What is the RSI technique of anesthesia?
Rapid Sequence Intubation (RSI) is a specialized procedure for achieving rapid airway control, particularly in emergency situations or when a patient is at high risk of pulmonary aspiration. The technique is characterized by the almost simultaneous intravenous administration of a potent sedative (induction agent) and a neuromuscular blocking agent (paralytic). The goal is to quickly render the patient unconscious and immobile to facilitate the swift and safe placement of a cuffed endotracheal tube (ETT) into the trachea.
Unlike standard anesthesia induction, RSI minimizes the time between the loss of consciousness and the protection of the airway with the ETT. It also avoids manual positive pressure ventilation with a bag-valve mask before intubation, which could force air into the stomach and increase the risk of regurgitation.
The 7-10 Ps of the RSI Process
The RSI procedure is a highly structured process that can be remembered by the mnemonic of the '7 to 10 Ps.' Clinicians must execute these steps efficiently and with careful attention to detail.
1. Preparation
Before any medication is administered, the team must be fully prepared. This involves a pre-procedural 'time-out' and confirming all necessary equipment and personnel are present and functional. Mnemonic devices like SOAPME (Suction, Oxygen, Airway, Pharmacology, Monitoring, Equipment) or O2 MARBLES (Oxygen, Masks/Monitoring, Airway, RSI drugs/Resus drugs, BVM/Bougie, Laryngoscopes/LMA, ETTs/ETCO2, Suction/State Plan) are often used to ensure nothing is missed. A plan for managing a difficult airway must also be in place.
2. Preoxygenation
This critical step involves providing the patient with 100% oxygen for several minutes, typically via a non-rebreather mask or high-flow nasal cannula. The goal is to maximize the oxygen reserves in the patient's lungs, increasing the amount of time they can tolerate a period of apnea during the intubation attempt before their oxygen saturation drops dangerously low.
3. Pretreatment
In specific clinical scenarios, certain medications may be administered to blunt the adverse physiological responses to intubation, such as an increase in heart rate or intracranial pressure. Examples include fentanyl, lidocaine, or atropine, though their use has become less common and is often reserved for specific conditions.
4. Paralysis with Induction
This is the core step of RSI, where the induction agent (sedative) and the neuromuscular blocking agent (paralytic) are administered rapidly and in close succession. It is critical that the paralytic is never given without a sedative, as this would result in a patient who is awake but unable to move or signal distress.
5. Protection and Positioning
Proper patient positioning, such as the 'sniffing position' (flexing the neck and extending the head), is used to align the airway axes and improve visualization. In cases of suspected cervical spine injury, in-line stabilization must be maintained. Historically, cricoid pressure (Sellick's maneuver) was used to compress the esophagus and prevent regurgitation, but its efficacy is controversial and it may sometimes hinder intubation.
6. Placement
Following drug administration and once the patient is sufficiently paralyzed, the laryngoscopy and endotracheal tube placement are performed. This is a time-sensitive step to minimize the period of apnea. The practitioner visualizes the vocal cords, passes the ETT, and inflates the cuff.
7. Proof of Placement
Confirming proper placement of the ETT is paramount. Multiple methods are used, including auscultation of bilateral breath sounds, chest rise, and, most reliably, continuous waveform capnography. The capnography measures end-tidal CO2, which should be present after successful tracheal placement.
8. Post-intubation Management
Once the ETT is secured, further sedation, analgesia, and ongoing mechanical ventilation are initiated. The patient is monitored closely for any changes in vital signs.
Pharmacology: Key drugs in RSI
Induction Agents (Sedatives)
- Etomidate: Favored for its minimal effect on cardiovascular stability, making it a good choice for hemodynamically unstable patients. However, it can cause adrenal suppression.
- Ketamine: Increases heart rate and blood pressure, making it useful in patients with hypotension or reactive airways disease, such as asthma.
- Propofol: Provides rapid onset but can cause significant hypotension, particularly in unstable patients.
Neuromuscular Blocking Agents (Paralytics)
- Succinylcholine: Historically the first choice for RSI due to its rapid onset and short duration of action. However, it carries several adverse risks.
- Rocuronium: An increasingly popular alternative to succinylcholine. While it has a slightly longer onset, it has a more favorable side-effect profile and can be rapidly reversed with the agent sugammadex.
Comparing neuromuscular blockers for RSI
| Characteristic | Succinylcholine | Rocuronium |
|---|---|---|
| Drug Class | Depolarizing neuromuscular blocker | Non-depolarizing neuromuscular blocker |
| Onset of Action | ~45-60 seconds | ~60 seconds |
| Duration of Effect | 6-10 minutes | 30-40 minutes or longer |
| Reversal Agent | No rapid reversal agent for paralysis | Can be rapidly reversed by sugammadex |
| Adverse Effects | Risk of hyperkalemia, malignant hyperthermia, bradycardia, fasciculations | Rare risk of allergy; no associated malignant hyperthermia |
| Considerations | Used cautiously due to numerous contraindications | Longer duration requires a plan for ongoing sedation |
Potential complications and considerations
Even with a precise protocol, RSI is not without risk. Potential complications include hypotension, hypoxia, and aspiration, particularly if there are delays or difficulties during the procedure. A failed intubation, where the ETT cannot be placed, is also a serious risk, necessitating a backup plan for airway management.
Careful patient selection and tailoring the drug choice to the individual's clinical status are key to mitigating risks. For instance, in a hemodynamically unstable patient, an induction agent like ketamine might be preferred over propofol, which can cause further drops in blood pressure. A pre-procedure assessment for a difficult airway is essential, as RSI is contraindicated in known or suspected difficult airway cases.
Conclusion
Rapid Sequence Intubation (RSI) is a critical procedure for emergency and critical care medicine, designed to secure a patient's airway efficiently while minimizing the significant risk of aspiration. By administering a sedative and paralytic almost simultaneously, the technique ensures rapid loss of consciousness and muscle paralysis, providing optimal conditions for endotracheal intubation. Success hinges on a well-drilled team, meticulous preparation, and a comprehensive understanding of the pharmacology of the agents used, along with careful monitoring to manage potential complications. While traditionally using succinylcholine, the rising use of rocuronium with its reversal agent, sugammadex, has provided a valuable alternative for many clinical scenarios, balancing speed with a more favorable safety profile.
