Preoxygenation, Reoxygenation, and Delayed Sequence Intubation in the Emergency Department

Scott D. Weingart, MD


J Emerg Med. 2011;40(6):661-7. 

In This Article

Delayed Sequence Intubation

In some circumstances, the patients who most desperately require preoxygenation impede its provision. Hypoxia and hypercapnia can lead to delirium, causing these patients to rip off their non-rebreather or NIV masks. This delirium, combined with the oxygen desaturation on the monitor, often leads to precipitous attempts at intubation without adequate preoxygenation. Thanks to the availability of novel pharmacologic agents, another pathway exists to manage these patients.

Standard RSI consists of the simultaneous administration of a sedative and a paralytic agent and the provision of no ventilations until after endotracheal intubation.[27] This sequence can be broken to allow for adequate preoxygenation without risking gastric insufflation or aspiration; we call this method "delayed sequence intubation" (DSI). 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.

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 the patient to be comfortable, but still spontaneously breathing and protecting their airway.

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 a NRB or, preferably, NIV.[28] A dose of 1–1.5 mg/kg by slow intravenous push will produce a calmed patient within ~ 45 s. Preoxygenation can then proceed in a safe controlled fashion. After a saturation of 100% is achieved, the patient is allowed to breathe the high fiO2 oxygen for an additional 2–3 min to achieve adequate denitrogenation of the alveoli. A paralytic is then administered and after the 45–60-s apneic period, the patient can be intubated.

In patients with high blood pressure or tachycardia, the sympathomimetic effects of ketamine may be undesirable. These effects can be ameliorated with small doses of benzodiazepine and labetalol.[28] In a slowly growing number of EDs, a preferable sedation agent is available for hypertensive or tachycardic patients. Dexmedetomidine is an alpha-2 agonist, which provides sedation with no blunting of respiratory drive or airway reflexes.[29] It also will slightly lower heart rate and blood pressure.[29] Acceptable conditions can be obtained with a bolus of 1 μg/kg over 10 min; if continued sedation is necessary, a drip can be started at 0.5 μg/kg/h.[30,31,32,33] In many U.S. hospitals, this agent has not yet moved from the operating room and intensive care unit to the ED, mainly due to cost.

Another advantage of DSI is that frequently, after the sedative agent is administered and the patient is placed on non-invasive ventilation, the respiratory parameters improve so dramatically that intubation can be avoided. We then allow the sedative to wear off and reassess the patient's mental status and work of breathing. If we deem that intubation is still necessary at this point, we can proceed with standard RSI as the patient has already been appropriately preoxygenated.

A video demonstrating the above concepts is available online at: