Case: A 68 year old man with a history of CVA, CAD, HTN, and COPD presents from his nursing home with several days cough and fever. He is brought in by EMS on nonrebreather mask and appears to be in severe respiratory distress with oxygen saturations in the 80's. After he is placed on BiPap, chest x-ray demonstrates infiltrates consistent with pneumonia. The decision to intubate the patient is made after he fails BiPap due to intolerance of the mask (he repeatedly attempted removing the mask) and continued poor oxygen saturation. Endotracheal intubation was successfully performed with RSI, though the patient briefly desaturated to 75% during the process.
Clinical question: Would delayed sequence intubation have benefited this patient and avoided desaturation?
Rapid sequence intubation, or RSI, is the preferred means of emergency airway management, allowing for a definitive airway in a short period of time and avoiding prolonged bag-valve-mask ventilation with the goal of minimizing the risk of aspiration . In RSI, both an induction agent and a neuromuscular blocking agent are administered in quick succession. Etomidate and succinylcholine are two commonly used medications for induction and paralysis, respectively. The major disadvantage of RSI is the potential for a "cannot intubate, cannot ventilate" situation . In a patient similar to the one above, this could lead to a precipitous drop in oxygen saturation and increases the risk of cardiac arrest from hypoxemia.
One alternative that could ameliorate pre-existing hypoxemia is delayed sequence intubation, or DSI. During DSI, the induction agent is first given to facilitate preoxygenation either by nonrebreather mask or non-invasive positive pressure ventilation (NIPPV). After a period of preoxygenation, the patient is then given a paralytic and intubated. DSI can be especially useful in situations where the patient has altered mental status or agitation that precludes adequate preoxygenation with a nonrebreather or NPPV mask. Successful preoxygenation by this method would theoretically provide the patient with a better oxygen reserve and buffer against desaturation during intubation attempts .
A prospective, observational study done by Weingart, et al. published in the Annals of Emergency Medicine investigated the degree of improvement in preoxygenation after a brief period of sedation with ketamine prior to intubation. Patient selection consisted of a convenience sample of 64 patients who were uncooperative with preoxygenation (e.g. not tolerating or removing the mask, inability to remain on the stretcher). Patients were administered 1 mg/kg of ketamine IV and preoxygenated for 3 minutes with high-flow nonrebreather or NIPPV if the nonrebreather did not raise SpO2 to >95%. The study found that saturations after increased from a mean of 89.9% to 98.8% immediately before intubation, a difference of 8.9% (95% confidence interval 6.4% to 10.9%). Two patients, both asthmatics, did not require intubation after DSI and were able to tolerate and be admitted on NIPPV . Although the major shortcoming in the study is the lack of randomization with a control arm, the study does demonstrate that DSI with ketamine can create a more favorable peri-intubation oxygen saturation, potentially providing a buffer against hypoxemic peri-intubation cardiac arrest.
Submitted by Phil Chan (@PhilChanEM), PGY-4
Faculty reviewed by Brian Fuller, MD, MSCI
 Salhi BA, Ander DS. Chapter 122. Intubation and Airway Support. Principles and Practice of Hospital Medicine. New York, NY: McGraw-Hill; 2012.
 Vissers RJ, Danzl DF. Chapter 29. Intubation and Mechanical Ventilation. Tintinalli’s Emergency Medicine, 8e. New York, NY: McGraw-Hill; 2016.