In anaesthesia and advanced airway management, rapid sequence induction (RSI) – also referred to as rapid sequence intubation or as rapid sequence induction and intubation (RSII) or as crash induction – is a special process for endotracheal intubation that is used where the patient is at a high risk of pulmonary aspiration. It differs from other techniques for inducing general anesthesia in that several extra precautions are taken to minimize the time between giving the induction drugs and securing the tube, during which period the patient's airway is essentially unprotected.
One important difference between RSI and routine tracheal intubation is that the anesthesiologist 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. RSI is typically used in patients who are at high risk of aspiration or who are critically ill and may be performed by anaesthesiologists, intensivists, emergency physicians or, in some regions, paramedics.
Uses
This 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 (such as gastroesophageal reflux disease or advanced pregnancy); or where the patient has become unable to protect their own airway even before anesthesia (such as after a traumatic brain injury).
Contraindications
There are relatively few absolute contraindications to a rapid sequence induction. The most significant contraindications include facial trauma that significantly distorts upper airway anatomy or complete airway obstruction (i.e. oropharyngeal cancer, hematoma, etc). As the sequence of RSI dictates that the patient is paralyzed prior to obtaining adequate airway access, there is the possibility that the patient is difficult to intubate. If unable to secure an airway access, the patient may be in a "cannot intubate, cannot ventilate" situation where the apneic period is prolonged and the patient does not receive oxygen. with the possibility of waking the patient with paralytic reversal medications such as sugammadex. Neuromuscular blockade agents are considered one of the highest anaphylaxis-inducing substances in the operating room, along with latex, penicillin, and chlorhexidine. Usual doses for midazolam are 1 mg to 2 mg where the older people receive smaller doses and obese people receive higher doses. Midazolam is metabolized in the liver and is excreted through the kidneys.
- Fentanyl – It is a synthetic, centrally-acting opioid. It suppresses pain and sympathetic stimulation. Sympathetic stimulation can cause further injury to those with heart disease, aortic dissection, and aortic aneurysm. Fentanyl is ideal because of its rapid onset, lack of histamine release, high lipophilicity, and short duration of action. The dosage is between 1 and 3 μg/kg. It is metabolized by liver. The most significant side effect is respiratory depression. Etomidate has minimal cardiovascular side effects, reduces intracerebral pressure (by reducing cerebral blood flow), and does not cause histamine release. Myoclonus, pain at the site of the injection, post-operative nausea and vomiting are common. While common, the incidence and severity myoclonus can be reduced with pretreatment lidocaine without affecting hemodynamic stability of the patient. The drug lessen the reuptake of the catecholamine, increases heart rate, blood pressure, and cardiac output, thus suitable for those with hypotension. However, it can worsen the cardiac depression and hypotension for those with depletion of catecholamines. The dosage is 1.5 mg/kg (usually 100 to 200 mg). It has quick onset of action, can cross the blood-brain barrier, wide tissue distribution, and can be hepatically cleared by the body quickly. Pain during peripheral administration of Propofol can be reduced by using pretreatment lidocaine or a large bore cannula. The dosage is 1.5 mg/kg. It is metabolized in liver. However, methohexital can cause respiratory depression, laryngospasm, venodilatation, myocardial depression, and hypotension. Additionally, it can also cause reduced cerebral blood flow and histamine release. It can cause distal thrombosis and tissue necrosis if given into the arterial system. Depolarizing blockers resembles the acetylcholine and activates the motor end-plate of the neuromuscular junction (NMJ). Meanwhile, non-depolarizing blockers competitively blocks the NMJ without activating the motor end plate. This is due to the upregulation of neuromuscular junctions. In patients with decreased plasma cholinesterase, the paralysis from succinylcholine can increase significantly in duration. While historically this was not the paralytic of choice in RSI due to the longer duration of action, with the recent approval of Sugammadex as a reversal agent the concern for a long duration of paralysis is reduced.
- Vecuronium – The dosage of this drug is between 0.08 and 0.1 mg/kg. Vecuronium is only used when there is a shortage of drugs such as succinylcholine and rocuronium. The dose of 16 mg/kg is used for immediate reversal after administration such as during RSI. The FDA initially did not approve Sugammadex due to concerns over potential allergic reactions, however it was subsequently approved on December 15, 2015, for use in the United States.
- Neostigmine – It can be used to reverse nondepolarizing neuromuscular blocking agents which cannot be reversed with Sugammadex, although its onset is much slower. It works by competitively inhibiting acetylcholinesterase, an enzyme that breaks down acetylcholine. This results in an accumulation of acetylcholine present in the neuromuscular junction, effectively reversing the paralysis of the patient.
thumb|Prehospital RSI training using a checklist
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 (after paralysis). 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 resulting in blood oxygenation is not different from that of quiet breathing volume for 3 minutes.
Newer methods of preoxygenation 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 (oral intubation). 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 a 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 (accelerated heart rate and increased intracranial pressure). This is supposed to have advantages in patients with ischemic heart disease and those with brain injury (e.g. after traumatic brain injury or stroke). Lidocaine is also theorized to blunt a rise in intracranial pressure during laryngoscopy, although this remains controversial and its use varies greatly. Atropine may be used to prevent a reflex bradycardia from vagal stimulation during laryngoscopy, especially in young children and infants. 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.
As described by Brian Arthur Sellick in 1961, cricoid pressure (alternatively known as Sellick's maneuver) 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, past 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, (via a thin secondary tube and a syringe), 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
Mispositioning of the endotracheal tube (in a bronchus, above the glottis, or in the esophagus) should be excluded by confirmation of end tidal , auscultation, fogging of the endotracheal tube, and observation of bilateral chest rise.
History
First described by William Stept and Peter Safar in 1970, "classical" or "traditional" RSI involves pre-filling the patient's lungs with a high concentration of oxygen gas; applying cricoid pressure to occlude the esophagus; administering pre-determined doses of rapid-onset sedative and neuromuscular-blocking drugs (traditionally thiopentone and succinylcholine) that induce prompt unconsciousness and paralysis; avoiding any artificial positive-pressure ventilation by mask after the patient stops breathing (to minimize insufflation of air into the stomach, which might otherwise provoke regurgitation); inserting a cuffed endotracheal tube with minimal delay; and then releasing the cricoid pressure after the cuff is inflated, with ventilation being started through the tube. There is no consensus around the precise definition of the term "modified RSI", but it is used to refer to various modifications that deviate from the classic sequence – usually to improve the patient's physiological stability during the procedure, at the expense of theoretically increasing the risk of regurgitation. The clinician that performs Rapid Sequence Induction and Intubation (RSII) 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 / succinylcholine / 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:
- choice of intravenous hypnotic agents as well as their dosage and timing of administration
- dosage and timing of administration of neuromuscular blocking agents
- avoidance of manual ventilation before tracheal intubation
- optimal position and whether the head-up, head-down, or horizontal supine position is the safest for induction of anesthesia in full-stomach patients
- application of cricoid pressure, which is also referred to as the Sellick maneuver.