Rapid Sequence Induction/Intubation (RSI): Risk Factors, Indications, and Technique

Rapid Sequence Induction/Intubation (RSI) is the preferred method of airway protection in critically ill patients, assuming they are at risk of gastric content aspiration.

This method includes the almost simultaneous administration of an induction agent and a neuromuscular blocking agent to create optimal intubation conditions and minimize the duration between drug-induced loss of airway protection and endotracheal tube placement, thereby reducing the risk and consequences of aspiration.

Indications

The main indication for conducting RSI is the risk of pulmonary aspiration.

An anesthesiologist has to perform rapid induction and intubation in the following situations:

• If patients scheduled for elective surgery have fasted appropriately but have risk factors for aspiration (such as delayed gastric emptying or esophageal pathology);
• If the patient is scheduled for emergency surgery, the fasting time was inadequate, or there are risk factors for aspiration (e.g., intestinal obstruction or upper gastrointestinal bleeding);
• For obstetric patients requiring elective or emergency anesthesia;
• For patients in critical conditions (e.g., altered consciousness, respiratory failure, seizures, multiple traumas).

Risk factors for pulmonary aspiration:

• Unreliable fasting data and non-compliance with recommendations;
• Pregnancy (>20 weeks);
• Obesity (BMI ≥40 kg/m²);
• Acute abdomen;
• Advanced chronic disease (e.g., gastroparesis in diabetes mellitus);
• Pathological conditions and injuries leading to gastric retention;
• A history of esophageal stricture, bariatric surgery, hiatal hernia, or gastroesophageal reflux.

Contraindications and precautions

Contraindications to RSI are relative. In general, it can be concluded that this method is far from the best choice. The most important contraindications are anticipated difficult intubation and inability to ensure reliable oxygenation (i.e., inability to ventilate with a mask or with supraglottic airway devices). In such cases, consideration should be given to awake intubation (with local anesthesia and/or minimal sedation) or another method that preserves spontaneous breathing to avoid sudden deterioration.

Stages of preparation for rapid sequence induction and intubation

Preparation for RSI considers the following:

1. Preparation of the patient (assessment of the patient’s airway for potentially anatomically and/or physiologically difficult airways). It includes:

• Possible functioning intravenous (IV) access (preferably two veins);
• Proper positioning (if possible, elevate the head and torso— head of bed elevation to 30 degrees; in obese patients and pregnant women, the “ramped position,” meaning horizontal alignment of the tragus of the ear with the sternal notch);
• Reliable preoxygenation;
• Optimization of the patient’s condition;

2. Preparation of equipment:

• Availability of necessary equipment (videolaryngoscope, manual laryngoscope, endotracheal tubes [ETT] of the required sizes, dilators, stylets, aspirator, supraglottic airway devices, nasal cannulas, set for Front of Neck Access [FONA], etc.);
• Availability of the necessary medications (induction agents, muscle relaxants, vasopressors, and inotropes).

3. Preparation of the team (role assignment and leader selection);

4. Preparation for potential difficulties (development of an airway management plan, including readiness to switch to a backup strategy in case of failure, e.g., the Plan A-D algorithm as per the Difficult Airway Society [DAS] 2025 recommendations).

Preoxygenation

The goal of preoxygenation is to accumulate an oxygen reserve, which will help delay the clinically significant desaturation during the apnea period that occurs after anesthesia induction and until successful tracheal intubation.

According to clinical studies’ results, desaturation below 90% following induced apnea in properly oxygenated patients is expected at the following time intervals:

1. Healthy adults: 6 to 8 minutes;
2. Infants (weighing appr. 10 kg): <4 minutes;
3. Adults with chronic diseases or obesity: <3 minutes;
4. Full-term pregnant women: <3 minutes.

Practical aspects of preoxygenation:

• Achieving end-tidal oxygen (ETO₂) >of 0.9.
• For spontaneously breathing patients, inhalation of 100% oxygen with a tightly fitting face mask for 3 minutes is conducted to achieve adequate denitrogenation (if circumstances do not allow, the alternative is maximum vital capacity breaths). Eight (8) such breaths can provide an adequate preoxygenation within the 1st minute.
• In expected difficult laryngoscopy and airway patency issues, high-flow nasal oxygenation (HFNO) should be considered.
• To prolong the safe period of apnea after loss of consciousness and cessation of spontaneous breathing, nasal cannulas with an oxygen flow of 15 l/min may be used (apneic oxygenation).
• In critical patients with hypoxemia (PaO₂/FiO₂ < 150), it is recommended to add constant positive airway pressure (CPAP) ventilation of 5-10 cm H₂O p. during preoxygenation with a face mask. Non-invasive ventilation (NIV) with bilevel positive airway pressure (BiPAP) may also be considered but should be avoided in patients at high risk of aspiration.
• In cases of evident agitation, drug-assisted preoxygenation may be used to ensure adequate ventilation without suppressing the respiratory drive.
• If a nasogastric tube was inserted, it should be aspirated and left open.

Optimization of the patient’s physiological condition

This process involves recognizing and eliminating physiological vulnerabilities. It is necessary because conditions like hypoxemia, hypotension/shock, severe metabolic acidosis, and right ventricular failure most often lead to intubation decompensation, even if tracheal intubation is performed quickly and smoothly.

