2.3 Scenario Practice for Airway, Respiration, and Ventilation

2.3 RSI and DSI Pharmacology in Practice

Rapid sequence intubation (RSI) is the near-simultaneous administration of a sedative (induction agent) and a neuromuscular blocker (paralytic) to create optimal intubating conditions while minimizing the aspiration window. It is a high-stakes paramedic skill governed by protocol and medical direction. Organize it with the seven Ps: Preparation, Preoxygenation, Pretreatment, Paralysis with induction (push induction then paralytic), Positioning/Protection, Placement with proof, and Post-intubation management.

Preparation and preoxygenation

Assemble suction, two laryngoscopes (DL and VL), the correct tube size, a bougie, an SGA rescue, and a cricothyrotomy kit before any drug is drawn. Preoxygenate to denitrogenate the lungs and build an oxygen reservoir — a non-rebreather plus a nasal cannula at 15 L/min, and leave the cannula on through the apneic period for apneic oxygenation. Aim for SpO2 of 100% before pushing drugs; the higher the starting saturation, the longer the safe-apnea time before desaturation.

Induction agents

Ketamine's old teaching that it raises intracranial pressure is now largely discredited; it is acceptable and often preferred in head injury because it maintains cerebral perfusion pressure. Its bronchodilating effect makes it the induction agent of choice in the crashing asthmatic.

Paralytics and contraindications

A paralytic is given immediately after the induction agent. The two paramedic agents differ sharply in duration.

Succinylcholine wears off fast (~6-10 min), which is reassuring if the airway attempt fails because the patient can resume spontaneous breathing sooner. Rocuronium produces a long paralysis (30-60+ min): an advantage for transport stability but a hazard in a cannot-intubate-cannot-oxygenate situation unless reversal (sugammadex) is available. With either agent, the cardinal post-intubation rule is to redose sedation/analgesia so a paralyzed patient is never left awake and aware — the paralytic blocks movement but provides no sedation.

Match the duration and depth of sedation to the paralytic. Succinylcholine is contraindicated in:

• Hyperkalemia or conditions that cause it (renal failure with elevated K+, crush injury, rhabdomyolysis)
• Burns or major crush/denervation injury older than ~24-72 hours (up-regulated acetylcholine receptors cause a lethal potassium surge; risk peaks 7-10 days post-injury)
• Personal or family history of malignant hyperthermia
• Chronic neuromuscular disease (ALS, multiple sclerosis, muscular dystrophy), stroke >72 h, denervation

When succinylcholine is contraindicated, rocuronium is the safe choice; its drawback is the long paralysis, which is dangerous in a cannot-intubate-cannot-oxygenate scenario unless reversal (sugammadex) is available.

Delayed sequence intubation (DSI)

DSI treats the agitated, hypoxic patient who fights preoxygenation. A dissociative dose of ketamine (about 1-1.5 mg/kg IV) sedates the patient without paralysis, so spontaneous breathing and airway reflexes continue. The crew then preoxygenates effectively for several minutes; only once SpO2 is optimized is the paralytic pushed and the tube placed. DSI is essentially "procedural sedation for preoxygenation" and has shown high first-pass success in prehospital studies.

Pretreatment, positioning, and post-intubation

The pretreatment step (a few minutes before induction) is now used selectively. Historically lidocaine and fentanyl were given to blunt the sympathetic and intracranial-pressure response in head injury, and atropine was considered for pediatric bradycardia from succinylcholine; current practice has narrowed these, so know that pretreatment exists but is protocol-specific rather than universal. Positioning places the patient ear-to-sternal-notch (ramp obese patients) and applies manual in-line stabilization for trauma.

After the tube is confirmed, post-intubation management is its own checklist: secure the tube and note the depth, set ventilation to a normal ETCO2 of 35-45 mmHg (avoid hyperventilation), continue sedation and analgesia, elevate the head of the stretcher when not contraindicated, and reassess placement after every move.

Anticipating the difficult and failed airway

RSI commits you to apnea, so always have a failed-airway plan ready: a supraglottic rescue device and a surgical-airway kit at the bedside before the first drug is pushed. If you cannot intubate but can oxygenate with a BVM or SGA, you have time to optimize and reattempt or transport. If you cannot intubate and cannot oxygenate (CICO) despite repositioning, suction, and an SGA, proceed without delay to a cricothyrotomy. Limiting attempts (generally no more than two to three), changing something each attempt (operator, device, position, bougie), and re-oxygenating between attempts are the behaviors that prevent the CICO spiral.

Pediatric and physiologic considerations

Weight-based dosing makes accurate weight estimation essential; use a length-based tape for children. Pediatric patients desaturate faster because they have higher oxygen consumption and smaller functional reserve capacity, so preoxygenation and apneic oxygenation matter even more.

The shock or hypotensive patient is also vulnerable: the induction agent and the positive-pressure ventilation that follows both drop venous return, and a patient on the edge can arrest peri-intubation, which is why a hemodynamically neutral agent like etomidate or a pressure-supporting agent like ketamine is preferred over midazolam in the unstable patient. Resuscitate before you intubate — correct profound hypotension and hypoxia first whenever the clinical situation allows.