Causes of Airway Collapse Under Anesthesia

General anesthesia and procedural sedation are associated with an increase in upper airway collapsibility, a phenomenon that underlies much of the perioperative risk of hypoxemia and airway obstruction. This phenomenon is also why anesthesia professionals specialize in airway management. The causes of airway collapse are reasonably well characterized and center on anesthesia-induced depression of the neuromuscular systems that normally keep the pharynx patent.

The pharynx is kept open by pharyngeal muscles, chief among them the genioglossus, against collapsing forces such as negative intraluminal pressure generated during inhalation. Research has shown that as the depth of propofol anesthesia increases, the critical closing pressure of the upper airway rises progressively, moving from a negative value—indicating a stable airway—toward a positive value indicative of a floppy, obstruction-prone airway (1). This shift was accompanied by a dose-dependent reduction in phasic muscle activity of the genioglossus, while tonic activity remained comparatively preserved, suggesting that, when under anesthesia, patients lose a reflex drive to the dilator muscles of the pharynx that is timed to breathing, leading to a greater risk of airway collapse (1).

A second mechanism involves suppression of the negative-pressure reflex itself. Under light anesthesia, a fall in pharyngeal pressure evokes a compensatory burst of genioglossus activity that helps resist collapse. Research showed that this reflex response, present at subanesthetic concentrations, is essentially abolished by deeper propofol anesthesia, implying a strong inhibitory effect on upper airway mechanoreceptor pathways in addition to central respiratory depression (1). Other research extended these findings by comparing propofol and sevoflurane at matched depths of anesthesia and found that both agents increase upper airway closing pressure and depress phasic genioglossus activity to a similar degree (4).

A systematic review covering lidocaine, propofol, dexmedetomidine, midazolam, pentobarbital, sevoflurane, desflurane, ketamine, and opioids found that nearly all studied agents produced some degree of airway narrowing or collapse, with propofol, sevoflurane, and opioids showing the most consistent dose-dependent effects, while dexmedetomidine and ketamine appeared comparatively airway-sparing, likely because they interact less with the GABAergic and opioid pathways that depress respiratory drive and pharyngeal muscle tone (2).

The relationship between anesthetic-induced collapsibility and the collapsibility observed during natural sleep is instructive but not interchangeable. One study compared critical closing pressure of the airway under propofol anesthesia versus during sleep in the same subjects and found the two measures were correlated, yet collapsibility was higher during anesthesia than during either non-rapid eye movement or rapid eye movement sleep (3). Proposed contributors to this anesthesia-specific vulnerability include a greater reduction in end-expiratory lung volume, more profound depression of respiratory pump and dilator muscle activity, and loss of arousal-based protective responses that are preserved, at least partially, during physiological sleep (3).

Airway collapse under anesthesia arises from depressed central respiratory drive, dilator muscle compensatory activation, and reduced lung volume, with the magnitude of effect linked to anesthetic depth across agents.