, or cardiovascular disease may benefit from pretreatment. Two common medications used in the pretreatment of RSI include Lidocaine and Atropine. Lidocaine has the ability to suppress the cough reflex which in turn may mitigate increased intracranial pressure. For this reason Lidocaine is commonly used as a pretreatment for trauma patients who are suspected of already having an increase in intracranial pressure. Although there is not yet definitive evidence to support this, if proper dosing is used it is safe. The typical dose is 1.5 mg/kg IV given three minutes prior to intubation. Atropine may also be used as a premedication agent in pediatrics to prevent bradycardia caused by hypoxia, laryngoscopy, and succinylcholine. Atropine is parasympathetic blocker. The common premedication dose for atropine is 0.01–0.02 mg/kg.

Paralysis with induction

With standard intravenous induction of general anesthesia, the patient typically receives an opioid, and then a hypnotic medication. Generally the patient will be manually ventilated for a short period of time before a neuromuscular blocking agent is administered and the patient is intubated. During rapid sequence induction, the person still receives an IV opioid. However, the difference lies in the fact that the induction drug and neuromuscular blocking agent are administered in rapid succession with no time allowed for manual ventilation.
Commonly used hypnotics include thiopental, propofol and etomidate. The neuromuscular blocking agents paralyze all of the skeletal muscles, most notably and importantly in the oropharynx, larynx, and diaphragm. Opioids such as fentanyl may be given to attenuate the responses to the intubation process. This is supposed to have advantages in patients with ischemic heart disease and those with brain injury. 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. Despite their common use, such adjunctive medications have not been demonstrated to improve outcomes.

Positioning

Positioning involves bringing the axes of the mouth, pharynx, and larynx into alignment, leading to what's called the "sniffing" position. The sniffing position can be achieved by placing a rolled towel underneath the head and neck, effectively extending the head and flexing the neck. You are at proper alignment when the ear is inline with the sternum.
The Sellick's maneuver, or cricoid pressure, may be used to occlude the esophagus with the goal of preventing aspiration.

Placement of tube

During this stage, laryngoscopy is performed to visualize the glottis. Modern practice involves the passing of a ‘Bougie’, a thin tube, passed the vocal cords and over which the endotracheal tube is then passed. The bougie is then removed and an inbuilt cuff at the end of the tube is inflated,, to hold it in place and prevent aspiration of stomach contents.
The position of the tube in the trachea can be confirmed in a number of ways, including observing increasing end tidal carbon dioxide, auscultation of both lungs and stomach, chest movement, and misting of the tube.

Postintubation management

Malpositioning of the endotracheal tube should be excluded by confirmation of end tidal CO2, auscultation and observation of bilateral chest rise.
One important difference between RSI and routine tracheal intubation is that the practitioner does not typically manually assist the ventilation of the lungs after the onset of general anesthesia and cessation of breathing, until the trachea has been intubated and the cuff has been inflated.

Additional considerations

Age can play a role in whether or not the procedure is warranted, and is commonly needed in younger persons. The clinician that performs RSI must be skilled in tracheal intubation and also in bag valve mask ventilation. Alternative airway management devices must be immediately available, in the event the trachea cannot be intubated using conventional techniques. Such devices include the combitube and the laryngeal mask airway. Invasive techniques such as cricothyrotomy must also be available in the event of inability to intubate the trachea by conventional techniques.
RSI is mainly used to intubate patients at high risk of aspiration, mostly due to a full stomach as commonly seen in a trauma setting. Bag ventilation causes distention of stomach which can induce vomiting, so this phase must be quick. The patient is given a sedative and paralytic agent, usually midazolam / suxamethonium / propofol and intubation is quickly attempted with minimal or no manual ventilation. The patient is assessed for predictable intubation difficulties. Laryngoscope blades and endotracheal tubes smaller than would be used in a non-emergency setting are selected.
If the patient on initial assessment is found to have a difficult airway, RSI is contraindicated since a failed RSI attempt will leave no option but to ventilate the patient on bag and mask which can lead to vomiting. For these challenging cases, awake fiberoptic intubation is usually preferred.

Controversy

Since the introduction of RSI, there has been controversy regarding virtually every aspect of this technique, including: