Update: Want more on DSI after you listen to the podcast below. My friend Minh Le Cong interviewed me on DSI on his amazing PHARM Podcast. It is an additional 45 minutes on newest thoughts on DSI.
On to Delayed Sequence Intubation (DSI)
You have a 50 y/o male with bad bilateral pneumonia. BP 108/70, HR 96, RR 28. He is delirious, agitated, and looks sick, sick, sick! Saturation is 70% on a nasal cannula; when you try to place the patient on a non-rebreather (NRB) he just swats your hand away and rips off the mask. It is obvious to everyone in the room that this patient needs intubation, but the question is how are you going to do it?
Your first impulse may be to perform RSI, maybe with some bagging during the paralysis period. This is essentially a gamble. 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 without a PEEP valve is unlikely to raise the saturation in this shunted patient, and if there is any difficulty in first-pass tube placement your patient will be in a very bad place.
A Better Way
Sometimes patients like this one, who desperately require preoxygenation will impede its provision. 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.
Standard RSI consists of the simultaneous administration of a sedative and a paralytic agent and the provision of no ventilations until after endotracheal intubation (1). 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.(2)
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.
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 a NRB, or preferably in a patient exhibiting shunt, by use of a non-invasive mask hooked up to ventilator with a CPAP setting of 5-15 cm H20 (or some of the new masks that don’t require a machine, but more on that soon). 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.
In patients with high blood pressure or tachycardia, the sympathomimetic effects of ketamine may be undesirable. While, these effects can be blunted with small doses of benzodiazepine and perhaps, labetalol (3), a preferable sedation agent is available for these hypertensive or tachycardic patients. Dexmedetomidine is an alpha-2 agonist, which provides sedation with no blunting of respiratory drive or airway reflexes (4-5). A dose of 1 mcg/kg administered over 10 minutes will lead to a sedated patient who will accept preoxygenation after 3-5 minutes in most cases.
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. In these cases, 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 by administering a conventional sedation agent (e.g. etomidate or additional ketamine) in combination with a paralytic, as the patient has already been appropriately preoxygenated.
A video demonstrating the above concepts is at: http://emcrit.org/misc/preox/