General anesthesia induces a state of controlled unconsciousness, facilitating painless surgeries and procedures. During general anesthesia, airway management is necessary for patients experiencing airway collapse. The mechanism of airway collapse during anesthesia involves a complex interplay of physiological and anatomical factors that are influenced by the drugs used to induce and maintain anesthesia, the positioning of the patient, and the patient’s individual anatomical characteristics.
The primary mechanism behind airway collapse during general anesthesia is the relaxation of the muscles that normally maintain the patency of the airway. Under normal conditions, several muscles play a role in keeping the airway open. The tongue and soft tissues at the back of the throat are held in place by various muscles that contract during normal breathing. The larynx contains muscles that help protect the airway by preventing food or liquid from entering the trachea. Finally, the muscles of the upper airway, including the pharyngeal and palatal muscles, keep the airway open during inhalation and exhalation. Because general anesthetics cause a loss of muscle tone, the muscles responsible for keeping the airway open relax, allowing the tongue and soft tissues in the throat to fall backward, potentially obstructing the airway. Without proper airway management, patients can quickly become hypoxic.
In addition to the direct effects of general anesthesia, sedative drugs such as propofol, benzodiazepines, and opioids further depress the central nervous system (CNS) and contribute to the mechanism of airway collapse. These medications decrease the body’s ability to respond to stimuli, including the reflexes that control airway protection (like swallowing or coughing). Opioids, for example, can depress the respiratory drive, making it more difficult for the body to respond to partial airway obstruction.
Anesthesiologists also commonly use neuromuscular blocking agents (NMBA) to induce muscle relaxation, allowing for easier intubation and better control over ventilation. However, while NMBAs relax the muscles of the body, they also affect the muscles that control breathing, including those that keep the airway open. Without these muscles functioning, the airway may collapse or become obstructed, especially if the patient is not adequately supported by mechanical ventilation or airway devices.
The position of the patient during surgery can also contribute to airway collapse. In a supine (lying on the back) position, gravity can cause the tongue to fall back and obstruct the airway, especially if the patient has a naturally large or floppy tongue, or if there is excessive relaxation of the upper airway muscles. This is particularly problematic in patients who are overweight or have obstructive sleep apnea (OSA), conditions that predispose them to airway collapse.
To counteract airway collapse, anesthesiologists often use airway support devices such as oral or nasal airways, endotracheal tubes, or laryngeal masks, all of which help to keep the airway open and provide ventilation. Anesthesiologists also evaluate the patient’s airway beforehand, position them to facilitate airway management (e.g. using the head tilt, chin lift method), and continuously monitor oxygenation.
Several factors are involved in the mechanism of airway collapse during general anesthesia. These factors include the relaxation of the muscles controlling the airway, the depressant effects
of anesthetic drugs, and the effects of positioning or anatomical characteristics. With careful management, anesthesiologists can minimize the risk and ensure patient safety during surgical procedures.