Modified vs classical rsi

What is RSI and why do we do it?

• RSI (rapid sequence induction) aims to reduce the risk of aspiration (stomach contents entering the lungs) during induction of anaesthesia.
• Key idea: minimise time between loss of airway reflexes and securing the airway (usually with a cuffed tracheal tube).
• Aspiration risk is higher with: full stomach, bowel obstruction, pregnancy, severe reflux, delayed gastric emptying (e.g. opioids, diabetes), reduced consciousness, emergency surgery.

Definitions (simple and exam-friendly)

• Classical RSI: pre-oxygenate → give induction drug + fast neuromuscular blocker → apply cricoid pressure (if used locally) → no mask ventilation → intubate as soon as ready → confirm tube and inflate cuff.
• Modified RSI: same goal (reduce aspiration risk) but allows controlled gentle mask ventilation (usually with low pressures) and/or other adjustments to improve oxygenation and safety.
• Both require a clear plan for failed intubation and difficult airway management.

When might you choose Classical RSI?

• Very high aspiration risk where you want to avoid any positive-pressure ventilation before the cuff is inflated (e.g. bowel obstruction with vomiting, active regurgitation).
• When you expect intubation to be straightforward and the patient is unlikely to desaturate quickly (good oxygen reserve).
• If local policy strongly favours classical technique for specific scenarios (follow departmental guidance).

When might you choose Modified RSI?

• High aspiration risk but also high risk of rapid desaturation: obesity, pregnancy, severe illness/sepsis, children, low functional residual capacity, hypoxia at baseline.
• When gentle mask ventilation is needed to prevent hypoxia while still aiming for rapid intubation.
• When you anticipate a potentially difficult intubation and want to prioritise oxygenation (oxygenation always comes first).

Core steps common to both (new-starter checklist)

• Preparation: suction working and within reach; airway equipment checked; difficult airway kit available; second anaesthetist/ODP briefed; monitoring on; IV access reliable.
• Positioning: head-up / ramped position often improves pre-oxygenation and laryngoscopy (especially obesity/pregnancy).
• Pre-oxygenation: aim for a tight mask seal and good end-tidal oxygen if available; consider nasal oxygen during laryngoscopy (apnoeic oxygenation).
• Induction: give an induction agent appropriate to physiology (be cautious in shock/sepsis); then neuromuscular blocker.
• Intubation: proceed when conditions are adequate; confirm with continuous waveform capnography; secure tube; start ventilation; consider NG/OG tube after airway secured if indicated.

Mask ventilation: the key difference in practice

• Classical RSI: avoid mask ventilation after induction (unless oxygenation is failing).
• Modified RSI: allow gentle mask ventilation to maintain oxygenation—use low inspiratory pressures (aim to keep pressure low to reduce stomach insufflation), good mask seal, and two-person technique if needed.
• If you need to ventilate during a “classical” RSI because saturations are falling, do it—hypoxia is more immediately dangerous than aspiration.

Cricoid pressure (Sellick): practical, safe approach

• Cricoid pressure is intended to reduce passive regurgitation by compressing the oesophagus; its benefit is debated and it can worsen laryngoscopy or ventilation.
• If used locally: apply at loss of consciousness, ensure trained assistant, and communicate clearly.
• If cricoid pressure makes ventilation difficult, worsens view, or impedes insertion of airway devices, ask for it to be reduced or released.

Drug choices (intro level, UK practice)

• Neuromuscular blocker: suxamethonium (fast onset/offset) or rocuronium (fast onset at higher dose; longer duration). Choice depends on contraindications, anticipated difficulty, and availability of reversal strategies.
• Induction agent: propofol commonly used but can cause hypotension; consider alternatives and dose reduction in haemodynamic instability (discuss with senior early).
• Opioid: may be used to blunt response to laryngoscopy but can worsen hypotension/apnoea—use cautiously in unstable patients.
• Always tailor to patient physiology and clinical urgency; if unsure, escalate early.

First-time scenarios and practical tips

• Emergency laparotomy/bowel obstruction: high aspiration risk—ensure suction ready, consider classical RSI approach but be prepared to ventilate gently if desaturation occurs.
• Obese or pregnant patient: pre-oxygenate meticulously, head-up/ramped, consider modified RSI with gentle ventilation to avoid rapid desaturation.
• Trauma with reduced consciousness: aspiration risk plus possible difficult airway—prioritise oxygenation, have a clear failed intubation plan, and involve senior help early.
• Sepsis/hypotension: induction can cause cardiovascular collapse—prepare vasopressors/fluids, consider dose reduction, and ask for senior support.

Failed intubation: minimum safe mindset

• Have a shared plan before starting: what will you do if you cannot intubate on first attempt?
• Limit attempts; optimise between attempts (position, blade choice, external laryngeal manipulation, suction, change operator).
• If you cannot intubate but can oxygenate: continue oxygenation (mask or supraglottic airway) and follow local difficult airway guidance.
• If you cannot intubate and cannot oxygenate: call for help immediately and proceed to emergency front-of-neck access per local protocol.