Delayed sequence intubation (DSI) is an alternative technique in optimization of preoxygenation for noncompliant patients with altered mental status. The technique is designed to improve preoxygenation by providing controlled sedation.1 The current evidence consists of data from small studies of patients sedated with ketamine and successfully preoxygenated and intubated.1-6 DSI evidence is based on a small series of cases. This technique can be successful for many patients, including those with asthma.
ANATOMY AND PATHOPHYSIOLOGY
DSI separates the administration of induction drugs from the administration of paralytic agents to allow preintubation oxygenation and denitrogenation of the patient.1 It has been described as procedural analgesia and sedation (Chapter 159) for the procedure of preoxygenation and denitrogenation. Denitrogenation makes the functional residual capacity of the lungs to be filled with oxygen to provide an oxygen reservoir. Ketamine is used as the induction agent (Chapter 12). The ketamine allows the patient to maintain airway reflexes and spontaneous respiration. DSI allows a longer time for intubation, increases the apnea time, decreases the risk of gastric insufflation, and decreases the risk of aspiration. DSI may prevent peri-intubation acidosis, carbon dioxide elevations, cardiac arrest, hypotension, hypoxemia, morbidity, and mortality.1 A bag-valve device is not used to ventilate the patient in DSI. This may result in a decreased gastric insufflation and the subsequent risk of aspiration.
The primary indication for DSI is to provide controlled sedation to achieve adequate preoxygenation and denitrogenation in the patient intolerant of desaturating (i.e., oxygen saturation < 93%) when emergent rapid sequence intubation (RSI) would be otherwise unsafe due to the risk of severe hypoxemia.1 Some patients may not need to be intubated once the sedation has led to dramatic increases in oxygen saturation. Improved cooperation along with the adequate oxygen saturation levels may allow the Emergency Physician to observe the patient before immediately continuing to intubation. Safe and controlled endotracheal intubation is performed to secure the patient’s airway once the oxygen reserve and saturation level have reached an appropriate value. DSI allows essential procedures (e.g., nasogastric tube placement) to be performed prior to intubation.
Contraindications include situations in which definitive airway control is needed in a non–spontaneously breathing patient. Patients who present with increased aspiration risk are not candidates for DSI. A relative contraindication is in the patient with hypertension, tachycardia, and increased intracranial pressure when the sympathomimetic effects of ketamine will be undesirable (Chapter 12). Contraindications to the administration of ketamine (Chapter 12) are contraindications to DSI. Patients under the influence of illicit substances or medications or with psychiatric disorders that cause delirium or hallucinations may experience additive effects with the administration of ketamine. Emergency Physicians with minimal to no experience with providing ketamine sedation should not provide DSI.