The incidence of obstructive sleep apnea is increasing. The diagnosis is typically made using overnight polysomnography in a sleep laboratory, a time consuming and expensive procedure. The standard therapy is continuous positive airway pressure at night, but this does not always work. Surgery can be performed, but requires anatomic determination of the reason for sleep apnea. Drug-induced sleep endoscopy (DISE) is a novel technique that allows visualization of the glottic structures during partial airway obstruction. Drug induced sleep endoscopy is typically accomplished by infusing propofol to the point of airway obstruction, at which point the glottis is visualized endoscopically.
How should propofol be administered to rapidly produce airway obstruction while avoiding hypoxia? In the United States, we don’t (and may never) have target-controlled infusion (TCI). In a previous article in this journal, the use of a control system that would produce an effect-site concentration of propofol based on a population of 10,000 simulated patients was described. Lacking TCI, Dr. Joshua H. Atkins, Department of Anesthesiology and Critical Care, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, and coauthors developed a propofol infusion technique for use during DISE. The results of this analysis are described in the article “Safety and Efficacy of Drug-Induced Sleep Endoscopy Using a Probability Ramp Propofol Infusion System in Patients with Severe Obstructive Sleep Apnea,” which was published in this month’s edition of Anesthesia & Analgesia.
The authors measured the oxygen nadir during DISE in 97 patients whose average BMI was 32 kg/m2 and compared it to the patient’s apnea-hypopnea index (AHI) from their prior sleep study. All DISE patients received 2 L/min supplemental oxygen via a nasal cannula placed in the mouth. As is the routine, supplemental oxygen was not used during the prior sleep studies in the subjects. The DISE studies were performed in an operating room with standard monitors and resuscitation equipment. No topical anesthesia was employed, and no intravenous drugs other than propofol were used. After the initiation of sedation, a pediatric bronchoscope was positioned to observe the velopharynx and the sedation sequence proceeded until the obstruction clinical endpoint was reached. All patients developed obstruction after about 4 minutes, at an estimated effect-site propofol concentration of 4.16 mcg/mL. Oxygen saturation nadirs during the sleep study were lower than DISE in all but 7 patients, an expected result since supplemental oxygen was not administered during the sleep study.
A propofol infusion will reliably induce airway obstruction, while permitting rapid recovery when the infusion is stopped. The reduced hypoxia with propofol induced airway obstruction compared to the hypoxia documented in the same subjects during natural sleep suggests that the propofol infusion has a favorable safety profile compared with falling asleep (!), which the subjects do every night. Nevertheless, 97 subjects is probably too few to rule out the possibility of injury from drug-induced airway obstruction leading to patient injury.
The authors have designed a propofol infusion algorithm to identify anatomic locations of partial to complete airway obstruction just prior to surgery yet avoiding hypoxia. The technique is exciting and might even be developed for procedures such as sedation for fiberoptic intubation. As Dr. David R. Hillman, Department of Pulmonary Physiology and Sleep Medicine, Sir Charles Gairdner Hospital, Perth, Australia, notes in the accompanying editorial titled “Anesthesia, Sleep, and Nasendoscopy,” “Sleep is not a homogenous state because it occurs in a variety of postures and consists of a number of stages with variable ventilatory drive and muscle activation. Hence, upper airway behavior during sleep may vary quite markedly from the carefully contrived circumstances of DISE. These relationships deserve further pursuit.” Furthermore, “Atkins et al. present an elegant anesthetic dosing strategy for DISE to ensure the end point of otolaryngological investigation is reached expeditiously and, in so doing, provide favorable preconditions for an orderly emergence.”