Rapid Sequence Induction
In this article Dr Irene Bouras, Consultant Anaesthetist at University College London Hospital, describes the principles and practice of Rapid Sequence Induction.
What is a Rapid Sequence Induction (RSI)?
Rapid sequence induction or intubation (RSI) is a technique which was first described in 1970  and is now routinely used for many emergency intubations.
RSI is performed in order to reduce the risk of aspiration (stomach contents entering the airway and lungs) during the induction of anaesthesia. Aspiration can be fatal and is the commonest cause of airway related morbidity and mortality during general anaesthesia as we learnt in Week 1 when we discussed the 4th National Audit Project (NAP4) report.
A recent international survey of over 10,000 airway experts on preferences for clinical practices associated with RSI  demonstrated a wide variation in practice, RSI has also been the topic of a discussion on Twitter: #rapidsequenceinduction. Here we describe the principles of RSI, the “classic” technique and discuss some of the variations.
What are the indications for RSI?
RSI is performed on patients that are at high risk of aspiration, for example:
- Patients with pre-existing conditions which predispose to regurgitation: gastro-oesophageal reflux, neurological or neuromuscular conditions affecting the airway and upper Gastro-Intestinal (GI) tract
- Patients with acute conditions which delay or prevent gastric emptying or impair airway reflexes: bowel obstruction, delayed gastric emptying due to trauma or drugs, reduced level of consciousness
- Patients who are not starved: intubation may be required for urgent life-saving care in patients who are not starved, patients with upper GI bleeds may have blood in their stomachs even if technically ‘fasted’
The use of gastric ultrasound, as discussed in Week 2, may help with risk-stratification, by identifying patients with a full stomach.
RSI involves 3 key objectives
Maximising the oxygen levels in the lungs prior to induction of anaesthesia
Minimising the time between induction of anaesthesia and intubation of the trachea with a cuffed tracheal tube
Preventing aspiration of stomach contents by optimising the patient position and the administration of cricoid force (see below) to occlude the hypopharynx, and by avoiding positive pressure ventilation until the trachea has been intubated
If a difficult or failed intubation is encountered during an RSI, oxygenation of the patient is the priority.
Preparing for a RSI
Patient - The procedure should be explained to the patient, particularly pre-oxygenation with a tight fitting facemask and the feeling of pressure on the neck when cricoid force is applied, as both of these occur before the patient is unconscious (see below). The patient’s position should be optimised to achieve the best chance of a good view at laryngoscopy, with the lower neck flexed, and the upper neck extended, also described as the “Flextension” position:
©Nicholas Chrime, Flextension term attributed to Tim Cook
Equipment – As well as the standard equipment, two sets of suction should be available if there is copious airway bleeding or significant gastrointestinal content. The adjuncts required for a ‘failed intubation’ should be immediately available as the anaesthetic assistant will not be able to leave once RSI has started.
You may want to read about SALAD (Suction Assisted Laryngoscopy and Airway Decontamination). This technique provides constant suction via a catheter in the upper airway, continuously removing vomit, blood and other materials, around which the practitioner intubates the patient.
Team - The strategy for managing a failed intubation or difficult ventilation should be described at the team brief, an intubation checklist is a helpful cognitive aid. A trained assistant is required to help and to provide cricoid force. A third person should also be available to seek help and extra equipment if problems arise.
In Week 4 we will discuss the intubation of the critically ill patient. in more detail.
Classical RSI Technique - step by step
1. Pre-oxygenation. After ensuring adequate position, IV access and monitoring, the patient should be pre-oxygenated. Pre-oxygenation replaces nitrogen, which is the predominant gas in the air and in our lungs, with oxygen. A tight fitting face mask is applied with 100% oxygen at high flow. In order to maximally pre-oxygenate the patient they should breathe spontaneously for 3 minutes or until the exhaled or End Tidal Oxygen (EtO2) is greater than 85%. Filling the lungs with oxygen increases the time to desaturation once spontaneous breathing ceases.
2. Administration of induction agents. A pre-determined dose of induction agent and neuromuscular agent are given in quick succession. Traditionally thiopentone and suxemethonium were used as they have a rapid and predictable onset and offset but many anaesthetists now use more modern drugs. It should be noted that even if drugs with a rapid offset are used, in the event of a failed or difficult intubation oxygenation and ventilation of the patient remain a priority as the patient will become hypoxic before they wake up.
