The Case

You enter the ambulance and find a 60 y/o female, supine on stretcher, who presents with possible bilateral pneumonia. BP 104/60, HR 100, RR 36. She is delirious, agitated, and looks quite sick! Saturation is 70% on a nasal cannula (NC). You elevate the head of the bed 30 degrees, and you try to place the patient on a non-rebreather (NRB) mask. Patient just swats your hand away and rips off the mask. It is obvious to you and your partner this patient needs to be intubated, but the question is how are you going to do it?

Your first thought may be to perform RSI, maybe with some BVM ventilation during the paralysis period. According to Dr. Scott Weingart, that would be very risky. “If you have first pass success, you (and your patient) may just luck out, allowing you to get the tube in and start ventilation before critical desaturation and the resultant hemodynamic instability. However, the odds are against you: bagging during RSI predisposes to aspiration, conventional BVM is unlikely to raise the saturation in this shunted patient, and if there is any difficulty in first-pass tube placement your patient will desaturate very quickly” (1).

A Different Sequence

Sometimes patients like this one, who desperately require preoxygenation will not tolerate it. Hypoxia and hypercapnia can lead to delirium, causing these patients to rip off their NRB or non-invasive ventilation (NIV) masks. This delirium, combined with the low oxygen desaturation on the monitor, often leads to precipitous attempts at intubation without adequate preoxygenation (1).

Standard RSI consists of the rapid administration of a sedative and a paralytic agent and the provision of no ventilations until after endotracheal intubation (2). This sequence can be broken to allow for adequate preoxygenation without risking gastric insufflation or aspiration; this method is called “delayed sequence intubation” (DSI) or “Medication-Induced Intubation” (MII).  (DSI consists of the administration of specific sedative agents, which do not blunt spontaneous ventilations or airway reflexes; followed by a period of preoxygenation before the administration of a paralytic agent (1).

Another way to think about DSI is as a procedural sedation, the procedure, in this case, being effective preoxygenation. After the completion of this procedure, the patient can be paralyzed and intubated. Just like in a procedural sedation, we want our patients to be calm, but still spontaneously breathing and protecting their airway (1).

The ideal agent for this use is ketamine. This medication will not blunt patient respirations or airway reflexes and provides a dissociative state, allowing the application of preoxygenation. A dose of 1–2 mg/kg by slow intravenous push will produce a calmed patient within ~ 30 seconds. Preoxygenation can then proceed in a safe, controlled fashion. This can be accomplished with both a NC and NRB at 15 L of oxygen or BVM ventilations with PEEP. After a saturation of > 95% is achieved, the patient is allowed to breathe the high fiO2 oxygen for an additional 2–3 min to achieve adequate denitrogenation. A paralytic is then administered and after the 45–60 second apneic period, the patient can be intubated (1).

Conclusion

DSI is a methodical, sequence of events that optimizes patient hemodynamics before intubation. Whether is oxygenation, ventilation or fluid resuscitation, RSI can be more harmful than helpful. It’s time prehospital clinicians approach each patient first to determine what, if any resuscitation is needed before intubation, and if needed, consider Delayed Sequence (medicated assisted) Intubation, rather than Rapid Sequence IInduction.

References:

  1. Weingart SD. Preoxygenation, reoxygenation, and delayed sequence intubation in the emergency department. J Emerg Med2010 Apr 7.
  2. Walls RM, Murphy MF. Manual of emergency airway management, 3rd edn. Philadelphia, PA: Lippincott Williams & Wilkins; 2008.
  3. Aroni F, Iacovidou N, Dontas I, Pourzitaki C, Xanthos T. Pharmacological aspects and potential new clinical applications of ketamine: reevaluation of an old drug. J Clin Pharmacol 2009;49:957–64.
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