Practical aspects of such an optimization:

• Maximally effective preoxygenation in patients with hypoxemia: use of NIV with high positive end expiratory pressure (PEEP) levels, which helps increase SpO₂ to at least 93% even before induction;
• Minimizing the apnea period in the presence of acidosis;
• Correction of pre-induction hypotension in patients with signs of hypovolemic shock (20-30 ml/kg IV bolus of isotonic solution or use of blood products, depending on suspected cause);
• If additional fluid administration is impossible (e.g., in decompensated acute heart failure) or hemodynamic instability persists after a bolus infusion, norepinephrine administration (initial dose starts from 5 μg/min) is required to normalize systolic blood pressure to 65 mmHg or to resolve clinical signs of poor perfusion;
• In the case of cardiogenic shock, infusion of an inotrope (e.g., dobutamine or milrinone) should be started.

Medications used in RSI

There are several categories of medications used in sequential induction and intubation, listed below.

Induction agents

Induction agents (sedatives) induce amnesia and prevent reflex sympathetic reactions to laryngoscopy (e.g., increase in intracranial pressure, tachycardia, hypertension, and laryngospasm), as well as improve intubation conditions.

The choice of a specific agent depends on the comorbidities, hemodynamic status, and RSI setting (intensive care unit, emergency department, etc.). The most common agents are as follows:

• Propofol (1-3 mg/kg). It’s the most versatile agent, which causes bronchodilation and has an anticonvulsant effect. It is a popular choice for hemodynamically stable patients, as it causes dose-dependent hypotension.
• Etomidate (200-300 μg/kg). This agent is suitable for patients with unstable hemodynamics.
• Ketamine (1-2 mg/kg). It is used in patients with life-threatening asthma (causes bronchodilation), hypovolemia, and circulatory shock.
• Midazolam (0.2-0.3 mg/kg). It’s conventionally used in combination with another agent (due to the much slower onset of action and increased unpredictability) and has an anticonvulsant effect, making it the first-choice agent for RSI in patients with status epilepticus.
• Thiopental (3-5 mg/kg). First-choice agent for the patients with refractory status epilepticus.

Muscle relaxants, or neuromuscular blocking agents (NMBAs)

They are an integral part of sequential induction and intubation, improving the larynx visibility and reducing the risk of complications. During RSI, a choice is made between rocuronium and succinylcholine:

• Succinylcholine (1-2 mg/kg). Provides adequate intubation conditions within 45-60 seconds. It should be avoided in patients with hyperkalemia and crush injuries, in those who have suffered severe burns in the last 24 hours, and in cases of risk of malignant hyperthermia and neuromuscular diseases associated with denervation.
• Rocuronium (1-1.2 mg/kg). Onset of action is comparable to that of succinylcholine; however, when using rocuronium, sugammadex should be available (at a dose of 2-16 mg/kg, it reverses muscle block within 3 minutes).

Adjuvants

Opioid pain relievers (fentanyl at a dose of 1-3 μg/kg, alfentanil 10-50 μg/kg, remifentanil 1 μg/kg, and lidocaine 1-1.5 mg/kg) to reduce the sympathetic response to laryngoscopy should be considered for use in patients with increased intracranial pressure, aortic dissection, and severe cardiovascular diseases.

Key conditions and controversial methods in RSI

Cricoid pressure (Sellick maneuver)

Pressure on the cricoid cartilage involves exerting force on the cricoid cartilage (force of 10N before loss of consciousness and 30N after loss of consciousness) to compress the esophagus between the posterior cricoid ring and the body of the fifth cervical vertebra. This maneuver is hypothesized to prevent aspiration of gastric contents.

Despite common use of cricoid pressure in the past, it is currently not recommended during laryngoscopy and intubation due to a lack of evidence clearly indicating a reduction in aspiration risk or improved outcomes.

Absence of venous access

Intravenous access is preferable for administering all the medications during RSI. If this is not feasible, a reasonable alternative is administering medication via intraosseous access, considering pharmacokinetic nuances.

If this access is also not feasible and there is a high risk of airway compromise, awake intubation should be considered.

Actions post-anesthesia induction: intubation and post-intubation management of the patient

Following the administration of induction agents and muscle relaxants, respiratory activity decreases and eventually ceases.

Key technical aspects of RSI at this stage:

1. Avoid bag-mask ventilation in patients with adequate preoxygenation (to prevent air entering the stomach); bag-mask ventilation is necessary in patients with severe hypoxemia;
2. Upon achieving complete neuromuscular block (absence of masseter tone), proceed with laryngoscopy (preferably video laryngoscopy);
3. Prioritize tracheal intubation with success on the first attempt;
4. Verify tube placement with waveform capnography (do not rely solely on fogging of the intubation tube and auscultation of lung fields) and secure the tube;
5. Perform a chest X-ray to determine the depth of ETT positioning;
6. Initiate mechanical lung ventilation (settings may require adjustments based on clinical situation);
7. Provide immediate post-intubation analgesia and sedation. Provide long-term analgesia and sedation as necessary, guided by validated sedation scales (e.g., Richmond Agitation-Sedation Scale, RASS);
8. Resolve post-induction hypotension as necessary.

A slight decrease in SpO₂ and blood pressure may be observed in the immediate post-intubation period. If these parameters do not restore quickly with fluids and PEEP ventilation, or if previously stable parameters suddenly deteriorate, the clinician should rule out intubation-associated adverse events, such as esophageal intubation, tension pneumothorax, breathing circuit disconnection, ETT obstruction, and ETT cuff rupture.

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Prospects for further development

• Use of ultrasound to assess aspiration risk and preoperative localization of the cricoid cartilage and cricothyroid membrane.
• Use of paratracheal pressure as an alternative to cricoid cartilage pressure to reduce air entry into the stomach and improve visualization during laryngoscopy.