3. Cricoid Force. This is a technique aimed at reducing the risk of of gastric contents entering the airway. The technique involves applying 10 N of force (equivalent to registering 1kg on a weighing machine) onto the cricoid cartilage (the only complete ring of cartilage in the trachea) before induction and increasing it to 30 Newtons (3kg) as the patient goes to sleep. This compresses the hypopharynx, which lies behind the cricoid cartilage, against the 6th cervical vertebrae.
4. Tracheal intubation Once the muscle relaxant has taken effect the trachea should be intubated as quickly as possible.
Cricoid force should not be removed until intubation has been confirmed by capnography and the cuff inflated.
The use of a videolaryngoscope with a remote screen helps optimise cricoid force as the operator and assistant can directly observe its effect. If you are unable to intubate the trachea with cricoid force applied, it should be adjusted or removed.
5. Extubation Patients at risk of aspiration at intubation are also at risk during extubation. They should not be extubated until their airway reflexes have returned. This will be discussed later this week.
Complications of RSI
Failed intubation There is a higher rate of failed intubation for all emergency intubations. The team should have an explicit strategy to deal with this, it should be discussed before induction.
Awareness There is an increased incidence of awareness associated with RSI: this is thought to be multi-factorial. Many cases are emergencies so it is possible that induction agents are under dosed to prevent cardiovascular instability. If there is difficulty or delay in intubating the patient the induction agents may have worn off before the inhalational agents or further IV hypnotics can be given. In Week 5 we will meet an anaesthetist who was aware during an RSI.
Although the classic RSI technique has been used for over 50 years there is no evidence that it is superior to other techniques at preventing aspiration. Over the years the validity of various components of the classical RSI have been questioned and have been modified.
As aspiration remains one of the biggest causes of anaesthesia related deaths, practice should be tailored and modified to minimise this risk. The different modifications, whether it is the technique of pre-oxygentation, the drugs used or the application of cricoid force, should be determined by the clinical circumstances.
Oxygenation Pre-oxygenation with a face mask may be difficult in confused or agitated critically ill patients. In these instances, it may be preferable to oxygenate with nasal cannula with oxygen flow increased to 12-15 L/min, or with high flow nasal oxygen (HFNO). The nasal cannula can be kept on the patient during attempts at intubation, allowing apnoeic oxygenation to continue.
The classical RSI uses thiopentone for induction and suxamethonium as a muscle relaxant. Other drugs are increasingly used as induction agents in RSI. Propofol improves the intubation conditions, however the haemodynamic instability it causes can be problematic. If significant haemodynamic instability is anticipated then ketamine, and the co-administration of vasoactive agents may be a more appropriate choice. Midazolam and judicious doses of opiates are also used by some anaesthetists as co-induction agents. Many anaesthetists use high-dose rocuronium instead of suxamethonium. If rocuronium is used, sugammadex (the reversal agent) should be immediately available in an adequate dose.
Cricoid force Cricoid force is widely used in the UK and many other countries despite the lack of compelling evidence for its use. In the next step we will discuss this technique and find out what you think about it.
Please share your experiences and strategies of RSI. Due to the wide variation in practice, do you think it would be useful to have a consensus on the best RSI practice?
Post your thoughts in the discussion. As this is a public forum, please be do not share any confidential information or any patient identifiable data. Please do ‘like’ and comment on other learners’ comments, too. Remember you can ‘follow’ other learners so you don’t miss their comments.
Move on now to the next step which discusses the use of cricoid force in more detail.
 Zdravkovic M, Berger-Estilita J, Sorbello M, Hagberg C A et al, An international survey about rapid sequence intubation of 10,003 anaesthetists and 16 airway experts. Anaesthesia. 2019 Oct 30. [Epub ahead of print]
 Mir F, Patel A, Iqbal R, Cecconi M, Nouraei SA. A randomised controlled trial comparing transnasal humidified rapid insufflation ventilatory exchange (THRIVE) pre-oxygenation with facemask pre-oxygenation in patients undergoing rapid sequence induction of anaesthesia. Anaesthesia. 2017 Apr. 72(4):439-443.
© UCL, materials shared with permission from Prof Tim Cook and Dr Nicholas Chrimes